EXPERIMENTAL AND ANALYTICAL STUDIES OF FAILURE MODES IN IOSIPESCU SPECIMENS UNDER BIAXIAL LOADINGS

This study is concerned with an extension of the traditional Iosipescu shear test to in-plane biaxial stress applications. A Biaxial Stress Test Fixture, which is based upon the original Iosipescu shear test and the Arcan in-plane stress method, is used to characterize mixed-mode failure phenomena in both isotropic (PMMA) and orthotropic (teak) Iosipescu specimens under externally applied biaxial loads. The fixture is used for generating failure data for a wide range of biaxial (dominated by shear) loading conditions. Finite element methods are used to evaluate the stress state at the notch tips (as a function of the notch-tip radius) of biaxially loaded Iosipescu specimens. In addition, a simplistic analytical approach has been applied to estimate the notch-tip stresses at the onset of failure. A high quality failure envelope has been generated for teak under a combination of shear and transverse tensile loading conditions. Results from the finite element analysis show that an absolute numerical evaluation of the stress distribution at the notch tips can be misleading if a linear-elastic material behavior is assumed. However, the analytical approach, which assumes a uniform stress state along the notch-root axis, is found to more accurately represent the notch-tip stresses. Preliminary results strongly indicate the potential of the Biaxial Iosipescu method as a reliable test procedure for biaxial stress applications.