Composite Patch Repair Research Articles

Buckling Strength Assessment of Composite Patch Repair Used for the Rehabilitation of Corroded Marine Plates

A common form of damage encountered in marine structures is the accumulation of corrosion in susceptible areas, which leads to material wastage. As a result, the structural strength of the members affected is compromised, endangering their safe operation in design loads. Consequently, structural instabilities may occur, such as buckling due to compressive or/and shear loads. An alternative repair practice for preventing such phenomena, approved for secondary load-carrying members, is the application of composite patches to the damaged area. In this preliminary study, this technique is examined in the scope of developing a framework that can be used to find the optimal solution for restoring the buckling strength of a corroded plate. The methods used to achieve this are based on finite element analysis (FEA) and design of experiments (DoE) to statistically analyze the aforementioned numerical calculations. By introducing the composite patch’s percentage coverage of its metal substrate and number of plies as design parameters, a response surface is generated with respect to the obtained factor of safety (regarding its reference uncorroded buckling strength). This list of data points is then evaluated, and an acceptable surface/list of design parameters’ combinations is generated.

Failure analysis of a steel pressure vessel with a composite wrap repair proposal

Two steel pressure vessels, part of an air compressor unit, failed during hydrostatic test at a pressure lower than proof pressure. Pressure drop and fluid leakage was noted during the test and later investigation revealed through-wall cracks on the shells of each vessel. Experimental and numerical investigation was employed to determine possible causes of failure and to propose a repair method for such vessels. Non-destructive testing (visual and ultrasonic) was performed to check the outer and inner surfaces of the vessel for possible cracks and to measure wall thickness. Optical and scanning electron microscopy was used to inspect crack surroundings and determine the size of the cracks. According to experimentally obtained results, excessive pitting corrosion at the bottom part of the vessel initiated cracks. In order to retain the functionality of the vessel, composite patch repair procedure is proposed. Numerical analysis was performed to determine pressure bearing capacity of the repaired vessel. Also, recommendations for avoidance of failure scenario for considered pressure vessels are given.

An Experimental and Numerical Study on the Use of Chirped FBG Sensors for Monitoring Fatigue Damage in Hybrid Composite Patch Repairs.

In this paper, chirped fibre Bragg grating (CFBG) sensors used to monitor the structural health of a composite patch used to repair an aluminium panel is presented. To introduce damage, a notch was produced at the centre of an aluminium panel. The repair consisted of bonding a pre-cured composite patch to the host panel using an aerospace-grade film adhesive; the sensor was embedded in the bond-line during fabrication of the repair. The repaired panels were subjected to tension-tension loading in fatigue. Cracks initiated and grew from both ends of the notch in the aluminium panels and the fatigue loading was stopped periodically for short periods of time to record the reflected spectra from the sensor. It was found that perturbations in the reflected spectra began to occur when the crack was within about 2 to 3 mm of the sensor location; after the crack passed the sensor location, the perturbations essentially stabilised. Predicted reflected spectra have been found to be in good agreement with the experiment, confirming that CFBG sensors can detect crack growth in patch-repaired panels.

Numerical model for composite patch repair of notched aluminum plates under impact loading

The damaged area for various structures can be effectively repaired using composite materials. With the effect of impact, damage can occur that cannot be clearly seen in the inner structure of a laminated composite. This can cause delamination and other damage modes in layered composite structures. In this study, three-dimensional dynamic progressive damage analysis was performed in adhesively bonded composite patch-repaired metal notched plates under impact loads to investigate the effect of external composite patch material and thickness. Three-dimensional Hashin damage models were used for the progressive damage model. A user-defined subroutine, VUMAT was written to transfer the damage models to finite element code. By writing a separate script in Python language that relates to the damage models, the weakness in the laminate of the composite patch was transferred to the finite element model with a different degradation model proposed. It was found that plastic deformations occurring after impact damage in the notched metal plates was prevented by the use of composite patches. While glass and carbon fiber exhibit similar behavior at lower impact velocities, the progress of damage is prevented by increasing patch thickness. These behaviors were confirmed by the numerical model and showed an advanced agreement with experimental results.

Numerical investigation of composite patch repair of inclined cracked panel using XFEM

The life extension of the structure is an important area of research. Composite patch repair is widely used in restoring the strength of the cracked structures. Effective repair should offer repair efficiency as well as repair durability. The crack exists in the structure usually involves mixed-mode loading condition and therefore the study of the panel with inclined crack is significant. This article aims to investigate the performance of the inclined cracked panel bonded with composite patch. Numerical analysis of inclined cracked panel is carried out in ABAQUS. The J-integral and interfacial stresses are investigated which confirms repair efficiency and durability respectively. The orientation of the material in the composite influences the amount of reinforcement applied to the cracked panel and hence the effect of different material orientations is evaluated. The effect of patch stiffness on J-integral and interfacial stresses is also investigated. The results obtained indicate that the patch with adequate stiffness can contribute to diminish the J-integral and interfacial stresses to enhance the performance.

