Dissertations / Theses on the topic 'Impact damage'
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Lloyd, James C. "Impact damage and damage tolerance of fibre reinforced advanced composite laminate structures." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/6891.
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The primary objective of this work is to experimentally examine the effect of various geometric parameters on the impact damage and damage tolerance of thin carbon/epoxy plate and panel structures. Due to the number of parameters involved in a low velocity impact event and the complexity of the damage created, determining what effect individual parameters have is extremely demanding, especially when some of the parameters may even be coupled. However, by experimentally simulating in a controlled manner, either the impact event or the damage created, the effect of individual geometric parameters can be isolated and determined. A quasi-static indentation test has been used to simulate an impact event. The parameters of indenter size, nose shape, plate size and boundary condition, were examined. Four different plate failure modes were identified. Indenter nose shape was found to be the dominant geometric parameter, as a change in nose shape resulted in a change in failure mode and hence maximum load. From this work, a set of geometric parameters was selected for impact testing. Impact testing at various Incident Kinetic Energies (IKE) was performed on an instrumented drop weight impact rig. From examination of internal and external damage, the development of damage to increasing IKE was determined and shown to have four distinctive phases. Coupled with strike and rebound velocity measurementsa, non-linear relationship between IKE-damage area was established and a delamination threshold energy level of 1.1 J was calculated. Damaget olerance assessmenot f impacted panels was then performed in a Compression-After- Impact (CAI) rig. Strain gauge responses allowed global and local behaviour to be compared to intact specimens. It was found that once a critical damage size was surpassed, a gradual nonlinear degradation in compressive strength was observed until a point was reached where no further degradation in performance was attained. Furthermore, propagation of internal damage in a stable and unstable manner was directly linked to the nature of sublaminate buckling behaviour. Damaget olerance assessmenot f artificially delaminatedp anels loaded in compressionw as then performed. A single artificial delamination of various size, shape and orientation, embedded at the centre of a panel was examined. Delamination width was found to be the dominant geometric parameter. Hence, when comparing a circular delamination to an elliptical one of the same area, the effect of orientation and shape is aspect ratio dependent. Finally, a comparison of impacted and artificially delaminated panels was made.
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Matemilola, Saka Adelola. "Impact damage to composite materials." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319939.
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Cantwell, W. J. "Impact damage in carbon fibre composites." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/7834.
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Alves, Marcilio. "Damage mechanics applied to structural impact." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484220.
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Sultan, Mohamed Thariq Bin Hameed. "Impact damage characterisation in composite laminates." Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556739.
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The overall purpose of this research is to detect and quantify low-velocity impact damage in structures made from composite materials. This research represents a study using simplified coupon specimens. The composite material chosen for the current research is a woven Carbon Fibre Reinforced Polymer (CFRP) prepreg with a MTM57 resin system (42%RW) with CF2900 fabric (280 g/m2, 12K and 2 x 2 twill fabric). This woven material was fabricated to produce coupon size specimens of 250 mm x 150 mm with II, 12 and 13 layers of thickness. Piezoelectric sensors of type SONOX® P5 were placed on three different locations on each of the coupon size specimens to record the responses along different directions of the ply and at different distances from the impact events. Two different approaches were used to record the acceleration response signals resulting from the impact excitation. The first approach used the LMS Testlab Impact Modal Analysis environment in order to acquire time data and produce spectra for a number of non-damaging impacts from a standard instrumented impulse hammer. The second approach used an instrumented drop-test rig to perform the potentially damaging impacts. The impact energies for this approach were set to range from 0.37 J to 41.72 J. The response signals from each test specimen were recorded using the LMS SCADAS III data acquisition system and saved for evaluation. To gather the appropriate information to make inferences regarding the extent of the damage, two different methods were used to estimate the damaged area. The first method measured the damage size using a vernier caliper directly on the impacted surface. The second method used developed X-ray films. For the latter method, the damage area was estimated as the rectangular area bounded by the width and length of the largest flaws visible parallel to the two plate axes. The correlation between the damage area in terms of the impact energy and force detected is presented and discussed. In this research, following a systematic series of experiments on the induction of impact damage in composite specimens, Scanning Electron Microscopy was used to inspect the topographies of the impacted surface at high magnifications. Two different approaches were used here to observe the type of failure modes. The first observation was on the surface defects of the impacted samples whilst the second type, usually categorised as destructive testing, visualised the cross-sectional defects to look at the internal damages. A damage model and damage pattern was developed from this work, which can provide sufficient information on the type and extent of damage. Both the damage model and pattern can be used to provide fundamental understanding of damage and failure mode progression in carbon fibre reinforced compo~ites with varying layer numbers and impact energies. Wavelet analysis is a well-known and powerful approach to feature extraction for problems in condition monitoring and damage detection. In this research, it is applied in the context of impact damage detection and quantification. The approach was based on response time signals recorded from the piezoelectric sensors. Damage indices in terms of Root Mean Square, Power Spectrum Density and Envelope Mean were presented. The results show that all three potential damage indices show a monotonic increase with impact energy and this behaviour is important when damage needs to be detected directly from the impact data. The current research was based on the idea of implementing machine-learning methods to identify and categorise (damaging and non-damaging) impacts using structural response data. To implement this idea, a novelty detection method using outlier analysis was used. This method has proved to be a successful in separating the damaged and non-damage features and classifying the types of failure modes. This method was considered an excellent approach to identify and categorise the impact events using structural response data.
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Craven, Richard. "Modelling of impact damage in composites." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/6094.
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The work presented in this thesis is a detailed study of impact damage subjected to tensile and compressive loading to determine the stiffness reduction of the damage region and identify the damage mechanisms and important parameters that control the severity of the stiffness reduction. Once the important damage parameters had been indentified a homogenised non-linear soft inclusion model was developed. This represents the mechanical and material behaviour of an impact damage region under tensile and compressive loading in a simple and easy to implement user material format. The influence of different damage parameters was determined by building ply level models of idealised impact damage with delaminations at every ply interface and fibre fracture cracks within the plies. Parametric studies were conducted on the shape and size of delaminations and on crack density and crack distribution under tensile and compressive loading and these models were validated against experimental results. In order to determine the influence of fractured fibres on the residual compressive stiffness the fibres were modelled at the micro scale with individual fibres embedded in an elastic-plastic matrix.
