Theoretical Analysis of the Surface Texture of Textile-Reinforced Thermoplastics

Endless fiber reinforced thermoplastic sheets (organic sheets) offer a range of mechanical properties (stiffness, strength, energy absorption) that make them interesting for many high-duty applications. However they often fail to come into operation due to cost and surface problems. Cost problems can occur in consequence of either expensive raw materials or of the investment outlay required for the impregnation and consolidation steps when only small quantities are produced. The surface problem on the other hand is caused mainly by the print-through of the reinforcing fibers and it affects especially those applications in the field of automotive exterior panels. The following article describes the work needed to analyze the material and the process parameters that influence the surface appearance. A finite element model has been created, that represents a semi-finished sheet with four layers of a 2/2 twill textile reinforcement. Based on that geometry various matrix characteristics as well as the vertical orientation of the reinforcing layers have been analyzed. Finally the influence of pressure and cooling rate during the consolidation process was investigated. The simulations helped to identify primary influence parameters and clarified the possibilities and also certain limitations concerning the surface quality of this material class.