复合材料层合板冲击后压-压疲劳寿命预测方法

针对冲击后复合材料层合板, 发展了含冲击初始损伤层合板的压-压疲劳寿命预测方法。该方法基于无损单向板的力学性能和疲劳特性, 对不同铺层参数、 不同几何尺寸以及不同冲击条件下层合板的疲劳寿命进行预测。为消除人为假设冲击损伤造成的误差, 对层合板在冲击载荷及冲击后疲劳载荷作用下的破坏进行全程分析, 即把冲击后层合板的实际损伤状态直接作为疲劳分析的初始状态。同时基于逐渐损伤思想, 推导了含冲击初始损伤层合板的应力分析过程, 建立了相应的三维逐渐累积损伤模型, 开发了参数化的复合材料层合结构冲击及冲击后疲劳破坏模拟程序, 为复合材料层合结构的抗冲击设计及其疲劳损伤扩展行为研究提供了较好的技术平台。      

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.     

层板复合材料的疲劳剩余寿命预报模型

应用可靠性分析的方法，导出了层板复合材料在疲劳载荷作用下的疲劳剩余寿命的预报模型。该模型已用典型层板复合材料在恒幅疲劳载荷作用下的实验数据进行了验证，实验结果表明，理论预测结果与实验值的接近程度是合理的。     

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。     

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。     

层板复合材料的疲劳剩余寿命预报模型

应用可靠性分析的方法 ,导出了层板复合材料在疲劳载荷作用下的疲劳剩余寿命的预报模型。该模型已用典型层板复合材料在恒幅疲劳载荷作用下的实验数据进行了验证。实验结果表明 ,理论预测结果与实验值的接近程度是合理的     

冷却方式对纤维增强复合材料疲劳寿命的影响

分别在自然冷却和风扇冷却条件下进行了两组某纤维增强复合材料的拉-拉疲劳性能试验，并对试验数据进行了比较和分析。结果表明，自然冷却时，由于加载频率过高而引起试验材料工作部分过热，使其疲劳寿命明显比采用风扇冷却时测试出的值偏低。因此，对采用较高加载频率或对温度较为敏感的纤维增强复合材料，在工程应用中，建议采用吹风散热装置，以延长该类材料制品的使用寿命。     

橡胶隔振元件频率疲劳的寿命预测

以天然橡胶哑铃型试柱为研究对象,进行频率为1 Hz、5 Hz、11 Hz的单轴拉伸试验,分析试验结果表明,随着频率的加大疲劳寿命呈现一种先上升后下降的趋势,并以最大主对数应变为损伤参量建立预测模型,结果表明预测精度均达到0.9以上。所建立的预测模型可用于建立天然橡胶材料的疲劳数据库。     

金属基复合材料疲劳寿命细观预测

本文以细观力学的平均场理论为基础,利用增量方法分析了金属基复合材料的疲劳性能,在每个增量过程把基体看作各向异性弹性材料来处理。首先利用数值方法求得了任意椭球夹杂在各向异性基体中的Eshelby张量,然后利用Mori-Tanaka平均场理论建立了复合材料应力与应变的增量关系。应用上述方法和基体的塑性混合强化模型及基体的疲劳寿命关系,本文分析了SiC/Al金属基复合材料的疲劳性能与微观结构的联系,并对复合材料的低周疲劳寿命进行预测。分析和预测结果和文献的实验相符合。      

Mode III fatigue delamination growth of glass fiber reinforced polymer woven laminates at cryogenic temperatures

This paper investigates the cryogenic fatigue delamination behavior of glass fiber reinforced polymer woven laminates under Mode III loading. Fatigue delamination tests were conducted using split cantilever beam specimens at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K). A finite element analysis was also employed to calculate the energy release rate. The temperature dependence of the fatigue delamination growth rate vs. energy release rate range is discussed. Fracture surfaces were examined by scanning electron microscopy to identify the delamination mechanisms under fatigue loading. The important conclusion we reach is that the Mode III fatigue delamination growth rates of woven laminates at cryogenic temperatures are lower than that at room temperature.     

