New specimen design for forming limit test of fibre metal laminates

Abstract:

In the process of deep drawing, the common failure modes of fibre metal laminates are wrinkling, fibre tensile fracture, and interface delamination. Inspired by the deep drawing test of metal, fibre strain can be introduced into the forming limit diagram when fibre tensile fracture and interface delamination failure are the main failure modes of fibre metal laminates. However, since the shape of the traditional metal strip specimen used for deep drawing test is an obstacle for the calculation of fibre strain in fibre metal laminates, a new notched specimen was designed in this study. The formability of glass fibre/polyamide resin (Gf/PA) composite-aluminum alloy laminate was investigated by comparing the forming tests of traditional strip specimens and the proposed notched specimens. Results show that the proposed notched specimen could ensure the calculated fibre strain level within 6%. Through the classification of different fibre strain intervals, it could be clearly divided that the failure form of deep drawing of laminates was fibre tensile fracture or interface delamination. It was found that the forming limit diagram of the notched specimen consisted of three regions: forming safety zone, fibre tensile fracture zone, and interface delamination zone. In addition, the forming limit curves obtained from the notched specimens could combine the deformation evolution with the failure mechanism, and more effectively characterize the deep drawing formability of fibre metal laminates.