Composite Patch Research Articles

Thoracotomy patch repair of large diaphragmatic herniae in a porcine model: a tale of two patches.

Congenital diaphragmatic herniae (CDH) may require patch closure in 50% of the cases. We assessed a biologic and composite mesh in aporcineCDH model. Left sided thoracotomy was performed in 20 pigs. Approximately, 30% of the diaphragm was excised and the patch (Surgisis® or Parietex®) inserted to close this defect. The pigs were killed at 6months and the diaphragm was harvested for biomechanical and histological assessment. The mean weight of the pigs at surgery and killing were 6.1kg (4.2-8.4kg) and 94.1kg (80-131kg), respectively. There were two recurrences and three eventrations, all with Surgisis®. There were less dense lung and abdominal adhesions in the Parietex group (P < 0.0001 and 0.025, respectively). The tensile strength of the Surgisis®, the Parietex® groups and controls were similar. There was significantly more muscle in-growth in the Parietex® patch over Surgisis® (p = 0.016). Parietex® and Surgisis® patches at 6months have a similar tensile strength to normal tissue. All recurrences and eventrations were in the Surgisis® group. Parietex® patches demonstrated more muscle in-growth into the patch compared to Surgisis®. This is the first study utilising Parietex® composite patch in the repair of large diaphragmatic defects in a porcine model.

Variable stiffness composite patch for single-sided bonded repair of composite structures

Variable stiffness composite patch for single-sided bonded repair of composite structures

Numerical investigation of patch geometry effect on the fatigue life of aluminum panels containing cracks repaired with CFRP composite patch using XFEM and CZM approach

This study investigated numerically the effect of using composite patches with various geometric shapes to improve the fatigue life of aluminum panels of AA7075-T6 and AA2024-T3 containing cracks and compared with the available experimental results. The Cohesive Zone Model (CZM) and Extended Finite Element Method (XFEM) were applied to static and fatigue analyses. Four types of rectangular, trapezoidal, left-oriented and right-oriented triangular composite patches were used in the numerical analysis. With the combination of XFEM and CZM methods, and using the Paris equation, the fatigue crack propagation and fatigue life of aluminum panels containing cracks can be reasonably predicted. A composite patch with a suitable shape and geometry, fatigue life of the repaired panel can be improved considerably. With a 204% improvement in fatigue life in comparison to the unrepaired panel, the repaired sample made of aluminum alloy AA2024-T3 alloy achieved the most significant improvement in fatigue life. In AA7075-T6 alloy samples repaired with composite patches, the samples repaired with rectangular and trapezoidal patches experienced the highest fatigue life increases, respectively with 342 and 290% compared to the unrepaired samples. The comparison of numerical simulation results with the available experiment results shows a good agreement.

Analysis of load-displacement curves of an adhesive-reinforced composite patch repaired plate using the combination of XFEM and CZM techniques

Since the development of the eXtended Finite Element Method (XFEM), Cohesive Zone Modelling (CZM), and the Virtual Crack Closure Technique (VCCT) for damage analysis in repaired structures, it has now become easy to validate experimental tensile tests carried out on damaged and repaired plates with a composite patch. In most cases, these tensile tests can be expensive and time-consuming due to surface preparation, cleaning, polishing, adhesive application, and the crosslinking time of the adhesive, which must be carefully considered. The analysis of damage in structures assembled by adhesive bonding is crucial to predicting their behavior under various loading conditions. Moreover, the analysis of experimental curves is in most cases translated a global behavior without taking into account the details that can influence the results. With the introduction of techniques (XFEM, CZM and VCCT), it is now possible to model different forms of damage, accounting for several mechanical and geometric parameters of the plate, patch, and adhesive. This work aims to analyze the behavior under tensile loading of a 2024-T3 aluminum plate presenting an initial crack of different lengths emanating from a central circular notch. This plate is repaired by a carbon/epoxy type patch through an adekit A140 adhesive. The combined use of XFEM to track damage in the plate and CZM for adhesive debonding allowed the acquisition of tensile load-elongation curves and the assessment of damage inflicted by loading on the plate. The results demonstrate that the combined use of XFEM and CZM techniques enables the identification of the adhesive debonding impact on the load transfer to the patch and consequently on the strength of the repaired structure. Furthermore, these highlight that the decrease in the effectiveness of the composite patch with increasing crack size is directly linked to the progressive deterioration of both the plate and the adhesive strength.

