Flaw growth thresholds in composites

本研究计划的目的是提出实验和建模方法，以确定基于断裂力学和疲劳裂纹萌生监测的复合材料损伤起始的疲劳极限，该监测使用基于模态声发射新方法（MAE）的波模传播[3-8]。通过导波模式的传播和信号内容的分析，该方法将被开发来确定疲劳极限相关的复合材料中的分层和裂纹萌生的发病，作为循环载荷和环境条件相关的温度和湿度的函数。 分析和数值建模工具将进行预测分层的开始和增长。裂纹扩展的起始分层将模拟虚拟裂纹闭合技术和凝聚区方法。实验程序和分析模型将被提出来确定复合材料的刚度损失引起的脱层的启动和传播，并测量脱层韧性在很宽的范围内的模式I /模式II的比率，以及为纯模式I和模式II加载。将使用断裂力学方法评价混合模式弯曲（MMB）试验配置的总应变能释放率G及其模式I（GI）和模式II（GII）分量。韧性测试结果和模态声发射数据相关的裂纹萌生将被用来定义分层的复合材料的起始标准信封。这些失效包络线将能够预测复合材料中的分层开始。

The objective of this research program is to propose experimental and modeling methodologies to determine endurance limit for damage onset in composite based on fracture mechanics and fatigue crack initiation monitoring using wave mode propagation based on Modal Acoustic Emission new approaches (MAE) [3-8]. Through an analysis of the guided wave mode propagation and signal contents, the approach will be developed to determine the endurance limit related to the onset of delamination and cracks initiation in composite materials, as function of cyclic loading and environmental conditions related to temperature and humidity. Analytical and numerical modeling tools will be performed to predict delamination onset and growth. Crack propagation of the starting delamination will be modeled by the Virtual Crack Closure Technique and Cohesive Zone method. Experimental procedures and analytical model will be proposed to determine composite stiffness loss induced by delamination initiation and propagation, and to measure delamination toughness over a wide range of mode I / mode II ratios as well as for pure mode I and mode II loadings. The total strain energy release rate G and its mode I (GI) and mode II (GII) components will be evaluated for the mixed-mode bending (MMB) test configuration using a fracture mechanics approach. Toughness test results and modal acoustic emission data related to crack initiation will be used to define the delamination initiation criteria envelope for the composite. These failure envelopes will enable predictions of delamination onset in composite materials.