Composite Patch Research Articles

Fatigue performance of cracked diaphragm cutouts in steel bridge reinforced employing CFRP/SMA

Under long-term service conditions, fatigue cracking occurs at the diaphragm arc-shape cutouts in the orthotropic steel deck (OSD) bridges subjected to vehicle-induced vibration and cyclical wheel load. To repair cracks of the diaphragm cutouts, this study proposes two repair methods of the carbon fiber reinforced polymer (CFRP) sheets and shape memory alloys (SMA)/CFRP composite patches on the basis of crack-stop holes. The crack-stop hole eliminates the obvious source of fatigue propagation at the crack tip, but it weakens the section and harms the entirety of the diaphragm. The edge of the crack-stop hole in the cracked section becomes a new stress concentration site and the potential crack initiation point. The CFRP sheets can effectively improve the stiffness and reduce the stress amplitude of the cracked part. Moreover, the SMA/CFRP composite patches can further introduce precompression by activating SMA to reduce the stress level. Relative to the reinforcement by the crack-stop hole only, the fatigue notch factor is reduced by 12.28% and 30.76% after bonding CFRP sheets and SMA/CFRP composite patches, respectively. The fatigue tests show that the bonding of CFRP sheets and SMA/CFRP composite patches can effectively postpone the initiation of fatigue cracks and inhibit crack propagation, so they are ideal repair methods for strengthening fatigue cracks of the diaphragm cutouts in the OSD bridges.

Effect of Patch Interface Strengthening on Mechanical Properties of Epoxy/Carbon Fiber Sheet by Double-Sided Patching

To repair the damage to the epoxy/carbon fiber laminate, a single-lap test was performed between sulfuric acid anodized aluminum plate and carbon fiber laminate to study the effect of the anodized layer on the interlaminar shear strength. Then, carbon fiber laminates were prepared by wet-laying method to simulate the damage caused by penetrating cracks, and double-sided adhesive sheets were made from 0.5[Formula: see text]mm thick 2024-T3 aluminum alloy and carbon fiber laminates to match the thickness and material of the simulated damage plate. The adhesive matrix used was E51 bisphenol-A epoxy resin with 1.5[Formula: see text]wt.% nanorubber added for modification and toughening. After double-sided patching, tensile tests were performed to investigate the effect of different materials on the tensile strength of double-sided adhesive patches. We observed SEM images of the fracture surface of the patch after tensile failure and analyzed the strengthening mechanisms of different material patches. The results show that the shear strength between the single-layer sulfuric acid anodized aluminum plate and the carbon fiber laminate is 9.792 MPa, which is 61.5% higher than the shear strength of the nonanodized aluminum plate. The tensile strength of the 2024-T3 aluminum patch specimen is 271.83 MPa, which is 48.43% and 23.97% higher than the perforated specimen without patch and the specimen with carbon fiber laminate patch, respectively, and reaches 72.56% of the undamaged carbon fiber laminate. The specimens with aluminum plate patches showed a maximum bending strength of 616.47 MPa, which increased by 70.83% compared to the 360.875 MPa of the perforated specimens. The maximum bending strength of the aluminum plate patch specimen reached 74.76% of that of the undamaged specimen. However, the maximum bending strength of the composite patch specimen is as high as 1101.9 MPa, far exceeding that of other samples. Due to the poor toughness of the sample, it cannot withstand large strains. The addition of 1.5[Formula: see text]wt.% nanorubber results in shear yield bands and induces silver grains to absorb a large amount of energy during stress deformation.

Quasi-static and fatigue analyses of aluminium structures repaired by CFRP patch bonding

In this work, quasi-static and fatigue analyses of the three most common adhesive repair geometries were performed considering composite patches and aluminium as parent material. Experimental three-point bending tests were accomplished on single-strap, double-strap and scarf repairs in order to obtain the load–displacement curves for quasi-static analysis, and compliance versus number of cycles curves for the fatigue studies. The main goals are to identify the static strength and fatigue lives for each type of adhesive repair. In addition, progressive damage analyses that rely on two cohesive zone models appropriate for quasi-static and high-cycle fatigue under mixed-mode I + II loading were performed. These models allow the simulation of damage initiation and propagation in the repairs under quasi-static and fatigue loading. It was found that both models are able to replicate the fundamental trends observed experimentally, thus establishing their effectiveness.

