Effect of core and facesheet thickness on mechanical property of composite sandwich structures subjected to thermal fatigue

Abstract

Sandwich panels made of polymeric composite materials used in hostile thermal fatigue environments are prone to microcracking due to internal stresses. The impact of micro-cracking as a result of thermal fatigue is more severe in sandwich structures as opposed to solid laminates. Four sandwich panel configurations are studied. They are quasi-isotropic panels made of polymeric carbon fiber reinforced skin bonded by adhesive to honeycomb Kevlar cores. Different facesheet and core thicknesses are investigated. Samples are subjected to thermal cycles from −195 °C to 150 °C. Microscopic inspection is performed at the sample cross-section for a number of cycles to observe the location and density of cracks. It is observed that cracks are formed mainly at the adhesive/composite interface. Also, microcracks are formed more in the core ribbon direction compared to the core transverse direction. For all samples, after 40 thermal cycles, the total crack length becomes saturated and remains almost constant and no more damage happens. To study the effect of microcracks on mechanical property, flatwise tensile test was performed at room temperature. By increasing the number of cycles, the crack area increases and the flatwise strength decreases. Experimental data indicates that the samples with higher core to facesheet thickness ratio has higher microcrack lengths and lower flatwise strength. Therefore, sandwich panels with thinner facesheet and thicker core are more susceptible to the damage if subjected to the thermal fatigue.