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Pandya, Kedar Sanjay. "Impact damage behaviour of lightweight materials." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270002.
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Impact damage resistance is an essential requirement of lightweight structural components for high-performance applications. The aim of this thesis is to study the impact damage and perforation behaviour of lightweight materials including thin aluminium alloy plates and carbon fibre reinforced epoxy composites. The focus of this investigation is on the stress state and strain rate dependence of failure, and the effect of microstructural modifications on indentation and impact response. The thesis is divided into three parts. In the first part (Chapter 2) the impact response of thin monolithic ductile aluminium alloy plates is investigated. Impact perforation experiments are performed using different projectile nose shapes to span a wide range of stress states at the onset of ductile fracture. Impact perforation behaviour, ballistic limit velocity, energy absorption capability and sensitivity to projectile tip geometry are evaluated. Modes of deformation and failure during impact are assessed experimentally. It is shown that modelling the stress state and strain rate dependence of plasticity and failure is crucial to accurately predict ductile fracture initiation in thin metal plates. In the second part (Chapters 3 and 4), the stress state and strain rate dependent yield and failure behaviour of epoxy resin is investigated. An iterative numerical-experimental approach is shown to be essential to develop a material model capable of predicting the failure behaviour of epoxy for a wide range of stress triaxialities across different regimes of failure. The influence of microstructural modifications in epoxy, through two different toughening strategies, on its failure behaviour is investigated. The effect of increasing the applied strain rate on the stress state dependent response of epoxy is investigated to provide an insight into the impact damage resistance of carbon fibre reinforced epoxy composites. In the third part (Chapter 5), experimental studies are conducted on the quasi-static indentation and impact perforation response of plain weave carbon fibre reinforced epoxy composites to investigate the effect of toughening the epoxy matrix to improve resistance to indentation and impact. The nose shape sensitivity of failure initiation in carbon/epoxy composite targets is assessed by considering indenters with different tip geometries. Conclusions and suggestions for future work are presented in Chapter 6.
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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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Selver, Erdem. "Tow level hybridisation for damage tolerant composites." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/tow-level-hybridisation-for-damage-tolerant-composites(8cf53f8c-165f-4e8b-b67f-f8fd34c327e2).html.
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Fibre reinforced composites have higher specific strength and stiffness in comparison to metals. However, composites are susceptible to impact damage resulting in degradation of mechanical properties especially compression strength. Numerous studies have been conducted to improve the impact damage tolerance of composite laminates using modified resin systems, thermoplastic matrices, 3-D fibre architectures and through thickness reinforcement. This work is primarily focussed on incorporating non dissolvable polypropylene fibres (PP) in a thermoset matrix for improving the damage tolerance. Commingling and wrapping techniques have been investigated. PP fibres have been incorporated at the preform stage and hence do not adversely affect the viscosity of the resin during infusion. The healing effect of PP fibres on impact damaged composite laminates when heating is introduced has also been studied. High velocity impact test results showed that using commingled glass/PP fibres increased the total energy absorption of composite laminates by 20% due to the extensive plastic deformation of the PP fibres and through the use of toughening mechanisms in the form of resin cracking and delamination. It has been found that PP fibres provide protection to the glass fibres during low velocity impact loading, so fewer fibre breakages occur which lead to improved residual properties compared with pristine glass laminates. Compression after impact (CAI) tests showed that the residual strength as a percentage of non-impacted strength increased with percentage of PP fibres used. For impact of 20-50J, glass/epoxy laminates retained 32 45% of their compressive strength while laminates with 7%, 13% and 18% PP fibres retained 37 50%, 42-52% and 43-60% of their compressive strength, respectively. It was also observed that glass/PP woven laminates had better compressive strength retention (62 83%) than the glass/PP non-crimp laminates (37-50%). Composite laminates with high-modulus PP fibres (Innegra) exhibited higher residual compression strengths in comparison to laminates with lower modulus PP fibres. For 15-50J impact, glass/Innegra laminates showed residual compression strength of 50 63% in comparison to 39-60%; laminates without thermoplastic fibres exhibited 33 43% residual compression strength. Modulus of thermoplastic fibres appears to be important at higher energy levels. Healing of damaged commingled laminates produced a significant reduction in the damage area and a corresponding increase in CAI strength after heating at 200ºC; CAI strength of healed laminates is about 85% of undamaged samples in comparison to 60% for non-healed samples. A novel micro-wrapping technique, developed in this work, demonstrated significant reduction in damage area (46%) in comparison to the commingling method. Core wrapped laminates had higher residual strength (43-60%) than glass laminates (33-43%). Better PP distribution in core-wrapped composites helped to decrease the PP rich areas and the impact damage did not propagate easily in comparison to commingled composites. However due to the reduction in damage area, impact energy absorption in core wrapped laminates was lower than for commingled.
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Green, Philip Charles. "Impact damage characteristics of carbon-epoxy composites." Thesis, University of Hertfordshire, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332277.
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Djahansouzi, B. "Effect of dynamic response on impact damage." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47033.
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Tippetts, Trevor 1977. "Modeling impact damage in laminated composite plates." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/82782.
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Symons, Digby Duncan. "Impact damage tolerance of carbon fibre reinforced plastics." Thesis, University of Oxford, 1998. https://ora.ox.ac.uk/objects/uuid:1db49475-ac42-4259-91aa-b84ee6718875.
