Determination of Crack Initiation Direction under Mixed Mode Loading For Elastic Plastic Material

Abstract

In many ductile materials, a defect in the form of a crack does not always lead to a catastrophic failure immediately upon loading. There is evidence of stable crack growth before instability sets in. The instability occurs at a load level higher than the initiation load. A design based on the initiation load may lead to an underutilization of a material. An improvement is possible and the full potential of a material can be utilized if the determination of stable crack growth can be done and the increased load capacity can be predicted. The stable crack growth behavior for AISI 4340 steel using CT specimen with sharp slit (0.05mm) under mode-I loading is presented. It is important to determine the parameters crack opening displacements and stress intensity, which strongly affects the ductile fracture of the body for compact tension shear type of geometry (CT specimen).

The present work is also concerned with determination of the stress intensity factor, and CTOA (Crack Tip Opening Angle) for AISI 4340 steel and aluminum. To determine the parameters like, LLD (it is one of the easiest measurement during the experiment), and crack initiation direction with the help of various theories like MTS (Maximum tangential stress), MTPS (Maximum tangential principal stress), Delta criteria, T-criteria, and Ip-theory is carried out. The work is done with the help of ANSYS 14.0 and results are compared with those available in literature.