Joint Resistance Research Articles

Microstructure and mechanical properties of butt-welded Ti/steel bimetallic sheet using various multi-principal filler wires

Ti/steel bimetallic sheets have attracted significant attention in various engineering fields. However, achieving high-quality welded joints of Ti/steel bimetallic sheet presents difficulties because of poor metallurgical compatibility and different thermal expansion coefficients between titanium and steel. In this study, four types of multi-principal filler wires with varying contents of Cu, Ni, and Ti elements were designed and manufactured to finish the welding of TA2/Q235 bimetallic sheets. The study investigated the effects of various filler wires on the hardness, tensile strength, corrosion resistance, and microstructure of the welded joints. An interesting finding is that the highest tensile strength of 327±6 MPa was achieved in the welded joint using FeCoNi2Ti0.5 filler wire, with a joint coefficient of ∼79.1 %. The highest hardness in the weld zones was achieved by using FeCoNiTi0.5 filler wire, while the lowest hardness was achieved using FeCoNiCu0.5 filler wire. Dendrite (DR), interdendritic (ID), and eutectic structures were consistently observed in these weld zones. The phases of the DR and ID were identified as Fe2Ti and FCC structures based on EBSD data. A high content of Ni in filler wires could reduce the size and content of the Fe2Ti phase in the weld zones of Ti/steel bimetallic sheets.

Analysis of the possibilities to increase abrasion resistance of welded joints of Hardox Extreme steel

This paper presents a heat treatment process designed to enhance the abrasion resistance of welded joints of Hardox Extreme steel, which is known for its high hardness (>600 HBW) and tensile strength (>2000 MPa). Despite these properties, the steel's weldability, characterized by a Carbon Equivalent Value (CEV) of 0.70, limits its use in applications like mining machinery where welding is essential. The key challenge in welding martensitic boron steels, such as Hardox Extreme, is the reduction in hardness and abrasion resistance in the heat-affected zone, along with cold cracking due to increased hardenability. This study investigates the abrasion resistance and microstructural properties of welded joints made with submerged arc welding (SAW) under different heat treatment conditions. The developed process achieved a uniform tempered martensite microstructure across all welded zones, increased hardness to over 550 HV in the weld material zone and improved the relative abrasion resistance by 25 % compared to the as-welded state.

Effect of corrosion environments on the mechanical properties of friction stir welded aluminum alloy AA3003

The article presents an experimental study on the corrosion resistance of the 3003 Aluminium alloy Friction Stir Welded (FSW) joint in different working environments. Three types of corrosive media at different temperatures were tested to see how they affected the FSW joint mechanical properties. The media were sodium chloride, hydrogen chloride, and ethylene glycol. In parallel with the study of the effect of temperature, static tensile tests were carried out on specimens taken perpendicular to the welding direction. Also, micro-hardness profiles were used to determine the influence of the parameters studied on the various weld zones. Finally, the effect of the most aggressive corrosive medium, temperature, and the inclusion of ethylene glycol on the crack propagation resistance of an FSW joint were studied. Fatigue-propagation tests at constant stress amplitude were carried out to understand what affects the fatigue crack propagation of welded joints after corrosive attack. The results showed that uniform and pitting corrosion were combined to cause FSW joint surface degradation. Corrosion damage does not appear to alter yield strength and ultimate stress values. However, FSW joints show a significant degradation in mechanical properties with increasing temperature and with the aggressiveness of the corrosive medium. The inclusion of ethylene glycol was found to delay the rate of crack propagation during testing, leading to an improvement in the service life of pre-corroded FSW joints.

