Evaluation of Energy Release Rate for Mode I Crack propagation in GFRP structures

Abstract

-Unstable propagation of a crack results in fracture due to applied stress. Fracture mechanics provides a methodology for prediction, prevention, and control of fracture in materials, components and structures subjected to static, dynamic, and sustained loads. De-lamination is considered to be the most occurring failure mode in composites, a partition of the layers that are stacked together to form laminates. Delaminations appear at stress free edges due to the difference in properties of the individual layers, at ply drops where thickness should be reduced, and at regions subjected to out-of-plane loading like bending of curved beams. An experimental analysis was performed for analyzing the energy release rate for mode I crack propagation of the DCB specimen for different volume fractions. Double Cantilever Beam Specimen was analyzed for mode I crack propagation subjected tensile load and Energy Release Rate was evaluated for different crack lengths using ANSYS 15. Virtual Crack Closure method was used to find the Energy Release Rate by considering the displacements (V) at the flagged nodes near the crack tip and then was compared with the analytical results. Virtual Crack Closure method showed very good agreement with the experimental results. Convergence was achieved through refinement and results were extracted for variation of SIF along the crack front. It was observed from the results that the ERR increased at a very slow rate in the beginning of the crack growth (a/w = 0.2 to a/w = 0.4). As a/w reached 0.5 there was a steep increase in the Energy Release Rate. This was purely because of the plastic zone at the crack tip getting increased. This in turn increases the resistance offered by the crack to the propagation. Keywords -Virtual Crack Closure Technique, Energy Release Rate, Crack propagation.I. INTRODUCTION De-lamination is considered to be the most occurring failure mode in composites, a partition of the layers that are stacked together to form laminates. Delaminations appear at stress free edges due to the difference in properties of the individual layers, at ply drops where thickness should be reduced, and at regions subjected to out-of-plane loading like bending of curved beams. Opening mode (mode I), the sliding shear mode (mode II), and the scissoring shear mode (mode III) are the three different modes of crack propagation. The fracture toughness linked with each fracture modes must be characterized and the equivalent strain energy release rates for each mode connected with the design and loading of interest must be evaluated to predict de-lamination onset and growth. M. Kenane et, al [1] carried out a de-lamination fatigue-crack growth experiments on unidirectional glass/epoxy laminates. Three specimen types were tested: double cantilever beam (DCB), mixed-mode bending (MMB), and end-loaded split (ELS), for mode I, mixed-mode I + II, and mode II loading, respectively. Fracture mechanics technology was applied through the principles of strain-energy release rate. The measured de-lamin...