Over five-times improved elongation-to-fracture of dual-phase 1180 steel by continuous-bending-under-tension

This paper reports the main results from an experimental investigation into the improved elongation-to-fracture (ETF) of the advanced high strength steel (AHSS) dual-phase (DP) 1180 by subjecting the material to the continuous-bending-under-tension (CBT) process. The investigation is carried out using a recently developed testing apparatus, where the specimen flows in a reciprocating fashion through a set of three rollers while it is continuously pulled in tension. The process parameters such as the roller depth defining the amount of bending and wrapping around the rollers and crosshead velocity applying the tensile force to the specimen are varied to maximize the ETF of the material. From the recorded force vs. displacement curves along the rolling direction (RD), 45 degrees, and transverse direction (TD), ETF of DP 1180 is found to improve with the crosshead velocity and with the bending depth up to a certain level, after which it decreases. The optimal parameters of 1.35 mm/s for the crosshead velocity and 3.5 for the normalized bending depth improve ETF of the material over five times in every testing direction relative to simple tension tests. The role of CBT in preserving high integrity of the material to large plastic strains is discussed. (c) 2018 Elsevier Ltd.