Aluminum Patch Research Articles

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.

Experimental and Numerical Investigation on Geometric Parameters of Aluminum Patches for Repairing Cracked Parts by Diffusion Method

Repairing cracked aerial structures using patches is a common way to restore mechanical properties, strength and extend fatigue life. The performance of such patches can be obtained by comparing the maximum amount of force tolerated by the repaired piece with the unrepaired piece. The shape and dimensions of the patch used to repair the crack and the way the patch is bonded affect the repair quality which are of great importance. Therefore, in this paper, we investigate the factors affecting the diffusion bonding between the patch and the piece. The impact of the shape of the aluminum patch attached on a 10 mm central crack piece and perpendicular to the loading direction (mode I) is studied experimentally and numerically. The optimum conditions for the diffusion connection including the pressure, time and temperature of the connection were obtained experimentally using a composite rotatable centered design and in the connection made under these conditions, the patch shape and aspect ratio was considered as variables of design, and the results were obtained for square, rectangular, circular and elliptical patches. At the end, it was found that the best connection under the pressure conditions of 570 °C, 70 bar and 100 min was formed and the rectangular patch efficiency was greater whereas its extent is more in line with crack than the other modes. At a fixed area, the different patch geometries investigated in this study were able to influence up to 80% of the maximum force tolerated by the repaired parts. Also, there is an acceptable convergence between experimental and numerical results.

Performance Evaluation of a Piezoelectric Energy Harvester Based on Flag-Flutter.

In the last few decades, piezoelectric (PZT) materials have played a vital role in the aerospace industry because of their energy harvesting capability. PZT energy harvesters (PEH) absorb the energy from an operational environment and can transform it into useful energy to drive nano/micro-electronic components. In this research work, a PEH based on the flag-flutter mechanism is presented. This mechanism is based on fluid-structure interaction (FSI). The flag is subjected to the axial airflow in the subsonic wind tunnel. The performance evaluation of the harvester and aeroelastic analysis is investigated numerically and experimentally. A novel solution is presented to extract energy from Limit Cycle Oscillations (LCOs) phenomenon by means of PZT transduction. The PZT patch absorbs the flow-induced structural vibrations and transforms it into electrical energy. Furthermore, the optimal resistance and length of the flag is predicted to maximize the energy harvesting. Different configurations of flag i.e., with Aluminium (Al) patch and PZT patch for flutter mode vibration mode are studied numerically and experimentally. The bifurcation diagram is constructed for the experimental campaign for the flutter instability of a cantilevered flag in subsonic wind-tunnel. Moreover, the flutter boundary conditions are analysed for reduced critical velocity and frequency. The designed PZT energy harvester via flag-flutter mechanism is suitable for energy harvesting in aerospace engineering applications to drive wireless sensors. The maximum output power that can be generated from the designed harvester is 6.72 mW and the optimal resistance is predicted to be 0.33 M.

Shear Wave Generation by Remotely Stimulating Aluminum Patches With a Transient Magnetic Field and Its Preliminary Application in Elastography.

This article presents shear wave generation by remotely stimulating aluminum patches through a transient magnetic field, and its preliminary application in the cross-correlation approach based ultrasound elastography. A transient magnetic field is employed to remotely vibrate the patch actuators through the Lorentz force. The origin, and the characteristics of the Lorentz force are confirmed using an interferometric laser probe. The shear wave displacement fields generated in the soft medium are studied through the ultrafast ultrasound imaging. The potential of the shear wave fields generated through the patch actuators for the cross-correlation approach based elastography is confirmed through experiments on an agar phantom sample. Under a transient magnetic field of changing rate of 10.44kT/s, the patch actuator generates a shear wave source of amplitude of 100 μm in a polyvinyl alcohol (PVA) phantom sample. The shear wave fields created by experiments agree qualitatively well with those by theory. From the shear wave velocity map computed from 100 frames of shear wave fields, the boundaries of cylindrical regions of different stiffness can be clearly recognized, which are completely concealed in the ultrasound image. Shear wave fields in the level of 100 μm can be remotely generated in soft medium through stimulating aluminum patches with a transient magnetic field, and qualitative shear wave velocity maps can be reconstructed from the shear wave fields generated. The proposed method allows potential application of the cross-correlation approach based elastography in intravascular-based or catheter-based cardiology.

