Mode decomposition in DCB and ENF tests with geometric and material assymetry

Abstract

Mode decomposition in interlaminar fracture tests initially designed for pure modes I and II as Double Cantilever Beam (DCB) and End Notcehd Flexure (ENF) is analyzed. In the initial proposal of those tests crack arms have geometric and material symmetry and the crack advance occurs through the middle plane of the laminate. In the current study, the possibilty of crack arms of different materials or with different thickness is included. Two mode decomposition criterions are considered after the analysis of a slice near the crack tip. Those criterions are based on the stress and displacement state in the non-cracked zone near the crack tip. Two points that before the crack advance were the same point are named homologous. When the cohesive zone is developing, the stresses in homologous points are the same due to the principle of action and reaction. Nevertheless, relative displacement can be normal, related to mode I, tangential, related to mode II, or a combiantion of both, related to mixed mode I-II. In the present work the relative tangential displacement related to mode III is not considered. The contributions to the energy release rate corresponding to bending and shear in each mode are analyzed. The results obtained are applied to asymmetric DCB and ENF tests.