Chloride corrosion resistance of wet joints in manufactured sand reinforced concrete prepared in plateau environment

The durability of three types of wet joints in manufactured sand concrete prepared in simulated plateau environment was investigated. And the accelerated corrosion test on specimens in the chloride salt solution and the static tensile test on corroded steel bars in specimens were carried out by sequence. The durability of different types of specimens prepared in plateau environment was compared by analyzing the development of concrete cracks, the corrosion morphologies of internal steel bars, the degradation of mechanical properties of steel bars, and the concrete microstructure. The results demonstrate that the development of concrete cracks and the distribution of crack width are affected by wet joint. The nonlinearity of variation of average crack width with actual corrosion rate is enhanced by wet joint. The strength and elongation of steel bars in concrete decrease evidently by wet joint. The strength and elongation loss of steel bars after corrosion is effectively reduced by the punched treatment on joint interface. There is no clear superiority or inferiority pattern for the durability of wet joint specimens with untreated interface (UI) and chiseled interface (CI), and the durability of wet joint specimen with punched interface (PI) is better than that of UI and CI specimens.

Hybrid rehabilitation of 3D RC beam-column joints using UHP-HFRC and FRP wrapping: Experimental evaluation and theoretical analysis

Beam-column joints are crucial elements in reinforced concrete (RC) structures subjected to seismic loading, as they are vulnerable elements prone to significant damage during earthquakes. Due to extensive structural damage, various methods have been developed to strengthen beam-column joints. However, research on rehabilitation and repair methods has been limited, with most studies focusing on 2-D joints and overlooking the confinement effect of corner beams on the joint core. This study aims to investigate novel hybrid rehabilitation systems, including ultra-high performance hybrid fiber-reinforced concrete (UHP-HFRC) and fiber-reinforced polymer (FRP) systems, alongside embedding reinforcement into heavily damaged 3-D beam-column joints subjected to pre-cyclic loading and subsequent cyclic loading. Parameters related to hysteresis response were obtained and discussed, such as ductility, lateral stiffness, dissipated energy, equivalent hysteresis damping, and pinching ratio of the tested specimens. The experimental findings revealed that utilizing an FRP and UHP-HFRC hybrid rehabilitation system enhanced ductility, dissipated energy, and lateral stiffness of heavily damaged joints by 25 %, 73 %, and 81 %, respectively, compared to the undamaged reference specimen. Additionally, a simplified design model was developed to predict the shear resistance of beam-column joints, incorporating principles of strut-and-tie. The theoretical design model was also validated against the experimental database, demonstrating a good accuracy with MV and COV of 0.97 and 13 %, respectively.

A full-bridge flux pump using two switches: numerical model and experimental prototype

Abstract High-temperature superconducting (HTS) magnets are promising in high field applications. However, due to inevitable joint resistance and flux creep, HTS magnets still face challenges in maintaining field stability in their closed-loop operation. HTS flux pumps can charge closed HTS magnets wirelessly, thus allowing lower cryogenic loading and more flexible arrangements in HTS magnet systems. In this work, a full-bridge flux pump using two AC field-controlled switches is proposed, which can charge HTS magnets during whole cycles. Therefore, the charging speed of the proposed full-bridge flux pump is at least one time larger than half-bridge flux pumps. A numerical model and an experimental prototype are developed to verify the working principle of the proposed full-bridge flux pump. Simulation and experimental tests are carried out to investigate the working characteristics of the proposed flux pump. The proposed flux pump has huge potential in the application scenarios where high charging speed is required.

Regression prediction model for shear strength of cold joint in concrete

The shear resistance of cold joint in concrete is influenced by various design parameters. Traditional mechanical models typically consider only a limited number of parameters to predict the shear strength of cold joints. This research aims to explore the complex nonlinear relationship between design parameters and cold joint shear strength using statistical method and machine learning technology. The goal is to develop a more accurate, reliable, and engineering applicable regression model for predicting shear strength. A dataset of 546 Z-shaped shear specimens characterizing cold joint in concrete was constructed, involving a total of 16 variables that may affect shear performance. Correlation analysis and recursive elimination were adopted to eliminate correlated and insignificant variables based on their importance. Multiple linear regression (MLR), random forest regression (RFR), and support vector machine regression (SVR) prediction models for cold joint shear strength were established based on rigorously screened variables and comprehensively evaluated using multiple methods. It was found that the most significant factors influencing the shear strength of cold joints are concrete strength, interface shear key, product of interface reinforcement strength and its reinforcement ratio, normal stress, fiber length of new concrete, casting method of the new concrete, and product of the fiber length and its tensile strength of old concrete. The MLR, SVR, and RFR models all exhibited superior performance relative to traditional mechanics-based models with regard to shear strength prediction of cold joints. The RFR model is recommended for predicting the shear strength of cold joints due to its superior evaluation indexes in comparison to the MLR and SVR models, and variable sensitivity analysis shows that it does not yield common-sense errors.

