Strong Joints Research Articles

Achieving superior strength and elongation from electrically assisted pressure joining of medium entropy alloy and Ti-6Al-4V

In the present study, two dissimilar alloys (Ti-6Al-4V and NbTiZr(MoTa)0.1) are joined using electrically-assisted pressure joining. This joining technique can produce components with superior mechanical properties (with a yield strength of ∼980 MPa and elongation of ∼10.5%), ensuring optimal performance under severe operating conditions. A detailed analysis of the joined interface related to phase analysis and mechanical mapping elaborated a strong joint having a high yield strength without any post-heat treatment. The findings of the present study contribute to the broader field of dissimilar metal joining and can serve as a reference for future research and development in the aerospace industry. This study demonstrates the feasibility of achieving strong and ductile solid-state joints between dissimilar alloys.

Seismic design and experimental testing of precast tolerance concrete shear wall subject to cyclic load

A precast tolerance concrete shear wall (PTCW) characterized by proper-length steel connectors is proposed to adjust the tolerance and improve the joint failure model of the precast wall. The design method for this wall is also presented in this study and verified by test results. Four full-scale walls, including two cast-in-situ walls (RCWs) and two precast walls (PCWs) with axial compression ratios of 0.2 and 0.3, respectively, were tested under lateral loading. The seismic behavior of the panels, including the failure modes, hysteretic behavior, strength envelope curves, stiffness degradation, energy dissipation, and steel strains, was analyzed and discussed herein. The test results showed that all four walls were in a flexural-shear failure mode, and the PCWs showed better performance in terms of hysteretic behavior, strength envelope, stiffness, and energy dissipation, particularly under an axial compression ratio of 0.3. Furthermore, the peak load of PCW1 (axial compression ratio is 0.2) and PCW2 (axial compression ratio is 0.3) increased by 5.93% and 15.51%, and the yield load increased by 12.1% and 11.39% compared with those of RCW1 (axial compression ratio of 0.2) and RCW2 (axial compression ratio of 0.3), respectively. The equivalent viscous damping coefficients of all four panels were higher than 0.05. The lateral bearing capacity of the walls increased with an increase in the axial compression ratio. Moreover, no visible damage or slippage was observed when the PCWs were demolished after testing. The main nonlinear strain was concentrated on the vertical bar and not on the connectors, indicating that the plastic hinge position was transferred from the joint interface to the wall panel. The results indicated that the use of steel connectors to strengthen the joints can achieve the seismic design concept of strong joints and weak members.

Fundamental study on high-quality welding of copper and aluminum by angled and superposed irradiation of blue and near-infrared lasers

In order to achieve sustainable development goals, decarbonization and low-carbonization are required. Electric and hybrid vehicles are indispensable for the conservation of natural environment, and the lightweight construction and the effective transfer of electricity become important. Thus, copper and aluminum have been increasingly recognized as important materials because of their excellent materials’ properties. However, in the welding of these materials, it is difficult to obtain strong joints because there are problems in the brittle intermetallic compounds and the welding defects due to different melting points between copper and aluminum. Especially in the joining of copper and aluminum by copper side irradiation, aluminum-rich intermetallic compounds (IMCs) of brittle state result in the decrease of mechanical strength. Therefore, mild heat input from copper to aluminum would be necessary to reduce the brittle IMC. Angled irradiation might result in the mild energy input to aluminum because it can be expected that aluminum would be heated by the reflected light inside the keyhole generated in copper according to its high light reflection. In addition, stable welding can be expected by the superposed irradiation of blue and near-infrared lasers because of high light absorption rate of blue laser to copper. The angled and the superposed irradiation could achieve a stable welding state, and the generation of aluminum-rich IMC becomes smaller. Angled irradiation of a near-infrared laser showed equivalent joining strength to the superposed irradiation of two wavelengths, and the combination of angled and superposed irradiation achieved a remarkable increase of joining strength in a cross tensile test by 80%.