Quantification of flexural fatigue life and 3D damage in carbon fibre reinforced polymer laminates

Carbon fibre reinforced polymer (CFRP) laminated composites have become attractive in the application of wind turbine blade structures. The cyclic load in the blades necessitates the investigation on the flexural fatigue behaviour of CFRP laminates. In this study, the flexural fatigue life of the [+45/−45/0]_2s CFRP laminates was determined and then analysed statistically. X-ray microtomography was conducted to quantitatively characterise the 3D fatigue damage. It was found that the fatigue life data can be well represented by the two-parameter Weibull distribution; the life can be reliably predicted as a function of applied deflections by the combined Weibull and Sigmodal models. The delamination at the interfaces in the 1st ply group is the major failure mode for the flexural fatigue damage in the CFRP laminate. The calculated delamination area is larger at the interfaces adjacent to the 0 ply. The delamination propagation mechanism is primarily matrix/fibre debonding and secondarily matrix cracking.     

Short time tensile behavior of unidirectional glass and carbon fiber reinforced polymer laminates with curved shapes

A newly developed confining system for rectangular columns required a wrapping, which sustained a large amount of parasitic bending due to the curved shape of the laminates at the cross-section corners. To investigate the effect of parasitic bending on unidirectional carbon (CFRP) and glass fiber (GFRP) reinforced polymer laminates, 4 ply coupons were laminated with a semi-elastic hybrid resin and cured in a curved shape. During the tensile tests, the curved coupons stretched and failed after further loading. Due to the parasitic bending, occurring during stretching, the tensile resistance was reduced by 48% for the CFRP and by only 18% for the GFRP coupons. Tests with high-strength, high-modulus epoxy resin laminated GFRP coupons were drawn upon and compared with the semi-elastic hybrid resin laminated GFRP coupons. There is a beneficial effect on the tensile resistance with the use of semi-elastic hybrid resin.     

Enhancement of delamination fatigue resistance in carbon nanotube reinforced glass fiber/polymer composites

We show that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) to the matrix of glass–fiber composites reduces cyclic delamination crack propagation rates significantly. In addition, both critical and sub-critical inter-laminar fracture toughness values are increased. These results corroborate recent experimental evidence that the incorporation of CNTs improve fatigue life by a factor of two to three in in-plane cyclic loading. We show that in both the critical and sub-critical cases, the degree of delamination suppression is most pronounced at lower levels of applied cyclic strain energy release rate, ΔG. High-resolution scanning electron microscopy of the fracture surfaces suggests that the presence of the CNTs at the delamination crack front slows the propagation of the crack due to crack bridging, nanotube fracture, and nanotube pull-out. Further examination of the sub-critical fracture surfaces shows that the relative proportion of CNT pull-out to CNT fracture is dependent on the applied cyclic strain energy, with pull-out dominating as ΔG is reduced. The conditions for crack propagation via matrix cracking and nanotube pull-out and fracture are studied analytically using fracture mechanics theory and the results compared with data from the experiments. It is believed that the shift in the fracture behavior of the CNTs is responsible for the associated increase in the inter-laminar fracture resistance that is observed at lower levels of ΔG relative to composites not containing CNTs.     

Frequency effects on the fatigue behaviour on carbon fibre reinforced polymer laminates

Test frequency exerts a considerable influence on dynamic mechanical behaviour of carbon fibre reinforced materials. In this study the effect of test frequency on the fatigue behaviour of the T300/914C system, a carbon fibre/epoxy matrix composite, is examined. Tension-tension fatigue tests were carried out at various stress levels and at three test frequencies (5, 10 and 20 Hz) for three specimen orientations (unidirectional, (0)₈, crossply (0°/90°)_4s and angleply (±45°c)_4s). A number of dynamic mechanical properties were monitored throughout specimen lifetimes and subsequently analysed — stress/life behaviour, maximum strain, normalised fatigue modulus, dynamic loss modulus, damping factor and specimen temperature. Frequency effects are found to profoundly influence the fatigue behaviour of both crossply and angle ply specimens. Angleply specimen fatigue response exhibits a strong dependence on test frequency, a fact that is reflected in the dynamic mechanical property responses monitored. The data obtained for unidirectional specimens is inconclusive due to the large degree of fatigue scatter observed.     

