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Khoo, Stephen W. "Low velocity impact of composite structures." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/7388.
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SerraniÌa-Soto, Florencia. "Low velocity impact of composite sandwich panels." Thesis, Queen Mary, University of London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398305.
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FENG, DIANSHI. "Simulation of low-velocity impact damage in sandwich composites." Doctoral thesis, Università degli Studi di Cagliari, 2014. http://hdl.handle.net/11584/266475.
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Composite materials have been increasingly used in many wind energy and transport applications due to their high strength, stiffness and excellent corrosion resistance. One of the main limitations of composites is their high susceptibility to impact-induced damage, which may result in significant strength reduction or even structural collapse. A detailed understanding of the extent and nature of impact damage is thus greatly needed for damage tolerance based structural design and a reliable estimation of the residual strength of a damaged structure.
In this thesis, fracture mechanics based progressive damage models, cohesive interface elements and crushable foam models were used to predict the structural response and internal failure mechanisms of sandwich composites subjected to low-velocity impact; various failure modes typically observed in composites including delaminations, fibre fracture and matrix cracking were simulated and implemented into ABAQUS/Explicit through user-defined subroutines VUMAT.
Numerical simulations were assessed and validated by a series of experimental analyses carried out through low-velocity impact tests (using drop-weight testing machine) and damage calibration tests (using X-radiography, Ultrasonics and optical microscopy of polished cross-sections). Good agreements were obtained between experiments and predictions not only in terms of structural responses as well as regarding the shape and size of internal damage under various investigated cases.
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Ramakrishnan, Karthik Ram Engineering & Information Technology Australian Defence Force Academy UNSW. "Low Velocity Impact Behaviour of Unreinforced Bi-layer Plastic Laminates." Awarded by:University of New South Wales - Australian Defence Force Academy. Engineering & Information Technology, 2009. http://handle.unsw.edu.au/1959.4/43918.
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Low velocity impact behaviour of bi-layered laminates of acrylic and polycarbonate was investigated using a combination of drop tower impact experiments and explicit finite element analysis in LS-DYNA. Material characterisation tests were conducted in tension and in compression to obtain material properties for input to the material model in the numerical analysis. Quasistatic plate bending tests were conducted at different loading rates to compare the quasistatic response of the materials to the impact behaviour. Impact tests on circular plates of monolithic acrylic and polycarbonate were carried out using an instrumented drop weight impact tester. The impact force histories were recorded and a multiparameter approach was used to determine critical energy. Acrylic exhibited radial cracking, spalling and pene- tration while polycarbonate underwent large deformation and failed by dishing and plugging. The damage caused by impact in the bilayered laminate included partial or full delamination at the interface and radial cracks in the acrylic layer. The low velocity impact responses were simulated using 8-noded solid elements in LS- DYNA. A node-splitting technique based on maximum tensile stress failure criterion and an erosion approach based on maximum principal stress criteria was used to model the failure of acrylic. A material model that takes into account the asym- metric behaviour in tension and compression was investigated. The delamination between the acrylic and polycarbonate plate was modelled by a tiebreak contact with a shear strength based failure. The results of the finite element simulations are in good agreement with the experimental data.
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Osakue, Edward E. "A study of friction during low-velocity impact." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq54598.pdf.
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Brown, Samuel Alexander. "Low velocity impact resistance of reinforced polymeric materials." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312834.
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Banik, Chandan Kumer. "High mass low velocity impact on concrete beams." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/160.
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David-West, Opukuro Sunday. "Low velocity impact studies on CFRP composite structures." Thesis, University of Strathclyde, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428854.
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Ehrich, Fabian. "Low velocity impact on pre-loaded composite structures." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24662.
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Low velocity impact is a serious hazard for laminated composite structures. It can result in considerable loss of mechanical performance and must be taken into account during the design process. Extensive knowledge of the composite damage processes and advanced numerical simulation tools can help find optimal designs and reducing development costs. In addition to normal service loads such as bending moments, shear forces, torques, pressure loads, etc. airframe structures also have to withstand impact loads resulting from hailstones, runway debris or tool drops during maintenance work. These impacts are likely to happen while the airframe is stressed under normal service loads. The superposition of service loads and impact loads is likely to alter the impact response of a structure compared to an unloaded structure. In this work, the influence of in-plane compressive loads on the low velocity impact response of carbon fibre epoxy composites is studied. Low velocity impact experiments on T800s/M21 UD carbon fibre epoxy laminates, under various compressive pre-strains, have been carried out with impact energies of up to 45J. The compressive pre-load applied to the structure was observed to significantly increase the impact damage and reduce the post-impact strength. To predict the damage resulting from impacts with and without pre-loads, a 2D damage model has been developed and implemented into the commercial finite element code ABAQUS/Explicit. The model is based on a combination of continuous damage mechanics and fracture mechanics with interactions between damage modes considered for both, damage initiation and damage propagation. Thereby damage degradation is following non-linear propagation laws. The model's material degradation is governed by the material's fracture toughnesses which are important material input parameters for the damage model. A detailed series of laboratory tests have been conducted to develop test set-ups for the measurement of translaminar fracture toughness values, which are used as input units for the damage model.
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Madjidi, Saeid. "Low velocity impact of obliquely inclined composite plates." Thesis, University of the West of Scotland, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535957.
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A study into the performance of CSM (Chopped Strand Mat) reinforced polyester laminates subject to low velocity impact at oblique angles is presented. The investigation encompasses both an experimental and theoretical assessment of the impact event, viz damage tolerance and residual material properties of flat, clamped composite plates. A short introduction is followed by a comprehensive review of the most relevant published literature on all aspects of impact induced damage. A theoretical analysis based on the use of damage toughness parameters is formulated to predict the residual tensile strength and stiffness properties of impact damaged plates. The analysis is further extended to determine the total internal stress distribution in the system. A combination of Hertzian contact, plate bending and finite element solution are used to establish the influence of plate inclination on the resulting stress state. Several common failure criteria were used to predict the extent of the damage. These predictions are compared with experimental data. Results from an extensive experimental programme are presented A fully instrumented test rig was used to assess the influence of imparted energy, impact force, and plate indentation with respect to surface indentation profiles, damage areas and micrographic evidence. The theoretical and experimental results are graphically presented, discussed in detail and exhibit good agreement. The study is finally concluded with comments summarising the most pertinent points derived from the present investigation together with recommendations for further work.
