Abstract

Thermoplastic composites bring many benefits in terms of mechanical properties and manufacturing. Possibility of healing and recycling and proper strength are some of these desirable characteristics. Automated fiber placement (AFP) process can be used to manufacture both thermoplastic and thermoset composite structures. However, manufacturing of thermoplastic composite structures with free edges using AFP process faces a big challenge. These structures such as flat laminates deform, and these undesirable deformations occur even during the manufacturing process of unidirectional laminates. The distortion of thermoplastic structures with free edges is mainly caused by development of temperature gradients and residual stresses. To investigate the temperature gradients and residual stresses, accurate heat transfer models need to be developed. In this study a two-dimensional transient heat transfer model was developed for thermoplastic structures manufactured by AFP process with a hot gas torch. The accuracy of heat transfer model for AFP process using hot gas torch is highly dependent upon the accuracy of hot gas/air and convection coefficient distributions in the vicinity of the substrate (thermal inputs). Therefore, mathematical models for both thermal inputs were developed in this study. Inter-layer thermal contact resistance and temperature dependencies of the material properties were considered, and the heat transfer model was validated by experimental results. Furthermore, a heat transfer model was developed to include the effects of time between each pass. Then, using the validated heat transfer models and considering temperature histories and the time between each pass, the development of temperature gradients was investigated for various types of mandrels.