The effect of internal stress on the identification of the mechanical behaviour of composite pipes

The curing of composite laminates (Fibres/Thermoset polymers) induces chemical and physical transformations, which are the first cause of residual stress. The second cause of residual stresses, and probably the main one in magnitude, is the shrinkage caused by the cooling which follows curing. Due to anisotropy of thermoelastic behaviour, the shrinkage of the laminate induces a complex stress field in each layer. The effect of residual stresses on the linear stress–strain relationship of thin laminate could be neglected. It is usually assuming that residual stresses do not affect the Young's modulus, the Poisson ratio, the shear modulus or the thermal expansion coefficients of layers. To simulate the elastic behaviour of thin laminate only the stacking sequence is taken into account even though residual stresses exist. For the non-linear behaviour the question is still opened. This paper discuss the question of the influence of residual stress on the parameters which govern non-linear behaviour.