Two-Dimensional Cure Simulation of Thick Thermosetting Composites

Abstract

An investigation into the two-dimensional cure simulation of thick thermosetting composites is presented. Temperature and degree of cure distributions within arbitrary cross-sectional geometries are predicted as a function of the autoclave temperature history. The heat conduction equation for two-dimensional, transient anisotropic heat transfer is coupled to the cure kinetics of the thermosetting composite material. A heat generation term, expressed as a function of cure rate and the total heat of reaction, is introduced to account for the heat liberated during the curing process. A generalized boundary condition formulation is employed, enabling arbitrary temperature boundary conditions to be enforced straightforwardly. An incremental, transient finite difference solution scheme is implemented to solve the pertinent governing equations and boundary conditions. The boundary-fitted coordinate system (BFCS) transformation technique is combined with the Alternating Direction Explicit (ADE) finite difference method in the solution strategy. Complex gradients in temperature and degree of cure are predicted and the influence of the tool on the curing process is demonstrated. Correlation between experimentally measured and predicted through-the-thickness temperature profiles in glass/polyester laminates are presented for various arbitrary temperature cure cycle histories. Several typical glass/polyester and graphite/epoxy structural elements of arbitrary cross-section (ply-drop and angle bend) are analyzed to provide insight into the non-uniform curing process unique to thick-sections. Spatial gradients in degree of cure are shown to be strongly dependent on part geometry, thermal anisotropy, cure kinetics and the temperature cure cycle. These spatial gradients directly influence the quality and in-service performance of the finished component by inducing warpage and residual stress during the curing process.

Multiscale Modeling of Residual Stress Development in Continuous Fiber-Reinforced Unidirectional Thick Thermoset Composites

“…Typically, these models involve three aspects: first, the coupled solution of cure kinetics and heat transfer equations to obtain the temperature and degree of cure profiles in the part; this is especially important for thick composites [8][9][10]; second, the development of models for resin, laminate, and composite property evolution with cure and temperature; and third, the solution of the structural mechanics equations to estimate the induced strains and residual stresses in the part. Models for composite property evolution during cure can be based on direct experimental measurements on the composite itself during cure [11][12][13][14].…”

“…In the subsequent, a simple implementation of the multiscale modeling framework is demonstrated in the context of a thick unidirectional continuous-glass-fiber-reinforced thermoset polyester matrix composite; this polyester system has been characterized by Bogetti and Gillespie [9,15]. The implementation of the first step of the multiscale modeling framework is described in Section 2; in this section the correlations derived by Bogetti and Gillespie [15] for calculation of the average properties of the unidirectional composite using self-consistent field micromechanics theory are summarized.…”

“…The composite system, composed of a polyester matrix unidirectionally reinforced with continuous glass fibers, was studied by Bogetti and Gillespie [9,15]. The properties of the resin, reinforcing fiber, and the composite are described subsequently in terms of three principal directions.…”

“…Cure process models provide a valuable tool to understand the effect of composite microstructure, part geometry, and processing parameters on the development of residual stresses; such models also provide a relatively inexpensive virtual means of optimizing cure processing to minimize the residual stresses. Process models for composite cure are available that address residual stress development at the part level [6,[8][9][10][11][12][13][14][15][16][17][18] or at the "meso" levels involving the microstructure or fiber-matrix interface [19][20][21][22][23]. However, a systematic framework for bridging the information at the two scales has not been demonstrated; such bridging of information is critical for obtaining realistic estimates of residual stresses at the fiber matrix interface and for arriving at an understanding of the efficacy of reinforcement.…”

Tooling design and microwave curing technologies for the manufacturing of fiber-reinforced polymer composites in aerospace applications

“…The study of processing a thick composite laminate found a very low heating rate before gel point which can control the temperature in an allowed range. But the manufacturing time is increased by 27% [74][75][76]. Autoclave curing thick-section laminates may cause anisotropy of viscosity and degree of curing.…”