Application of a variational mechanics stress analysis and energy-based failure criteria to the microdrop debond test for evaluation of the adhesion quality of several fiber-matrix systems

The interfacial adhesion quality between a fiber and a matrix is a significant property of fibrous composite materials. The fiber-matrix bond influences many bulk mechanical properties including the shear strength, tensile strength, compressive strength, and hygrothermal degradation resistance. Therefore, if two materials are united into a composite for a specific application, the interfacial properties must be controlled. This control requires a quantification of the properties that govern the fiber-matrix adhesion. In particular, a reliable test method and applicable stress and failure analysis are required. By comparing both the shear-lag stress analysis and a recently derived variational mechanics stress analysis to actual microdrop debond test data, a reliable value for the adhesion quality of the fiber-matrix interface can be determined.; In this study carbon, aramid, and glass fibers were imbedded in a microdrop of epoxy resin. These microdrops were then debonded from the fiber using the microdrop debond technique and their peak load recorded. By varying fiber type, fiber diameter, and microdrop length and diameter, the theoretical predictions of the variational mechanics stress analysis and the energy release rate failure criterion have been confirmed.; Using this variational mechanics analysis, debond loads have been accurately predicted over a wide range of microdrop lengths, microdrop diameters, and reinforcing fiber types. According to statistical comparisons and qualitative plot comparisons, the energy release rate failure criterion predicted the debond force more accurately than either the average shear criterion or the total energy failure criterion.