Chitosan-Collagen Electrospun Nanofibers Loaded with Curcumin as Wound-Healing Patches.

Composite chitosan-collagen nanofibrous mats embedded with curcumin were prepared via a single-step electrospinning procedure and explored as wound-healing patches with superior biological activity. A mild crosslinking protocol consisting of a short exposure to ammonia vapor and UV radiation was developed to ensure proper stability in physiological-like conditions without affecting the intrinsic biocompatibility of chitosan and collagen. The fabricated composite patches displayed a highly porous, homogeneous nanostructure consisting of fibers with an average diameter of 200 nm, thermal stability up to 200 °C, mechanical features able to ensure protection and support to the new tissues, and water-related properties in the ideal range to allow exudate removal and gas exchange. The release kinetic studies carried out in a simulated physiological environment demonstrated that curcumin release was sustained for 72 h when the mats are crosslinked hence providing prolonged bioactivity reflected by the displayed antioxidant properties. Remarkably, combining chitosan and collagen not only ensures prolonged stability and optimal physical-chemical properties but also allows for better-promoting cell adhesion and proliferation and enhanced anti-bacteriostatic capabilities with the addition of curcumin, owing to its beneficial anti-inflammatory effect, ameliorating the attachment and survival/proliferation rates of keratinocytes and fibroblasts to the fabricated patches.

Taguchi Optimization of Geometrical Factors of a Polymer Composite Patch in Crack Repair

For the repair of a crack in thin aluminium sheets, polymer composite patching is one of the better repair techniques. During service, when the load acts, the patch separates from the substrate due to the stresses developed at the interface. This separation of the patch from the substrate largely depends on the geometrical factors of the patch, i.e. length, width and thickness. The optimum geometrical factors need to be incorporated for the effective and economical repair of the cracks. In this work, the optimum combination of the geometrical factors, i.e. length, width and thickness of the polymer composite patch, is obtained using the Taguchi technique with the help of the results generated in the numerical analyses.

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.

Comprehensive progressive damage analyses of mixed‐mode repaired panels: How composite patch sizes and layups affects restarting fatigue crack growth

AbstractIn this paper, comprehensive progressive damage analyses are performed to evaluate the effects of patch sizes and layups on restarting crack growth of single‐side repaired aluminum panels with central inclined cracks under high cycle fatigue loading. Complicated nonlinear damage behavior of adhesive bonding, composite patch, mixed‐mode cracks, and fatigue loadings require precise numerical tools to consider and analyze the coupling effects of various damages on fatigue life of such complex component. In progressive damage analysis, high cycle fatigue cohesive zone modeling is used for debonding of patch, and high cycle fatigue continuum damage model used for composite patches. Practical composite patch layups and sizes are selected in huge number of models, and the restarting crack growth life is predicted. The obtained results show the possibility of increasing the restarting crack growth life using an appropriate composite patch layup and geometry dimensions.

Probiotic-loaded calcium alginate/fucoidan hydrogels for promoting oral ulcer healing

Probiotics are beneficial bacteria located in the oral cavity which exhibit antimicrobial properties and contribute to the regulation of immune function and the modulation of tissue repair. Fucoidan (FD), a marine prebiotic, may further enhance the ability of probiotics to promote ulcer healing. However, neither FD nor probiotics are attached to the oral cavity and neither are well-suited for oral ulcer healing owing to the wet and highly dynamic environment. In this study, probiotic-loaded calcium alginate/fucoidan composite hydrogels were developed for use as bioactive oral ulcer patches. The well-shaped hydrogels exhibited remarkable wet-tissue adhesion, suitable swelling and mechanical properties, sustained probiotic release, and excellent storage durability. Moreover, in vitro biological assays demonstrated that the composite hydrogel exhibited excellent cyto/hemocompatibility and antimicrobial effects. Importantly, compared to commercial oral ulcer patches, bioactive hydrogels show superior therapeutic capability for promoting ulcer healing in vivo by enhancing cell migration, inducing epithelial formation and orderly collagen fiber deposition, as well as facilitating neovascularization. These results demonstrate that this novel composite hydrogel patch demonstrates great potential for the treatment of oral ulcerations.

