Higher Tensile Shear Strength Research Articles

Evaluation of Joint Strength for CFRPs and Aluminum Alloys by Friction Stir Spot Welding Using Multi-Stage Heating

To reduce car body weight, multi-material structures with lightweight materials such as carbon-fiber-reinforced plastics (CFRPs) and aluminum alloys (Als) are used to replace parts of steel components, and joining technologies for such dissimilar materials are essential. Friction stir spot welding (FSSW) is one of the technologies used to rapidly and strongly join dissimilar materials. FSSW for carbon-fiber-reinforced thermosetting resin (CFRTS) and Als has been developed using composite laminates with integrally molded thermoplastic resin in the outermost layer. To suppress excessive heating under the tool, this study investigated whether multi-stage heating with a non-heating time during joining affects the heat distribution and strength properties of the joint. Due to heat diffusion in Al during the non-heating time, multi-stage heating can suppress excessive heating under the tool compared to continuous heating, resulting in up to 27% larger welded area, up to 37% smaller decomposed area, and up to 6% lower maximum temperature. The use of multi-stage heating results in up to 5% higher tensile shear strength and 210% longer fatigue life by reducing the thermal decomposition of CFRP matrix resin and PA12 resin.

Explosive Welding of Aluminum and Cast Iron for Potential Transportation and Structural Applications

This study explores the feasibility of explosive welding to join dissimilar materials: aluminum (JIS A1050‐H24) and two cast iron types (JIS G 5501 and JIS G 5502), which are challenging to weld due to the presence of graphite in the cast iron. Further, the impact of explosive thickness (28, 38, and 47 mm) on weld quality is investigated, considering microstructure and mechanical behavior. Increasing explosive thickness correlates with a thicker local melted zone. Remarkably, in investigations, a novel morphology that diverges from conventional patterns is observed. The weld interface of explosively bonded materials exhibits anchor formation, a unique interlocking structure. These anchors play a significant role in establishing a robust mechanism between bonded surfaces. JIS A1050‐H24 shows minimal hardness variation, while cast iron exhibits significant variations with increased explosive thickness. Tensile shear tests showcase robust clad plate strength, with fractures primarily in JIS A1050‐H24 regions instead of at the interface. The highest tensile shear strength is achieved with an explosive thickness of 38 mm. Overall, explosive welding of aluminum with cast iron creates a strong, durable, and lightweight material with enhanced performance characteristics, making it promising for diverse industrial applications due to its outstanding properties.

Enhancing the ultrasonic plastic welding strength of Al/CFRTP joint via coated metal surface and structured composite surface

Ultrasonic plastic welding (UPW) is a promising technology for joining metal to carbon fiber reinforced thermoplastic composite (CFRTP) but shows poor joint strength in the existing studies. This work conducts UPW of AA6061 aluminum alloy to carbon fiber reinforced PA66 (CF/PA66) by employing a polymer coating as an interlayer. Simple metal surface grinding and silane coupling agent (SCA) treatment are used to strengthen the bonding of the metal/coating interface. Structured CF/PA66 surface fabricated by ultrasonic embossing acts as energy directors to improve the bonding strength of the coating/plastic interface. The results show that relatively high tensile-shear strength (about 31.0 MPa) can be obtained. Micro-mechanical interlocking and chemical bonding (Al-O-C and Al-O-Si bonds) are considered as the bonding mechanism of the metal/coating interface.

Effect of adhesive on friction stir spot welding of AZ31B magnesium alloy sheets

ABSTRACT AZ31B magnesium alloy sheets were lap-joined with adhesive only, friction stir spot welding (FSSW) only, and also with FSSW after adding adhesive between sheets. The produced joints were comparatively studied regarding joint cross-section geometrical features and defects that occurred at joint interface, microstructure, microhardness, tensile shear strength, and fracture surface evaluation. For joints made with FSSW only, cracks formed at underside of top sheet just above interface of sheets. However, joining with FSSW while there is adhesive between sheets eliminated formation of cracks and enabled weld width to enlarge significantly. Additionally, adhesive presence at interface of sheets joined by FSSW drastically reduced hook defect formation in the weld . The hook sizes of joints of FSSW with adhesive were so small as to be negligible compared to those of FSSW adhesive-free. Consequently, joints of FSSW with adhesive had much higher tensile shear strength. However, due to their brittle fracture, they displayed much less ductility than adhesive-free FSSW joints. The joints made via just adhesive had the lowest strength and elongation. Microstructure and microhardness of joints made by FSSW without and with adhesive were slightly different from each other. The main factors determining joint strength were adhesive, hook and weld size.