Reliability-based multi-objective optimization design of composite patch repair structure using artificial neural networks

Due to the parameter differences and the existence of random factors, the performance of composite repair structure shows a large dispersion. In order to obtain stronger, lighter and more reliable repair structure, multi-objective optimization design of carbon fiber reinforced polymers (CFRP) laminate repair structure is investigated by combining the reliability theory, artificial neural networks and the genetic algorithm. First, a 3D simulation model of the composite laminate patch repair structures is established using the 3D Hashin criterion and the cohesive region model. Then, the Latin Hypercube sampling (LHS) method is used to realize the random sampling, and the strength proxy model of the repair structure is established by using Back-propagation artificial neural network, further a multi-objective optimization model with tensile strength, reliability and weight as objective functions is built considering the design parameters and the random parameters. Finally, NSGAⅡalgorithm is used to solve the multi-objective optimization problem, and a set of solutions on the Pareto front surface are obtained, also the optimal design parameters of the composite repair structure meets the requirements is obtained.

Crack assessment in spiral-welded pipelines repaired by composite patch: a SMART and failure assessment diagram approach

Crack assessment in spiral-welded pipelines repaired by composite patch: a SMART and failure assessment diagram approach

New Prediction Of Cracks Propagation In Repaired Steel Plate With Bonded Composite Patch At Cyclic Loading

Abstract This study presents a numerical prediction of the fatigue life of steel panels repaired by a composite patch. The effect of length cracks, the stress ratio R and properties of the patch is presented. The obtained results show that the bonded composite repair significantly reduces the stress intensity factors at the tip of repaired cracks. The results are in a good agreement with those in the literature. The Monte Carlo method is used to predict the distribution function governing crack propagation in fatigue analysis. In computing the failure probability of the structure, we consider the statistical uncertainty associated with key variables, along with the previously discussed model uncertainty. The results obtained highlight the considerable impact of variations in crack length and stress ratio on the distribution function. Notably, uncertainty in these parameters significantly amplifies the probability of structural failure in plates, thereby diminishing overall structural durability.

Effect of temperature and adhesive defect on repaired structure using composite patch

In structural engineering, composite patch repairs are widely used to address cracked structures. However, their behavior under thermo-mechanical loading remains complex and less understood. This study examines the repair of a center-cracked plate subjected to both mechanical and thermo-mechanical environments, using finite element analysis in ANSYS. The repair effectiveness is evaluated using the Stress Intensity Factor (SIF) at the crack tip. Findings reveal that increased temperature substantially elevates SIF values. Boron/epoxy patches are most effective under mechanical loading, yielding the lowest SIF, while graphite/epoxy patches excel under thermo-mechanical loading due to their lower Coefficient of Thermal Expansion (CTE). Patch thickness influences SIF differently based on loading conditions; thicker patches decrease SIF under mechanical loading but increase it under thermo-mechanical loading. Furthermore, adhesive defects, particularly at the crack tip, markedly increase the risk of adhesive failure, especially under thermo-mechanical conditions. This research underscores the significant impact of temperature variations on the efficiency of structural repairs, contributing to a deeper understanding of composite patch repair performance in cracked structures.

Design of piezoelectric quasi— zero—stiffness metastructures for improved low—frequency vibration isolation

Abstract In this paper, a novel type of piezoelectric quasi–zero stiffness (QZS) metastructure is proposed and the improved vibration isolation performance is investigated. A piezoelectric QZS metastructure is composed of curved beams covered with piezoelectric macro–fiber composite patches, to which digital circuits are connected. Based on the principle of minimum potential energy and the mode superposition method, the constrain on the geometry and material parameters of the piezo–curved beams to achieve QZS is given. According to this design criterion, 1D, 2D and 3D piezoelectric QZS metastructures are designed, and their improved low–frequency vibration isolation characteristics are comprehensively analyzed through theoretical, numerical and experimental studies. It is demonstrated that by optimizing the parameters of the resonant transfer functions implemented in the digital circuits, high–level damping localized near the first resonant peak can be introduced into the curved beams. As a result, the resonant peaks of the metastructures can be reduced without compromising the isolation performance beyond those peaks.

