Tensile Shear Tests Research Articles

Experimental investigation and analytical prediction on bond behaviour of CFRP-to-concrete interface with FRP anchors

Hybrid bonded technology with fiber-reinforced polymer (FRP) anchors can effectively improve the load capacity of carbon fiber-reinforced polymer (CFRP)-to-concrete interface. To investigate the reinforcement effect of FRP anchors, tensile shear tests of seventeen CFRP-concrete bonded joints with additional FRP anchors were conducted in this paper. The effects of the construction sequence, anchor position, and type of FRP anchor were considered in the experimental investigation. It was found that bonding CFRP sheet before installing FRP anchor and construction simultaneously could ensure the integrity of FRP anchor and provide a better anchor effect. The ultimate load-carrying capacity was increased with the increasing of plate length after anchor, that is the effect of anchor position. From the results of specimens with different types of FRP anchors at the same location, the FRP anchor composed of multiple small anchors can take effect earlier. By fitting the test results, the exponential bond-slip model for the CFRP-to-concrete interface and the elastic constitutive model for the FRP anchor were obtained. Further, substituting the two constitutive models, analytic theoretical models for load-slip curves and strain distribution were derived to predict the bond behavior of FRP anchored CFRP-to-concrete interface in this paper. The comparison between the prediction results and experimental data shows the good predictive accuracy of these analytical models.

Improving the performance of steel aluminum resistance spot welding joints based on steel coating design

The surface coating of steel significantly impacts intermetallic compounds (IMC) distribution and the performance of steel aluminum resistance spot welding (RSW) joints. In this paper, four sheets of steel with different surface coating were individually designed for welding with aluminum alloy. The results showed that the welded steel with coating performs better than that of Bare plate, while the welded steel with galvannealed (GA) coating has better performance than galvanized (GI) coating. The joints with GA coating failed in button pullout (PF) under tensile shear tests, while others failed in an interface (IF). The reason can be that the surface alloying zinc plating helps improve the combination reaction of Fe and Al, and the Zn will undergo a ternary combination reaction with Fe and Al to form a new compound containing Zn. The presence of the Zn layer can promote the interfacial reaction between steel and aluminum, and the welded joint performance reduces the impact of oxide film, even when the coating is thicker than 10 μm.

Robotic friction stir welding in lightweight battery assembly of extrusion-cast aluminium alloys

The present study focuses on developing lightweight assembly of two different aluminium alloys extruded and high pressure die cast (HPDC) for battery frame assembly in BEV. The goal is to produce defect-free welds in lap configuration with smooth surface finish. Stationary shoulder friction stir welding (SSFSW) was employed with welding speeds of 3–15 mm/s. EBSD analysis revealed two groups of grains in the stir zone (SZ) due to dynamic recrystallization. Moreover, the grain size of the SZ significantly decreased compared to both alloys. The cast alloy contains large iron particles, and that were broken by the rotating probe, and the stirred material consisted of fine dispersed precipitates. Tensile-shear test found the fracture location at the hook area near to cast, and a model representing fracture behavior is also discussed. With increasing welding speed from 3 to 5 mm/s, the tensile strength found ∼95 and ∼100 MPa, respectively without any significance difference in the fracture behavior and location. Overall, this study provides valuable insights such as materials mixing, grain refinement, and joint strength in dissimilar joining using SSFSW. The findings could be useful in developing optimized welding parameters and improving the overall quality and productivity of the SSFSW process for battery pack assembly in BEV.

