Stress Transfer Analysis Of Fiber Reinforced Composites Under Different Conditions

The key factor of influencing the mechanical properties of fiber-reinforced composites is the interfacial stress transfer efficiency. Usually, a representative volume element model about single fiber is established to analyze stress transferring.. The study of the effect of temperature on stress transfer with an imperfect bonding is rarely seen. This thesis discusses the temperature effect on stress changing with imperfect bonding. In the shear lag model, radial stress and hoop stress of fiber and matrix are generally assumed far less than axial stress, the paper considers the radial stress or hoop stress effect on the stress transfer. Some research showed that fiber/matrix interface is an interface layer with thickness, assuming that elastic modulus variation with thickness in the interface layer, which is inhomogeneous materials. The thesis analyze inhomogeneous interface layer effects on fiber axial stress and interfacial shear stress using fiber pull out model.The main conclusion of this paper are as follows:(1)The same temperature change above a higher temperature, the greater increase of the maximum fiber axial stress and maximum interface shear stress. The greater of axial tensile stress, the smaller increase of maximum fiber axial stress and maximum interface shear stress due to temperature change. When the aspect ratio and the axial tensile stress are constant, the weaker bonding degree between fiber and matrix, the less increase of maximum fiber axial stress caused by the temperature change. If the bonding degree and axial tensile stress are constant and the same of temperature change, the greater aspect ratio, the more stress increment caused by temperature.(2)Using shear-lag model considering radial stress or hoop stress it is found that radial or hoop stresses lower the fiber axial stress and interfacial shear stress. In the case of a weak level of bonding, their effects on fiber axial stress can be ignored.(3)Based on fiber pull-out model, it is found that fiber axial stress increases with the increase of interface layer thickness. When the interface layer is constant, fiber axial stress decreases with the increase of matrix elastic modulus, fiber axial stress decreases with the increase of fiber volume fraction. Increase of interface layer thickness can lead to the maximum of interfacial shear stress decreases. When the interface layer is constant, the maximum of interfacial shear stress increases with the increase of the matrix elastic modulus. The increase of fiber volume fraction will increase the maximum of interfacial shear stress of fiber/interphase, but have little effect on maximum of interfacial shear stress of interphase/matrix.