Shape evolution and characteristics of carbon fiber reinforced polymer surface in laser ablation

Carbon fiber reinforced polymer (CFRP) has been far-ranging used for structural components in structural engineering. Laser paint removal is promising in the repair and maintenance of CFRP structural components. However, there are still many unknowns relating to laser paint removal, and the existing theory and practice are insufficient to guide the industrial application of laser paint removal from CFRP laminate. This paper uses nanosecond laser cleaning experiments on the paint of CFRP laminate surface to study the cleaning mechanism and cleaning effect of different process parameters for removing the paint. The surface morphology and three-dimension morphology of laser-cleaned samples are observed to reveal the cleaning quality. In addition, after laser paint removal, the nanostructures are generated on the carbon fibers (CFs) surface. The thermodynamic behavior of CFRP laminate during laser paint removal is discussed by the combination of experimental results and theoretical analysis. The contact angle measurements and single lap joints experiments demonstrate laser-cleaned surfaces present better wettability and higher tensile shear strength than other cleaning methods. This study provides a theoretical and experimental basis for the application of laser paint removal from CFRP laminate.

Influence of adhesive thickness and defect on mechanical property of adhesive bonded joint of flexible polymer substrate and cable for solar panel application

Flexible polymer substrate and flat polymer cable were adhesive bonded to fabricate the solar panel in the present study. The relationship between the adhesive thickness, mechanical properties and fracture morphologies of the joints were systematically investigated to figure out how the adhesive layers with different thickness affected the joints’ mechanical properties. The influence of the defects on the joint quality was also studied via an artificial defect introduction method. Adhesive failure accompanied with low tensile-shear strength was easy to occur to the joints with extremely thin adhesive thickness due to the weak boundary formation between the adhesive and the adherent. When the adhesive thickness increased, the joints started to show the cohesive failure with higher tensile-shear strength since the adhesive completely fill the surface crevices. The joints’ mechanical properties however decreased again with further increasing the adhesive thickness, owing to the generation of more defects and higher residual stress within the thicker adhesive layer. On the other hand, adhesive failure was more likely to occur around the defect, which significantly deteriorated the joints’ mechanical properties. The defect located in the center of the bonding area led to a larger adhesive fractured area, thereby having a greater impact on the mechanical properties in comparison to the same-size defect located in the corner or the marginal center.

Durability of sandwich structures with a maximized natural raw material basis: comparison of expanded polystyrene, cellulose foam and polylactic acid subjected to UV-rain aging

In this study, alternative core materials to commercial cork were searched for. Additionally, aging of new core materials was studied. Bio-based materials in sandwich structures can be useful for sports equipment, transportation, and furniture with much less impact on the environment in comparison with their synthetic counterparts. In this paper, sandwich panels made of fiber-reinforced polymer (FRP) skins and various sustainable core materials with a core thickness of 6 mm were studied. The core materials were: cork, expanded polystyrene (EPS), cellulose foam, and 3D-printed polylactic acid (PLA) honeycomb lattice. FRP composites made of flax fibre reinforcement and bio-based epoxy resin (30% bio-content) were used to manufacture the skins to compete the glass fibre reinforced rival composite. The experimental analysis of the panel performance focused on the out-of-plane behavior and aging due to conditioning in an ultraviolet (UV) irradiation-rain cabinet. The results showed that under mechanical and environmental loading, the sandwich composite with cellulose foam had comparable or even better mechanical performance under shearing load, including UV-rain effects, than structures with EPS cores. Failure localization was studied using digital image correlation (DIC). The 3D-printed PLA honeycomb sandwich structures had a high absolute flatwise tensile strength and shear strength but also greatest degradation by the UV-rain aging.

Review of polymer-matrix composites welded to aluminium alloys

This review covers previous work by different scholars on welding polymer-matrix composites to aluminium alloys between 2015 and 2021. The highest tensile shear stress measured for the joint between polymer-matrix composite and aluminium (AA7075) alloy was 59.9 MPa. Welding using top-thermic friction stir was the method that produced the desired outcome. Additionally, the aluminium (AA2024) alloy and fibre-reinforced polymer composite were joined using an ultrasonic metal welding procedure, which produced a weld with a high tensile shear strength of roughly 58 MPa. The friction-aided joining of carbon fibre-reinforced polyphenylene sulphide composites and aluminium (AA7075) alloy has been studied by researchers. A laser treatment was applied to the aluminium surface to enhance the interlocking between the two materials being combined. This development was reported to cause inadequate bonding between the polymer-matrix composite and the metal. Despite this, the joints demonstrated significant load-bearing capacities of up to 10.7 kN.