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Zheng, Daihua. "Low Velocity Impact Analysis of Composite Laminated Plates." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1194991384.
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Hassan, Mohamad. "The low velocity impact response of sandwich structures." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/9415/.
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In this study, the mechanical properties and fracture behaviour of a range of core materials have been investigated in order to elucidate the impact properties of sandwich structures. Initially, the compression properties of the core have been evaluated at quasi-static and impact rates of strain. It has been shown that the plastic collapse strength of the cores is highly rate-sensitive, increasing by up to one hundred percent in passing from quasi-static to dynamic rates of loading. Subsequently, the SENB (Mode I) and shear (Mode II) fracture properties of the polymer foams were evaluated. Mode I tests have shown that the crosslinked PVC foams and the PET foams fail in a brittle manner, however, the linear PVC foams fail in a ductile mode. Here, it has been shown that the Mode II shear toughnesses of the crosslinked PVC foams were up to thirty-five times greater than their corresponding Mode I values. Following this, a series of indentation tests were conducted on polymer-foam sandwich structures and their response was characterised using a Meyer indentation law of the form P = Can. It has been shown that the value of the exponent parameter, n, does not vary significantly with the properties of the core or the skin, typically being close to unity for all tests. The contact stiffness, C, was found to depend on the plastic collapse strength of the foam, the indentor radius and the properties of the skin. It has been shown that a plot of contact stiffness against plastic collapse strength, containing all of the quasi-static and dynamic data, appears to yield a unique curve. Subsequently, the perforation resistances of a range of foam-based sandwich structures were investigated. The influence of the plastic collapse stress of the foam in determining the failure thresholds of the front and rear composite skins has been established. Here, a simple model has been used to successfully predict failure of the top surface composite skin in the sandwich structures. In addition, the force associated with perforating the lightweight core has been shown to be strongly dependent on the shear strength of the polymer foam. The perforation response of sandwich structures based on fully-recyclable materials has also been investigated. The design of the SRPP skin has a significant effect on the energy-absorbing characteristics of the sandwich structure, with the performance of systems based on multiple layer skins greatly exceeding that associated with a monolithic skin. It has been shown that when normalised by the areal density of the panels, those sandwich structures with multiple layer skins out-perform systems with monolithic skins as well as conventional GFRP/aluminium honeycomb sandwich structures.
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Shen, Zeng. "Characterisation of low velocity impact response in composite laminates." Thesis, University of Hertfordshire, 2015. http://hdl.handle.net/2299/16334.
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A major concern affecting the efficient use of composite laminates in aerospace industry is the lack of understanding of the effect of low-velocity impact (LVI) damage on the structural integrity. This project aims to develop further knowledge of the response and damage mechanisms of composite laminates under LVI, and to explore the feasibility of assessing the internal impact damage with a visually inspectable parameter. The response and damage mechanisms of composite laminates under LVI have been investigated experimentally and numerically in this project. Various parameters including the laminates thickness, lay-up configuration, repeated impact, and curing temperature have been examined. The concept and the phenomena of delamination threshold load (DTL) have been assessed in details. It was found that DTL exists for composite laminates, but the determination of the DTL value is not straightforward. There is a suitable value of range between the impact energy and the laminates stiffness/thickness, if the sudden load drop phenomenon in the impact force history is used to detect the DTL value. It is suggested that the potential menace of the delamination initiation may be overestimated. The composite laminates tested in this project demonstrate good damage tolerance capacity due to the additional energy absorption mechanism following the delamination initiation. As a result, the current design philosophy for laminated composite structure might be too conservative and should be reassessed to improve the efficiency further. To explore the feasibility of linking the internal damage to a visually inspectable parameter, quasi-static indentation (QSI) tests have been carried out. The dent depth, as a visually inspectable parameter, has been carefully monitored and assessed in relation to the damage status of the composite laminates. It is proposed that the damage process of composite laminates can be divided into different phases based on the difference in the increasing rate of dent depth. Moreover, the internal damage has been examined under the optical microscope (OM) and the scanning electron microscope (SEM). Residual compressive strength of the damaged specimen has been measured using the compression-after-impact (CAI) test. The results further confirm the findings with regard to the overestimated potential menace of the delamination initiation and the proposed damage process assumption. The proposed damage process assumption has great potential to improve the efficiency and accuracy of both the analytical prediction and the structural health monitoring for damages in composite laminates under low-velocity impact.
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Williams, J. "An assessment of low velocity impact damage of composite structures." Thesis, University of the West of Scotland, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377571.
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Nassiopoulos, Elias. "Localised low velocity impact performance of FLAX/PLA biocomposites." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9682.
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Natural fibre composites are fast emerging as a viable alternative to traditional materials and synthetic composites. Their low cost, lightweight, good mechanical performance and their environmentally friendly nature makes them an ideal choice for the automotive sector. The automotive industry has already embraced these composites in production of non-structural components. At present, however, research studies into composites made of natural fibres/bio-sourced thermoplastic resins are at infancy stage and such works are rare in the literature. This study therefore focuses on the mechanical properties of poly(lactic) acid (PLA) flax reinforced composites for structural loaded components. The aim was to investigate the performance of flax/PLA biocomposites subjected to localized low velocity impacts. To start with, a detailed literature study was conducted covering biocomposites and PLA in particular. Next, a series of composite samples were manufactured. Morphological and thermal studies were also conducted in order to develop an in-depth understanding of their thermo-mechanical properties, including crystallinity, thermal response and their related transition temperatures. This was followed by localized impact studies. The influence of temperature, water uptake and strain rates to the material tensile strength and modulus, as well as the damage characteristics and limits that lead to failure were studied. Furthermore, in the present work different methods and existing material models to predict the response of biocomposites were assessed. A case study was then performed using these models to understand, develop and improve the side crash performance of a superlight city car prototype.
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Djeukou, Armel. "Meshfree methods for low velocity impact analysis of composites." Aachen Shaker, 2009. http://d-nb.info/998456241/04.
