Study Of Plastic Fracture Based On The New Method Of Plasticity

ABSTRACT:The flaws in materials or structures may be derived from metallurgical defects, machining process, manufacturing, assembling or the damage during the using process. Some flaws present directly in the form of cracks, which are formed simply under the effect of fatigue loads or combined effect of fatigue loading and residual stress field. The germination and expansion of the flaws in structures can conceal severe dangers. On the one hand, they undermine the carrying capacity and corrosion resistance of mechanical structures seriously. On the other hand, the stress concentration generated in the working process can lead to low stress-induced damage and even cause sudden catastrophic failure. Therefore, the study of crack problems has theoretical significance as well as great application value.There are many fracture forms. But the existing fracture criterions are only suitable for some particular crack problems, Such limitations lead to their small ranges of application. It’s difficult to find a fracture criterion and fracture theory that is applicable to most kinds of crack problems. In this paper, according to the new method of plasticity, the stress fields of the crack tips have studied by theoretical analysis and finite element analysis. The main contents and conclusions of this thesis are as follows:1.The development and research on linear elastic fracture mechanics and elastic-plastic fracture mechanics have been recalled.So has the application of finite element method in fracture mechanics.2.The new method for solving plasticity has been introduced systematically, which contains its unified basic equations, the physical interpretation and solving method.3.Based on the new plastic method, the stress fields of the crack tip in elastic-plastic fracture problems have been calculated by ANSYS, and are compared with those obtained from classical methods.4.The stress intensity factors of the mode I fracture,of which a wide range is yielding,have been calculated by using the new method and also their critical values represented by the stress intensity factors.5.According to the new plastic approach,a new fracture criterion for the elastic-plastic fracture problems of the mixed mode Ⅰ+Ⅱ has been established based on many experimental data. Lots of existing experimental results have verified the applicability and accuracy of this new fracture criterion.