Average Peel Strength Research Articles

Chitosan quaternary ammonium salt-oxidized sodium alginate-glycerol-calcium ion biobased self-healing hydrogels with excellent spontaneous repair performance.

Self-healing hydrogels have attracted wide attention because of their potential applications in various fields. However, the complex processes, environmental requirements, and insufficient functionality limit their practical application. Herein, we synthesized a chitosan quaternary ammonium salt-oxidized sodium alginate-glycerol-calcium ion (HACC-OSA-Gly-Ca2+) biobased hydrogel with a multi-network structure that exhibits excellent self-healing abilities. This was achieved by utilizing reversible dynamic imine bonding, electrostatic interactions, Ca2+ ions as crosslinking points, and hydrogen bonding. The oxidation of sodium alginate (SA) with sodium periodate was carried out to obtain oxidized sodium alginate (OSA) with varying oxidation degrees. The resulting OSAs were then introduced into a glycerol-water solvent system containing chitosan quaternary ammonium salt (HACC) and calcium chloride, and this reaction successfully prepared the biobased eco-friendly self-healing hydrogel. The impacts of the oxidation degree (OD) of OSA on the microscopic morphology, mechanical properties, viscoelastic properties, swelling properties, and self-healing properties of the corresponding synthetic hydrogels were investigated. The outcomes indicated that the optimal HACC-OSA-Gly-Ca2+ hydrogel possessed good mechanical properties, with a tensile stress of 0.0132 MPa and elongation at break of 551.38%. Furthermore, the multiple bond interactions led to a high self-healing ratio (100%), with an elongation at break of about 614.29%, and excellent adhesion ability (average peel strength of 6.38 kN m-1) on various substrates. Additionally, the composite hydrogels exhibited excellent water retention, thermal stability, and resilience, making them promising for various potential applications. Moreover, the properties of the composite hydrogels could be facilely and finely tuned by varying the oxidation degree of OSA and ratio of each component. Thus, the presented strategy could enrich the construction as well as application of biopolymer-based self-healing hydrogels.

Rheology, mechanical properties and peel adhesion of hot-melt adhesive based on thermoplastic polyurethane/nanosilica

A series of thermoplastic polyurethane hot-melt adhesive formulations have been synthesized by melt blending of polyether-based thermoplastic polyurethane and different nanosilica, C5, and C9 hydrocarbon loadings. Different analyses, including FESEM, tensile strength, rotational rheometry, T-peel strength with polyester fabric, and nitrogen gas permeability, are conducted to examine the properties of the prepared adhesive formulations. The results show that the addition of 0.25 wt% of nanosilica increased the tensile properties of the polyurethane slightly and improved the T-peel strength with the polyester fabric. On the other hand, adding 5 wt% of C5 hydrocarbon tackifier reduced the tensile properties a bit, reduced the storage and loss modulus, and increased the T-peel strength with the polyester fabric. On the other hand, adding the C9 tackifier reduced the tensile strength more than the counterpart formulation including C5, reduced the storage and loss modulus and increased the T-peel strength. A noteworthy result was that the addition of nanosilica in the presence of C5 or C9 tackifiers lowered the loss and storage modulus and complex viscosity Adhesive formulation with 5 wt% of C5 tackifier has the highest average and maximum peel strength with about 20 and 35% higher strength than neat TPU.

The Growth of Intermetallic Compounds and Its Effect on Bonding Properties of Cu/Al Clad Plates by CFR

Cu/Al clad plates prepared using a corrugated + flat rolling (CFR) technique were annealed at 300–450 °C for 10–240 min. Furthermore, the interfacial diffusion behavior and the bonding properties of the Cu/Al clad plates were studied in detail. The results demonstrated that, at the initial stage of the annealing process, the development of the first IMCs layer was restrained by the high atomic concentration gradient in the new bonding interface zone, and the second intermetallic compounds (IMCs) layer preferentially formed in the new bonding interface zone, leading to a slight increase in the growth activation energy of the clad plates. In addition, the atoms’ diffusion behavior at the peak and trough interfaces was not significantly affected by the matrix microstructure, and there was no discernible difference in the growth activation energy at these two positions. Ultimately, it was shown that the maximum average peel strength at the peak and trough interfaces reached 53.07 N/mm and 41.23 N/mm, respectively, when annealing at 350 °C for 10 min.

A Biohybrid Material With Extracellular Matrix Core and Polymeric Coating as a Cell Honing Cardiovascular Tissue Substitute.

