Plate N Sheet 4 Crack [UPDATED]
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Analytical and numerical models are presented to simulate the failure of RC beams strengthened with FRP plates and flexible sheets. Different failure mechanisms, from ductile to brittle, can be simulated and verified. The proposed analytical model takes into account the influence of concrete confinement in the compression zone due to the presence of the stirrups and the tensile softening properties of concrete. This allows following more accurately the crack propagation and the failure mechanism of the flexural member. The numerical model is based on finite element analysis (FEA), follows the smeared crack approach, and uses standard elements available in a commercial package. Comparisons with experimental data obtained from strengthened RC beams tested in the laboratory are presented.
In this paper, Charpy impact tests were conducted on cracked aluminum plates repaired with FML composite patches. The effects of the crack characteristics and patch lay-up sequence on the energy absorption of the specimens were investigated experimentally. In order to reduce the test numbers, the design of experiments method was used, and the results were predicted by response surface method. The effect of repairing on the fracture parameters [stress intensity factor (SIF), J-integral, and crack propagation direction (CPD)] at the crack front was calculated using three-dimensional (3D) finite element analysis. The results show that the value of the energy absorption increases when the crack angle increases and that the patch lay-up sequence has a significant role on the efficiency of the repair. When the location of the metal layer of the patch is near the repaired surface of the specimen, the value of the energy absorption increases.
Many researchers calculated the stress intensity factor (SIF) at the crack tip of repaired cracks. Among them, Callinan et al. [11], Jones and Chiu [12], Chung and Yang [13], Bachir Bouiadjra et al. [14], and Ayatollahi and Hashemi [15] used the finite element (FE) method to investigate the effect of composite patching on the SIF of a crack as an important measure for analyzing the performance of the composite reinforcement technique.
Tsai and Shen [16] obtained the SIF for thick aluminum plates having a central crack in both repaired and unrepaired cases. They showed that the SIF decreased in the presence of composite patch and that SIF variation was very significant in a doubly asymmetric plate.
Ouinas et al. [17] performed a numerical investigation on cracked aluminum plate repaired with octagonal composite patch in mode I and mixed mode conditions. They examined the effect of mechanical and geometrical properties of the patch on the SIF in the crack tip. They concluded that the SIF at the crack tip is inversely proportional to the increase in the patch rigidity. They also observed that in mixed mode condition, the reduction of the SIF value in opening mode (mode I) is more important than that in shear mode (mode II).
Nabousli et al. [18] performed nonlinear analysis of the adhesively bonded composite patch to investigate its effects on the damage tolerance of the repaired structure. They showed that the crack-opening displacement and the SIF value of the repaired plate in geometrically nonlinear analysis are smaller than the ones in the linear analysis. Chung and Yang [19] conducted experimental tests on thick Al6061-T6 panels repaired by a single-sided fiber-reinforced composite patch. They showed that the fatigue life of the patched plates increases about four to six times compared to that of the unpatched plates.
Okafor et al. [20] used adhesively bonded composite patches for repairing cracked aircraft aluminum panels. They found that the maximum skin stress decreases significantly after the patch is bonded. The maximum value of skin stress occurs at the crack tip when the panel is unpatched, whereas for the patched panel it shifts to the patch edges.
Sabelkin et al. [21] performed experimental and analytical investigations on fatigue behaviors of cracked 7075-T6 aluminum panels repaired by one-sided adhesively bonded composite patch. They observed that the residual strength and the fatigue life of the patched panels increase considerably.
Khalili et al. [23] conducted the Charpy impact test on edge-cracked aluminum plates repaired with one-sided composite patch. They noticed that the carbon patches have better characteristics than glass patches in reinforcing the cracked plates. In another similar research [24], they repaired notched aluminum specimens with metallic, composite, and FML patches. They observed that FML patches were more effective than the other patches in reinforcing the notched specimens.
The aim of the present study is to assess the effect of crack characteristics (crack length and crack angle) and patch lay-up sequence on single-sided cracked aluminum plates repaired with the FML composite patches on one side. For this purpose, Charpy impact tests were conducted on the patched and unpatched cracked specimens. The effect of repairing on the fracture parameters such as SIF, J-integral, and CPD at the crack front was also calculated using 3D FE analysis (FEA).
