Tailored planar S-shaped samples for in-situ characterization of adiabatic shear banding under controlled stress triaxialities

• Novel S-shaped shear sample design for adiabatic shear band analysis • Superposition of tension or compression on dominant shear • Ultra-high-speed strain mapping and thermal measurements • Stress-induced martensite as in-situ indicator of local stresses Formation of adiabatic shear bands (ASB) as a deformation mechanism occurs particularly at high (shear) strain rates in metallic materials. A detailed analysis of ASB nucleation and growth, and of the contributions of the underlying mechanisms such as thermal or microstructural softening, is experimentally challenging. In this study, we present newly designed S-shaped sample geometries that allow an in-situ characterization of shear banding under different stress states. Local shear deformation occurs in a geometrically well-defined shear zone during uniaxial compression of the S-shaped samples. Considering both numerical simulations and experimental measurements, we demonstrate that the predominant shear stress can be superimposed with either tensile or compressive stresses by slightly varying the geometry of the shear zone. Moreover, we show that the sample geometry is ideally suited for the application of digital image correlation for strain (rate) mapping as well as temperature measurements at high loading velocities. Metallographic preparation of the samples prior to testing enables in-situ microstructural observations during dynamic deformation. The sample geometry is validated by dynamic experiments using a Ti-10V-2Fe-3Al alloy in a Split-Hopkinson Pressure Bar (SHPB) under nominal strain rates of >10 3 s -1 (which corresponds to local shear rates up to 10 5 s -1 ). Our experimental and numerical results demonstrate that the novel sample geometry facilitates detailed investigations focused on the formation and growth of adiabatic shear bands.