Substrate constraint and adhesive thickness effects on fracture toughness of adhevive joints

摘要

The adhesive thickness effect on fracture behaviour of adhesive joints has been studied using the boundary effect model recently developed for specimen size effect on fracture properties of concreta,and the essential work of fracture model for ligament (uncracked resion)effect on largescale sield of bulk metals and polymers.The leading common mechanism responsible for the non linear elastic fracture mechanic behaviours,Such as dehesive thickness effect of adhesive joints,specimen size effect of brittle heterogeneous materials and notch dependence of deeply notched metal and polymer specimens,is discussed.These two frecture mechanics models shown that the height variation of a fracture process zone (FPZ)or a plastic zone is directly responsible for and change in fracture energy measurements such as the specific fracture energy G_f and the dcritical strain energy release rate G_C.Both models show that G_f is rapidly reduced when the crack-tip appraches the back-face boundary of a sjpecimen because only a limited FPZ or plastic zone height hFPZ can ebe developed in the boundary region.In the case of a thin adhesive joint,the development of a plastic zone height is limited by the thickness of the adhesive sandwiched between the upper and lower adherends or substrates.Consequently,a linear relationship bwtween the adhesive joint toughness and dehesie thickness is established.Tesh results on adhesive joints from the literature are analysed and compared with the new adhesive joint failur model based on the two well-established fracture mechanics models developed for other material systems.