ObjectiveTo investigate the feasibility of a hybrid material in which decellularized pericardial extracellular matrix is functionalized with polymeric nanofibers, for use as a cardiovascular tissue substitute.BackgroundA cardiovascular tissue substitute, which is gradually resorbed and is replaced by host's native tissue, has several advantages. Especially in children and young adults, a resorbable material can be useful in accommodating growth, but also enable rapid endothelialization that is necessary to avoid thrombotic complications. In this study, we report a hybrid material, wherein decellularized pericardial matrix is functionalized with a layer of polymeric nanofibers, to achieve the mechanical strength for implantation in the cardiovascular system, but also have enhanced cell honing capacity.MethodsPericardial sacs were decellularized with sodium deoxycholate, and polycaprolactone-chitosan fibers were electrospun onto the matrix. Tissue-polymer interaction was evaluated using spectroscopic methods, and the mechanical properties of the individual components and the hybrid material were quantified. In-vitro blood flow loop studies were conducted to assess hemocompatibility and cell culture methods were used to assess biocompatibility.ResultsEncapsulation of the decellularized matrix with 70 μm thick matrix of polycaprolactone-chitosan nanofibers, was feasible and reproducible. Spectroscopy of the cross-section depicted new amide bond formation and C–O–C stretch at the interface. An average peel strength of 56.13 ± 11.87 mN/mm2 was measured, that is sufficient to withstand a high shear of 15 dynes/cm2 without delamination. Mechanical strength and extensibility ratio of the decellularized matrix alone were 18,000 ± 4,200 KPa and 0.18 ± 0.03% whereas that of the hybrid was higher at 20,000 ± 6,600 KPa and 0.35 ± 0.20%. Anisotropy index and stiffness of the biohybrid were increased as well. Neither thrombus formation, nor platelet adhesion or hemolysis was measured in the in-vitro blood flow loop studies. Cellular adhesion and survival were adequate in the material.ConclusionEncapsulating a decellularized matrix with a polymeric nanofiber coating, has favorable attributes for use as a cardiovascular tissue substitute.

Mechanical Properties of Cold Sprayed Aluminium 2024 and 7075 Coatings for Repairs

This study investigates the mechanical properties of aluminium 2024 (Al-2024) and aluminium 7075 (Al-7075) cold-sprayed materials and coatings for repairs. It aims to determine the acceptable data needed to meet regulatory requirement when substantiating cold spray repairs. The study focuses on repairs of non-principal structural element (PSE) structures such as skin and panels that are prone to corrosion and wear. For cold spray repair of such components, the microstructure, tensile, peel, bearing, and bending strength from the repair process and powder materials of Al-2024 and Al-7075, were identified and investigated in accordance with MIL-STD-3021. Results show an average coating porosity of <1.2% for both materials. Average tensile strength was 247.1 MPa (with elongation of 0.76%) for Al-2024 and 264.0 MPa (with elongation of 0.87%) for Al-7075. Al-2024 has an average peel strength of 71.9 MPa, while Al-7075 is at 48.9 MPa. The Al-2024 bearing test specimens gave a maximum load strength before failure of 633.6 MPa, while the Al-7075 gave 762.7 MPa. The bending tests show good flexibility for coating thickness ranges of typical skin and panel parts. The results show that cold spray can be used to restore thickness and oversized hole diameters for Al-2024 and Al-7075 skin and panels. The bearing test conducted in this study has also demonstrated a new test method to determine the bearing load and yield strength of a cold spray-repaired hole in a plate.

Effect of annealing and cold rolling on interface microstructure and properties of Ti/Al/Cu clad sheet fabricated by horizontal twin-roll casting

