Effects of Material and Manufacturing Variations on Dimensionally Stable Composite Structure

Abstract

Composites offer the major advantage of tailorable coefficients of thermal expansion (CTE's). Theoretically, zero-CIE composite structures can be designed, but in practice their CTE's deviate from zero due to variations in materials and manufacturing techniques. An analytical technique to find laminate elastic, thermoelastic, and hygroelastic properties and their standard deviations from ply properties, manufacturing variables, and their standard deviations and correlations is presented. Attention is concentrated on the in-plane coefficients of thermal expansion and the analogous coefficients of out-of-plane thermal bending and warping. Based on statistical information about the materials and manufacturing processes used, both the mean values and, more significantly, the standard deviations of these values are computed. In the case of laminates designed with zero mean values the standard deviations become the performance metrics. Experimental results are presented which verify the analytical techniques. The out-of-plane thermal deformations of over 90 specimens cut from both unsymmetric and symmetric laminates are measured. The experimental and analytical results are correlated, and show good agreement. The analysis is also used in sensitivity studies to aid in the understanding of the mechanisms of thermally induced deformations, and to identify the manufacturing factors and material properties that are most important to minimizing them.