含低速冲击损伤复合材料层合板剩余压缩强度及疲劳性能试验研究

对T300/QY8911复合材料层板进行了低速冲击、 冲击后压缩以及冲击后疲劳试验研究。通过对冲击后的层板进行目视检测和超声C扫描获得了层板受低速冲击后的若干损伤特征; 在压-压疲劳试验中, 测量了损伤的扩展情况。讨论了冲击能量与损伤面积以及冲击后剩余压缩强度的关系, 分析了含冲击损伤层合板在压缩载荷及压-压疲劳载荷下的主要破坏机制。结果表明, 低速冲击损伤对该类层板的强度和疲劳性能影响很大, 在3.75 J/mm的冲击能量下, 层板剩余压缩强度下降了65%; 在压-压疲劳载荷作用下, 其损伤扩展大致可分为两个阶段, 占整个疲劳寿命约60%的前一阶段损伤扩展较为缓慢; 而疲劳寿命的后半阶段损伤则开始加速扩展, 并导致材料破坏。     

Post-Impact Mechanical Characterisation of Glass and Basalt Woven Fabric Laminates

Two woven fabric laminates, one based on basalt fibres, the other on E-glass fibres, as a reinforcement for vinylester matrix, were compared in terms of their post-impact performance. With this aim, first the non-impacted specimens were subjected to interlaminar shear stress and flexural tests, then flexural tests were repeated on laminates impacted using a falling weight tower at three impact energies (7.5, 15 and 22.5J). Tests were monitored using acoustic emission analysis of signal distribution with load and with distance from the impact point. The results show that the materials have a similar damage tolerance to impact and also their post-impact residual properties after impact do not differ much, with a slight superiority for basalt fibre reinforced laminates. The principal difference is represented by the presence of a more extended delamination area on E-glass fibre reinforced laminates than on basalt fibre reinforced ones.     

Low-energy charpy impact of interleaved CF/EP laminates

Carbon fiber (CF) reinforced epoxy (CF/EP) laminates laid up in different ways (cross-ply and quasi-isotropic) with and without various adhesive interlayers (A) were studied under three-point bending using instrumented low-energy impact at single and multiple bounces. Interleaves were a modified EP resin on polyester fabric, a modified EP resin, and a polyethersulphone (PES) film. The impact response depends strongly on whether the CFs are oriented longitudinally (L) or transversely (T) to the hammer edge in the outer bounced ply. The threshold incident energy (E _in,th) associated with severe damage to the laminates was much lower with the longitudinal outer ply.The impact fatigue response of the transverse cross-ply (TCP) and quasi-isotropic (TQI) composite beams showed that stiffness degradation starts at a certain a threshold number of impact (NOI) and follows a logarithmic decay as a function of NOI. This is in close analogy to fatigue tests under usual conditions. Deterioration in stiffness can be assigned to the relative change in the secant slope (E _max/x _max) of the load-displacement (F-x) traces. The related load-time (F-t) traces flatten due to impact fatigue so that their load maximum (F _max) shifts toward higher contact time.The efficiency of the interleaving was assessed in both single (atE _in,th3 J) and repeated impact (atE _in=1 J). The first technique allowed us to differentiate between the various interleaves, whereas the latter contributed to finding the optimum stacking and position of the interleaves.     

Characterisation of impact response of metallic foam/ceramic laminates

Abstract

The impact response of laminated composites consisting of alternate layers of Al alloy foam and Al₂O₃ was studied experimentally in low and intermediate velocity regimes. Low velocity impacts (1.2–2.8 m s^-1) were conducted using an instrumented falling weight apparatus and were compared with static indentation tests (0.2×10^-4 m s^-1). Intermediate velocity impacts were carried out by means of both Hopkinson bar (60 m s -1)and gas gun (200 m s^-1) tests. Post­impact damage was assessed using X-ray radiography and microscopy. It was found that there is good correlation between low velocity impact and quasi­static responses. In both cases, penetration of the layered targets resulted in the formation of a distinctive plug. Increasing impact velocity (intermediate velocity range) switched the penetration mode from plugging to fragmentation, giving rise to an increase in the absorbed energy. In this range, impacts led to localisation of damage in the region under the projectile. Furthermore, a comparison has been made between the penetration response of foam laminates and dense metal laminates of equivalent areal density. Preliminary results suggest that the dense metal laminates are superseded by the foam laminates on an energy absorption basis.     

Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates

Vacuum infusion (VI) is being considered as a viable alternative to more traditional hand lay-up (HL). Main reason in favor of the more costly technique is the cleaner and friendlier work environment. Moreover, VI potentially offers another important benefit over HL in that prepreg levels of resin may be achieved, resulting in stronger and lighter laminates. The present paper compares the two manufacturing techniques on the basis of the response to repeated impact loading. The laminate is a thick non-symmetric glass-fiber-reinforced plastics intended for nautical application. Four impact velocities (1.5, 2.2, 3.1 and 3.8 m/s) were considered, and a minimum of four specimens for any given velocity were subjected to 40 repeated impacts or up to perforation. The impact response was evaluated in terms of damage progression by visual observation of the impacted specimens, evolution of the peak force and of the bending stiffness with the number of impacts and by calculating the Damage Index (DI), a damage variable recently proposed by the authors to monitor the penetration process in thick laminates. Results point out that for impact velocities for which no perforation occurs within test duration, the experimental data essentially overlap. On the contrary, for perforation tests, HL specimens survived more impacts before perforating absorbing more total energy than VI specimens. Plots of the DI variable against the number of impacts were observed to exhibit an initial linear portion, owing to a stable process of damage accumulation within the laminate, and to undergo an unstable growth a few impacts before perforation. When comparing the VI and HL specimens it was observed that, given an impact energy, the level of damage at first impact as well as the rate of stable damage accumulation is alike for the two sets of specimens. On the contrary, it is the number of impacts of the stable damage accumulation region which is lower for VI specimens.     

复合材料层板低速冲击后剩余压缩强度

对两种材料体系和铺层的复合材料层合板进行低速冲击后压缩强度试验 , 以研究低速冲击后层合板的压缩破坏机理。讨论了表面凹坑深度、 背面基体裂纹长度、 损伤面积以及剩余压缩强度与冲击能量的关系。在试验研究的基础上 , 建立了复合材料低速冲击后剩余强度估算的一种椭圆形弹性核模型。该模型将冲击损伤等效为一刚度折减的椭圆形弹性核 , 采用含任意椭圆核各向异性板杂交应力有限元分析含损伤层合板的应力应变状态 ,并应用点应力判据预测层板的压缩(或压、 剪)剩余强度。理论分析与试验结果对比表明 , 该模型简单有效。      

圆孔对GLARE层合板抗冲击性能的影响

为获得圆孔对玻璃纤维增强铝合金（GLARE）层合板抗冲击性能的影响规律,采用40 J的冲击能量对无孔和含圆孔GLARE层合板进行了落锤低速冲击试验,获得了冲击载荷、挠度和能量-时间曲线。应用ABAQUS/Explicit有限元分析软件对试验进行模拟,并预测了圆孔直径对GLARE层合板抗冲击性能的影响。结果显示:在低速冲击下,GLARE层合板纤维层的失效模式以分层损伤和纤维断裂为主;随着圆孔边缘至冲击中心距离的增加,层合板的冲击载荷峰值提高,而挠度峰值减小;数值模拟结果与试验结果的比较验证了模型的合理性;随着圆孔直径的增大,GLARE层合板的抗冲击性能逐步劣化。      