In this study, a Ti/Al/Cu three-layer clad sheet was fabricated using horizontal twin-roll casting (HTRC) technology. The interfacial morphology, interfacial microstructure and phases, interfacial bonding strength, micro-hardness, and tensile properties of the clad sheet under different annealing and cold rolling conditions were investigated. The surface morphology of the titanium, copper and aluminum sheets after peeling was observed. Compared with the traditional compounding process, the cast-rolling bonding process can realize the direct combination of molten metal and solid metal strip and achieve higher bonding strength. In the as-cast sheet, the thickness of the diffusion layer is 3.6 μm and the average peel strength (APS) is 20.2 N/mm at the Ti/Al interface, meanwhile the values at the Cu/Al interface are 3.2 μm and 13.8 N/mm. Before the formation of intermetallic compound (IMC) at the interface, increasing annealing temperature can improve the bonding strength by promoting atomic interdiffusion. Further cold rolling can also improve the bonding strength by forming a wavelike interface. Under the action of huge rolling force, the matrices that were not well bonded in the cast-rolling process are contacted at the atomic scale, and as a result new bonding regions are created. By improving the interfacial bonding strength, appropriate annealing and cold rolling processes make the deformation of clad sheet more cooperative. According to the results obtained in this study, the best subsequent processing technology for Ti/Al/Cu clad sheet fabricated by HTRC is annealing at 300 °C for 1.5 h followed by a single pass cold rolling with 40% reduction.

Effects of annealing temperature on the interfacial microstructure and bonding strength of Cu/Al clad sheets produced by twin-roll casting and rolling

Abstract In this paper, Cu/Al clad sheets were prepared by twin-roll casting and multi-pass cold rolling. Annealing treatment was performed at temperatures of 250 °C, 300 °C, 350 °C and 400 °C, separately. The influences of the annealing temperature on the interface layer structure, peel strength and peeled surface microstructure of the clad sheets were studied. The crack propagation behavior in the peeling process of the clad sheets was revealed, and the strengthening mechanism of the interface was explained. The results showed that the Cu/Al interface metallurgical bonding rate increased and the intermetallic compound layer thickness could be controlled within 550 nm after annealing at 250 °C, which encouraged more cracks to propagate along the Al matrix, and the average peel strength could reach approximately 39 N/mm. However, after high-temperature annealing treatment (350 °C and 400 °C), the clad sheet broke completely in the intermetallic compound layer, and a large number of cleavage fractures appeared, which caused the bonding strength to decrease sharply.

Proof of Concept of a Surrogate High-Adhesion Medical Tape Using Photo-Thermal Release for Rapid and Less Painful Removal

AbstractMedical tapes often hold critical devices to the skin so having high adhesion for the lifespan of this product is of great importance. However, the removal process is challenging for caregivers and patients alike, often a painful process that can cause medical adhesive-related skin injury (MARSI). By using an industrial thermally sensitive tape, a surrogate photosensitive tape was developed that switched from the equivalent of high-adhesion medical tape to low-adhesion medical tape. This resulted in an 86% reduction in the average peel strength when heated from 45 to 55 °C using a custom test apparatus. To photo-release the prototype tape (PT), a near-infrared (NIR) absorbing layer was painted on the visibly clear thermal-sensitive tape and an NIR optical wand using 15-LEDs (940 nm) with thermal feedback control was designed and tested. Preliminary performance of photo-to-thermal conversion was numerically modeled with transient results matching experimental measurements with 96.8% correspondence. Using the verified energy conversion model of the surrogate photosensitive tape, a new NIR optical wand was designed for rapid and noncontact release of a future medical tape at 10 deg lower than the release temperature (RTemp) of the custom adhesive, called UnTape. Numerical simulations compared to the thermal skin pain threshold of 45 °C predicts photo-release within 1.1 s of NIR exposure (85.5% absorption in PT at < 1.3 W/cm2). The unique properties of the multifunctional UnTape system (tape and portable NIR wand) may allow even stronger skin adhesion for critical medical devices while concurrently reducing the risk of MARSI upon photo release and easy removal.

Corrosion protection and thermal and mechanical properties for epoxy–thiol–imidazole systems of improved performance

Epoxy–thiol–imidazole system is promising for microelectronic packaging areas, such as underfills and low-temperature fast curing adhesives, but there is little knowledge on the corrosion resistance of this system. In this article, the anticorrosion and thermal and mechanical properties were characterized by theoretical and experimental methods and were understood from a fundamental perspective of structure. The cure behaviors were evaluated by differential scanning calorimeter. The mechanical and thermal properties were characterized by dynamic mechanical, thermomechanical, and thermos-gravimetric methods. The water absorption process was monitored using gravimetric measurement. Results show that among compositions of variable thiol–epoxy molar ratios, the one with ratio 0.25 has the best anticorrosion property and improved mechanical property, as well as good water resistance at room temperature. Both the average tensile strength and modulus increased initially and then declined with the addition of thiol part, while the average peel strength increased to above thrice the value of that of neat epoxy–imidazole system for thiol–epoxy 1:1 system.