Investigation of the Influence of Aluminosilicate Adhesives Modified with Magnesite on the Strength Properties of Glued Wood Products

The work is devoted to the study of magnesite influence on the strength properties of glued wood products with aluminosilicate adhesive. It they shown that the introduction of magnesite in the composition of aluminosilicate glue in the amount from 0.5 to 1.5 % contributes to an increase in the shear strength along the fibres by 1.57 times compared to the normative requirement (not less than 4 MPa). It we found that the bending strength of glued wood on a toothed spike is 1.4 times higher than the normative (not less than 26 MPa). After fire tests, no destruction of the glue joint on the spike we observed, and the bending strength of the samples increases proportionally to the introduction of magnesite in the glue composition. Water resistance of glue joints on the toothed spike when the samples we kept for 48 hours at the temperature 20 °С is higher than the standard value and increases with the increase of magnesite content in the glue composition. After boiling at the temperature 100 °С for 3 hours the samples containing 1.5 % magnesite meet the normative requirements (3 MPa).

Investigating the Influence Mechanism of Different Shielding Gas Types on Arc Characteristics and Weld Quality in TA2 Laser–Arc Hybrid Welding

The effective welding of a 6 mm thick TA2 pure titanium medium-thickness plate was achieved by laser–arc hybrid welding (LAHW) with helium–argon mixed shielding gas. Conducted research on the influence of helium–argon mixed shielding gas on plasma and arc characteristics during welding, and its further impact on the microstructure, internal porosity defects, tensile properties, and corrosion resistance of welded joints was explored. The study demonstrated that under the shielding gas with 75% helium, the arc width narrowed significantly from 6.96 mm to 2.61 mm, achieving a 63% reduction, which enhanced the concentration of arc heat flux density. Achieved a well-formed weld with no surface spatter and significantly reduced the internal porosity rate from 3.02% to 0.47%, which is an 84% decrease. Tensile fractures are located in the base material, all exhibiting plastic failure. The corrosion resistance of the welded joint initially increased and then decreased with the increase of helium content in the shielding gas, peaking at 75% helium content.

An Electromagnetic-Thermal Modeling Method for the Joint Resistance of the CORC Cable

An Electromagnetic-Thermal Modeling Method for the Joint Resistance of the CORC Cable

Effects of CuO nanoparticles on SAC composite solder joints: Microstructural and DFT study

In this paper, novel application possibilities of CuO nanoparticles were investigated in SAC0307 solder alloy for composite soldering purposes. CuO nanoparticles in 0.25 and 0.5 wt% were mixed into the solder paste to produce composite solder joints. Solder joints were manufactured using standard surface mounting technology from different solder pastes. The solder joints were loaded in an 85 °C/85RH% temperature and humidity test for 4000 h. It was found that the CuO composite solder joints showed improved mechanical quality due to the microstructural refinement, which was studied using scanning electron microscopy (SEM) and focused ion beam (FIB) analysis. On the other hand, the corrosion resistance of CuO joints decreased, as they suffered localized corrosion extensively, which produced longer and more Sn whiskers on their surface than on the reference SAC0307. Density functional theory (DFT) calculations proved that CuO can bond to Sn, but CuO is not chemically inert in the solder bulk. CuO can start a cyclic reaction with the dispersed Cu6Sn5 intermetallics, which produces SnO2 in the solder bulk, ultimately enhancing corrosion. Therefore, CuO nanoparticles are suggested to be applied only in non-corrosive environments, such as space applications.