压缩预应力对复合材料层板抗冲击损伤性能的影响

为确定压缩预应力对复合材料层板抗冲击损伤性能的影响,首先对不同压缩预应力下的碳纤维/双马树脂CCF300/5428层板进行了低速冲击和准静态压痕试验,然后通过热揭层和冲击后压缩试验分别得到了层板分层面积和剩余强度。结果表明:压缩预应力会大幅降低层板的接触刚度和弯曲刚度,从而导致相同冲击能量下层板凹坑深度和背部基体开裂长度增大;对于准静态压痕过程和相同冲击能量下的冲击过程,分层起始载荷和峰值载荷均随压缩预应力的增大而减小;在相同冲击能量下,随着压缩预应力的增大,层板内部分层总面积及冲击能量吸收比不断增大,剩余压缩强度不断降低。因此,压缩预应力会降低复合材料层板的冲击损伤阻抗,对损伤容限性能不利,在对承受压缩载荷结构的试验验证过程中应考虑压缩预应力对抗冲击损伤性能的影响。      

Effects of fibre/matrix adhesion on carbon-fibre-reinforced metal laminates—II. impact behaviour

Quasi-static, low-hanging and high-velocity impact tests have been conducted in order to study the effect of fibre/matrix adhesion on the impact properties of fibre-reinforced metal laminates. Differences in fibre/matrix adhesion were achieved by using treated or untreated carbon fibres in an epoxy resin system. Chemical removal of the aluminium layers and a sectioning technique were applied to examine and characterize the impact damage in the laminates. The results show that the laminates with the weaker fibre/matrix adhesion exhibit larger damage zones, although the back face crack length and permanent indentation after impact are smaller for a given impact energy. Residual tensile strength after impact is also higher for the untreated fibre laminates due to increased fibre/matrix splitting in the composite layer.     

复合材料层板低速冲击后疲劳性能实验研究

通过对T300/5405复合材料层板进行低速冲击后的压-压疲劳实验,研究含不同冲击损伤层板的压缩性能与其在多级应力水平下的疲劳寿命与损伤扩展,并讨论冲击能量、应力水平、损伤扩展对层板疲劳寿命的影响。结果表明:冲击损伤明显降低层板的剩余强度;在低应水平下,冲击能量越大,含冲击损伤层板的疲劳寿命越小;疲劳实验中损伤经历平稳扩展和快速扩展两个阶段,其中平稳扩展阶段约占总体寿命的80%,快速扩展阶段约占总体寿命的20%,损伤扩展速率随着应力水平降低而减小。     

Evaluation of impact damage mechanism of multi-axial stitched CFRP laminate

This study focuses on multi-axial stitched fabric, which is a thick, high performance reinforcement for large-scale composite structures. The effects of impact damage on multi-axial stitched CFRP laminates molded by vacuum-assisted resin transfer molding (VARTM) method were evaluated. Impact damage within material was evaluated by ultrasonic scanning device and optical cross-sectional observations. Probed images obtained by both non-destructive and destructive methods were compared, and internal damage distributions of multi-axial stitched CFRP laminates were clarified. In addition, residual compressive strength and fatigue property of impact-damaged CFRP laminates were evaluated by in situ damage growth monitoring using the thermo-elastic stress analyzer (TESA). Three-dimensional damage distribution of impacted CFRP laminate was obtained from ultrasonic C-scan images and cross-sectional photographs. Damage progress behavior was observed on a destructive and non-destructive basis by post-impact fatigue (PIF) test.     

铺层混杂对复合材料层压板侵彻性能的影响

本文利用MTS和冲击侵彻测试装置，研究了由芳香族聚酰胺纤维、高强聚乙烯醇纤维制成的织物通过不同铺层方式与酚醛/PVB树脂复合的层压板的准静态和冲击侵彻性能。结果表明，芳香族聚酰胺织物层的加入能显著提高高强维纶织物树脂复合材料层压板的准静态侵彻刚度。随着芳纶混杂体积分数的提高，铺层混杂复合材料层压板的准静态侵彻阻力、穿孔能量（或单位面密度穿孔能量）将随之增加。从防护装具性能/重量比和性能/价格比的角度考虑，在芳香族聚酰胺与高强聚乙烯醇织物铺层混杂复合材料层压板中，高强聚乙烯醇纤维混杂体积分数可以确定为20%左右。     

Hybrid composites based on polyethylene and carbon fibres Part 3: Impact resistant structural composites through damage management