Bond performance between cementitious grout and normal concrete subjected to freeze–thaw damage

Owing to the increasing application of cementitious grout in strengthening projects in cold regions, the freeze–thaw durability of the bond between cementitious grout and concrete has attracted attention. This study investigates the bond performance of a cementitious grout–normal concrete interface after FTCs through splitting tensile and slant shear tests at different angles. The microstructure of the cementitious grout–concrete interface is observed via backscattered electron (BSE) microscopy. The results show that FTCs rapidly reduce the splitting bond strength and slant shear bond strength of the interface. After 240 FTCs, the splitting and slant shear bond strengths decrease by 40.7%–72.4% and 46.1%–57.3%, respectively. An increase in substrate strength significantly enhances the interfacial bond strength, particularly the slant shear bond strength. Freeze–thaw damage to the substrate reduces the interfacial bond strength and frost resistance. The slant shear strength increases significantly with the slant shear angle. The effects of FTCs on the interfacial shear strength parameters are reflected through a rapid decrease in cohesion, whereas the interface internal friction angle remains relatively unaffected. Empirical formulas for calculating the interface bond strength are obtained from experimental data and validated. The BSE images show that cracks begin to appear at the cementitious grout–normal concrete interface as the number of FTCs increases, thereby decreasing the interfacial bond strength.

Process optimization of robust bonding between DP590 and AA6061 using resistance riveting welding

The process of resistance riveting welding (RRW) has the potential to be a cost-effective and efficient method for joining dissimilar materials. However, the impact of process parameters on the mechanical properties of the joints is not well understood. To address this issue, the study proposed an optimization method to maximize the cross tensile peak load and tensile shear peak load of the joint. A total of 54 experiments were conducted with different process parameters. Cross tensile and tensile shear tests of the joints were conducted, and then the cross-sectional morphology and microstructure of the joints and the intermetallic compounds at the interface were observed. And finally the fracture morphology of the joints was analyzed. The results showed that the total heat input and heat input per unit time were the main factors affecting the joint properties. Then a process optimization model based on a combination of snake optimization algorithm, support vector regression model, and multi-objective optimization Grey Wolf algorithm was established. The established optimization model was experimentally validated and found to be effective in quickly establishing an accurate prediction and optimization model for the RRW process. This study provides important technical guidance for the application of the RRW process and the utilization of the optimization model in other industrial scenarios.

Development of a cold spot joining method that enables sound joining of carbon steel below the A1 temperature

A novel solid-state joining method, which we call cold spot joining (CSJ), was successfully developed. In this joining concept, the material in the vicinity of the interface is plastically deformed using high pressure to form the joining interface, and impurities at the interface are expelled to the outside. Medium-carbon steel sheets were joined using the CSJ method under various process conditions. The joining temperature can be modified by the pressure applied during CSJ. Microstructural observations and hardness distributions revealed that proper pressurisation led to a joining temperature below the A1 point and prevented the formation of brittle martensitic phase. A sound S45C joint showing plug rupture at the base metal under both tensile shear and cross-tension tests was successfully fabricated by providing appropriate applied pressure and energising conditions.

Improved Mechanical Properties of SUS304/AA5083 Dissimilar Joint by Laser Ablation Pretreatment in Vortex- Friction Stir Lap Welding

To obtain a high-quality Al/steel dissimilar joint, a micro-groove-assisted vortex-friction stir lap welding (MG-VFSLW) process was developed. Through prefabricating micro-grooves on the steel plate surface by laser ablation, high-quality mechanical interlock and metallurgical bonding were obtained simultaneously in the MG-VFSLW process. The weld formation, interface microstructure, mechanical properties, and failure mode in MG-VFSLW were studied by comparing them with those in VFSLW. The results showed that a line load of the AA5083/SUS304 dissimilar joint up to 485.9 N/mm was obtained by MG-VFSLW, which is 40.1% higher than that in VFSLW. Remarkable intermetallic compound layers and cracks were found in VFSLW. The cracks were closely related to the oxides on the interface. However, in MG-VFSLW, cross-riveting aluminum rivets and steel rivets were formed on the interface due to the micro-grooves and flashes made by the laser ablation. Good metallurgical bonding was also formed between AA5083 and SUS304. No remarkable intermetallic compound layers and cracks occurred. During the tensile shear tests, the aluminum rivets were cut off and some dimples and tear ridges existed on the fracture surface. In short, the high strength of the Al/steel lap joint in MG-VFSLW was attributed to the high-quality mechanical interlock and metallurgical bonding.