Numerical analysis on the strength prediction of composite bonded repairs under different loading scenarios

In the last years, aeronautical industry has developed certified composite patch bonded repairs for damage tolerant structures, but only restoring metallic components. The mechanical behaviour of composite bonded repairs has been investigated since the development of composite damage tolerant structures is directly dependent on this technology. This study presents a strength prediction on carbon-epoxy adhesively repaired component, using ARALDITE® 2015 for the repairing and recurring to ABAQUS®, applying cohesive zone modelling (CZM), four different load conditions: tension, compression, upward bending and downward bending were tested. Four types of repairs are analysed: Single-Strap, Double-Strap, Scarf and Two-Stepped. The obtained results state that the Double-Strap repair withstand higher loads considering all the applied load cases when compared with the other geometries. Scarf and Two-Stepped repairs could achieve promising behaviours and they should be optimized, considering the advantages related to embedded patch repairing. Generally, the overlap length revealed to favour higher strengths, specially increasing from 5 to 10 mm. Failure paths were demonstrated, revealing proper relations with strength predictions.

Study of the Behavior of the AL 2017-A Aluminium Plate Corroded and with Horizontal Cracks Treated by the Technique of Composite Materials

Abstract This work presents a comprehensive study consisting of two aspects: a numerical analytical aspect and a laboratory experimental aspect. The numerical study was a three-dimensional finite element numerical analysis of performance of corroded and horizontally cracked aluminium plates, which were repaired by composite patching. The effect of the composite types on the variance of the damaged area of the adhesive (FM-73) and their efficiency on the stress intensity factor were studied. In the experimental study, corroded aluminium plates were prepared and repaired them using technology of the composite. The results showed that the panels that were repaired with composite (boron/epoxy) give values of stress intensity factor (KI) and damaged area ratio (DR) less than the other two studied composites (glass/epoxy and graphite/epoxy), and increase the ultimate strength of plates damage, and this leads to the conclusion that (Boron/epoxy) increases the performance and durability of (Al 2017-A) plates.

Flexible reversible polymer nano-composite thin film patch for wearable temperature sensor

A flexible polymer nano-composite thin film patch for wearable temperature sensors was fabricated, which presents excellent energy storage and temperature indication properties. In this composite patch, conductive silver (Ag) nanoparticles (NPs) were used as functional fillers while polyvinyl alcohol (PVA) used as polymer material. The effects of Ag NPs concentration on morphology and temperature indication were experimentally investigated using a field-emission scanning electron microscope (FE-SEM), thermogravimetric analyser (TGA) and differential thermal analysis (DTA). The findings showed that Ag was uniformly distributed across matrix membranes. Also, the prepared PVA-Ag nanocomposite thin film patch showed improved mechanical properties and conductivity. The consequence of X-Ray Diffraction (XRD) displayed a semi-crystalline nature. The results show the potential for incorporating subordinate AgNP concentrations as a substitute to enhance performance in terms of mechanical, thermal, and antibacterial qualities without treatment. The electrical properties were studied through the current-voltage(I–V) characteristics showing the linear I–V ohmic contact and low contact resistance. With heat storage and temperature regulation capabilities, a flexible polymer nano-composite patch for a wearable temperature sensor was created and has significant promise for use in the future in energy storage, thermal management, and wearable temperature sensors.