In the present study, the cracked specimens are made of aluminum alloy plate AA1035 (Vatco Co., Tabriz, Iran) [25]. The thickness of the specimens is 3 mm. The mechanical properties of this material were measured by tensile test (Alborz koosha Co., Tehran, Iran) according to ASTM E8M 09-2010 standard [26] and are given in Table 1. The geometry of the patched specimens is shown in Figure 2. The uncracked specimens were prepared with a water jet machine (HYDRAjet, GA, USA). Then, an initial crack was generated in the specimens by a wire cutting machine (Charmilles, Russia) (electrical discharge machining). This paper takes into account the effect of two main crack characteristic parameters: the crack length and the crack angle. Three different crack lengths and crack angles were considered. The ratio of the initial crack lengths to the specimen width (a/w) was considered to be equal to 0.1, 0.3, and 0.5. The crack angle θ was also considered to be θ=0°, 30°, and 45° (Figure 2). Figure 3 shows nine different configurations of the specimens.
The FML composite patches were fabricated with two woven glass fiber (T (90°)/M200-E10, China) as the fiber (F hereinafter) layers and one thin aluminum (A, hereinafter) sheet (AA1035, 0.3 mm) as the metal layer. In this study, the effect of the FML patch lay-up sequence is investigated. For simplification, different codes were assigned to each specimen. The codes B and C refer to the unpatched and patched specimens, respectively.
Three different patch lay-up sequences were performed on the cracked specimens. The code C1 represents the patch lay-up sequence of fiber-fiber-aluminum (F-F-A). This means that the fiber layer is bonded to the cracked plate and the metal layer is on the furthest point from the repair surface. Similarly, the code C2 demonstrates that the lay-up sequence is A-F-F, and finally, the code C3 shows that the lay-up sequence is F-A-F. In the case of C2, the metal layer is exactly bonded to the cracked specimen, whereas in C3 the metal layer is in the middle of the patches. The digits after the letter C correspond to patch lay-up sequence, crack length, and crack angle, respectively, which are described in Table 2. The digits after the letter B correspond to crack length and crack angle, respectively.
In this section, nine different configurations of unpatched cracked specimens were tested. Figure 6 and Table 3 depict the results of these tests. It is clear that when the crack length increases, the value of the energy absorption decreases. It can also be observed that the value of the energy absorption increases when the crack angle increases. This is due to the mix mode condition at the crack tip for crack angles 30° and 45°. In these cases, the crack propagation direction (CPD) changes to 0° (mode I) after impact, as shown in Figure 7. This change in CPD leads to more energy absorption.
The value of energy absorption is 53 J for the uncracked specimen. This value decreases to 20.83 J for a crack length ratio of a/w=0.5. When the crack angle changes from 0° to 45°, the value of the energy absorption increases more than 20% for the unpatched specimen with a crack length ratio of a/w=0.5. Similarly, this difference for the ratios a/w=0.3 and a/w=0.1 are equal to 9% and 2%, respectively. When the crack length increases, the crack must extend a longer distance to reach mode I condition, and therefore, the amount of energy absorption increases.
The energy absorption value of untested specimens can be predicted by using Eq. (1). Figure 8 depicts the 3D response surface plot of the predicted model. This figure demonstrates the effect of FML patch type (X1) and crack angle (X3) on energy absorption values for the specimens with the crack length ratio of a/w=0.5.
The amount of energy absorbed by the structure changes with the patch lay-up sequence variation. The maximum energy absorptions were related to C2 patch types, which consisted of the A-F-F lay-up sequence. It can be concluded from the obtained results that the location of the metal layer in the patch lay-up has a significant role in the efficiency of the repair. When the location of the metal layer is near the base structure (patch type C2) the value of the energy absorption increases and vice versa. Whenever the metal layer is near the repaired surface, the whole structure becomes more ductile. Therefore, the structure can absorb more energy. Brittle fracture occurs when the metal layer is placed in the middle of the patch lay-up or even farther from the repaired surface. This is because the fiber layer is less ductile. For example, when the fiber layer fails, the metal layer fails suddenly, too. It is worth mentioning that the effect of the crack characteristics (crack length and crack angle) is not notable when the specimens are repaired with C2 type patches. 2b1af7f3a8