Cracked Aluminum Plate Research Articles

Experimental and numerical analysis of the behavior of rehabilitated aluminum structures using chopped strand mat GFRP composite patches

PurposeThis paper comprehensively addresses the influence of chopped strand mat glass fiber-reinforced polymer (GFRP) patch configurations such as geometry, dimensions, position and the number of layers of patches, whether a single or double patch is used and how well debonding the area under the patch improves the strength of the cracked aluminum plates with different crack lengths.Design/methodology/approachSingle-edge cracked aluminum specimens of 150 mm in length and 50 mm in width were tested using the tensile test. The cracked aluminum specimens were then repaired using GFRP patches with various configurations. A three-dimensional (3D) finite element method (FEM) was adopted to simulate the repaired cracked aluminum plates using composite patches to obtain the stress intensity factor (SIF). The numerical modeling and validation of ABAQUS software and the contour integral method for SIF calculations provide a valuable tool for further investigation and design optimization.FindingsThe width of the GFRP patches affected the efficiency of the rehabilitated cracked aluminum plate. Increasing patch width WP from 5 mm to 15 mm increases the peak load by 9.7 and 17.5%, respectively, if compared with the specimen without the patch. The efficiency of the GFRP patch in reducing the SIF increased as the number of layers increased, i.e. the maximum load was enhanced by 5%.Originality/valueThis study assessed repairing metallic structures using the chopped strand mat GFRP. Furthermore, it demonstrated the superiority of rectangular patches over semicircular ones, along with the benefit of using double patches for out-of-plane bending prevention and it emphasizes the detrimental effect of defects in the bonding area between the patch and the cracked component. This underlines the importance of proper surface preparation and bonding techniques for successful repair.Graphical abstract

Reinforcement of cracked aluminum plates using polymeric composite patches embedded with prestressed SMA wires

Many studies have been performed on composite patches as reinforcement of cracked metal sheets. However, in most previous research, composite patches without prestressing have been used to repair cracks. In the present study, a novel method for repairing cracked aluminum sheets is proposed by using polymer composite patches with embedded prestressed Nitinol shape memory alloy (Ni-Ti SMA) wires. Elastic-plastic finite element analysis of an aluminum plate, with a central crack in the pure mode I and the mixed-mode I/II fracture, repaired with SMA wires reinforced composite patch (SMA-CP) was performed. The peel stress on the adhesive layer between the composite patch and the aluminum plate was calculated to evaluate the performance and efficiency of the repair. The effect of the prestress of the embedded Ni-Ti SMA wires on the efficiency of the composite patch was examined. The results show that embedding prestressed SMA wires in the composite patch reduces the stiffness ratio of the patch. Also, the value of the J-integral and the size of the plastic area compared to the patch without SMA wires were decreased.

Experimental and numerical study to determine the optimum type of composite material used in the repair of corroded and cracked Al A2017A aluminum plates

This study included two aspects - an experimental study and a numerical study – to determine which type of composite materials is more efficient in repairing corroded and cracked aluminum plates that have been repaired by the composite material technique. In the numerical study, the adhesive damage area theory was used to analyze the effect of corrosion and inclined crack behavior of Al 2017 A aluminum plate under thermo-mechanical loading. The effects of crack inclination and temperature change were highlighted as well as the effects of patch shape and type. In the experimental study, we prepared corroded sheets, repaired them with several types of composite materials, and then subjected them to tensile strength until wear. The results obtained either through a numerical or experimental study, proved that the boron/epoxy type composite is the most efficient in rust repair compared to the other types used in this study.

Analysis of the effect of localized corrosion shape on a cracked and notched 2024 AL plate repaired with composite patch under thermo-mechanical loading

This study highlights the analysis of corrosion shape effects under thermo-mechanical loading on the development of damage in corroded and cracked aluminum plates. This study is divided into two parts, the numerical analytical part, was performed to compare the effect of the corrosion geometry on the repair and adhesive damage; We analyzed the effects of damaged areas on the level of corrosion in the adhesive layer of three composite materials (boron/epoxy, glass/epoxy, and graphite/epoxy), and studied the change of the stress intensity factor for circle or square-shaped corrosion. The second part related to an experimental study of the corrosion shape on the ultimate strength of the damaged plate repaired by the boron/epoxy composite material. The results obtained, indicated that the effect of the circular shape of corrosion is small compared to the square shape. The type of composite material (boron / epoxy) has proven its optimal effect on repair.

