Dissertations / Theses on the topic 'Digtal Image Correlation'

La riduzione del rumore generato dagli pneumatici in rotolamento rappresenta una delle principali e più difficili sfide per le case produttrici di pneumatici. Negli ultimi anni, infatti, c’è stato un sempre crescente interesse verso questo argomento a seguito delle richieste provenienti dal mondo automobilistico e delle nuove normative in termini di riduzione dell’inquinamento acustico, che impongono un forte abbattimento del rumore generato dagli pneumatici. Oggigiorno, le case automobilistiche tendono a richiedere pneumatici sempre più silenziosi per garantire livelli di confort sempre più elevati all’interno dell’abitacolo e in quest’ottica gli pneumatici giocano un ruolo fondamentale. Col passare degli anni, è stato fatto un notevole passo avanti in termini di abbattimento del rumore generato dal sistema di propulsione, principalmente attraverso l’isolamento acustico dell’abitacolo e, dal momento che la seconda fonte di rumore dopo il motore è rappresentata proprio dagli pneumatici, si capisce come mai ci sia la richiesta di pneumatici silenziosi. Il rotolamento degli pneumatici sull’asfalto, infatti, genera un rumore piuttosto fastidioso che viene percepito in maniera fortemente sgradevole all’interno del veicolo. Inoltre, questo aspetto sta diventando ancor più importante a seguito della massiccia diffusione delle auto ibride ed elettriche, in cui il rumore del motore è fortemente ridotto o addirittura eliminato. Dall’altro lato ci sono le nuove normative riguardo la riduzione dell’inquinamento acustico delle nostre città che impongono anch’esse un forte abbattimento delle emissioni sonore dello pneumatico, per di più da conseguire anche in tempi molto stretti. La somma di queste due richieste impone quindi uno studio approfondito di questo aspetto a partire dalla necessità di approfondire quali sono i meccanismi di generazione del rumore. Quando si parla di rumore generato dagli pneumatici, occorre fare una distinzione tra “in-vehicle noise” and “exterior noise”: il primo rappresenta il rumore percepito dagli individui all’interno dell’abitacolo, mentre il secondo si riferisce al rumore emesso dallo pneumatico nell’ambiente esterno ed è la componente che viene percepita dalle persone all’esterno della vettura. Esiste poi anche una seconda distinzione basata sul meccanismo di generazione del rumore. Secondo questa classificazione, è possibile distinguere tra “Structureborne noise” e “Airborne noise”: nel primo caso il rumore è legato all’interazione dello pneumatico con altri componenti del veicolo che genera delle forze al mozzo che si traducono in vibrazioni e rumore a bassa frequenza (250 Hz); la seconda componente dipende solamente dallo pneumatico e dalla sua interazione con l’aria. Questo secondo gruppo è responsabile principalmente del rumore esterno, ma ha anche una componente ad alta frequenza (fino a 2000 Hz) che rientra all’interno dell’abitacolo. Da questa breve introduzione si capisce come il fenomeno analizzato sia molto complesso, in quanto comprende diverse componenti che sono molto diverse tra loro, sia in termini di meccanismo che di range di frequenza, e pertanto richiedono studi e contromisure dedicate. Per ottenere una riduzione del rumore così consistente, è necessario un drastico cambiamento del modo in cui viene approcciato il problema, poiché si è capito come sia necessario considerare questo aspetto fin dalle prime fasi dello sviluppo di un nuovo pneumatico, accanto a tutte le performance classiche, quali bassa resistenza al rotolamento, handling o braking. Finora, invece, la silenziosità era vista come una caratteristica secondaria o un optional. Generalmente ci si occupava di questo aspetto solo in caso di reclami da parte di una casa automobilistica o se le emissioni sonore dello pneumatico erano di poco al di sopra dei limiti e non c’era quindi la possibilità di ricevere l’omologazione ed essere immesso sul mercato. Si trattava comunque di problemi di piccola entità che con piccoli cambiamenti a livello di pattern era possibile in qualche modo risolvere. Tuttavia, si capisce come si trattasse di un approccio basato sull’esperienza degli ingegneri, ma non sorretto da una base teorica. Per poter abbattere le emissioni acustiche dello pneumatico è necessario in primo luogo comprendere quali sono i meccanismi di generazione del rumore, in modo da sviluppare uno pneumatico che abbia una struttura e un disegno del battistrada cosiddetti “noise-oriented”. Secondo diversi studi, tra i tanti meccanismi di generazione del rumore, il più importante è rappresentato dalle vibrazioni dello pneumatico in rotolamento, pertanto questo lavoro è incentrato proprio su questo aspetto. Il lavoro è diviso in due sezioni principali; la prima parte è focalizzata sulla caratterizzazione dinamica dello pneumatico, mentre nella seconda parte viene presentata un’innovativa caratterizzazione dinamica di alcuni suoi componenti per valutare la loro influenza sulle emissioni acustiche. In entrambi i casi vengono presentati dei casi studio per esporre i principali risultati conseguiti all’interno di questo progetto. Come detto, la prima parte della presente tesi è dedicata alla misura delle vibrazioni dello pneumatico attraverso lo sviluppo di un set-up innovato basato sulla tecnica 3D Digital Image Correlation (3D-DIC). Questa tecnica ha diversi vantaggi e permette di superare i limiti dello stato dell’arte, rappresentato dalle misure effettuate con il Vibrometro Laser Doppler. Per una misura di questo tipo occorre una tecnica che sia in grado di misurare un oggetto in movimento, quindi deve essere una tecnica senza contatto e deve essere in grado di misurare all’interno di un range molto ampio (0 – 2000 Hz). Finora l’unico strumento in grado di eseguire una tale misura era il Vibrometro Laser Doppler, anche se con diversi limiti, come ad esempio la possibilità di misurare solamente il fianco dello pneumatico o i tempi molto lunghi, in relazione al numero di punti da acquisire, che possono provocare variazioni delle condizioni al contorno. La DIC è una tecnica nata principalmente per misure statiche o quasi statiche di deformazioni o spostamenti, tuttavia le moderne fast cameras possono rappresentare una valida alternativa al vibrometro laser in quanto sono caratterizzate da frame rate molto elevati, ragion per cui è possibile misurare spostamenti estremamente piccoli e, quindi, è possibile usare tale tecnica anche per misure di vibrazioni ad alta frequenza. L’utilizzo di tale set-up ha richiesto un lungo lavoro di ottimizzazione, ampiamente descritto in questa tesi, necessario per valutare l’effetto di tutti i principali parametri che influenzano l’acquisizione e, in particolare, è stato necessario capire come poter sfruttare al meglio la strumentazione disponibile per poter eseguire le misure necessarie. Gli attuali limiti tecnologi, infatti, permettono di avere frame rate estremamente elevati, ma al tempo stesso non è possibile avere risoluzioni troppo spinte, altrimenti la dimensione delle immagini sarebbe troppo grande e le attuali velocità di trasferimento dei dati non sarebbero in grado di seguire la frequenza con cui vengono acquisite le immagini stesse. Per tale motivo è richiesto un adattamento dell’inquadratura a seconda del range di frequenze che si vuole studiare. Le vibrazioni dello pneumatico in rotolamento si dividono in due grandi gruppi: le vibrazioni a bassa frequenza (fino a circa 250 Hz) sono caratterizzate da spostamenti di ampiezza elevata che investono tutta la struttura dello pneumatico e per questo sono detti modi di carcassa; ad alta frequenza, le vibrazioni sono generate dagli impatti dei blocchetti del battistrada sull’asfalto che causano spostamenti molto piccoli dei punti localizzati intorno la zona di contatto e sono vibrazioni che rimangono fortemente localizzate in quella zona e non possono essere misurate lavorando con un’inquadratura sull’intero fianco. Nonostante la DIC sia una tecnica di misura full-field, lavorando con un range in frequenza molto ampio e, considerando le dimensioni dello pneumatico, non è possibile sfruttare del tutto questa proprietà. Infatti, se il focus è la bassa frequenza, si può utilizzare un’inquadratura sull’intero fianco, ma se si vogliono studiare le alte frequenze, è necessario usare un’inquadratura focalizzata sulla zona di contatto, che è stato dimostrato essere la zona più rappresentativa del comportamento vibrazionale dell’intero pneumatico. Nell’ambito della misura delle vibrazioni dello pneumatico in rotolamento, l’utilizzo di tale set-up, ha permesso di raggiungere un importante obiettivo, cioè quello di misurare la corona dello pneumatico, che rappresenta una grande innovazione in quanto non è possibile eseguire questa misura con altre tecniche a causa delle discontinuità introdotte dal pattern che rendono impossibile l’utilizzo del vibrometro laser. In questo modo è possibile avere una caratterizzazione dinamica completa dello pneumatico e, attraverso due casi studio, è stato dimostrato come è possibile usare questa tecnica per fornire nuove utili informazioni agli ingeneri di sviluppo. In particolare, dallo studio di diversi pneumatici è emerso come sia possibile ottenere una forte riduzione del rumore con pneumatici in cui le vibrazioni del fianco sono molto smorzate, anche se questo comporta un incremento della mobilità della corona. Questa affermazione è stata dimostrata presentando due casi studio, in cui quest’effetto viene ottenuto con due differenti soluzioni tecniche. Infine, l’intero set-up di misura è stato validato sia in condizioni statiche che dinamiche attraverso il confronto con il vibrometro laser. Il confronto mostra come ci sia un’ottima corrispondenza tra le due misure e permette di evidenziare come la maggiore sensibilità del vibrometro permetta di misurare l’intero range di frequenza con un’unica misura, ma la risoluzione spaziale è piuttosto bassa. La seconda parte del lavoro, invece, introduce un innovativo approccio allo studio del problema, in quanto considera l’effetto di alcuni componenti della struttura dello pneumatico sull’emissione acustica. Tale metodo vuole far fronte alla difficoltà degli ingegneri di scegliere quale sia il materiale di rinforzo più adatto per la struttura di uno pneumatico silenzioso, dovendo scegliere tra una lista molto ampia di candidati. Finora tale problema veniva risolto producendo un prototipo per ogni soluzione tecnica o materiale da testare, i prototipi venivano testati acusticamente e quello che risultava essere più silenzioso veniva scelto. In questo modo si spendono molto tempo e molto denaro, ma soprattutto non si capisce quali siano i meccanismi di generazione del rumore, non si capisce perché un materiale sia migliori di un altro e per di più non viene fatta la caratterizzazione dei materiali. L’utilizzo di tale procedura è dettato dalla mancanza di una caratterizzazione dinamica dei materiali. Sebbene esista una caratterizzazione dinamica delle gomme utilizzate per produrre le mescole così come una dettagliata caratterizzazione dei materiali in termini di proprietà fisiche e meccaniche, non esiste una caratterizzazione di campioni compositi di gomma e corde di materiali di rinforzo. In realtà una minima caratterizzazione esiste, ma viene fatta su campioni molto piccoli e in condizioni quasi statiche che serve solo a definire i valori di rigidezza “in-plane” and “out-of.plane”. Il problema è che non si tratta di una caratterizzazione noise-oriented perché non tiene conto del comportamento dinamico del provino. L’approccio proposto, invece, considera dei campioni costruiti allo stesso modo in cui si possono trovare nella struttura dello pneumatico, cioè sono piccole travette di gomma calandrate con immerse delle corde di materiale di rinforzo. La nuova procedura si basa sulla caratterizzazione di tali provini utilizzando la tecnica DIC ed è possibile in questo modo definire l’effetto di ogni materiale in termini di mobilità dei campioni analizzati. In questo modo si possono selezionare i materiali che rispettano determinate condizioni e i test su pneumatico servono solo per conferma, quindi il loro numero sarà ridotto drasticamente con notevole risparmio di tempo e soldi. Anche in questo caso l’ottimizzazione del set-up ha richiesto molto tempo, in particolare per la definizione della struttura dei campioni. Il confronto di misure acustiche su pneumatico in rotolamento, caratterizzazione dinamica dello pneumatico e misure vibrazionali sui campioni ha permesso di definire che i materiali di rinforzo da preferire sono quelli che aumentano la mobilità della corona, in quanto si riduce la mobilità del fianco che è la principale sorgente di rumore. Tutto questo ragionamento è supportato da un caso studio presentato nell’ultimo paragrafo. In conclusione, un nuovo sistemata per la misura delle vibrazioni dello pneumatico in condizioni di rotolamento è stato sviluppato, ottimizzato e validato attraverso il confronto con il Vibrometro Laser Doppler, sia in condizioni statiche che dinamiche. Il nuovo set-up permette di eseguire misure anche sulla corona, non realizzabili con nessun’altra tecnica. Lo stesso set-up è stato utilizzato per la caratterizzazione dinamica di componenti dello penumatico.
