A Multi-Gage-Length Tensile Specimen for Simultaneous Multi-Strain-Rate Testing

Characterizing the strain-rate sensitivity of metallic alloys is critical for developing accurate constitutive models, yet traditional sequential methodologies inevitably introduce complex transient history effects. This study proposes a novel Multi-Gage Length (MGL) tensile specimen designed to overcome these limitations by inducing a simultaneous multi-rate kinematic spectrum within a single testing event. Functioning as a multi-ligament array, the geometry is designed to generate different local engineering strain rates across sub-gages of varying lengths within a single loading event. The methodology was validated using SAE 1020 low-carbon steel, with apparent macroscopic responses aligning with established monotonic loading models. Digital image correlation was employed for kinematic tracking; although full-field mapping was constrained by pixel-resolution boundaries in narrow ligaments, a point-to-point virtual extensometer approach successfully captured a nearly six-fold strain rate divergence between central and peripheral sections. Experimental results further identified a critical boundary condition regarding universal testing machine acceleration, revealing that failure in high-speed nominal trials often occurs entirely within the acceleration phase. Supporting rate-independent finite-element analysis revealed heterogeneous deformation and evolving strain-rate ratios, establishing stage-dependent kinematic partitioning among the ligaments. Ultimately, this framework increases experimental information density and provides a potential basis for future inverse finite-element identification of rate-dependent constitutive parameters.