Integrated thermal-structural simulation of unidirectional composite laminates

Abstract

Composites make for excellent structures for their high strength-to-weight and stiffness-to-weight ratios. However, the lack of dimensional accuracy in composite parts often gives rise to high manufacturing costs and high scrap rates in the aircraft industry. The cost and scrap rate of composite parts are the result of curing-process-induced deformation. There is a great interest in increasing the ability to understand and predict cure-induced distortions associated with cure-induced residual stresses by obtaining accurate material properties. This dissertation focused on thermal- and curing-induced stress analysis of unidirectional composite laminates by establishing material properties to ultimately provide an efficient and accurate representation of an integrated simulation model. An accurate and acceptable simulation model may prevent most of the current trial-and-error parts manufactured in the aircraft industry. Material properties were established through coupon testing routed from flat plates manufactured in accordance with the relative American Society for Testing and Materials (ASTM) standards and requirements. The material used for this dissertation was carbon AS4 HexPly® 8552 epoxy resin prepreg. Coupon testing included the following data: Stress-strain data as a function of temperature and degree of cure (elastics modulus, shear modulus, and Poisson's ratio), coefficient of thermal expansion as a function of temperature, and degree of cure. The material properties were used as input results to develop an accurate thermal curing simulation model using Marc an MSC one software. The simulation model was compared with actual manufactured parts to indicate the amount of displacement, caused by residual stresses. The simulation and actual parts included a balanced [0/90]4 and unbalanced [0/90]4 layup and were manufactured using the traditional bag layup method and cured in an autoclave. The manufactured plate results were compared with the simulation using a ROMER absolute arm. This dissertation produced successful material properties, but the curing simulation model lacked the dimensional accuracy to predict material behaviour under thermal curing. A deviation of 2,98 % and 1,80% in the maximum displacement was obtained for the balanced and unbalanced layup with a minimum value of 96,42% and 91,7%. This dissertation provides a platform for future studies investigating carbon fibre composite as a solution for dimensional accuracy in the aviation industry.