Repairing cracked aluminum plates by aluminum patch using diffusion method

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

The Effect of Oxidation on the Far-Field Scattering of Aluminium Patch Antennae from Visible to UV

In this paper we evaluate the effect of oxidation on the total power scattered in the far field by a 60nm radius Al sphere in the presence of a substrate comprised of either Al or silica (SiO2). Using an effective medium approach to model the Al particle with an outer layer of alumina (Al2O3), we find that the UV peak of total energy scattered in the far field shifts towards longer wavelengths for volume fractions of Al2O3 up to 20%. When particles with these volume fractions are held above an Al substrate, enhancement of two orders of magnitudes of the far-field power radiated by a dipole in the gap can be observed. For larger volume fractions of Al2O3, the total intensity of light scattered is significantly reduced.

Investigation of the Lamb Wave Modes Sensitivity in the Inspection of Bonding between Aluminum and Composite Patch

Nowadays, composite patches are widely used to repair damaged metal structures in different industries. In order to assure the perfect performance of these structures, the bonding between composite patches and metal structures should be inspected. Ultrasonic Lamb waves are among the common methods for assessment of the bonding between the composite patches and metal plates. The main goal of this research is to evaluate the sensitivity of the ultrasonic Lamb wave modes in bonding inspection. For this purpose, dispersion curves of an aluminum plate bonded to a composite patch were obtained and using the through thickness stress distribution, the sensitivity of existing modes to the bonding was evaluated. An experimental examination was also performed to generate the possible modes obtained from the theory and to show the effect of disbond on the output signals. Based on the experimental results, the mode which had been predicted to be more sensitive to the bonding was more affected by the disbond. Three Lamb wave modes were excited for inspecting the disbond between aluminum and composite with the angle wedge transducer. As it was theoretically predicted, the Lamb wave mode with higher values of shear stress in the adhesive layer was more affected by the disbond. On the other hand, disbond detection using the mode with poor values of shear stress at the adhesive layer was difficult. These results were concluded from the amplitude change percentage due to disbond in the experiments.

Enhanced Failure Load Bearing in Adhesively Bonded Strap Repairs: Numerical Analysis and Experimental Results

Adhesively bonded repairs are frequently used to repair aluminum structures due to their attractive options compared to traditional methods such as welding or riveting. A new method of increasing the repair’s strength against uniaxial tensile loads is used in this study. For this purpose, standard single-strap (SS) and double-strap (DS) repairs were produced with aluminum patch. In the first step, an epoxy-based adhesive was employed to create SS and DS repairs using neat adhesive and 0.5 wt.% reduced graphene oxide (RGO)-reinforced adhesive. Afterward, samples of SS and DS joints with the reinforced adhesive were manufactured to study the effect of the added RGO. Uniaxial tensile tests were conducted and above 30% enhancement in the ultimate load was observed in the joints bonded with reinforced adhesive. The repaired joints were analyzed by finite element (FE) method using cohesive zone modeling technique to obtain failure loads. For this purpose, two sets of tests (a) double cantilever beam and (b) end notch flexure tests were implemented to estimate the cohesive zone model CZM parameters. Comparing the results obtained from experiments and the numerical simulations shows that FE models accurately predict the failure load in the reinforced and unreinforced repaired joints.

Variation in aluminium patch test reactivity over time.

Contact allergy to aluminium has been reported more frequently in recent years. It has been pointed out that positive patch test reactions to aluminium may not be reproducible on retesting. To investigate possible variations in patch test reactivity to aluminium over time. Twenty-one adults, who had previously reacted positively to aluminium, were patch tested with equimolar dilution series in pet. of aluminium chloride hexahydrate and aluminium lactate, four times over a period of 8 months. Thirty-six of 84 (43%) serial dilution tests with aluminium chloride hexahydrate and 49 of 84 (58%) serial dilution tests with aluminium lactate gave negative results. The range of reactivity varied between a negative reaction to aluminium chloride hexahydrate at 10% and/or to aluminium lactate at 12%, and a positive reaction to aluminium chloride hexahydrate at 0.1% and/or to aluminium lactate at 0.12%. The highest individual difference in test reactivity noticed was 320-fold when the two most divergent minimal eliciting concentrations were compared. The patch test reactivity to aluminium varies over time. Aluminium-allergic individuals may have false-negative reactions. Therefore, retesting with aluminium should be considered when there is a strong suspicion of aluminium contact allergy.

