as crack size increases in the pf,1 iv-I ,1 materials, SIF tends to converge to values
seen in homogeneous/isotropic bodies.
Many methods have been proposed, to calculate SIFs for cracks subjected to
mixed-mode loading conditions in isotropic elastic solids. Some commonly used
methods are J integral [11, 12], virtual crack extension [13, 14], modified crack
closure integral and displacement extrapolation methods [15] etc. None of these
proposed methods are able to provide the complete solution for all the three modes
(Mode I, II and III) of SIF for anisotropic material.
Atkinson et al. [16] presented the idea of calculating mixed mode SIF using
Fredholm equation transformation. They used a center cracked Brazilian disc
(BD) test specimen made of isotropic material. The mode mixity ratio for the BD
specimen is a function of the crack angle with respect to the load vector. Results
were presented for varied crack angles and hence mode mixity ratios. Small crack
approximation was also taken and the results were found to be in accordance with
Awaji and Sato [17], but it did not incorporate anisotropy in the model and was
limited to Mode I and II SIFs.
Su and Sun [18] studied various kinds of 2-D anisotropic cracks to evaluate SIF
under mixed-mode loading condition. Fractal finite element method (FFEM) [19]
was used to calculate Mode I and II SIFs for 2-D anisotropic plate. The variation
of the SIFs with material properties and orientations of a crack was presented. It
was shown that SIFs were not sensitive to the variation of shear modulus. Hwu
and Liang [20] used remote boundary data to calculate SIFs for 2-D anisotropic
material. It eliminated the error in SIF calculation, caused by abrupt change in
the stresses near crack tips, by finding equivalent formulation for SIF by using
only remote boundary responses (displacements, stresses and strains), cooperating
with the necessary geometric data. A special boundary element was developed
which removed the requirement of meshing around the crack boundary. Through