No abstract

No abstract

No abstract

A model for the consolidation of thermoplastic composites based on commingled yarns was developed. The evolution of composite void content during consolidation was related to the processing parameters and the material properties. Additionally, the analysis relied on experimental investigation of the yarn structure, taking into account a distribution in dry fiber bundle sizes. Residual porosity was considered to result from pore closing at a given stage during fiber bundle impregnation. The accuracy of the model was assessed by conducting consolidation experiments using a unidirectional commingled yarn fabric made of polyamide 12 resin and carbon fibers. Excellent correlation was found between predicted and experimental void contents. The model aided prediction of suitable processing conditions and identification of the main physical and geometrical parameters influencing the consolidation rate.

A model to predict the macroscopic in-plane residual stress state of semicrystalline thermoplastic composite laminates induced by process cooling is presented. Heat transfer during processing is based upon an incremental transient formulation that consists of a finite difference heat transfer analysis coupled to the crystallization kinetics. Micromechanics is used to evaluate the instantaneous spatial variation of mechanical properties as a function of temperature and degree of crystallinity. Residual stresses are based upon an incremental laminate theory that includes temperature gradients, shrinkage due to crystallization and thermal contraction. Temperature dependent relaxation times are used to model first order viscoelastic effects. A parametric study is conducted to explore the sensitivity of residual stresses to process history. Input parameters varied include surface temperature history (cooling rate), the amount of shrinkage caused by crystallization and the relaxation time at the reference temperature. The model predictions were in good agreement with experimental residual stress measurements for unidirectional graphite (AS4) reinforced polyetheretherketone (PEEK) laminates.