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Carbon fibre reinforced plastic (CFRP) is a composite composed of very high strength and stiffness carbon fibres within a polymer matrix. Low mass and cost make CFRP attractive for aerospace applications. At present application of CFRP is limited by the poor residual strength and fatigue properties of the material following impact damage, and because of the limited understanding of the problem. Damage to CFRP results in a combination of fibre fracture and matrix cracking. The strength of CFRP perpendicular to the fibre direction is relatively poor and so the material is generally used as a laminate of unidirectional plies of different fibre orientations. Laminates are particularly prone to delamination, this is matrix cracking which separates plies. In this thesis techniques for measurement of damage type and severity in CFRP are evaluated. These are used to quantify the distribution of damage resulting from hard body impacts at high, low and quasi-static incident velocities. A composite material damage model in a dynamic finite element analysis computer program (DYNA 3D) was used to predict the experimentally measured impact damage. However the prediction was found to be insufficiently accurate for reliable use by designers. Recommendations are made for improvements in the numerical modelling of impact damage in CFRP. Mechanical tests that provide data on the effect of impact damage on the residual strength of CFRP specimens are reported. These show that providing impact damage is limited to delamination, with little fibre fracture ocurring, the compressive residual strength will be more severely reduced than the tensile property. Strain gauge measurements show that this effect is caused by local compressive buckling of the delaminated plies in the impact damaged area. Lquivalent hole sizes, causing the same residual strengths as in the impact damaged specimens, are given. Cyclic load tests were conducted providing stress-life data for impact damaged specimens of CFRP. The data fit a stress-life diagram divided into three scatter band regions: static fracture; cycle dependent damage growth; and infinite life. Qualitative and quantitative observations are given of the progression of damage in a fatigue after impact damage test. Strain gauge and force/extension measurements show the presence of creep and energy absorption in undamaged and impact damaged CFRP. Much of the observed behaviour may be explained by a viscoelastic model. Because of the presence of viscoelastic creep it is suggested that the fatigue mechanism must depend on interacting cycle dependent and time dependent mechanisms.
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Shi, Yibing. "Barely visible impact damage in polymer composite laminates." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334270.
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Habib, F. A. "Evaluation of repeated impact damage in composite structures." Thesis, University of the West of Scotland, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234257.
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Amish, Mohamed Belkasem. "Drilling fluids filtration and impact on formation damage." Thesis, Robert Gordon University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404919.
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Wolf, Edward. "Impact damage mechanisms in several laminated material systems." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12823.
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Kraft, Michael John. "Impact damage response of graphite/epoxy fabric structures." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/41231.
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Augustson, Julia, and Madeleine Bogg. "Impact Damage Assessment : In collaboration with Saab aerostructures." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277881.
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This project that has been executed in collaboration with Saab aerostructures deals with how three materials, aluminum, titanium and corrosion resistant steel react when they are affected by different energy levels. These energy levels serve the purpose of representing damages that can happen in storage and handling to components used in production. A literature study was made to gather information regarding the treated materials as well as some methods that can be used to test a materials property. The goal of the project is to create a tool for Saab to use in their production in order to first estimate the energy levels that created a mark on a material and secondly evaluate if a crack can be suspected, by consequence evaluate if a NDT (non-destructive test) is required. The experiment was executed as such that all of the materials were put through drop-tests simulating different energy levels, with two different strikers, blunt and sharp, and then the materials were examined. Non-destructive testing was made on all of the marks made on the different materials using penetrant- or eddy current-method to see if there were any cracks formed in the material after impact. The experiment did not show signs of any cracks from the tested energy levels. However, it showed that crack propagation is highly dependent on the shape of the striker. To make the experiment more reliable and give a better result more energy levels would have needed to be tested. Also, a large number of different strikers and more non-destructive testing methods would have to be used.Detta projekt som har utförts i samarbete med Saab aerostructures behandlar hur tre material, aluminium, titan och rostfritt stål reagerar när de blir utsatta för olika energinivåer. Dessa energinivåer ska simulera skador som kan uppkomma under hantering och förvaring av komponenter i Saabs produktion. En litteraturstudie har utförts för att samla information om materialen samt om några testmetoder som kan användas för att utvärdera ett materials egenskaper. Målet med projektet är att få fram ett tillvägagångssätt för Saab att i första hand uppskatta energinivåerna bakom ett slagmärke i ett material, därefter bedöma ifall en sprickinitiering kan misstänkas och därmed avgöra huruvida komponenter som utsatts för energinivåer behöver undergå oförstörande provning eller om de kan fortsätta användas i produktionen utan någon form av testning. Ett experiment utfördes genom att utsätta samtliga av materialen för dropp-tester med olika energinivåer med två olika slagdon, trubbigt och spetsigt, för att sedan kunna undersöka om sprickor hade propagerats. Oförstörande provning gjordes på alla simulerade skador antingen via penetrantmetoden eller virvelströmsprovning, för att se om det bildats sprickor i de olika materialen efter slaget. Experimentet visade inte på några sprickor vid de testade energinivåerna. Däremot såg man att sprickinitiering beror bland annat på slagdonets utformning, där en skarpare form ökade risken för sprickor. För att experimentet ska bli mer pålitligt och ge ett bättre resultat hade fler energinivåer behövt testas, en större variation av slagdon hade behövt användas samt att man hade behövt använda fler typer av oförstörande provning.
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Liu, Ning. "Composite materials impact damage detection using neural networks." Thesis, Aston University, 2002. http://publications.aston.ac.uk/11838/.
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This thesis considers two basic aspects of impact damage in composite materials, namely damage severity discrimination and impact damage location by using Acoustic Emissions (AE) and Artificial Neural Networks (ANNs). The experimental work embodies a study of such factors as the application of AE as Non-destructive Damage Testing (NDT), and the evaluation of ANNs modelling. ANNs, however, played an important role in modelling implementation. In the first aspect of the study, different impact energies were used to produce different level of damage in two composite materials (T300/914 and T800/5245). The impacts were detected by their acoustic emissions (AE). The AE waveform signals were analysed and modelled using a Back Propagation (BP) neural network model. The Mean Square Error (MSE) from the output was then used as a damage indicator in the damage severity discrimination study. To evaluate the ANN model, a comparison was made of the correlation coefficients of different parameters, such as MSE, AE energy, AE counts, etc. MSE produced an outstanding result based on the best performance of correlation. In the second aspect, a new artificial neural network model was developed to provide impact damage location on a quasi-isotropic composite panel. It was successfully trained to locate impact sites by correlating the relationship between arriving time differences of AE signals at transducers located on the panel and the impact site coordinates. The performance of the ANN model, which was evaluated by calculating the distance deviation between model output and real location coordinates, supports the application of ANN as an impact damage location identifier. In the study, the accuracy of location prediction decreased when approaching the central area of the panel. Further investigation indicated that this is due to the small arrival time differences, which defect the performance of ANN prediction. This research suggested increasing the number of processing neurons in the ANNs as a practical solution.
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Melnikov, Alexei. "Damage and Fatigue in Cross-Linked Rubbers." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1280198428.
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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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Amico, Peter joseph. "Damage Reduction Strategies for a Falling Humanoid Robot." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78765.