Sound attenuation in ducts using locally resonant periodic aluminum patches

In recent years, the control of low frequency noise has received a lot of attention for several applications. Traditional passive noise control techniques using Helmholtz resonators have size limitations in the low frequency range because of the long wavelength. Promising noise reductions, with flush mounted aluminum patches with no size problems can be obtained using local resonance phenomenon implemented in acoustic metamaterial techniques. The objective of this work is to introduce locally resonant thin aluminum patches flush mounted to a duct walls aiming at creating frequency stop bands in a specific frequency range. Green's function is used within the framework of interface response theory to predict the amount of attenuation of the local resonant patches. The two-port theory and finite elements are also used to predict the acoustic performance of these patches. No flow measurements were conducted and show good agreement with the models. The effect of varying the damping and the masses of the patches are used to expand the stop bandwidth and the effect of both Bragg scattering and the locally resonant mechanisms was demonstrated using mathematical models. The effect of the arrays of patches on the effective dynamic density and bulk modulus has also been investigated.

Validation of low frequency noise attenuation using locally resonant patches.

Since conventional silencers in acoustic ducts have problems of size limitations at low frequencies and being prone to high backpressure, locally resonant aluminum patches are introduced in acoustic duct walls aiming at creating frequency stop bands in the low frequency region (below 1 KHz). With these flush mounted patches, promising noise reductions, with no such drawbacks, can be obtained, building on local resonance phenomenon implemented in acoustic metamaterials techniques. The objective of the current paper is to experimentally validate the performance of an array of flexible side-wall-mounted patches inside ducts. The experimental results are compared with Analytical Green's function method as well as Numerical Finite Element Method and a close agreement was found. The results show that the presence of the patches singly or periodically can play a prominent role in designing any acoustic bandgap materials. The effect of the arrays of patches on the effective dynamic density and bulk modulus has also been investigated.

Integrated Millimeter-Wave Antennas for On-Chip Communication

This paper introduces the design and analysis of circularly polarized (CP) and dual-polarized on-chip microstrip antennas for wireless communication at 60 GHz. The CP on-chip antenna consists of a circular aluminum patch with two overlapped circular slots fed by the transmission line. The radiation characteristics of the CP have been analyzed using the finite integration technique and finite element method based electromagnetic solvers. The CP antenna introduces left-hand circular polarization and employs as on-chip transmitter. A design of dual-polarized on-chip microstrip antenna at 60 GHz is investigated and is employed as on-chip receiver. The dual ports of the dual polarized antenna are designed with high isolation between them in order to be used as a two on-chip receivers. The radiation characteristics of the dual-port antenna have been calculated. The effect of the separation distance between the CP-antenna and the dual-polarized antenna on the same chip has been investigated. The performance parameters like the reflection coefficient, transmission coefficient, and the transmission gain of the two antennas at different separation distances have been introduced.

Comparison between composite and metallic patches for repairing aircraft structures of aluminum alloy 7075 T6

In this study, experimental and numerical investigations were carried out in order to compare the performances of composite and metallic patches for repairing aircraft structures. In the experimental part, an accelerating aging of the composite was realized by the immersion of the composite patch in distilled water. The fatigue lives of notched plates repaired with aged composite patch, non-aged composite patch and aluminum patch were measured. The obtained results show that the composite patch is more beneficial than the aluminum patch if there is no significant water absorption by the composite. In the numerical part, the stress intensity factor at the crack tip was computed for aged and non-aged composite patches and for aluminum patches. The numerical results confirm the experimental ones, the reduction of the stress intensity factor by the composite patch is more significant than the aluminum patch but the water absorption reduces significantly the repair efficiency.

Experimental Characterization of Nanofilm Microstrip Antennas

We report on the experimental characterization of microstrip antennas where the radiating patch is entirely composed of nanofilms-chromium, aluminum, titanium, or nickel (the first two 15 nm thick and the latter two 20 nm thick). The nanofilms are excited indirectly through an aperture coupled feeding mechanism. The aluminum patch structure is seen to behave as an antenna with outstanding radiation performance and shows an ultrawideband response. The results demonstrate the potential for these antennas for system-on-chip, space application, and other specialized applications.