Development of light weight transparent bullet proof polymeric laminates

AbstractArmed vehicles, improvised explosive device blast‐proof vehicles, require their windshields and windows to be transparent and yet be resistant to high‐velocity impact of splinters. Hence, composite which is of ballistic grade and yet transparent is in real need for all these applications. This study is dedicated to finding a practical solution for using transparent polycarbonate (PC) laminate made using solvent vapor bonding for ballistic applications. The solvent that was proved to be best for solvent vapor bonding of polycarbonate sheets was dichloromethane, as the bond strength was observed to be high from the results of lap shear tensile test. The transparency retention is reasonably high when solvent vapor bonding was used and the toughness has increased near to 50% in comparison with nonlaminated PC. In this study, a polycarbonate laminate with dimensions 150 × 150 × 40 mm made using solvent vapor bonding and is tested with two 9‐mm bullets fired with velocity of 430 m/s from a distance of 5 m. The laminae successfully stopped both the bullets without any back face signature and there was no brittle failure as such, rather delamination happened at interface of laminae since it has essentially absorbed the impact energy of bullet.Highlights Solvent vapor bonding of polycarbonate laminate. Transparent ballistic shield with layer of polycarbonate laminate. Enhancement of mechanical properties of solvent‐vaporized bonding polycarbonate laminate. Ballistic testing of transparent polycarbonate laminate.

High Cycle Fatigue Testing of Lap Shear RSW Joints from Martensitic MS1400 Steel Sheets

Resistance spot welding (RSW) is one of the most common welding methods for steel sheets, as it is mainly used to join the automotive body structure parts. Different types of ultra-high strength steels (UHSS) have become widely used in the automotive body to obtain the required demands such as lower car weight, improving crashworthiness behavior, and enhancing strength–ductility combination. Martensitic UHSS belong to the highest grades width their tensile strength above 1000 MPa. During the lifetime of the vehicle cyclic loading generally occurs, therefore the optimization of welding technology should be performed considering the fatigue resistance of the welded joints. In our research 1 mm thick standardized lap shear sheets of martensitic MS1400 steel were welded by a TECNA 8007 RSW equipment with two different welding parameter combinations. The idea was to analyze the effect of welding and pulsation parameters on joint properties under static and cyclic loading. The welding parameters have been calibrated to produce the same weld nugget size for both technological combinations. Macroscopic, hardness, and tensile-shear tests were carried out to determine the fundamental mechanical characteristics of the RSW joints. The relation between the weld nugget microstructure and mechanical properties was explored. The high cycle fatigue (HCF) tests were performed on an MTS 810.23 universal electro-hydraulic materials testing system. A statistical approach was applied during the preparation and evaluation of the investigations, which increased their reliability. Measured and analyzed data of the lap shear welded joints, prepared by different technological parameters, were compared and discussed. The parameters of the HCF experiments were calculated considering the Japanese testing method (JSME S 002-1981). In most of the samples it was observed from both welding parameter combinations that the fatigue cracks initiate and grow in curvature shape in the softened part of the heat-affected zone towards the base metals in both directions symmetrically. A slight difference was observed in the HCF resistance of the welded joints prepared by different welding parameters.