Deep-Subwavelength-Optimized Holey-Structured Metamaterial Lens for Nonlinear Air-Coupled Ultrasonic Imaging.

Ultrasound non-destructive testing (NDT) is a common technique used for defect detection in different materials, from aluminium to carbon-fiber-reinforced polymers (CFRPs). In most cases, a liquid coupling medium/immersion of the inspected component is required to maximize impedance matching, limiting the size of the structure and materials. Air-coupled inspection methods have recently been developed for noncontact inspections to reduce contact issues in standard ultrasonic inspections. However, transmission of ultrasound in air is very inefficient because of the enormous impedance mismatch between solids and air, thus requiring a signal amplification system of high-sensitivity transducers. Hence, the captured signal amplitude may not be high enough to reveal any wave distortion due to defects or damage. This work presents a design of a holey-structured metamaterial lens with a feature size of λ/14 aiming at improvement of acousto-ultrasonic imaging using air-coupled transducers. The required effect is obtained by matching geometrical parameters of the proposed holey-structured metamaterials and the Fabry–Perot resonance modes of the structure. Transmission tests have been conducted on different fabricated metamaterial-based structures, to assess the frequency component filtering of the proposed method in both acoustic (f = 5 kHz, 20 kHz) and ultrasonic range (f = 30 kHz, 40 kHz). Results showed an improved sensitivity of damage imaging, with an increase in amplitude of the design frequencies of the lens by 11 dB. Air-coupled inspections were conducted on a stress-corrosion cracked aluminum plate and impacted CFRP plate using the holey-structured lens. Results showed an improvement in the damage-imaging resolution due to a wave-amplitude increase across the defective features, thus demonstrating its potential as an efficient and sensitive inspection tool for damage-detection improvement in geometrically complex components of different materials.

Predicting failure of cracked aluminum plates with one-sided composite patch

Composite patch repairs are an alternative to weld repair methods to arrest crack growth in metal plates. While these repairs have been effective, it has been difficult to use basic linear elastic fracture mechanics (LEFM) theories and design methods based on LEFM to predict the efficacy of patch repairs because the repaired plate exhibits bending and significant crack tip plasticity. In this investigation, we have studied the effect that one-sided low modulus composite patch repairs have on the development of crack tip plasticity on the free surface and through the thickness using large strain area and volume, total axial stress balance, and the free surface J-integral. Digital Image Correlation (DIC) and three-dimensional finite element analysis with first order elements were used to understand the evolution of crack tip plasticity and strain energy release rate to develop a simplified prediction method identifying a characteristic crack opening displacement prior to crack tip behavior of a one-sided composite patch repaired Center-Cracked Tension (CCT) specimen transitioning from Small Scale Yielding (SSY) to Large Scale Yielding (LSY), and eventually the re-initiation of crack growth. This method was then validated by comparing the predicted characteristic transition load to observed ultimate patched CCT specimen load capacity. Results correlated well with predictions when the composite patch was perfectly bonded to the aluminum and predicted characteristic transition loads more than 90 $$\%$$ greater than LEFM based failure predictions and 25 $$\%$$ lower than observed ultimate failure loads, demonstrating the potential to use this method for patch repair optimization.

Fatigue Life Appraisal and Its Corrected Stress Intensity Factor for Repaired Off-CentrallyCracked Aluminum Plates.

This paper presents an experimental study on the fatigue life estimation of off-centrally cracked aluminum plates. Typical theoretical equations for off-central, central and edge cracks were reviewed and compared in terms of their sensitive parameters and applicability. A finite element model has been validated in its capacity in modelling the influences of eccentricity and crack size on the boundary correction coefficients. The Forman equation has been employed along with numerical results for the prediction of fatigue lives. Based on the test data, the fatigue life results of aluminum plates with and without patched laminate repair have been compared with codified fatigue classes. It is demonstrated that the repair at the crack tip close to the plate edge is effective in the fatigue life improvement for off-centrally crackedaluminum plates.

