Design and Experimental Assessment of a Continuous Bending Under Tension (CBT) Test Device for Universal Testing Machines

Continuous bending under tension (CBT), also known as cyclic bending under tension, is an experimental deformation technique capable of achieving large plastic strains under relatively low tensile loads. However, the broader application of CBT testing remains dependent on the availability of dedicated experimental setups and the suitable adaptation of conventional mechanical testing systems. This study presents the design and development of a CBT testing device intended for integration with conventional universal testing machines. The proposed system consists of four main subsystems: specimen grips, a roller train, a motor system, and a supporting structure. The developed device was experimentally assessed using DP600 advanced high-strength steel and AA6022-T4 aluminum alloy sheets with nominal thicknesses of 1.5 and 2.0 mm, respectively, under selected CBT operating conditions. The system successfully performed CBT tests, enabling the acquisition of force–elongation responses, cycles to fracture, and post-test specimen observations. The experimental results reproduced the characteristic CBT response, showing significantly higher total elongation compared with uniaxial tensile testing while requiring substantially lower tensile forces. The developed device demonstrated operational and mechanical stability, providing a practical platform for laboratory-scale investigations of sheet metal deformation behavior under CBT loading conditions.