Combined experimental/numerical investigation of directional moisture diffusion in glass/epoxy composites

Abstract

A combined experimental and numerical investigation is conducted on the anisotropic water diffusion behaviour of unidirectional glass/epoxy composites. Experimental diffusivity values are obtained by immersing thin material slices for each of its planes of orthotropy extracted from a thick composite panel and interphase measurements are performed using thermal analysis. In order to elucidate the observed anisotropy, the diffusion process is modelled at the microscale using a representative volume element (RVE) of the material with random fibre distribution. Water concentration gradients are applied to the micromodel and a homogenisation procedure is used to retrieve the macroscopic diffusivity coefficients. The influence of the interphase around the fibres on the diffusion process is modelled by making the matrix diffusivity a function of the distance to the nearest fibre using a level set field. The models are used to fit the experimental data and test a number of hypotheses that may explain the observed anisotropy. The effect of fibres acting as barriers for water movement is found to partially explain the observed transverse diffusivity. However, a fit is only obtained by allowing faster diffusivity at the interphase. In the longitudinal direction, a fit can only be found by allowing for orthotropic interphase diffusivity.

Effects of Hygrothermal Ageing on the Interphase, Fatigue, and Mechanical Properties of Glass Fibre Reinforced Epoxy

“…The measured or expected saturation values also appear reasonable. Authors such as Rocha et al [1,16] have published comparable results with detailed diffusion studies for comparable materials. With immersion in 50 • C salt water, a saturation of 1.07% mass gain was almost reached after 18 weeks.…”

“…Typically, the diffusion along the fibre direction is faster than transverse to it. As, for example, Rocha et al [16] studied the direction-dependent diffusion behaviour of salt water immersed GFRP samples at 50 • C, comparisons can be made. Even though the fibre and matrix composition differ slightly, the good accordance of the diffusion coefficients of the presented specimen and the results published for a transverse diffusion direction is noticeable.…”

A combined experimental/numerical investigation on hygrothermal aging of fiber-reinforced composites

“…This solution implicitly assumes that water diffusion in the resin is well represented by a one-phase Fick solution. The diffusivity vector is pre-computed through a homogenization process [34] and is considered constant, leading to a linear transient diffusion problem.…”

Degradation of basalt fiber–reinforced polymer bars in seawater and sea sand concrete environment

“…The OH − progression through the BFRP bar was observed at distinct temperatures 32°C, 40°C, 48°C, and 55°C and in a time period of 63 days with a homogenized diffusion value calculated referring Wang et al 25 However, literature evidence 40 suggests that in the interphase region closer to the fibers, diffusion may happen faster. Similarly, several studies also suggest diffusivity to be anisotropic 41 but have realized the value to be approximately similar in the x and y directions. However, some papers 21,42 have provided different diffusivity values for fibers and resins as the composite bars are a heterogeneous material but have ultimately used the homogenized value for further calculations.…”