Friction shear stress on the tapered surface of the punch has been directly detected using friction sensors during the taper cup test. An aluminum alloy circular cylinder block was used for the test piece with various lubricants. Punch load increased with the frictional stress on the tapered punch surface. The increase in frictional stress with the stroke was estimated to be due to the increase in surface expansion ratio on the tapered punch surface during punch insertion. The relationship between the frictional stress on the punch and the punch load was compared by FEM analysis using friction shear and friction factors. By this study, it was confirmed that the friction sensor can detect frictional stress directly under lubrication, and it will be applicable to the detection of the local friction change during forging under high pressure and under an increasing surface expansion ratio.

The homogenization method is effective for analyzing macroscopic mechanical properties from the substructure of a material. In perforated sheet metal, macroscopic mechanical properties depend on the pattern of hole arrangement. In this study, the macro-plastic properties of perforated sheets with 60º standard staggered and 90º square arrangements are modeled. Biaxial stress is applied to the unit cells given the periodic boundary condition, and the contours of equal plastic work are obtained. The yield surfaces of the perforated sheets on the tension-compression combined stress state are strongly affected by the hole arrangement. To model the yield surface, a yield function for the rotational symmetry peculiar to the perforated sheet is proposed. The yield surfaces are modeled using the CPB2006 yield function that takes into consideration tension-compression asymmetry. Also, a surface-interpolated differential hardening model is applied to model the changes of yield surfaces. The analysis results obtained using the modeled yield surfaces are compared with the experimental ones obtained on the uniaxial tensile and deep drawing tests. The results of both tests show good agreement.