FINITE-ELEMENT ANALYSIS OF AXIAL SPLITS IN COMPOSITE IOSIPESCU SPECIMENS

In this paper, a finite element analysis of skew-symmetric splits alon g the fiber direction in unidirectional composite Iosipescu specimens is performed. The energy release rates G(I), G(II), and G(total) assoc iated with axial splits in cracked Iosipescu specimens under external biaxial loading conditions are computed by four different numerical sc hemes: displacement correlation, displacement extrapolation, J-integra l, 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 condit ions, with G(I) and G(II) varying with the crack length a. For short a nd medium crack lengths G(I) > G(II) while for long cracks, G(II) is d ominant. The energy release rates G(I), G(II), and G(total) are strong ly dependent on the biaxial type of loading. The G-estimates obtained by the modified crack closure integral schemes are found to be the mos t accurate among all the numerical schemes chosen in this study. In th e analyses of axial splits in composite Iosipescu specimens, the displ acement correlation and extrapolation techniques yielded poor results. For long crack lengths, the analytical results from the beam theory a nalysis are in fair agreement with those from the modified crack closu re integral schemes; however, for short and medium crack lengths, ther e is a significant difference between the analytical and numerical res ults. 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.