Finite element analysis of axial splits in composite Iosipescu specimens

In this paper, a finite element analysis of skew-symmetric splits along the fiber direction in unidirectional composite Iosipescu specimens is performed. The energy release rates G _I, G _II, and G _total associated with axial splits in cracked Iosipescu specimens under external biaxial loading conditions are computed by four different numerical schemes: displacement correlation, displacement extrapolation, J-integral, and the modified crack closure integral. Using beam theory analysis, an analytical solution for the energy release rates is also proposed. Axial splits in Iosipescu specimen propagate under mixed mode conditions, with G _I and G _II varying with the crack length a. For short and medium crack lengths G _I>G _II, while for long cracks, G _II is dominant. The energy release rates G _I, G _II, and G _total are strongly dependent on the biaxial type of loading. The G-estimates obtained by the modified crack closure integral schemes are found to be the most accurate among all the numerical schemes chosen in this study. In the analyses of axial splits in composite Iosipescu specimens, the displacement correlation and extrapolation techniques yielded poor results. For long crack lengths, the analytical results from the beam theory analysis are in fair agreement with those from the modified crack closure integral schemes; however, for short and medium crack lengths, there is a significant difference between the analytical and numerical results. In composite Iosipescu specimens, stable crack propagation (mode I dominant) can be achieved by increasing the tension/shear ratio in the external loading boundary conditions.