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。     

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。      

缝合复合材料层板低速冲击及冲击后压缩实验研究

通过对缝合复合材料层板进行低速冲击和冲击后压缩实验, 研究了不同类型的缝合复合材料层板的冲击损伤特性及冲击后压缩的剩余强度。实验研究表明: 基体损伤和分层是缝合层板与未缝合层板低速冲击的主要损伤模式, 缝合层板具有更好的抗冲击性能, 更高的冲击后压缩强度。缝合密度越大的层板其抗冲击性能越好, 冲击后压缩强度越高。缝合方向为0°的缝合层板较缝合方向为90°的缝合层板具有更好的抗冲击性能和更高的冲击后压缩强度。增加0°方向铺层, 减少45°、-45°方向铺层, 可以提高缝合层板的抗冲击性能和冲击后压缩强度。     

Interlaminar tensile strength (ILTS) measurement of woven glass/polyester laminates using four-point curved beam specimen

Based on a review of the current methods for the measurement of interlaminar tensile strength (ILTS), a novel specimen of a four-point curved beam is evaluated for this purpose. Detailed finite element analysis is carried out to investigate the appropriateness of the data interpretation formula. A simple design method to choose the appropriate parameters in order to guarantee the delamination failure is provided. This specimen is used to measure the ILTS of woven glass/polyester laminates. The results are found to be comparable with other methods. The most attractive advantage of this test method is its simplicity and that it requires no special techniques in specimen preparation and test set-up.     

复合材料加筋板低速冲击损伤及剩余压缩强度试验研究

采用落锤法对复合材料加筋板进行了低速冲击损伤（LVI）试验,根据复合材料加筋板构型,设计了冲击支持支架,研究了支持支架的间距对冲击结果的影响;用相同的冲击能量对复合材料加筋板结构中3处典型位置进行冲击,得到不同位置的损伤形貌;分别对完好件和损伤试验件进行压缩试验,将试验结果进行对比,分析不同位置的冲击损伤对结构压缩性能的影响。试验结果表明：在相同的冲击能量下,支持支架间距越小,所造成的冲击损伤越严重;在50 J冲击能量下,筋条区蒙皮处的冲击所造成的损伤不易观察,筋条间蒙皮处的冲击所造成的损伤最为明显,而筋条边缘蒙皮处的冲击可以导致筋条边缘的脱粘;冲击损伤会使加筋板屈曲载荷轻微下降,筋条间蒙皮和筋条区蒙皮冲击损伤对压缩结果影响相对较小,筋条边缘处的冲击会引起损伤处蒙皮的子层屈曲,并影响结构破坏形式,使结构压缩承载能力有较为明显的下降。     

Numerical analysis of influence factors on low-velocity impact damage of stitched composite laminates

Abstract

A 3D dynamic finite-element model is proposed in this paper to simulate the damage development process of stitched laminates subjected to low-velocity impact. The strain-based Hashin criteria and a sudden degradation scheme are employed to determine the intra-laminar damage initiation and evolution; a mix-mode bilinear constitutive model is adopted to evaluate the inter-laminar delamination damage. The predicted numerical results agree well with the available experimental data, thus validating the proposed damage analysis model. Moreover, the influence factors, including the thickness of laminates, stitching density, diameter of stitching thread and strength of stitching thread, are analyzed and discussed in detail.     

Effect of woven yarn angle on the low-velocity impact damage response of fibre woven thermoplastic composites

Fibre woven thermoplastic composites (FWTC) are widely used in aerospace and other fields because of their excellent performance. During service, FWTC structures are inevitably subjected to low-velocity impact (LVI), which can cause invisible damage and eventual failure of the material. At the moment, studies on FWTC mostly focused on the orthogonal woven yarns while there's few reports about the effect of the yarn angle changing on the woven material's LVI damage response. This study aims at the effect of yarn angle changing on the damage behaviour of FWTC. A method for preparation of nonorthogonal prepregs was proposed, by which FWTC laminates with different yarn angles (60°, 75°, and 90°) were prepared for LVI tests. The results show that the maximum impact displacement and the impact duration of the impactor decrease with the decrease of the yarn angle when the FWTC laminate is subjected to LVI, while the maximum impact force shows an increasing trend. This indicates that the smaller yarn angle causes the better load-bearing capacity of the FWTC laminate under LVI conditions, while the orthogonal FWTC laminate is more ductile. The damage morphology indicated by the impact of the FWTC laminate are matrix cracks and yarn breaks, and the damage area increases with the decrease of yarn angle, where the damage of orthogonal laminate is more serious more concentrated. The results found in this paper can provide useful guidance for engineering applications and failure analysis of FWTC.     

