Single-sided Composite Patches Research Articles

Improving the performance of damage repair in thin-walled structures with analytical data and machine learning algorithms

In the last four decades, bonded composite repair has proven to be an effective method for addressing crack damage propagation. On the other hand, machine learning (ML) has made it possible to employ a variety of approaches for mechanical and aerospace problems and such significant approach is the repair mechanism and hence ML algorithms used to enhance in the present work. The current work investigates the effect of the single-sided composite patch bonded on a thin plate under plane stress conditions. An analytical model was formulated for a single-sided composite patch repair using linear elastic fracture mechanics and Rose's analytical modelling. From the analytical model, the stress intensity factors (SIF) were calculated by varying all possible parameters of the model. Next, ML algorithms were selected, and comparative studies were conducted for the best possible performance and to identify the parametric effects on optimum SIF. Also, the analytical model is validated with existing work, and it shows good agreement with less than 10% error. This study is particularly important for designing the single-sided composite patch repair method based on analytical modelling. Also, it is important to compare ML algorithms with analytical solutions in regression applications.

Fatigue crack growth in aluminum panels repaired with different shapes of single-sided composite patches

In this study, the effects of patch shape on the performance of bonded composite repairs on aircraft structures are investigated using experimental and numerical approaches. Fatigue tests under constant amplitude loading, with a positive stress ratio, are performed on V-notch cracked specimens using two aluminum alloys, 2024-T3 and 7075-T6 that are repaired with bonded carbon/epoxy patches. Three composite patch shapes are used: rectangular, trapezoidal, and triangular. Left- and right-oriented triangular patch shapes are used to analyze the effects of the patch orientation on the repair efficiency. Numerical models are built with these patch shapes and orientations. The stress intensity factors and adhesive stresses are computed to numerically evaluate the repair performances obtained with the different patch shapes and orientations. The experimental results demonstrate that rectangular patches provide the most efficient repair, whereas the triangular shape with a left-orientation may lead to catastrophic results, particularly with the 2024-T3 aluminum alloy. The numerical results concur with the experimental observations.

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.

Experimental study on mechanical performance of cracked aluminium alloy repaired with composite patch

This study represents the experimental investigation on the mechanical behaviour of edge-cracked aluminium plates repaired with single sided composite patch. In this work, the adhesively bonded composite patch repair technique has been used for the reliability of the cracked aluminium structural components as well as to extend its life. More uniform and load transfer into the patch, easy application for reduced risk of corrosion and reduced stress concentration are some of the significant advantages of this technique. For some applications the adhesively bonded composite patching is the only alternative technique to costly component replacement. For this technique, at first the cracked and uncracked specimens were fabricated using AA 1080 aluminium alloy of 3 mm thickness and bonded with single side composite patch. For making the patch in the woven E-glass fiber was used for the reinforcement. Two lay-ups were used i.e. 4-ply and 6-ply in case of woven E-glass fiber and so far the aluminium specimens are considered, they have three edge-crack of different lengths. Now according to ASTM standards, two different tests were carried out on these specimens i.e. Tensile Test, Bending Test and Hardness test. The obtained experimental results are compared with the results for cracked, uncracked and repaired, unrepaired cracked specimens. The effect of patching on the mechanical properties of the cracked plate is more significant. In each loading case, the best patches are reinforced with aluminium alloy and the tensile, bending loading tests are conducted again for the repaired specimens with these patches.

Analyses of cracks in thick stiffened plates repaired with single-sided composite patch

This study investigated the effect of composite patches applied to thick stiffened plates with single-sided repairs. A simplified analytical model was derived to predict the reduction in the mode I strain energy release rates resulting from the single-sided composite patches. Finite element analyses were also conducted to compute the mode I strain energy release rates with and without composite patches, and their results were compared to the analytical model prediction. Furthermore, changes in the location of the neural axis with single-side patches were examined with their effects on the effectiveness of the patch repair with variations in both material and geometric parameters of the patch and plate. The neutral axis location in the patched plate played an important role to influence the effectiveness of the composite patch.

Mixed-mode 3-D crack propagation of repaired thin aluminum panels using single-side composite patches

Three dimensional finite element analyses of the single-side repaired panels using glass/epoxy composite are performed considering the general mixed mode conditions and real crack-front shape modeling (RCFM) during the crack propagation procedure. Variations of the fracture parameters through the thickness of the panels for the initial crack configuration and crack growth behavior of the repaired panels with various patch lay-ups are investigated. The effect of considering KIII on the small and large crack growth of repaired panels are also studied. The obtained lives are compared with the previously obtained lives using simplified FEM procedure and experimental results by the authors.

Numerical and experimental fatigue crack growth analysis in mode-I for repaired aluminum panels using composite material

Abstract Crack-front shape is an important parameter influencing the stress intensity factor and crack propagation rate in asymmetric repaired panels. In this study, the numerical and experimental fatigue crack growth behaviour of centrally cracked aluminum panels in mode-I condition repaired with single-side composite patches are investigated. It is shown that the crack growths non-uniformly from its initial location through the thickness of a single-side repaired panel. There is a good agreement between the propagated crack-front shapes obtained from finite element analysis with those obtained from the experiments for various repaired panels with different patch thicknesses. Furthermore, effects of plate and patch thickness on the crack growth life of the repaired panels are investigated. The experimental results show that the crack growth life of thin panels may increase up to 236% using a 16 layers patch. However, for thick panels, the life may extend about 21–35% using a 4 layers patch. Implementing of 8 and 16 layers patches has not a significant effect on the life extension of thick panels with respect to the 4 layers patch life.