Damage tolerance and impact resistance have become key parameters for composite materials in structural applications. In this paper a toughening concept for structural composites based on the hybridization of carbon fibres with high performance polyethylene (HP-PE) fibres is presented. Impact behaviour of hybrid HP-PE/carbon laminates was studied using a falling weight impact test. The effect of the addition of HP-PE fibres as well as the effect of the adhesion level of these fibres on the impact resistance of hybrid HP-PE/carbon structures was investigated. Hybridization results in structural composites exhibiting a significantly better resistance to impact damage than all-carbon laminates due to a change in energy absorption mode. After hybridization more energy is stored in the HP-PE component and consequently less energy is available for damage in the structural carbon component, resulting in a reduction in impact damage and improved post-impact properties.     

Fatigue residual strength of circular laminate graphite–epoxy composite plates damaged by transverse load

The research dealt with the relation between damage and tension–tension fatigue residual strength (FRS) in a quasi-isotropic carbon fibre reinforced epoxy resin laminate. The work was organized in two phases: during the first one, composite laminates were damaged by means of an out-of-plane quasi-static load that was supposed to simulate a low velocity impact; in the second phase, fatigue tests were performed on damaged and undamaged specimens obtained from the original composite laminates. During the quasi-static transverse loading phase, damage progression was monitored by means of acoustic emission (AE) technique. The measurement of the strain energy accumulated in the specimens and of the acoustic energy released by fracture events made it possible to estimate the amount of induced damage and evaluate the quasi-static residual tensile strength of the specimens. A probabilistic failure analysis of the fatigue data, reduced by the relative residual strength values, made it possible to relate the FRS of damaged specimens with the fatigue strength of undamaged ones.     

Describing the Flexural Behaviour of Cross-ply Laminates Under Cyclic Fatigue

The objective of this work is to derive modelling of the fatigue behaviour of cross-ply laminates from the experimental results obtained in the case of three-point bending tests. Modelling the fatigue behaviour is based on the stiffness reduction of test specimens. Firstly, experimental results are described using interpolation functions. Then, the characteristic coefficients of these functions are studied as function of the laminate properties and loading conditions. This approach allows to predict the fatigue life of composite laminates while avoiding a large number of fatigue tests. Wöhler curves are used to compare the experimental and analytical results, and a good agreement is found between the results. Next, a simple approach is considered to define a damage parameter. It is based on the analogy between the mechanical behaviour and the fatigue damage evolution of composite laminates during fatigue tests. The developed models are applied to analyse the influence of constituents on the fatigue behaviour and damage development of composite materials under fatigue loading.     

Impact resistance and tolerance of interleaved tape laminates

This paper presents and discusses the results of low-velocity impact and compression-after-impact (CAI) tests conducted on interleaved and non-interleaved carbon/epoxy tape laminates. Olefin film interleaves provided a strong interface bond, resulting in a reduction in projected damage area. These interleaves changed the stress distribution under impact and restricted delamination formation at the ply interface. An investigation into the compression behaviour of these laminates revealed a reduction in undamaged strength using olefin interleaves. This was attributed to the lack of lateral support for fibres at the fibre/interleaf interface, allowing fibre microbuckling to occur at a low load. Low modulus copolyamide web interleaves resulted in an increase in damage area and minor changes to CAI strength. Examination of laminate cross-sections revealed that this was due to both the open structure of the interleaf and poor resin/interleaf adhesion. High shear modulus polyethylene interleaves resulted in a significant decrease in damage area at various impact energies, with CAI strength improved compared to the non-interleaved laminates.     