Numerical simulation and properties analysis of Ta10W alloy joints prepared by electron beam welding

Vacuum electron beam welding has the characteristics of concentrated energy, controllable heat input, almost no pollution, and a small heat-affected zone. In this study, the Ta10W alloy was successfully connected by electron beam welding (EBW), and numerical simulations were employed to examine the distribution of temperature and stress fields throughout the welding process. Additionally, the influence of EBW on the microstructure and corrosion resistance of the welded joints was scrutinized. Findings indicate that the welding heat process led to a reduction in grain boundary energy, thereby facilitating thermal activation processes that contributed to grain growth. Grain boundary migration and possible dynamic crystallization led to the appearance of the coarse columnar crystal structure in the welded joint. A three-dimensional, nonlinear, transient, thermo-mechanically coupled finite element model was developed for the electron beam welding of Ta10W alloy. The shape characteristics and size of the weld and transient thermal cycles calculated by numerical simulations were in reasonable agreement with experimental results. Electron beam welding reduced the corrosion resistance of the Ta10W alloy, and the corrosion product was mainly composed of Ta, O and Na.

Experimental investigation on seismic performance of CHS T-joints in salt spray environment

This paper aims to investigate the seismic performances of circular hollow section (CHS) T-joints with different regions of corrosion damage. A total of seven CHS T-joint specimens with various corrosion degrees were applied to conduct the quasi-static tests of brace axial cyclic loading, and the effects of corrosion damage on the hysteresis behavior and failure mode were discussed. Experimental results indicated the brace corrosion only had a slight influence on the seismic performance of CHS joints, while the corrosion difference on two sides of the brace might cause an additional bending moment and damage accumulation to accelerate the plastic collapse of the connection zone. Compared with the corrosion on the brace, the resistance of CHS joints was more susceptible to the corrosion located in the chord wall, resulting in the axial cyclic carrying capacity and stiffness of CHS joints significantly decreasing with the increase of chord corrosion level. However, the increasing corrosion on the chord would affect the final fracture behavior and fracture position, so the total energy dissipation and deformation of CHS joints presented a complicated and nonlinear degradation trend. In addition, corrosion damage simultaneously had an impact on reducing the bending capacity of the chord, and this phenomenon not only caused the differences between the degradation rates of axial tensile and compressive strength of CHS joints but also affected the failure mechanism and local deformation of CHS joints under the brace axial cyclic loading.

Development of a multi-pancake HTS magnet operated in persistent current mode based on superconducting joint of REBCO coated conductors

Developing closed-loop magnets that operate in a persistent current mode (PCM) is crucial for achieving higher resolution and sensitivity in NMR and MRI devices. To the best of our knowledge, we report a novel closed-loop multi-pancake (MP) HTS magnet operated on PCM based on a novel jointless winding method with superconducting joints of REBCO coated conductors (CCs). The in-field characteristics of the CC and the joints were investigated to determine the operating parameters of the magnet. The steady central field of the magnet reached ∼408.4 mT at 77 K with an operating current of 16.5 A. The joint resistance was inferred from a higher excitation current of 17 A to be at least less than 2.5 × 10−10Ω. Although the I c value of the joint was considerably lower than that of the CC at self-field, it could maintain similar comparable or even higher in-field I c compared to the CC, which is immensely beneficial for magnet applications. This study provides some insights into the design and construction of closed-loop MP magnets operating in PCM.

Effect of Different Lap Angles on Corrosion Resistance of SUS304 Stainless Steel Joints Welded by TIG Welding

Effect of Different Lap Angles on Corrosion Resistance of SUS304 Stainless Steel Joints Welded by TIG Welding

Effect of Rotational Velocity on Mechanical and Corrosion Properties of Friction Stir-Welded SUS301L Stainless Steel.

