Testing of a hot stamped axial crush member with tailored properties – Experiments and models. (May 2017)

• Record Type: Journal Article
• Authors: Omer, Kaab; ten Kortenaar, Lukas; Butcher, Clifford; Worswick, Michael; Malcolm, Skye; Detwiler, Duane
• Is Part Of: International journal of impact engineering. Volume 103(2017:May)
• Page Start: 12
• Page End: 28
• Publication Date: 2017-05
• Subjects: Axial crush -- Tailored hot stamping -- Energy absorption -- In-die heating -- GISSMO; Impact -- Periodicals; Shock (Mechanics) -- Periodicals; Impact -- Périodiques; Choc (Mécanique) -- Périodiques; Impact; Shock (Mechanics); Periodicals; 620.1125
• DOI: 10.1016/j.ijimpeng.2017.01.003
• Languages: English
• ISSNs: 0734-743X

Abstract

Highlights: Tailoring the properties of crush rails can lead to favorable axial crush behavior. The graded soft zone parts displayed high energy absorption. The graded soft zone parts displayed the least susceptibility to buckling. Numerical models predicted energy absorption within a 10% range of accuracy. Abstract: The effect of tailoring the properties of a hot stamped axial crush rail on its axial crush response is investigated. Four configurations of rails of thickness 1.2 and 1.8 mm were formed: a non-tailored (fully martensitic) configuration and three tailored configurations in which one-half of the rail was quenched while the other half was formed in tooling that was heated at different temperatures (in the range 400–700°C). Impact experiments showed that the non-tailored, fully hardened components did absorb the highest energy (15.4–24.1 kJ at 165 mm displacement), but exhibited extensive tearing and fracture. The tailored configurations with a single soft zone were less susceptible to fracture, but the thinner rails were more likely to buckle and absorbed less energy (9.7–20.5 kJ at 165 mm) as a result. Graded tailored configurations with two soft zones and one hard zone did not buckle and absorbed slightly higher energy. The results show that tailoring can introduce graded properties to promote a progressive folding deformation mode, thereby improving energy absorption without fracture. Numerical models of the forming and impact response were developed in which strain rate-sensitive constitutive properties and fracture limit strain versus triaxiality loci were prescribed to be a function of the as-formed hardness and microstructural phase fractions. The models were able to predict the energy absorption of the various axial crush rails to within 10% accuracy, as well as the large difference in extent of tearing occurring in the fully martensitic versus tailored configurations.