Dissertations / Theses on the topic 'Fiber metal laminates'

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.

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.

The first part of the diploma thesis with name „Hybrid adhesive bonded joints of metals and composite materials“ comprise surface pretreatment review. There is also mentioned current review of adhesives for composite and aluminium adherends. The second part of the thesis is dedicated to lap hybrid joint shear strength tests. The effects of adherend thickness, overlap lenght and surface pretreatment on shear strength were investigated. Measured parameters of hybrid joints are proved with a FE analysis with enough accuracy. Conclusions could be used for optimum design of hybrid joint with aluminium and composite adherends.

Abstract The objective of this study was a values evaluation of fracture toughness of fiber-metal laminates (FML) compounded from carbon fibers in epoxy matrix and aluminium plates of lay-up 6/5. Samples with unidirectional and bidirectional orientation were tested experimentally. In the case of unidirectionally oriented samples an effect of moisture absorption to epoxy matrix on the values of fracture toughness was reviewed. A fracture toughness calculation was realized by COD method firstly. A bigger pop-ins in F – COD diagram as critical moments for "delta"c evaluation were considered; it was determined by 5% tangential line. It was found out, that results of this measurement weren’t in agreement with plane deformation condition and for this the results couldn’t be rated as fracture toughness "delta"Ic. A method of J integral for fracture toughness evaluation was used consequently. A test of elastic compliance changes before J integral calculation by all of samples was performed. Beginning of stable grow of crack was determined by this method. A critical forces Fc from beginnings were established, which were used for calculation of Jc. A functional dependence of elastic compliance on crack opening had specific waved shape before its linear (up to exponential) grow. It was observed in all cases. The critical forces Fc from the end of “wave” preceding the continual grow of compliance were determined. Equations stated in standards for J integral calculation were used, which are for metal materials normally used. Despite this was found out all of results of Jc were in good agreement with plane deformation condition and could be rated as fracture toughness JIc. In this study were found out these pieces of knowledge about fracture toughness of FML CARE: Unidirectional CARE had fracture toughness JIc about 76 kJ/m^2 and the same type but with bigger amount of absorbed moisture had JIc about 4 % higher. In this case negative moisture influences on CARE weren’t found. Bidirectional CARE had fracture toughness JIc about 31 kJ/m^2; it was about 65 % less then in the case of unidirectional CARE

Includes bibliographical references.
Fibre metal laminates (FMLs) are composite materials that consist of layers of metal and fibre reinforced polymers. FMLs are used in the construction of aircraft fuselage skins, such as the Airbus A380. GLARE, the only commercially available FML, is of particular interest due to its damage tolerance and potential impact and blast resistance. GLARE is not commercially available and attempts at manufacturing FMLs similar to GLARE at the Blast Impact Survivability and Research Unit (BISRU) laboratories have been unsuccessful. The FMLs readily exhibited debonding between the aluminium and glass fibre reinforced epoxy, often upon handling prior to impact or blast events. The purpose of this study was therefore to investigate manufacturing techniques in order to produce FMLs that would be able to withstand impact and blast loads. Adhesive surface pre-treatment techniques and manufacturing methods typically employed in aircraft construction were investigated with particular emphasis on the adhesion of aluminium to epoxy in FMLs. This interface was of particular interest as good bonding facilitates load transfer under dynamic loading and was identified as the point of failure of the previously manufactured FMLs. The effects of surface treatment techniques used to enhance adhesion were investigated under quasi-static conditions using Single Leg Bend tests. Chemical surface treatments such as alodining, etching, anodising, silane treatments and combinations thereof were investigated. The effect of resin and the inclusion of a film adhesive were also investigated. The silane treatments were identified as the chemical treatments that provided the best adhesion, however the film adhesive significantly improved the fracture toughness regardless of the chemical surface treatment.