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.     

基于遗传算法的碳纤维增强树脂复合材料层合板单搭胶接结构的多目标优化

基于遗传算法对碳纤维增强树脂复合材料(CFRP)层合板单搭胶接结构进行了多目标优化,以提高其结构性能.首先,通过三维Hashin准则和三角形内聚力模型建立三维有限元模型来预测CFRP层内损伤过程、层间失效和胶层损伤过程,并通过试验验证其有效性.其次,利用拉丁超立方抽样(LHS)方法和二次多项式响应面法(RSM),基于搭...     

基于纤维束增强树脂基复合材料测试的单向层合板层间剪切性能的预估方法

纤维束增强树脂基复合材料（FBC）及其单向层合板在标准Iosipescu剪切实验中表现出非常相似的破坏特征,然而测量得到的剪切强度却有明显差异。本文使用两种碳纤维和两种环氧树脂制备了3种FBC和单向层合板,对FBC剪切强度和单向层合板层间剪切强度进行了测量与分析。应用界面单元方法分析了纤维束与基体之间的界面应力场,发现FBC剪切试件中纤维束/基体界面附近的应力状态为拉剪耦合,而单向层合板中界面处于纯剪切应力状态,这一差异导致FBC剪切实验测量的强度低于单向层合板的剪切强度。本文基于Yamada-Sun强度理论建立了FBC剪切强度与单向层合板剪切强度之间的关系模型,应用该模型预测的单向层合板剪切强度与实测强度之间达到良好的一致性,相对偏差为10%左右。根据本文提出的方法,通过制样较简单的FBC试验能够预测和评估相应单向层合板的层间剪切性能。     

基于深度学习的短纤维增强聚氨酯复合材料性能预测基于深度学习的短纤维增强聚氨酯复合材料性能预测

结合深度学习在图像识别领域的优势,将卷积神经网络（CNN）应用于有限元代理模型,预测了平面随机分布短纤维增强聚氨酯复合材料的有效弹性参数,并针对训练过程出现的过拟合,提出了一种数据增强的方法。为验证该代理模型的有效性,比较了其与传统代理模型在预测有效杨氏模量和剪切模量上的精度差异。在此基础上结合蒙特卡洛法利用卷积神经网络代理模型研究了材料微几何参数不确定性的误差正向传递。结果表明:相对于传统代理模型,卷积神经网络模型能更好地学习图像样本的内部特征,得到更加精确的预测结果,并在训练样本空间外的一定范围内可以保持较好的鲁棒性;随着纤维长宽比的增大,微几何参数的不确定性对材料有效性能预测结果会传递较大的误差。      

Mechanical fatigue in aluminium at elevated temperature and remaining life prediction based on natural frequency evolution

Fatigue is one of the principle damage mechanisms in materials especially at elevated temperatures. It possesses a great influence on the material properties and the possible working life. In this work, a novel technique for the analysis of fatigue at elevated temperature is suggested. Material fundamental frequency and its drop are used as the key parameters to predict the remaining useful life of a selected shape specimen, which is operated under low‐cyclic fatigue loading at elevated temperature. Experiments are performed on aluminium 1050 with two different lengths of a non‐prismatic cantilever beam at room temperature, 100, 200 and 300 °C, respectively. The experimental data is further transformed in to an empirical correlation that can predict specimen useful life. The error in this life prediction is less than 5%, and it reduces more once the frequency drop is increased.