An attempt to design a universal specimen for any multiaxial loading conditions

Abstract

The design of the multiaxial testing specimen is a challenging for the arbitrary loading conditions. We find that the stress of the inner thin region of biaxial/multiaxial testing specimen is not in proportion to one of the outer thick region. Therefore, a large magnitude of anisotropy in strength of the biaxial/multiaxial testing specimen may result in its failure before realizing the required stress state. Moreover, it makes the design of the multiaxial testing specimen unreliable for the arbitrary loading conditions. We have first attempted to obtain a universal design of a standard biaxial/multiaxial testing specimen for all materials which can also be employed to realize any stress state at its center, and found it impossible. Alternatively, we have adopted a typical composite material and optimized its geometry to realize widely representative stress modes at the center of a testing specimen. We have focused on obtaining the less number of biaxial/multiaxial testing specimen that can be employed for all stress modes. Overall, this work can be used as a guideline of specimen design for a reliable failure prediction of the composite structures under complex loading conditions.