Vibro-acoustic control of a programmable meta-shell with digital piezoelectric shunting

In this paper, a programmable piezoelectric meta-shell is designed to actively control the structural and sound radiation responses. The meta-shell consists of a cylindrical shell, Macro-fiber Composite (MFC) patches and digital shunting circuits. Due to the electro-mechanical coupling effect of the MFC patches, the mechanical properties of the meta-shell structure can be tuned by changing the electric field. The high-order digitally resonant circuits are designed to realize programmable control of the bandgap behaviors of the meta-shell. An analytical structural dynamic model for analyzing the vibration and radiated sound responses of the programmable piezoelectric meta-shell in light fluid is established. The vibro-acoustic characteristics of the meta-shell with the piezoelectric shunting and the effects of electric parameters (including dimensionless gain and electric damping ratio) on the structural and acoustic control performances of the shell are discussed. Experiments on the vibration and acoustic control of a programmable piezoelectric meta-shell are carried out to verify the high-order bandgap characteristic and its programmability. The experimental results demonstrate that the vibration and sound radiation responses of the shell can be effectively suppressed in multiple frequency bands.

P192 POSTINFARCTION VENTRICULAR SEPTAL DEFECT: MANAGEMENT AND A NEW SURGICAL OPTION FOR CLOSURE

Abstract Postinfarction ventricular septal defect is a rare mechanical complication of myocardial infarction, with difficult management, debated closure timing and high mortality rates. Standard repair techniques – infarcectomy and infarct exclusion through a left ventriculotomy – are surgically challenging and have high risk of operative mortality and frequently suboptimal results. We report the case of a 66–year–old patient with a 1.4 cm septal rupture developed after a sub–acute STEMI. At the admission, he had chest pain and moderate dyspnoea, EKG showed inferior STEMI with increased myocardial necrosis markers. Echocardiography showed a preserved ejection fraction, akinesia of the inferior, posterolateral walls and of the posterobasal septum, with septal rupture at this level and 1.5 Qp/Qs ratio. A total occlusion of proximal right main coronary artery was found at coronary angiography. After the heart team meeting, we performed a new modified closure, in urgent setting, using two hand–made composite patches (Fig. 1) parachuted through a transversal aortotomy and a right atriotomy, without left ventriculotomy (Fig. 2). In the 7th postoperative day a second septal rupture was detected at the echocardiographic control. After two weeks follow–up in optimized medical therapy, we decided to complete the closure of the later developed septal rupture percutaneously using an Amplatzer device. Six months after the event, the patient is still asymptomatic and echocardiography documents a 50% ejection fraction, with trivial residual left–to–right shunt and normal valve function. Computed tomography scans confirmed optimal surgical result. Timing, management and surgical strategy are still on debate. Our technique is effective, simple, reproducible and provides good result (Fig. 3) and can be perfectly integrated in a hybrid approach.

Adhesive Composite Hydrogel Patch Based on a Polyaspartamide Derivative to Treat Atopic Dermatitis

AbstractTransdermal patches offer significant advantages as a drug delivery system due to their ability to bypass first‐pass metabolism, sustain drug release, and provide predetermined dose and application area. However, to be effective, transdermal patches must have optimal adhesion and drug‐loading capacity. In this study, an adhesive composite hydrogel patch consisting of poly(N‐2,3‐dihydroxypropyl aspartamide) (PDHPA), a polyaspartamide derivative, and mesoporous silica nanoparticles (MSNs) are developed. To prepare the hydrogel, boric acid (BA) is utilized as a crosslinker to form reversible bonds between multiple hydroxyl groups in the polymer and BA. The PDHPA‐BA hydrogel exhibits dynamic reversibility, self‐healing properties, and a pH‐dependent sol–gel transition. The addition of MSNs with abundant hydroxyl groups improves the mechanical performance, adhesion properties, and self‐healing rate of the PDHPA‐BA hydrogel. In addition, MSNs enable the loading of hydrophobic drugs, such as dexamethasone (Dex), onto the hydrogel. Using the Dex‐loaded adhesive composite hydrogel as a transdermal patch, the severity of atopic dermatitis in a mouse model indicated by suppression of dermatitis score, epidermal thickness, number of mast cells, and serum interleukin‐4 levels is successfully reduced. These results suggest that the composite hydrogel patch is a highly promising transdermal drug delivery system for effectively treating inflammatory skin diseases.

Long-Term Fate and Efficacy of a Biomimetic (Sr)-Apatite-Coated Carbon Patch Used for Bone Reconstruction.