Improved interfacial strength of Ti/Ti ultrasonic welds by introducing α/β/α heterogeneous bonding interface

We investigated ultrasonic welding (USW) of pure α-Ti sheets, which exhibited an insufficient weldability due to the extensive formation of cracks caused by sliding friction during the USW. To overcome this issue, an α/β/α heterogeneous interfacial microstructure was designed by introducing a thin Fe interlayer, a beta stabilizer, between α-Ti sheets. The diffusion of Fe interlayers triggered the formation of a continuous β-Ti thin layer (⁓1–2 μm) without Fe–Ti intermetallics near the bonding interface after USW. The continuous thin β-Ti layer exhibited a significant improvement in the joining of the brittle α-Ti, where the bonding strength was increased from 350 to 1700 N. This study provides a potential approach to design an interfacial microstructure that promotes the formation of a deformable phase, overcoming the inherent brittleness of hexagonal close-packed metals and enabling production of strong joints.

ABAQUS-based hysteresis performance analysis of thorough-diaphragm bolted connection between concrete-filled steel tubular column and steel beam

Concrete-filled steel tube can effectively improve the compressive strength of members, so it is widely used in high-rise buildings, bridges and tunnels. However, there are only limited studies on the hysteresis performance of through-diaphragm plates in steel pipe concrete. In light of the current situation, this paper establishes a model of thorough-diaphragm-diaphragm bolted connection TDBC structure using numerical simulation software ABAQUS, conducting monotonic loading and cyclic displacement loading on it to study the hysteretic performance of this structure. The results reveal that the semi-rigid connection of TDBC contributes to the outwards displacement of the plastic hinge in the beam-column joint, indicating a hysteretic good performance. Furthermore, this study also finds that the flange and web area of steel beams present obvious ductile damage characteristics, which is in line with the design philosophy of strong joints and weak members, reproducing the actual damaging process to a certain extent.

Seismic behaviour of a wall-type concrete-filled steel tubular column with an end plate steel beam reinforced joint

To solve the problem of square concrete-filled steel tubular columns (CFSTCs) protruding from the walls and occupying indoor spaces, this study proposed a wall-type concrete-filled steel tubular column (WCFSTC) with end-plate steel beam in-plane and out-of-plane joints. The construction details, assembly process, and performance parameters of the WCFSTC with end-plate steel-beam-reinforced joints are presented. The seismic performance of four full-scale specimens under a low-cycle horizontal load, influence of side-plate height on the seismic performance of the specimenswere studied based on the test. According to the test results, the ductility, hysteresis curve, skeleton curve, and energy-dissipation capacity of the specimens were studied. A finite element model was developed and verified experimentally. The effect of the end-plate and column thickness on the seismic performance of the joints was investigated using the finite element model with variable reference analysis of the end-plate and column thickness. The results showed that the specimens exhibited good seismic performance whilst meeting the requirements of ‘strong joints and weak members’, and the thickness of the end plate had an important influence on the seismic performance of the specimens.

Study on the collapse performances of fabricated single-layer spatial network structures based on discrete beam elements

Using discrete beam elements to simulate the mechanical properties of assemble joints, the collapse performances of free-form, cylindrical, and K6 spherical surface latticed shells were analyzed. The effects of grid sizes, rise-span ratios, and connection behaviors on structural collapse performances were discussed. The main conclusions were obtained: (1) By conducting an integral scaled model test of a free-form latticed shell, the accuracy of the collapse analysis model with discrete beam elements was verified. (2) Multiple collapse shapes were obtained for the latticed shells with various structural parameters. To ensure an excellent collapse-resistant capacity, the grid size should not exceed 4 m, and the rise-span ratio is suggested as 1/4 for the cylindrical latticed shells, and the grid size should not be greater than 3 m, and the rise-span ratio should not be less than 1/4 for the spherical surface latticed shell. (3) The connection behaviors of assemble joints significantly influence the structural collapse-resistant capacity. When the stiffness and bearing capacity of the assemble joint drop to 50% of the joint designed based on “strong joints and weak tubes”, the robustness index decreases rapidly. However, more than 80% of the collapse load is still reserved for the cylindrical latticed shell and approximately 60% for the spherical surface latticed shell.

