SEM of Erosive Wear Mechanisms of Kevlar Fiber Reinforced Composites

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The use of laminated composite materials, such as glass fiber reinforced polymers (GFRP), offer better advantages over traditional materials such as steel, aluminum and wood, in their mechanical and physical properties such as: rigidity, mechanical resistance, low density and greater durability for design purposes of marine structural components such as boats, ships, marine platforms, including wind and hydrokinetic turbine blades [1]. However, when these materials are exposed to severe environmental and climatic conditions such as high humidity, changes in temperature, ultraviolet radiation, rain and seawater aging, their mechanical properties are severely affected [2]. The effect of saline water aging on the mechanical properties of composite materials reinforced with glass fiber and kevlar has been studied [3]. The effects of aging on the mechanical behavior of materials composed of epoxy resin with glass fiber and kevlar fiber were studied. On the other hand, the erosion behavior of solid particles in epoxy composites reinforced with unidirectional fiberglass and carbon has been investigated. SEM images revealed that erosion is characterized by microcracking and detachment of fibers from the matrix [4]. The study of composite materials exposed in saline environments allows us to understand the effects that this aggressive environment causes on these materials for applications in the manufacturing of components such as hydrokinetic turbine blades [5]. This work is carried out with the purpose of knowing the wear mechanisms due to the effect of erosive wear that occurs in composite materials in aged (exposed to saline water) and un-aged conditions. Tests were carried out on hybrid laminated compounds (carbon with kevlar), reinforced on their surface with kevlar fiber. Laminated composites were manufactured with hybrid fiber, adding to the arrangement two layers of kevlar fibers on the external surface as reinforcement and Epolam 2015 resin was used as a matrix. In the stacking of the fibers, an arrangement bidirectional 0/90° was considered. To obtain the composite materials, the vacuum-assisted resin infusion manufacturing process was used. The accelerated aging process was carried out by immersion in saline water using a Cole-Parmer thermostatic bath with a capacity of 20 l. The saline water was prepared by mixing purified water and salt pellets until reaching 3.5% salinity. For the erosive wear tests, the following was considered: sea sand impact speed of 4.7 m/s, an impact angle of 90°, sand flow pressure of 4.5 bar (450 kPa) and a room temperature of 20°C were used. To observe the erosive wear mechanisms, a JEOL JSM-6610LV scanning electron microscope was used. In Figure 1, the effect of erosion by solid particles, caused in the fibers is observed, where the mechanism of plastic deformation and the shear action, caused by the impact of the sand particles can be seen; with the plastic deformation being more evident in the fibers of the laminated composites subjected to the aging process with respect to the un-aged laminated composites; which manifests itself as a lower plastic deformation in the matrix that was not exposed to aging, being harder and less ductile, and is also reflected as a greater tearing of the fibers [6, 7]. Surfaces of specimens and SEM images of erosion effects on fibers. a) Un-aged, b) Aged.