Resistance Spot Weldability of Aluminum Alloy with 6 wt.% Magnesium

To ensure safety and reduce the weight of vehicles, studies are being actively conducted on different aluminum alloys that have strength higher than conventional aluminum alloys. The development of high-performance aluminum alloys through magnesium content control is underway. Research on manufacturing techniques, such as, welding for application to the car body parts of these materials is required. In this study, the resistance spot weldability of an aluminum alloy with 6 wt.% magnesium (Al-6Mg) was evaluated and compared with the commercial aluminum alloy 5052, 6061 (Al5052, Al6061). The suitable welding range of the Al-6Mg was found to have a welding current of 24 kA to 28 kA, and a similar level of Al6061. The welding heat input was almost the same for the three materials, which resulted in no difference in the diameter of the nuggets. There was no significant difference of the porosity ratio between Al-6Mg and Al5052; however, the porosity ratio of Al6061 was higher. The alloy with the highest tensile shear strength, hardness and energy absorption of a welded joint was Al-6Mg. The low porosity ratio and high hardness of the Al-6Mg alloy caused the relatively high tensile shear strength and energy absorption of the welded joint.

In-situ modification of low molar ratio urea–formaldehyde resins with cellulose nanofibrils for plywood

This study describes the in-situ modification of low molar ratio urea–formaldehyde (UF) resins with cellulose nanofibrils (CNFs) to improve the poor performance of resins synthesized with different methods (Synth 1 and Synth 2) when adding second urea. UF resins were in-situ modified with CNFs dissolved in a mixture of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) during the alkaline reaction step. Results showed that CNF addition enhanced the resin properties, such as shorter gelation time, faster curing rates at low activation energy, higher tensile shear strength (TSS), and lower formaldehyde emission (FE), compared to those of neat resins. The dry and wet TSS values of plywood bonded with UF resins modified with 3% CNFs synthesized using Synth 2 increased by 30% and 42%, respectively, and the FE value was decreased by 22% and 42%, respectively. These results reveal that in-situ modified UF resins with CNFs showed better performance than neat UF resins and that Synth 2 was more favorable than Synth 1.

Formability and mechanical property of refill friction stir spot–welded joints

The effects of rotation speed and plunge depth on macro/microstructures and mechanical properties of dissimilar 2195/2219 aluminum alloy joints produced by refill friction stir spot welding (RFSSW) were investigated. The results show that some shallow annular grooves present on the joint surfaces depending on the process parameters. Besides, hook defects are in the form of downward bending due to the higher strength of 2195 aluminum alloy. The change of rotating speed has no apparent influence on hook defect, while the increase of plunge depth makes the height of the hook defect increase significantly. The higher tensile-shear strength is associated with increased rotation speed. However, as the plunge depth increases, the tensile-shear strength rises first and then decreases. The highest tensile-shear strength measured is 6480 N, for a rotation speed of 1600 rpm, and plunge depth of 2.5 mm. Besides, there are two kinds of fracture modes present: the plug fracture and the shear-plug fracture.

Thermal Spray Application on the Dissimilar Metals Weld between Aluminum and Steel

Physical and mechanical properties differences between aluminum and steel, especially melting points, make them unable to be welded easily. Moreover, a hard and brittle intermetallic compound (IMC) is always formed at the interface of aluminum and steel. The thermal spray method was proposed to make interlayer for improving fusion and avoiding hard and brittle intermetallic compounds (IMC) at the interface of joined materials. Based on solubility into both steel and aluminum, nickel was chosen as interlayer material. The aim of this research was to investigate the effect of nickel layer thickness and welding variables on the properties of dissimilar metals diffusion welded between steel and aluminum. Nickel was layered into the steel surface using the thermal spray method before the joining process. The nickel interlayer thickness was in the range from 0.2 mm to 1.0 mm. Steel and aluminum were then welded by using the diffusion weld method. The constant pressure of 5 Mpa and constant holding time of 180 s were performed in diffusion welding, while the temperature was varied, i.e. 500°C, 525°C, and 550°C. The thickness of the formed IMC layer increased along with the increase of the diffusion welding temperature. The highest tensile shear strength was obtained by the joint with the welding temperature of 525°C. The nickel interlayer successfully avoided the formation of Fe-Al IMC and formed a stronger and more ductile diffusion area, and thus increased the strength of the steel and aluminum joint.