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Instability of humanoid robots is a common problem, especially given external disturbances or difficult terrain. Even with the robustness of most whole body controllers, instability is inevitable given the right conditions. When these unstable events occur they can result in costly damage to the robot potentially causing a cease of normal functionality. Therefore, it is important to study and develop methods to control a humanoid robot during a fall to reduce the chance of critical damage.
This thesis proposes joint angular velocity strategies to reduce the impact velocity resulting from a lateral, backward, or forward fall. These strategies were used on two and three link reduced order models to simulate a fall from standing height of a humanoid robot. The results of these simulations were then used on a full degree of freedom robot, Viginia Tech's humanoid robot ESCHER, to validate the efficacy of these strategies.
By using angular velocity strategies for the knee and waist joint, the reduced order models resulted in a decrease in impact velocity of the center of mass by 58%, 87%, and 74% for a lateral, backward, and forward fall respectively in comparison to a rigid fall using the same initial conditions. Best case angular velocity strategies were then developed for various initial conditions for each falling direction. Finally, these parameters were implemented on the full degree of freedom robot which showed results similar to those of the reduced order models.Master of Science
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Casas-Rodriguez, Juan P. "Damage in adhesively bonded joints : sinusoidal and impact fatigue." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/11814.
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The main aim of this research was to investigate the behaviour of adhesive joints exposed to repeated low-velocity impact i.e. impact fatigue (IF), and to compare this loading regime with standard fatigue (SF), i.e. non-impacting, constant amplitude, sinusoidal loading conditions. Two types of lap joint configuration using rubber toughened modified epoxy adhesives were used and exposed to various loading conditions in order to determine the fatigue behaviour of the joints for each load conditions. The fatigue life was investigated using bonded aluminium alloy (7075-T6) single lap joint (SLJ) specimens, where it was seen that IF is an extremely damaging load regime compared to SF. Different trends were visible in force-life plots for these two types of loading. In SF a gradual decrease in the fatigue life with increasing load was observed, whereas, in IF a significant decrease in life was seen at relatively modest levels of maximum force after relatively few cycles. Comparisons of the fatigue life show a considerably earlier failure in IF than in SF for comparable levels of force and energy. Additionally, it was demonstrated that the maximum force per cycle, loading time, stiffness and strength decreased as a result of damage generated in the sample during IF.
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Tsang, Pui Ho Wilson. "Impact resistance and damage tolerance of composite sandwich panels." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11925.
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Ai, Huirong Saleeby Jason B. "Shock-induced damage in rocks : application to impact cratering /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-05262006-173355.
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Lakdawala, Seema Sailesh. "Impact of DNA damage proteins on the adenoviral lifecycle." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3373343.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed Oct. 19, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 172-200).
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Jia, Hongyu. "Impact Damage Resistance of Shape Memory Alloy Hybrid Composite Structures." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30572.
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The strain energy absorption of shape memory alloy (SMA) bars and beams under tension and bending loading was studied. A theoretical model is presented that can give quantitative relations between the martensite fraction, the applied load, and the strain energy absorbed in the shape memory alloy (SMA). It was found analytically that the super-elastic SMA demonstrates a high strain energy absorption capability. The closed- form solution of the strain energy absorption capability of SMA bars is a simple and useful tool in the design of energy absorption applications of super-elastic SMA. The nonlinear equations for SMA hybrid composite plates, which can be used for low velocity impact or quasi-static contact loading, are derived. The governing equations include the transverse shear deformation to the first-order, large deformation of the plates, and SMA/epoxy lamina. The equations are derived in the general form with general boundary conditions and general stack of angle ply. The equations can be simplified to special forms in the specific applications.
A theoretical study of the impact force and the strain energy absorption of an SMA/graphite/epoxy composite beam under a low-velocity impact has been performed. The contact deformation, the global bending deformation, the transverse shear deformation, and the martensitic phase transformation of the super-elastic SMA fibers are studied. The energy absorbed by the SMA hybrid composite is calculated for each task of the absorption mechanisms: contact deformation, global bending deformation, and The analysis methods and models developed in this dissertation are the first reported research in modeling SMA composite under low velocity impact and quasi-static loading. The models and methods developed here can be used for further study and design of SMA composites for low velocity impact or quasi-static loading in failure process.Ph. D.
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Teh, Kuen Tat. "Impact damage resistance and tolerance of advanced composite material systems." Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06062008-170512/.
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Rhead, Andrew T. "Analysis and optimisation of postbuckled damage tolerant composite laminates." Thesis, University of Bath, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520992.
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Barely Visible Impact Damage (BVID) can occur when laminated composite material is subject to impact, i.e. from runway debris or dropped tools, and may result in a significant reduction in the compressive strength of composite structures. A component containing BVID subjected to compression may fail via a number of mechanisms. However, it is assumed that the impact damage problems to be modelled will fail by delamination buckling leading to propagation of damage away from the original site. This precludes problems where the initial mechanism of failure is via kink banding or buckling of the full laminate. An analytical model is presented, for application to various composite structures, which predicts the level of compressive strain below which growth of BVID following local buckling of a delaminated sublaminate will not occur. The model is capable of predicting the critical through-thickness level for delamination, the stability of delamination growth, the sensitivity to experimental error in geometric measurements of the damage area and additionally establishes properties desirable for laminates optimised for damage tolerance. Problems treated with the model are split into two impact categories; ‘face’ (i.e. an out-of-plane skin impact) and ‘free edge’ (i.e. an in-plane stiffener edge impact) and two compressive loading regimes; ‘static’ and ‘fatigue’. Analytical results for static and fatigue compression of face impacted plates show an agreement of threshold strain to within 4% and 17% of experimental values respectively. In particular, for impacts to the skin under a stiffener subject to static loading the model is accurate to within 5%. An optimised laminate stacking sequence has shown an experimental increase of up to 29% in static strength can be achieved in comparison to a baseline configuration. Finally, compression testing has been undertaken on three coupons in order to validate an analysis of static free edge problems. Analytical results are, on average, within 10% of experimental results. An optimised laminate is theoretically predicted to increase static compression after free edge impact strength by at least 35%.
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Faidi, Salah Eddin. "The impact damage and the instrumented impact testing of epoxy coating and bulk polymer." Thesis, University of Manchester, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244148.
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Tsigkourakos, George. "Experimental and numerical analysis of damage in CFRP laminates under static and impact loading conditions." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13284.
