PSI - Issue 17

Waleed H. Alhazmi et al. / Procedia Structural Integrity 17 (2019) 292–299 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Fiber reinforced polymer, FRP, plates and sheets have been increasingly used in the construction industry due to their superior properties (Li 2003). There is no doubt about the simplicity of this technique or about the high corrosion resistance and high stiffness and strength to weight ratios of FRP. Although the effect of introducing holes into the unidirectional FRP section requires careful design, the ROBUST project concluded that the bolted plate end anchorage system is both practical and effective (Hollaway and Leeming 1999). It is worth to note that, the ROBUST bolted anchorage system used 15 mm thick bonded GFRP anchorage block to ensure the composite plate sustains no damage due to the introduction of the drilled hole which is associated with high localized stress concentrations. Fatigue damages in FRP have been extensively investigated (Plumtree and Sorensen 2002; Ormiston and Hodges 1972; Salkind 1972). Salkind (1972) found that, the S-N (stress versus number of cycles to failure) curve of boron epoxy composite is much flatter than the S-N curves of the metals. The susceptibility of composite materials to effects of stress concentrations such as those caused by notches, holes, etc., is much less than for metals (Salkind 1972; Plumtree and Sorensen 2002). Failure in long fiber-reinforced laminated composite structures containing stress concentration areas, such as circular holes or bolt-loaded holes, has been one of the technological issues by many researchers during the last decades (Huh and Hwang 1999; Chen 2001). The mechanisms of such failures are significantly affected by fiber orientation, relative strength of the matrix and fiber and the bond strength between them. The main objective of the present work is to understand the failure mechanism of unidirectional carbon FRP plate containing a circular hole or a bolt-loaded hole subjected to uniaxial either static or cyclic loading. 2. Background 2.1. Failure Modes in Tensioned FRP plate Containing a Circular Hole A circular hole in tensioned FRP plates may be classified into three types as follows (Yan et al. 1999): (1) open hole tension: the FRP plates were subjected to uniaxial tension with no constraint imposed on the hole, (2) filled hole tension: a bolt, ϕ = dB, was inserted inside the hole, ϕ = dH, with/without a clamp-up load. A washer, ϕ = dW, was inserted between a bolt head and tail and the FRP plate to distribute the clamp-up load. The FRP plates were subjected to uniaxial tension, and (3) bolted joint, bolt-loaded hole: double-lap bolted joints were subjected to a uniaxial load with/without clamp-up load. In the case of open-hole tension, the mode of failure mainly depends on the fiber/matrix interface. A weak interface results in longitudinal crack propagation along the interface, while a strong interface results in transverse crack propagation across fibers leading to premature composite failure. However, an interface of intermediate strength leads to optimum composite performance between these extreme conditions. Based on the specimen geometry and the interfacial strength of unidirectional FRP, the crack emanating from notches, such as circular holes, may grow parallel to the loading and fiber direction, i.e. notch insensitive (Rao, Odette, and Ritchie 1992). There are five basic failure modes in mechanically fastened joints in FRP (Yan et al. 1999): net-tension, shear-out, bearing, cleavage and pull-through. Net-tension failure is associated with matrix and fiber tension failures due to stress concentrations. Bearing failure leads to an elongation of the hole. Shear-out failure can be regarded as a special case of bearing failure. Shear-out and bearing failures result primarily from the shear and compression failures of fiber and matrix. Cleave failures are associated with both an inadequate end distance (e) and too few transverse plies. Pull-through failure occurs mainly with countersunk fasteners or when the plate thickness (t) to hole diameter (dH) ratio, t/dH, is sufficiently high to precipitate failure. 2.2. Stress Concentration Factor in Composite Materials Containing an Open Circular Hole Open holes, notches, scratches, inclusions, and so on, all produce concentrations of strain and stress. Stress concentrations can seriously weaken brittle materials and can shorten the fatigue life of both ductile and brittle