A Study on the Best Conventional Shapes for Composite Repair Patches

Abstract Adhesively bonded repair patches are an excellent approach for repairing locally damaged composite components. If correctly applied, fiber-reinforced patches may restore/increment the mechanical response of damaged laminates without significantly increasing the structure’s mass or altering its geometry. However, in order to take full advantage of this repairing technique, one must employ patches with a minimal surface area and maximum efficiency in incrementing the strength of the component. The present work aims to study optimum-based patch shapes for conventional repair geometries, namely rectangular and elliptical. Shell Finite Elements models were used to simulate a parent plate, which is a rectangular flat laminate with a central trespassing damage region. Unbalanced single-ply patches were modeled on the upper surface of the damaged laminate. The patches' efficiency was computed as its capability in restoring the modal response of the repaired component to its undamaged configuration. Sequential linear programming was employed alongside shell finite element models to obtain optimal geometrical parameters for the patches' shape. The study cases comported two different boundary conditions and two stacking sequences. The optimum-base repair patches were defined regarding size and fiber orientation angle.

Patch shape and size effect on performance of in-situ scarf patch repair in aircraft panel

Patch repairing technique is effective and efficient approach to enhance structural performance of aged aircraft panels. The presented work emphases on studying the patch shape and size effect on scarf composite patch repair of aluminium aircraft panel under thermal, thermo-elastic and mechanical load. In this work, patched repaired structural member has been simulated by ABAQUS software to find out the performance of patch repair in term of patch thickness and patch shape. Five different patch shapes are chosen to analysis: circular, square, hexagonal, rectangular and trapezoidal with different patch thickness 1, 2, 3, 4, 5 mm. The Heat transfer and coupled temp-displacement analysis has been performed under cure temperature 394 K for in-situ patch repair model. The analysis of the critical von-Mises stress and heat flux load distribution in composite patch repair system allows us to estimate performance in composite patch repair system. The results show that patch shape and size has significant effect on magnitude of heat flux load and induced von-Mises stress. Trapezoidal shape of composite patch repair has lower value of von-Mises stress and heat flux load as compared to all four shapes of composite patches.

Damage detection & localization on composite patch repair under different environmental effects

This paper presents a structural health monitoring (SHM) methodology for detecting damage in a composite bonded repair. The application of guided wave based techniques in a step-sanded bonded repair under operational and environmental load is thoroughly investigated. A two step damage detection and localization algorithm is presented, were in the first level the path damage indices (PDIs) for each transducer pair is calculated. The PDIs are then compared to a set threshold (based on the environmental and operational conditions) to increase the reliability of damage detection while reducing false alarm. In addition, a self-diagnosis approach based on electro-mechanical impedance (EMI) measure is proposed to identify the faulty sensors prior to the diagnosis. Once the transducer pairs with possible damage in their path has been selected, the second level of the proposed methodology is damage localization. To address the challenge of edge reflection, complex geometrical shape and layup of the repair patch which introduced anisotropy to the wave propagation, a novel damage detection based on probability imaging technique is proposed. The methodology is developed based on assigning probabilities of damage to the Minimal Intersection Score (MIS) to reduce the path saturation related to each path having the same probability of damage being located anywhere along it. The proposed method, uses a smart sub-division technique based on Voronoi Tessellation which is adaptable to any shape (circular, rectangular, elliptical). The reliability of the proposed method is then demonstrated with experimental results on a composite step-sanded repair subjected to impact damage under vibration and temperature variations, and the choice of input parameters such as wave form and excitation frequency on the probability of detecting damage is demonstrated.

Composite patch repair of damaged tubular members from flare boom structures subjected to compressive loads

Conventional repair method for steel structures requires cutting and welding processes, which in offshore platforms may impose several disadvantages. Composite material repair has become an alternative for the rehabilitation of damaged structures and has been widely applied in other industries. In this work a numerical-experimental investigation evidences the effectiveness of the composite patch repair for flare boom corroded tubular elements subjected to axial compressive loads. A finite element model developed to determine the minimum composite laminate thickness that recovers the structural element strength is validated through numerical simulations. Twelve API 5L grade B reduced scale steel tubes with central perforations and similar longitudinal and transverse slenderness, respectively defined by length to radius of gyration of the cross-section area and diameter to thickness ratios, are tested covering the range of interest for full scale members. The composite material consists of a hybrid fabric made of carbon and glass fibers impregnated with epoxy resin. Severe localized corrosion is considered conservatively, idealized as a circular perforation in half the element length. In many cases the maximum load of the repaired tube even exceeded the intact tube capacity. Moreover, it is shown that sufficient load capacity recovery is achieved for the conditions assumed.

