STUDY ON THE EVALUATION METHOD OF HTE FRACTURE TOUGHNESS OF CFRP LAMINATES.

研究了CFRP层合板断裂韧性的估算方法。在这项研究中。用线性断裂力学方法可以较好地预测CFRP试件裂纹尖端的应力场。在此基础上，对有限元、边界元等数值方法进行了研究。首先进行了断裂试验和数值分析，估算了I型断裂韧度GIC。提出了一种实验与分析相结合的新方法。该方法不需要在试验过程中测量裂纹长度。其次，提出了一种评价II型断裂韧度的方法。在这种方法中，需要估计上下裂纹面的接触面积以及它们之间的接触力分布。为此，编制了一种新的边界元程序，它可以很好地估计接触面积和力的分布。通过在估算方案中引入该方法，可以方便地估算II型断裂韧度。最后，本文提出了混合模式试件，并通过三维有限元分析对混合模式的状态进行了校核。计算了三维J积分，并将其分解为应力强度因子KI、KII和KIII三种模式。结果表明，这类试件虽然发生了复合型断裂，但断裂模式以I型为主。结论是，应考虑采用另一种包括方式一、方式二和方式三的方法。这个问题引起了广泛的关注，日本、美国和欧洲之间的一个新项目正在计划中。作为这个新项目的一部分，我将继续努力建立一种新的方法来估计CFRP层合板的混合模式断裂韧性。

The method to evlauate the fracture toughness of CFRP laminates is studied. in this research. The linear fracture mechanics can be used with good accuracy to predict the stress field At the crack tip of CFRP specimen. Then the some numerical methods, for example, finite element method and boundary element method, are available in this study. At first, the fracture experiment and numerical analysis are carried out and the mode I fracture toughness, GIC, is estimated. A new method combining the experiment and analysis is proposed. By this method, it is not necessary to measure the crack length during the experiment. Second, a method to evaluate the fracture toughness of mode II is proposed. In this method, it is necessary to estimate the contact area between upper and lower crack surfaces and the contact force distributions between them. A new BEM code is made for this purpose, and it enables to estimate the contact area and force distributions with good accuracy. By introducing this method in the estimation scheme, the fracture toughness of mode II can be estimated easily. Finally the mixed mode specimen is proposed in this research and the state of mixed mode is checked by the three dimensional finite element analysis. Three dimensional J integral is evaluated and it is decomposed into three modes of stress intensity factors, KI, KII, and KIII. It is shown that though mixed mode fracture occurred in this type of specimen, the fracture mode is mode I dominant. It is concluded that another method to include mode I, II and III should be considered. This problem no attracts a wide attention and a new project between Japan, United States, and Europe is being planned. I will continue to effort to establish a new method to estimate the mixed mode fracture toughness of CFRP laminates as a member of this new project.