Measurement and prediction of residual strains and stresses during the cooling of a glass fibre reinforced PA66 matrix composite

Abstract

The forming process of thermoplastic composites inevitably leads to the development of residual stresses. This study proposes a model to predict the residual stresses at the ply level of a thermoplastic composite. It accounts for heat transfer, crystallization kinetics and the mechanical behaviour of the laminate. The model is applied to the cooling of a polyamide 66 (PA66) matrix reinforced with continuous glass fibres. The Stress Free Temperature is considered as the starting point of stresses accumulation within each ply. It is experimentally identified by monitoring the curvature evolution of composite coupons with temperature, leading to a temperature of 200°C. The evolution of the curvatures of [90404] laminates are recorded with a digital image correlation technique. They are compared with the curvatures predicted with the model, which permits to validate it. The predicted stresses distribution is then discussed, as well as the impact of several parameters on the stresses intensity.

Residual Stress in Engineering Materials: A Review

“…Simultaneous cooling conditions and CNT reinforcement effects were studied in another paper, [ 162 ] indicating that the influence of cooling conditions on the residual thermal stresses becomes more significant when the CNT percentage decreases. A recently published study regarding the cooling effect on the ply‐scale residual stresses and curvature in asymmetric GFRP composites [ 163 ] has presented a model based on the modified laminate theory, for the first time, accounting for the development of material thermomechanical properties during cooling. It is worthwhile noticing that there might be constraints in the cooling process of materials, for example, some alloys could become significantly harder when cooled to particular temperatures.…”

Residual stresses developed in thermoplastic composites during laser-assisted tape laying

“…In this work, the model based on the modified CLT developed in [15] for the study of the residual stresses during compression molding has been adapted to study the formation of theses stresses during tape placement on the SPIDE-TP, an online consolidation process based in Cetim, Nantes-France. The mechanical model is enriched with a complex representative thermal history and fed with crystallization and thermomechanical properties of the material described in the next sections.…”