The reduction of the noise generated by rolling tire is becoming one of the most important and difficult challenges for tire manufactures. The growing interest in tire noise performances is related both to the requirements coming from the car industry and the new regulations regarding the reduction of the acoustic pollution of our cities. Car manufacturers require silent tire in order to guarantee a high comfort level inside the car. During last years, a lot of work has been done in order to make the interior of the cars as comfortable as possible and the current cockpit insulation can significantly reduce the noise coming from the engine, so, in order to further increase the comfort level, they ask for silent tires. According to several studies, in fact, the engine is the first noise source in a moving car followed by the rolling tire noise, so it is easy to understand the reason why there is such a requirement. The noise generated by rolling tires is completely different from the engine noise in terms of frequencies and the cockpit insulation cannot reduce it in the whole frequency range of interest (0 – 2000 Hz). This aspect is even more important with the new electric or hybrid engines, where the noise is completely or partially deleted. When talking about rolling tire noise, two main classifications have been defined. According to the first classification, “in-vehicle” and “exterior noise” can be distinguished: the first one refers to the noise perceived inside the car, while the second one is the noise heard by the people outside the car, i.e. the noise that propagates in the external environment. The second classification is based on the noise generation mechanism. In this case, “Structureborne noise” and “Airborne noise” can be distinguished: the first one refers to that noise component related to the interaction between rolling tire and car components resulting in spindle forces causing low frequency vibrations (up to 250 Hz) that are mainly responsible for the in-vehicle noise, while the “Airborne noise” refers to those mechanisms which depends on the tire only and on its interaction with the air. This second group mainly generates high frequency noise propagating in the surroundings, but it has also a contribution entering inside the car. On the other side, there are new regulations that impose a significant reduction in terms of exterior noise. From this short introduction it is clear how complex the analysed phenomenon is, because, even if the noise source is the same, each noise component is different from the others and requires dedicated studies and countermeasures. Tire manufacturers have understood that, in order to satisfy these requirements in terms of noise reduction, it is necessary to complete change how the tire noise study is approached, because noise performance must be considered from the first stages of the development as well as the other classic performances, such as handling, braking, rolling resistance and so on. In fact, the noise reduction to be achieved is very consistent, so it necessary to deeply understand how noise is generated to define the features of a noise-oriented tire structure. In the past years, a low noise level was considered an optional, mainly because it was quite easy to respect the limits imposed by regulations to obtain the approval for the commercialization. If there were some noise problems, they were solved with some changes in terms of pattern design based on the experience of the engineers, but the reduction obtained was very low. To significantly reduce the noise emission, it is necessary to investigate and understand how noise is generated and evaluate the effect on the noise emission of every tire components and materials used in tire construction. To do this, it is necessary to better understand the noise generation mechanisms, in fact, even if a lot of researchers have studied this phenomenon for decades, it is still not completely clear how noise is generated. According to several studies, among all the mechanisms the most important are the vibrations of the rolling tire. This is the main topic of this work and it is analysed in two different ways: from a global point of view through a complete dynamic characterization of the rolling tire and from a more detailed point of view looking at the dynamic characterization of samples of tire components. The first part of the thesis deals with the measurement of tire vibrations using an innovative set-up based on the 3D - Digital Image Correlation (DIC) technique. It has several advantages if compared with the current techniques, among which the possibility to measure irregular and inhomogeneous surface is one of the most important because it allows to perform significative measurement on tire crown. This is one of the innovations introduced in this work, since this measurement cannot be performed with other techniques. As well as the state of art technique, that is the Laser Doppler Vibrometer (LDV), the DIC is a non-contact technique, but it does not require a smooth and homogenous surface and this feature is exploited to measure the crown of the rolling tire. It is characterized by the so-called tread pattern, that is a sequence of blocks, so the LDV cannot be used because every block causes a spike in the LDV signal, while the DIC does not have this problem, since it compares two images to define the displacement of the measurement points. Even if it is a full-field technique, this feature cannot be completely exploited on a rolling tire, because of the width of the frequency range of interest and the size of the tire compared with the current resolution of the available cameras. The DIC technique was born to perform displacement and deformation measurements in static or quasi-static condition, but the modern fast cameras, characterized by very high frame rates, suggest the possibility to use this technique to perform vibration measurement. Since the DIC measure the displacements, it is necessary to have a high frame rate in order to detect also the very small displacements that characterise the high frequency vibration and the modern fast cameras satisfy this requirement, even if the resolution it is not too high, because the size of the image will be too high and there would not be the possibility to transfer the images with the same rate of the acquisition one. For this reason the frame size must be adequate to the frequency range of interest: if the low frequency carcass modes are investigated, the full-view on the sidewall can be used, but if the high frequency vibrations must be studied, it is necessary to focus the cameras on the contact patch area, in order to measure the small displacement generated by the impact of tread blocks with the road. These displacements are strictly localized in the contact patch area and a full-sidewall view cannot detect them: when the cameras are focused on a smaller area, the resolution of the system is increased because the pixels are focused on a smaller area and smaller displacements can be measured. The new set-up has been validated through the comparison with LDV both in static and dynamic condition in both the framing configurations. This is probably one of the main disadvantages of this technique, but it is a limit of current technologies because it is not possible to produce cameras with high resolution and high frame rate. The correlation between DIC and LDV measurement is very good, the LDV’s accuracy is a little bit higher, but it depends on the measured quantity (velocity VS displacement). The new dynamic characterization of tire crown and its comparison with sidewall provide new information about rolling tire vibrations that suggest some countermeasures for the development of a noise-oriented tire structure. provide new information not available in the past years. Two case studies are described to demonstrate the potentialities of the new set-up and demonstrating how an important noise reduction can be achieved. In the second part of this PhD project, the same set-up has been used to perform an innovative dynamic noise-oriented characterization of cord-rubber composite samples to evaluate the effect of reinforcing materials on the noise emission. It represents a completely new approach to the problem because it is a tentative to correlate the noise emission with tire structure components. A lot of work has been done to characterize rubber and reinforcing cords, but there are some problems: they are characterized separately, the size of the samples is very small and it is not representative of what happens on the real tire, it is a static or quasi-static characterization and if, a composite sample is used, in these conditions the only in-plane and out-of-plane stiffness values can be extracted. This procedure is useful to completely characterize the rubber used for tire compound and the reinforcing materials in terms of their mechanical properties, but it is useless in predicting noise emission, because the frequency response of the samples is unknown. The lack of these information is related to the approach used until now. As previously stated, in the past years tire silence was a secondary requirement and, when the first limitations in terms of noise emission had to be satisfied, a very expensive strategy in terms both of time and money has been used: the choice of the reinforcing material is performed producing a tire prototype for each candidate material, testing all the tires and identifying the tire that score the lowest noise emission. Nowadays, the reduction imposed is so strong, that tire developers are forced to consider the noise target from the first stages of the development in order to produce a noise-oriented tire structure and the absence of such a characterization has emerged. The approach proposed in this thesis considers samples produced in the same way they can be found on the final tire and the analysis of their mobilities suggest which are supposed to produce a reduction of noise emission. The final response comes from the test of a prototype tire, but in this way the selection of the proper materials is faster and, at the same time, the number of tests on tire and the prototypes produced is significantly reduced and the mechanism understanding is improved. In order to obtain good and useful results it important to define the correct structure of the samples, in fact even if the idea is to characterize the cap ply or body ply layers, the sample must contain also the belt package for global stiffness and mass reasons: if the belt is not used, the samples produced are very lightweight and the variation of the cord cause significant variations in terms of mass and stiffness with a shift in terms of resonance frequencies that it is not related to mechanical properties of the cord materials or sample thickness, but it is related to the mass variation only. When the belts are applied, the samples have almost the same mass and stiffness and the effect of the different cap ply layers is a variation in terms of mobility. The results obtained for a group of samples have been compared with those coming from the dynamic characterization of the corresponding final tire and their acoustic measurements, showing a good correlation between the measurement on samples and entire tires. The performed measurements suggest that the new approach produce interesting results and this procedure can be effectively used. For sure other test on other samples must be performed to confirm the first results and to define a database of materials. In conclusion it can be said that an innovative measurement set-up for the dynamic characterization of rolling tire has been developed and validated. Both sidewall and crown can be characterized with the new set-up. At the same time, an innovative approach for noise reduction based on the characterization of tire components has been proposed.