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Engineering composites and especially long fibre carbon composites have been in high demand not only in aerospace and automotive applications, but also in high end everyday applications. In aerospace, carbon composites are used predominantly for secondary structures attached by joints or fasteners to various alloys or even different composites, and are exposed to service loads and repetitive impacting. Impact fatigue (IF) is not studied adequately for long cycles and relevant literature is investigating mainly drop weight tests and high speed projectile experiments. The main aim of this research was to investigate the behaviour long fibre CFRP'S exposed to repeated low-velocity, low energy impacts, and to observe the damage effects of this regime on the structural integrity of these materials. Two types of specimen configurations using CFRPS's were used and exposed to loading conditions relevant to the Izod impact fatigue test (IIFT), and the tensile impact fatigue test (TIFT), in order to determine the fatigue behaviour of the specimens for each of these load conditions. For the IIFT, the fatigue life was investigated using IM7/8552 unidirectional specimens and T700/LTM45 cross-ply specimens were utilised for the TIFT. The specimen thicknesses were altered in both cases and parametric studies were carried out, where it was seen that IF results in high level of scatter and the apparent decrease in life was seen at relatively modest levels of maximum force after relatively few cycles. In the case of the IIFT, a durability limit was not apparent which increases the complications when designing against IF. In the case of the TIFT the stiffness deterioration was reflected as an increase of the loading time, in the force vs time graph, over the total fatigue life span. Fatigue crack growth was investigated using fractography and X-ray micro-CT at the micro and macro level. It was seen, that IF had the potential to initiate cracks and to cause their propagation at low levels of loading. For the IIFT, a single crack was growing substantially in the fibre direction and across the sample width causing matrix cracking and probably breaking of some fibres, which acted as impact wave guides since matrix cracks were propagating initially along the length of the fibres. In the case of the TIFT multiple damage modes were presented (matrix cracks, axial splits and delaminations). Their sequence and progression was successfully v captured and contrasted against the number of impacts. Axial splits governed the damage scenario, with delaminations extending between them and the free edges. For the TIFT, IF was studied using the force-life (F-Nf) and energy-life (E-Nf) curves. The tests undertaken showed that when halving the thickness of the laminates the fatigue life presented a 10-fold decrease as well as higher scatter. Finite element modelling was undertaken to validate the experimental data of the TIFT test. Successful simulation of a single impact was carried out using a fully transient 3-D model of the actual experiment configuration which involved geometric non-linearities in addition to the multiple contact conditions. The analysis was undertaken using the Abaqus 6.11 explicit solver. Since the numerical single impact results (force vs time response) was in agreement with the experimental results, the crack modes, experimentally observed, were also incorporated in the model utilising the use of the cohesive zone elements (CZE).
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Millington, Susan. "The influence of some physical properties of carrots on their damage characteristics." Thesis, Cranfield University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294214.
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Cahoon, Lindsey Charlene. "Micro-CT Inspection of Impact Damage in Carbon/Epoxy Rods." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6350.
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Various configurations of unidirectional carbon/epoxy composite rods were impacted radially, inspected using micro-CT scanning equipment, and tested in axial compression to measure the residual strength after impact. This data was used to correlate the relationship between impact energy, residual strength, and the peak crack area and total crack volume along the length of the specimens. These specimens represent local members of open three-dimensional composite lattice structures (e.g., based on isogrid or IsoTruss® geometries) that are continuously fabricated using advanced three-dimensional braiding techniques. The specimens were radially impacted with 2.5 J (1.9 ft-lbs), 5.0 J (3.7 ft-lbs), 7.5 J (5.6 ft-lbs), 10 J (7.4 ft-lb), 15 J (11 ft-lbs), and 20 J (15 ft-lbs) of energy, and compared to undamaged control specimens. The unidirectional core specimens were 8 mm (5/16") in diameter and were consolidated with various sleeve configurations and materials. Sleeves differed in types (bi-directional braided sleeves or unidirectional spiral wraps), nominal sleeve coverage of the core fibers (full or half), and sleeve material (Nomex Thread or Dunstone Hi-Shrink Tape). The unsupported length of the specimens used in this research was 50.8 mm (2") to ensure a strength-controlled compression failure rather than a failure due to buckling. After impact, the specimens were scanned using a micro-CT scanner at resolutions of 50 and 35 microns and subsequently tested in axial compression. The micro-CT scan images were analyzed to measure the crack areas along the specimen. From this analysis, the peak crack area and total crack volume along the length of the specimen was calculated. Similar to past research, as the impact energy increases, the residual compression-strength-after-impact decreases. As the impact energy increases, specimens with shrink tape sleeves had the largest increase in peak crack area and overall crack volume while specimens with full spiral sleeves had the lowest increase in peak crack area and overall crack volume. A bimodal increase is evident in the peak crack area and total crack volume over the length of the specimen where specimens impacted at 15 J (11 ft-lbs) showed the highest peak crack area across all sleeve types. There is a slight correlation between the increase in peak crack area and overall crack volume and the decrease in residual compression strength after impact. Shrink Tape, while yielding a higher quality specimen with greater compression strength prior to impact, did not protect the specimens against damage due to impact as well as other sleeve types. This was shown by the large decrease in residual compression strength after impact and increase in peak crack area and overall crack volume as the impact energy increased.
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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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Preston, Sarah Jane. "The impact of shell damage on Calliostoma zizyphinum (Gastropoda: Trochidae)." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241431.
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Breen, Charles Edward Pitt. "Impact damage in thick carbon fibre reinforced plastic laminated composites." Thesis, University of Bristol, 2007. http://hdl.handle.net/1983/426d2091-43e8-4d4a-ae7a-b0ded8dea0e2.
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Sztefek, Pavel. "Inverse method for stiffness determination of impact damage in composites." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5556.
