Dimensional stability of composite in a space thermal environment

In this study, strain gages have been used to investigate variations in thermal expansion coefficient (CTE) with damage of two representative aerospace structural materials, AS4/3501-6 and XN-70/RS3. Refinements in the measurement technique allowed the accurate determination of very low CTEs. The longitudinal and transverse CTEs of unidirectional composites were determined over the temperature range −101° to 121°C. From these data, the CTEs of cross-ply laminates were predicted by using classical laminated plate theory and verified experimentally. Specimens of these laminates were then subjected to a series of uniaxial tensile loadings or thermal cycles −101°C to 121°C (−150° to 250°F) to produce cracks within the transverse plies of the laminate. The laminate CTE was measured after increments in the mechanical loading or thermal cycling and the corresponding crack density quantified by microscopic examination of a polished specimen edge. The CTE variation with crack density in the cross-ply laminate was predicted by using a 2-D variational model and an exact 3-D laminate theory. The results indicate that the variation in CTE due to ply cracking in a cross-ply laminate can be quantitatively predicted under mechanical loading as well as thermal cycling.