This thesis examines the feasibility of combining Digital Image Correlation (DIC) with laser speckle based methods to form a new hybrid deformation measurement method called Digital Laser Speckle Image Correlation (DilSIC). Consequently, this method does not require any sample preparation and allows for the measurement of displacement of micro structures in addition to large displacements. In this technique, a coherent 30mW-632nm laser beam is expanded with 40X lens and then illuminated on the target surface to produce a fine, homogenous laser speckle pattern. Images were captured before and after deformation due to external load and the whole field displacement and strain were determined by the DIC method. This technique could measure displacement less than 30-μm with high accuracy when a 120mm × 80mm area of the surface was inspected. Up to 10% strain was measured by this technique with high accuracy during the whole range. Eventually the sub-surface crack was located successfully, which is a revolutionary achievement in NDT optical methods. This method was tested in different material, with different roughness. Aluminum sheet and rubber material were used mostly. This method could broaden the capability of displacement measurement and subsurface crack detection in wide range of materials.

Digital Laser Speckle Image Correlation (DiLSIC) is a technique that utilizes a laser generated speckle pattern with Digital Image Correlation (DIC). This technology eliminates the need to apply an artifact speckle pattern to the surface of the material of interest, and produces a finer speckle pattern resulting in a more sensitive analysis. This investigation explores the parameters effecting laser speckle patterns for DIC and studies DiLSIC as a tool to measure surface strain and detect subsurface defects on pressure vessels. In this study a 632.8 nm 30 mW neon-helium laser generated the speckle pattern by passing through the objective end of an objective lens. All experiments took place in a lab setting on a high performance laminar flow stabilizer optical table.This investigation began with a deeper look at the camera settings that effect the effectiveness of using laser speckles with DIC. The first studies were concentrated on the aperture size (f-stop), shutter speed, and gain (ISO) of the camera. Through a series of zero-correlation studies, translation tests, and settings studies, it was discovered that, much like white light DIC, an increased gain allowed for more noise and less reliable measurements when using DiLSIC. It was shown that the aperture size and shutter speed will largely depend on the surface composition of the material, and that these factors should be investigated with each new sample of different surface finish.To determine the feasibility of using DiLSIC on pressure vessels two samples were acquired. The first was a standard ASTM filament wound composite pressure vessel (CPV) which had an upper load limit of 40 psi. The second was a plastic vessel that had internal subsurface defects added with the use of an air pencil grinder. Both vessels were put under a pressure load with the use of a modified air compressor that allowed for multiple loading cycles through the use of a pressure relief valve. The CPV was mapped out in 10-degree increments between the 90° and 180° markings that were on the pressure vessel, occurring in three areas, each one inch apart. The CPV had a pressure load applied to at 10, 20, 30,and 40 psi. DiLSIC was able to measure increasing displacement with increased loading on the surface of the CPV, however with a load limit of 40 psi no strains were detected. The plastic vessel had known subsurface defects, and these areas were the focus of the investigation. The plastic vessel was loaded with a pressure load at 5, 10, 12, 15, 17, and 20 psi. The 5 psi loaded image was used as a reference image for the correlation and decorrelation consistently occurred at 20 psi. This investigation proved that DiLSIC can detect and locate subsurface defects through strain measurement. The results were verified with traditional white light DIC, which also showed that the subsurface defects on pressure vessels were detectable. The DIC and DiLSIC results did not agree on maximum strain measurement, with the DiLSIC prediciting much larger strains than traditional DIC. This is due to the larger effect out-of-plane displacement has on DiLSIC. DiLSIC was able to detect subsurface defects on a pressure vessel. The median measured hoop strain was in agreement for DiLSIC, DIC and the predicted hoop strain for a wall thickness of 0.1 inches. However, DiLSIC also produced unreliable maximum strain measurements. This technique shows potential for future applications, but more investigations will be needed to implement it for industrial use. A full investigation into the parameters surrounding this technique, and the factors that contribute the most to added noise and unreliability should be conducted. This technology is being developed by multiple entities and shows promising results, and once further advanced could be a useful tool for rapid surface strain measurement and subsurface defect detection in nondestructive evaluation applications. Therefore, it is recommended to continue further investigations into this technology and its applications.

The performance of paperboard materials in packaging application has been investigated and evaluated for a long time. This is because it plays a decisive role for product protection and decoration in packaging applications. Potential damages during transportation sometimes affect the consistency of the performance. Therefore, the capability of the material to resist these external disturbances was of interest. A multiply paperboard was chosen as the experimental material. The analysis conducted in this thesis aimed to reveal the tensile behavior in the cross-machine direction (CD) of the material against various kinds of local or global changes. The changes included global and local climate variations, cutouts, and regional weakening and strengthening, which were applied during the intervals between preloading and reloading. The digital image correlation (DIC) analysis computed the time-varying strain fields from the gray level information contained in the recorded videos of loading processes.  The generated strain fields were imported to post analysis. Comparison between comparable stages (two stages with the same average strain value from different loading sections) was considered as the scheme of isolating the influences of the changes and investigating them individually. The cosine image similarity method and the eigenface algorithm were used to validate this scheme, while the directional average calculation and the strain field compensation method were introduced to realize the isolation. The differences between the front and back outer plies of the paperboard sheets were detected as individual. Moreover, both global and local climate changes were affecting the strain distributions of the specimens proportionally on account of the moisture ratio within the material. In addition, the invisible mechanical weakening and strengthening were captured evidently with the analysis, which caused strain concentrations due to the uneven distribution of expansion capability. The relaxation and bending in unloading processes were two of the primary disturbing factors within all the deformed specimens, which were related to time and bending direction, correspondingly.
Egenskaperna hos kartongmaterial för förpackningstillämpningar har varit ett ämne att undersökning under lång tid. Detta för att dessa egenskaper spelar en avgörande roll som produktskydd och dekorativ utformning i mängde av tillämpningar. Potentiella skador under transport påverkar bland annat materialets tillförlitlighet och prestandard. Därför är det aktuellt att undersöka samt förstå materialets förmåga att motstå yttre störningar. Experimentmaterialet som användes bestod av en typ av flerskiktskartong. Analyser som utfördes i denna avhandling har syfte att identifiera de mekaniska förändringarna i materialets dragegenskaper i tvärsmaskin-riktningen (CD) på grund av olika lokala eller globala förändringar. Förändringarna innefattar både globala och lokala klimatvariationer, utskärningar, och lokala försvagningar samt förstärkningar. Dessa förändringar infördes vid intervallet mellan på- och avlastning. Den digital bildkorrelations analys (DIC) användes för att beräknade de tidsvarierande töjningsfälten från den grånivåinformationen i som registrerades med hjälp av inspelade videor under belastningen  Den genererade töjningsfälten importerades för vidare analys. Två tillstånd med liknande medelvärde av töjningsnivån från olika delar av belastningen jämfördes, detta för att isolera påverkan av förändringarna och undersöka dem individuellt. Två olika metoder för jämförelse av bilderna (cosine image similarity och eigenface algorithm) användes för att validera analysschemat, där riktning-medelvärdesberäkningar och töjningsfälts kompensations-metoden användes för att realisera dessa isoleringar. Enstaka skillnader upptäcktes mellan de främre och bakre ytskikten på kartongarken. Dessutom påverkades töjningsfördelningarna för proverna både av den globala och lokala klimatförändringar på grund av fukttillståndet i materialet. Vidare kan de osynliga mekaniska försvagningar och förstärkningar tydligt fångas med de utförda analyserna, vilket ledde till töjningskoncentrationers uppkomst på grund av det inhomogena expansions-förmåga hos arket. Relaxationen och böjningen vid avlastning relaterade till tid och böjningsförmåga var två av de primära faktorerna som påverkade analysens kvalité.

Advanced composite materials are widely used for many structural applications in the aerospace/aircraft industries today. Joining of composite structures using adhesive bonding offers several advantages over traditional fastening methods. However, this technique is not yet employed for fastening the primary structures of aircrafts or space vehicles. There are several reasons for this: There are not any reliable non-destructive evaluation (NDE) methods that can quantify the strength of the bonds, and there are no certifications of quality assurance for inspecting the bond quality. Therefore, there is a significant need for an effective, reliable, easy to use NDE method for the analysis of composite adhesive joints. This research aimed to investigate an adhesively bonded composite-aluminum joints of variable bond strength using digital image correlation (DIC). There are many future possibilities in continuing this research work. As the application of composite materials and adhesive bond are increasing rapidly, the reliability of the composite structures using adhesive bond should quantified. Hence a lot of similar research using various adhesive bonds and materials can be conducted for characterizing the behavior of adhesive bond. The results obtained from this research will set the foundation for the development of ultrasonic DIC as a nondestructive approach for the evaluation of adhesive bond line.