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Soto, Masip Albert. "Development of efficient numerical models for the simulation of low velocity impact and compression after impact on composite structures." Doctoral thesis, Universitat de Girona, 2018. http://hdl.handle.net/10803/664503.
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Fiber reinforced composite materials are nowadays used in several industrial applications that pursue structural weight reduction to reduce fuel consumption. The stiffness-to-weight and strength-to-weight ratios of composite materials made them an excellent choice for aerospace applications. However, impact loads is one of the major design concerns of aeronautical structures made by laminate composite materials. It is especially the case of Low Velocity Impact (LVI) events that despite leading to barely visible impact damage can significantly reduce the mechanical performance of composite structures. Reliable numerical models can help in reducing the actual amount of physical tests that are time-consuming and costly. Nevertheless, impact simulations are computationally intensive and their application in large composite structures is limited. Furthermore, the numerical models require many parameters that affect their efficiency, accuracy, objectivity and robustness. The present thesis aims to define a clear and efficient methodology to build reliable numerical models for the LVI and Compression After Impact (CAI) simulation of composite structures that can be applied in challenging applications of scientific and industrial interest. Firstly, the present work describes a methodology to simulate LVI and CAI on composite laminates that is validated experimentally at the coupon level. The key definitions are discussed and especial attention is devoted to the definitions that affect the computational efficiency. Novel formulas, which are useful for optimum mesh discretization, are proposed to predict the cohesive zone length of composites undergoing delamination under pure fracture modes. A numerical benchmark of different finite element types and interaction technologies commonly used in the literature is performed to compare their computational performance and accuracy. Furthermore, criteria to efficiently define cohesive numerical parameters are proposed. Numerical simulations can help in the understanding of the damage sequence of polymer based composite laminates during an impact event, which can be a difficult task to perform experimentally when dealing with a large number of plies. The proposed methodology is applied to predict the LVI and CAI of thin ply fabric laminates, which is a computationally challenging case due the large number of plies and interfaces involved. The numerical results indicate that matrix cracking effects can be assumed negligible for the studied thin ply laminate while delamination and especially the fiber traction separation law shape are important for accurate predictions. Finally, the methodology is applied for the prediction of relatively large composite sub-components with the aim to show that the proposed methodology enables analyses at larger scales. It is demonstrated the potential of the methodology and employed techniques to address problems of industrial interest such as the strength prediction of both undamaged and damaged stiffened panelsEls materials compòsits són actualment utilitzats en diferents sectors industrials que busquen la reducció de pes estructural amb la finalitat de reduir el consum de combustible. La rigidesa i resistència que ofereixen en relació amb el seu pes els ha convertit en una excel·lent opció per aplicacions aeronàutiques. No obstant això, les càrregues a impacte són una de les principals preocupacions en el disseny d’estructures aeronàutiques fabricades amb laminats de material compòsit. És especialment el cas d’impactes a baixa velocitat que deixen dany difícil de detectar durant inspeccions visuals però que poden reduir significativament la resistència de l’estructura. L’ús de models numèrics fiables pot ajudar a reduir l’actual nombre d’assaigs experimentals que són costosos tant en temps com econòmicament. Tanmateix, l’aplicació de models numèrics en estructures de material compòsit de gran dimensió es veu limitada pel cost computacional que representen. A més, els models numèrics requereixen moltes definicions que afecten la seva eficiència, precisió, objectivitat i robustesa. La present tesi té com a objectiu desenvolupar una metodologia clara i eficient per realitzar prediccions fidedignes d’impacte a baixa velocitat i compressió després d’impacte en estructures de material compòsit que pugui ser aplicada en casos de rellevància científica i industrial. En primer lloc, es descriu una metodologia per a la simulació d’impacte a baixa velocitat i compressió després d’impacte en laminats de compòsit la qual és validada experimentalment a escala de proveta de laboratori. Les definicions més importants es discuteixen i es té especial atenció en aquelles que afecta l’eficiència computacional. Per una òptima discretització del model és desitjable conèixer la longitud de zona cohesiva. Noves fórmules per predir la longitud de zona cohesiva en delaminació es proposen per modes purs de fractura. Es realitza un estudi numèric comparatiu de diferents tecnologies d’element finit i d’interacció cohesiva típicament utilitzades en la literatura amb la finalitat de comparar la seva precisió i eficiència computacional. A més, es proposen criteris per definir paràmetres numèrics del model cohesiu que afecten el temps computacional. Els models numèrics poden ajudar a entendre la seqüència de dany durant esdeveniments d’impacte, els quals poden ser complicats d’analitzar experimentalment. La metodologia proposada s’aplica per predir la resposta a impacte i compressió després d’impacte en laminats de capes primes. És un cas que representa un repte computacional per l’elevat nombre de capes i interfases involucrades. Els resultats numèrics contrastats experimentalment indiquen que els efectes de trencament de matriu es poden obviar mentre que la delaminació i especialment la forma de la llei cohesiva de la fibra són de gran importància en les prediccions de laminats de capes primes. Finalment, la metodologia s’aplica per la predicció de sub-components rigiditzats de material compòsit amb la finalitat de mostrar que la metodologia permet anàlisis a escales majors. Es demostra el potencial de la metodologia i tècniques utilitzades per adreçar problemes d’interès industrial com és la predicció de la resistència d’un panell rigiditzat abans i després de ser danyat per un eventual impacte
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Lucchi, Andrea. "Numerical simulation of low velocity impact on fiber metal laminates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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The diffusion of composite laminates in aerospace industry has been slowed down by complexity in the prediction of fracture behaviours. In this respect the delamination phenomenon caused by Low-Velocity Impacts has been a critical issue. Several criteria that predict the delamination onset and growth have been analysed. The subsequent study has been focused on Cohesive Zone Models able to predict both initiation and propagation of delamination. Several models that represent the dynamic response of composite structures to impacts have been presented. An explicit FEM has been developed to perform 3D simulations of different layup configurations of Al2024T3 and Woven Carbon Prepreg Laminates subjected to a Low-Velocity Impact. ABAQUS, Dassault Systèmes Simulia Corp. has been employed to perform the numerical simulations. Specific attention is paid to the cohesive failure representing delamination.
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Chib, Amit Soschinske Kurt A. "Parametric study of low velocity impact analysis on composite tubes." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2006/t004.pdf.
