Abstract:Crack propagation until fracture is an important criterion to predict a structure‘s service life. In order to increase the latter, the cracked component needs to be repaired or replaced. In the present study, a finite element analysis has been carried out to investigate the effects of adhesive thickness, patch thickness and crack length on the passive repair performance of a center-cracked rectangular aluminum plate under mode-I loading condition using an ANSYS package. A comprehensive parametric study shows t… Show more
“…31 For instance, thicker patches will lead to higher failure loads. 32,33 Upon investigating the failure surfaces for repaired samples, similar failure modes were generally observed for both repair methods, explaining the similar strength values presented in Figure 13. TW specimens repaired by US consolidation and vacuum bagging shown in Figure 14(a) and (b), and PW vacuum-bagged specimens shown in Figure 14(f), characteristically failed by net tension failure.…”
Section: Mechanical Testingsupporting
confidence: 62%
“…31 For instance, thicker patches will lead to higher failure loads. 32,33 Figure 13.Strength of open-hole and repaired samples from configuration shown in Figure 5 for UD, PW, and TW laminates. For the unnotched UD sample, strength value was taken from the material's technical data sheet.…”
Ultrasonic welding is a common fusion bonding technique to join unreinforced and reinforced thermoplastics. It is expected that applying ultrasonic vibrations to thermoset prepregs can produce heat generation to promote resin flow and consolidation. This paper discusses the feasibility of using ultrasonic vibrations as a high-speed repair technique for carbon fiber/epoxy prepregs to replace the traditional vacuum-bagging scarf setup. Three material types were investigated: out-of-autoclave unidirectional and plain weave prepregs (Cycom® 5320) and a general purpose twill weave prepreg (AS4/Newport 301). Two welding modes were considered: time and travel (vibrations stop once the desired vertical displacement is reached). For each mode, vibration time, travel, force, and amplitude were investigated. Cross-sectional analysis showed that void content equal to or below the vacuum-bagged samples could be achieved with ultrasonic consolidation to meet aerospace standards (≤2%). The following ultrasonic parameters were recommended to preserve prepreg tows integrity and minimize void content: vibration time below 1.0 s, travel between 12.5% and 50% of sample's initial thickness, force equal to or below 100 N, and amplitude below 41.3 μm. Temperature values recorded during the ultrasonic process reached the manufacturer's cure temperature range (120℃ to 180℃), with a predicted maximum degree of cure of 0.24. Interlaminar shear strength values were comparable for ultrasonically consolidated and vacuum-bagged samples. Soft and hard repair patches were applied to open-hole tensile coupons, with up to 50% strength recovery for both repair methods. Overall, ultrasonic consolidation has potential as a time- and cost-efficient repair method for thermoset prepregs.
“…31 For instance, thicker patches will lead to higher failure loads. 32,33 Upon investigating the failure surfaces for repaired samples, similar failure modes were generally observed for both repair methods, explaining the similar strength values presented in Figure 13. TW specimens repaired by US consolidation and vacuum bagging shown in Figure 14(a) and (b), and PW vacuum-bagged specimens shown in Figure 14(f), characteristically failed by net tension failure.…”
Section: Mechanical Testingsupporting
confidence: 62%
“…31 For instance, thicker patches will lead to higher failure loads. 32,33 Figure 13.Strength of open-hole and repaired samples from configuration shown in Figure 5 for UD, PW, and TW laminates. For the unnotched UD sample, strength value was taken from the material's technical data sheet.…”
Ultrasonic welding is a common fusion bonding technique to join unreinforced and reinforced thermoplastics. It is expected that applying ultrasonic vibrations to thermoset prepregs can produce heat generation to promote resin flow and consolidation. This paper discusses the feasibility of using ultrasonic vibrations as a high-speed repair technique for carbon fiber/epoxy prepregs to replace the traditional vacuum-bagging scarf setup. Three material types were investigated: out-of-autoclave unidirectional and plain weave prepregs (Cycom® 5320) and a general purpose twill weave prepreg (AS4/Newport 301). Two welding modes were considered: time and travel (vibrations stop once the desired vertical displacement is reached). For each mode, vibration time, travel, force, and amplitude were investigated. Cross-sectional analysis showed that void content equal to or below the vacuum-bagged samples could be achieved with ultrasonic consolidation to meet aerospace standards (≤2%). The following ultrasonic parameters were recommended to preserve prepreg tows integrity and minimize void content: vibration time below 1.0 s, travel between 12.5% and 50% of sample's initial thickness, force equal to or below 100 N, and amplitude below 41.3 μm. Temperature values recorded during the ultrasonic process reached the manufacturer's cure temperature range (120℃ to 180℃), with a predicted maximum degree of cure of 0.24. Interlaminar shear strength values were comparable for ultrasonically consolidated and vacuum-bagged samples. Soft and hard repair patches were applied to open-hole tensile coupons, with up to 50% strength recovery for both repair methods. Overall, ultrasonic consolidation has potential as a time- and cost-efficient repair method for thermoset prepregs.
“…This means the shear stress transfer from the patch to the damaged plate is high and bonding is strong when it is thinner. Indeed, previously, it has been recommended that the adhesive thickness provide a higher reduction in SIF when it is thinner or between 0.25 mm to 0.35 mm [ 30 ]. Whenever the thickness of the adhesive bond increases, a small reduction is found in the NSIF.…”
Over the last four decades, numerous studies have been conducted on the use of bonded composite repairs for aircraft structures. These studies have explored the repair of damaged plates through experimental, numerical, and analytical methods and have found that bonded composite repairs are effective in controlling crack damage propagation in thin plates. The use of double-sided composite repairs has been found to improve repair performance within certain limits. This study focuses on these limits and optimizes double-sided composite repairs by varying adhesive bond and composite patch parameters. The optimization process begins with a finite element analysis to determine the stress intensity factor (SIF) for various variables and levels, followed by the application of the Taguchi method to find the optimal combination of parameters for maximizing the normalized SIF. In conclusion, we successfully determined the stress intensity factor (SIF) for various variations and normalized it for optimization. An optimization study was then performed using the Taguchi design and the results were analyzed. Our findings demonstrate the repair performance of bonded composite patches using a cost-effective and energy-efficient approach.
“…In recent investigations on the bonded composite repair of damaged structures, numerous studies have reported using the FE method [ 23 , 24 , 25 ] and experimental work [ 26 ] compared with analytical work. Additionally, the stress concentration factor (SCF) has played an important role in fracture parameters, and it has been reduced using a bonded composite patch with the same FE method [ 27 , 28 ].…”
Over the past four decades, the use of composite materials for the repair of cracked structural plates with glued patches has been extensively studied. Attention has been focused on determining a mode-I crack opening displacement, which is important in tension load and in preventing the failure of a structure due to small damages. Therefore, the significance of conducting this work is to determine the mode-I crack displacement of the stress intensity factor (SIF) using analytical modeling and an optimization method. In this study, an analytical solution was obtained for an edge crack on a rectangular aluminum plate with single- and double-sided quasi-isotropic reinforcing patches, using linear elastic fracture mechanics and Rose’s analytical approach. Additionally, an optimization technique with the Taguchi design was used to define the optimal solution of the SIF from the suitable parameters and levels. As a result, a parametric study was conducted to assess the mitigation of the SIF using analytical modeling, and the same data were used to optimize the results via the Taguchi design. This study successfully determined and optimized the SIF, demonstrating an energy- and cost-efficient approach to address damage control in structures.
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