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The limited knowledge of stiffness reductions is a major problem in reliably predicting the post-impact strength of composite structures. This work describes development and application of a non-destructive approach for evaluation of the inplane stiffness of impact damage in composites. The approach combines an inverse method linked to a finite element model and non-contact full-field measurements. The material parameters of impact damage are determined by iteratively matching the finite element model to displacement fields measured optically during post-impact loading. A first order, gradient optimization technique coupled with a modified quadratic algorithm is employed. The method is validated on a reference finite element model with axisymmetric damage containing several concentric zones having different properties, and the influence of measurement noise is examined. The approach is applied to in-house experiments with impacted carbon/epoxy laminates to determine their quasi-isotropic mechanical properties in tension and compression. The resulting stiffness distributions are presented and the corresponding nonlinear behaviour of the damage is described. To examine the effect of the type of damage on the mechanical properties a thorough fractographic analysis of the impacted specimens was undertaken. The tensile stiffness is found to be mainly affected by fibre fracture, while the compressive stiffness is strongly linked to delamination buckling. The approach has further been extended for detection and evaluation of multiple impact damage zones at arbitrary locations as well as for stiffness identification of the damage in orthotropic laminates. The accuracy of both extensions is presented and discussed. Finally, possible future applications of the approach are considered.
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Peters, Diane S. "Impact damage evaluation of high performance polymeric composite material systems." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-08222009-040525/.
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Beheshty, M. H. "Interaction between impact damage and fatigue in fibre reinforced plastics." Thesis, University of Bath, 1997. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362306.
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LOI, GABRIELA. "NONLINEAR ACOUSTIC TECHNIQUES FOR IMPACT DAMAGE DETECTION IN COMPOSITE MATERIALS." Doctoral thesis, Università degli Studi di Cagliari, 2022. http://hdl.handle.net/11584/332671.
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Due to their high stiffness–to–mass ratio, fiber-reinforced materials have been intensively used in several engineering branches. Nevertheless, their low resistance to low-velocity impacts may question their use in critical load-bearing structures. Impacts may result in the emergence of barely visible internal damage. Although not severe enough to cause the catastrophic failure of the inspected component, the impact-induced damage may compromise its load-bearing capability. The need to detect the onset of internal damage has led to an ever-rising interest in Structural Health Monitoring (SHM). Nowadays, although the underlying physics is still not clear, the SHM approaches based on nonlinear acoustic phenomena are widely used to provide information on the structural integrity of composite materials. This thesis focuses on two nonlinear acoustics techniques, namely the Scaling Subtraction Method (SSM) and the Nonlinear Vibro-Acoustic Modulation (VAM), to further assess their effectiveness in detecting the occurrence of impact damage in composite beams.
The Scaling Subtraction Method accounts for the global nonlinear content of the system response to infer information on its integrity and ability to withstand critical loads. Mainly applied to granular media, the SSM was proven to be effective in identifying the onset of internal damage also in metals and composites. However, the quality of the provided indications was highly affected by the selection of the interrogating frequency, usually chosen among the resonance frequencies of the inspected system. The need for preliminary modal analysis and the lack of a robust algorithm to pick the resonances with the highest sensitivity to damage prevent the SSM from being a reliable NDT tool. In an attempt to overcome these limitations, this thesis proposes a novel SSM-based approach relying on the use of a broadband impulsive excitation. To demonstrate the feasibility of a pulse-based SSM approach, a composite beam has been alternatively excited through impulsive or pure-tone harmonic excitations tuned at different natural frequencies in both pristine and damaged conditions. The results showed the proposed approach to be a rather promising option for detecting the onset of low-velocity impact damage in composite materials.
The Nonlinear Vibro-Acoustic Modulation relies upon simultaneously driving the inspected structure with two waves of distinct frequencies and amplitudes. The presence of defects perturbates the propagation of the two impinging waves leading to the emergence of modulation sidebands that can be exploited to infer information on the material properties degradation. In recent years, the analysis of modulation sidebands has been applied to detect the onset of internal damage in both metal and non-metallic structures. Nonetheless, since some critical issues still have to be investigated, this thesis aims to further assess whether the selection of some testing parameters may affect the effectiveness and the sensitivity of the VAM. For this purpose, three identical composite beams have been subjected to multiple low-velocity transverse impact loads to induce the emergence of a pattern of modulation sidebands around the probe frequency peak and, subsequently, tested under different boundary conditions and through different actuation-sensing scenarios. The obtained results showed that the amplitude of the modulation sidebands tends to increase with the damage severity. However, the trial of a set of pump frequencies revealed the VAM to be highly sensitive to the selected natural frequency. Similarly, the pump excitation amplitude was shown to affect the quality of the provided indications. In addition, the method capability to identify the changes in the sample integrity slightly varied with the considered sensing-actuation scenario, even though it was the sensor positioning to be found the factor susceptible to affect the method performance to a greater extent.
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Bull, Peter H. "Damage tolerance and residual strength of composite sandwich structures." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3757.
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The exploitation of sandwich structures as a means toachieve high specific strength and stiffness is relatively new.Therefore, the knowledge of its damage tolerance is limitedcompared to other structural concepts such as truss bars andmonocoque plate solutions.
Several aspects of the damage tolerance of sandwichstructures are investigated. The influence of impact velocityonresidual strength is investigated. Sandwich panels withfaces of glass fiber reinforced vinylester are impacted bothwith very high velocity and quasi static. The residual strengthafter impact is found to be similar for both cases of impactvelocity.
Curved sandwich beams subjected to opening bending momentare studied. Faceñcore debonds of varying size areintroduced between the compressively loaded face sheet and thecore. Finite element analysis in combination with a pointstress criterion is utilized to predict the residual strengthof the beams. It is shown that it is possible to predict thefailure load of the beams with face-core debond.
Using fractography the governing mode of failure ofcompressively NCF-carbon is characterized. Sandwich panelssubjected to compression after impact are shown to fail byplastic micro buckling.
The residual compressive strength after impact of sandwichpanels is investigated. Sandwich panels with face sheets ofnon-crimp fabric (NCF) carbon are subjected to different typesof impact damages. Predictions of residual strength are madeusing the Budiansky, Soutis, Fleck (BSF) model. The residualstrength is tested, and the results are compared topredictions. Predictions and tests correlate well, and indicatethat the residual strength is dependent on damage size and notthe size of the damaged panel.
A study of the properties of a selection of fiberreinforcements commonly used in sandwich panels is conducted.The reinforcements are combined with two types of core materialand three types of matrix. Also the influence of laminatethickness is tested. Each combination materials is tested inuni-axial compression, compressive strength after impact andenergy absorption during quasi static indentation. Thespecimens which are tested for residual strength are eithersubjected to quasi-static or dynamic impact of comparableenergy level. Prediction of the residual strength is made andcorrelates reasonably whith the test results. The tests showthat if weight is taken into account the preferred choice offiber reinforcement is carbon.