Critical bone defect repair remains a major medical challenge. Developing biocompatible materials with bone-healing ability is a key field of research, and calcium-deficient apatites (CDA) are appealing bioactive candidates. We previously described a method to cover activated carbon cloths (ACC) with CDA or strontium-doped CDA coatings to generate bone patches. Our previous study in rats revealed that apposition of ACC or ACC/CDA patches on cortical bone defects accelerated bone repair in the short term. This study aimed to analyze in the medium term the reconstruction of cortical bone in the presence of ACC/CDA or ACC/10Sr-CDA patches corresponding to 6 at.% of strontium substitution. It also aimed to examine the behavior of these cloths in the medium and long term, in situ and at distance. Our results at day 26 confirm the particular efficacy of strontium-doped patches on bone reconstruction, leading to new thick bone with high bone quality as quantified by Raman microspectroscopy. At 6 months the biocompatibility and complete osteointegration of these carbon cloths and the absence of micrometric carbon debris, either out of the implantation site or within peripheral organs, was confirmed. These results demonstrate that these composite carbon patches are promising biomaterials to accelerate bone reconstruction.

Effect of the stiffness ratio on the growth of repaired fatigue cracks with composite patch

The objective of this study is to develop an analytical model to predict the fatigue life of aluminum alloy panels repaired by a carbon/epoxy patch. The study includes two parts: an experimental part where fatigue tests were conducted on notched specimens of 2024 T3 and 7075 T6 aluminum alloys repaired by unidirectional carbon/epoxy patches in order to measure the crack propagation rate (da/dN) after bonding of the patch. The second part of the work consists in numerically calculating the stress intensity factor range (ΔK) at the tips of repaired cracks. A fatigue life prediction model was established for repaired plates based on the Paris law. This model relates the Paris constants to the stiffness ratio between the patch and the aluminum plate. The model of fatigue life prediction can be useful for the patch repair designers. The obtained results show that the fatigue life is highly improved by the composite patch specially for the aluminum alloy 2024 T3. The number of cycle at failure increases with the increase of the patch thickness. The stress intensity factor at the crack tip is reduced by the patch repair which leads to a slowdown in the propagation of the crack.

An electrospun scaffold functionalized with a ROS-scavenging hydrogel stimulates ocular wound healing.

Ocular alkali burn is a serious ophthalmic emergency. Highly penetrative alkalis cause strong inflammatory responses leading to persistent epithelial defects, acute corneal perforation and severe scarring, and thereby persistent pain, loss of vision and cicatricial sequelae. Early and effective anti-inflammation management is vital in reducing the severity of injury. In this study, a double network biomaterial was prepared by compounding electrospinning nanofibres of thioketal-containing polyurethane (PUTK) with a reactive oxygen species (ROS)-scavenging hydrogel (RH) fabricated by crosslinking poly(poly(ethylene glycol) methyl ether methacrylate-co-glycidyl methacrylate) with thioketal diamine and 3,3'-dithiobis(propionohydrazide). The developed PUTK/RH patch exhibited good transparency, high tensile strength and increased hydrophilicity. Most importantly, it demonstrated strong antioxidant activity against H2O2 and 2,2-di(4-tert-octylphenyl)-1-picryl-hydrazyl (DPPH). Next, a rat corneal alkali burn model was established, and the PUTK/RH patch was transplanted on the injured cornea. Reduced inflammatory cell infiltration was revealed by confocal microscopy, and lower expression levels of genes relative to inflammation, vascularization and scarring were identified by qRT-PCR and western blot. Fluorescein sodium dyeing, hematoxylin and eosin (H&E) staining and immunohistochemicalstaining confirmed that the PUTK/RH patch could accelerate corneal wound healing by inhibiting inflammation, promoting epithelial regeneration and decreasing scar formation. STATEMENT OF SIGNIFICANCE: Ocular alkali burn is a serious ophthalmic emergency, characterized with persistent inflammation and irreversible vision loss. Oxidative stress is the main pathological process at the acute inflammatory stage, during which combined use of glucocorticoids and amniotic membrane transplantation is the most widely accepted treatment. In this study, we fabricated a polyurethane electrospun nanofiber membrane functionalized with a ROS-scavenging hydrogel. This composite patch could be a promising amniotic membrane substitute, possessing with a transparent appearance, elasticity and anti-inflammation effect. It could be easily transplanted onto the alkali-burned corneas, resulting in a significant inhibition of stromal inflammation and accelerating the recovery of corneal transparency. The conception of ROS-scavenging wound patch may offer a new way for ocular alkali burn.

