Modification of the Shear-Compression Specimen for Large Strain Testing

A modified shear-compression specimen (SCS), for large strain testing over a wide range of strain rates is presented. The original SCS design includes two rectangular slots that are machined at 45 degrees with respect to the longitudinal axis. The modification consists of creating two diametrically opposed semi-circular slots. The new "circular" specimen is first thoroughly investigated numerically under quasi-static and dynamic loading using an elasto-plastic material model. The results of the comparison between the two-slot designs confirm the feasibility of the new specimen for larger strain testing and indicates its advantages over the rectangular slot design: larger strain range characterization, failure and fracture within the gauge, and constant Lode parameter during plastic deformation. Both types of SCS as well as cylindrical specimens are used to characterize the flow behavior of steel 1020, in the quasi-static and dynamic regimes using a split Hopkinson pressure bar. Dog-bone specimens are also tested quasi-statically in tension. A very good agreement is achieved for the results of all specimens in both the quasi-static and dynamic regimes. The numerical validation procedure shows that the flow stress of 1020 steel obtained with the new SCS is similar to 3 % lower in the quasi-static regime, and 8 % lower in the dynamic regime with respect to the flow stress of the rectangular SCS. This difference is attributed to effect of the third invariant of the stress deviator (i.e., Lode parameter), which is considerably lower in the new SCS design.