Fibre-metal laminates (FMLs) are hybrid structures comprising interleaved metal sheets and fibre reinforced polymer composites. In this work the performance of fibre metal laminated plates under blast loading is studied numerically. The FML panels are made of alternating layers of aluminium and glass fibre/polypropylene (GFRP) with different number of layers of aluminium and composite and in the panels with equal number of layers, with different thicknesses of GFPP. The panels are subjected to global blast loading uniformly distributed over the surface of the panel and to local blast loading applied at the centre of the panel with a spatial exponential decay towards the edges. The displacements of the front and back faces are found to increase linearly with increasing impulse. The results for global blast loading are correlated with experimental results obtained by Langdon et.al [doi:10.1016/j.euromechsol.2007.09.003] and for localised blast loading with experimental studies conducted by Langdon et.al [doi:10.1016/j.ijimpeng.2006.05.008 , doi:10.1016/j.ijimpeng.2006.05.009]. A good correlation between the experimental and numerical results is found. Back face debonding is found in all the panels for both load cases. The results are also compared with the response of mild and armour steel plates having the same areal densities as FML panels. It has been shown that for the same impulse, the displacement of mild steel plate with the same areal density is approximately twice the back face displacement of FML for global blast and depends upon the thickness of mild steel plate. Therefore, for global blast loading FML performs better and can withstand higher impulses without rupture whereas mild steel plate tears apart for global blast loading and in certain cases for local blast loading. On the other hand, the displacements in armour steel are 70% to 80% of the corresponding FML panel with same areal density when subjected to global or local blast loading.

A finite element model of fibre metal laminate (FML) fuselage was developed in order to evaluate its impact response under survivable crash event. To create a reliable crash finite element (FE) model of FML fuselage, a ‘building block approach’ is adapted. It involves a series of validation and verification tasks in order to establish reliable material and damage models, verified impact model with structural instability and large displacement and verified individual fuselage structure under crash event. This novel development methodology successfully produced an FE model to simulate crash of both aluminium alloy and FML fuselage under survivable crash event using ABAQUS/Explicit. On the other hand, this allows the author to have privilege to evaluate crashworthiness of fuselage that implements FML fuselage skin for the whole fuselage section for the first time in aircraft research field and industry. The FE models consist of a two station fuselage section with one meter longitudinal length which is based on commercial Boeing 737 aircraft. For FML fuselage, the classical aluminium alloy skin was replaced by GLARE grade 5-2/1. The impact response of both fuselages was compared to each other and the results were discussed in terms of energy dissipation, crushing distance, failure modes, failure mechanisms and acceleration response at floor-level. Overall, it was observed that FML fuselage responded similarly to aluminium alloy fuselage with some minor differences which conclusively gives great confidence to aircraft designer to use FML as fuselage skin for the whole fuselage section. In terms of crushing distance, FML fuselage skin contributed to the failure mechanisms of the fuselage section that lead to higher crushing distance than in aluminium alloy fuselage. The existence of various failure modes within FML caused slight differences from the aluminium fuselage in terms of deformation process and energy dissipation. These complex failure modes could potentially be manipulated to produce future aircraft structure with better crashworthiness performance.

The present thesis investigates the machining performance of an aerospace structural material commercially known as GLARE fibre metal laminate and its metal constituent aluminium Al2024-T3 aerospace alloy using commercially available solid carbide twist drills. The objective is to quantify the effects of the cutting parameters and two modern coolant technologies on cutting forces and a number of hole quality parameters. The generated drilling cutting forces, quality of machined hole and drilling-induced damage and defects when drilling GLARE fibre metal laminates were experimentally studied. Drilling-induced defects and damage investigated were surface roughness, burr formation at both sides of the workpiece and interlayer burr, hole size and circularity error, chip formation as well as damage described at the macro level (delamination area) using computerised tomography (CT) scan, and at the micro level (fibre matrix debonding, chipping, adhesions, cracks) using scanning electron microscopy (SEM). The experimental results have been statistically analysed using full factorial and response surface methodology statistical techniques to generate multiple regression models which makes it attractive as an indirect tool predicting the machining outputs prior the start of actual tests. Moreover, the analysis of variance (ANOVA) was employed to determine the percentage contribution of drilling parameters on cutting forces and hole quality outputs. The results indicated that the presence of coolant during the drilling process of GLARE could significantly improve hole quality. The use of cryogenic liquid nitrogen was found to eliminate the formation of waste on the borehole surface and burr formation at the hole exit. Using minimum quantity lubrication coolant was found to reduce the workpeice temperature compared to dry drilling at room temperature. Both coolants reduced the surface roughness compared to dry drilling but increased the cutting forces especially when using cryogenic liquid nitrogen. The cutting parameters results indicated that a maximum operating feed rate of 300 mm/min and a maximum spindle speed of 6000 rpm is recommended for superior hole quality results. Moreover, drilling at or below those levels of cutting parameters did not lead to severe delamination or fibre pull outs in the laminate compared to the higher cutting parameters used in the study. In addition, the fibre orientation and workpiece thickness were found to play a significant role on surface roughness and hole size but did not have a considerable impact on cutting forces due to the small thickness of glass fibre layers in the laminate. Adhesion and built up edge was found to be the main wear mechanism when drilling monolithic aluminium alloy, while adhesion and abrasion of the primary and secondary facets of the drill were identified to be the main wear process that occurs in drilling GLARE laminates.

Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to high rate loading such as blast or impact. Proper design of such structures requires thorough characterisation of the material behaviour over a range of loading rates from quasi-static to impact. This thesis investigated the quasi-static and impact response of Glass Fibre Polypropylene (GFPP) in compression, bending and delamination. The bending and delamination response of Fibre Metal Laminates (FMLs) based on GFPP and aluminium was also investigated at quasi-static and impact rates. High strain rate (5x10^2 to 10^3 /s) compression tests were conducted on GFPP using a compressive Split Hopkinson Pressure Bar (SHPB) and a Direct Impact Hopkinson Pressure Bar (DIHPB), in the through-thickness and in-plane directions. In both loading directions, the peak stress of GFPP increased linearly with the logarithm of strain rate. For in-plane loading, the failure modes were dominated by localised fibre buckling and kink bands, leading to delamination. The through thickness loading produced macroscopic shear and spreading failure modes. However, both of these failure modes are linked to in-ply fibre failures, due to through thickness compression causing transverse tensile strain. Previous studies of similar materials have not explicitly stated the link between through thickness compression and fibre failure associated with transverse tensile strain. A novel test rig was developed for Three Point bend testing at impact rates. The specimen was supported at the outer points on a rigid impacter and accelerated towards a single output Hopkinson Pressure Bar (HPB), which impacted the specimen at its midspan. Previous impact bend test rigs based on HPBs were limited to testing specimens with deflections to failure up to approximately 1mm, whereas the rig implemented herein measured deflections up to approximately 10 mm. This configuration permits the output HPB to be chosen purely on the magnitude of the expected impact force, which resulted in superior force resolution to configurations used in other studies. The HPB Impact Bend rig was used to test GFPP and aluminium-GFPP FML specimens, at impact velocities ranging from 5 to 12 m/s. The flexural strength of GFPP increased with strain rate, while the flexural response of the FML specimens was relatively insensitive to strain rate. v Several candidate delamination test geometries were investigated at quasi-static displacement rates (1 mm/min), and the Single Leg Bend (SLB) test was identified as suitable for adaptation to higher rate testing. Single Leg Bend delamination tests of both GFPP and FML specimens were performed using the HPB Impact Bend rig, at impact velocities of 6 to 8 m=s. The shape of the force displacement response for the high rate testswas markedly different from the quasi-static tests, for both the GFPP and FML specimens. Finite element (FE) simulation of the quasi-static and impact rate SLB tests on GFPP indicated that the difference was probably due to the interaction of flexural vibrations and stress waves in the specimen and the impacter cross member. The experimental results and FE analysis suggest that the delamination fracture toughness of GFPP decreases slightly as strain rate increases. High rate delamination tests on FML specimens resulted in unstable crack growth.

The present thesis investigates the performance of current aerospace structural materials such as Glare, a fibre metal laminate, to the catastrophic consequence of sabotage-induced blast loadings on commercial aircraft. The aim is to quantify the effects of these blast events and establish if remedial action can in some manner increase the chances of aircraft survivability. Within the EU funded VULCAN consortium, a coordinated effort has been devised to determine the dynamic deformation and fracture behaviour of structural materials subject to blast loadings using both experimental and numerical techniques. Test data from small-scale experimental blast trials have been verified and validated by the author using robust and efficient finite element models. Numerical studies have shown that Glare has potential to be a strong candidate for blast attenuating structures, exhibiting superior blast resistance compared to monolithic aluminium plates. Furthermore, a blast vulnerability and survivability analysis was devised to illustrate various failure scenarios in scaled fuselage structures. To address the macroscopic crack propagation in large-scale shell structures to blast loadings, well-controlled dynamic fracture experiments have been performed. This configuration, which consists of closed-end pressurised barrels with a through-thickness crack, is designed to capture the underlying dynamic phenomena under investigation whilst keeping the computational effort manageable. Quantitative fracture metrics obtained from high speed imaging systems have shown that Glare exhibits much lower average crack velocities than Aluminium 2024-T3 and CFRP. Experimental boundary and loading conditions served as well-defined input parameters to large-scale finite element models using cohesive elements. It has been shown that rate-independent cohesive models, initially verified using quasi-static fracture toughness tests, are insufficient to capture the dynamic crack growth rates. Alterative rate-dependent models have been discussed and implemented which take into account the influence of loading rate on the cohesive traction and energy dissipation. An inverse problem of cohesive zone modelling is performed to obtain mode-I cohesive zone laws. The comparison shows that both the experiments and the numerical simulations result in very similar crack initiation times and produce crack tip velocities of acceptable agreement.

Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas.
This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.

This study investigates scaling effects in a novel fibre-metal laminate (FML) system based on a thermoplastic matrix. The material is based on an aluminium alloy, a selfreinforced polypropylene composite and a polypropylene film acting as an interlayer adhesive. Initially, the mechanical characterisation of the FMLs and 'their constituents are characterised in tension, flexure and under impact loading. Additionally, the level of adhesion between the composite and aluminium constituents is characterised using fracture mechanics procedures. The performance of the FML is investigated aI!d compared to that offered by its constituents, enabling the advantages of these novel hybrid systems to be highlighted. Two different laminate constructions are employed here, these being an [AI, 0°/90°]5 FML and an [AI, +/- 45°]5 FML. Pronounced differences were observed between the two laminates, with the strain to failure of the latter being approximately 50% greater than the former. Interestingly, flexural tests revealed that the fibre orientation did not affect either the maximum stress or the strain at failure of the FML. Abstract ABSTRACT J. G. Carrillo The second part of the study focuses on investigating scaling effects in this FML system. Here, scale model tests are used to predict the full-scale behaviour of fibremetal laminates. Two laminates are investigated in this part of the research programme, these being [Aln, 00/900 n]5 and [Aln, +/- 45°n]5 with n = '14, Y2, % and 1. Tensile tests are undertaken on laminates prepared using three different scaling approaches, these being ID (scaling the thickness dimension), 2D (scaling the inplane dimensions) and 3D scaling, where all of the dimensions are scaled appropriately. Here, a small decrease in the value of these parameters was observed with increasing specimen size, suggesting that modest scaling effects do exist. Additionally, flexural tests are carried out using a 3D scaling approach, giving a direct comparison with the results generated in tension. The final part of this section investigates scaling effects in the low velocity impact response of the FMLs. Here, it is shown that the impact energy to initiate fracture in the FMLs does not exhibit any size dependency. Other test parameters, such as the impact duration are shown to obey the scaling law, with less than ten percent deviation from the normalised data being observed.

Neste trabalho estuda-se o comportamento de laminados fibra-metal em regime de impacto, a partir de uma abordagem teórica, numérica e experimental. Os materiais estudados consistem em camadas finas intercaladas de alumínio 2024-T4 e de um novo material termoplástico de polipropileno (PP) de alta resistência mecânica. Eventos de impacto de baixa e alta velocidade contra placas destes laminados foram realizados a partir de um martelo de impacto e de um canhão pneumático, respectivamente. Nestes experimentos buscou-se identificar as condições limite de ruptura e perfuração das amostras, assim como parâmetros de comportamento do material. O laminado fibra metal de PP (ou TFML) e seus constituintes foram caracterizados a taxas de deformação entre 10-4 / s e 102 / s, utilizando-se máquinas de ensaio universal comerciais e um dispositivo desenvolvido especificamente para este estudo, capaz de caracterizar materiais em taxas intermediárias de deformação. Os modelos teóricos de Jones e Reid-Wen foram adaptados para utilização com TFMLs, sendo capazes de identificar o comportamento do material em regime de baixa e alta velocidade de impacto, respectivamente. Um modelo numérico do TFML em regime de impacto foi desenvolvido utilizando o programa comercial LSDyna. Resultados experimentais e teóricos foram confrontados com esse, apresentado boa correlação na predição do limiar de falha e limite balístico do material. Uma vez que o comportamento do TFML ao impacto foi modelado, buscou-se identificar o efeito da distribuição de camadas e composição de constituintes no comportamento do material ao impacto. Estudos também foram conduzidos com o intuito de identificar a influência da taxa de deformação, geometria do indentador e localização do impacto no comportamento dos laminados. Por fim, uma configuração de TFML foi proposta visando melhoria de seu desempenho ao impacto.
In this work, the behaviour of fibre-metal laminates under impact loading is studied by using theoretical, numerical and experimental approaches. The material is a combination of thin aluminium 2024-T3 layers and an innovative high strength thermoplastic polypropylene material. Low and high velocity impact events were performed using a falling weight machine and a gas-gun projectile launcher, respectively. The thermoplastic fibre-metal laminates (or TFML) and its constituents were mechanically characterized in the range of strain rates between 10-4 / s and 102 / s , using commercial universal testing machines and a specifically designed rig for tensile tests at intermediate strain rates. The Jones and Reid-Wen theoretical models were adapted to be used with TFML plates. A finite element model of the TFML under impact events was developed using LS-Dyna software. The numerical model revalled results that were compared with the theoretical models and the experimental data, providing reasonably similar results. Once the TFML impact behaviour was identified and modelled, the effect of the layers distribution and constituent composition on the TFML impact response was studied. Studies of the strain rate effect, identor geometry and the impact location were also performed. Finally, a TFML configuration was suggested in order to improve the TFML impact performance.

