Formability Improvements of DP 1180 Subjected to Continuous Bending-Under-Tension

摘要

There continues to be a desire to incorporate advanced high strength steels (AHSS) into automotive and other applications in order to reduce the overall weight of the final product. However, these materials exhibit limited ductility prior to fracture and require high forming forces. One means to address these concerns, at least in a laboratory setting, is by subjecting the material to continuous-bending-under-tension (CBT). In this procedure, a set of three rollers reciprocate over the gauge length of the specimen while the material is continuously pulled in tension. The adjustable parameters during CBT testing are the roller depth, the crosshead velocity (which applies the continuous, tensile force to the specimen), and the carriage speed for the reciprocating rollers (which is typically set to the highest value possible while maintaining a safe process). The formability improvements obtained through CBT processing are decreased applied force and increased elongation to fracture. The latter is achieved by assuring that during the CBT process the entire gauge length elongates to the maximum possible value before fracture occurs. Past research has shown that the concentrated deformation in the fracture location of a tensile specimen is similar to the deformation over the entire gauge length of a CBT processed specimen. In this paper, a parameter space study of the DP 1180 AHSS is conducted in order to determine the optimal roller depth and crosshead velocity to achieve the maximum formability improvements for this material. The results demonstrate a promising means to improve displacement (approximately four times over that in simple tension) prior to fracture for this AHSS when subjected to CBT processing.