ANALYSIS OF FORMING LOADS FOR THERMOPLASTIC COMPOSITE LAMINATES

Using Mindlin plate theory, a model for the forming of thermoplastic c omposite laminates is presented. The transverse strain in the plate th eory is used to account for the slippage between adjacent plies. This interply slip is characterized by a rate dependent constitutive model that is adopted from an experimentally determined relation between the interply shear stress and interply slip velocity. A laminate under cy lindrical bending assumptions is used to demonstrate the methodology a nd to examine the contributions of temperature and loading rate to the amount of compressive stress in the surface ply located on the inner radius of curvature. An experiment which allows measurement of the loa d histories required to form a thermoplastic composite laminate by the matched die molding process is described. Load histories for two lami nates and two forming rates at a typical melt-phase forming temperatur e are presented along with the histories given by the forming model. U sing a hydraulic hot press and two-stage matched die mold, the upper l imit on forming rate at a specific forming temperature is demonstrated . Forming above this rate results in wrinkling of the plies on the inn er radius of curvature. Copyright (C) 1996 Elsevier Science Limited