Increasing use of composite materials in industry brings the need for newer and more practical methods to evaluate them. Widespread use of composite materials heavily depends on the manufacturer’s ability to unquestionably ensure its safety, given how much the user trusts them. Non-Destructive Evaluation (NDE) can be used to evaluate adhesive bondline health. This thesis employs Digital Image Correlation (DIC) method, one of the known methods in NDE, and combines it with an embedded speckle pattern in order to obtain valuable information from within the adhesive bondline. By recording the movement of the speckles and analyzing their behavior according to DIC algorithms, a strain map of the adhesive is drawn. An adhesive strain map helps find defects that might be out of sight using conventional NDE methods. This thesis discusses different possible materials to be used as the speckle pattern and chooses the one shows better results based on different criteria. Then employing the material, it records the speckle pattern using optical and ultrasonic methods to draw a strain map. By analyzing the obtained strain maps, defects within the bondline are revealed.

Digital Image Correlation (DIC) is an optical and numerical method capable of accurately providing full-field, two-dimensional (2-D) and three-dimensional (3-D) surface displacements and strains. 3-D DIC is typically done using two cameras that view the measured object from differing oblique directions. The measured images are independent and must be spatially connected using a detailed calibration procedure. This places a large demand on the practitioner, the optical equipment and the computational method. A novel approach is presented here where a single color-camera is used in place of multiple monochrome cameras. The color-camera measures three independent Red-Green-Blue (RGB) color-coded images. This feature greatly reduces the scale of the required system calibrations and spatial computations because the color images are physically aligned on the camera sensor. The in-plane surface displacements are obtained by performing traditional 2-D DIC in a single color. The out-of-plane information is obtained by a second 2-D DIC analysis and triangulation using oblique illumination from a differently colored light source. Further, the camera perspective errors associated with out-of-plane displacements can independently be measured during this second DIC analysis of the oblique illumination pattern. The 3-D Digital Image Correlation is completed by combining the 2-D correlations for each color. The design and creation of an example apparatus is described here. Experimental results show that the single-camera method can measure 3-D displacements with to within 1% error, with precision of the in-plane and out-of-plane measurements being consistently less than 0.04 and 0.12 pixels, respectively.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

Thesis (M.S.)--Southern Illinois University Carbondale, 2006.
"Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 70-74). Also available online.

Electronic Speckle Pattern Interferometry (ESPI) provides a sensitive technique for measuring surface deformations. The technique involves comparison of the speckle phase angles within surface images measured before and after material deformation. This phase angle comparison requires that the speckle positions be consistent in all images. A lateral shift between images by just one pixel substantially degrades ESPI measurements, while a shift of two or more pixels typically causes complete speckle decorrelation and compromises the measurement entirely. To prevent such lateral motions, the specimen and the optical system must be rigidly fixed. This requirement typically prevents use of the ESPI method in applications outside laboratories or where it is necessary to remove the specimen from the optical setup between ESPI measurements. Here, Digital Image Correlation (DIC) is used to track speckle motion caused by specimen displacement between ESPI measurements. The measured images can then be mathematically shifted to restore the original speckle locations, thereby recorrelating the ESPI measurements. Examples are presented where ESPI measurements are successfully made with specimen shifts in excess of 60 pixels. A novel ESPI measurement technique where the specimen is removed in between ESPI measurements is also developed and validated.

This research project on the campus of Southern Illinois University Carbondale is an extension to the inquiry into the feasibility and reliability of the technology known as Digital Laser Speckle Image Correlation (DiLSIC). This is a hybrid approach of combining two existing technologies. The first being Digital Image Correlation (DIC) which is a nondestructive evaluation commonly used to find displacement, in-plane strain, as well as deformation. The second being the of laser speckle patterns. This hybrid has achieved level of resolution measured to be 3.4μ. DiLSIC increases the application ability of the DIC technique to situations that generally would not be an option to use. DiLSIC needs no artifact speckle patterns to be applied to the specimen as a preparation for nondestructive testing. In DIC testing, the surface of a specimen must artifact speckles applied to the subject surface. Often the application of artifact speckles is not desirable or possible. DiLSIC is an acceptable alternative to the previously discussed industry-wide practice. This method broadens the usage of the DIC technique to situations which previously were not possible. This technology can identify, quantify, and detect the distribution of strain and stress concentrations in composite structures. For this study, a honeycomb-backed glass fiber reinforced polymer (GFRP) panel from a Cessna aircraft exterior luggage door was obtained and a defect panel is created. The panel is constructed with one area containing a repair compliant with manufacturer standardized methods and a repair area is not compliant and consists of multiple incorrect repair steps. An area with no repair is also tested to act as a control for comparison and quantification. The results for the inspected areas showed a linear strain increase in the noncompliant repair. The data plot for the compliant repair showed a trend of following the same basic curve as the no repair area. A verification process follows the DiLSIC testing consisting of using Infrared Thermography, Air-coupled ultrasonic, and white light artifact speckle DIC. These tests show DiLSIC is a viable alternative to the testing that is available in the industry. DiLSIC can detect defect location, size, geometry and map strain to determine the difference between compliant and noncompliant repairs when compared to a base level non-repair area

While machine perfusion of explanted kidneys is theoretically superior to standard cold storage, it may damage potential transplants unless machine-associated swelling is controlled. This thesis presents the effects of perfusate tonicity on renal swelling during hypothermic machine perfusion. Phosphate buffered solution (PBS) and PBS supplemented with 5% w/v mannitol were used as isotonic (289 mOsm/kg) and hypertonic (568 mOsm/kg) perfusates, respectively. Porcine kidney pairs were procured then flushed and machine perfused; the right and left kidneys were assigned opposite perfusates. An experimental methodology was developed to image porcine kidneys undergoing hypothermic machine perfusion (5 deg C) for 15 minutes followed by 120 minutes without perfusion to quantify surface displacement (renal swelling) with digital image correlation (DIC). Surface displacement and size (thickness) were compared between the right and left kidneys of each pair. In addition, discharged renal fluids (i.e., filtrate and venous outflow) and biopsies were collected. On average, kidneys perfused with the mannitol solution were smaller in size than the kidneys perfused with PBS (p < 0.05) at the start and end of each experiment; however, there was no significant difference between the renal sizes at the end of the 15 minute perfusion interval (p > 0.05). Thus, hypertonic and isotonic perfusates yielded different renal swelling outcomes (i.e., physical size and surface displacement), which suggests that perfusate tonicity influences renal swelling. These experiments are the first time ex vivo renal surface displacement measurements have been collected during machine perfusion.
Master of Science

La technologie des éoliennes est mature et le marché est avec le temps devenu compétitif. Un levier pour diminuer les coûts de l’exploitation des éoliennes réside dans l’optimisation de la maintenance des turbines. Dans ce contexte, cette étude se focalise sur l’état de la tour de l’éolienne. La durée de vie de la tour est influencée par des paramètres incertains liés à l’environnement et les aléas matériaux. Ceci rend très difficile la prédiction de la durée de vie d’un mât et des marges importantes sont prises lors de son dimensionnement. Cependant des éoliennes se sont déjà effondrées dans le monde, à chaque fois lors d'épisodes climatiques violents. Les deux phénomènes de ruine identifiés sont le flambement local de la tour et l'arrachement de sa partie supérieure. Des sources académiques ou industrielles ont également rapporté la découverte de fissures sur quelques turbines aux interfaces soudure-matériau. Une réflexion concernant la criticité d'une fissure vis à vis du flambement et de sa propagation brutale a été menée dans le cas où la tour est soumise à des chargements violents. Des simulations éléments finis ont permis de montrer que la propagation brutale de fissure était le phénomène dimensionnant pour la prolongation de durée de vie d'une tour d'éolienne fissurée.Pour s'assurer de l'intégrité des structures des techniques de suivi de santé ont été développées. Celles-ci sont en général réalisées à partir de capteurs extrapolant un état de santé global à partir de données locales (accéléromètres, jauges de déformations). Le risque est qu'un défaut reste invisible mais soit tout de même critique pour la structure. Il est donc essentiel de revisiter les outils de prédiction à partir de données de sites relatives à l’endommagement de la tour et des structures les supportant. Dans le cadre de ce travail de thèse des méthodes basées sur l'imagerie et plus particulièrement la Corrélation d'Images Numériques (CIN) ont été développées. Pour aborder le problème, deux approches à différentes échelles ont été considérées.La première, à l’échelle structurale, consiste à reconstruire le champ de déplacement de l'éolienne vue comme une structure unidimensionnelle. La présence d'un défaut induira une perte de raideur latérale, et donc une (quasi-)discontinuité dans le champ de rotation. Les défis relatifs à cette partie sont doubles : l'absence de contraste sur la tour et la prise de photos en extérieur sur une grande structure. Une technique de CIN intégrée a été utilisée afin de diminuer le nombre d'inconnues du problème et réduire les incertitudes de mesures. Il a été montré que l'influence d'un défaut, plus particulièrement d'une fissure, serait trop faible par rapport aux incertitudes de mesures. Cependant, suivant cette approche, une méthode innovante d'analyse modale de tour d'éolienne a été développée et les deux premières fréquences propres ont pu être déterminées avec précision.La seconde est une stratégie de contrôle de la structure à l'échelle mésoscopique. Celle-ci se base sur un dispositif de caméras bon marché à l'intérieur de l'éolienne couvrant les soudures circonférentielles au niveau des zones de plus fortes contraintes. L'idée est d'établir pour chaque caméra lorsque la structure est considérée comme saine une base modale de déplacement caractéristique de cet état grâce à des techniques de réduction de modèle. Au cours du temps, si un défaut sous-jacent ou traversant apparait, celui-ci induira une perturbation du champ de déplacement qui pourra être détectée à l'aide d'indicateurs globaux tels que l'écart en déplacement ou les résidus de corrélation.Afin de déterminer si la détection d'un défaut aux deux échelles est faisable ou non, la prise en compte de l'incertitude de mesure en regard de l'influence d'un défaut est primordiale. Alors, un cadre mathématique de la CIN optimale à N champs a été proposé et validé
Wind turbine technology is mature and the market has become very competitive over time. A lever to reduce the costs of wind turbine operation lies in optimizing turbine maintenance. In this context, this study focuses on the wind turbine tower. The lifetime of the tower is influenced by uncertain parameters related to the environment and material hazards. This makes it very difficult to predict the tower lifetime, and large safety factors are used when dimensioning it. However, around the world, a few wind turbines have already collapsed, each time during extreme climatic episodes. The two identified ruin causes are the local buckling of the tower and the tearing off of its upper part. Academic and industrial sources have also reported the discovery of cracks on some turbines at the weld-material interfaces. An investigation of the criticality of a crack with respect to buckling and its fatal propagation has been carried out in the case where the tower is subjected to violent loads. Finite element simulations showed that the fatal crack propagation was the limiting phenomenon for the life extension of a cracked wind turbine tower.To ensure structural integrity, health monitoring techniques were developed over time. These are generally carried out using sensors extrapolating a global state of health from local data (accelerometers, strain gauges). The risk is that a defect remains invisible but is nevertheless critical for the structure. It is therefore essential to revisit the prediction tools based on site data. Within the framework of this work, methods based on imagery and more particularly Digital Image Correlation (DIC) have been developed. To address the problem, two approaches at different scales have been considered.The first, at structural scale, consists in reconstructing the wind turbine displacement field considered as a one-dimensional structure. The presence of damage will induce a loss of lateral stiffness, and thus a (quasi-)discontinuity in the field of rotation. The challenges for this part are twofold: the lack of contrast on the tower and the capture of outdoor photographs on a large structure. An integrated DIC technique was used in order to reduce the number of unknowns in the problem and to lower the measurement uncertainties. It was shown that the influence of a damage, especially a crack, would be too small regarding the measurement uncertainties. However, an innovative method of wind turbine tower modal analysis was developed and the first two natural frequencies could be determined accurately.The second strategy is focused on a mesoscopic scale. It is based on a low-cost camera system, inside the wind turbine, covering the circumferential welds in the regions of highest stress. The idea is to establish for each camera, when the structure is considered sound, a displacement modal basis using model reduction techniques. Over time, if an underlying or through defect appears, it will induce a disturbance in the displacement field which can be detected using global indicators such as displacement deviation or DIC residuals.In order to determine whether the detection of damage at both scales is feasible or not, it is essential to take into account the measurement uncertainty. Therefore, a mathematical framework of the optimal CIN with N fields has been proposed and validated