A patch comprising human umbilical cord-derived hydrogel and mesenchymal stem cells promotes pressure ulcer wound healing

Pressure ulcers (PUs) are common skin injuries known for their high morbidity, rapid onset, susceptibility to infection, and challenging healing process. One potential therapy for PUs is cell-based therapy using mesenchymal stem cells (MSCs). However, poor survival and low cell retention of MSCs on skin lesions limit their therapeutic effects and applications. In this study, we prepared an extracellular matrix (dECM) hydrogel decellularized from the human umbilical cord (UC). A patch composed of UC-dECM and UC-MSCs was employed in the treatment of PUs in C57BL/6 mice. Our results indicate that the UC-dECM hydrogel effectively sustains cell viability, enhances the stemness-related gene expression in UC-MSCs, and promotes human umbilical vein endothelial cells (HUVECs) migration and angiogenesis. Compared to the groups treated with the patch containing only UC-dECM, injection of UC-MSCs or gauze dressing, the patch combining UC-dECM hydrogel with UC-MSCs significantly accelerated PU healing. This positive outcome can be attributed to the promotion of tissue re-epithelialization, collagen deposition, angiogenesis, and inflammation inhibition. Our results suggest that the composite patch, comprised of UC-dECM hydrogel and UC-MSCs, may be a promising therapeutic approach for PU treatment.

Experimental investigation on composite patch repair for cracked aluminum structures

Experimental investigation on composite patch repair for cracked aluminum structures

Determination of an optimum patch configuration in the repair of a center crack in thin aluminum sheet using polymer composite patch

AbstractThe formation of cracks and their growth is an issue of concern in structural applications incorporating thin metal sheets. Adhering cracked region with a patch of composite material has proved effective in repairing cracks. Determining an optimum configuration of composite patch is still a challenge as a shorter patch may not be effective and a larger patch leads to wastage of resources. An appropriate methodology is required for specifying an optimum patch configuration in terms of its length, width, and thickness. The work presented prescribes a methodology for obtaining an appropriate combination of geometrical parameters of the composite patch. The computational tools like finite element analysis and response surface method have been incorporated. This is an extensive work consisting of a number of iterations of numerical analyses carried out for different combinations of the length and width of the patch. The results were also obtained for three different patch thicknesses in which the number of plies were increased from a single ply to three plies. The optimum size was obtained for each of the three patch thicknesses. Finally, a methodology for obtaining the most appropriate patch configuration based on the practical constraint of a small available area is prescribed.Highlights The crack repair in a thin structural sheet using fiber reinforced polymer composite patch separates at the interface. The optimum size of the patch needs to be used for an effective repair. The work consists of a combination of experiments and numerical simulations using finite element analysis. Response surface methodology is employed in this optimization study.

Constructing Mg-phytic acid enhanced hydrogel patch with janus structure for antibacterial and angiogenic urethral repair

Due to bacteria in urine and inadequate blood supply, urethral defect repair faces great clinical difficulties. Inspired by the natural structure of the urethra, in this study, we designed a multifunctional hydrogel urethral patch with a Janus structure. The inner layer was a double-network hydrogel of polyvinyl alcohol/carboxymethyl chitosan (PVA/CMCS) enhanced by natural phytic acid (PA) and Mg2+ (Mg2+-PA/PVA/CMCS). The outer layer was composed of poly (L-lactic acid) (PLLA) nanofibers to form a hydrophobic barrier, coupling via a micelle layer to ensure interfacial bonding. The patch exhibited mechanical properties matching soft tissues, with maximum tensile strength and toughness of 1.69±0.13 MPa and 24.7±0.9 MJ/m3, respectively, under the strengthening effect of Mg2+-PA chelation. Therein, the 4 % Mg2+-PA/PVA/CMCS composite patch could maintain unilateral hydrophobicity for at least 14 days and demonstrated an antibacterial rate of 99.0 %±0.1 % against E. coli. In PBS, the patch could deliver Mg2+ for at least 7 days and stabilize the surrounding pH environment for up to 28 days. In vitro cell experiments indicated that the 4 % Mg2+-PA/PVA/CMCS composite patch could promote the human umbilical vein endothelial cell (HUVEC) proliferation and migration, with the angiogenic protein expression enhanced more than 1.2 times compared with the Control group. In conclusion, the patch constructed in this study may provide a new approach to clinical urethral injury repair.