FE-Simulation and Experimental Characterisation of Environmental Effects on the Diffusion and Mechanical Performance of Hyperelastic Adhesive Joints

In operational applications, hyperelastic adhesive joints are exposed to environmental conditions (moisture and temperature) that affect their mechanical performance. The understanding of how the environment can influence the joint durability through both static and cyclic loading is a key aspect to ensure safety and avoid over-dimensioning. The current work presents an investigation of the effect of environment conditions on the diffusion and mechanical performance of two different hyperelastic adhesive joints (a polyurethane and a silicon-modified polymer). To assess the process of moisture mass diffusion, pure adhesive samples were weighted for 387 days when subjected to outdoor weathering conditions. An FEA-diffusion procedure method was demonstrated by (i) predicting the saturation concentration at steady conditions of 40 °C/15% r.h. (40/15) and 40 °C/60% r.h. (40/60), and (ii) predicting the experienced mass change due to outdoor weathering. The reversibility of the effect of conditioning at 40 °C/60% r.h. on the mechanical properties of the adhesives was assessed via quasi-static and fatigue tensile shear testing. The results support the conclusion that conditioning with the surrogate climate of 40 °C/60% r.h. does not cause irreversible damage, as any potential decrease in shear modulus, tensile shear strength and fatigue life due to 40/60 conditioning can be reversed by re-drying at 40/15.

An Optimization Study on Resistance Spot Welding of DP600 Sheet Steel via Experiment and Statistical Analysis

Resistance Spot Welding (RSW) is widely used in many automotive, boiler, and ship manufacturing industries. Therefore, the optimization and effectiveness of the RSW process are very useful and cost-efficient processes in addition to improving weld quality. This study used various welding parameters to investigate the optimization of the RSW process of Advanced High Strength Steel (AHSS). RSW was carried out using different welding times, currents, and electrode pressure values. Microstructural analysis, nugget formation, and tensile shear test were performed on samples. This study applied the Taguchi method and ANOVA to set up the welding process and optimize its results. Microstructural characterization showed that the weld nugget microstructures had a high-volume fraction of martensite. Using the Minitab software, Taguchi (DOE) and ANOVA on the tensile shear test results showed that welding current is more effective than clamping pressure on the tensile shear load-bearing capacity (TLBC). However, clamping pressure affects the weld current effects on weld performance. Additionally, the TLBC of RSW samples increases, whereas increasing the clamping pressure leads to a decrease in TLBC and nugget dimensions. Consequently, a detailed analysis of the RSW coefficients and their effects led to optimized results.

Research on corrugated interface formation mechanism and mechanical properties of the CFR flat Mg/Al clad plate

Corrugated-flat rolling (CFR) process was employed to manufacture the Mg/Al clad plate at 400 °C. The CFR process can produce flat Mg/Al clad plate with excellent shape and corrugated interface. EBSD analysis and tensile-shear tests were conducted to study the corrugated interface characteristics of the flat plate, revealing its strengthening mechanism. After the second-pass flat rolling process, the interface intermetallic compounds (IMCs) layer formed by heat treatment between passes broke, causing new bonding interface observed in the gap between the fractured IMCs. Intermittently distributed IMCs played a “pinning” role on the Mg/Al interface and restrained each other with the new bonding interface, which can improve the cooperative deformation ability of Mg plate and Al plate, and enhance the interface bonding strength. The interface tensile-shear strength at trough position was 33.97 MPa, which was higher than that at the peak position (24.17 MPa). During the second-pass flat rolling process, strong compressive stress was applied, improving the stress uniformity of the flat plate and refining metal grains, resulting in an improvement in tensile properties. The rolling UTS of flat plate was 255.77 MPa, and the fracture EL was 5.72%.

Optimisation of Vacuum Brazing Conditions for Joining Stainless Steel 321 Sheets by Nickel Based Braze Foil for Regenerative Rocket Nozzle Applications by Taguchi Method