Modelling of a cracked aluminium plate repaired with composite octagonal patch in mode I and mixed mode

Adhesively bonded composite patch repair technique has been successfully applied in military aircraft repair and has recently been expanded to commercial aircraft industry. This technique is applied to extend the service life of cracked aluminium components. In this paper, the finite element method is applied to analyse the central crack’s behaviour repaired by a boron/epoxy composite patch. The effects of the mechanical and geometrical properties of the patch on the variation of the stress intensity factor at the crack tip were highlighted. The obtained results show that the stress intensity factor at the crack tip, repaired by an octagonal patch of height 2 c/3, is reduced by 5% with regard to the one repaired by an octagonal patch of size ‘ c’. For a height patch of c/3 the reduction is about 7%. The maximum reduction of composite patch of fibres in y-direction is about 30% compared to the aluminium patch. This reduction doubles when a composite patch of fibres in x-direction is used. The adhesive properties must be optimised to increase the performance of the repair of structures by such reinforcement.

Resonant enhancement of emission and absorption using frequency selective surfaces in the infrared

We investigate the infrared properties of frequency selective surfaces consisting of aluminum patches on silicon substrates. Resonant behavior is found not only in the transmission and reflection, but also in the absorption and emission of these surfaces. The resonance location is a controllable function of the surface pattern. Simple model calculations reproduce well the qualitative behavior of our samples.

The Effects of Patch Properties on the Debonding Behavior of Patched Beam-Plates

The debonding characteristics of patched structures are investigated in this study by means of an analytical model. In particular, the effects the lay-up sequence and edge-tapering of a carbon-reinforced epoxy patch, as well as the beveling of an aluminum patch, have on the initiation, stability, and extent of the debonding are considered. The results presented show that both the degree of edge-tapering and the patch properties must be carefully selected in order to optimize the patched structure. It is also shown that when designing a patched system, it is important to model the correct boundary and load conditions to correctly simulate the debonding behavior. [S0094-4289(00)02204-0]

Arrestment of cracks in plane extension by local reinforcements

Crack stoppers ahead of an edge crack in panels under tensile load are analyzed. They consist of rectangular and semi-annular patches placed symmetrically on both sides of the panel and at a finite distance ahead of the crack tip. Depending on this distance, the predicted crack path could remain straight or curve. Moreover, the crack could either be arrested or run through the reinforcements. Such a behavior can be determined from the local and global stationary value of the strain energy density function. The degree of instability is reflected by an index parameter that accounts for the effect of load, geometry and material. Edge crack plexiglass specimens were made by reinforcing them with steel and aluminum patches placed at different distance from the crack. For sufficiently low local energy intensity, the crack would run straight and arrest at the patch regardless of the other variables. As the local energy intensity is increased, crack would tend to curve and lead to complete fracture of the patched specimens. This is equivalent to moving the patch closer to the crack tip. The test results agree well with the predictions made from the strain energy density theory.

Vaccination granulomas and aluminium allergy: course and prognostic factors

21 children who had cutaneous granulomas following immunization with a vaccine containing aluminium hydroxide, and who had positive patch tests to aqueous aluminium chloride and/or to a Finn Chamber, were followed for 1 to 8 years. During the period of observation, the symptoms cleared in 5 children, improved in 11, and remained unchanged in 5. The course of the granulomas could not be correlated with sex or atopy, nor with intensity of the initial aluminium patch test. 4 children were patch tested again with aluminium.

Sanitary Napkin Dermatitis due to the Perfume

Deodorant sanitary napkins are being used with increasing frequency. This is a case report of a patient with a puzzling vulvar dermatitis, which was due to the perfume in the deodorant sanitary napkin. Report of a Case A 38-year-old woman sought treatment in September 1977 with a perineal dermatitis that had been present for six months. She had been treated with many topical preparations without benefit. On examination she had a well-demarcated area of dermatitis on the labia, extending onto the anal area. Patch testing to the routine North American Contact Dermatitis seriesshowed positive results (Table 1). All patch tests were applied for 48 hours, using an occlusive technique with aluminum patch test strips. 1 Further questioning showed that she was worse during her menstrual period. Just prior to the onset of the dermatitis, she had begun using deodorized tampons and deodorized sanitary napkins. Patch testing results with the