Thermal Effects on the Compressive Behavior of IM7/PETI5 Laminates

Abstract

The effect of changing operating temperature on the compressive response of IM7/PETI5 composite laminates is investigated within this paper. The three temperatures evaluated for this study were 129, 21, and 177 °C, a spectrum from cryogenic to an elevated operating temperature. Laminate compressivestrength property testing was conducted to generate strength data at the three operating temperatures of interest for several lay-ups. The Wyoming Combined-Load Compression fixture was chosen for the compression testing. The current investigation determined that the torque applied with utilizing the fixture needs to be adjusted for changing operating temperature. A three-dimensional finite element analysis model of a [90/0]8s composite laminate subject to compressive loading is developed. The model is used to study the key attributes of the laminate that significantly influence the state of stress in the laminate. Both the resin-rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are included in the analysis model. For the laminate modeled, conducting nonlinear analyses using temperature-dependent material properties was determined to be unnecessary for the operating temperatures studied. Simply using the temperature-dependent material properties measured at the operating temperature of interest while conducting a more expeditious linear analysis was sufficient for predicting stresses accurately for the current problem. The unique three-dimensional analysis results revealed that the application of an applied compressive axial load in the 0-degree direction decreased the interlaminar stresses present in the laminate initially due to curing. Therefore, failure was concluded not be attributable to the interlaminar stresses in the composite laminate being studied when a compressive load is applied. The measured laminate strength increase with a decrease in temperature is determined to be due to the increase in the lamina compressive axial strength with a decrease in temperature.