This paper outlines the optimisation of vacuum brazing conditions for joining titanium stabilised Stainless Steel SS321 sheets by Ni-based braze alloy (Ni-Mn-Cr-Co-Si) as brazing filler metal (BFM) for two shelled rocket nozzle applications. This is a specialized brazing technique in which multiple parameters such as temperature, time, argon pressure in the furnace and vacuum level in the channels between the shells are to be precisely controlled in a complex furnace. Brazing temperature, holding time, surface pressure in terms of dead weight and vacuum levels were identified as parameters having significant effect on the bonding strength of a braze joint. Taguchi method was used as a statistical technique for design of experiments to optimise brazing conditions in terms of shear strength. L9(34 ) orthogonal array was designed for conducting the experiments with four parameters at three levels ie temperature (1190oC, 1230oC,1270oC), holding time (10min, 20min, 30min), surface pressure (100kPa, 150kPa, 200kPa) and vacuum level (0.133Pa, 1.33Pa, 13.3Pa). The optimised set of parameters ie temperature: 1230oC, time: 20min, pressure: 100kPa, vac. level: 1.33Pa has been arrived at by Taguchi method via statistical analysis through analysis of means (AVOM) and analysis of variances (ANOVA). Confirmatory test for optimised conditions agreed well with the Taguchi analysis. Also, extensive optical metallography and energy dispersion X-ray analysis across the joint were carried out to study the metallographic morphology across the joint. The fractured surfaces during lap shear tensile testing have also been studied under SEM.

Durability of GFRP and CFRP Bars in the Pore Solution of Calcium Sulfoaluminate Cement Concrete Made with Fresh or Seawater.

Calcium sulfoaluminate cement concrete (CSAC) reinforced by fiber-reinforced polymer (FRP) bars, termed bars for brevity, is a good alternative to steel-reinforced concrete in marine environments due to the corrosion resistance of FRP and the lower pH of CSAC. For the first time, multi-mechanical tests are conducted to compare the durability of glass FRP (GFRP) to that of carbon FRP (CFRP) after exposure to CSAC pore solution. The bars were immersed in a simulated pore solution of CSAC made with either fresh water and river sand or with seawater and sea sand. Solution temperature was held constant at 30 °C, 45 °C or 60 °C for 30, 60, 90 and 180 days of immersion. Tensile, horizontal and transverse shear tests, as well as detailed microstructural analyses, were conducted to determine the level and mechanisms of degradation for each type of bar. Sea salt increases the degradation of both bars, but it degrades GFRP more than CFRP. The bars' retained tensile strength is a reliable indicator of their durability, while their post-exposure horizontal and transverse shear strengths are found inconsistent and counter intuitive. In the GFRP, the fiber, the epoxy matrix and their interface suffered damage, but in the CFRP, the carbon fiber was not damaged. Under the test conditions in this study, the maximum reduction in the tensile strength of the GFRP was 56.9% while that of CFRP was 15.1%. Based on the relevant ASTM standard, the CFRP bar satisfies the alkaline resistance requirement of the standard in the CSAC pore solution with and without salt, whereas the GFRP bar does not meet the same requirement in the above pore solution with salt.

Microstructural characterization and mechanical properties in resistance spot welding of Q&P980 steel involving “effective softening” at the fusion boundary

This study proposes a welding process for Q&P980 steel that involves prolonged post-weld pulses. The process effectively softens the nuggets and results in welded joints with excellent comprehensive mechanical properties. The relationship between microstructural characteristics, element distribution and mechanical properties of weldments was elucidated for the samples subjected to different heat input histories. The microstructure evolution was analyzed using electron probe micro-analyzer (EPMA), electron backscatter diffraction (EBSD), and the mechanical properties of the spot welds were evaluated at room temperature by tensile shear (TS) and cross tension (CT) tests. The findings indicate that the softened area expands from the fusion boundary towards the opposite direction of the nugget as the heat input increases. A mixed microstructure of martensite and retained austenite, characterized by a larger size of prior austenite grains and lower kernel average misorientation, is formed in the “effective softening” region. This region provides serves as the primary location for crack nucleation and governs the propagation path of cracks within the halo ring-like softening zone, which has a significant impact on the fracture mode of the weld. The energy absorption in the TS test was increased by 95.40% compared to the single pulse weld (SPW), while the best combination of strength and energy absorption of the weldment in CT test was 7.2 kN and 64.24 J, respectively.