Post-repair residual stresses and microstructural defects in wind turbine blades: Computational modelling

Wind turbine blades require regular maintenance and repair. The post-repair reliability and lifetime depend on the quality and method of repair. Residual stresses present in the repaired sections of the blades are one of the reasons for reduced lifetime and premature failure of repaired blades. Residual stresses occur due to the thermal cycle used to cure the composite repair patch or adhesive and chemical shrinkage during curing. The presence of voids further aggravates the magnitude of the residual stresses. To investigate these effects, analytical models are used to study the cure kinetics and void evolution while the development of residual stresses during the post-gelation period of curing and the effect of the voids are obtained using coupled temperature-displacement analysis in ABAQUS. User subroutines (UEXPAN, HETVAL and UMAT) are used to define the chemical shrinkage, heat generation due to curing and cure-dependent modulus. Both hard and soft patch repair models are considered. It is found that the temperature cycle used affects both the time taken for complete cure and the residual stresses developed in the adhesive. Increasing the first dwell temperature decreases the time to cure but increases the residual stresses. Also, the presence of voids is found to cause stress concentration regions, with stresses increasing up to 2 to 2.5 times the average stresses. Therefore, a balance is needed to minimise the time taken for the repair process while maintaining residual stresses as low as possible, especially in wind turbine repair applications.

A paintable composite hydrogel patch for potential wound dressings

Hydrogel has incomparable advantages in promoting chronic wound healing due to its high-water content, softness and excellent physiological activity. However, as a treatment platform, most hydrogel dressings are fixed at the wound site in block form, which is difficult to fully contact and fit with the tissue, limiting their efficacy. Here, a composite hydrogel that can be conveniently painted to material surface and closely adhered is developed. The hydrogel is obtained through a double network strategy and multiple non-covalent interactions between N-(3,4-dihydroxyphenylethyl) acrylamide (NA)-acrylic acid-acrylamide terpolymer, nano Fe3O4 and chitosan. NA monomer with catechol-like structure can significantly improve the adhesion strength of the hydrogel to 25.06 kPa, which is superior to the commercially available fibrin glue (∼11.5 kPa). Notably, the high-efficiency paintability of the hydrogel can be achieved just by the initiation of ultra-trace potassium persulfate. The hydrogel patch also exhibits satisfactory mechanical properties and cytocompatibility. Hence, this multifunctional hydrogel will be conveniently painted to the wound bed as a patch without adverse liquid leakage, providing an optimistic material for chronic wound treatment.

Optimization of Structural Damage Repair with Single and Double-Sided Composite Patches through the Finite Element Analysis and Taguchi Method

Over the last four decades, numerous studies have been conducted on the use of bonded composite repairs for aircraft structures. These studies have explored the repair of damaged plates through experimental, numerical, and analytical methods and have found that bonded composite repairs are effective in controlling crack damage propagation in thin plates. The use of double-sided composite repairs has been found to improve repair performance within certain limits. This study focuses on these limits and optimizes double-sided composite repairs by varying adhesive bond and composite patch parameters. The optimization process begins with a finite element analysis to determine the stress intensity factor (SIF) for various variables and levels, followed by the application of the Taguchi method to find the optimal combination of parameters for maximizing the normalized SIF. In conclusion, we successfully determined the stress intensity factor (SIF) for various variations and normalized it for optimization. An optimization study was then performed using the Taguchi design and the results were analyzed. Our findings demonstrate the repair performance of bonded composite patches using a cost-effective and energy-efficient approach.