Experimental and numerical simulation of steel/steel (St/St) interface in bi-layer sheet metal

Layered metallic materials (LMMs) offer a better combination of different mechanical properties in comparison to monolithic sheets. Hot roll-bonding is an effective and economic processing approach for fabricating LMMs. Because of improved mechanical properties, LMMs can be used in shipbuilding, nuclear reactors, manufacturing of various chemical tanks and pressure vessels. Delamination of layered sheet is often a problem in industrial applications. Therefore, delamination initiation and propagation needs to be predicted. In this study, delamination behavior of Steel/Steel (St/St) bi-layered sheet, prepared using roll bonding technique at preheating temperature of 950 °C and thickness reduction of 47%, is studied using T-peel test. The fracture toughness and average peel strength are measured experimentally. By using the experimental fracture toughness, numerical simulation is performed using surface-based cohesive zone model (SCZM). Both bilinear and linear-exponential traction-separation laws are considered to study damage initiation and propagation behavior. It is observed that the exponential softening predicts damage evolution more accurately as compared to linear softening law.

Experimental Study on Peeling Properties of T Type Brazing Joint

As the key component of the high temperature gas cooled reactor (HTGR), the performance of the plate fin heat exchanger determines the working efficiency and life of the HTGR. Although the plate-fin structure has lots of advantages such as high efficiency, compact structure, low manufacturing cost, its application will be affected by the vacuum brazing technology and harsh conditions, like high temperature and high pressure. In the practical application of plate-fin heat exchanger, the process of "splitting" between the fin and the diaphragm is very similar to that of the adhesive joint and the delamination of the composite. In the present study, a T-type specimen was designed for the the peel testing of brazed joints. Five kinds of specimens were designed based on the difference between the weld gap and the thickness of the sample base material. The tests were carried out under 450°C and 650°C at five kinds of loading rates, respectively. The peel force-displacement curves of standard samples were obtained . The maximum peel strength and average peel strength were calculated. In addition, the influence of base metal thickness, brazing gap, loading rate and test temperature on the maximum peel strength were analyzed by controlling variable method. Keywords: brazing joint; T-type peel test

Interfacial Characterization and Bonding Properties of Copper/Aluminum Clad Sheets Processed by Horizontal Twin-Roll Casting, Multi-Pass Rolling, and Annealing

The copper/aluminum (Cu/Al) clad sheets were produced on a horizontal twin-roll caster and then were multi-pass rolled and annealed. The thickness of the as-cast clad sheet was 8 mm. Rolling was performed with total reductions of 12.5%, 25%, 37.5%, 50%, and 62.5%, separately. The effects of the rolling and annealing processes on the interface and peel strength of the Cu/Al clad sheets were investigated. The evolution of the interface and crack propagation were studied. The interface thickness of the as-cast clad sheet reached 9 μm to 10 μm. The average peel strength (APS) was only 9 N/mm. After multi-pass rolling, the peel strength first slightly increased and then gradually decreased with the increase of the rolling pass number. After annealing, the peel strength remarkably improved. The APS reached 25 N/mm when the rolled thickness was 7 mm. The improvement in the peel strength was due to the following three factors: (1) mechanical locking formed in the Cu/Al direct contact region after rolling, (2) the region of the Al matrix fracture, and (3) mechanical biting from the Cu/Al direct contact region.

Important insights into polyurethane nanocomposite-adhesives; a comparative study between INT-WS2 and CNT

Owing to their outstanding variety of properties, nanoparticles attracted considerable interest for developing a new age of novel polymer nanocomposites and adhesives. Among them, inorganic nanotubes (INTs) of tungsten disulfide (WS2) and carbon nanotubes (CNTs) have been identified as unique candidates for many industrial applications by virtue of their superior mechanical, thermal and tribological properties. In this work, a comparative study between INT-WS2 and multi-walled carbon nanotubes (MWCNTs) regarding the properties of structural polyurethane (PU) adhesives is presented. Specifically, we evaluate the thermomechanical properties, chemical and micro-phase structure, bonded joints performance in lap shear and peel modes, and fracture mechanisms, with aiming to highlight some of the differences between these nanotubes. The added content spanned over the range of 0.3, 0.6, 0.9 and 1.2wt% of INT-WS2, while CNTs are incorporated at the same volumetric fractions (e.g., 0.1, 0.2, 0.3 and 0.4wt%). According to the results of the tests, in all measured aspects, INT-WS2 outperformed the carbon counterparts. With regards to the thermomechanical attributes, the hard segment Tg of the PU increased by 14°C at 0.6wt% INTs, whereas CNTs recorded only modest improvement of 8°C at the nanocomposite loaded with 0.4wt%. The structural bonding performance indicates an improvement of 117% and 38% in the shear and peel strengths at 0.9 and 1.2wt% INTs, respectively, while CNTs show moderate changes. Interestingly, the changes are also reflected by the interplay between the hard and soft segments of the PU, and different fracture mechanisms operating within the nanocomposites. At any rate, the combined attributes of >20MPa in the shear strength and approximately 2N/mm in (average) peel strength, targets the PU/INT nanoadhesives as promising alternative for conventional epoxy systems which has similar shear strength with inferior peel strength.