Gluing Characteristics of Giant Bamboo Using Four Commercial Adhesives

The study aimed to determine the bonding performance of laminated giant bamboo[Dendrocalamus asper (Schult.) Backer] glued with four commercial adhesives (PVAc-D3, PUR, UF, PF) at different surface pairings (pith-pith, pith-skin, and skin-skin) and glue spread rates(100, 150, and 200 g/m2). Kiln-dried giant bamboo poles were ripsawn, planed, and cut to length to produce slats for lamination. Slats for surface roughness and wettability tests were sanded with 180-grit sandpaper on both skin and pith surfaces. Surface roughness of the skin and pith was measured using Mitutoyo SJ–210 Surftest unit, whereas wettability was determined via the sessile drop method. Giant bamboo slats were bonded using specific lamination parameters for each adhesive. Tensile shear tests at dry and wet conditions were performed on the laminates to determine bond strength. The results showed that the bamboo pith had a rougher texture than the skin but with insignificant contact angle differences. Moreover, PVAc-D3 and PUR gave the highest and lowest initial contact angles on both sides, respectively, with PUR maintaining the smallest values throughout the contact duration. Adhesive, surface pairing, and some interactions (adhesive x glue spread and adhesive x surface pairing) significantly affected the dry shear strength, whereas adhesive and adhesive x surface pairing influenced wet shear strength. PUR-bonded laminates had the highest dry shear strength, followed by PF, PVAc-D3, and UF. In terms of wet shear strength, only PVAc-D3 did not conform to the minimum glue bond strength requirement of more than 1 MPa and cohesive bamboo failure of at least 40% (PNS 2099:2015). Skin-skin and pith-pith surface pairing yielded the highest and lowest dry shear strengths, respectively. Increasing the amount of glue did not translate to a stronger bond. PUR, UF, and PF are feasible alternatives to PVAc-D3 in engineered bamboo production for various end-uses.

High strength injection molding welding and interface crystal phase changes in polyamide 6

AbstractInjection molding is a widely used method for production of plastic components, offering both simplicity and high strength. In this study, secondary injection molding was utilized to weld polyamide 6 (PA6). The welded samples were evaluated for the welding strength via a shear tensile test. Three process parameters of mold temperature, injection temperature, and injection speed were varied to determine the optimal conditions for welding. A polarizing microscope analysis of the welding interface revealed formation of a shish kebab layer (SKL) structure, which significantly contributed to the welding strength. A differential scanning calorimetry analysis of the welded samples showed that changes in the crystallinity at the interface were closely related to the welding strength under different injection molding conditions. To analyze the crystal phase of the interface after welding, we propose the use of Fourier‐transform infrared spectroscopy area scanning to obtain the relationship between the phase transformation and welding strength. Additionally, microhardness testing is proposed as a means of evaluation of the welding effect. Overall, this study highlights the importance of optimization of process parameters in secondary injection molding to achieve strong welds in PA6, where the SKL structure and crystallinity changes at the interface have crucial roles.Highlights The high welding shear strength reaches 80% of the base material. The interfacial crystalline structure has a significant impact on the strength. The crystalline changes were analyzed using FTIR region scanning. The relationship between microhardness and welding strength was obtained. The wide‐ranging conditions have reference value for industrial production.

Identification of intermetallics in the laser-welded joint of rare-earth magnesium alloy and the corresponding strengthening mechanisms

