Effects of Sheet Thickness on the In-Plane Stretch Forming Limit in an Aluminum Sheet

Abstract

An investigation concerning the effects of sheet thickness on the in-plane stretch forming limit in 1 100 aluminum sheets with thicknesses of 0.5 to 1.0 mm, prepared by electropolishing, has been carried out experimentally and analytically. Development of surface roughness is represented by a linear relation between surface roughness are observed. However, the forming limit which depends on the thickness is observed, and less thickness results in a decreased forming limit. Good agreement between measured and theoretical strains from modified M-K theory is obtained. The thickness dependence of a half angle of pointed vertex, θ₀, is introduced in Gotoh theory, assuming that the onset of localized necking in a sheet is the result of a bifurcation from a state of uniform deformation. The values of θ₀ are in the range between 70 and 90 degrees in all the materials examined and satisfy the relation θ₀=π/2-q₁ε^^-q0, in which the coefficients q₀ and q₁ are material constants.