聚醚醚酮基复合材料的疲劳寿命表达式及累积疲劳损伤预测

通过对短碳纤维增强聚醚醚酮基复合材料的疲劳寿命试验数据的分析，给出了其疲劳寿命表达式，进而给出了适于两级不定载荷谱下累积疲劳损伤度及其概率分布区间的预测方法。     

复合材料的分层损伤系数

分层损伤系数k=(1—E/E_0)/2是计算复合材料叠层板的层间断裂韧度Gc的重要参数之一。在美国航空航天局制定的有关方法中(NASA RP1142)k近似取为0.16,对于国内大多数的树脂基复合材料来说,是否能够采用这一近似参数尚需讨论。本文讨论了国内具有代表性的几种树脂基复合材料叠层板的分层损伤系数k,结果表明,若要对比不同基体的复合材料叠层板的层间断裂韧性,有必要分别计算它们各自的k值,而不能简单地使用NASA方法中所给出的近似参数。本文还测定了叠尾板的拉伸破坏临界模量,试验结果表明,层板的破坏临界模量低于完全分层时的模量。     

复合材料加筋壁板损伤识别的概率成像方法

由于不需要超声导波的波速和传播时间,损伤概率成像方法特别适合于复合材料结构的损伤识别。但是其损伤概率分布函数是一种不精确的分布概率,会造成损伤定位精度的降低,从而会影响其在实际工程结构中的应用。为了提高其损伤定位精度,提出了一种改进的损伤概率成像方法。该方法通过利用损伤因子与损伤距离激励-传感通道直达路径的相对距离的关系,对损伤概率成像方法的损伤概率分布函数进行了改进。通过对复合材料加筋壁板上不同位置损伤的识别,对所提方法的有效性进行了验证。实验结果表明,该方法不仅能对复合材料加筋壁板的单损伤进行准确定位,而且能对两个损伤进行有效识别。     

基于代理模型的复合材料加筋壁板分层损伤定量监测方法

通过建立损伤指数与分层损伤参数间的定量关系,对复合材料加筋壁板分层损伤进行准确定量监测,提出了一种基于代理模型的分层损伤定量监测方法。该方法包括代理模型的建立和逆求解两个过程,通过插值拟合方法建立表征分层损伤参数与损伤指数间定量关系的多项式代理模型;采用损伤概率成像算法获得相对距离和损伤指数,将其代入代理模型中,得到所对应的分层损伤面积;实现对分层损伤进行定量评估的目的。通过一个复合材料加筋壁板分层损伤的定量监测实验,对所提方法的有效性进行了验证。结果表明:基于代理模型的复合材料分层损伤定量监测方法可以实现对分层损伤位置的准确定位,定位误差低于6%;且可实现对分层面积的准确定量评估,定量误差不超过5%。      

含分层损伤复合材料加筋层合板的动承载能力

采用有限元方法研究了含穿透分层损伤复合材料加筋层合板的动力响应和承载能力。根据复合材料层合板一阶剪切理论, 推导了复合材料层合板单元的刚度阵和质量阵列式;同时采用Adams 应变能法与Rayleigh阻尼模型相结合的方法, 构造了相应的阻尼阵列式;为了防止在低阶模态中分层处出现的上、下子板不合理的嵌入现象, 建立了含分层损伤复合材料加筋层合板动力分析中分层分析模型和虚拟界面联接模型。并采用Tsai提出的刚度退化准则和动力响应分析的精细积分法, 对在动荷载作用下含分层损伤复合材料加筋层合板结构进行了破坏和承载能力分析。通过典型算例分析, 分别讨论了外载频率、分层深度、筋的位置以及破坏过程中刚度退化对含损伤复合材料加筋层合板动力响应特征和承载能力的影响, 得到了一些具有理论和工程价值的结论。     

含冲击损伤的复合材料层合板寿命的研究进展

本文根据近二十年来国内外有关含冲击损伤复合材料层合板疲劳研究的文献,从试验方法和理论分析方法两方面综述了其研究方法的进展,分析了各寿命预测模型的特点和存在的问题,并对今后的发展趋势进行了展望。     

基于分层理论的螺栓连接夹芯复合材料加筋结构振动特性

针对采用螺栓连接方式固定的夹芯复合材料加筋结构,表层采用分层理论单元、芯层采用体单元,结合有限元方法计算固有频率和振型。通过试验验证,有限元计算结果与试验结果吻合,并得到了在有限元分析中模拟实际结构边界条件的处理方法。试验结果对比表明,与钢制结构相比,夹芯复合材料加筋结构前三阶固有频率提高2倍以上,夹芯复合材料加筋结构能大幅提高整体结构刚度,改善结构的振动特性。      

基于剩余应变的复合材料结构寿命预测

为实现对复合材料结构的寿命预测,对已有的复合材料疲劳寿命预测模型进行了研究,确定了基本的刚度降模型,提出了剩余应变的概念,并将其应用到渐进疲劳损伤方法中,以Abaqus为平台,编写UMAT子程序,实现了对复合材料结构的寿命预测及疲劳损伤扩展分析.针对某碳纤维增强复合材料TS800开展相关试验,试验结果与预测结果吻合较好.研究表明,本文所改进的渐进疲劳损伤方法能较好地完成对复合材料结构的寿命预测.     

