A Multiphysics Numerical Framework for Epoxy Resins

Abstract

Epoxy resins are increasingly used in critical structural components with widespread applications in the transportation, construction and energy industries. The wind energy sector is one of the fastest growing commercial markets for epoxy resins, meaning that the structural behaviour of epoxy resins is becoming a key area of research, especially regarding its application to wind turbines. Wind turbines, particularly those in off-shore installations, are subject to a wide range of environmental conditions, most notably large variations in humidity and temperature. Both moisture and increased temperatures have been observed to have a significant impact on the stiffness and strength of epoxy resins. These environment effects, coupled with complex time dependent mechanical behaviour, means that the accurate prediction of the structural performance of epoxy resins has not yet been fully described.

This thesis presents a multiphysics framework for the simulation of hygrothermal ageing in epoxy resins. The constitutive model formulated in this thesis consists of a non-linear viscoelastic and viscoplastic mechanical model, physically coupled with a Fourier heat conduction model and a Fickian diffusion model. Degradation based on a glass transition surface is implemented to describe the multi-state behaviour of epoxy resins. To justify the model assumptions, DMA and creep tests are performed on epoxy resin specimens and their temperature dependent mechanical behaviour is established. A number of numerical benchmark tests and case studies are performed using a finite element implementation of the numerical framework. It is shown that the multiphysics framework can capture the characteristic mechanical and hygrothermal ageing behaviour exhibited by epoxy resins. Recommendations are provided for further development of the numerical model and calibration of the material properties. In a secondary study, a mesh sensitivity analysis is performed on an existing viscoelasitc-viscoplastic-damage model and recommendations for an improved formulation are provided.