Design of a Shear Test Fixture System and Optimization of a Metal Shear Specimen for Cyclic Loading

The objective of the present paper is to investigate the optimization of the existing sheet metal specimen geometry and the optimization of fixtures for fatigue shear tests. Simple static shear tests are used for the material characterization of sheet metal and composite materials. It is well known that it is difficult to achieve pure shear conditions in the specimens because of stress concentrations. Moreover, buckling must be prevented during cyclic tensile and compressive loads, which can be achieved with suitable fixtures. This paper proposes a symmetric specimen geometry for alternating in-plane loads, where the location of crack initiation is predicted and stress concentration is minimized. The design of the geometry was supported with numerical simulations. According to the final specimen geometry, unique fixtures were developed, based in part on the standard ASTM D7078, Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method, solution. The fixtures allow operation at elevated temperatures, easy specimen change, universal use on different test rigs, and possible extension to other specimen shapes. By the proposed fixture system, any type of cyclic test can be performed (i.e., alternating, pulsating, or variable). The fixtures are suitable for measuring strain with mechanical extensometers, video extensometers, or digital image correlation. The experimental shear tests on aluminum 6061 specimens showed comparable shear strain fields as calculated by the finite element method.