The over-notched flexure test method for determining the fracture toughness and bridging law of laminates

Abstract

This work introduces a novel approach for analyzing the over-notched flexure (ONF) test, aiming to calculate the fracture toughness and bridging law. The important feature of this new methodology lies in obviating the necessity for continuous observation of crack length and relative sliding displacement at the tip of pre-crack, and extra tests for determining flexural modulus. Formulations are derived for compliance, fracture toughness, sliding displacement at the tip of pre-crack, and the corresponding bridging stress. To validate the accuracy of this approach, a comprehensive assessment is conducted based on experimental results from T800/epoxy and E-glass/polyester laminates with various stacking sequences. Comparisons between the calculated fracture toughness and bridging law from the proposed approach and the experiment results present a satisfactory consistence between each other. Furthermore, finite element analysis of the ONF test is carried out. The obtained bridging law is incorporated into a tri-linear cohesive law for simulating delamination. The good agreements between the load–displacement response from tests and predictions provide further validation of the proposed method. This method can simplify the testing process and reduce experimental errors, which makes it easy for application.