Strain Measurement on Cracks Using Fiber Bragg Gratings for Use in Aircraft Composite Skin Repairs

Fiber Bragg grating (FBG) sensors have been widely used for measurements of strain and temperature in a host of different applications, including aerospace in composite wings, fuselage structures, and other critical components. Here, we report on a method to measure highly localized intense stress fields, generated at the initialization point of a crack, or crack-tip, using Fiber Bragg Gratings (FBG) inscribed in highly photosensitive hydrogenated germanium and boron co-doped fiber. From the spectral characteristics of short and long FBGs, bonded on a test aluminum coupon with a crack, which simulated damaged skins of an aircraft, the local stresses near the cracks were measured and assessed. As a case study, bespoke composite repair patches were designed and bonded on a coupon, incorporating a number of gratings to monitor the stress distribution with applied force in the composite patch, near the crack.

Comparison of SCC behaviour of crack in thin aluminium structure with and without single sided composite patch repair

Comparison of SCC behaviour of crack in thin aluminium structure with and without single sided composite patch repair

Bonded composite patch repair’s fiber VF effects on damaged Al-plates fatigue employing a multi-scale algorithm

Recently, bonded composite patch repair, because of its significant advantages over traditional methods, has been highly accepted in several industries, particularly in aerospace applications. In this paper, a multi-scale finite element algorithm is proposed to simulate crack growth of repaired plates under fatigue load by considering the effects of composite micro-scale properties. The algorithm is verified through conducting an experimental set up and the proposed model is in reasonable agreement with experiments. The influences of different fiber volume fractions (VF), number of layers and fiber orientation of composite patch on the fatigue responses of adhesively bonded patch are investigated. For this purpose, Python scripts are written to automatically increase the size of the crack in ABAQUS. In this study, glass–epoxy and boron–epoxy patches are selected with volume fraction 0.1 to 0.7, the numbers of layers of 4, 8 and 16 as well as 5 different fiber orientation lay-ups. The maximum enhancement of fatigue life experimented by the variation of volume fraction is 133% in the mentioned range. Also, increment in the number of cycles by about 287% and 172% were seen per different number of layers and fiber orientation, respectively.

The Effect of corrosion on the quality repair of the aluminum alloy A 5083 H11 by bonded composites

In this paper, the effect of corrosion on the performance of the bonded composite patch repair in aluminum alloy A5083 marine structure was investigated using three dimensional finite element methods. To this end, two patches made in carbon/epoxy and boron/epoxy, bonded on corroded plates with and without crack, were tested under different applied loads. The effect of both corrosion and cracked materials on the damage of the adhesive FM73, was also highlighted. The obtained results show that, the corrosion has a significant effect on the quality repair performance. Indeed, it is proved that, the rate of damage increases with the increase of the applied load, and is more significant in the case of plates cracked and repaired by carbon/epoxy patch. Hence, the best performances were obtained using boron/epoxy patches

Performance assessment and optimization of hybrid composite patch repair of aircraft structure

PurposeIn this article, a novel hybrid composite patch consisting of unidirectional carbon fiber and glass fiber is considered for repair of the aircraft structure. The purpose of this paper is to assess the performance of hybrid composite patch repair of cracked structure and propose an optimized solution to a designer for selection of the appropriate level of a parameter to ensure effective repair solution.Design/methodology/approachElastic properties of the hybrid composites are estimated by micromechanical modeling. Performance of hybrid composite patch repair is evaluated by numerical analysis of stress intensity factor (SIF), shear stress, and peel stress. Design of experiment is used to determine responses for a different combination of design parameters. The second-order mathematical model is suggested for SIF and peel stress. Adequacy of the model is checked by ANOVA and used as a fitness function. Multiobjective optimization is carried out with a genetic algorithm to arrive at the optimal solution.FindingsThe hybrid composite patch has maintained equilibrium between the SIF reduction and rise of the peel stress. The repair efficiency and repair durability can be ensured by selection of an optimum value of volume fraction of glass fiber, applied stress, and adhesive thickness.Originality/valueThe composite patch with varying stiffness is realized by hybridization with different volume fraction of fibers. Analysis and identification of optimum parameter to reduce the SIF and peel stress for hybrid composite patch repair are presented in this article.

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.