Aplicações dos laminados híbridos metal-fibra incluem, além da indústria aeronáutica, as indústrias naval e automobilística. Diferentemente do setor aeronáutico, pesquisas sobre impactos mecânicos nas duas outras áreas da mobilidade são freqüentemente limitadas pela disponibilidade de equipamentos laboratoriais, de modo que é desejável o desenvolvimento de procedimentos de baixo custo para a determinação da resistência e tolerância a danos por impacto dos materiais de construção. Neste trabalho, a resistência a danos por impacto transversal do laminado híbrido metal-fibra Glare-5® foi determinada via três diferentes metodologias. A primeira utiliza um aparato sofisticado aparato Laser-Doppler para monitorar a aceleração e desaceleração de um impactador esférico de aço com 5 mm de diâmetro durante o evento do choque mecânico. O segundo método se baseia apenas nos valores de carga (força aplicada) vs. o tempo de impacto para a obtenção da energia absorvida pelo material. O terceiro considera somente os dados da velocidade do impactador, ou projétil, imediatamente antes e após o impacto. Concluiu-se que os valores de energia obtidos segundo as duas primeiras metodologias são similares, com o Laser-Doppler gerando resultados levemente não-conservadores, comprovando assim a possibilidade da derivação da resistência ao impacto do laminado através de um experimento simples e rápido, que utiliza apenas uma célula de carga digital para a monitoração da força aplicada em função do tempo. O terceiro método apresentou resultados substancialmente superiores às duas primeiras metodologias, sendo classificado como inadequado aos propósitos do projeto. Determinou-se que o laminado híbrido Glare-5®; absorve entre 60% e 80% da energia disponibilizada em impactos ditos leves, no intervalo de 1 a 6 Joules. Por fim, comprovou-se que a rigidez do material (módulo de elasticidade) é a propriedade residual (numa base de tolerância a danos) mais clara e consistentemente degradada pelo impacto previamente aplicado ao material.
Applications of hybrid fiber-metal laminates include, besides aeronautical industry, the automotive and naval industries. Unlike aeronautical field, impact research activities in the former areas of mobility industry are frequently limited by available laboratory equipment, so that it would be desirable to develop low-cost procedures to determine impact resistance and tolerance properties of construction materials. In this work, the transversal (trans-thickness) impact resistance and tolerance of hybrid fiber-metal laminate Glare-5® have been determined via three different methodologies. The first one utilizes sophisticated apparatus comprising a Laser-Doppler device to monitor deceleration/re-acceleration of 5 mm-diameter steel-ball impactor during the mechanical shock event. The second approach merely relies on the force (applied load) vs. impact time for determining the absorbed energy during the dynamic process. The third methodology requires only impactor velocity data points, immediately before and after the impact. It has been concluded that the energy values obtained from Laser- Doppler and load cell methods are very similar, with the former method producing slightly non-conservative results, allowing one to rapidly derive the impact resistance of hybrid laminate materials through very simple experimental set-ups employing digital load cells only. The third method presented somewhat higher results as compared to the concurrent techniques, so that it has been considered as inadequate for the research purposes. This study has shown that the fibre-metal laminate Glare absorbs between 60% and 80% of the apported impact energy during light impact events (ranging from 1 to Joules). Last, but not the least, materials stiffness was the most clearly and consistently imparted residual mechanical property (in a damage tolerance basis) due to the previous applied impact loading.

