Composite Curing Simulation in Abaqus: A Practical Implementation Guide

1. Core Methodology and Governing Equations

Composite curing simulation in Abaqus couples thermo-chemical and mechanical analyses to predict residual stresses, dimensional changes, and final material properties. The implementation revolves around solving the heat transfer equation with an internal heat generation term from the exothermic resin reaction:

ρC_p ∂T/∂t = ∇·(k∇T) + ρH_r dα/dt

Where dα/dt is the cure kinetics rate, typically modeled using the autocatalytic Kamal-Sourour equation:

dα/dt = (k_1 + k_2 α^m)(1 - α)^n
k_i = A_i exp(-E_i/RT)

Simultaneously, mechanical properties evolve from viscous fluid to elastic solid using user-defined field variables (USDFLD) or material models like CHILE (Cure Hardening Instantaneously Linear Elastic).

2. Step-by-Step Modeling Workflow

2.1. Material Definition and Property Evolution

Create temperature- and cure-dependent material properties in Abaqus/CAE using tabular data or user subroutines. Essential properties include:

Table 1: Required Material Evolution Tables

Implement using the Material → General → Depvar module with solution-dependent state variables (SDVs).

2.2. Cure Kinetics Implementation

Define the resin reaction model in a UMATHT or HETVAL subroutine. For standard kinetics without user coding:

1. Use Heat Transfer step with Internal Heat Generation
2. Define H_r (total heat of reaction) in material properties
3. Specify cure kinetics parameters via tabular input using User Defined Field

2.3. Coupled Temperature-Displacement Analysis Setup

Model → Edit Attributes → Analysis Type: Coupled Temp-Displacement
Step Module:
  - Create Step: Coupled Temperature-Displacement, Transient
  - Time period: Total cure cycle duration
  - Incrementation: Initial=0.01, Minimum=1e-10, Maximum=0.1*cycle_time
  - Solution Technique: Full Newton (recommended)

2.4. Boundary Conditions and Thermal Loading

Apply the autoclave or tooling temperature profile as a prescribed temperature boundary condition to all surfaces contacting the tool. For convective heating:

Load Module → Create Load → Surface film condition
  - Film coefficient: h (W/m²K)
  - Sink temperature: Use Amplitude to define cure cycle

3. Critical Modeling Strategies

3.1. Element Selection and Mesh Considerations

• Use coupled temperature-displacement elements (C3D8T or C3D6T for composites)
• Maintain aspect ratio < 10, especially through thickness
• Minimum 4 elements through ply thickness for accurate gradient capture
• Enable Hourglass Control with enhanced formulation

3.2. Contact Definition for Tool-Part Interaction

Interaction Module:
  - Contact Property: Tangential (friction=0.3), Normal (Hard Contact)
  - Thermal Conductance: Include for accurate heat transfer
  - Consider using *Contact Pair* rather than *General Contact* for stability

3.3. Residual Stress Calculation Methodology

Residual stresses develop from three mechanisms:

1. Thermal expansion mismatch between plies
2. Chemical shrinkage during cross-linking
3. Tool-part constraint during cool-down

Extract using Field Output Requests:

• S: Stress components
• TEMP: Temperature
• USER FIELD: Degree of cure (α)
• U: Displacements (for spring-in prediction)

4. Results Interpretation and Validation

4.1. Key Output Metrics

• Process-induced deformation (warpage, spring-in)
• Through-thickness cure gradient (ΔT_max < 10°C typically)
• Final degree of cure (α > 0.95 for full cure)
• Residual stress distribution (interface between plies critical)

4.2. Post-Processing Workflow

1. Plot temperature vs. time at center and surface nodes
2. Compare with DSC experimental data for cure validation
3. Extract path plots of stress through critical sections
4. Animate deformation to identify warpage modes

5. Common Pitfalls and Best Practices

5.1. Convergence Issues and Solutions

5.2. Computational Efficiency Optimization

• Use symmetry where possible (¼ or ½ models)
• Implement adaptive time stepping with maximum increment limits
• Store only essential field outputs (reduce .odb size by 60%)
• Consider Model Change for tool removal simulation

6. Advanced Extensions and Applications

6.1. Multi-Scale Modeling Integration

Link macro-scale cure simulation with:

• Micro-mechanics (Digimat-MAP) for ply-level properties
• Process optimization (Isight coupled simulation)
• Structural performance (co-simulation with fatigue analysis)

6.2. Manufacturing Defect Prediction

Extend the model to predict:

• Porosity formation (void growth models)
• Fiber washing in infusion processes
• Interply shear during layup

7. Conclusion and Next Steps

Successful composite curing simulation requires careful attention to material evolution, cure kinetics implementation, and boundary condition representation. The methodology outlined provides a robust framework for predicting process-induced deformations and residual stresses that directly impact dimensional tolerances and structural performance.

For advanced applications, consider implementing stochastic methods to account for material variability, or coupling with computational fluid dynamics for autoclave flow uniformity analysis. Validation against experimental data—using Digital Image Correlation for displacements and embedded sensors for temperature—remains essential for model credibility and refinement.