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Thesis (M.S.)--Wichita State University, Dept. of Mechanical Engineering."August 2006." Title from PDF title page (viewed on October 2, 2006). Thesis adviser: Kurt Soschinske. Includes bibliographic references (leaves 84-87).
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Pillai, Govind Ramakrishna Lankarani Hamid M. "Response of adhesively bonded composite joints to low velocity impact." Diss., A link to full text of this thesis in SOAR, 2006. http://soar.wichita.edu/dspace/handle/10057/676.
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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering."December 2006." Title from PDF title page (viewed on Nov. 4, 2007). Thesis adviser: Hamid M. Lankarani. Includes bibliographic references (leaves 64-67).
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Foos, Bryan Carl. "Damage progression in composite plates due to low velocity impact." Connect to resource, 1990. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1156873311.
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Conner, Ryan P. "Fluid Structure Interaction Effects on Composites Under Low Velocity Impact." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/7324.
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In this study composite materials were tested in different fluid environments to determine the role of Fluid Structure Interaction with these composites under a lower velocity impact. The purpose of this research is to develop a better understanding of possible marine applications of composite materials. This was done using a low velocity impact machine and two composite types. The first composite is made from a multi-ply symmetrical plain weave 6 oz. E-glass skin. The test area of the composites is 12 in by 12 in (30.5 cm by 30.5 cm) with clamped boundary conditions. The testing was done using a drop weight system to impact the center of the test area. A Plexiglas box in conjunction with the impact machine was used to keep the top of the composite sample dry while it was submerged in approximately 15 inches (38.10 cm) of water. The second composite type was constructed using the same methods, but was made from a Carbon Fiber Reinforced Polymer (CFRP) instead of the E-glass skin. These samples were pre-cracked and tested using the same impact machine in 15 inches (38.10 cm) of water. The overall size of these samples was 42 cm long and 3 cm wide forming a long thin rectangular shape. The test area of these samples was a 20 cm long section of the sample with the outsides being clamped to achieve the desired boundary conditions. Two variations of these samples were tested. The first was reinforced with Multi-Walled Carbon Nanotubes (MWCNTs) and the second had no reinforcements at the interface layer in front of the pre-cracks. Output from both tests was recorded using strain gauges and a force impact sensor. The results show that an added mass from the water plays a large role in the Fluid Structure Interaction with composites due to the similar densities of water and the composites.
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Paran, Alexander P. "The low-velocity impact response of thin, stiffened CFRP panels." Thesis, University of Sheffield, 1999. http://etheses.whiterose.ac.uk/3475/.
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An extensive study of into the static loading response and low-velocity impact response of plain and stiffened CFRP panels was conducted. The study investigated the impact response of the CFRP panels over a range of impact energies that include incident kinetic energies sufficiently high to cause complete penetration of the panel by the impacting mass. Static tests were also conducted by driving a hemispherical-nosed indentor into the panel up to displacements that resulted in the complete penetration of the panel by the indentor. Results from these tests suggest that the static perforation energy could predict the impact perforation energy with reasonable accuracy. A lumped-parameter mass-spring-damper model that attempted to incorporate the effects of material damage to the panel response was developed. The model was found to be sufficiently accurate in predicting the response of thin panels to static and impact loads up to the critical delamination force threshold. Assessment of the damaged panels through Penetrant-Enhanced X-Ray methods led to the identification of damage transition energy thresholds that differentiate between changes in damage mechanism. The damage transition energy thresholds were found to be constant fractions of the impact perforation energy.
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Ainsworth, Kim. "Low velocity transverse impact of filament wound E-glass/epoxy resin pipes." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293699.
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Antoine, Guillaume Olivier. "Computational Design of Transparent Polymeric Laminates subjected to Low-velocity Impact." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/51232.
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Transparent laminates are widely used for body armor, goggles, windows and windshields. Improved understanding of their deformations under impact loading and of energy dissipation mechanisms is needed for minimizing their weight. This requires verified and robust computational algorithms and validated mathematical models of the problem.
Here we have developed a mathematical model for analyzing the impact response of transparent laminates made of polymeric materials and implemented it in the finite element software LS-DYNA. Materials considered are polymethylmethacrylate (PMMA), polycarbonate (PC) and adhesives. The PMMA and the PC are modeled as elasto-thermo-visco-plastic and adhesives as viscoelastic. Their failure criteria are stated and simulated by the element deletion technique. Values of material parameters of the PMMA and the PC are taken from the literature, and those of adhesives determined from their test data. Constitutive equations are implemented as user-defined subroutines in LS-DYNA which are verified by comparing numerical and analytical solutions of several initial-boundary-value problems. Delamination at interfaces is simulated by using a bilinear traction separation law and the cohesive zone model.
We present mathematical and computational models in chapter one and validate them by comparing their predictions with test findings for impacts of monolithic and laminated plates. The principal source of energy dissipation of impacted PMMA/adhesive/PC laminates is plastic deformations of the PC. In chapter two we analyze impact resistance of doubly curved monolithic PC panels and delineate the effect of curvature on the energy dissipated. It is found that the improved performance of curved panels is due to the decrease in the magnitude of stresses near the center of impact.
In chapter three we propose constitutive relations for finite deformations of adhesives and find values of material parameters by considering test data for five portions of cyclic loading. Even though these values give different amounts of energy dissipated in the adhesive, their effect on the computed impact response of PMMA/adhesive/PC laminates is found to be minimal. In chapter four we conduct sensitivity analysis to identify critical parameters that significantly affect the energy dissipated. The genetic algorithm is used to optimally design a transparent laminate in chapter five.Ph. D.
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Antoine, Guillaume O. "Computational Design of Transparent Polymeric Laminates subjected to Low-velocity Impact." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/51232.
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Transparent laminates are widely used for body armor, goggles, windows and windshields. Improved understanding of their deformations under impact loading and of energy dissipation mechanisms is needed for minimizing their weight. This requires verified and robust computational algorithms and validated mathematical models of the problem.