碳纤维织物布层压复合材料湿热环境疲劳后剩余压缩强度

为了研究湿热环境对碳纤维织物布层压复合材料疲劳性能的影响,开展了碳纤维织物布含中心孔层压板疲劳试验和剩余压缩强度试验,并为湿热环境拉-压疲劳试验自行设计了湿热环境试验箱。参照ASTM标准设计加工了疲劳试验夹具和压缩试验夹具,分别在标准环境条件(温度(23±2)℃、相对湿度(50±5)%RH),湿热环境条件(温度(70±2)℃、相对湿度(85±5)% RH)下对试件进行拉-压疲劳试验,之后分别进行了剩余压缩强度试验。以标准环境疲劳试验件的剩余压缩强度为基准值,对比湿热环境疲劳试验件的破坏载荷对应的极限压缩强度,计算其与基准值的差值。通过试验结果对比,得到湿热环境下试验件疲劳后剩余压缩强度下降了14%,该湿热环境对载荷谱下的碳纤维织物布层压复合材料试验件疲劳后剩余压缩强度影响较小。      

复合材料层压板抗冲击行为及表征方法的实验研究

对14种复合材料体系约800个试样进行了冲击阻抗和含损伤层压板压缩强度试验研究,研究发现对于同一种复合材料层压板的冲击能量-凹坑深度曲线和凹坑深度-压缩破坏应变曲线均存在拐点,在出现拐点后内部的分层损伤叠加面积基本不再增加,压缩剩余强度基本不再降低,表面冲击部位开始出现纤维断裂。研究表明,采用传统CAI来表征损伤容限性能的方法可能得到与实际结构损伤容限特性相反的结论。因此,提出了利用拐点附近特性来表征复合材料层压板的抗冲击行为（包括损伤阻抗和损伤容限）的建议,即分别采用QSI方法得到的准各向同性层压板的最大接触力F_max和压缩破坏强度（应变）的门槛值CAIT来表征复合材料层压板的损伤阻抗和损伤容限行为。      

Bearing strength of commingled boron/glass fiber reinforced aluminum laminates

The bearing properties of recently developed hybrid fiber/metal laminates, or COmmingled Boron/glass fiber Reinforced Aluminum laminates (COBRA), are investigated in this study. The bolt-type bearing tests on GLass REinforced aluminum laminates (GLARE), non-commingled hybrid boron/glass/aluminum fiber/metal laminates (HFML) and COBRA were carried out as a function of e/D ratio, metal volume fraction, fiber volume fraction, and fiber orientation. Experimental results show that with the same joint geometry and metal volume fraction, the commingling of boron fibers improves the bearing strength of fiber/metal laminates. Observations show the boron/glass fiber prepreg, transverse to the loading direction, results in a bearing mechanism that effectively increases the bearing strength. The bearing strength of COBRA with longitudinal fibers is lower than that with transverse fibers due to the fact that shearout failure takes place before maximum bearing strength is reached. The experimental results show that, with only either transverse fiber orientation or longitudinal fiber orientation, COBRA with 18% boron fiber volume fraction possesses a higher bearing strength when compared to HFML with 6% boron fiber volume fraction. In addition to the properties in COBRA with parallel-plies commingled prepreg, the bearing properties of various COBRA with [0°/90°] and [0°/90°/90°/0°] cross-ply commingled prepregs are also discussed.     

整体中空夹层复合材料低速冲击损伤及剩余强度实验研究

简要论述了整体中空夹层复合材料低速冲击及冲击后剩余强度的研究情况,选取了三种不同规格的试件进行了不同能量下的低速冲击试验和冲击后的拉伸,压缩强度试验,得到不同能量下材料的损伤情况和强度变化曲线。实验结果与国外相关文献进行了对比,与文献结果具有一致的变化规律,对整体中空夹层复合材料的运用及推广有一定得参考意义。     

Effect of fibre/matrix adhesion on residual strength of notched composite laminates

Effects of fibre/matrix adhesion and residual strength of notched polymer matrix composite laminates (PMCLs) and fibre reinforced metal laminates (FRMLs) were investigated. Two different levels of adhesion between fibre and matrix were achieved by using the same carbon fibres with or without surface treatments. After conducting short-beam shear and transverse tension tests for fibre/matrix interface characterisation, residual strength tests were performed for PMCLs and FRMLs containing a circular hole/sharp notch for the two composite systems. It was found that laminates with poor interfacial adhesion between fibre and matrix exhibit higher residual strength than those with strong fibre/matrix adhesion. Major failure mechanisms and modes in two composite systems were studied using SEM fractography. The effective crack growth model (ECGM) was also applied to simulate the residual strength and damage growth of notched composite laminates with different fibre/matrix adhesion. Predictions from the ECGM were well correlated with experimental data.     

