Academic literature 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

Optical image correlation has been demonstrated for recognition of patterns and images by comparing against stored reference filters corresponding to known images. Optical implementation of this operation is highly desirable because image correlation can be generated in an analog fashion using common optical elements, providing considerable speed advantages over digital computation. Spatial light modulators have been used as the filters in a vanderLugt correlator configuration, but low throughput and slow download times, particularly for a large number high resolution images, were major drawbacks. Using a wavelength multiplexed holographic element for storage of the reference image filters provides increased access speed, and the recent availability of visible wavelength, tunable external cavity semiconductor lasers, wavelength multiplexing becomes practical. In this paper, we report on an optical image correlation system using a holographic storage element for fast access speed and translation tolerance. Amplitude and phase encoded transparencies, as well as spatial light modulators, were used as the input image sources.

Texture correlation, a modified digital image correlation procedure, utilizes the natural texture of biological tissues to measure displacement fields between two consecutive digital images [1]. This algorithm is based on the assumption that a pixel within an image can be characterized by a unique intensity pattern of a subset of pixels surrounding it. The displacement of the unique subset can be tracked by comparing the reference and deformed image.

Techniques for performing digital image recognition on speckled images are presented. Rather than performing speckle reduction, the speckled image is correlated directly with a reference function. Statistical properties of the correlation value are derived using the multiplicative noise model for image plane speckle. It follows that the correlation value is a Gaussian random variable. Statistical detection theory dictates that images are distinguishable when the standard derivations of the correlation values are small compared to the separation of the mean values. Several reference functions are considered for both intensity correlation and correlation for which the input speckled images are clipped. One reference function considered is the incoherent image of the desired object: another is the maximum-likelihood reference function. Experiments performed on planar rough objects indicate good agreement between theory and experiment. The best ability to discriminate is obtained using the maximum-likelihood reference function.

Mechanical characterization of inhomogeneous and/or geometrically complex biological tissues requires precise and accurate determination of strain fields. Digital image correlation is a well established technique for determining strain fields on the surfaces of deforming materials. The technique involves matching patterns between pairs of images to estimate the displacement of certain regions or features on a sample. 2 Image correlation has also been used to track deformations in dynamic magnetic resonance images of heart and brain. 3

A high-power LED can generate tremendous heat under the operation, which causes the LED chip undergo large deformation. LED Wire Bonds may undergo deformation because of the mismatch between the LED chip and substrate. Presently, measurements of deformation and strain in operational electronics are limited to measurement on a cut-plane using techniques including digital image correlation and moiré interferometry based techniques. There is need for tools and techniques that can help quantify the in-situ chip deformation and interconnects inside the LED. Digital Volume Correlation (DVC) has been used in conjunction with X-ray Micro-CT for three-dimensional measurement of deformation and strain in LEDs under operational stresses. The Digital Volume Correlation has been used to correlate the undeformed image with deformed images by computing correlation functions throughout each voxel. The deformed images have been generated by CT scanning over the object while the LED is operational. The correlation function computation starts at specific fixed subset window in the reference image, and searches every possible subset window in the deformed image to identify the deformation in the electronic structure. Once the displacement components have been derived, the strain components have been computed by calculating the gradients of the displacement field. In this paper, the full strain field, both in-plane and out-plane strain, will be presented, and the LED chip deformation shape will be analyzed.

When the classical joint transform correlator (CJTC) was applied to pattern recognition, one of the most well known disadvantages was that the cross correlation signals between the object and the reference patterns as well as those between the reference patterns themselves would join closely in the same output plane. This fact causes inconvenience to identify the necessary output correlation signals between the object and the references, especially when a large number of references was used in the input image. Q.Zhan and T.Minemoto(1) proposed the subtracted joint transform correlator(SJTC) to remove the correlation signals between the references from the output plane, and the binnary subtracted joint transform correlator(BSJTC) to improve furthermore the output correlation results. According to the SJTC and BSJTC, the cross correlations between the references had been successfully removed from the output plane by subtracting the Fourier power spectrum of the references from the joint Fourier power spectrum of the input image. Thus far, the subtraction processing was performed by a computer. In this paper, a new all-optical SJTC system is proposed. In this system, a holographic interference was introduced to perform the subtraction of the Fourier power spectrum of reference patterns. There is not any digital processing by a computer in the system, it is possible to achieve the real time SJTC. The experimental arrangement of the system, the shift-invariant characteristics and the dscriminability of input patterns are described in the following.

Fractal textures occur in natural scenary or satellite images (clouds, ocean waves). However, processing of fractal image data to extract measurements such as fractal dimension is highly computation-intensive when serial digital methods are used. Massively parallel nonlinear optical processing methods are proposed to characterize fractal images in real time. A photorefractive real time image processor performing a combined convolution/correlation operation is used to measure the correlation dimension of sample fractal patterns. The optical algorithm employs an image autocorrelation performed simultaneously with an optical convolution by using a spatially multiplexed array of 9–100 discs of various radii setting a range of scales. A digital neural network in the correlation plane evaluates the maximum intensity in each light patch and computes the fractal dimension. By placing phase screens or window functions in the third port, additional fractal analyses may be accomplished, including iterated function system encoding. Double convolution involving two different images and a kernel provides scale sensitive image comparison, closely related to wavelet analysis. Real time nonlinear optical coprocessing appears useful in several different approaches to characterization of fractal imagery. Preliminary experimental results will be presented.

The extension of digital image correlation method to ultrasonic C-scan acoustical speckle images of the bulk is presented in this paper. The approach discussed in this paper is ideally suited to composite materials such as particulate composites, fiber-reinforced plastics, and laminated composites. It can also be effectively employed for critical surfaces that are not within view, such as interfaces and back surfaces. Images taken prior to and after deformation are analyzed to estimate a deformation profile from changes in the image. The aim of the method is to find the displacements and strains of small subsets from the second image relative to the first one. This is accomplished by comparing the intensity levels of the subsets in the images. The speed and accuracy of the system is enhanced by the genetic algorithms(GAs) which are used to optimize correlation of images. An ultrasonic C-scan system was used to obtain the intensity images of the front or back surface of an isotropic or composite material. Three experimental tests were conducted to illustrate the application of Ultrasonic C-scan digital image correlation method. These tests include: 1) uniform translation, 2) small angle rotation, and 3) uniform deformation. A laminated carbon/epoxy composite panel (305×305×8 mm) was used for uniform translation and small angle rotation tests. A rubber specimen was used to perform the uniform axial deformation test. The results of correlated displacements (angles) are compared to the actual displacements (angles). The accuracy and applied limitation of the three experiments are also illustrated in this paper.

A novel Digital Particle Image Velocimetry (DPIV) correlation method is introduced which estimates the displacement using the phase content within the Fourier based cross-correlation. The use of weighted least squares and robust least squares estimation is introduced in order to improve the linear phase estimation of this technique. Spectral filters are constructed using the energy content of PIV images to define weighting functions for the dominant singular vector regressions. This performance of this technique is measured using Monte Carlo simulations of DPIV images. The resulting error analysis demonstrates substantially reduced errors for higher particle-image diameters for images containing low amounts of noise. For high noise images, the reduction in bias and RMS errors is not as drastic due to limitations of extracting the phase information. However, this correlation technique is able to eliminate peak-locking errors, shown to be a substantial source of error in noisy images, by directly extracting the displacement information in the spectral domain.