Test MethodStrain distribution in cruciform specimens subjected to biaxial loading conditions. Part 2: Influence of geometrical discontinuities

In this paper, the influence of the geometrical design on the strain distribution in cruciform specimens is investigated. It will be shown that geometrical discontinuities, such as the milled zone and the fillet corners which are, respectively, introduced in the cruciform specimen to obtain a more uniform biaxial strain distribution and to guide the loads into the centre zone, result in local high strain concentrations. For this purpose, the digital image correlation technique and the finite element method were employed to trace the origin of these concentrations. It also appeared that the type of load, whether it was applied in a uniaxial or biaxial way, had a minor influence on the observed strain concentrations. The same conclusion could be drawn for the effect of the fibre orientation on the development of these strain intensities. Moreover, this study reveals that the geometrical irregularities lead to complex stress states which make the cruciform specimen fail prematurely. This complicates the determination of the true ultimate biaxial strength of a composite material.