Micromechanical analysis of the off axis rate-dependent inelastic behaviorof unidirectional AS4/PEEK at high temperature

The rate-dependent nonlinear stress-strain behavior of a unidirectional car bon fiber-reinforced composite AS4/PEEK at high temperature has been examin ed under displacement- and load-controlled conditions, together with the ef fects of unloading on the off-axis response. The monotonic tensile stress-s train curves at high temperature show marked nonlinearity for the off-axis angles in the range 10 degrees < theta < 60 degrees, regardless of loading rate and control mode. A permanent strain clearly appears after unloading f or all off-axis angles except 0 degrees. The hysteretic response to consecu tive unloading and reloading is of the Masing type, and the width of the hy steresis loop depends on off-axis angle. The off-axis flow stress in the su bsequent nonlinear regime, as well as the initial slope of the stress-strai n relationship, depends on loading rate. These observations reveal that the off axis deformation of the unidirectional AS4/PEEK shows viscoelastic and viscoplastic natures. To predict the off-axis rate-dependent nonlinear str ess-strain behavior of AS4/PEEK, a simple micromechanics model has been dev eloped using the Aboudi's method of cells for composite homogenization and the; Chaboche model for description of the rate-dependent inelastic behavio r of the PEEK matrix. The micromechanics model has favorably reproduced the rate-dependence and nonlinearity of the off-axis tensile behavior of AS4/P EEK at high temperature. (C) 2001 Elsevier Science Ltd. All rights reserved .