Damage modelling of epoxy material under uniaxial tension based on micromechanics and experimental analysis

Abstract

Epoxy is a widely used thermosetting polymer in various engineering fields to develop composites. Studying its damage and fracture behaviour under various loading conditions is highly important. In this work, a micromechanics-based damage model is developed for understanding the damage initiation and growth in epoxy. To support this damage model, tests are performed for obtaining mechanical properties and to study the damage behaviour of epoxy. Diglycidyl ether of bisphenol A (DGEBA) resin with triethylenetetramine (TETA) hardener in 10:1 ratio are mixed and cured to make the epoxy. To give a physical meaning to damage, the model quantifies the damage as volume fraction of a spherical void in a unit representative volume element (RVE) of epoxy material. Degraded effective properties are computed for damaged RVE using standard mechanics-based micromechanical approach. A second-degree polynomial is established for effective stiffness with damage at any loading instance. This functional form of degraded stiffness in terms of damage is used in constitutive relations. A strain energy- based approach is used to compute thermodynamic forces, a state variable used for the evolution of damage. A damage evolution model is proposed with two material-specific parameters which are determined using experimental tests. The model is implemented by user material subroutine (UMAT) in commercial finite element software, Abaqus/Standard. The proposed model accurately captures the tensile behaviour of the epoxy material and gives capability to simulate an epoxy material’s damage behaviour from its initiation till failure or macrolevel rupture under uniaxial tensile loading. The developed model predicts the behaviour of the material in agreement with experimental results.