Here we have developed a mathematical model for analyzing the impact response of transparent laminates made of polymeric materials and implemented it in the finite element software LS-DYNA. Materials considered are polymethylmethacrylate (PMMA), polycarbonate (PC) and adhesives. The PMMA and the PC are modeled as elasto-thermo-visco-plastic and adhesives as viscoelastic. Their failure criteria are stated and simulated by the element deletion technique. Values of material parameters of the PMMA and the PC are taken from the literature, and those of adhesives determined from their test data. Constitutive equations are implemented as user-defined subroutines in LS-DYNA which are verified by comparing numerical and analytical solutions of several initial-boundary-value problems. Delamination at interfaces is simulated by using a bilinear traction separation law and the cohesive zone model.
We present mathematical and computational models in chapter one and validate them by comparing their predictions with test findings for impacts of monolithic and laminated plates. The principal source of energy dissipation of impacted PMMA/adhesive/PC laminates is plastic deformations of the PC. In chapter two we analyze impact resistance of doubly curved monolithic PC panels and delineate the effect of curvature on the energy dissipated. It is found that the improved performance of curved panels is due to the decrease in the magnitude of stresses near the center of impact.
In chapter three we propose constitutive relations for finite deformations of adhesives and find values of material parameters by considering test data for five portions of cyclic loading. Even though these values give different amounts of energy dissipated in the adhesive, their effect on the computed impact response of PMMA/adhesive/PC laminates is found to be minimal. In chapter four we conduct sensitivity analysis to identify critical parameters that significantly affect the energy dissipated. The genetic algorithm is used to optimally design a transparent laminate in chapter five.Ph. D.
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Lee, Jounghwan. "Compressive behaviour of composite laminates before and after low velocity impact." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409121.
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Djeukou, Armel [Verfasser]. "Meshfree methods for low-velocity impact analysis of composites / Armel Djeukou." Aachen : Shaker, 2009. http://d-nb.info/1161300538/34.
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Hou, Jinping. "Assessment of low velocity impact induced damage on laminated composite plates." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325271.
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Butalia, Tarunjit S. "Dynamic response of advanced composite plates subjected to low velocity impact /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487935573772341.
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Keerthi, Sandeep. "Low Velocity Impact and RF Response of 3D Printed Heterogeneous Structures." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1514392165695378.
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Cartmel, Paul. "A laboratory simulation of low velocity projectile impact on thin plates." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/9048.
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Includes bibliographical references.This project concerns the development of a test apparatus that will both accurately simulate a projectile impact event and provide an accurate means of analysing a material response to projectile impact events. A low velocity apparatus, based on the conventional instrumented drop tower apparatus, was designed and constructed. The apparatus is instrumented in order that the penetration resistance force history and impact velocity can be measured by a data acquisition system for further analysis. A software package, developed specifically for the apparatus, manipulates the acquired load-time trace and generates the necessary force and energy-deflection curves. A series of tests were performed to verify the validity and reproducibility of the results. The plastic deformation that occurs during a rebound impact event is compared to the plastic deformation as measured by the impact testing apparatus. These tests show that the apparatus can accurately measure the plastic deformation that occurs during a rebound impact event. A series of reproducibility tests proved that the apparatus is capable of generating almost identical force-deflection curves for tests conducted with given impact parameters. A series of tests were performed to analyse the impact response of the ductile material, aluminium alloy grade 1200. The aim of these tests is to illustrate the performance capabilities of the test apparatus and to analyse the influence of individual system variables, such as impact velocity, kinetic energy and projectile shape, on the impact response of a ductile material. The impact apparatus generates force-deflection curves that are in agreement with the observed impact response. The essential features that define a material response to impact loading such as stiffness, yield point and point of maximum load were identified on the force-deflection curves. A secondary aspect of this study was to investigate the impact behaviour of aluminium and glass laminate plates. The impact response of the laminate plates was compared to that of singular glass and aluminium plates. The apparatus is capable of generating force-deflection curves for the short duration, impact response of a singular 6mm thick glass plate and well as the highly sensitive laminate plate tests.
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Carboni, Marina. "Evaluation of ballistic materials for back protection under low velocity impact." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0430104-131552.
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Shi, Yu. "Modelling low velocity impact behaviour of composite laminates used in aerospace." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/6978/.
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Patel, Shivdayal. "Probabilistic analysis of composite plates under low and high velocity impact." Thesis, IIT Delhi, 2017. http://localhost:8080/xmlui/handle/12345678/7061.
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de, Luna Richard M. "EFFECT OF LOW VELOCITY IMPACT ON THE VIBRATIONAL BEHAVIOR OF A COMPOSITE WING." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1551.
Full textAbstract:
Impact strength is one of the most important structural properties for a designer to consider, but it is often the most difficult to quantify or measure. A major concern for composite structures in the field is the effect of foreign objects striking composites because the damage is often undetectable by visual inspection. The objective for this study was to determine the effectiveness of using dynamic testing to identify the existence of damage in a small scale composite wing design. Four different impact locations were tested with three specimens per location for a total of 12 wings manufactured. The different impact locations were over the skin, directly over the rib/spar intersection at the mid-span of the wing, directly over the middle rib, and directly over the leading edge spar. The results will be compared to a control group of wings that sustain no damage. The wing design was based on an existing model located in the Cal Poly Aerospace Composites/Structures lab. The airfoil selected was a NACA 2412 airfoil profile with a chord length of 3 inches and a wingspan of just over 8 inches. All parts cured for 7 hours at 148°F and 70 psi. The wings were each tested on a shaker-table in a cantilever position undergoing 1g (ft/s2) acceleration sinusoidal frequency sweep from 10-2000 Hz. The 1st bending mode was excited at 190 Hz and the 2nd bending mode was excited at 900 Hz. After the pre-impact vibrational testing each wing was impacted, excluding the control group. To verify the experimental results, a finite element model of the wing was created in ABAQUS. The frequency and impact numerical results and the experimental results were in good agreement with a percent error for both the 1st and 2nd mode at around 10%.
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Liu, Hongquan. "Ply clustering effect on composite laminates under low-velocity impact using FEA." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7310.
Full textAbstract:
With the development of the design and manufacture technology, composite
materials are widely used in the aeronautical industry. But, one of the main
concerns which affects the application of composites is foreign object impact.
The damages induced by the Low Velocity Impact (LVI), which can significantly
reduce the strength of the structures, can’t be easily inspected routinely. The
so-called Barely Visible Impact Damages (BVID) due to LVI typically includes
interlaminar delamination, matrix cracks and fibre fracture at the back face.