Investigation on bonding strength of steel/aluminum clad sheet processed by horizontal twin-roll casting, annealing and cold rolling

In this work, a stainless steel/aluminum clad sheet was produced successfully by horizontal twin-roll casting. The interface morphology, element distribution and bonding strength of the clad sheets after different annealing and cold rolling processes were investigated using optical microscopy, electron probe micro-analyzer and T-type peel test. The surfaces of the steel and aluminum sheets after peeling were studied using scanning electron microscopy. In the as-cast clad sheet, a 3μm thick diffusional layer exists at the Fe/Al interface. The average peel strength is 12N/mm. Suitable annealing treatment can greatly improve the bonding quality of the interface. The average peel strength increases with increasing annealing temperature, from 12N/mm at 450°C to 21N/mm at 510°C. After annealing at 540°C, the diffusional layer becomes almost three times the original thickness, which results in a sharp drop in the average peel strength to 5N/mm. Cold rolling processing also improves the bonding strength of the clad sheets. The average peel strength of the clad sheet annealed at 510°C increases as the reduction in thickness by cold rolling increases, from 23N/mm for 25% reduction, to 28N/mm for 40% reduction.

Microstructure and mechanical properties of dissimilar pure copper foil/1050 aluminium composites made with composite metal foil manufacturing

In this paper, we present mechanical testing and microstructural analysis carried out on a number of layered composites of aluminium 1050 and pure copper foils. The parts were made by an additive manufacturing process termed as Composite Metal Foil Manufacturing. It is a combination of Laminated Object Manufacturing and brazing. The effectiveness of the process is validated with lap shear testing, peel testing, microstructural analysis and tensile testing. Joining dissimilar metals is generally difficult but the process is capable of achieving this goal with ease. Tests were carried out on lap joints with varying thickness to assess the effect on the bond. Tensile lap shear strength was also calculated using thicker plates by observing cohesion failure. The peel test showed a good bond consistency in all the specimens with an average peel strength of 20MPa. Microstructural analysis showed a large proportion of bonded area which is essential for proper bonding. Comparative tensile test was conducted among dog-bone specimens machined from solid aluminium 1050 block, copper block and composite Al/Cu specimen. The results showed that the specimen made by composite metal foil manufacturing fractured at a load value that is 11% higher than that of aluminium but lower than that of copper for the same overall thickness of the test specimens. This yielded a new composite that could be used for different applications based on its suitability.

Study of the correlation between flexible food packaging peeling resistance and surface composition for aluminum-metallized BOPP films aged at 60°C

ABSTRACTThis study investigated the correlation between surface composition and peeling resistance in food packaging films by studying the heat aging of fabricated films over varying periods of time. The films consisted of a layer of aluminum (Al) metallized, biaxially oriented polypropylene (BOPP) bonded with a polyurethane (PU) adhesive onto another polymeric layer of low-density polyethylene (LDPE). The Al metallized films were prepared by physical vapor deposition (PVD) and aged at 60°C for either 5 or 15 days. The resulting aluminum surfaces were analyzed using X-ray photoelectron spectroscopy (XPS) and found to contain aluminum oxide (Al2O3) and trihydroxide (Al(OH)3). The XPS characterization also revealed a 29% increase in the Al(OH)3 layer thickness of the aged sample relative to a non-aged sample. Atomic force microscopy (AFM) was applied on investigations of possible morphology changes. The aluminum and PU adhesive surface energies were also determined using contact angles measurements and the aluminum surface energy was found to increase by as much as 11.7% compared to the non-aged sample, while the PU adhesive surface energy was at least 65% higher than that of the metallic substrate. The peeling resistance of the laminated aluminum was determined by average peel strength measurements and it was found that the variation in peel strength was related to changes in the Al2O3 layer thickness. The delaminated samples were analyzed using scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) and showed the cohesive failure of the aluminum film.