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Ferramentas de processamento e análise digital de imagens foram desenvolvidas com a finalidade de avaliar a evolução da textura morfológica e cristalográfica da microestrutura da liga de alumínio 7075 sob diferentes níveis de deformação plástica por compressão uniaxial. Amostras da liga de alumínio 7075-T6 passaram por um processo de recozimento pleno seguido de um estágio de compressão uniaxial, obtendo níveis de deformações entre 25 e 65%. As microestruturas das amostras foram avaliadas em função dos parâmetros morfológicos dos precipitados, da reorientação dos planos cristalográficos dos grãos e da orientação das subestruturas formadas durante o processo de deformação. Para a caracterização foram utilizadas técnicas de difração de raios-X, microscopia eletrônica, microscopia óptica utilizando técnicas de polarização linear e circular, microscopia correlativa e processamento digital de imagens. Os resultados de difração de raios-X indicaram uma reorientação do plano cristalográficos (200) para o (220) após a deformação, e as técnicas de microscopia eletrônica identificaram precipitados de Mg2Si, Al7Cu2Fe e Al6(FeCu) na liga. A análise morfológica dos precipitados indicou uma maior fragmentação dos precipitados devido à maior ativação do plano (331) a partir de 39% de deformação. Por meio do processamento de imagens foi encontrada uma tendência de correlação entre os planos cristalográficos e a fração de área das fases, enquanto que os parâmetros morfológicos das subestruturas formadas durante o processo de deformação permitiram avaliar apenas qualitativamente o nível de encruamento das amostras.
Digital image processing and analysis tools were developed to perform the AA 7075 crystallographic and morphologic texture evaluation under different level of plastic deformation by uniaxial compression. Samples of AA 7075-T6 were submitted to full annealing process followed by uniaxial compression, thus obtaining deformations between 25 and 65% of thickness. The samples microstructure evaluation was performed considering: precipitates morphological parameters, crystallographic lattices reorientation and deformation substructure orientation. The characterization technics were: X-ray diffraction, electron microscopy, optical microscopy with polarization light, correlative microscopy and digital images processing. Xray diffraction results showed that the crystallographic plane (200) was reoriented to (220) after compression. The EDS analysis identified precipitates of Mg2Si, Al7Cu2Fe e Al6(FeCu). The precipitates morphological analysis showed an increase in fragmentation due to plane (331) at 39% of deformation. The digital image process of the samples etched with Barker reagents indicated a correlation between area fraction and the diffraction peaks, and the deformation substructures analysis made viable a qualitative characterization of the hardening process.
FAPESP: 2011/00403-2

Mechanical parameter characterization of very thin polymer films using digital im- age correlation is performed in this work. At present days DIC is widely used in the construction, food industries, and aviation. Despite advantages when compared to other conventional methods, but users still face difficulties with the analysis of thin polymers like low-density polyethylene (LDPE) and polyethylene terephthalate (PET) thin polymer films. For the application of sprays to obtain the best pattern quality as well as the potential of thin-film material properties tempering from the stochastic pattern paint. This research work will investigate the effect of several spray paints on the material response of thin polymer film. It also shows how to achieve good surface traction, time effect, and the type of spray to be used for DIC analysis. Finally, this research also studies how the width of the specimen affects the wrinkling effect, which is a common phenomenon while testing the thin polymer films and exhibits the appropriate width for reducing wrinkles on thin polymer films.

Digital Particle Image Velocimetry (DPIV) is a planar measurement technique to measure the velocity within a fluid by correlating the motion of flow tracers over a sequence of images recorded with a camera-laser system. Sophisticated digital processing algorithms are required to provide a high enough accuracy for quantitative DPIV results. This study explores the potential of a variety of cross-correlation filters to improve the accuracy and robustness of the DPIV estimation. These techniques incorporate the use of the Phase Transform (PHAT) Generalized Cross Correlation (GCC) filter applied to the image cross-correlation. The use of spatial windowing is subsequently examined and shown to be ideally suited for the use of phase correlation estimators, due to their invariance to the loss of correlation effects. The Robust Phase Correlation (RPC) estimator is introduced, with the coupled use of the phase correlation and spatial windowing. The RPC estimator additionally incorporates the use of a spectral filter designed from an analytical decomposition of the DPIV Signal-to-Noise Ratio (SNR). This estimator is validated in a variety of artificial image simulations, the JPIV standard image project, and experimental images, which indicate reductions in error on the order of 50% when correlating low SNR images. Two variations of the RPC estimator are also introduced, the Gaussian Transformed Phase Correlation (GTPC): designed to optimize the subpixel interpolation, and the Spectral Phase Correlation (SPC): estimates the image shift directly from the phase content of the correlation. While these estimators are designed for DPIV, the methodology described here provides a universal framework for digital signal correlation analysis, which could be extended to a variety of other systems.
Master of Science

Modern hydraulic fracturing designs assume that drilled formations are both isotropic and homogeneous, and fractures are linear and symmetrical. However, unconventional resources are often obtained from formations that are both anisotropic and heterogeneous, resulting in complex fracture behavior. The objective of this study is to evaluate fracture behavior based on the influence of anisotropy and water saturation. Isotropic and homogeneous Austin Chalk, Berea Sister Gray Sandstone, and Silurian Dolomite, laminated anisotropic and heterogeneous Parker Sandstone, Nugget Sandstone, and Winterset Limestone Carbonate, and fully anisotropic and heterogeneous Edwards Brown Carbonate cores were ordered for testing. Brazilian discs were cut according the ISRM and ASTM standards, and prepared as dry, brine saturated, and fresh water saturated samples. All samples were fractured by the Brazilian test, and laminated anisotropic samples were tested at various loading angles (0?, 15?, 30?, 45?, 90?). Tensile strengths were calculated using the peak load of the primary fracture of each sample, and the fractures were observed for geometrical trends. Additionally, the strain development of each fracture was analyzed through the application of Digital Image Correlation (DIC) software. The results determined that anisotropy and saturation can decrease the tensile strength of a formation. The fracture geometries were influenced by planes of anisotropic lamination, and fully anisotropic rocks produced winding, erratic fractures. DIC allowed for closer 101 examination of fracture development, and identified that saturation can cause failure along lamination planes subjected to less than the maximum, load induced stress. This research can be utilized to improve the hydraulic fracturing design models to optimize formation fractures, and increase revenue for the oil and gas industry.

The range of applications for composite materials is growing, but understanding of the effect of defects is limited, as is the ability to detect them. Versatile non-destructive testing (NDT) techniques, that can be deployed rapidly and reliably, to detect and monitor damage in composite components are vital to the continued growth of this sector. This research investigates the application of Digital Image Correlation (DIC) as an NDT technique for monitoring delamination defects in Fibre Reinforced Polymer (FRP) composites. The research has matched physical experiments with Finite Element (FE) modelling. Four types of glass-fibre reinforced epoxy matrix composite structural elements were designed and manufactured to assess this application of DIC. The first two types of structural elements were flat coupons containing fully embedded delaminations, artificially introduced using two different methods. It was found that by placing these specimens in three-point bending, near surface delaminations, one ply below the surface being monitored, would cause a plateau in the surface strains. This plateau in strains was used to measure the embedded defect sizes. The size of the delamination was consistently overestimated from the interpretation of the strain fields. This was improved with the assistance of FE modelling to identify the relationship between the feature and the delamination. Pulse thermography was found to be a better technique for measuring the size of these defects. The third type of specimen was a flat coupon containing a milled-slot, which was fatigued to grow a delamination at the foot of the milled slot, and the delamination measured visually. For this specimen, the DIC results showed good correlation with the visually determined delamination lengths with an empirical fit applied to the strain results. Both lock-in thermography and pulse thermography were used to measure the delamination size of the same specimens and showed reasonable correlation with the visually determined delamination lengths. Finally, tubular specimens containing embedded PTFE delamination-defects were fatigued at different ratios of tension and torsion. DIC of the specimens loaded at the fatigue load ratio at which the delaminations were grown could not be used to quantify the size of the delaminations. The work has shown that DIC can be used to monitor delaminations in some structural elements, however the type of loading needs to be considered to ensure sufficient influence on the surface strains to enable strain features that can be used to measure the size of delamination.

