Load Transfer, Interface Characterization and Toughening Mechanism of Composites

摘要

A Micromechanics Measurement Technique called SIEM (Speckle Interferometry withElectron Microscopy) has been developed which has a spatial resolution of 10(exp -6) m and a displacement resolution of 10(exp-9) m. It utilizes a random pattern of submicron particles as markers on a specimen. Their movements under load are used for displacement/strain calculations through a correlation scheme. It has been successfully applied to the determination of the mechanical property of composite interphases. It is also applied to the determination of crack tip deformation along a bimaterial interface. It is found that even in a region as small as 100 (micrometers) squared there is no evidence pointing to the existence of an oscillatory stress field. It is shown that the William's asymptotic solution can be expressed in a form that indicates that the stress field at an interfacial crack tip is intrinsically asymmetric with respect to the phase angle. An interfacial toughness function is proposed that possesses this feature. This function agrees very well with the then existing five sets of experimental data in the open literature. Three dimensional photoelasticity is used to study the load transfer characteristics of strongly and weakly bonded interfaces due to the presence of dilatational strain of a sphere. The result compares favorably with theoretical predictions of H.Y.Yu of the Naval Research Laboratory.