Numerical evaluation of the ENF and 4ENF tests for the shear toughness estimation of adhesive joints

Adhesive bonding is widespread in several fields, ranging from construction, packaging, automotive industry, aeronautics and medical applications. As a result, it becomes increasingly necessary to reliably estimate their mechanical behaviour. Modern strength prediction techniques such as Cohesive Zone Modelling (CZM) are based on energetic principles. In the context of CZM, the shear fracture toughness (GIIC) is one of the most influential parameters for the strength prediction. This work aims to make a numerical evaluation of the End Notched Flexure (ENF) and Four-Point End Notched Flexure (4ENF) tests to determine GIIC and to provide shear CZM laws for further application in design. Three adhesives were tested: Araldite® AV138, Araldite® 2015 and SikaForce® 7752. An inverse technique was used to obtain the shear CZM laws of the three adhesives. A parameter sensitivity study was also performed to assess the influence of varying GIIC and the cohesive shear strength (ts0). It was concluded that the GIIC values for each adhesive obtained by the ENF and 4ENF tests are in good agreement. The inverse method enabled obtaining unique shear CZM laws for both ENF and 4ENF tests, which revealed a good agreement between these test configurations.