THE INFLUENCE OF SHEAR ON THE FAILURE MODE OF THE TRANSVERSELY ISOTROPIC FIBER-COMPOSITE

Failures of fiber-reinforced composites are satisfactorily described b y criteria based on failure functions of the form of a general tensori al polynomial whose coefficients belong to the appropriate components of the failure tensor H. While pure shear loading along any principal plane of an anisotropic material creates unequal pure shear failure st resses, pure shear loading along the transverse isotropic plane result s in equal pure-shear failure stresses of the sign of the applied shea r stress. The failure stresses of orthotropic laminae subjected to any in-plane off-axis loading are studied in this paper. It is shown that the mode of shearing of the orthotropic materials depends on the rela tive orientation of the external load with respect to the orientation of anisotropy of the material. Experimental evidence with fiber-reinfo rced composites corroborates the theory developed. Furthermore, a phen omenon of strengthening of failure under normal stress develops for a certain range of simultaneous applications of additional shear stress.