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Dubary, Nicolas. "Optimisation numérique et expérimentale de la tolérance aux dommages d’impact d’un stratifié composite aéronautique." Electronic Thesis or Diss., Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0038.
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Dans un souci majoritaire de gain en masse et pour l’intégration de solutions innovantes et de structures hautes performances dans les applications actuelles, les matériaux composites occupent une place grandissante au sein des structures aéronefs. Cependant, ils restent vulnérables aux sollicitations hors-plan tel que l’impact, dues par exemple à une chute d’objet pendant une opération de maintenance. Cet événement peut drastiquement réduire leur tenue résiduelle sans pour autant laisser de marque visible en surface. Pour répondre aux exigences réglementaires et permettre une utilisation saine en service, les structures composites sont donc souvent surdimensionnées.Ces travaux de thèse portent sur l’étude expérimentale et numérique de la tolérance aux dommages d’impact (TDI) d’un stratifié composite aéronautique. Entre méthodologie et technique, le thème de recherche propose une étude complète de l’intégrité d’une structure composite, permettant l’apport de connaissances ainsi qu’une compréhension approfondie de la TDI.Le dimensionnement des structures composites s’appuie sur les méthodes aéronautiques d’inspection visuelle des endommagements définissant les charges acceptables et requises par la structure. En effet, la détectabilité de l’endommagement permet une intervention de réparation sur la structure : tant que l’endommagement n’est pas détecté (BVID : Barely Visible Impact Damage), les performances de la structure doivent rester élevées. De nouveaux concepts de stratifiés composites hybrides sont proposés puis testés expérimentalement dans le but d’améliorer la TDI et d’approfondir également la connaissance du comportement des stratifiés composites. Ces concepts sont établis à partir d’un cas de référence, ensuite décliné sous différentes configurations de stratifiés composites hybrides. La démarche expérimentale de la TDI est alors menée depuis l’impact jusqu’à la compression après impact pour définir les deux indicateurs principaux de cette étude : l’indentation permanente et la tenue résiduelle.En parallèle, le modèle développé à l’ICA, le Discret Ply Model (DPM), est utilisé pour proposer une démarche de dimensionnement de stratifié intégrant la philosophie de la TDI. Des améliorations de modélisation et son extension aux stratifiés composites hybrides sont ensuite proposées. Elles ouvrent sur l’utilisation du DPM comme un outil d’aide au dimensionnement des structures composites. Cette démarche est en parfaite cohérence avec l’intégration des approches numériques pour assister les études expérimentales, s’intégrant dans le cadre du « Virtual Testing »Coupling with will of mass gain, use of innovative solutions and high performance structures in today’s industrial applications, composites are more and more present in aeronautical structures. However, they are still vulnerable to out-of-plane loading such as impact, due to falling objects during a maintenance operation for instance. This event can drastically reduce their residual strength without let a visible mark onto the surface. Therefore in order to meet requirements and drive to healthy use in service, composites structures are often oversized.This work deals with the experimental and numerical study of the Impact Damage Tolerance (IDT) of an aeronautical composite laminate. An overall study of composite structures integrity leads to a deeper knowledge of the IDT.The approach is based on aeronautical methods for the damages visual inspection: the damage detectability defines the required load that the structure has to sustain. Indeed, the detectability of the damage allows a repair intervention on the structure: as long as the damage is not detectable (BVID), the performance of the structure must remain high. Proposed concepts are experimentally tested to improve the TDI and to bring to more understanding in the behavior of composite laminates. These concepts are based on a reference case, and then declined under different configurations of hybrid composite laminates. The experimental approach of TDI is carried out from impact to compression after impact to define the two main indicators: permanent indentation and residual strength.The model developed at ICA, the Discrete Ply Model (DPM), is used to propose a numerical designing approach according to the TDI philosophy. Modeling improvements are implemented to extend to hybrid composite laminates. This step opens up on the use of DPM as a tool to assist the composite structures sizing. This advanced is in respect with the integration of numerical approaches to support experimental studies, integrating within the framework of "Virtual Testing"
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Binte, Mokhtar Hanan. "Contribution to the study of impact damage on composite laminates : the effect of hygrothermal ageing and preloading." Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS045.
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Ce travail a pour but d'étudier la tolérance à l'impact de 3 stratifiés carbone/époxy soumis simultanément à différents types de chargements hygrothermiques et mécaniques. Ces stratifications présentant des caractéristiques mécaniques globales particulières d'isotropie, il s'agit ici de déterminer l'influence de la séquence d'empilement sur le développement de l'endommagement lors d'un impact. Dans un premier temps, la cinétique de vieillissement hygrothermique des trois stratifications est étudiée et analysée. Ensuite, leur tolérance à un unique impact ainsi qu'à des impacts répétés est évaluée. L'endommagement résultant de ces impacts est analysé par contrôle ultrasonore. La morphologie générale et l'amplitude de l'endommagement dans la profondeur des matériaux sont mises en relation avec les propriétés mécaniques et la séquence d'empilement spécifique à chaque stratifié. Dans un deuxième temps, l'influence combinée de plusieurs sollicitations est étudiée. Différents scénarii associant un vieillissement hygrothermique ainsi qu'un ou deux impacts sont mis en oeuvre. L'endommagement résultant est mis en rapport avec les temps relatifs de vieillissement et la position des impact durant le cycle de vieillissement. Ensuite, l'influence d'une précharge de traction sur la tolérance à l'impact est mise en évidence. Un montage spécifique a été conçu et fabriqué pour réaliser ces tests. Enfin, l'association d'un vieilllissement hygrothermique et d'une précharge de traction est abordée afin d'identifier la sollicitation la plus pénalisant en terme de tolérance et d'impactThis study examines impact damage processes in three types of CFRP composite materials simultaneously subjected to different hygrothermal and mechanical loading conditions. The composite structures tested are chosen for having particular global isotropic responses when loaded, the aim being to ascertain the exact influence of lay-up sequence on impact damage propagation. The work is presented in four main sections. Firstly by establishing hygrothermal ageing dynamics for the three composite structure types and their behaviour when impacted once or several times ; impact damage is measured and analysed using ultrasonic method. The extent and general morphology of the damage through the material thickness is correlated with mechanical properties and lay-up sequence specific to each material. Secondly the influence of simultaneous load combinations is examined. These include different durations of hygrothermal ageing associated with single or double impacts.The resulting damage incurred is analysed with respect to overall ageing time and time during the ageing cycle when the impact was applied. Thirdly the effect of tensile loading during impact on damage within the material was studied. This was achieved using a specially designed test apparatus that allows loading and impacting conditions to be independently modified. By associating a high-speed digital camera to film specimen impacts it is possible to evaluate a relationship between overall composite specimen stiffness and the impact damage. Finally, in order to identify the most unfavourable situation with regard to impact damage resistance an association between hygrothermal ageing and an applied tensile load is examined
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Erdem, Savas. "Impact load-induced microstructural damage of concrete made with unconventional aggregates." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12497/.