Morphology and distribution of intermetallic compounds in the heat-affected zone (HAZ) are easily altered during welding thermal cycles, contributing to the softening of the HAZ. Finding solutions to mitigate the softening and enhance the strength of the joint is currently at the forefront of Mg alloy processing and manufacturing. In this work, 0.7 mm thick Ce-containing Mg alloy sheets were successfully joined using fiber laser welding. The microstructure of the joint was observed employing scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Accordingly, the phase compositions in both HAZ and fusion zone (FZ) were determined. Subsequently, the mechanical properties of the joint were evaluated through tensile-shear and hardness tests. The results revealed that the HAZ experienced softening, retaining 76.6% of the strength of the base metal in the tensile-shear test. Interestingly, intermetallics composed of conventional alloying elements within the HAZ transformed into coral-like structures during the welding thermal cycles, whereas the morphology and distribution of intermetallics containing rare-earth (RE) elements barely changed. As a result, the joint exhibited cracks along the boundaries of the coral-like precipitates during tensile loading. In comparison, both intermetallics consisting of conventional elements and those containing RE elements were fragmented into micron-sized fine particles in the FZ, leading to an increase in the strength of the FZ. Ultimately, the mechanisms responsible for the softening of the HAZ and the strengthening of the FZ were elucidated, presenting a promising welding solution for Mg alloys.

Effect of GO-modified epoxy on the bond behavior of old-new concrete and comparison with different surface preparation techniques

The interface of old to new concrete is the weakest plane during retrofitting and repairing of concrete structures, resulting in the interface or adhesive failure of the composite formed. Various surface preparation techniques and adhesives have been used and reported in the literature to improve the bond behavior of concrete-to-concrete interface. Epoxy is a commonly used adhesive to bond existing concrete with new overlay concrete, as it provides high adhesion and chemical resistance; however, inadequate roughness and low strength negatively affect the epoxied concrete joints, causing poor bonding at the concrete interface. On the other hand, the use of graphene oxide (GO) in epoxy showed significant enhancement in its mechanical properties. Hence, in the present study, GO-modified epoxy has been proposed as an adhesive to improve the bond performance of the interface between existing and new concrete by conducting split tensile, bi-surface shear, and slant shear tests. Simultaneously, a comparison has been carried out with other frequently used surface preparation techniques such as grinding wire brushing (GW), grooves, and adding carbon and glass fiber laminate over the existing concrete with and without neat (plain) epoxy. The GO-modified epoxy has been prepared using three different GO concentrations; out of them, 0.05% by weight turned out to be the optimum concentration and performed best under all bond strengths and resulted in concrete failure instead of adhesive failure. Furthermore, scanning electron microscopy (SEM) revealed homogeneous dispersion of GO at 0.05% by weight and formation of the bond between GO and cement hydrates with both concrete interfaces. As a result, GO-modified epoxy turned out to be a high-strength adhesive to join existing concrete with fresh overlay concrete for strengthening, retrofitting, and repairing concrete structures and shows an effective composite action.

Resistance spot weldability of Fe66Cr16.5Ni14.1Si3.4 advanced high strength steel using D-optimal design of experiment method

Using advanced high-strength steels in automobiles has created a new challenge to achieve acceptable welds. The present study evaluates the weldability of the new generation of advanced high-strength steels in the FeCrNiSi alloy group. Hence, utilizing the design of experiment (DOE), it was obtained how the parameters namely the welding current, welding time, and electrode force affect the final properties. Additionally, the acceptable range of parameters for achieving an acceptable weld nugget in terms of size and strength was obtained. Accordingly, the nugget size effects on mechanical properties, namely energy absorption capability, failure mode in tensile-shear test, and microhardness were evaluated. The parameters were statistically significant and showed a high degree of reliability (95%) in terms of nugget size. The range of acceptable parameters for 1 mm thick steel and type A electrode was 9–21 cycles for welding time, whereas for welding current were 4–7 KA, 5 to 6.5 KA, and 5.7 to 6.5 KA at 2, 3, and 4 KN electrode force, respectively. Due to the grain growth in the heat-affected zone (HAZ), the HAZ softening was observed in the microhardness profile. All samples demonstrated desired fracture mode due to the HAZ softening, the ductile austenitic microstructure, the absence of brittle phases, and easy nugget rotation in the tensile-shear test. By increasing the nugget diameter from 3 to 5.1 mm, the peak load and the energy absorption of the spot welds exceeded from 5.4 KN to 6.5 KN and from 10 to 31 J, respectively.