Experimental research of formability limits in different thicknesses of polycarbonate sheets

Abstract

This experimental investigation evaluates the methodologies for determining the forming limits by necking and fracture in polycarbonate (PC) sheets. The proposed approaches are based on two methodologies that are commonly utilized in sheet metal forming. To that end, Nakajima tests for polymer specimens with different strain loading paths were carried out for 1 mm, 2 mm and 3 mm thickness. The evaluation of the principal strains was accomplished by means of Digital Image Correlation (DIC) and thickness measurements to obtain failure strains were performed. The experimental results highlighted the different behaviour attained in polymers and metals, and the need of establishing a suitable adaptation of the methodologies used in sheet metal forming, especially due to the elastic recovery of polymers that cannot be neglected. This analysis allowed obtaining accurate formability limits by necking and by fracture for the PC sheets of 1, 2 and 3 mm of thickness, additionally these results were compared with the formability limits for PVC sheet of 3 mm of thickness. The representation of these formability limits within the principal strain space allowed establishing a general framework for analysing the fracture limit, which is the relevant forming limit in incremental sheet forming processes.