Dans cette étude, les propriétés mécaniques des FML renforcés de jute tissé 3D et hybrides de jute tissé 3D renforcé ont été étudiées. Le renfort tissé 3D à quatre couches a été fabriqué avec du fil de jute en utilisant quatre types de motifs imbriqués, par ex. Orthogonal Through Thickness OTT et Orthogonal Layer to Layer OLL imbriqué. La technique d'infusion sous vide a été utilisée pour la fabrication de FML avec renfort en jute tissé 3D. Après l'optimisation du renforcement tissé 3D, les FML renforcés hybrides ont été développés dans lesquels le tissu tissé OTT 3D a été pris en sandwich entre une peau tissée 2D. Quatre types de fibres différents ont été utilisés pour fabriquer une peau tissée 2D, par ex. jute, aramide, carbone et verre tandis que trois types différents de matrice ont été utilisés, par ex. époxy, PVB et PP. La presse à chaud par compression a été utilisée pour développer des FML hybrides renforcés. L'aluminium utilisé pour fabriquer tous les FML a été anodisé avant d'être utilisé pour la fabrication. Les propriétés adhésives ont été étudiées pour vérifier la qualité du traitement de surface, la liaison métal-composites et l'effet des fibres et de la matrice. Les propriétés monotones et dynamiques ont également été étudiées. Les propriétés adhésives ont été caractérisées à l'aide de tests de pelage en T et de pelage au rouleau flottant. Les propriétés monotones ont été analysées à l'aide d'essais de traction et de flexion. Les performances d'impact à faible vitesse ont été déterminées en utilisant un test d'impact à faible vitesse. Les résultats ont montré que la surface en aluminium anodisé avait une énergie libre de surface élevée, de sorte que le meilleur mouillage de l'aluminium peut être obtenu par anodisation par rapport à d'autres types de préparations de surface. Les résultats de l'analyse du collage ont montré que les propriétés de délaminage étaient principalement influencées par la nature du matériau adhésif plutôt que par le type de structures de renforcement. La nature de la matrice influence également le type de défaillance car avec l'époxy, la défaillance dominante était cohésive tandis qu'avec la matrice thermoplastique, elle s'est transformée en défaillance adhésive et intra-laminaire. La plasticité et la ductilité de la matrice ont plus influencé les propriétés finales que le type de rupture, malgré la rupture cohésive de l'époxy, la matrice thermoplastique avait plus de force de délamination. Les propriétés de traction et de flexion des FML renforcées de jute tissé OTT 3D étaient supérieures à celles des FML renforcées tissées OLL 3D en raison de la fraction de volume de métal plus élevée, ce qui était possible grâce à une construction plus serrée du tissu OTT. Les propriétés de traction et de flexion des composites hybrides renforcés et des FML ont été influencées par le type de matrice et le matériau de la peau 2D. Les propriétés globales plus élevées ont été obtenues avec une matrice époxy suivie d'une matrice PVB. Les FML à base de PVB ont montré que leurs propriétés étaient comparables à celles de l'époxy. Le test de flexion a montré que les FML hybrides à base de PP échouaient prématurément en raison d'une délamination entre la peau synthétique et l'âme tissée 3D. L'époxy et le PVB ont montré une meilleure imprégnation du renfort contrairement au PP dans lequel seul un verrouillage mécanique a été observé. Les propriétés d'impact dynamique des composites hybrides et des FML ont montré que les caractéristiques de dissipation d'énergie étaient influencées par la matrice et l'hybridation du renforcement
In current study the mechanical properties of 3D woven jute reinforced and hybrid 3D woven jute reinforced FMLs were investigated. The four-layered 3D woven reinforcement was made with jute yarn using four types of interlocking patterns e.g. Orthogonal Through Thickness OTT and Orthogonal Layer to Layer OLL interlocking. The vacuum infusion technique was used for the fabrication of FMLs made with 3D woven jute reinforcement. After the optimization of 3D woven reinforcement the hybrid reinforced FMLs were developed in which OTT 3D woven fabric was sandwiched between 2D woven skin. Four different kinds of fibres were used to make 2D woven skin e.g. jute, aramid, carbon, and glass while three different kinds of matrix were employed, e.g. epoxy, PVB and PP. The compression hot press was used to develop hybrid reinforced FMLs. Aluminium used to make all FMLs was anodized before using for fabrication. The adhesive properties were investigated to check the quality of surface treatment, metal-composites bonding and effect of fibres and matrix. Both monotonic and dynamic properties were also investigated. The adhesive properties were characterized using t-peel and floating roller peel tests. The monotonic properties were analyzed using tensile and flexural tests. The low velocity impact performance was determined using drop weight low velocity impact test. The results showed that the anodized aluminium surface had high surface free energy so the better wetting of aluminium can be achieved by anodizing as compared to other type of surface preparations. The adhesive bonding analysis results showed that the delamination properties were mainly influenced by the nature of adhesive material rather than the type of structures of reinforcement. The nature of the matrix also influences the type of failure as with the epoxy the dominant failure was cohesive while with thermoplastic matrix it changed to adhesive and intra-laminar failure. The plasticity and ductility of matrix influenced the final properties more than the type of failure, in spite of cohesive failure of epoxy the thermoplastic matrix had more delamination force. The tensile and flexural properties of OTT 3D woven jute reinforced FMLs were higher than the OLL 3D woven reinforced FMLs due to the higher metal volume fraction, this was possible due to tighter construction of OTT fabric. The tensile and flexural properties of hybrid reinforced composites and FMLs were influenced by the type of matrix and material of 2D skin. The overall higher properties were achieved with an epoxy matrix followed by PVB matrix. The PVB-based FMLs showed that their properties were comparable with the epoxy. The flexural test showed that hybrid FMLs based on PP were failed prematurely due to delamination between synthetic skin and 3D woven core. Both epoxy and PVB showed better impregnation of the reinforcement unlike PP in which only mechanical interlocking was seen. The dynamic impact properties of hybrid composites and FMLs showed that the energy dissipation characteristics were influenced by matrix and hybridization of reinforcement