Optimization of composite patch repair for center-cracked rectangular plate using design of experiments method

The repair of aircraft structures using composite material patches are well known in aerospace industries. In the present work composite patch bonded with a superglue over a cracked rectangular plate under uniform uniaxial tensile stress is considered. A three-dimensional finite element method was used to define the stress intensity factor for a repaired plate at mode-I crack propagation. Later, the design of experiments method was used to investigate the parametric effect on repair structure in order to achieve the optimum solution. The size and mechanical properties of the adhesive bond and composite patch that affect the repair quality are considered as the parameters for reduction in stress intensity factor. The outcome of this work will serve as a guideline for designer to improve the repair quality and durability.

Towards hybridization of composite patch in repair of cracked Aluminum panel

Purpose The maintenance of aircraft structure with lower cost is one of the prime concerns to regulatory authorities. The carbon fiber-reinforced polymer (CFRP) patches are widely used to repair the cracked structure. The demands and application of CFRP compel its price to increase in the near future. A distinct perspective of repairing the cracked aluminum panel with the hybrid composite patch is presented in this paper. The purpose of this paper is to propose an alternative patch material in the form of a hybrid composite patch which can provide economical repair solution. Design/methodology/approach The patch hybridization is performed by preparing the hybrid composite from tows of carbon fiber and glass fiber. Rule of hybrid mixture and modified Halpin–Tsai’s equation are used to evaluate the elastic constant. The stress intensity factor and interfacial stresses are determined using finite element analysis. The debonding initiation load is evaluated after testing under mode-I loading condition. Findings The hybrid composite patch has rendered the adequate performance for reduction of stress intensity in the cracked panel and control of interfacial stresses in the adhesive layer. The repair efficiency and repair durability of the composite patch repair was ensured by incorporation of the hybrid composite patch. Originality/value The studies involving patch hybridization for the application of composite patch repair are presently lacking. The influence of the patch stiffness, methodology to prepare the hybrid composite patch and effects of hybridization on the performance of composite patch repair is presented in this paper.

Numerical optimizing and experimental evaluation of stepwise rapid high-pressure microwave curing carbon fiber/epoxy composite repair patch

Numerical models of multi-layer composite laminates with various fiber orientations and fiber layers were investigated under adhesively bonded repair condition by ABAQUS. Stress intensity factors (SIF) of bonded structure systems were calculated by J integral method. Results indicated that composite laminate with [90/90/90] fiber orientation and three fiber layers exhibited the lowest numerical SIF value. The laminates reinforced by carbon fiber with corresponding orientation were experimentally prepared in a two-step high-pressure microwave curing and traditional thermal curing methods on the basis of simulated results, respectively. Mechanical and curing properties of laminates prepared by two curing methods were characterized and compared by means of tensile tests and differential scanning calorimetry (DSC). In comparison to the thermal curing method, the laminate can be prepared more effectively by means of microwave curing method, and the laminate with [90/90/90] fiber orientation and three fiber layers showed the optimal static mechanical performance and the highest curing degree due to the synergistic effect of dipolar induced effect and heating effect generated by microwave, which was in well agreement with the results of numerical simulation.

A smart multi-functional printed sensor for monitoring curing and damage of composite repair patch

A novel multifunctional diagnostic sensor is developed as a cost-effective, in-service structural health monitoring system for determining the initial quality of curing of a bonded composite repair patch and assessing its long-term durability on composite structure. The proposed multi-functional sensor technology involves the creation of a ‘tailor-to-order’ 2D conductive patterns onto step-sanded repair surface of composite repair patch using inkjet printing. In employing this methodology, bondline quality during curing and in service was successfully assessed via impedance spectroscopy and resistance change measurements, respectively. The ability of this technology to effectively monitor the integrity of the bondline and the extent of damage in real-time was investigated by subjecting the scarf-repaired carbon fiber reinforced polymer panels to 3-point bending fatigue and low-velocity impact tests. The obtained results were compared with those of transient infrared thermography and ultrasound inspection techniques, thus validating the proposed method.

Pipeline repair by composite patch under temperature and Pressure loading

In this study, the three-dimensional finite element method is used to analyze an API 5L X70 steel cylindrical pipeline subjected to an internal pressure load by calculating the stress intensity factors and the integral J at the peak of crack in elastic and elastoplastic behavior. The effectiveness of composite patch repair bonded to the cracked surface is highlighted. The effects of the geometrical and mechanical properties of the composite patch and the adhesive on the effectiveness of the repair were highlighted. The variation of the stress intensity factor at the crack tip is used to evaluate the repair performance. The results obtained show that the residual heat stress significantly increases the stress intensity factor at the bottom of the crack, which reduces the effectiveness of the repair.