基于超弹性特性的SMA复合材料层合板低速冲击损伤数值模拟方法

基于ABAQUS有限元软件结合VC++6.0程序设计,建立了含不同铺层角度、不同排列密度形状记忆合金(SMA)纤维的复合材料层合板有限元模型。将基于Brinson本构模型的SMA分段线性超弹性模型以及判断复合材料层内失效的三维HASHIN失效准则编译至ABAQUS/VUMAT子程序,使用界面单元模拟复合材料层间区域,建立了SMA复合材料层合板的低速冲击损伤及冲击后剩余强度数值模拟方法。对比了不含SMA纤维层合板、含SMA纤维层合板、含普通金属丝层合板在不同冲击能量下的损伤响应。进一步分析了SMA纤维体积分数和直径变化对冲击响应的影响。冲击后剩余压缩强度模拟结果表明:冲击能量为16J时,含体积分数25%、直径0.5mm的SMA纤维层合板的冲击后剩余压缩强度相比不含SMA纤维层合板提高5.78%、相比含普通金属丝层合板提高4.69%。随着SMA纤维体积分数提高,层合板的抗低速冲击能力增强,当体积分数一定时,较细的(0.3mm)SMA纤维比粗的(0.6mm)SMA纤维对层合板的抗低速冲击能力增强效果更好。     

On the rate of growth and extent of the steady damage accumulation phase in repeated impact tests

In the paper, data of repeated impact tests performed on seven laminates of different lay-up and thickness are used to illustrate how the damage index (DI), a damage variable recently introduced by the authors to monitor the range of the penetration process in thick laminates, can be applied in case of repeated impact tests to get information on the rate of initial steady damage accumulation as well as on the onset of severe damage modes.Curves of the rate of growth of the DI in the steady phase (ΔDI/ΔN) vs. the normalised impact energy (ratio of the impact energy E_i and the laminate penetration threshold P_n) show no significant damage accumulation besides initial specimen indentation for impact energies below 0.2P_n. For intermediate levels of impact energy, repeated impact tests are characterised by an initial region of steady damage accumulation followed by an abrupt change in the rate of damage growth a few impacts before laminate perforation. For higher impact energies (E_i/P_n > 0.4–0.45), no phase of steady damage accumulation is present, suggesting that severe damage mechanisms take place from the very first impacts. Values of the DI at the end of the steady phase (DI_unsteady) are shown to be rather peculiar to each laminate regardless of the impact energy used in the tests and therefore may be used to get a first indication of the laminate performance to repeated impacts. The extent of the steady phase may also be used to compute the total energy absorbed by the laminate in the steady damage accumulation phase (E_aTOT__steady).     

Fatigue properties of multifunctional metal‐ and carbon‐fibre‐reinforced polymers and intrinsic capabilities for damage monitoring

Carbon‐fibre‐reinforced polymers (CFRP) structures offer enhanced lightweight potential in comparison with monolithic metallic concepts. Brittle failure behaviour and the insufficient level of electrical conductivity limit the lightweight potential of composites. One promising new approach to solve these issues is the additional integration of metal fibres. Structural components are subjected to cyclic loads during their lifetime. Therefore, the present study focuses on the influence of additional steel fibre reinforcement on the fatigue behaviour of CFRP laminates. Magnetic properties are determined because of the deformation‐induced phase transformation of the chosen austenitic steel fibres, which are also applied as intrinsic damage sensors. Interrupted fatigue tests are carried out accompanied by scanning electron microscopy to obtain differences in failure mechanisms. Beside a detailed overview of the steel fibre influence on the fatigue properties of conventional CFRP structures, the functional evidence of a new method for nondestructive testing by a magnet inductive measuring device is shown.     

Hybrid composites based on aramid and basalt woven fabrics: Impact damage modes and residual flexural properties

The low-velocity impact behaviour of hybrid laminates reinforced with woven aramid and basalt fabrics and manufactured by resin transfer moulding was studied. Specimens with different stacking sequences were tested at three different energies, namely 5, 12.5 and 25 J. Residual post-impact properties of the different configurations of aramid/basalt hybrid laminates were characterized by quasi static four point bending tests. Post-impact flexural tests have been monitored using acoustic emission in order to get further information on failure mechanisms. Results indicate that hybrid laminates with intercalated configuration (alternating sequence of basalt and aramid fabrics) have better impact energy absorption capability and enhanced damage tolerance with respect to the all-aramid laminates, while basalt and hybrid laminates with sandwich-like configuration (seven basalt fabric layers at the centre of the laminate as core and three aramid fabric layers for each side of the composite as skins) present the most favourable flexural behaviour.