Studies On The Stress Intensity Factor And Non-singular Stress In Central Cracked Disk

Brittle material such as rock tends to bear far-field compression stress, under the effect of load, crack will occur the extension. The pre-crack in rock will be closed when the compressive stress is greater than the crack closure stress. The contact between two crack surfaces have an important affects in the distribution of tip stress field of crack and displacement field. In this paper, based on the linear elastic fracture mechanics, using the weight function method to study the stress intensity factor of near crack tip, and the finite element method(FEM) numerical method to calculation the non-singular stress of near crack tip.The weight function is a theoretical method that calculates the stress intensity factors. Due to its relevance to the geometric shape of specimens, calculation on codition of different load has great superiority. In this study, an analytical solution of SIFs in central cracked Brazilian disk specimen subjected to both confining pressure and diametrical force is proposed. This solution is derived from the weight function method, and considers the effect of friction on the crack surfaces. The results show that the confining pressure not only has great influence on the value of Ki, and also the same significant influence on the value of KII, when the crack closes the confining pressure. Furthermore, the KII decreases with the increasing of friction coefficient on the crack surfaces when the crack is closed, which indicate that the existence of the friction prevent the propagation of the crack, leaving out bigger stress intensity factor. The analytical results of weight function and the numerical of FEM results are in good agreement with each other and show that the correctness of the theoretical analysis in this paper.When the crack is closed, the non-singular stresses at the crack tip includes both parallel (Tx) and perpendicular (Ty) to the crack plane on crack initiation. In this study, using the stress field of crack tip, dervies the calculation formula of stress mothod Ty. Compared FEM results to theoretical solution, the results verfies the correctness of this paper. It indicates that when the crack is not closed, using ANSYS to determine non-singular stresses by using the stress and displacement methods and the interaction integral method have a good applicability; but when the crack is closed, only the FEM by using stress methods is in conformity with the theoretical solution. Compared with no acccount of crack closure, the value of T-stress consider the crack closure will decrease. By considering the different fraction coefficient on the crack surfaces, it shows that the friction coefficient has no influence on the non-singular stresses.The modifield maximum tangential stress criterion by introduction of the friction cofficient and the non-singular stresses to determine the crack initiation. It is shows that, the crack initiation angles not only related with the crack angle, and when the crack is closed it also related to the fraction coefficient between the crack surfaces. The crack initiation angle predicted by the modified maximum tangential stress coincide well with the experimental tests, which indicates that the fraction coefficient and non-singular stress term both an important parameter affects the crack extension behavior.