Fiber Metal Laminates (FML) are hybrid composites with alternate layers of orthotropic fiber reinforced polymers (FRP) and isotropic metal alloys. FML can exhibit a nonlinear thermo-viscoelastic behavior under the influence of external mechanical and non-mechanical stimuli. Such a behavior can be due to the stress and temperature dependent viscoelastic response in one or all of its constituents, namely, the fiber and matrix (within the FRP layers) or the metal layers. To predict the overall thermoviscoelastic response of FML, it is necessary to incorporate different responses of the individual constituents through a suitable multi-scale framework. A multi-scale framework is developed to relate the constituent material responses to the structural response of FML. The multi-scale framework consists of a micromechanical model of unidirectional FRP for ply level homogenization. The upper (structural) level uses a layered composite finite element (FE) with multiple integration points through the thickness. The micromechanical model is implemented at these integration points. Another approach (alternative to use of layered composite element) uses a sublaminate model to homogenize responses of the FRP and metal layers and integrate it to continuum 3D or shell elements within the FE code. Thermo-viscoelastic constitutive models of homogenous orthotropic materials are used at the lowest constituent level, i.e., fiber, matrix, and metal in the framework. The nonlinear and time dependent response of the constituents requires the use of suitable correction algorithms (iterations) at various levels in the multi-scale framework. The multi-scale framework can be efficiently used to analyze nonlinear thermo-viscoelastic responses of FML structural components. The multi-scale framework is also beneficial for designing FML materials and structures since different FML performances can be first simulated by varying constituent properties and microstructural arrangements.

碩士
中原大學
機械工程研究所
86
The fiber-metal laminate, ARALL, is considered that a through crackin aluminum layer and delaminates on the interfaces are studied. The Boundary of delamination is assumed as an ellipse. Under cyclic in-plane loading, thefatigue crack growth is investigated. Based on a special finite element model developed by Yeh, energy release rate at crack tip and delamination tip are determined. The FEM results of energy release rates have been treated by curve fitting and the equations are obtainedwith the effect of crack length ratio and delamination aspect ratio. Paris' law is applied and the simulation of fatigue crack growth is proceeding. The results of energy release rates and fatigue crack growth for several casesare provided.