Meaning
Numerical simulation methods that calculate the distribution and evolution of temperature fields in complex geometries enable the design of safe and efficient cure cycles for composite parts. In industrial applications, finite element heat transfer analysis is used to predict thermal gradients and prevent localized overheating. This method divides the physical part and its tooling into a grid of smaller elements to calculate thermal conduction and heat generation.
Accurate simulations are critical for thick-section parts where internal exotherms can exceed the degradation temperature of the polymer.
Thermal Modeling
Transient thermal behaviors of the tool and composite are solved by applying conservation of energy equations across the discretized mesh. When employing finite element heat transfer calculations, the anisotropic thermal conductivity of the composite laminate must be accounted for, as heat flows much faster along the fiber direction than through the thickness. The simulation incorporates heat transfer coefficients at the boundary surfaces to represent convection from the oven or autoclave gas.
This detailed modeling prevents the formation of thermal stresses that lead to warping after the part is cooled and removed from the mold.
Cure Kinetics Integration
Thermal calculations must be coupled with chemical reaction models to account for the heat generated by the exothermic polymerization. As the reaction proceeds, it acts as an internal heat source that varies with temperature and conversion. The simulation updates the thermal properties of each element at each time step, capturing the feedback loop between temperature and cure rate.
Process Validation
Discrepancies between the calculated temperatures and the sensor readings are used to refine the boundary conditions of the model. This validation step is required before the simulation can be used to sign off on production heating profiles. High-fidelity results reduce the need for physical trials, accelerating the path from prototype to qualified production part.
