Mixed mode fracture analysis in a ductile adhesive using semi-circular bend (SCB) specimen

An improved semi-circular bend (SCB) specimen is introduced to obtain the mixed mode fracture envelope of a ductile adhesive with a considerable fracture process zone ahead of the crack tip. This specimen has been used for brittle adhesives fracture energy measurement. The proposed test procedure is very simple to implement and does not require any special loading fixture. The specimen is able to cover the whole mixed-mode ratios from pure mode I to pure mode II. Experiments are carried out on the manufactured specimens and the fracture loads are used in an inverse approach to obtain the fracture energy of the adhesive joints. The cohesive zone modelling (CZM) technique is employed as the data reduction method. Proper geometrical parameters for SCB joints are chosen through a wide-range of numerical simulations based on a linear elastic formulation. It is shown that the crack growth does not affect the mixed-mode ratio for the proposed adhesive joint. Another advantage of this specimen compared to the existing beam-based approaches (such as end-notched flexure (ENF), mixed-mode bend (MMB), etc.) is its lower risk of plastic deformation in the adherends. The mixed mode fracture enve-lope in the tested adhesive is obtained and the results of fracture energy under pure mode I loading are validated with the results of double cantilever beam (DCB) tests successfully.

Automated summary

An improved SCB specimen is introduced for obtaining the mixed mode fracture envelope of a ductile adhesive with a significant fracture process zone ahead of the crack tip. The proposed test procedure is simple and does not require special loading fixtures, covering the whole range of mixed-mode ratios. Experimental results show that crack growth does not affect the mixed-mode ratio of the adhesive joint.