Influence of microstructural defects and hydrostatic pressure on water absorption in composite materials for tidal energy

Abstract

The lifespan and economic viability of tidal energy devices are constrained, in part, by the complex degradation of the tidal turbine blade materials due to prolonged immersion in a hostile sub-sea environment. Seawater penetration is a significant degradation mechanism in composite materials. This work aims to investigate the influence of microstructure and hydrostatic pressure on water absorption in four polymer composites which are candidate materials for use in tidal energy devices. These materials are: a Glass Fibre (GF) powder epoxy, a Carbon Fibre (CF) powder epoxy, GF Ampreg epoxy and a chopped fibre GF Polyether Ether Ketone (PEEK). X-ray CT (computed tomography) is used to characterise the voids, resin-rich areas and other manufacturing defects present in each material. These defects are known to significantly alter the rate of moisture diffusion, as well as the total uptake of water at saturation. The samples are then exposed to accelerated water aging and hydrostatic pressurisation in order to simulate a range of expected sub-sea operating conditions. The 2 material micro-structure, the matrix material and pressurisation level are shown to strongly influence both the moisture absorption rate and total water uptake. Significant volumetric changes are also noted for all samples, both during and after aging. X-ray CT scans of specimens also provide a unique insight into the role of voids in storing water once a material has reached saturation.

Optimisation of Water Absorption Parameters of Dual-Filler Filled Composites Using Taguchi and Moderated Taguchi Techniques

“…From the extensive literature review, it was noted that investigations concerning the novel ways to establish the optimal parametric setting which produce minimum water absorption in dualfiller epoxy composites are missing (Ajibade et al, 2017a,b,c;Grogan et al, 2018).…”

“…It was declared that the uptake of water for the jute-fortified composite together with its hybrids by means of glass with or without carbon obeys Fickian-similar characteristics. Grogan et al (2018) study the impact of microstructure as well as hydrostatic pressure on the absorption of polymer composites by water since they are to be used as structures in devices for tidal energy development. It was disclosed that defects developed changed the complete uptake of water during the saturation state.…”

Optical Fiber Sensors for the Detection of Hydrochloric Acid and Sea Water in Epoxy and Glass Fiber-Reinforced Polymer Composites

“…It is apparent from this table that the hydrostatic pressure affects the diffusion coefficient of water at 80 °C. Several studies have attempted to clarify the effect of hydrostatic pressure on water diffusion in composite materials [16,17,18], but the published results are contradictory. However, it is difficult to foresee, in general terms, the role of hydrostatic pressure, since the overall effect is due to a balance between the free-volume reduction (due to the increasing compression forces on the composites) and the increase of the absorption driving force (due to the increasing chemical potential in the liquid phase).…”

Manufacture of High-Performance Tidal Turbine Blades Using Advanced Composite Manufacturing Technologies

“…Similar to a number of previous studies (Grogan et al [18] and Walls et al [6]), test specimens were placed in an water conditioning tank at 50 °C, in order to accelerate the aging of the composite material over the period of the testing programme. Along with the test specimens, two sets of traveller specimens, which were 25 × 25 mm and either 1 mm or 2 mm in thickness, were also immersed in the water conditioning tank in order to monitor water absorption of the composite material by recording the change in mass of the specimens.…”