Investigation of T-stress and tensile strength effect on crack tip conditions and crack initiation angle in off-axis laminate composite

Abstract

In this work, five different yield criteria have been used, maximum tangential stress (MTS), maximum energy release rate (MERR), Hill-48, Hill-90, and Barlat-93, in order to determine crack initiation angle. A study is performed to investigate the effect of T-stress on crack initiation angle. For this purpose, the elastic–plastic core region is plotted, and the R-criterion suggests that the crack initiates along local minimum (negative value) or global minimum (positive value) direction depending on the stress state at the crack tip. It is found that a negative value of T-stress makes the crack move toward the loading direction (T-axis), or in other words, the crack initiation angle decreases. It also turns out that MERR and Barlat criteria show a better result for crack initiation angle. The yield surface and elastic–plastic core region have also been plotted for different tensile strengths. For the case when transverse tensile strength equals to z-direction tensile strength, Hill-48, Hill-90, and Barlat show the same yield surface, and approximately, the same crack initiation angle. Also, when transverse tensile strength is smaller than longitudinal tensile strength, crack tends to move toward x-direction (local coordinate placed on crack tip). Finally, a FE simulation is performed to numerically determine SIFs.