Papers by Keyword: Composite Patch

Abstract: This work consists of the study is to analysis by the finite element method the effect of the ageing of the adhesive exposed simultaneously to the temperature and water on the degradation of its mechanical properties and consequently on the transfer of loads from the plate to patch. The stress intensity factor was evaluated according to immersion time and temperature. Several parameters have been taken into consideration, namely the properties of the composite patch, temperature, water absorption, rate and length of crack, the distribution of maximum shear stresses in the adhesive and peel in the patch were also analyzed.

Abstract: In addition of binding the patch to the cracked material, adhesives play an important role in bonded composite repair because they make the bridge of transfer of loads between the patch and the cracked material. Indeed, any damage in adhesives will affect the efficiency and the performance of the repaired structure by composite patches.In this paper, two different adhesive shapes were numerically investigated, using finite element method in order to estimate the damage zone area on the adhesive bonded composite repair in 5083 marine grade aluminum alloy and its effect on the efficiency and performance of the repaired structure. The obtained results proved that the circular shape causes less damage than the rectangular one for the three crack lengths chosen. Moreover, both shapes of adhesive maintain their performance repair without disband risk and without reaching the critical value defined by Ban and co-authors (Dr=0.2474). Furthermore, it is concluded that the damage zone increases with the increase of the adhesive thickness and the decrease of the patch thickness and the use of circular shape is more effective than the rectangular one for the configurations and loading conditions studied.

Abstract: This paper describes an experimental study on the use of Lamb wave propagation for the integrity assessment of the composite patch system. Composite repairs are performed to the cracked specimen. Two piezoelectric sensors were installed around the composite patch. The piezoelectric sensor response was recorded periodically during the fatigue test. Three types of the damage index based upon the piezoelectric sensor response were selected and calculated to describe the health of the composite patch system. The results show that the damage index based upon the waveform relativity has the best correlations with the expanding process of the damage of the composite patch system.

Abstract: The effect of the graphite/epoxy composite patch parameters on the static and fatigue strength of the cracked aluminum plate was investigated experimentally. A series of specimens repaired by six types of composite patches including four different patch lengths and two different patch thicknesses were tested on the material tester. Specimens single-sided repaired and double-sided repaired by the same composite patches were also tested. The experiment results show that composite patches can provide an improvement in static and fatigue strength of the cracked aluminum plate, double-sided repair is more effective than single-sided repair, if the thickness and the length were selected properly, the composite patches can significantly enhance the strength of the repaired specimens.

Abstract: To cope with global warming and environmental protection in recent years, the requirements for clean energy are enhancing, and the installation of wind power, as one of such energy, is increasing in various countries. Nevertheless, the connection of wind blades and support blades often break when wind turbine are running. To avoid such a problem in the design stage or the successive reinforcement through proper methods has become an urgent problem in engineering. Commercial software, Solidworks Simulation, is used for simulating stress distribution and the patch reinforcement design in this paper. The analyses show that the maximum stress of the original design not being reinforced with patches has exceeded the tensile strength of the material and result in the breaks and damage of the entire structure. Using composite patches to reinforce the interface of wind blades and the supportive structure could effectively reduce the maximum stress and the displacement of deformation. Moreover, patches could effectively reduce the maximum stress that the optimal reinforcement should take a larger fillet into account.

Abstract: In this study, finite element method is used to investigate the fracture analyses, crack growth trajectory and fatigue life of curved stiffened panels repaired with composite patches subjected to combined tension and shear cyclic loadings. For this purpose, 3-D finite element modeling are performed for consideration of real 3-D crack-front in general mixed-mode conditions. Contact elements are used between the crack surfaces on two crack sides to prevent interferences of crack surfaces and a complementary program was developed to handle the automatic fatigue crack growth modeling. The effects of various patch layups and shear-tension loading ratios on fracture parameters of the aluminum panel are investigated. It is shown that in low shear to tension ratios like 0.4, the patch layup of [90]₄ (perpendicular to the initial crack) is more efficient than the patch with layups angle along the tension loading. As the shear to tension ratio increases, effect of patch layups with orientations of almost perpendicular to the crack trajectory on fatigue crack growth life is increased comparing with the patch layups parallel to the tension orientation like [90]₄.

Abstract: Multi-walled carbon nano-tubes and carbon fiber reinforced epoxy resin (MWCNTs/CF/EP) composite patch was prepared by the route of hot-melt impregnation. The results of the mechanical properties shown that adding MWCNTs had made the tensile strength and interlaminar shear strength increased by 9.79% and 3.1%, separatively. It was detected using the ultrasonic non-destructive technique that the composite patch had a good interlaminar combination with no defects as obvious resin enrichment or insufficient gel content except for some slight stratification phenomenon in few parts. The high heat-resistance obtained by TG.

Abstract: This study investigates the application of laminated composite patches for enhancement of flutter behavior of perforated metallic plates repaired with an external composite patch. Due to material anisotropy and discontinuity in geometry involved in flutter analysis of repaired plates, closed form solutions are practically unobtainable. Numerical studies using commercial finite element software were conducted to investigate the effects of variation in lamination parameters on the flutter boundary of perforated plates repaired with cross-ply composite patches. Both ply-level and sub-laminate level configurations are investigated. Presented results illustrate that flutter boundaries of perforated plates can be changed by choosing proper stacking sequence for composite patches.

Abstract: The performance of perforated metallic plates repaired with laminated composite patches is presented in this study. A square aluminum plate with a central circular cutout is considered as a damaged structural element. Numerical studies using commercial finite element code were conducted to investigate the effects of variation in laminate parameters such as number of plies, fiber orientation, and stacking sequences on free vibration responses of the repaired plates. Particular emphasis is placed on the effect of imperfect bonding (patch debonding). A quantitative measure for the effectiveness of the composite patches parameters is taken to be the relative change in natural frequencies of the deboned patches compare to the patches with perfect bonding. The results presented herein indicated that, vibration response of a repaired perforated metallic plate is affected by the number of plies, stacking sequences of the patch and the quality of bonding between the patch and the base plate.

Abstract: In this paper, fatigue crack growth trajectories, crack-front shape and life of the single-side repaired thick aluminium panels with glass/epoxy patch are analyzed. This investigation is performed using three dimensional finite element fracture analyses in general mixed-mode conditions (Mode I, II and III). The obtained fatigue crack growth trajectories, crack-front shapes and lives of the repaired panels with the patch lay-ups of [90]4 and [-45]4 are compared with the available experimental results produced by the authors.