Shaping Forming and Modeling of Advanced High Str

Authors: Mark R Stoudt

Publish Date: 2016/05/27

Volume: 68, Issue: 7, Pages: 1830-1831

PDF Link

Abstract

Throughout the transportation industry there is a need to reduce vehicle weight and improve fuel economy which has heightened the demand for new sheet alloys The numerous advances in alloy design and production have produced numerous advanced highstrength steel AHSS sheet alloys that demonstrate an excellent combination of properties In most cases AHSS alloys demonstrate superior strength compared to the traditional alloys used for automobile components and for this reason replacing components made from traditional steel alloys with those made from AHSS is a good strategy to achieve weight reduction However the property data and constitutive laws available for many of these alloys are limited or inadequate for use in the complex models used to predict the behavior during sheet metal forming The ensuing inability to accurately predict the deformation behavior during forming impedes widespread incorporation of these advanced alloys in many applicationsThe enhanced mechanical properties associated with AHSS alloys are largely achieved through complex phase transformations and heattreatment protocols Since the microstructure determines the properties a fundamental understanding of the microstructural evolution in AHSS alloys is an essential component for further refining the properties of existing alloys or for developing new alloys The papers in this section highlight some recent advances pertaining to the characterization forming and modeling of AHSS alloysThe first paper “Measuring the Influence of Pearlite Dissolution on the Transient Dynamic Strength of RapidlyHeated Plain Carbon Steels” by Mates et al describes a series of high strain rate compression measurements that were conducted while the steel was undergoing transformation from a lamellar pearlite/αferrite structure to austenite The authors conducted measurements in a model system that consisted of three plain carbon steels with differing carbon contents Their results demonstrated that the kinetics of the pearlite to austenite transformation are extremely fast and that the strength of the steel is substantially reduced during the transformation due to the transient strength effect produced by the decomposition of the pearliteThe second paper “Ductility of Advanced High Strength Steel in the Presence of a Sheared Edge” by Ruggles et al describes how the ductility of the steel sheet is influenced in the vicinity of a sheared edge The authors conducted experiments on two AHSS alloys with similar strengths ie Dual Phase 980 DP980 and TransformationInduced PlasticityAssisted BainiticFerritic 980 TBF980 using both a standard tensile test protocol and an incremental tensile straining technique developed for use in a scanning electron microscope Digital image correlation was used to determine the changes in the effective strain at the microstructural level for both measurements Their results revealed that TBF980 had significantly better ductility than DP980 due to a higher propensity for localization around the hard phases present in the DP980 This effect was exacerbated in the vicinity of a sheared edgeThe third paper “Evaluation of Springback for DP980 S Rail using Anisotropic Hardening Models” by Choi et al reports the results of their modeling of the springback ie the unexpected change in shape that occurs in a component after forming in an automotive “Srail” component The authors compared the deformation behavior predicted by two constitutive models the YoshidaUemori model and the homogeneous anisotropic hardening HAH model against the physical measurements taken from an Srail stamped from a DP980 steel sheet Both models are based on isotropic and kinematic hardening and are designed to capture the Bauschinger effect transient hardening and permanent softening that occurs after there is a change in the strain path Their results demonstrated that of the springback prediction models evaluated the HAH model best agreed with the experimental results

Keywords: