Thermo-Mechanical Characterisation of In-Plane Properties for CSM E-glass Epoxy Polymer Composite Materials – Part 1: Thermal and Chemical Strain

The in-plane thermo-mechanical properties and residual stresses of a CSM E-glass/Epoxy
material are characterised through the use of DSC and TMA. The measured data is used to
generate material models which describe the mechanical behaviour as a function of
conversion and temperature. The in-plane thermal expansion coefficient (a) of the composite
material decreases above the glass transition temperature (Tg), which is compensated
by a higher out of plane deformation above Tg. Comparison of a and chemical
shrinkage measurements suggests that chemical bonds between the polymer matrix and
the glass fibres are formed prior to shrinkage of the epoxy matrix, i.e., at an early processing
stage. This suggests that production of composites with low residual stresses
requires focus on reactivity between the matrix and the sizing rather than the matrix cure
properties. As a consequence, residual stresses in the composite material are mainly a
result of restricted cure shrinkage rather than mismatch between thermal expansion
coefficients.