Process induced transverse shear stresses in thick unidirectional pultruded profiles

The residual stresses in the transverse to the fiber direction might be critical for unidirectional composites since their transverse shear strength is relatively low. Transverse shear behavior therefore needs to be analyzed carefully for thick pultruded profiles which have been increasingly used in structural load bearing applications. This is a necessary task to avoid potential crack formation during the process and to minimize the process induced damage level. In the present work the process induced residual stresses are predicted for a 100 100 mm unidirectional pultruded square profile made of glass/polyester. A thermochemical model is coupled with a mechanical model using the finite element method. The temperature and degree of cure distributions are calculated for three di erent preheating temperature defined at the pultrusion die inlet, namely Tinlet = 20 C, 40 C and 60 C. Mechanical constraints are formed due to the through thickness cure gradients and elastic modulus variation. The nonuniform internal constraints yield in an internal shear deformation. The transverse shear stresses are found to be more critical than the transverse normal stresses in tension.