Residual strength distribution of impacted glass/epoxy laminates with embedded shape memory alloy at low temperature

This paper evaluated the strength reduction and probabilistic behaviors of the residual flexural strength for impacted glass/epoxy laminates with embedded shape memory alloy (SMA) wires at various temperatures. A series of impact tests were performed on base (glass/epoxy laminates without SMA wires) and SMA laminates (glass/epoxy laminates with embedded SMA wires) at temperatures of 293 K, 263 K and 233 K. Three point flexural tests were then carried out so as to investigate the post-impact strength at the aforementioned temperatures. Strength reduction behavior of impacted laminates could be described by Caprino’s residual strength prediction model. A probabilistic model was developed in order to estimate the variation in residual strength of the impacted laminates with temperature. As the temperature decreased, the variation in residual strength increased due to the embrittlement of the constituent materials of the laminates at lower temperatures. When compared to the base laminates, the SMA laminates exhibited a higher variation in residual strength, especially at lower temperatures.     

复合材料层合板冲击损伤及剩余强度研究进展

综述了受低速冲击后复合材料层合板的损伤研究进展,重点介绍了倍受复合材料工程结构设计师所关注的含损复合材料层合板的剩余拉伸及压缩强度问题,最后对有待于进一步研究的问题进行了展望.     

An engineering approach for predicting residual strength of carbon/epoxy laminates after impact and hygrothermal cycling

A semi-empirical analysis on residual compressive strength (RCS) of carbon/epoxy woven composite laminate was developed which included the damage effects caused by impact and hygrothermal cycling. Impact damage is modelled as a soft inclusion with an exponentially reduced stiffness and the stiffness is further reduced due to hygrothermal cycling. A complex variable method was used to determine the in-plane stress distribution near the impact-induced damage and point stress failure criterion is then used to predict the failure load. Based on the semi-empirical model, the RCS can be related to damage width, damage intensity, undamaged strength and a degradation factor due to hygrothermal cycling. The results from the analysis coincide reasonably well with the experimental data for the plain-woven fabric laminates.     

刚性卵形头弹撞击角度对编织复合材料层合板侵彻特性的影响

利用一级气炮发射卵形头弹撞击2 mm厚度的编织复合材料层合板,撞击角度分别为0°、30°和45°,通过高速相机记录弹靶撞击过程,并获得弹体速度数据。基于拟合公式处理试验数据,计算获取弹道极限,分析撞击角度对弹道极限、靶板能量吸收率及其失效模式的影响规律及机制。结果表明：弹体撞击角度为45°时,靶板弹道极限最高,其次为0°,撞击角度为30°时最小。随着冲击角度增加,层合板损伤形状从菱形逐渐转变为椭球形,损伤面积随冲击速度增加而增大,且45°冲击时层合板损伤面积最大,0°和30°冲击时损伤面积近似相等。弹体初始撞击角度对靶体失效模式存在影响,弹体撞击角度为0°时,纤维断口主要是剪切应力导致的横截面。撞击角度为30°时,纤维断口主要是剪切应力和拉伸应力导致的斜截面。45°斜撞击时,纤维断口主要是拉伸应力导致的横截面。     

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。      

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.     

电热载荷对修补碳纤维增强复合材料冲击后压缩性能的影响

为了研究碳纤维复合材料(CFRP)修补结构在电热载荷环境下的冲击性能,采用自制的电热损伤测试平台,测试了修补后CFRP层板在不同电流下试样的表面温度分布和电阻变化规律,对修补后CFRP层板进行了低速冲击和冲击后剩余压缩强度(CAI)测试,并对冲击损伤失效特征进行了对比分析。结果表明:低电流对修补后CFRP层板的抗冲击性能影响较小,CAI呈现略微增长的趋势;随着电流强度的增加,电热产生的高温对修补界面层产生破坏,导致材料抗冲击性能减弱,CAI明显降低。     

Experimental study of damage characteristics of carbon woven fabric/epoxy laminates subjected to lightning strike

This paper experimentally investigates the damage characteristics of two stacking sequenced ([45₂/0₂/−45₂/90₂]s, [30₂/0₂/−30₂/90₂]s) carbon woven fabric/epoxy laminates subjected to simulated lightning strike. Characteristics of the damage are analyzed using visual inspection, image processing, ultrasonic scanning and scanning electron microscope. The mechanical properties of post-lightning specimens are then studied. Observations show that as the lightning strike is intensified, an enlarged resin pyrolized area appears majorly along the weft orientation while the delamination region extends equally to both of the warp and the weft direction. The resin/fiber interfacial bonding is severely damaged by a thermal–mechanical effect due to lightning strike infliction. Mechanical testing further shows that the stacking sequence can influence the failure significantly. Compared with prepreg taped material, the restrained damage area due to special designed stacking sequence, lamina thickness and the weft nylon binder make the woven fabric reinforcement a good choice for the fabrication of lightning protection structures.