Dimensional stability of composite in a space thermal environment

In this study, strain gages have been used to investigate variations in the rmal expansion coefficient (CTE) with damage of two representative aerospac e structural materials, AS4/3501-6 and XN-70/RS3. Refinements in the measur ement technique allowed the accurate determination of very low CTEs. The lo ngitudinal and transverse CTEs of unidirectional composites were determined over the temperature range -101 degrees to 121 degreesC. From these data, the CTEs of cross-ply laminates were predicted by using classical laminated plate theory and verified experimentally. Specimens of these laminates wer e then subjected to a series of uniaxial tensile loadings or thermal cycles -101 degreesC to 121 degreesC (-150 degrees to 250 degreesF) to produce cr acks within the transverse plies of the laminate. The laminate CTE was meas ured after increments in the mechanical loading or thermal cycling and the corresponding crack density quantified by microscopic examination of a poli shed specimen edge. The CTE variation with crack density in the cross-ply l aminate was predicted by using a 2-D variational model and an exact 3-D lam inate theory. The results indicate that the variation in CTE due to ply cra cking in a cross-ply laminate can be quantitatively predicted under mechani cal loading as well as thermal cycling. (C) 2000 Elsevier Science Ltd. All rights reserved.