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Understanding the correlation between the mix proportions, micro structural characteristics, and macro-scale properties of concrete (i.e. the process-structure-properties relationship) is fundamental to achieving a more advanced understanding of how to apply and optimise this abundant engineering material. Although, concrete has been traditionally evaluated by its physico-mechanical and functional properties; development of advanced and effective inspection techniques during the last decade has demonstrated that fundamental macro-level properties of concrete depend, to a great extent, on its properties at the micro- and nano levels. This research was intended to make a quantitative assessment of impact load-induced micro-structural damage in concrete and, more particularly, to investigate the influence of ITZ micro-and nano local properties (as influenced by aggregate characteristics) on the impact load-induced cracking behaviour of concrete. Five different types of concrete mixtures were designed with the same total water cement ratio either by using natural aggregates as reference or by totally replacing the natural coarse aggregate with unconventional aggregates (such as copper slag, blue brick, sintered fly ash and tyre rubber) having significant differences in strength, shape and surface texture, porosity and roughness, and elasticity. A range of advanced techniques including X-ray diffraction, mercury porosimetry, 3D X-ray computed tomography coupled with digital image analysis, laser surface profilometry, 3D nanotech vertical scanning interferometry and scanning electron microscopy fitted with energy-dispersive X-ray spectrometer were used to characterize the aggregates and the concrete micro-structures. Based on the results obtained a possible mechanism for the micro-structural damage in concrete was proposed. Poorer aggregate characteristics alone could be responsible for a greater ITZ deterioration after loading but the results demonstrated that in fact, the aggregate causes a change in the ITZ conditions and it is these altered ITZ conditions that have a major effect on overall mix behaviour and govern the damaging process of concrete under impact loading. It was also concluded that the presence of a weak and porous ITZ has two opposite effects on the failure process. First, the chemical and porosity heterogeneities within the ITZ can cause fluctuations/disordering in the cracking (fracture) path, resulting in an increase in the tortuosity and corresponding fracture energy dissipation. Second, a weak and porous ITZ transfers less stress from the matrix to the aggregate particles. This leads to a lower compressive strength but increased toughness due to micro crack path lengthening and energy dissipation. Finally, the effect of the aggregate on the surface area roughness of the ITZ was established for the first time in the concrete literature. The roughness number of the area near the ITZ was found to positively correlate with dissipated surface fracture energy. An increase in the roughness number is associated with an increase in the dissipated fracture energy. The significance of this correlation however, lies in the fact that the rougher near – ITZ fraction of the bulk paste is more resistant to cracking at the macro level. Findings from this study will lead to a better understanding of the impact load-induced micro-structural damage phenomena. In addition, the micro-structural data from SEM and X-ray CT obtained during impact and mechanical testing of the concrete mixtures could be used to develop a multi-scale finite element model to simulate and predict the behaviour and fracture damage of concrete subjected to dynamic loading.
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Sofocleous, Katerina. "Controlled impact tests on composite materials : damage development and energy analysis." Thesis, University of Surrey, 2008. http://epubs.surrey.ac.uk/2249/.
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In addition to their many advantages, one of the disadvantages of composite materials is that they can have low impact resistance due to their brittle nature. Recently there has been growing interest in the use of shape memory alloys (SMAs) to reinforce composites subjected to impact.
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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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Davies, Peter Nicholas Hugh. "Multiple impact jet apparatus : equipment and high-speed rain damage studies." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293390.
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Watson, Simon A. "The modelling of impact damage in Kevlar-reinforced epoxy composite structures." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395462.
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Thomas, Suzanne Louise. "The effect of impact damage on the fatigue life of steel." Thesis, University of South Wales, 2008. https://pure.southwales.ac.uk/en/studentthesis/the-effect-of-impact-damage-on-the-fatigue-life-of-steel(f643b32c-410c-4e7b-b5c1-0f5738715ab6).html.
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The aim of the research was to investigate the effect of impact damage on the fatigue life of steel using both experimental and finite element methods. Any component that is subjected to a single impact may have not only noticeable surface damage, but also residual stresses in its surface and subsurface layers. These residual stresses may reduce or possibly improve the fatigue life of the component. The objectives of the research were, therefore, to investigate what effect the size of an impacting object has on the fatigue life of a specimen and also to evaluate experimentally how the amount of single impact energy affects the fatigue life of specimens. Furthermore, three dimensional, non-linear transient numerical models were developed, which were used to show the surface and subsurface residual stresses produced as a result of the impact. The specimens used in the experimental programme were made from two different types of cold-rolled, mild steel strip; namely Bending Quality Bright Steel (BS1449), and '070M20' Carbon Steel (BS970). To investigate what effect the size of an impacting object has on the fatigue life of a specimen, the impactors were produced in six sizes; 10mm, llmm, 12mm, 18mm, 25mm and 40mm radii, and in order to determine how the amount of impact energy affects the fatigue life of a specimen, the height of the impactor hammer head was adjusted to impact heights of 410mm, 276mm, 163mm and 87mm, thus altering the amount of impact energy imparted into the specimen. The current study found that the fatigue life of a specimen is greatly reduced due to a single impact and that the greater the height of the impact, and consequently the higher the impact energy, then the lower the fatigue life of the specimen becomes. It was also noted that the reduction in fatigue life due to the single impact is not affected by the size of impactor but by the energy of the impact, as a single impact at the chosen impact energy for this study will impart residual stresses in the specimen which causes a normalisation in the reduction in the fatigue life of the specimen.