Friction stir welding was utilized to obtain high-quality SUS301L stainless steel joints, whose mechanical and corrosion properties were thoroughly evaluated. Sound joints were obtained with a wide range of rotational velocities from 400 to 700 rpm. The microstructures of the stir zone primarily consisted of austenite and lath martensite without the formation of detrimental phases. The ultimate tensile strength of the welded joints improved with higher rotational velocities apart from 400 rpm. The ultimate tensile strength reached 813 ± 16 MPa, equal to 98.1 ± 1.9% of the base materials (BMs) with a rotational velocity of 700 rpm. The corrosion resistance of the FSW joints was improved, and the corrosion rates related to uniform corrosion with lower rotational velocities were one order of magnitude lower than that of the BMs, which was attributed to the lower martensite content. However, better anti-pitting corrosion performance was obtained with a high rotational velocity of 700 rpm, which was inconsistent with the uniform corrosion results. It could be speculated that a higher martensitic content had a negative effect on the uniform corrosion performance, but had a positive effect on the improvement of the anti-pitting corrosion ability.

Sn99Ag0.3Cu0.7–TiO2 composite solder joints and their influence on thermal parameters of power components

PurposeThis paper aims to investigate the influence of composite solder joint preparation on the thermal properties of metal-oxide-semiconductor field-effect transistors (MOSFETs) and the mechanical strength of the soldered joint.Design/methodology/approachReinforced composite solder joints with the addition of titanium oxide nanopowder (TiO2) were prepared. The reference alloy was Sn99Ag0.3Cu0.7. Reinforced joints differed in the weight percentage of TiO2, ranging from 0.125 to 1.0 Wt.%. Two types of components were used for the tests. The resistor in the 0805 package was used for mechanical strength tests, where the component was soldered to the FR4 substrate. For thermal parameters measurements, a power element MOSFET in a TO-263 package was used, which was soldered to a metal core printed circuit board (PCB) substrate. Components were soldered in batch IR oven.FindingsShear tests showed that the addition of titanium oxide does not significantly increase the resistance of the solder joint to mechanical damage. Titanium oxide addition was shown to not considerably influence the soldered joint’s mechanical strength compared to reference samples when soldered in batch ovens. Thermal resistance Rthj-a of MOSFETs depends on TiO2 concentration in the composite solder joint reaching the minimum Rthj at 0.25 Wt.% of TiO2.Research limitations/implicationsMechanical strength: TiO2 reinforcement shows minimal impact on mechanical strength, suggesting altered liquidus temperature and microstructure, requiring further investigation. Thermal performance: thermal parameters vary with TiO2 concentration, with optimal performance at 0.25 Wt.%. Experimental validation is crucial for practical application. Experimental confirmation: validation of optimal concentrations is essential for accurate assessment and real-world application. Soldering method influence: batch oven soldering may affect mechanical strength, necessitating exploration of alternative methods. Thermal vs mechanical enhancement: while TiO2 does not notably enhance mechanical strength, it improves thermal properties, highlighting the need for balanced design in power semiconductor assembly.Practical implicationsIncorporating TiO2 enhances thermal properties in power semiconductor assembly. Optimal concentration balancing thermal performance and mechanical strength must be determined experimentally. Batch oven soldering may influence mechanical strength, requiring evaluation of alternative techniques. TiO2 composite solder joints offer promise in power electronics for efficient heat dissipation. Microstructural analysis can optimize solder joint design and performance. Rigorous quality control during soldering ensures consistent thermal performance and mitigates negative effects on mechanical strength.Social implicationsThe integration of TiO2 reinforcement in solder joints impacts thermal properties crucial for power semiconductor assembly. However, its influence on mechanical strength is limited, potentially affecting product reliability. Understanding these effects necessitates collaborative efforts between researchers and industry stakeholders to develop robust soldering techniques. Ensuring optimal TiO2 concentration through experimental validation is essential to maintain product integrity and safety standards. Additionally, dissemination of research findings and best practices can empower manufacturers to make informed decisions, fostering innovation and sustainability in electronic manufacturing processes. Ultimately, addressing these social implications promotes technological advancement while prioritizing consumer trust and product quality in the electronics industry.Originality/valueThe research shows the importance of the soldering technology used to assemble MOSFET devices.