This thesis investigates the appropriateness of a simplified, open-source digital image correlation (DIC) software for use in quasi-static, structural testing utilizing two-dimensional (2D) DIC measurements. DIC is a non-contact optical measurement technique that uses computer vision to track unique attributes on the surface of an object. For structural testing, traditional instrumentation such as displacement sensors and strain gages are impractical for full field measurements due their limited ability to capture large amounts of data. However, over the past decade, DIC has proven a successful method for full-field kinematics measurements, making it an appealing tool for collecting high densities of accurate data. This thesis specifically studies the accuracy and limitations of the DIC software, MODEM, for various test specimens and loading conditions. This research work is part of an experimental program comprised of three phases. The first stage was conducted by another investigator on aluminum coupons tested in pure tension. These results were used to calibrate parameters (speckle pattern density, lighting, and camera settings) used with the DIC software. The second stage included pure compression tests on concrete cubes and concrete cylinders to compare the difference in results between: (i) surface curvature, (ii) camera distance, (iii) surface treatment, and (iv) speckle pattern color. The final stage involved analysis of a tension test of a concrete prism completed at the University of Auckland in an effort to assess how MODEM could be utilized to accurately detect onset and propagation of concrete cracking. Results showed the most accurate DIC strains were within 5% error when compared to traditional instrumentation for aluminum loaded in tension and within 6% error for concrete loaded in compression/tension. This level of accuracy is comparable to existing open source and commercial DIC software utilizing 2D DIC analysis. Therefore, MODEM can be used to provide accurate 2D DIC strain measurements for small and medium scale structural test specimens when using the following parameters: (i) the surface of the specimen is planar, (ii) the camera is placed accordingly so the maximum amount of zoom can be used, (iii) the surface of a test specimen is free of debris or imperfections, and (iv) a high contrast and evenly distributed speckle pattern is used. Computational analysis of the results showed that known material properties can be used to calibrate, or remove errors from, the DIC results when traditional instrumentation is not available. Additionally, results showed MODEM strain contours can be used for initial detection of cracks in concrete loaded in tension while MODEM tracking performance can be used to characterize the centerline and orientation of cracks. The experimental tests provide critical information on how to set up, run, and analyze DIC results when using MODEM. The full field measurements are of value in providing accurate data for structural testing to develop a better understanding of material response and structural performance, since large-scale tests are typically limited by a sparse number of data points when using traditional instrumentation.

Digital Image Correlation (DIC) is a widely used full-field measurement technique in the field of experimental mechanics because of its simplicity and ease of implementation. However, owing to the inherent complexity of DIC error sources, the problem of DIC error reduction and uncertainty quantification is still unsolved and has received considerable attention in recent years. The existing work on DIC error reduction is usually focused on specific error sources, e.g. local smoothing techniques are normally applied to reduce errors due to image acquisition noise. Moreover, DIC uncertainty quantification methods are usually derived from a subset-based DIC framework with an assumption of Gaussian image noise. Established methods are normally subject to an ad-hoc choice of parameterisation and might only be able to achieve a local optimum. On the other hand, originally developed in geo-statistics, Kriging is known as optimal interpolation to predict interpolated values using random variables as a realization of a Gaussian process. The Kriging technique has the excellent capability in global optimisation and uncertainty quantification. It is advisable to make an attempt to introduce the Kriging method to DIC to facilitate the solution of error and uncertainty issue. The main purpose of this thesis is to offer a generic and global method that can reduce general DIC errors and quantify measurement uncertainty for displacement and strain results based on Kriging regression from Gaussian Process (GP) and Bayesian perspective. Firstly, a new global DIC approach known as Kriging-DIC was developed through incorporating the Kriging regression model into the classical global DIC algorithm as a full-field shape function. The displacement field of the Region of Interest (RoI) is formulated as a best linear unbiased realisation that contains correlations between all the samples. The measurement errors of control points are accounted for through a global regularisation technique using a global error factor. With the aid of the Mean Squared Error (MSE) determined from the Kriging model, a self-adaptive updating strategy was developed to achieve an optimal control grid without artificial supervision. The developed Kriging DIC method was compared with subset-based DIC, FE-DIC and B-Spline DIC by using synthetic images and open-access experimental data. The effectiveness and robustness of Kriging DIC was verified by numerical examples and an experimental I-section beam test. Secondly, a Kriging-based DIC uncertainty quantification method was proposed to quantify uncertainty of displacement and strain results of the subset-based DIC through a post-processing analysis based on Kriging regression. The subset-by-subset uncertainty was estimated through the subset-based DIC framework and derived as a function of the inverse of the Hessian matrix and residual of Sum of Squared Difference (SSD). This local subset-based uncertainty was then integrated into Kriging regression formula allowing uncertainty quantification of displacement field from a global sense. Based on Cholesky decomposition and covariance matrix solved by the Kriging formula, a multivariate normal sampling process was used to quantify the strain uncertainty whereas displacement gradients were calculated by a Finite Difference technique. Both numerical case studies and an experimental cantilever beam test were employed to test the method, which was found to be able to improve the accuracy of displacement and strain results and quantify corresponding uncertainties. Furthermore, a new approach was developed to calculate strain results by means of Kriging gradients, which was also compared with a state-of-the-art PLS local fitting algorithm. In summary, the main contribution of this thesis is the development of a global DIC algorithm (i.e. Kriging-DIC) and a Kriging-based DIC uncertainty quantification approach. These two methods provide great potential to globally improve DIC measurement accuracy and quantify uncertainties of displacement and strain results.

The primary objective of this research is to conduct further evaluation of ultrasonic digital image correlation (UT-DIC) on strain map analysis and defect detection of adhesive joints with embedded speckle pattern. UT-DIC is a non-destructive evaluation method that utilized ultrasonic C-scan images for whole field strain and displacement analysis. Acrylic glass, epoxy resin system and metal shavings with high acoustic impedance of a specific weight were used to create the samples which were loaded under tension. Defects with varying shapes and sizes were implemented by surface preparation to understand the limits of this approach. UT-DIC and optical DIC strain map results were compared, and it was found that each approach detected certain shapes of defect better than the other.

Concrete structures in marine environments frequently experience long-term deterioration due to environmental exposure. This exposure results in surface damage with the subsequent spalling of concrete, which has a significant effect on the long-term durability of the structure. The reinforced concrete jetty investigated in this study suffered similar problems. The concrete jetty is located on the South East England coast. The jetty consists of a deck that is part precast and part in-situ cast, which is supported by steel, concrete and a sheet pile wall. Five decades after its construction, erosion by sea water is the most serious problem facing the jetty structure and has resulted in significant deterioration and surface damage. This project was established to evaluate the damage level of the jetty using an extended non-destructive measurement approach with an FEA simulation. The basic non-destructive measurement technique used in this investigation is a digital image correlation (DIC) optical system. The current DIC technique is limited to detecting macro cracks; thus, this investigation aims to develop an Extended Digital Image Correlation (EDIC) method to extend the capability of the current DIC from measuring the strain field to detecting multiscale cracks and predicting micro crack propagation. There is an industrial necessity to enhance the damage assessment level based on micro-crack detection. The EDIC study was performed empirically and demonstrated an important role in detecting damaged zones and multiscale cracks, including micro- and macro-cracks of the concrete surface. The EDIC can be used for further studies on detailed damage mechanisms in concrete and other engineering materials, such as timber or masonry structures. The assessment provide information on the current structural degradation, load bearing capacity and safety margin of the damaged jetty. To simulate the ageing jetty numerically, a material model of the ageing concrete was created in terms of the tested core samples obtained from the jetty structure, and the model was implemented in an UMAT subroutine in ABAQUS for FEA simulation. The mechanical properties of the ageing jetty obtained from the experimental tests proved to be suitable, with a compressive and tensile strength of approximately 67 MPa and 4.2 MPa, respectively, and the elastic modulus was 38728 MPa. Using the DIC in situ assessment and FEA simulation, the damage evaluation was completed. The results indicated a considerable decrease in the structural stiffness of the damaged jetty of approximately 40%. The load bearing capacity of the damaged jetty reported was approximately 240 tonnes. Despite the significant damage, the safety margin under the current practical loading condition (162 tonnes) is still high, i.e., approximately 1.48. However, due to the severe condition of the damaged jetty located in an aggressive marine environment and the loading impacts, it is highly recommended that the cracks and corrosion be immediately stopped and controlled. Furthermore, for safety reasons, any additional loads in conjunction with the current practical load (162 tonnes) should be avoided.

Extreme temperatures have increasingly played an important role in engineering applications, including leading edges during hypersonic flight, spacecraft re-entry, and propulsion systems. In order to design for such thermo-mechanical conditions, materials must be characterized using suitable measurement methods. DIC is a popular and versatile method in full-field measurement. In brief, DIC compares images of a sample between its undeformed and deformed state in order to get displacement and strain field maps. Since the images are acquired from digital cameras, it is important to have high contrast images for meaningful correlation. Exposure time is a pivotal camera setting relating to camera sensitivity. Alteration in exposure time results in variation of image contrast, thereby affecting DIC correlation. Also, it is well known that at extreme temperatures, materials emit light which can saturate DIC camera sensors, but the light can be mitigated using optical bandpass filters. In previous work, many have shown that blue bandpass filters can effectively extend the temperature range of DIC, and our lab has shown that ultraviolet (UV) filters can extend the range further. In this thesis, four different temperatures: room temperature, 1300°C, 1450°C, and 1600°C were tested by rigid-motion experiments. At each temperature level, UV images were acquired in order to examine the variation of DIC error over the whole range of exposure time. UV images were acquired at exposure times ranging from 500μs to 61,000μs, which are the minimum and maximum possible values for the cameras used in this thesis. The results showed that there were higher errors of UV-DIC at extremely dark or bright exposure times where as errors were generally insignificant at intermediate exposure times. In order to perform meaningful DIC up to 1600oC, the exposure time for the camera used in this thesis is suggested to be set between 10,000μs and 40,000μs.

