ECCOMAS Thematic Conference on Mechanical Response of Composites R. Marat-Mendes et.al. (eds.) Porto, Portugal, 12–14 September 2007 MODE III FRACTURE BEHAVIOUR OF LAMINATED COMPOSITE WITH ECT Rosa M. Marat-Mendes 1 , Manuel M. Freitas 2 1 ESTSetúbal, Instituto Politécnico de Setúbal, Escola Superior de Tecnologia Estefanilha, 2910-761 Setúbal, Portugal. e-mail: rmendes@est.ips.pt 2 IST, Instituto Superior Técnico R. Rovisco Pais, 1, 1049-001 Lisboa, Portugal. mfreitas@dem.ist.utl.pt Keywords: Mode III, ECT test, Fracture toughness, Delamination, Three-dimensional finite element analysis. Abstract. An analytical and experimental investigation was carried out on a UE400 REM GLASS UD PREPEG glass/epoxy laminates to evaluate the edge crack torsion test (ECT) to obtain Mode III strain energy release rate, G III , of laminated composites. The ECT samples consists of a [90/(±45) 3 /(ט45) 3 /90] s laminate with an artificial delamination introduced by a non-adhesive Teflon foil of 13μm thickness at the mid-plane along one edge. The objective of this paper was to characterize the ECT test method to determine its suit- ability for inducing mode III delamination growth. To do so, it was used an original ECT test fixture consisted of a load frame whereby the specimen was positioned between three support pins, and load was applied via a fourth pin. In order to perform an analysis of the behaviour of the specimens, a three-dimensional fi- nite element analysis was performed. The Mode III fracture toughness was obtained from a compliance calibration method and applying the Ribiki-Kanninen method. The analysis re- sults were used to calculate the distribution of mode I, mode II, and mode III strain energy release rate along the delamination front. In order to detect the delamination growth, a C’Scan analysis before and after testing was performed on the ECT specimens. Further inspection of the failure surfaces is required to identify the damage and determine if delamination grows under mode III in the specimens.