PREDICTION OF FORMING LIMIT STRAINS UNDER STRAIN-PATH CHANGES - APPLICATION OF AN ANISOTROPIC MODEL-BASED ON TEXTURE AND DISLOCATION-STRUCTURE

Strain-path changes strongly influence the forming limit:strains of sh eet metals. The value of the limit strains is greatly affected by mate rial-related effects such as initial anisotropy, transient hardening, Bauschinger effect and cross hardening. A model which can describe the se mechanical behaviours has been developed on the physical basis of t exture and dislocation structure , and applied in conjunction with the Marciniak-Kuczynski analysis of the forming limit strains. The result s are represented in forming limit diagrams (FLDs) in which the formin g limit strains are indicated. The calculation successfully predicts s ome of the experimental tendencies which cannot be reproduced by conve ntional phenomenological models. Furthermore, the model has been used to discuss the effects of texture and dislocation structure on the FLD s. Especially, it is suggested that transient hardening caused by the latent part of the persistent dislocation structure significantly redu ces the forming limit strain for a strain-path change from equi-biaxia l stretching to uniaxial tension. (C) 1998 Elsevier Science Ltd. All r ights reserved.