CHARACTERIZATION AND NUMERICAL MODELING OF ADVANCED AUTOMOTIVE LIGHTWEIGHTING MATERIALS

The automotive industry is being challenged to manufacture vehicles to meet the fuel- efficiency, emission and crashworthiness. New generation steels such as high strength steels (HSS) and advanced-/ultra-high strength steels (AHSS/UHSS) are gaining popularity in the automotive industry due to their appealing strength-to-weight ratios. The utilization of these steels has prompted research to seek solutions on issues arising during sheet metal forming processes, e.g., springback prediction/control, edge cracking prediction and avoidance, formability performance prediction and enhancement, etc. This thesis is focused on developing experimental techniques to characterize the forming properties for AHSS, on exploring fundamental principles of their mechanical behavior and on establishing material modeling frameworks to predict the observed behaviors. The key ingredients for the typical material modeling framework are: the uniaxial hardening curve, initial and subsequent yielding surfaces, and the flow rule. To accurately characterize these material behavior parameters, a series of standard and novel mechanical tests are performed on the standard and custom testing facilities. The 4-point bending, uniaxial tension and plane-strain tension tests are conducted to assess the elastic and plastic anisotropy and the degradation of elastic modulus after plastic deformation. Experiments are performed on typical automotive steels, namely DQSK, DP 590/980/1180 and MS 1700. The measured elastic anisotropy is modeled using orthotropic elasticity theory. Furthermore, the plastic work contours are constructed using uniaxial and plane-strain tension test data and the corresponding anisotropic yield functions of Hill 1948 and Yld2000-2D are calibrated