Computer Simulation Of Planar Microcrack Growth Process And Correlation Experiment

Fatigue damage of engineering materials is often characterized to be a local phenomenon of microcracks initiating and propagating in solids. Lankford and Suresh have supposed that the 'irregular behavior' of naturally initiated microcracks is closely related with the local crystallography. The term 'irregular behavior' means the common observations of large scatter in growth rate data and the noticeably higher average growth rates of microcracks in fatigue, with respect to that of large cracks. Unfortunately, people do not pay enough attention to the importance of this phenomenon.X.D Li and K.S. Ravichandran put forward the K variation and anisotropy as well as the influence of anisotropic K to the behavior of microcracks' propagation at an international conference. They have done some in-depth research work about these aspects.It has been found that the grain-orientation-geometry-induced local anisotropy produces large variations in K along front of microcracks, when the crack size is of the order of few grain diameters. Synergetic effect of grain orientation and geometry of broken grains control K variations and evolution along the microcrack front. The K variations may diminish at large crack sizes, signifying a shift of K calculation to bulk stress dependence from local stress dependence.The phenomenon of K variation and anisotropy is highly regarded increasingly. While the appearance of K anisotropy alone the microcrack front along with its physical significance and geometrical connotation is a great challenge to traditional conception and compute method of K.Compared with other elements, K along microcrack front should be the most representative one in physical significance during we recognize the material damage behavior and the engineering applying process. For this reason, the local influence of anisotropic microstructure to the stress intensity factor (K) becomes very important when evaluating the critical crack damage of engineering components.The research work includes modeling programming and correlative experimentation two part. The modeling program part is to develop a visual simulating program, which can illustrate the microcrack propagating process from a material structure weakness. It is also expected to provide a numerical base for computing anisotropy K along microcrack front. The experiment part is to design interrelated exam plans to investigate the relation between anisotropy K along microcrack front and the local microstructure, acquire the correlated exam datum for the establishment of microcrack propagating criterion.