Dissimilar Joining of Immiscible Fe–Mg using Solid Metal Dealloying

Joining of Mg alloy to steel has received wide attention for design of multi-materials. This letter describes joining of immiscible pure iron and pure magnesium (Fe–Mg), as a simplified model, performed by solid metal dealloying (SMD) between Mg and Fe100−xNix interlayers that were preliminary joined to the Fe part by diffusion bonding. SMD formed an Fe–Mg bicontinuous composite with interconnected morphology at the Fe–Mg weld interface. The effect of Ni composition x in the interlayer on the weld strength was examined. Strong joints were obtained when 30 < x < 50 at.%, which caused Mg base-metal fracture due to a well-interconnected Fe–Mg structure. When too little (x < 30 at.%) or too much (x > 60 at.%) Ni was added, interfacial fracture occurred due to limited dealloying reaction and formation of an isolated Fe product surrounded by a large amount of brittle Mg2Ni.

Experimental and Numerical Studies on the Seismic Performance of New Assembled Concrete Frame Beam–Column Joints

A new type of assembled concrete beam–column joint based on a bolted connection was proposed, aiming to complete the post-earthquake node repair work by replacing precast beams and bolts. To study the seismic performance of the new beam–column joints, two full-scale components of the new joints were fabricated and subjected to low cyclic loading. The whole process from crack generation to component failure was investigated in detail, and seismic performance indicators such as the hysteresis curve, skeleton curve and stiffness degradation curve were compared and analyzed. Based on the experimental results, ABAQUS finite element software was applied to numerically simulate cast-in-place joints and test joints. Based on the failure mechanism of the new assembled beam–column semi-rigid joints, a stress analysis of semi-rigid joints was carried out. The research results show that the two new joints have good seismic performance and energy dissipation performance. Bolts and precast beams are the main stress components, and the repair of new joints can be completed by replacing bolts, which meets the seismic design concepts of “strong columns and weak beams” and “strong joints and weak components”. The larger the diameter of the bolts, the higher the load capacity and the lower the stiffness degradation rate. The finite element simulation results are high-accuracy and can well reflect the seismic performance of the components. It is found that cast-in-place joints are better in energy dissipation capacity than test joints, but the ultimate bearing capacity of test joints is better than that of cast-in-place joints. Based on the experimental stress characteristics of the nodal core zone, a mechanical analysis model of the nodal core zone of the new assembled concrete beam–column joints is proposed, and shear force calculation equations for the core zone of the new assembled concrete beam–column rigid joints and semi-rigid joints are derived.

“Play in the Joints” Among the Religion Clauses: Rebuilding the Strong Joints the Framers Formed

“Play in the Joints” Among the Religion Clauses: Rebuilding the Strong Joints the Framers Formed

The analysis of the effect of assembly joints technology on the strength of adhesive joints of poly(methyl methacrylate) (PMMA) used in advertising elements: Assembly joints technology of PMMA

The aim of the article was to present issues related to the influence of the assembly joints technology (the type of adhesive material and the adhesive application) on the strength of the adhesive joints of poly(methyl methacrylate) (PMMA) used in the production of advertising elements. Angular adhesive joints, which are one of the types of joints made in the construction of advertising elements, were used in the study. The bonded material was poly(methyl methacrylate) (PMMA) of 8 mm thick. Two types of adhesives were used to make the adhesive joints: one-component solvent-based adhesives and methylene chloride as a solvent. Experimental tests determined the wettability of the surface of the adherends (with and without a protective coating) and the work of adhesion based on the measurement of the contact angle, as well as the strength of adhesive joints in accordance with the ISO 4578 standard. Based on the results of strength tests, it can be seen that the use of a solvent allows for obtaining equally strong joints as with the use of solvent. The purposefulness of using coatings protecting not only against dirt or mechanical damage in the form of scratches was also confirmed, but also the possibility of increasing (security) adhesive properties, defined in this case by wettability.