Dynamic Response of Composite Steel Lining Structure under Blast Loading

According to the advantages of high tensile resistance and high shear strength of composite steel plate, a new antiexplosion protection method of composite steel plate lining structure is put forward. The numerical model of explosion impact of subway tunnel with composite steel plate lining structure was established by dynamic analysis software. The transient dynamic response of lining structure with the composite steel plate was simulated when explosion occurred. The research results show that the influence of explosive quantity on each point of composite steel plate lining structure is different and the change of acceleration near the centre of the detonation source is generally greater than the multiple of the increase of explosive quantity. The increase of velocity and displacement is basically consistent with the quantity of explosive. The influence of axial stress on the lining structure is the least, and the influence of the lining structure is greater in the y-direction than in the x-direction. The research results can provide the plan and basis for the emergency response of the subway tunnel.

Microencapsulation of polymeric isocyanate for the modification of urea-formaldehyde resins

This study was conducted to prepare the microcapsules of polymeric 4-4 diphenyl methane diisocyanate (MpMDI) by interfacial polymerization using two different surfactants (Tween 40 and Gum Arabic) for the modification of urea-formaldehyde (UF) resins. MpMDI obtained by Tween 40 (TW-MpMDI) were spherical, smooth, and small diameter, while those prepared by Gum Arabic (GA-MpMDI) were irregular, rough surface, and larger diameter. Attenuated total reflection–Fourier transform infrared (ATR-FTIR) spectra of two types of MpMDIs confirmed the successful microencapsulation of pMDI by detecting the isocyanate (NCO) groups after rupturing the shell of MpMDIs. As the MpMDI content in UF resins increased, the non-volatile solids content, pH, gelation time, viscosity, and exothermic peak temperature of UF/MpMDI adhesives slightly increased. Plywood bonded with UF/MpMDI adhesives had 15% higher tensile shear strength (TSS) and 30% higher modulus of rupture (MOR) than those of the plywood bonded with neat UF resins owing to the formation of urethane (HN-(CO)–O-R) bonds. In particular, plywood bonded with UF/TW-MpMDI had higher TSS and MOR values than those bonded with UF/GA-MpMDI adhesive. Regardless of the surfactant types, the formaldehyde emission decreased about 54% with 5% MpMDI addition into UF resins. These results and statistical analysis revealed that 1% TW-MpMDI addition into UF resins provided a proper balance between good adhesion and low formaldehyde emission for plywood.

Mechanical, electrochemical and structural characteristics of friction stir spot welds of aluminium alloy 6063

The work presents the friction stir spot welding (FSSW) of AA6063. The evolving properties due to the influence of process parameters and the efficacy of metallurgical, structural, mechanical, and electrochemical integrities were studied. FSSW was conducted on 2mm thickness by varying the rotational speed of 600, 900 and 1200 rpm and the dwell time at 10 and 15 s. The evolving microstructures, hardness, corrosion, shear tensile behaviours and X-ray diffraction characteristics of the as-received material and the welds were studied. As the tool rotational speed increased at a constant dwell time, a smooth and debris free spot welds were noticed, more HAZ formations became visible and more intermetallic phases of aluminium magnesium (AlMg) were formed although with very low peaks during structural assessment. Furthermore, the hardness values increased up to a certain limit and then decreased, the corrosion properties in artificial seawater (ASW) shown significant improvement on the spot-welded samples and the tensile shear strength was also improved. It would be recommended that spot welds at 900 rpm and 10 and/or 15 s for applications where the hardness is significant imperative and at 1200 rpm with 10 and/or 15 s dwell time where higher tensile shear strength is required and lastly, 1200 rpm at 15 s where corrosion application is significant.

Influence of the laser-based surface modification on the bond strength for friction press joining of aluminum and polyethylene

Friction press joining is an innovative joining process for the production of plastic-metal joints without additives, in an overlap configuration. In order to achieve a high bond strength, the metallic joining partner is pretreated with laser radiation. Subsequently, heat is induced by friction and pressure during the joining process, causing the thermoplastic material to melt and adhere to the metallic joining partner. In this work, the temperature distribution during the process in the composite is analyzed and characterized. It was found that the occurring temperatures and temperature differences are not only dependent on the rotational speed, but also on the feed rate. It is also shown that the friction surface temperature can be used as an indirect control variable for a model-based, closed-loop control. Based on these findings, various surface modifications forthe metallic joining partner were investigated and analyzed with regard to the maximum strength of the joint. It was observed that the highest tensile shear strength can be achieved with a quasi-chaotic nano structure. In addition, the joining compound was characterized by a thin section, facilitating the identification of specific zones in the joint. These investigations show the high potential for friction press joining of plastics and metals, and form the basis for a model-based control of the joining zone temperature.