Numerical analysis of cracked aluminum plate repaired with multi-scale reinforcement composite patches

In this study, numerical modeling is used to investigate the performance of a single-sided composite patch with different scale fillers, as reinforcement of a cracked aluminum plate under static tension. The main concerns of previous studies are about the geometry of patches, composite layups, and failure of adhesive. In this research, the effect of patch properties such as size and fiber volume fraction, the thickness of patch, and thickness of adhesive on the overall performance of the cracked aluminum plate are investigated numerically. Indeed, first, a 3 D representative volume element (RVE) is adopted to calculate the mechanical properties of carbon nanotube (CNT)/epoxy and carbon fiber (CF)/epoxy composite patch at each specified volume fraction for investigating the effect of patch properties on the performance of a single-sided patch for crack repairing. In this regard, the cohesive zone model is adopted to analyze the debonding between the epoxy matrix and reinforcement to characterize the mechanical properties of composite patches. Finally, a linear 3 D finite element analysis is performed to calculate the stress intensity factor (SIF) for cracked aluminum plate repaired by a single-sided composite patch at each specified reinforcement volume fraction for different thickness of patch and different thickness of adhesive. The results demonstrated that the stress intensity factor highly depends on the patch properties (patch stiffness) in addition to patch thickness and adhesive thickness.

Elastoplastic analysis of cracked Aluminum plates with a hybrid repair technique using the bonded composite patch and drilling hole in opening mode I

The objective of this study is to analyze the performance of composite bonding repair, hole drilling and the combination of the two techniques (hybrid repairs) by tensile tests and to show the interest of a hybrid repair versus to other processes. These repair techniques can apply in different branches of engineering: mechanical, aerospace, civil, naval, etc. The finite element method with the ABAQUS code was used to model the mechanical behavior of the different repair techniques. The Notch Stress Intensity Factor (NSIF) is adopted to model the behavior of the cracked notch based on the volumetric method. The size of the plastic zone, the intensity of the normal σyy stress, the peel stress and CTOD are combined to model the proposed technics repairs. Although the bonded composite is very strong, the application of a drilling hole results in additional energy absorption and reduces the level of the maximum normal stress by about 50% compared to a simple patch only. The use of a hybrid repair has a high resistance compared to other proposed methods, improves the mechanical strength and increases the life of the cracked structure compared to a single composite joint and a repair by drilling hole only.

Repairing cracked aluminum plates by aluminum patch using diffusion method

The aim of this work is to scrutinize the importance of diffusion bonding temperature, pressure and time on the repair of a cracked aluminum plate while the maximum tensile strength under a quasi-static loading has been investigated. The diffusion method was used to connect aluminum patches to repair the central and mode I cracks in thin aluminum plates. Here, the process of repairing cracked pieces made of aluminum or aluminum alloys involved a chemical and mechanical step to remove aluminum oxide and press the patch and piece under the temperature difference at a certain time. The repaired pieces underwent a quasi-static tensile loading while the maximum tolerable amount of force was obtained in different situations. Having assigned five temperatures, 300, 400, 500, 550 and 600 C, as well as four test times 30, 60, 120 and 180 min and five different pressures 10, 20, 50, 80 and 110 bar, we utilized fractional factorial design approach to perform 40 tests while there was seen a 10 mm initial crack in repaired samples. Experimental results showed that the optimum connection was resulted at 550 °C and the pressure of 80 bars within 120 min where the maximum force tolerated by the repaired vs. the unrepaired piece increased by 92 %. Therefore, having weighed the repair method using the diffusion bonding, we suggest that this type of the repair method can be a proper and cheap alternative to composite and adhesive patches.

A 3D analysis of crack-front shape of asymmetric repaired aluminum panels with composite patches

Through this study, a numerical simulation based on 3D in order to investigate the effect of Crack-front shape on the stress intensity factor and fatigue crack growth behavior of center cracked aluminum plate repaired asymmetrically with a bonded composite patch. Consequently, Skew degree is a significant effect on stress intensity factor (SIF) distribution along the crack front in thick panels more than thin panels. Moreover, Fatigue life was calculated using different averages stress intensity factor of patched panel determined from the uniform crack front model and skew crack front model obtained from FEM and when comparing fatigue life values obtained from the finite element model with experimental values were shown a good agreement.