Recrystallised alumina is used as a high performance crucible material. Its thermal shock resistance is known to be affected by component shape, and also by processing variables, since the defects and internal stress at both the microscale (i.e. between grains due to anisotropic crystal properties) and macroscale (i.e. due to differential shrinkage during sintering) influence the fracture strength. The aim of this thesis is to study the nucleation and growth of defects in pure alumina and Cr-doped alumina, and to investigate how their behavior is affected by residual stresses, such those introduce by thermal expansion of the crystal grains. In this thesis, digital image correlation is applied to polycrystalline aluminas (i.e. Cr-doped alumina and pure alumina with average grain 3.6 µm and 1.5 µm respectively) that are stressed in an optical microscope. The defect size and the surface crack opening displacement were measured using digital image correlation. The distribution and population of crack nucleating defects were obtained by in-situ observation of the stressed surface and by analysis with digital image correlation. These data are then compared with independent measurements of the defect population using Hertzian indentation, from which defect populations are derived for the pure and Cr-doped alumina samples. Grain boundary plane and grain orientations in the vicinity of crack nuclei were characterised by electron microscopy. Crack nuclei were shown to develop at boundaries predicted to have high tensile thermal strains, caused by the orientation of the grain boundary plane relative to the adjacent grains, such as basal plane grain facets. The techniques of focused ion beam (FIB) milling and electron backscatter diffraction (EBSD) characterization of the crystallographic orientations and structure of cracked grain boundaries were used to provide data for a model to explain the cracking of these boundaries as a result of the thermal strains and the anisotropic thermal expansion behaviour of alumina.

This thesis is concerned with the evaluation, in-situ, of the elastic strain energy release rate of cracks. This can define the criteria for crack propagation, and it is usually necessary to obtain this via calculation from the geometry and applied load. A new method is proposed, based on the conjoint use of digital image correlation to measure full-field displacements and finite element to extract the strain energy release rate of surface cracks. It has been extended to 3-D datasets with the use of digital volume correlation and tomographic imaging. A finite element model with imported full-field displacements measured by DIC/DVC acting as boundary conditions is solved and the J-integral is calculated. For linear elastic materials, modal contributions can be separated via the interaction integral. The method has been benchmarked using synthetic datasets to assess its sensitivity to noise and experimental uncertainties. It is very robust to experimental noise and can be used without knowledge of the specimen geometry and applied loads. The application of the method in 2-D is demonstrated in an analysis of experimental data for a mode I fatigue crack, introduced to an aluminium alloy compact tension specimen. Analysis of mixed-mode cracks in 2-D is shown on a PMMA sample with the Arcan geometry. In 3-D, static loading of a fatigue crack in nodular graphite cast iron is studied and the results from the method are compared with those obtained via a field-fitting approach. Diffraction analysis of polycrystalline materials can determine the full tensor of the elastic strains within them. Maps of elastic strains can thus be obtained typically using synchrotron X-rays or neutrons. A method is presented to calculate the elastic strain energy release rate of a crack from 2-D diffraction strain maps. The diffraction data is processed via a finite element approach to obtain the parameters required to calculate the $J$-integral. A validation is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of synchrotron X-ray diffraction strain maps of a propagating fatigue crack in a bainitic steel, before and after an overload. Finally, a complex case study of stable fracture propagation in polygranular isotropic nuclear graphite is presented. Synchrotron X-ray tomography and strain mapping by diffraction were combined with DVC and image analysis to extract the full-field displacements and elastic crystal strains. The displacement fields have been analysed using the developed methods to extract the critical strain energy release rate for crack propagation. Non-linear properties described the effect of microcracking on the elastic modulus in the fracture process zone. The analysis was verified by comparison of the predicted and measured elastic strain fields.

Cold rolled aluminum is a widely used metal in industry. The forming limit diagram (FLD) which is commonly used to predict safe deformation parameters currently fails to predict the uniform elongation after non-proportional strain path often found in industrial operations. In this work, a non-proportional strain path change in aluminum alloy 3104 going from plane strain tension to uniaxial tension was investigated. Plane strain tensile tests have been carried out to various pre-strains (3%, 6% and 9%), followed by uniaxial tensile tests at various orientation with respect to the tensile direction (0°, 45° and 90°). Digital image correlation (DIC) was employed to analyze the strain distribution in the sample during deformation. The mechanical response was studied as a function of pre-strain and reloading angle to quantify the effect of strain path change on AA3104.

Understanding vertebral mechanics is of interest for identifying persons at risk of fracture, whether that is due to everyday loading such as in osteoporotic fracture or as a result of dynamic loading leading to a traumatic fracture. Vertebral fractures negatively impact the quality life of patients and represent a large financial burden on the healthcare system. A powerful but underutilized tool that can be used to study vertebral loading and fracture is digital image correlation (DIC). DIC is a non-contact optical method for measuring the displacement on the surface of materials, including bone. In this thesis, DIC was used in a laboratory setting to provide a more complete understanding of the response of vertebral bodies to compressive loading. The first investigation compared measurements from DIC with strain gages, a commonly accepted experimental method for measuring the bone surface response. For porcine vertebral bodies, the agreement was strong between the strain gages and DIC-measured strains indicating that DIC can be successfully used on bone. Based on those findings, experimental studies were performed using DIC to identify fracture of the anterior cortex and to quantify rate-dependency of the vertebral body response. For the fracture study, high DIC strains on the anterior cortex of vertebral bodies corresponded well with the locations of damage identified by observation of the video. For the rate-dependency study, the DIC displacement patterns were similar for the slow and fast rate tests, but the displacements from the slow rate tests had higher magnitudes, as expected for viscoelastic materials such as bone. Finally, specimen-specific finite element (FE) vertebral body models were created and DIC was used to validate the displacement and stiffness response. The FE models were predictive of the experimental stiffnesses measured using DIC on the surface of the vertebrae. This thesis demonstrates the utility of DIC for experimental vertebral body investigations and for validation of FE models. Through these studies and future work, DIC has advanced and will continue to advance the understanding of vertebral mechanics under everyday loads as well as in simulated osteoporotic and healthy bone trauma.
Applied Science, Faculty of
Graduate

Two-phase Ti6246 alloy is a light weight material exhibiting very high strength at higher temperatures compared to the commonly used Ti64 alloy. This particular alloy is used at the later stages of compressor discs within the aero engines. However, compressor discs undergo a number of cyclic stresses, which could eventually lead to fatigue failure. In order to optimize the microstructure for design and lifing models, an improved understanding of the localised deformation mechanisms is crucial, particularly at the surface, as cracks can be initiated leading to failure and in turn affect the life expectancy of the component. Two-phase alloys in use have very complex lamellar microstructures comprising of a mixture of coarse and fine phases and their role in deformation can be very complex and difficult to understand. The focus of this study was particularly based on the importance of the beta phase in strengthening two-phase microstructures. Therefore, this study has been simplified to compare model lamellar microstructures, which have particular sizes of beta phase in between alpha lamellae. Digital Image Correlation along with high resolution imaging was used to develop a detailed understanding of the localised deformation in these microstructures. Widening the beta phase in-between alpha lamellae caused a more homogenous deformation, while ageing the beta phase with fine secondary alpha strengthened the microstructure. However, all microstructures showed that the single continuous alpha layer at beta grain boundaries depicted the highest amount of deformation, which can be detrimental for the life of the component. The behaviour of slip at the α/β interface not only depended on the size of the phases but also depended on the neighbouring crystallographic orientations and the relationship of the two phases, specifically the alignment of the close packed slip directions. Strain maps of these microstructures were subsequently related to corresponding Schmid factor maps and crystal plasticity models to improve this understanding.

碩士
國立中興大學
機械工程學系所
102
The present study has developed a plane displacement measurement system based on a digital image correlation method. For these purposes,the strain of large deformation was defined as 40%. A series of analyses was performed on the images before and after deformation, including correlational analysis, connected component labeling, and shape interpolation function analysis. Furthermore, optimizations were made employing displacement equations and brightness of transformation models, in conjunction with Newton’s method. Iterative methods were used to find the underwent displacement of an object after deformation,finally determining the surface displacement field and the strain field. However, the use of Newton’s method iteration methods requires inputting an initial value. These values must first be derived by marking each connected area with connected component labeling, then constructing a grid with this data and corresponding the before-after images based on this grid. The methods of this study were to print prepared images onto the object being tested, then to record digital images of the object before and after deformation. Analysis was conducted with software based on digital image correlation theory and shape function, to determine the displacement field of the object’s surface,concluding with a discussion of the displacement field derived from analysis, and possible improvements to be made for future investigations.

碩士
國立中興大學
機械工程學系所
99
Digital image correlation method is a non-contact, non-destructive optical measuring method, the principle is the second image by comparing each pixel with the first image (reference image) in the fixed point of reference pixel correlation to find images from the second image with the first reference pixel has a maximum correlation of the pixels, the point that this reference in the second pixel of the image of the corresponding points in the statistics there are several kinds of method used to calculate the correlation coefficient, used in digital image correlation method is the most common use of Pearson''s correlation coefficient for correlation matching of operations. In this study, obtained by deformation of the surface before and after images, and image distortion as a reference image before using the digital image correlation method to find the reference image of each pixel in the deformed image of the integer corresponding to the point, and by a simple displacement equation and the brightness of the transformation model with the theory of the Newton equation of motion optimization, and then obtained through iteration after the surface displacement and strain in the deformation of sub-pixel part, and then calculate the displacement and strain by filtering the of smoothing, and then obtain the deformed surface in the global displacement field and strain field.

