A micromechanics-based analysis for tailoring glass-fiber-reinforced thermoplastic laminates with near-zero coefficients of thermal expansion

This paper presents an attempt at tailoring fiber composite laminates with near-zero coefficients of thermal expansion (CTEs) in one particular in-plane direction by using conventional low-cost glass fibers. Specifically, laminates of symmetric and balanced ±θ angle-ply lay-ups in a glass/polypropylene system have been examined. An absolute strain-measurement technique utilizing a scanning laser extensometer has been applied to experimental determination of the ply-angle dependence of the laminate in-plane thermal expansion behavior in the range from room temperature to 120°C at a heating/cooling rate of 0.5°C/min. A preliminary analysis based on the classical thin-laminate theory predicts near-zero CTE values at θ of around 30° but experimentally, a laminate with θ≈30° shows an average CTE value of about −8×10−6/K. To evaluate this discrepancy in a quantitative manner, a refined analysis based on a well-accepted ‘mean-field’ micromechanics formulation has been developed, taking into account a possible inelastic effect caused by creep of the matrix material. A set of closed-form expressions for the laminate effective in-plane CTEs is obtained, and experimental data are thereby reasonably assessed.