A Theoretical and Experimental Study on the Critical Clamping Force for Suppressing Buckling in In-Plane Tension-Compression Testing of Sheet Metals.

Accurate characterization of the Bauschinger effect is essential for improving springback prediction in simulations of complex sheet-metal components. However, in-plane tension-compression tests are prone to compressive instability and wrinkling during reverse loading, and the selection of clamping force still lacks a theoretical basis. In this study, a critical clamping force prediction model was developed based on energy conservation and the Cao-Boyce instability criterion. The model establishes the relationship between the critical clamping force, material strength coefficient, strain-hardening exponent, specimen geometry, and effective support area. Finite element simulations and experiments were conducted to investigate the contact state, local support effect, and instability-mode transition of Q890 high-strength steel, 2A14 aluminum alloy, and 304 stainless steel under different clamping forces. For Q890 steel, the critical clamping force interval was 900-1000 N, within which the compressive instability strain increased from nearly 0 to 0.085 and the instability mode changed from single-wave to double-wave buckling. After calibrating the boundary correction coefficient using Q890 steel, the predicted critical clamping forces for 2A14 aluminum alloy and 304 stainless steel were 594 N and 278 N, respectively. The optimized clamping forces enabled smooth cyclic tension-compression curves.