A computer-aided specimen design to induce shearing strain around a hole

The local torsion process which involves an axisymmetric torsional loading around the design position of a hole in a structure has recently found important applications for grain refinement in tubes and fastener holes. The specimen design is a pre-requisite for any experimental investigation of the local torsion process. The purpose of this study is to investigate a number of potential designs which enable the implementation of the local torsion. These designs include a mandrel to twist the specimen and a range of connection configurations between the mandrel and the specimen including threaded, hexagonal and spline bindings. In order to understand the process requirements and for estimating the effect of design parameters, a coupled numerical analysis of the specimen is utilized, involving a non-linear finite element analysis using Abaqus. A sequence of computational steps with different boundary conditions at the interface is devised to simulate the coupled problem. The proposed configurations are compared for their abilities to perform the local torsion and produce the shearing strain within an annular zone around the hole. This allows investigation of the effectiveness of each design for the implementation of the local torsion. The distribution of strain accumulated around the hole in the radial direction is studied after carrying out the process. Finally, a specimen–mandrel assembly design is recommended to ensure that the process can be successfully implemented.