Friction assessment in uniaxial compression test: A new evaluation method based on local bulge profile

Barreling in uniaxial compression test is widely used for friction evaluation, flow stress correction and unequal deformation quantification. However, the friction evaluation methods based on the maximum and top radii of the deformed cylinder are valid only at low level of friction because the contact of lateral surface with anvil desensitizes barreling to friction. To avoid this disadvantage, the effect of friction on bulge profile was investigated by finite element (FE) simulation and experiment. It was found that the slope of bulge curvature at the contact point is more sensitive to friction than other geometrical parameters. Though FE simulation tends to underestimate the side surface foldover, the predicted local bulge profile near the contact point is in good agreement with experiment. The slope of bulge curvature at the contact point is a good parameter to quantify friction condition and it can be measured by fitting to the local bulge profile. The calibration curves were obtained by FE simulation. The effects of material properties and initial aspect ratio on calibration were revealed. An empirical model considering the effect of material properties was developed for rapid friction estimation. The proposed method was applied to different lubricating conditions and surface states for three different materials. It shows good applicability in upsetting type deformation with normal pressure close to the flow stress.