Optimal temperature profiles for minimum residual stress in the cure process of polymer composites

Manufacturing of polymer composites using a curing process requires the specification of the temperature as a function of time, i.e., the temperature profile. It is of utmost importance that the selected profile satisfies a number of criteria which include the minimum residual stresses, minimum cure cycle time and full degree of cure. The development of residual stresses during the cure cycle is one of the most important problems as they affect the strength and the mechanical properties of the final product adversely. The object of the present study is to determine the optimal temperature profiles used during curing in order to minimise these stresses. Numerical simulation is used to study the development of stresses during curing based on a process model which includes the effects of chemical and thermal strains and the viscoelastic material behaviour. The process model is implemented to conduct a parametric study to observe the trends and characteristics of the residual stress history varying engineer controllable input parameters. The gradients of the applied temperatures at different dwell times are identified as essential process parameters. An optimised curing cycle based on this observation is developed using the results of the parametric study. The optimal cycle achieves substantial reduction in the residual stresses and curing time for fully cured composites as compared to manufacturer recommended cycles.

[1]  N. Casillas,et al.  Isothermal and temperature programmed kinetic studies of thermosets , 1989 .

[2]  S. White,et al.  Cure Cycle Optimization for the Reduction of Processing-Induced Residual Stresses in Composite Materials , 1993 .

[3]  G. Springer,et al.  Effects of Cure on the Mechanical Properties of Composites , 1988 .

[4]  John W. Gillespie,et al.  Two-Dimensional Cure Simulation of Thick Thermosetting Composites , 1991 .

[5]  R. Pitchumani,et al.  Optimal cure cycles for the fabrication of thermosetting-matrix composites , 1997 .

[6]  S. Tsai,et al.  Introduction to composite materials , 1980 .

[7]  Brian D. Harper,et al.  On the effects of environmental conditioning on residual stresses in composite laminates , 1985 .

[8]  B. Joseph,et al.  Experimental characterization of autoclave‐cured glass‐epoxy composite laminates: Cure cycle effects upon thickness, void content, and related phenomena , 1997 .

[9]  Scott R. White,et al.  Process Modeling of Composite Materials: Residual Stress Development during Cure. Part II. Experimental Validation , 1992 .

[10]  Chieh-Li Chen,et al.  Optimal design of the cure cycle for consolidation of thick composite laminates , 1996 .

[11]  M. Darby,et al.  Residual stresses and the optimum cure cycle for an epoxy resin , 1989 .

[12]  Scott R. White,et al.  Process Modeling of Composite Materials: Residual Stress Development during Cure. Part I. Model Formulation , 1992 .

[13]  H. T. Hahn,et al.  Mechanical property and residual stress development during cure of a graphite/BMI composite , 1990 .

[14]  Y. Weitsman,et al.  Residual Thermal Stresses Due to Cool-Down of Epoxy-Resin Composites , 1979 .

[15]  Prasad Dhurjati,et al.  Implementation of Model-Based Optimal Temperature Profiles for Autoclave Curing of Composites Using a Knowledge-Based System , 1994 .

[16]  Richard Schapery,et al.  A method of viscoelastic stress analysis using elastic solutions , 1965 .