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Determination of CTEs of cured epoxy and polyester (PET) stitching threads

Coefficients of thermal expansion (CTEs) of constituents in fiber-reinforced composites are among the key thermal parameters that need to be defined for material selection, modeling and structural design. This article presents an experimental approach for determining the CTEs of two constituents in a non-crimp fabrics (NCFs) reinforced composite system by means of dynamic mechanical analysis (DMA), mechanical tests at various temperatures and the principle of composite micromechanics. The constituents include the matrix (a cured epoxy resin) and the polyester (PET) stitching threads that are used to assemble multi-layered reinforcements comprising NCFs. CTEs of the cured epoxy resin were measured by both DMA and thermal mechanical analysis, and CTEs of PET threads were successfully estimated from those of the epoxy resin and a PET/epoxy composite in both transverse and longitudinal directions by means of composite micromechanics. DMA was found, in this study, to be an effective technique that can be used to determine the CTEs of polymers and polymer threads in a wide range of temperatures on the basis of proper calibration.