Experimental and Numerical Investigation of Second Mode of Failure in Unlike End Notch Flexure Samples (Composite/Steel)

Metallic pipelines are mainly corroded and damaged in operation that replacing damaged lines or their local welding is sometimes not feasible or economical, so for resolving the corrosion and functional damage of metallic pipelines, localized repair using composites as one of the most effective and cost effective solutions is used. The connection of composite repair to the metal substructure in this method is one of the most important design parameters. Therefore, deriving the important parameters at the junction will help engineers in designing and predicting the interlaminar crack initiation and propagation at the joint interface of composite repair to the metal substrate. Therefore, to investigate the second mode of failure in this method, the strain energy release rate is calculated experimentally and numerically in a steel/GFRP bond. According to an experimental standard for calculating the second mode strain energy release rate, ASTM-D7905, experimental tests are accomplished for three symmetric and asymettric unlike end-notched flexure specimens and a relationship for the thickness of each material to have symmetric specimens is proposed. To validate the thickness calculation relationship, the finite elemental modeling of unlike samples using virtual crack closure technique is used which indicates the good agreement of experimental and numerical results. Compareing the experimental results obtained in force-displacement diagrams of symmetric and asymmetric samples in crack propagation showed that the second mode strain energy release rate of symmetric samples are more than asymmetric and about 1.6 times as large.