Effect of Microstructure and Texture on Mechanical Properties of Resistance Spot Welded High Strength Steel 22MnB5 and 5A06 Aluminium Alloy

The present study aims to investigate the effect of microstructure and texture on mechanical properties of resistance spot welding of high strength steel 22MnB5 and 5A06 aluminium alloy as a function of welding parameters. The pseudo-nugget zones (NZs) at the steel side have undergone full recrystallisation with a fine-grained ferrite structure containing a small amount of retained austenite and a high hardness of approximately 500 HV, which is a 35% increase in hardness compared to the base material (BM) with fine lath martensitic structure. The NZs at the Al side contain both a recrystallisation texture and shear texture. Higher tensile shear strength with increasing weld time could be linked to the random texture at the Al side. The highest tensile shear strength was achieved at an intermetallic layer thickness of 4 mm.

The Role of Intermetallic Compounds in Controlling the Microstructural, Physical and Mechanical Properties of Cu-[Sn-Ag-Cu-Bi]-Cu Solder Joints

A lead-free Sn-2.5Ag-0.7Cu base solder with different weight percentages of bismuth (0, 1, 2.5, 5) was used. Thermal properties, microstructure, wettability and mechanical properties were investigated. By decreasing the degree of undercooling, microstructure improved, the eutectic structure become finer and the size of β-Sn and intermetallic compounds decreased. By the addition of bismuth to SAC257 solder, the spreading ratio increased from 80.46% to 85.97, indicating an improvement in wettability. In order to investigate the joint properties, alloy solders were bonded to copper substrate, and the structure of the interface, tensile-shear strength and the fractured surfaces were studied. It was observed that the thickness of the intermetallic compounds of Cu6Sn5 at the interface decreased with the addition of bismuth, and the lowest thickness of the interfacial IMCs was found in the SAC257-1Bi solder joint, which decreased about 14% compared to the base solder. Also, the Cu/SAC257-1Bi/Cu bond had the highest tensile-shear strength and elongation percentage among the alloy solders, which has a tensile-shear strength of about 30% and an elongation percentage of about 38% higher than the base solder joint.

Friction stir lap welding of Al to Mg assisted by ultrasound and a Zn interlayer

The friction stir lap welding (FSLW) joints of Al/Mg dissimilar alloys presented better formation and higher tensile shear strength when the Mg alloy was selected as the upper plate. Compared with Zn-added FSLW, the Zn-added FSLW assisted by ultrasound further enlarged the effective lap width, improved the mechanical interlocking and attained the finer disperse Mg-Zn intermetallic compounds in the stir zone. The maximum tensile shear strength of the joint assisted by ultrasound and a Zn interlayer reached 268 N/mm. This hybrid process with the ultrasound and the Zn interlayer provides a new method to obtain a high-quality Al/Mg dissimilar welding joint.

Adhesive bonding of CFRP: a comparison of different surface pre-treatment strategies and their effect on the bonding shear strength

A promising joining technology for thermoset CFRP is adhesive bonding. However, the mechanical performance is influenced negatively by contaminants, like release agents, as well as an excess of matrix in the top layer. In order to generate most suitable surface qualities prior to the bonding process, carbon fibre reinforced plastics are treated with different – UV (355 nm) and IR (1064 nm) – lasers. The results are compared to commonly applied grinding surface preparation. The preliminary results on surface properties, e.g. energy and topography point towards high levels of free surface energy, as well as new originated surface structures. After the bonding process mechanical tests are subsequently carried out in Mode II, to characterize the final joint by its tensile shear strength. Finally, the individual fracture behaviour is examined in post mortem analysis. The results indicate that it is possible to increase the tensile shear strength of the joints to a maximum, which equals the interlaminar shear strength of the CFRP-laminate. Therefore, ultrashort pulsed IR-laser techniques show the best reproducibility and the highest tensile shear strength. In addition, IR-laser treatment is expected to have the highest potential for later applications.