Robustness Analysis of CFRP structures under thermomechanical loading uncluding manufacturing defects

Abstract

Carbon fibre reinforced plastics (CFRP) show superior weight-specific properties compared to metals. However, the structural behavior is more complex when exposed to thermomechanical load conditions, for instance in engine, turbine or battery environments or in space applications. The properties of CFRP decrease with increasing service temperature due to the temperature-dependency of their plastic matrix system. Yet, within current industrial design processes, temperature limits are defined with high conservatism. Therefore, additional load carrying capabilities at higher temperatures, before complete loss of mechanical performance, are not exploited. This study is presenting an enhanced analysis process for robust composite design by considering temperature-dependent material behavior, effects from manufacturing deviations and uncertainties from thermomechanical loading conditions.

A sequential finite element (FE) analysis strategy is utilized to assess the mechanical performance of a structure under thermal load conditions until glass transition temperature. The current investigations use nonlinear temperature-dependent material models to account for the corresponding stiffness and strength reduction. Based on the thermal load conditions and the structural concept, different temperature distribution will occur within the part and therefore, thermal expansion results in varying development of structural deformation and stress. Moreover, the temperature field causes locally decreased material properties. Evaluation of forces, stresses and strains allows assessing the structural performance. Inherent material uncertainties, local property knock-down resulting from fibre-placement defects and deviations of thermal load conditions are introduced to analyze the structural robustness. The work focuses on the analysis strategy and describes the approach of material modelling and applied uncertainties. Finally, results of the presented methodology are shown for a thin-walled stiffened CFRP structure.