飞机复合材料结构损伤的预测方法

针对复合材料结构损伤机理的复杂性,很难准确预测结构损伤状态,本文提出一种基于动态主元分析(DPCA)和最小二乘支持向量机(LS-SVM)相结合的复合材料结构损伤演化预测新方法,并针对复合材料结构损伤特性,采用疲劳振动试验进行结构损伤预测研究。首先,采用经验模态分解(EMD)方法对多传感器采集的复合材料结构健康信息进行自适应分解,得到不同传感器下的多个本征模态分量(IMF),并通过计算各阶IMF分量的奇异熵作为各传感器的特征信息;然后采用DPCA对多传感器的奇异熵进行降维融合,得到融合后的奇异熵特征,再对其采用距离形态相似度方法定义结构健康指数;最后将结构健康指数作为建模数据,创建LS-SVM预测模型,并通过预测模型对飞机复合材料结构健康指数进行预测,其预测结果直接反映了飞机复合材料结构的健康状态。试验验证表明,该方法可有效地实现飞机复合材料结构损伤预测效能,具有很好的工程应用价值。     

基体损伤对分层复合材料加筋板动力特性的影响研究

基于Mindlin假定的复合材料层合板单元和层合梁单元,推导了复合材料加筋板的刚度阵和质量阵;采用Adams应变能法与Rayleigh阻尼模型相结合的方法,构造了相应的阻尼阵列式;建立了分层损伤特征的三板模型和表征基体微裂纹损伤的基体损伤模型;并推导了一种基于Hertz型非线性接触法则的虚拟联接单元模型,以避免在振动分析过程中在低阶模态中分层处出现的上、下子板间不合理的嵌入现象;在上述模型和理论基础上,采用精细积分法求解含损伤结构的动力响应。对典型数例进行参数讨论,表明在动载荷作用下,嵌入分层损伤以及在振动过程中诱发的基体微裂纹损伤的演化将明显地影响加筋层合板的动力特性。     

基于频率识别纤维增强树脂复合材料加筋板的分层损伤

以纤维增强树脂（FRP）复合材料加筋板为研究对象,通过对比分层损伤发生前后FRP复合材料加筋板的振动频率变化,来识别FRP复合材料加筋板中的分层损伤。构建了人工神经网络（ANN）和基于有代理模型的优化算法（SAO）两种逆向检测算法,利用FRP复合材料加筋板在损伤前后发生的一系列频率变化值来逆推出FRP复合材料加筋板中的分层位置和大小。分别采用数值验证和实验验证来双重检验ANN和SAO两种算法的识别精度和效率。数值验证结果表明:ANN和SAO两种逆向检测算法对分层损伤位置和大小的识别最大误差分别是5.04%（ANN）和5.24%（SAO）,证明方法在理论上可行。实验验证结果表明:ANN在使用实测频率数据进行识别时预测精度很差,无法得到有效的分层损伤信息;而采用SAO可以较好地预测试件中的分层损伤,且对分层大小的预测比对分层位置的预测精度更高,其中,对贯穿损伤和底板损伤的大小预测误差分别不超过2.05%和9%,而四个试件中有两个试件预测的分层与实际的损伤部位存在重合（重合率分别为34%和32.65%）。因此,当前提出的ANN和SAO在理论上可行,但实际应用时都会受到不同程度实测数据误差的影响,相比ANN而言,SAO算法有更好的鲁棒性,在采用实测频率时也可以较为准确地预测出试件中的分层损伤。      

含分层损伤的复合材料格栅(AGS)板的非线性热屈曲分析

采用基于复合材料一阶剪切效应理论的有限元法分别研究了含分层损伤的复合材料层合光板、 单向加筋板和格栅加筋(AGS)板的热屈曲性态。在分析中考虑材料热物理性质与温度相关特性, 同时在分层前缘采用了位移约束条件以保证分层区域的各子板的变形相容要求。3种结构的典型算例分析和结果的比较表明, 复合材料格栅(AGS)板具有很强的抗热屈曲的能力, 但是, 分层损伤将使其临界温度降低, 同时还会导致热屈曲的模态发生改变。本文中提出的方法和所得结论对AGS结构的热承载能力预测和损伤容限设计将具有参考价值。      

