Anisotropic water diffusion in mechanical joints of fiber-reinforced composite panels: numerical study
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TECHNICAL PAPER
Anisotropic water diffusion in mechanical joints of fiber‑reinforced composite panels: numerical study Edmunds Zīle1 · Andrey Aniskevich1 · Daiva Zeleniakiene2 Received: 24 January 2020 / Accepted: 13 August 2020 / Published online: 25 August 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020
Abstract This paper presents numerical study on the effect of diffusion anisotropy on the accumulation of moisture in the net-tension and shear-out failure planes in fiber composite bolted connection. A composite plate containing four bolt holes was investigated. The effect of the edge distance-to-hole diameter ratios and the distance between two holes-to-hole diameter ratio was analyzed. The diffusion process was described by Fick’s law, and it was assumed that moisture is penetrating only through bolt holes in the composite joints. Technical computing software Mathematica was used to solve the 2D diffusion equation over the plate region and find the moisture concentration distribution. The numerical approach was validated against analytical expressions for diffusion in 2D plate. It was found that diffusion anisotropy ratio strongly influences the equilibrium moisture content. It was shown that depending on the joint geometry, there are significant differences in moisture content on the expected failure paths because of sorption anisotropy, which can lead to premature failure due to the increased damage done to the composite matrix, interface, interphase, and fibers. Keywords Composite · Water diffusion · Bolted connection · Numerical
1 Introduction Fiber-reinforced polymer (FRP) composites are widely employed in aerospace, automotive, and marine industries. Composites have advantages of high specific strength and stiffness over metals which greatly reduce the weight of the structure and lead to the cost savings. Mechanical joints with fasteners such as bolts, rivets, pins, and screws are widely used to join together laminates parts to obtain the specific geometry and features for various applications. Example geometry of the plate with four bolt holes and notations is shown in Fig. 1. The main issue associated with the mechanical joints is the presence of regions with high stress concentrations due
Technical Editor: Paulo de Tarso Rocha de Mendonça. * Edmunds Zīle [email protected] 1
Institute for Mechanics of Materials, University of Latvia, Riga 1004, Latvia
Department of Mechanical Engineering, Kaunas University of Technology, 51424 Kaunas, Lithuania
2
to the introduction of structural discontinuities such as holes which reduce the efficiency of the joint. Pin joints are often used because of their low cost, simplicity, and easy disassembly for repair. Common failure modes of pin joint composite plates are shown in Fig. 2. These modes are identified as net-tension, shear-out, and bearing depending on the joint geometry, arrangement of laminates, and fiber orientation angle [1]. In addition, the failure may consist of mode combinations such as cleavage which is comb
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