The testing of curved specimen leads to the question whether the eccentric force arm (due to a shifted centre of mass in the curvature) has an influence on the stress distribution within the test specimen. Ideally, a uniform stress pattern throughout the cross section is assumed. Stress concentrations across the width of the specimen are undesirable, as Weibull statistics for the evaluation of failure probability take a uniformly stressed volume into account. The aim of this numerical analysis is to model the test set-up and determine the stress concentrations for different curvature parameters. A simple analytical model resulted in stress concentration factors of up to 2.5 of the average applied stress
FE model of test specimen (click to enlarge)
The finite element model is produced in MSC/PATRAN and modelled in ABAQUS. Two materials are defined as seen in the figure (red: zirkonia tape, white: aluminium). The elements are 3D solids C3D20 with full integration. Variable parameters of the model are defined for the curvature: the arc radius, the thickness, and the span length. The resulting arc angle is defined by these parameters. These parameters are given by the experimental measurements. One element through the thickness was used for the relatively thin zirkonia tape, while the aluminium was modelled with 3 elements through the thickness. Both geometrically linear and non-linear simulations is performed.