Strength analysis of aluminium foil parts made by composite metal foil manufacturing

A number of different parts for mechanical testing were produced using composite metal foil manufacturing (CMFM). This process is a combination of laminated object manufacturing and brazing technology. Aluminium is one of the toughest metals to join and CMFM can achieve this task with ease. By using aluminium 1050 foils of 0.1 mm thickness, various parts were made according to British and International Standards, including lap joints, peel specimens, dog-bone specimens and tested for their mechanical properties. A special, 80 % zinc and 20 % aluminium by weight, brazing paste was utilized for joining the foils together. The test of the single lap joints show that none of the specimens failed at the bonded area and the failure was always due to fracture of the parent metal. Cohesive failure was also observed for the single lap joints by using 10 mm thick aluminium metal plates. It helped in calculating the lap shear strength which is a useful design parameter. The peel test showed good bond consistency in all the specimens with an average peel strength of 20 MPa. Comparative tensile test was conducted with a dog-bone specimen machined from a solid block of aluminium 1050 and specimens made with CMFM. The results showed that the specimens made by CMFM fracture at force values that are higher than that of the parent metal. This demonstrates that CMFM has the capability to produce high quality and stronger parts as compared to conventional machining methods employed for the production of metal parts. The effect of using different number of layers for the same cross-sectional area has also been investigated.

Mechanical Properties of Thin-Film Parylene–Metal–Parylene Devices

Structures and testing methods for measuring the adhesion strength, minimum bending diameter, and bending fatigue performance of thin film polymer electronic architectures were developed and applied to Parylene-metal-Parylene systems with and without the moisture barrier Al2O3 (deposited using atomic layer deposition (ALD)). Parylene-metal-Parylene interfaces had the strongest average peel test strength and Parylene-Parylene interfaces had the weakest peel. Layers of ALD Al2O3 deposited within the device increased the average peel strength for Parylene-Parylene interfaces when combined with silane A-174, but did not increase the Parylene-metal-Parylene interface. Metal traces in the middle of 24 µm thick Parylene-metal-Parylene devices had a minimum bending diameter of ~130 µm before breaking and being measured as an open circuit. The addition of one layer of Al2O3 above the traces allowed them to be completely creased when bent away from the Al2O3 layer without producing an open circuit, but increased the minimum bending diameter to ~450 µm when bent away from the Al2O3. Although fatigue testing produced cracks in all devcies after 100k bends, the insulation of the Parylene-metal-Parylene devices without Al2O3 performed well with electrochemical impedance spectroscopy (EIS) showing only small decreases in impedance magnitude and small increases of impedance phase at low frequencies. However, devices with Al2O3 failed during EIS due to Al2O3 being deteriorated by water.

Comparison of Microparticles and Nanoparticles Effects on the Bonding of Roll Bonded IF Steel

In the present work, the effect of silicon carbide (SiC) particle size on the characteristics of cold roll bonded interstitial free (IF) steel strips, such as bond strength and peeled surface were carried out and compared to those of IF steel strip without particles. The bond strength was evaluated by the peeling test and scanning electron microscopy. It was found that with increasing thickness reduction, the bond strength of IF steel strips improved. The results also indicated that the presence of SiC particles (both micro and nano) decreased the bond strength of IF steel strips. Also, with increasing the particle size, the bond strength improved. It was found that for sample with microparticles compared to sample with nanoparticles, beyond the 80 % thickness reduction, a sudden increase in the average peel strength was observed. Finally, the results indicated that in the presence of nanoparticles between strips there were two types of unbonded area and the bond strength of these two areas was quite similar to each other.

Comparison of single and double pass friction stir welding of skin–stringer aviation aluminium alloy

To enhance the strength of the skin–stringer structures used in aircraft, comparative tests between single and double pass friction stir welding (FSW) were performed. Aluminium alloy was used for the skin (2524-T3, 1·8 mm) and stringer (7150-T77511, 2·4 mm). An equilateral right angled structure was used, and perfect joints without internal defects were obtained. Tensile, peel and metallographic tests were also implemented. The results show that the average peel strength of a double pass FSW joint is at least twice that from single pass FSW. Therefore, double pass FSW is an effective way of improving the connection strength of an aircraft skin–stringer structure.