Modeling and optimization of acantilevered energy harvester partially covered by a macro fiber vomposite patch

Piezoelectric energy harvesters (PEH) are recognized as smart structural devices, offering researchers an innovative approach to estimate the energy harvested from real vibration sources. This work presents linear analytical methods for predicting the energy harvested from an unimorph cantilevered beam with a proof mass, with a substrate partially covered by a Macro Fiber Composite (MFC) patch. In order to enhance a PEH that can generate more density of electrical power, a new framework for MFC harvesters with discontinuous geometries using Euler-Bernoulli assumptions is proposed. The length of the harvester can be divided into three parts of uniform beams followed by applying appropriate continuity conditions. Mixing rules are used to derive the equivalent properties of the MFC patch which is considered as five layers. The active layer contains a piezoceramic macro fibers embedded within an epoxy matrix, which is fully covered by electrode and Kapton layers. The excitation of the system is assumed to be at its base. The proposed method is validated through experimental comparison issued from the literature. The results indicate that the location of the MFC patch has a significantly affect to the density of electrical power, the optimal resistance and the natural frequencies.

Effect of repair patch nature on J-integral reduction in notched plates

PurposeThe purpose of this research is to evaluate the effectiveness of different repair patch materials in reducing the stresses at the crack tip of a 2024-T3 aluminum plate. This involves a numerical analysis using the finite element method (FEM) to estimate the reduction in the J-integral value, with the goal of identifying how various parameters related to the patch materials, adhesive properties and loading conditions influence the structural integrity of the repaired plate.Design/methodology/approachThe methodology of this research involves conducting a numerical analysis using the FEM to estimate the reduction in the J-integral value at the crack tip of a 2024-T3 aluminum plate. Three types of patches – metal, composite and functionally graded material (FGM) – were examined under tensile loading conditions, and Adekit-A140 adhesive was used to bond these repair patches to the aluminum plate.FindingsThe analysis considered various parameters, including crack length, the nature of fibers in the composite material, the gradation exponent for FGM patches and the nature of the face in contact with the adhesive for the FGM patch. Additionally, stress analysis was conducted, examining the J-integral values for the plate, shear stress in the adhesive layer and peel stress in the composite patch. The findings highlight that modifying the nature of the repair patch used can significantly enhance the structural integrity of the repaired plate.Originality/valueThe study analyzed J-integral values, shear stress in the adhesive and peel stress in the composite patch. Various parameters, including crack length, fiber type, gradation exponent and adhesive contact face nature, were considered. Results demonstrate that the J-integral value can be significantly reduced by altering the repair patch type, highlighting the effectiveness of customized patch materials in enhancing structural integrity.

Study on the buckling behavior of aluminum alloy sheets - before and after repaired with composite patches

In this paper, the compressive buckling behavior of aluminum alloy plates with an elliptical hole of various sizes is investigated. In order to improve the stability of these thin plates, T700/QY8911 composite laminate is used as a patch to repair the hole. The study included an analysis of the critical and post-critical behaviour using experimental and numerical methods. Experiments focus on buckling loads, post-buckling behavior and the relationship between sizes of holes and buckling load. Meanwhile, the buckling load and buckling mode are determined by finite element analysis, using linear analysis of eigenvalue problems modes, and then, the nonlinear analysis of structures with initiated geometrically imperfection is carried out, studying its post-buckling behavior, damage behavior and transfer of load. The results show that the buckling load of the open-hole specimen is related to size of opening. The existence of patch has a significant influence on stress distribution, and the buckling capability of repaired specimens is noticeably improved to the plate without a hole. And the compression experimental results are consistent with the numerical results, revealing that the developed finite element model of the structure is correct.

Theoretical and experimental study of active vibration control of rotating composite laminated beams using Fx-NLMS algorithm

In the study, an adaptive active vibration control model of rotating composite laminated beam is presented by using the filtered-x normalized least mean square (Fx-NLMS) algorithm, and the experimental study is carried out based on the closed-loop control system. The macro fible composite (MFC) patches is employed to contruct the closed-loop control system of rotating composite laminated beam. By considering peizoelectric coupling effect and the influence of rotating angular velocity, the novel analysis model of vibration transfer function of rotating composite laminated beam with MFC patches is established. The calculation accurancy of the theoretical analysis model is validated by the experimental results. The experimental and simulation studies demonstrate that the low-frequnecy vibration of rotating composite beam is effectively controlled by using the lightweight system. The excellent stability and convergence effect of the closed-loop control system are obtained in the experimental testings. Moreover, the filter orders and learning factor on the active vibration control effect of the rotating composite beam are also stuided and discussed. This work provides a novel appoach for the low-frequency vibration control of the rotating cantilever beams by employing lightweight system.

