Numerical Analysis of Micro-Residual Stresses in a Carbon/Epoxy Polymer Matrix Composite during Curing Process

Area of Science:

• Materials Science
• Mechanical Engineering
• Composite Materials

Background:

• Thermoset-based carbon fiber-reinforced polymers (CFRPs) undergo curing, transforming from gel to solid state.
• Micro-residual stresses arise from differing fiber and polymer properties during curing, impacting mechanical performance.
• These stresses can initiate failure propagation, especially in thinner fiber gaps.

Purpose of the Study:

• To analyze micro-residual stress development in CFRPs using computational micromechanics.
• To predict the influence of these stresses on the mechanical performance of unidirectional CFRPs.
• To investigate the effect of various parameters on micro-residual stress levels and strength properties.

Main Methods:

• Development of a representative volume element (RVE) numerical model in Abaqus®.
• Simulation of the thermo-curing process coupled with a mechanical constitutive model using user-subroutines.
• Experimental characterization of bulk resin properties and curing behavior for model setup.

Main Results:

• Micro-residual stresses peak in thinner fiber gaps, exceeding the resin's yield stress (55 MPa) without causing damage.
• Transverse strength is reduced by at least 10%, while elastic properties remain largely unaffected.
• Numerical predictions of effective properties align well with macro-scale experimental measurements.

Conclusions:

• Micro-residual stresses significantly impact the transverse strength of CFRPs.
• Sensitivity analysis shows thermal expansion, chemical shrinkage, resin modulus, and cure temperature influence stress levels and strength.
• Computational micromechanics provides accurate predictions of stress development and mechanical performance in CFRPs.