Study on fire resistance of high performance concrete nonplanar beam-wall joints

The utilization of high performance concrete (HPC) in the core region of beam-wall joints can enhance the structural integrity and load-bearing capacity of prefabricated buildings. However, due to the high-temperature bursting characteristics of HPC, the mechanical properties of the joints degrade prematurely under fire. In this paper, the fire resistance of HPC nonplanar beam-wall joints was investigated using high-temperature experiments and numerical simulations. First, the prefabricated beam-wall joint and the cast-in-place beam-wall joint proposed in this study were subjected to high-temperature and post-fire static loading tests, enabling a comparative analysis of their fire resistance and load-bearing capacity. The results demonstrated that the utilization of HPC in the core region of the prefabricated beam-wall joints can enhance its load-bearing capacity and fulfill the fire resistance requirements. Subsequently, a finite element model of the nonplanar beam-wall joint was established based on test results to investigate the influence of different structural parameters on its post-fire mechanical properties. The results demonstrate that the diameter of vertical reinforcement in the wall can significantly influence the post-fire load-bearing capacity of the joints, while the concrete strength in the core area of the joints has little impact on the post-fire bearing performance of the joints. Compared to the conventional cast-in-place beam-wall joints with normal strength concrete, the prefabricated beam-wall joints have superior fire resistance and post-fire load-bearing performance.

Friction stir welding of as-cast and pre-aged Al–Si–Zn–Mg–Fe alloy: Microstructure, mechanical and corrosion properties

Al–Si–Zn–Mg–Fe alloy in as-cast and artificially aged (T6) conditions was friction stir-welded with a traveling speed of 200 mm/min and a rotation speed of 800 rpm. Their microstructure, mechanical and corrosion properties were investigated. α-Al, Si, Mg2Si, MgZn2 and Fe-rich phase were detected in the as-cast and pre-aged Al–Si–Zn–Mg–Fe before and after FSW. The secondary phases in pre-aged Al–Si–Zn–Mg–Fe after FSW are slightly more than those in the as-cast Al–Si–Zn–Mg–Fe after FSW. For the pre-aged Al–Si–Zn–Mg–Fe after FSW, the grains are refined and the dislocation density decreases. Hardness of the pre-aged Al–Si–Zn–Mg–Fe is higher than that of the as-cast one, whereas the hardness of weld nugget zones (NZs) of the both FSWed Al–Si–Zn–Mg–Fe joints is lower than their base materials, and the strength coefficients of both FSWed joints of the as-cast and pre-aged Al–Si–Zn–Mg–Fe are 0.82 and 0.9 respectively. The ultimate tensile strength (UTS) and yield strength (YS) of the pre-aged Al–Si–Zn–Mg–Fe after FSW (UTS = 208.86 MPa and YS = 156.72 MPa) is about 35% higher than that of as-cast Al–Si–Zn–Mg–Fe after FSW (UTS = 159.4 MPa and YS = 112.06 MPa) mainly due to the smaller grain size and more precipitates in the former. The corrosion resistance (CR) of the FSWed joint of the pre-aged Al–Si–Zn–Mg–Fe is the highest, owing to the most refined grain size, highest HAGBs, lowest KAM, increase in the close-packed {111} (α-Al) texture, dispersed particles of secondary phases, followed by the pre-aged Al–Si–Zn–Mg–Fe and then the FSWed joint of the as-cast Al–Si–Zn–Mg–Fe, and the as-cast one is the lowest.

Mechanical properties and corrosion resistance of TC4 titanium alloy joints by plasma arc welding + gas tungsten arc welding combination welding

Mechanical properties and corrosion resistance of TC4 titanium alloy joints by plasma arc welding + gas tungsten arc welding combination welding