Rehabilitation and reinforcement of cracked pavements using crack sealers and composite patches

Cracking is a significant concern for pavements and should be appropriately treated during road, highway, and runway rehabilitation. This study investigates the behavior of asphaltic materials under tensile and shear loading modes in intact, fractured, and repaired conditions. With this aim, several methods and materials are utilized for repairs, such as poring adhesive into the crack (using bitumen, neat epoxy resin, and polymer concrete adhesives) and patching the crack with textile (by glass fiber and epoxy resin or bitumen). These tests were conducted at +10 °C, with a three-point bending loading configuration, the same as the actual loading configuration of pavements. Criteria such as failure load, failure work, and post-failure work, as well as failure patterns, were assessed to assess the effectiveness of repairs. Numerical analysis was also performed, and a constitutive model was presented. The ultimate tensile capacity of the cracked specimen is measured at 63 % lower than the intact condition (778 N). The ultimate tensile load of the bitumen-repaired specimen is higher than that of the cracked specimen, but it is still 11 % lower than that of the intact condition. The ultimate tensile capacity of epoxy resin repaired and polymer concrete repaired specimens are 88 % and 79 % higher than the intact specimen (about 1400 N). The ultimate tensile load of the fabric patch reinforced specimen that used bitumen as the adhesive is 38 % higher than the intact specimen (1075 N), while for the case of using the epoxy resin adhesive, this value is 258 % (2788 N). Observations of tensile failure patterns show that, because bitumen is viscoelastic, failure in bitumen-repaired specimens happens in bitumen necking mode and starts at the repaired crack tip. In other cases, the failure occurred far from the pre-crack plane.

A composite patch loaded with 2-Deoxy Glucose facilitates cardiac recovery after myocardial infarction via attenuating local inflammatory response

Local inflammatory microenvironment in the early stage of myocardial infarction (MI) severely impaired cardiac recovery post-MI. Macrophages play a pivotal role in this process. A classical glycolytic inhibitor, 2-Deoxy-Glucose (2-DG), has been found to regulate the excessive pro-inflammatory macrophage polarization in the infarcted myocardium. This study investigated the effect of 2-DG-loaded chitosan/gelatin composite patch on the infarct microenvironment post-MI and its impact on cardiac repair. The results showed that the 2-DG patch significantly inhibited the expression of inflammatory cytokines, alleviated reactive oxygen species (ROS) accumulation, repressed the proinflammatory polarization of macrophages, attenuated local inflammatory microenvironment in the ischemic hearts, as well as improved cardiac function, reduced scar size, and promoted angiogenesis post-MI. In terms of mechanism, 2-DG exerts anti-inflammatory effects through inhibiting the NF-κB signaling pathway and reducing the assembly and activation of the NLRP3 inflammasome. These findings suggest that 2-DG composite patch may represent a promising therapeutic strategy for cardiac repair after MI.

Evaluation of the Composite Skin Patch Loaded with Bioactive Functional Factors Derived from Multicellular Spheres of EMSCs for Regeneration of Full-thickness Skin Defects in Rats.

Transplantation of stem cells/scaffold is an efficient approach for treating tissue injury including full-thickness skin defects. However, the application of stem cells is limited by preservation issues, ethical restriction, low viability, and immune rejection in vivo. The mesenchymal stem cell conditioned medium is abundant in bioactive functional factors, making it a viable alternative to living cells in regeneration medicine. Nasal mucosa-derived ecto-mesenchymal stem cells (EMSCs) of rats were identified and grown in suspension sphere-forming 3D culture. The EMSCs-conditioned medium (EMSCs-CM) was collected, lyophilized, and analyzed for its bioactive components. Next, fibrinogen and chitosan were further mixed and cross-linked with the lyophilized powder to obtain functional skin patches. Their capacity to gradually release bioactive substances and biocompatibility with epidermal cells were assessed in vitro. Finally, a full-thickness skin defect model was established to evaluate the therapeutic efficacy of the skin patch. The EMSCs-CM contains abundant bioactive proteins including VEGF, KGF, EGF, bFGF, SHH, IL-10, and fibronectin. The bioactive functional composite skin patch containing EMSCs-CM lyophilized powder showed the network-like microstructure could continuously release the bioactive proteins, and possessed ideal biocompatibility with rat epidermal cells in vitro. Transplantation of the composite skin patch could expedite the healing of the full-thickness skin defect by promoting endogenous epidermal stem cell proliferation and skin appendage regeneration in rats. In summary, the bioactive functional composite skin patch containing EMSCs-CM lyophilized powder can effectively accelerate skin repair, which has promising application prospects in the treatment of skin defects.