Quality Evaluation of Blanking Cross-Section Based on Fractal Theory

Characterizing the cross-section quality after blanking test is a difficult task in the punching industrial field. At present, the main evaluation method for the cross-section quality is to measure the relative ratio of smooth-sheared length and fracture length. However, the relative length ratio can not reveal the complexity of the fracture surface and can not fully characterize the details of the cross section profile. As a promising theory, fractal theory has been widely used in the metal research field and has a great advantage on the quantitative characterization of the quality of blanking cross sections. Based on the Mandelbrot fractal theory, the relative length ratios of different blanking cross sections were measured and the fractal dimension of each fracture surface were calculated. The results show that with the decrease of the fractal dimensions of the blanking cross section, the quality of fracture surface becomes better. Numerical simulations of the blanking process show that the smooth fracture zone is determined by the shear stress, and the fracture zone is determined by the tensile stress. The upper limit of fractal dimension for the blanking section can be estimated by measuring the fractal dimension of the fracture profile of tensile specimen.