Cyclic viscoelastic-viscoplastic behavior of epoxy nanocomposites under hygrothermal conditions: A phase-field fracture model

Abstract

In this study, a finite deformation phase-field formulation is developed to investigate the effect of hygrothermal conditions on the viscoelastic-viscoplastic fracture behavior of epoxy nanocomposites under cyclic loading. The formulation incorporates a definition of the Helmholtz free energy, which considers the effect of nanoparticles, moisture content, and temperature. The free energy is additively decomposed into a deviatoric equilibrium, a deviatoric non-equilibrium, and a volumetric contribution, with distinct definitions for tension and compression. The proposed derivation offers a realistic modeling of damage and viscoplasticity mechanisms in the nanocomposites by coupling the phase-field damage model with a modified crack driving force and a viscoelastic-viscoplastic model. Numerical simulations are conducted to study the cyclic force-displacement response of both dry and saturated boehmite nanoparticle (BNP)/epoxy samples, considering BNP contents and temperature. Comparing numerical results with experimental data shows good agreement at various BNP contents. In addition, the predictive capability of the phase-field model is evaluated through simulations of single-edge notched nanocomposite plates subjected to monolithic tensile and shear loading.

Figures (8)

• Figure 1: Planar dimensions of the specimen for conditioning and mechanical loading-unloading tests with a thickness of 2.3 mm. All dimensions are in millimeters.
• Figure 2: Loading and boundary conditions imposed on quarter of the specimen because of symmetry, and a two-dimensional FE model composed of 1563 Q4 elements.
• Figure 3: Effect of moisture on the force–displacement response of the epoxy at room temperature and the deformation rate of 1 mm/min: (a) dry sample, and (b) saturated sample.
• Figure 4: Contour plots of damage in the dry epoxy sample for imposed displacements of (a) 3.32 mm, (b) 3.34 mm, and (c) 3.35 mm.
• Figure 5: Effect of moisture on the force–displacement response of BNP(5 %wt)/epoxy at room temperature and the deformation rate of 1 mm/min: (a) dry sample, and (b) saturated sample.