碩士
國立雲林科技大學
機械工程系碩士班
92
This text presents a new numerical conception of digital image correlation to measure full-field strain in planar specimen which is suffering external force. This new method can afford strain information on entire field of specimen surface by processing two digital images which were respectively caught from the unforced and forced specimen. The new numerical procedures here aim at making this method a widely applicatory strain measuring method. It means that ideally this method can be applied in various conditions. Two numerical iterative methods are used to conclude the whole optimized strain solution in this research. Both two numerical methods can appropriately be called “selectively exhaustive optimization”.This is because each iterative method is an exhaustive optimization method with techniques of reducing time consumption. While all numerical procedures finished, the optimized strain solutions are verified and compared with the experimental results from MTS.

Except for aerodynamics forces, all vehicle excitation forces are generated at the tyre-road interface. Considering low speed applications, such as terramechanics where the aerodynamics force are negligible, the road-tyre interaction is of extreme importance. Crucial variables which govern the forces generated at the tyre-road interface are tyre side-slip angle, tyre longitudinal slip ratio and terrain pro le. Solutions to measure these variables exist for smooth hard roads but the solutions experience challenges on rough and o -road terrain. Digital Image Correlation is concerned with tracking the changes of a scene in a sequence of images or in images obtained from multiple viewpoints. These methods are frequently used in micro and nano-scale mechanical testing due to its ease of implementation and use as well as its non-contact approach. As a result these techniques are being implemented in many elds from material testing, physics, lm animations and engineering. The aim of this thesis is to investigate the applications of Digital Image Correlation in vehicle dynamics using cost e cient o -the-shelf digital cameras and lenses. The following three vehicle dynamic problems are investigated: The measurement of the vehicle side-slip angle, longitudinal slip-ratio of a pneumatic tyre and high delity terrain pro ling. The vehicle side-slip angle can be used as a measure of the vehicle stability and therefore be used to improve the e ectiveness of vehicle stability controllers. The tyre side-slip angle is also a vital measurement in characterising the lateral force characteristics of pneumatic tyres. A planar measuring method using Digital Image Correlation is shown to accurately measure the side-slip angle. The method is expanded by developing two additional algorithms which can measure all translational and rotational velocities. These methods are validated on both smooth surfaces and rough o -road terrain. A method is also implemented whereby the longitudinal slip ratio of a tyre can be measured using a single camera. Therefore, doing away with the conventional method of using three independent measurement systems. Features in the contact patch, encompassing both the tyre and the road, are tracked in a sequence of images. The features are classi ed into features lying on the tyre, road and outliers using a clustering algorithm. This enables the system to determine the tyre and road velocities from which the slip ratio is determined. High delity terrain pro ling is performed using a calibrated stereographic rig to obtain a three dimensional point cloud of the scene which is being viewed. The point cloud generated at one sample contains a grid of points encompassing a large area with points spaced both laterally and longitudinally. Overlapping point clouds are generated and joined using various registration techniques. The joined point clouds are sub-sampled to obtain a regularised grid of point containing a single point cloud of non overlapping points. The proposed techniques create new possibilities in the eld of vehicle dynamics. Enabling the side-slip angle to be measured in rough of road conditions while providing additional measurements. The longitudinal slip ratio which is measured directly at the contact patch could pave the way for better understanding the mechanism of the longitudinal tyre force generation. The inexpensive road pro ling systems enables multiple sensors to be used in terramechanics tests to determine the impact of a vehicle on the environment. The thesis presents the mere tip of the ice berg concerning digital image correlation used in vehicle dynamics with many more possibilities waiting to be discovered.
Thesis (PhD)--University of Pretoria, 2015.
tm2015
Mechanical and Aeronautical Engineering
PhD
Unrestricted

Digital image correlation (DIC) is a powerful experimental technique for measuring full-field displacement and strain. The basic idea of the method is to compare images of an object decorated with a speckle pattern before and after deformation in order to compute the displacement and strain fields. Local Subset DIC and finite element-based Global DIC are two widely used image matching methods; however there are some drawbacks to these methods. In Local Subset DIC, the computed displacement field may not satisfy compatibility, and the deformation gradient may be noisy, especially when the subset size is small. Global DIC incorporates displacement compatibility, but can be computationally expensive. In this thesis, we propose a new method, the augmented-Lagrangian digital image correlation (ALDIC), that combines the advantages of both the local (fast and in parallel) and global (compatible) methods. We demonstrate that ALDIC has higher accuracy and behaves more robustly compared to both Local Subset DIC and Global DIC.

DIC requires a large number of high resolution images, which imposes significant needs on data storage and transmission. We combined DIC algorithms with image compression techniques and show that it is possible to obtain accurate displace- ment and strain fields with only 5 % of the original image size. We studied two compression techniques – discrete cosine transform (DCT) and wavelet transform, and three DIC algorithms – Local Subset DIC, Global DIC and our newly proposed augmented Lagrangian DIC (ALDIC). We found the Local Subset DIC leads to the largest errors and ALDIC to the smallest when compressed images are used. We also found wavelet-based image compression introduces less error compared to DCT image compression.

To further speed up and improve the accuracy of DIC algorithms, especially in the study of complex heterogeneous strain fields at various length scales, we apply an adaptive finite element mesh to DIC methods. We develop a new h-adaptive technique and apply it to ALDIC. We show that this adaptive mesh ALDIC algorithm significantly decreases computation time with no loss (and some gain) in accuracy.

碩士
國立高雄大學
土木與環境工程學系碩士班
104
Unmanned aerial vehicle (UAV) can be used to take aerial photographs, and it has been rapidly developed in many fields in recent years. This study uses digital image correlation method (DIC) to increase precision of image stitching and three-dimensional terrain model. DIC will be applied in two ways. Firstly, DIC is used to locate control points’ image positions in different photos, so that the precision of image stitching and three-dimensional terrain model will increase by raising control points’ precision. Secondly, DIC is used to match feature points which extracted by SURF algorithm and then these points are imported into Pix4dmapper to increase the precision of image stitching and three-dimensional terrain model. An experiment is carried out to compare the precision of various image matching methods, such as SIFT, SURF, BRISK as well as DIC. The results of different movements in x and y directions show that the precisions of SIFT、SURF and BRISK range from 0.1 to 1 pixel and the precision of DIC is 0.02pixel. It shows that DIC is more accurate than the other methods. Furthermore, this study compares two different methods adopted to obtain the image coordinates of control points. In one of the method, the control points’ image coordinates are positioned manually. The other method will use DIC method to improve the precision of manually positioned control points. Ladder specimen’s results show that the positioning precision by using DIC is 0.08 mm while the manual positioning precision is 0.201 mm, 3D model specimen’s results show that the positioning precision by using DIC is 0.48 mm while the manual positioning precision is 0.696 mm. It shows that applying DIC to positioning control points can improve the precision. Eventually, this study carries out two indoor experiments to evaluate the influence of different amounts of DIC connection points and SURF connection points on the precision of image stitching and three-dimensional terrain model. According to the altitude error of check points from ladder specimen and 3D model specimen, we can find that importing DIC connection points can increase the precision of image stitching and three-dimensional terrain model. The magnitude of improvement will be raised as the amount of connection points increases, and its effect is better than importing SURF connection points. Ladder specimen’s result shows that the altitude error is 0.08mm without connection points. The best result is 0.049mm while importing DIC connection points. The 3D model specimen’s result shows that the altitude error is 0.48mm without connection point. The best result is 0.27mm while importing DIC connection points. These results show that applying DIC to image stitching and three-dimensional terrain model establishment can actually improve the precision.

碩士
國立臺北科技大學
電機工程系研究所
100
With the coming of age of the digital era, it brings us a colorful digital life. However, the authenticity of digital image has become an important issue as the digital image is easily modified. Region duplication is a common and simple way to modify or tamper the digital image. The recent methods proposed in literature are based on spare image invariant feature (such as SIFT, SURF), and can effectively detect the geometric and brightness tampering. However, they fail to detect the tampering when the image invariant feature is inadequate, and often misclassify the original contents as the duplication tampering when the image contains the intrinsic repeated elements. Our method proposes a modified SIFT algorithm, an image invariant feature clustering analysis, and local outlier detection to improve the above problem. In order to locate the tampering region, we design an adaptive tampering locating method based on image local region correlation and image texture feature. We evaluate our proposed approach on tampered images with and without intrinsic repeated elements, and the geometry and brightness of the tampered duplicated region is further altered by an automatic forgery program. The experimental results and analyses demonstrate that our proposed method is robust and effective in region duplication detection.

In the structural engineering community, a need exists for a non-contact two-dimensional measurement system which could provide information for field monitoring and greatly enhance the accuracy of numerical structural models. Recent advances have enabled the use of digital image correlation (DIC) to calculate the surface displacements of chosen targets in a series of digital images with a high degree of accuracy. Images are recorded during an experiment and are afterwards post-processed to find relevant information including, but not limited to, a) global displacement, b) relative displacement and c) changes in strain. In this research, a series of experiments were conducted to create measurement techniques for monitoring steel and reinforced concrete (RC) structures utilizing DIC. However, to ensure accurate DIC measurements, the addition of artificial texture from lightly applied spray paint on finished concrete was investigated and was determined to noticeably improve results. Furthermore, the placement of the digital camera relative to the structure being monitored was shown to control not only the desired field of view in the region of interest, but also the resulting image texture and DIC measurement accuracy. The DIC technique was applied to monitor and understand two important aspects of structural evaluation: a) the movement along shear planes and b) the evaluation of changes in strain due to curvature in beam elements. To monitor the change in crack width and slip, a method was created and validated on a series of artificial and reinforced concrete images for the cases of pure shear, pure flexure and combine flexure and shear. Curvature was found to impact the crack slip measurement, but its effect can be removed by using an innovative averaging technique. The curvature of a steel HSS and RC beams was found by using virtual DIC strain gauges and the horizontal strain profile. Results matched well with the curvature from electrical foil gauges and numerical models when the gauge length was maximized and selected so that the effects of cracking were accounted for.
Thesis (Master, Civil Engineering) -- Queen's University, 2012-09-28 09:36:04.274