Effects of adhesive disbond and thermal residual stresses on the fatigue life of cracked 2024-T3 aluminum panels repaired with a composite patch

The technology of bonded composite repair has displayed its effectiveness in increasing the residual fatigue life of cracked aeronautical structures. However, two major phenomena reduce the performance of this technique; the adhesive disbond by the fatigue load and the thermal residual stresses due to the adhesive curing. In this study, the effects of the adhesive disbond and the thermal residual stresses on the fatigue life of repaired cracked aluminum plate were analyzed experimentally and numerically. Fatigue tests were performed on cracked 2024-T3 aluminum alloy specimens repaired using carbon/epoxy patches that have artificial disbonds, to highlight the adhesive disbond effect. Fatigue tests were performed on repaired specimen bonded with elevated temperature cure and ambient temperature cure adhesives to evaluate the effect of the thermal residual stresses. To analyze the effects of the two phenomena, the finite element method was used to compute the stress intensity factor at the front of repaired cracks. The experimental results indicate that fatigue life is significantly reduced by the presence of an initial adhesive disbond and thermal residual stresses. The numerical results are consistent with the experimental observations, and reveal that the stress intensity factor increases with an increase in the disbond width. Moreover, it also increases in the presence of thermal residual stresses.

Investigation of patch hybridization effect on the composite patch repair of a cracked aluminum plate: A pragmatic approach

ABSTRACTA distinct perspective of using the hybrid composite patches with varying stiffness for repair of a cracked Al 6061-T6 plate and its influence on repair performance is presented. The hybrid composite patches of carbon and glass fibers are considered. The volume fraction of constituents is selected in accordance with the required stiffness ratio. Numerical analysis is performed to evaluate the J-Integral, reduction factor of SIF and interfacial stresses. Patch hybridization has restricted the J-Integral and shown positive impact on interfacial stresses at the edges. The obtained results indicate that the hybrid composite patches have ensured alternative and effective repair solution.

The fatigue failure study of repaired aluminum plates by composite patches using Acoustic Emission

The aim of this study is to investigate the failure of cracked aluminum plates repaired by one-side composite patches under fatigue loading using Acoustic Emission (AE) and fractography images. Rectangular specimens made of 6061 aluminum alloy with central through thickness pre-cracks were repaired using glass/epoxy laminated patches. The specimens were subjected to the fatigue loading and AE technique was employed to monitor the effect of the repair patch on the damage progression. First, different stages of damage evolution were studied based on the mechanical data and fractography images. Then, the AE energy utilized to characterize failure process of the specimens. To this aim, AE signals of the aluminum cracking and adhesive layer failure were discriminated according to their energy content. The effect of patch thickness and layup on the failure behavior of the specimens were also studied. Finally, it is concluded that AE is a powerful technique to characterize the failure process of a repaired cracked aeronautic structure by composite patches.

Numerical Analysis of Asymmetrically Bonded Composite Patch Repair and Effect of In-Plane Skewed Crack Front on the SIF

A nonlinear 3-D finite element analysis was conducted to analyze the crack front behavior of a center cracked aluminum plate, asymmetrically repaired with composite patch. According to experimental observations, the crack front was modeled as an inclined shape from the initial state where the crack front is straight and parallel to the thickness direction from the patched side toward the un-patched side. The skew degree is found to strongly influence the stress intensity factor (SIF) distribution along the crack front. In effect, the obtained trends of the SIF’s distribution are different and changes during crack growth stages. The main finding is that regardless the crack front shape (inclination), the average stress intensity factor through the crack front remains constant and consequently, it means to be an effective parameter to estimate the fatigue life and crack growth of the asymmetrically patched structures. The performed models gave good results compared to the literature and the different findings correlate well with the experimental observations and make sense with a realistic crack development.

