Search Results

In a study of the Bauschinger effect, data were collected from three sources in the published literature. Quantitative stress-strain data were taken from these papers, and the results re-analyzed. The resulting database has 44 lots of sheet steels, including drawing quality, interstitial free, bake hardening, HSLA (and related grades), dual phase, TRIP, recovery annealed, and martensitic grades. In analyzing the data, it is found that use of the 0.05% yield strength on reversal instead of the conventional 0.2% yield strength provides more generality in explaining the results. In this analysis, the Bauschinger effect is characterized by a term (BE), which is the difference between the steel strength just prior to reversal and the 0.05% yield strength on reversal normalized by the strength just prior to reversal. An initial prestrain of 2% is needed to establish a dislocation morphology that can be generalized across many of the steel grades.

A three-dimensional surface profilometer has been used to examine the surface morphology in various regions of stamped automotive steel parts. This analysis provides insight into the nature of the surface morphology development during stamping. For this work, four stamped zinc-coated sheet steel sections were considered. Each of the sections was examined with the 3-D surface profilometer in a variety of regions suspected to show different surface morphology due to differences in forming. Upon analysis of the surface height frequency histograms, different modes of deformation on the part surface were identified and categorized. Three modes of surface deformation were observed - “simple pressing”, “pressing with small scale sliding and bending” and “pressing with gross sliding, stretching and bending”. Each mode had a distinctive set of characteristics in the frequency height histograms. These modes were observed in both galvannealed steel sheet and hot-dipped galvanized steel sheet.