Previous researches have shown that the results of LVI test are similar to that of
the Quasi-Static Load (QSL) test. The initiation and propagation of delamination
can be detected more easily in the QSL test and the displacement and reaction
force of the impactor can be controlled and measured much more accurately.
Moreover, it is easier to model QSL tests than dynamic impacts.
To investigate the impact damage induced by LVI, a Finite Element (FE) model
employing cohesive elements was used. At the same time, the ply clustering
effect, when several plies of the same orientation were stack together, was
modelled in the FE model in terms of damage resistance and damage size. A
bilinear traction-separation law was introduced in the cohesive elements
employed to simulate the initiation and propagation of the impact damage and
delamination.
Firstly, a 2D FE model of the Double Cantilever Beam (DCB) and End Notched
Flexure (ENF) specimens were built using the commercial FEM software
ABAQUS. The results have shown that the cohesive elements can be used to
simulate mode I and mode II delamination sufficiently and correctly.
Secondly, an FE model of a composite plate under QSL but without simulating
damage was built using the continuum shell elements. Agreement between the
FEA results with published test results is good enough to validate the capability
of continuum shell elements and cohesive elements in modelling the composite
laminate under the transverse load condition (QSL). Thirdly, an FE model containing discrete interface delamination and matrix
cracks at the back face of the composite plate was built by pre-setting the
cohesive failure elements at potential damage locations according to the
experimental observation. A cross-ply laminate was modelled first where fewer
interfaces could be delaminated. Good agreement was found in terms of the
delamination area and impactor’s displacement-force curve.
Finally, the effect of ply clustering on impact damage resistance was studied
using Quasi-Isotropic (QI) layup laminates.
Because of the limited time available for calculation, the simulation was only
partly completed for the quasi-isotropic laminates (L2 configuration) which have
more delaminated interfaces. The results showed that cohesive elements
obeying the bilinear traction-separation law were capable of predicting the
reaction force in quasi-isotropic laminates. However, discrepancies with the test
results in terms of delamination area were observed for quasi-isotropic
laminates. These discrepancies are mainly attributed to the simplification of
matrix cracks simulation and compressive load at the interface in the thickness
direction which is not taken into account.
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Tong, Y. "The low velocity impact fatigue and stress relaxation behaviour of composite materials." Thesis, Swansea University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639251.
Full textAbstract:
The low velocity impact, tension-tension fatigue and stress relaxation behaviour of glass fibre and natural fibre composites were investigated. For glass fibre composites, two fibre architectures ([±45o]4 and [0/90o]2s) and two matrix resins (polyvinyl-ester and polyester) were used. Non-woven randomly oriented hemp fibre mat was used as reinforcement of natural fibre composites. The effects of low velocity impact on residual tensile properties, fatigue life and modulus degradation behaviour during cyclic loading were investigated. Damage mechanisms of the composites during impact and fatigue loading were discussed. It was found that modulus degradation behaviour of composites was strongly dependent on the reinforcing fibres and their architecture. Multistage modulus degradation behaviour with gradual reduction in modulus was observed during fatigue loading of [±45o]4 glass fibre composites. For hemp fibre composites, however, no decrease in modulus was observed before final fatigue failure. Low velocity impact did not significantly change the modulus degradation behaviour of composites during fatigue loading. Since the normalized S-N curves for undamaged and impacted samples superimposed, the fatigue life of impact damaged composites could be predicted from knowledge of the S-N curve of non-impacted composites and the static residual strength of impact damaged composites. Stress relaxation curves of [±45o]4 and [0/90o]2s glass fibre composites were compared, and the effects of initial stress, impact damage, fatigue loading and the combination of impact and fatigue were investigated. Mechanisms of stress relaxation of composites were discussed. Stress relaxation curves of the glass fibre composites could be modelled by a simple logarithmic equation. Stress relaxation tests were found useful to characterise the loading history of composites.
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Malhotra, Anjum. "Low velocity edge impact on composite laminates : damage tolerance and numerical simulations." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8571.
Full textAbstract:
Composite laminates are increasingly being used in more complex structural applications where edges and cut outs are inevitable. These applications include wing skins of military and civil aircraft, further aerospace applications as well as automotive panels and critical structures. Composite components in such applications are highly susceptible to damage. Composites behave in a different manner to conventional metallic materials, which has introduced several design problems not previously encountered. One such problem has been the susceptibility of the material to accidental low energy impacts which frequently leave no visible mark on the impacted surface but considerable internal damage. Investigation of the residual strength and stiffness of composites after edge impact has become important for the design of aerospace components. Previously, the research work involved central impact of composite laminates but in this research we are investigating edge impact behaviour of composite laminates as parts of composite structures are particularly vulnerable to impacts, including near the edge of an inspection port or other aperture. Furthermore, impacts to such areas may lead to more severe damage near the edge of the laminate rather than the surface. Thus the present work extends these investigations to impact on the edge of composite laminates. The thesis includes both experimental investigations and finite element simulations of impact damage on the plane of the laminate near the edge (near-edge), and on the edge (on-edge) of composite laminates. A comparison with centre impact with on and near-edge impact is done to understand the damage on the edges and away from the edges. A new design has been developed and implemented to perform edge impact experiments. The research investigated the effects of various parameters like thickness, absorbed energies, force-time histories and damage behaviour of composite laminate. The damage size and mechanisms have been explored. Impact simulation was carried out using finite element code Abaqus. Explicit solution technique of the code was used to analyse the edge impact phenomenon. Results of the finite element analysis were compared with experiments. The residual strength of the laminates under compressive and tensile loading has been measured. Tensions after impact (TAI) tests were conducted to evaluate the residual load carrying capacity. The effect of edge impact on the low velocity impact response and the residual tensile strength is discussed via the test results. This thesis also includes computed tomography as the main technique for micro level damage characterisation and investigates the study of damage mechanisms of glass/epoxy laminates subjected to edge impact with varying energy levels and thickness. Computed Tomography aims to provide damage behaviour such as internal damage state, delaminations during different types of edge impact.
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Namala, Kiran Kumar. "Low velocity impact on glass fibre reinforced epoxy composites: experiments and simulation." Thesis, IIT Delhi, 2016. http://eprint.iitd.ac.in:80//handle/2074/8191.
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Worrall, Christopher Michael. "The behaviour of composite sandwich beams and panels under low velocity impact conditions." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333578.
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Fan, Jiying. "Investigation of the behaviour of fibre metal laminates subjected to low velocity impact." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548766.
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Turner, Andrew Joseph. "Low-Velocity Impact Behavior of Sandwich Panels with 3D Printed Polymer Core Structures." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1496345616948541.
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Shaik, Dawood Mohamed Sultan Ibrahim. "Piezoelectric actuators for delamination control in composite plates subjected to low velocity impact." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6204.
Full textAbstract:
The potential of MFC actuator as a tool for reducing low velocity impact induced delamination has been investigated using LS-DYNA explicit code. For this purpose, three different piezoelectric actuation models were implemented through its user defined material subroutine, namely, the linear strain model, electric field dependent model and induced strain model. The induced strain model was found to provide the best match with experimental results for actuation strain prediction, hence used in impact investigations. In predicting the delamination, a newly formulated damage model was used as it was found that the existing damage models in LS-DYNA are simplistic and rate sensitive. An independent three-dimensional piezoelectric finite element code was developed and used to study the effects of design and actuation parameters on the actuation characteristics of the MFC. The parametric study was meant to determine a laminate-actuator system that would allow sufficient presence of the piezoelectric effects in it. A selected laminate-actuator system was later used to investigate the effects of piezoelectric control actions on the impact force and displacement for purely elastic impact cases. For simply supported laminate it was found that the peak impact force and displacement could be reduced by applying a counter moment to the incoming impact load, whereas for clamped laminate the same was achieved by regulating the laminate stiffness at the impact point. The technique of impact force reduction confirmed that delamination could be reduced. However, this concept could not be experimentally verified as the design requirements could not be practically implemented. The actuator required voltages beyond its operating range to reduce delamination even in the case of very low energy impact. This is something not achievable with the existing piezoelectric materials. Assuming powerful piezoelectric actuators are not impossible in near future, this study could provide useful information for an attempt to validate this concept.
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Anderson, Todd Alan 1971. "An analytical and experimental investigation of sandwich composites subjected to low-velocity impact." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289090.
Full textAbstract:
This study involves an experimental and analytical investigation of low-velocity impact phenomenon in sandwich composite structures. The analytical solution of a three-dimensional finite-geometry multi-layer specially orthotropic panel subjected to static and transient transverse loading cases is presented. The governing equations of the static and dynamic formulations are derived from Reissner's functional and solved by enforcing the continuity of traction and displacement components between adjacent layers. For the dynamic loading case, the governing equations are solved by applying Fourier or Laplace transformation in time. Additionally, the static solution is extended to solve the contact problem between the sandwich laminate and a rigid sphere. An iterative method is employed to determine the sphere's unknown contact area and pressure distribution. A failure criterion is then applied to the sandwich laminate's stress and strain field to predict impact damage. The analytical accuracy of the present study is verified through comparisons with finite element models, other analyses, and through experimentation. Low-velocity impact tests were conducted to characterize the type and extent of the damage observed in a variety of sandwich configurations with graphite/epoxy face sheets and foam or honeycomb cores. Correlation of the residual indentation and cross-sectional views of the impacted specimens provides a criterion for the extent of damage. Quasi-static indentation tests are also performed and show excellent agreement when compared with the analytical predictions. Finally, piezoelectric polyvinylidene fluoride (PVF2) film sensors are found to be effective in detecting low-velocity impact.
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Song, Changpeng. "Low velocity impact testing and computed tomography damage evaluation of layered textile composite." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/4759.
Full textAbstract:
In this work, the low-velocity impact resistance of layered carbon fiber polymer matrix five harness satin textile composites has been studied. A series of impact characterization tests at different impact energy levels was performed using an Instron 8200 Dynatup impact tester. Real-time measurements of impact load, deflection, and energy were recorded and analyzed, and impact damage was assessed.
Impact damage in the textile composites with respect to different impact energy levels has also been studied using computed tomography (CT). Two different CT systems, ZEISS METROTOM 1500 and Siemens MicroCAT II, were used for the quantitative damage assessment. The capabilities of both systems to evaluate low-velocity impact damage in layered carbon fiber polymer matrix composites were investigated.
The micro-CT scans produced detailed visualization of cracks and delamination in the damage zones of the impacted textile composite specimens. However, the MicroCAT CT system is limited to the analysis of small articles and is unable to scan composite specimens of the standard size (squares of 6 in. by 6 in.) used in the low-velocity impact characterization tests.
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Carter, Jeffrey Scott. "Effects of Low Velocity Impact on the Flexural Strength of Composite Sandwich Structures." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1327.
Full textAbstract:
The use of composite sandwich structures is rapidly increasing in the aerospace industry because of their increased strength-to-weight and stiffness-to-weight characteristics. The effects of low velocity impacts on these structures, however, are the main weakness that hinders further use of them in the industry because the damages from these loadings can often be catastrophic. Impact behavior of composite materials in general is a crucial consideration for a designer but can be difficult to describe theoretically. Because of this, experimental analysis is typically used to attempt to describe the behavior of composite sandwiches under impact loads. Experimental testing can still be unpredictable, however, because low velocity impacts can cause undetectable damage within the composites that weaken their structural integrity. This is an important issue with composite sandwich structures because interlaminar damage within the composite facesheets is typical with composites but the addition of a core material results in added failure modes. Because the core is typically a weaker material than the surrounding facesheet material, the core is easily damaged by the impact loads. The adhesion between the composite facesheets and the core material can also be a major region of concern for sandwich structures. Delamination of the facesheet from the core is a major issue when these structures are subjected to impact loads.