Charpy Impact Response of the Cracked Aluminum Plates Repaired with FML Patches using the Response Surface Methodology

<p style="margin: 0cm 0cm 10pt; text-align: justify; line-height: normal;">Here, the effect of fiber metal laminate (FMLs) patches was studied for repairing of single-sided cracked aluminum plates experimentally to see their response to Charpy impact tests. The main desired parameters were composite patch lay-up, crack length, and crack angle each one in three levels. All experimental attempts generated and followed based on the design of experiments method by using of response surface methodology. The predicted energy absorption values obtained from the model were in good agreement with the experimental results. No matter the specimens were repaired or not, as the crack length was increased the energy absorption of the structure was decreased. The experimental results also showed that for lengthen cracks, increasing of the crack angle had more effect on energy absorption. Also it was observed that the patch lay-up effective on the impact response of the specimens. The more the metal layer was departed from the aluminum plate and the FML patches interfacial surface, the less energy was absorbed in the structure.</p>

Optimization of composite patch repair for maximum stability of crack growth in an aluminum plate

In this paper, the configuration parameters of pre-designed composite patch repair are optimized with the aim of achieving the highest level of stability of crack growth in aluminum in the presence of some constraints such as weight, load sustainability, shear stress in the adhesive layer and maximum stress in the patch. For this purpose, the patch is modeled in full scale by ABAQUS, a commercial finite element code. The crack growth process is simulated with the extended finite element method under uniaxial tensile loading, and the Cohesive Zone Model is used to model the progressive damage in the adhesive of the composite patch repair. Also, sensitivity analysis is performed on the configuration parameters and it is shown that three parameters, i.e. width, stiffness ratio, and height of the patch are more important. Nonlinear fracture mechanics concepts have been used in calculating the stability of crack in the cracked aluminum plate. The results show that optimization based on the method proposed in this paper causes the stability of crack growth to increase by 21% while the patch weight is reduced by 52%.

A Study on the Charpy Impact Response of the Cracked Aluminum Plates Repaired with FML Composite Patches

Fiber metal laminates (FMLs) are widely used in aerospace industries nowadays. Reparation of the cracks in these advanced materials was first done by some aeronautical laboratories in the early 1970s. In this study, experimental investigations were done on the effects of repairing the edge-cracked aluminum plates using the FML patches. The repairing processes were conducted to characterize the response of the repaired structures to the Charpy impact tests. The composite patches were made of one aluminum layer and two woven glass–epoxy composite layers. Three different crack lengths, crack angles, and patch lay-ups were examined. It was indicated that for the lengthen cracks, the effect of increasing the crack angle on energy absorption in the structure was more. When the ratio of crack length to the specimen width, i.e., a/w, is 0.5, the energy absorption per unit area of the specimens having different crack angles but the same patch lay-ups was so different. It was also observed that the percentage of the absorbed energy of 45° cracked angle specimens was about 25% higher than the 0° ones. Also it was observed that the lay-up of the patches and the place where the metal layer was embedded in the FML patches had an important effect on the impact response of the tested specimens. The more the metal layer of the patches is far from the interfacial surface of the aluminum plate and the FML patches, the less the energy absorbs in the structure.

Effects of Adhesive Bond on Active Repair of Aluminium Plate Using Piezoelectric Patch

Research activities on active repairs and stress control of structures using piezoelectric actuators and adhesive bond have received much attention in recent years. The function of the adhesive bond on active repair is to transmit the induced stresses by the piezoelectric actuator to the host structure in order to reduce the stress intensity on the crack front. Assessment of repair performance of adhesive bonds is done based on the transfer of the shear and peel stress concentration in the adhesive layer. In the present work, three dimensional finite element analyses have been carried to understand the effects of adhesive properties on active repair performance of a cracked aluminium plate under mode I. Adhesive efficiency is evaluated by the stress intensity factor (SIF) as a fracture criterion. The results show that SIF varies inversely with the adhesive layer’s shear modulus.

Fracture Analysis of Double-Side Adhesively Bonded Composite Repairs to Cracked Aluminium Plate Using Line Spring Model

A line spring model is developed for analyzing the fracture problem of cracked metallic plate repaired with the double-sided adhesively bonded composite patch. The restraining action of the bonded patch is modeled as continuous distributed linear springs bridging the crack faces provided that the cracked plate is subjected to extensional load. The effective spring constant is determined from 1-D bonded joint theory. The hyper-singular integral equation (HSIE), which can be solved using the second kind Chebyshev polynomial expansion method, is applied to determine the crack opening displacements (COD) and the crack tip stress intensity factors (SIF) of the repaired cracked plate. The numerical result of SIF for the crack-tip correlates very well with the finite element (FE) computations based on the virtual crack closure technique (VCCT). The present analysis approaches and mathematical techniques are critical to the successful design, analysis and implementation of crack patching.