含离散源损伤复合材料加筋板的拉伸特性

通过对含有离散源损伤的复合材料加筋板的拉伸试验和有限元模拟,研究了离散源损伤的损伤扩展与破坏特性。结果表明:复合材料加筋板的离散源损伤用穿透蒙皮切断桁条的切口来模拟是合适的,蒙皮上的穿透切口前端有很高的应力集中,桁条被切断导致加筋板传力路线改变;基于Hashin失效准则的渐进损伤有限元数值模拟方法,可以有效地模拟含切口加筋板的宏观损伤扩展和破坏过程,计算结果与试验值吻合较好。      

Analysis of impact-induced damage and delamination in the composite shell of a helmet

The impact energy absorption by helmets is of vital importance to the safety of motorcyclists during accidents. The paper is concerned with the study of damage and delamination, which are the principal modes of failure and energy absorption, in a composite shell and their influence on the impact performance of a helmet. Numerical simulations were conducted with different composite shells made of cross-ply laminate, woven fabric, and glass mat. The effectiveness of the numerical model is established using available experimental results from the literature. Hashin failure criteria and cohesive zone model (CZM) were used for predicting the in-plane damage and delamination in composite plies, respectively. An interface layer having a bilinear relationship between traction and relative displacement was placed between the plies of the composite shell to predict the delamination. The influence of damage and delamination in shells made of composite materials on impact-induced forces is evaluated and their performance is compared with helmet shells made of Acrylonitrile Butadiene Styrene (ABS).     

湿热环境下考虑累积失效和分层损伤AGS结构的稳定性

对湿热环境下考虑累积失效和分层损伤的先进复合材料格栅加筋结构(AGS)的稳定性进行了数值分析。基于一阶剪切理论和Von Karman非线性变形假设建立了含分层损伤复合材料 A GS结构的有限元模型,并推导了考虑温度和湿度效应的AGS结构有限元列式,同时给出了材料破坏准则。通过典型算例讨论了湿热环境、累积失效及分层损伤等因素对复合材料AGS结构稳定性的影响,数值结果表明当上述因素导致结构的屈曲模式发生突变时,其对 A GS结构稳定性能的影响是不容忽视的。     

Predicting low-velocity impact damage on a stiffened composite panel

An intralaminar damage model, based on a continuum damage mechanics approach, is presented to model the damage mechanisms occurring in carbon fibre composite structures incorporating fibre tensile and compressive breakage, matrix tensile and compressive fracture, and shear failure. The damage model, together with interface elements for capturing interlaminar failure, is implemented in a finite element package and used in a detailed finite element model to simulate the response of a stiffened composite panel to low-velocity impact. Contact algorithms and friction between delaminated plies were included, to better simulate the impact event. Analyses were executed on a high performance computer (HPC) cluster to reduce the actual time required for this detailed numerical analysis. Numerical results relating to the various observed interlaminar damage mechanisms, delamination initiation and propagation, as well as the model’s ability to capture post-impact permanent indentation in the panel are discussed. Very good agreement was achieved with experimentally obtained data of energy absorbed and impactor force versus time. The extent of damage predicted around the impact site also corresponded well with the damage detected by non destructive evaluation of the tested panel.     

Numerical and experimental analysis of delamination in the T-stiffener integrated composite structure

In this article, two kinds of cohesive zone models (CZMs; exponential and bilinear) are used to evaluate the delamination behaviors of a composite T-stiffener integrated structure. First, based on the analysis of the bilinear CZM using maximum nominal stress damage initiation criterion and power law energy criterion, both the macroscopic mechanical response and the failure process are predicted, which analyzed the influences of the various cohesive zone parameters on the failure load and the damage patterns. Second, both the strength and the fracture characterizations about various T-stiffener integrated composite structures are studied in the experiment, which have a good agreement between the numerical result and the experimental data. Finally, the relationships among the failure load and the thickness of the skin, and the clamp distance are established; also, the energy release rates of the T-stiffeners for the failure process are predicted. These results will play an important role for designing and evaluating the strength and reliability of composite T-stiffener integrated structures.     

Influence of post-buckling behaviour of composite stiffened panels on the damage criticality

In stiffened panels with defects, such as skin delaminations or stringer debonding, buckling may occur prior to the designed critical buckling load. Depending on the damage parameters, such defects may also affect the post-buckling behaviour and consequently the structural performance. An automated finite element (FE) modelling tool has been developed to predict the post-buckling behaviour of panels. It was coupled with a linear elastic fracture mechanics approach to determine damage criticality, based on the “no-growth” principle. The structural behaviour in the post-buckling range and its interaction with the damage parameters were analysed. Local buckling occurred as a result of localised stiffness reduction in the damage region. Global buckling occurred when sufficient in-plane strain was reached. The onset of local buckling was an important factor on stringer debonding criticality as the local buckling mode had an effect on the corresponding global buckling. In comparison, the onset of local buckling for the skin delamination was lower due to the thin sub-laminate separation. However, it was less influential on the damage criticality because the local buckling slowly dissipated in the far post-buckling range. It was found that the initiation of local buckling, and the interaction between the local and global buckling mode, would determine the damage criticality.