Effects of composite patches on fatigue crack propagation of single-side repaired aluminum panels

The major concern of this review paper is the effect of crack-front shape on fatigue crack growth of the repaired aluminum panels with single-side composite patches in Mode-I condition. It is experimentally and numerically shown that the crack growths non-uniformly from its initial position along the thickness of a single-side repaired panel and the crack-front shape are an important parameter influencing the stress intensity factor and crack propagation rate. Furthermore, effects of plate and patch thickness on the crack growth life of the repaired panels are investigated. It is shown that the lives obtained from uniform crack growth modeling using unpatched surface results are too conservative and the lives calculated using the mid-plane results are non-conservative by the order of 35–90%. It is also shown that the differences between the lives obtained from the non-uniform crack growth modeling and the experimental results are about 10%. A simple method is also introduced to predict the crack growth life of single-side repaired aluminum panels avoiding the complex crack growth analysis based on the non-uniform crack growth or real crack-front shape modeling. Therefore, the results of even a 2D analysis may be used to estimate the crack growth life of the repaired panels. The obtained results are verified with the available experimental results.

Experimental fatigue crack growth and crack-front shape analysis of asymmetric repaired aluminium panels with glass/epoxy composite patches

In this study, we investigate the experimental fatigue crack-growth behaviour of centrally cracked aluminium panels in mode-I condition which have been repaired with single-side composite patches. It shows that the crack growths non-uniformly from its initial location through the thickness of the single-side repaired panels. The propagated crack-front shapes are preformed for various repaired panels with different patch thicknesses. It is shown that there are considerable differences between the crack-front shapes obtained for thin repaired panels with various patch thicknesses. However, the crack-front shapes of thick repaired panels are not significantly changed with various patch thicknesses. Furthermore, effects of patch thickness on the crack growth life of the repaired panels are investigated for two typical thin and thick panel thicknesses. It shows that the crack growth life of thin panels may increase up to 236% using a 16 layers patch. However, for thick panels, the life may extended about 21–35% using a 4 layers patch, and implementing 8 and 16 layers patches has not a significant effect on the life extension with respect to the 4 layers patch life.

Experimental study of repair efficiency for single-sided composite patches bonded to aircraft structural panels

Fatigue response of cracked aluminum panels repaired with a single-sided composite patch is examined. Fatigue tests were carried out under various temperature and humidity conditions. From the experimental results of fatigue tests, the repair efficiency for single-sided composite patches bonded to cracked aluminum panels is evaluated using the range of stress intensity at crack tip. The effect of temperature on the repair efficiency can be found by comparing the results of crack growth at 353 K, 300 K and 223 K. Likewise, the effect of humidity on their repair efficiency can be found by comparing the results of crack growth at 90%, 50% and 25% relative humidity. Other factors that reduce the repair efficiency are also discussed.

Residual stress development during the composite patch bonding process: measurement and modeling

Abstract This paper presents an experimental technique for monitoring residual stress development throughout the composite patch repair curing process. Using this technique, process-induced strains and specimen warpage during a number of different cure cycles were measured for a simulated single-sided composite patch repair of an aluminum substrate. Models for adhesive cure rate and glass transition behavior of the patch adhesive resin (FM 300-1K) were combined with a simple bi-metallic strip model to predict specimen warpage and strain behavior during cure. Model predictions were compared with experimental measurements and were used to assist in the development of optimized cure cycles. Using these optimized cycles, it was found that it was possible to achieve significant (>20%) reductions in patch warpage and at the same time, minimize processing time and obtain a high final adhesive degree of cure. Experimental observations suggest that an improved patch model incorporating adhesive viscoelastic behavior during cure would assist in achieving additional process improvements.

Fatigue of Cracked Plates Repaired with Single-Sided Composite Patches

Fatigue of cracked plates repaired with single-sided composite patches is studied via both analytical and experimental approaches. A finite element model, which considers out-of-plane bending effects induced by asymmetric repair, is presented to determine the crack tip opening displacements of the repaired plates subjected to in-plane loading. The modified crack closure technique is used to calculate the stress intensity factor of the repaired plates. Fatigue life of the repaired plates is studied via the use of Paris law for crack propagation. The effects of cracked plate and composite patch thicknesses on the fatigue crack propagation of repaired plates containing different types of cracks are investigated. Fatigue tests of aluminum C-T specimens repaired with single-sided composite patches are performed, and the test data are used to validate the analytical approach. It has been shown that the repair of a cracked plate with a single-sided composite patch may have beneficial or adverse effects on the fatigue life of the repaired plate depending on the thicknesses of the patch and the cracked plate. .

Fatigue of cracked plates repaired with single-sided composite patches

Fatigue of cracked plates repaired with single-sided composite patches