This study investigated, through experimental and numerical analysis, how varying the core and facesheet material combination affected the flexural strength of a composite sandwich subjected to low velocity impact. Carbon, hemp, aramid, and glass fiber materials as facesheets combined with honeycomb and foam as core materials were considered. Three layers of the same composite material were laid on the top and bottom of the core material to form each sandwich structure. This resulted in eight different sandwich designs. The carbon fiber/honeycomb sandwiches were then combined with the aramid fiber facesheets, keeping the same three layer facesheet design, to form two hybrid sandwich designs. This was done to attempt to improve the impact resistance and post-impact strength characteristics of the carbon fiber sandwiches. The two and one layer aramid fiber laminates on these hybrid sandwiches were always laid up on the outside of the structure. The sandwiches were cured using a composite press set to the recommended curing cycle for the composite facesheet material. The hybrid sandwiches were cured twice for the two different facesheet materials. The cured specimens were then cut into 3 inch by 10 inch sandwiches and 2/3 of them were subjected to an impact from a 7.56 lbf crosshead which was dropped from a height of 38.15 inches above the bottom of the specimen using a Dynatup 8250 drop weight machine.
The impacted specimen and the control specimen (1/3 of the specimens not subjected to an impact) were loaded in a four-point bend test per ASTM D7250 to determine the non-impacted and post-impact flexural strengths of these structures. Each sandwich was tested under two four-point bend loading conditions which resulted in two different extension values at the same 100 lbf loading value. The span between the two supports on the bottom of the sandwich was always 8 inches but the span between the two loading pins on the top of the sandwich changed between the two loading conditions. The 2/3 of the sandwiches that were tested after being impacted were subjected to bending loads in two different ways. Half of the specimens were subjected to four-point bending loads with the impact damage on the top facesheet (compressive surface) in between the loading pins; the other half were subjected to bending loads with the damage on the bottom facesheet (tensile surface).
Theoretical failure mode analysis was done for each sandwich to understand the comparisons between predicted and experimental failures. A numerical investigation was, also, completed using Abaqus to verify the results of the experimental tests. Non-impacted and impacted four-point bending models were constructed and mid-span deflection values were collected for comparison with the experimental testing results. Experimental and numerical results showed that carbon fiber sandwiches were the best sandwich design for overall composite sandwich bending strength; however, post-impact strengths could greatly improve. The hybrid sandwich designs improved post-impact behavior but more than three facesheet layers are necessary for significant improvement. Hemp facesheet sandwiches showed the best post-impact bending characteristics of any sandwich despite having the largest impact damage sizes. Glass and aramid fiber facesheet sandwiches resisted impact the best but this resulted in premature delamination failures that limited the potential of these structures. Honeycomb core materials outperformed foam in terms of ultimate bending loads but post-impact strengths were better for foam cores. Decent agreement between numerical and experimental results was found but poor material quality and high error in material properties testing results brought about larger disagreements for some sandwich designs.
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Minnaar, Karel. "Experimental and numerical analyses of damage in laminate composites under low velocity impact loading." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/15812.
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Demerath, Brandon Michael. "Low velocity impact damage assessment in IM7/977-3 cross-ply composites using 3D computed tomography." Thesis, University of Iowa, 2015. https://ir.uiowa.edu/etd/1583.
Full textAbstract:
Low-velocity impact damage in IM7/977-3 carbon fiber reinforced polymer (CFRP) composites was investigated using 3D computed tomography (CT). 32-ply IM7/977-3 symmetric cross-ply composites were impacted at different impact energy levels and with different impactors (DELRIN® resin flat-ended cylindrical and tool steel hemispherical strikers) using an Instron 8200 Dynatup drop-weight impact machine. The impact energies were chosen to produce slightly visible damage, characterized by short cracks on the impacted surface and little delamination on the non-impacted surface (29.27 J), and barely visible damage, characterized by indentation on the impacted surface but no visible delamination on the back surface of the specimens (20.77 J). Internal damage was assessed using the Zeiss METROTOM 1500 industrial CT scanning system, and CT images were reconstructed using VGStudio MAX and the MyVGL 2.2 viewer. To determine the extent of the damage zone, impacted 152.4 mm square composite plates were initially scanned. As the relatively large specimen size did not allow for evaluation of internal cracks and isolation of delamination at ply interfaces, smaller specimens that enclosed the damaged region (45 mm square plates) were cut out and imaged. The CT scan results showed that volume of the impact damage zone had a generally positive correlation with impact energy, maximum load, and maximum deflection, but that the relationship was generally weak. Absence of a definite correlation between damage volume and impact energy was unexpected, as the difference in the impact energy was up to 30%.
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Yuksel, Serhan. "Low Velocity Impact Analysis Of A Composite Mini Unmanned Air Vehicle During Belly Landing." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610575/index.pdf.
Full textAbstract:
Mini unmanned Air Vehicles (UAV) have high significance among other UAV's, in different categories, due to their ease of production, flexibility of maintenance, decrease in weight due to the elimination of landing gear system and simplicity of use. They are usually built to meet '
hand launching'
and '
belly landing'
criteria in order to have easy flight and easy landing features. Due to the hand take-off and belly landing features there is no need to have a runway and this feature is a very significant advantage in operational use. In an operation, belly landing mini UAV'
s may encounter tough landing areas like gravel, concrete or hard soil. Such landing areas may create landing loads which are impulsive in character. The effect of the landing loads on the airframe of the mini unmanned air vehicle must be completely understood and the mini UAV be designed accordingly in order not to damage the mini UAV during belly landing. Typical impact speeds during belly landing is relatively low (<
10 m/s) and in general belly landing phenomenon can be treated as low velocity impact. The purpose of this study is to analyze the impact loads on the composite substructures of a mini UAV due to the belly landing. '
Gü
ventü
rk'
Mini UAV which is designed and built in METU Aerospace Engineering Department, is used as the analysis platform. This study is limited to the calculation of stresses and deformation that is caused by the low velocity impact forces encountered during belly landing. The main purpose of this work is to help the designer in making design decisions for a mini UAV that is tolerable to low velocity impact loads. Initial part of the thesis includes analytical treatment of low velocity impact phenomenon. In the simplified analytical approach the loading is assumed as quasistatic and comparisons of such a simplified method of analysis is made with explicit finite element solutions on isotropic and composite plate structures to investigate the applicability of simplified analytical method of analysis. Belly landing analyses of the mini UAV are done by MSC.Dytran, which is an explicit finite element solver. Model building and post processing are done via MSC.Patran. Stress and deformation response of the mini UAV is investigated by performing low velocity impact analysis using sub-structure built-up approach.