Effect of nanostructured zinc coating on high joining strength of polymer/galvanized high-strength steel composite via injection molding

This study proposed a hybrid joining technique for polymer and galvanized high-strength steel (GHSS) based on injection molding. Hot water treatment (HWT) was proposed to produce a nanoscale needle-like structure on the zinc coating surface to enhance the joining strength. We successfully obtained strong joints of GHSS and polybutylene terephthalate (PBT) via HWT with minimal damage to the zinc coating. The effects of HWT conditions on the tensile shear strength were evaluated and the optimized strength reached 23 MPa. The quantitative relationship between the nanostructured surface texture and the joining strength was analyzed. The number of structure peaks (Np) showed a strong positive correlation with the joining strength. The joining mechanism was investigated through TEM observation of the cross section and XPS analysis of the treated metal surface. Mechanical interlocking was the essential reason for the high joining strength. The results proved the feasibility of the proposed strategy and its potential for practical application.

Study of the Effect on Friction Welded Surface on Copper Aluminium Juncture

The economical and highly productive method of welding is used to join a dissimilar material. The quality of welded joint with high efficiency is obtained from friction welding process. The intention of the current work is to assess the progress of solid state juncture of dissimilar materials of aluminum 6082 and copper. The strong joints were developed using frictional heat and external pressure. The friction welded joints were tested under welding strength and surface analysis using scanning force microscopy (SFM). Rotational speed, friction pressure and forging pressure were used to evaluate the performance of the welded joints. Optimize the welding strength and hardness was attained through taguchi method.

Test and Bearing Capacity Calculation of a New Energy-Dissipated Precast Shear Wall

At present, most precast shear walls are implemented in accordance with the method equivalent to a cast-in-place structure, where the joint is complicated, and the construction is difficult. According to the characteristics of precast shear wall structures, the design method of “strong horizontal joints, weak vertical joints” for a precast shear wall structure is proposed. The existing horizontal joint method was used to form strong horizontal joints, and the damper was used to connect the vertical joints to form weak vertical joints. It can reduce the pouring of concrete and improve construction efficiency. Three types of specimens (Rectangle shape, T shape, L shape) were designed. Low cycle reciprocating load tests were carried out under different axial compression ratios (0.1, 0.3), and the bearing capacity and ductility of the specimens were studied. The results show that the precast shear wall structure has good mechanical properties. The ductility coefficient is close to or greater than three, and the maximum ductility coefficient is 3.62. The specimens have good ductility. The relative displacement of the damper is greater than 1.75 mm. All the dampers yield and dissipate energy, which improves the seismic performance of the structure and plays a good role in connecting the wall limbs. The strain distribution law of the specimen section is discussed, the simplified mechanical calculation model is given, and the calculation method of flexural capacity of a precast shear wall structure is put forward.

On the fully additive manufacturing of PC/AlSi10Mg hybrid structures

The fabrication of strong and lightweight polycarbonate and AlSi10Mg aluminum alloy hybrid joints entirely through additive manufacturing was successfully demonstrated. AlSi10Mg substrate with submillimeter-sized mushroom-shaped structures on the surface were printed by laser powder bed fusion (LPBF), being subsequently hybridized with PC via fused filament fabrication (FFF) using the AddJoining approach. The structures drawn on the metal surface were properly filled with the polymer during printing, ensuring good interfacial adhesion and thus providing PC/AlSi10Mg hybrid joints with excellent lap-shear strength of 10.8 ± 0.6 MPa.

The Joining of Copper to Stainless Steel by Solid-State Welding Processes: A Review.

Joining immiscible materials such as copper and stainless steel together is a significant concern due to distinct mechanical and metallurgical properties across the joint line, such as melting points, the coefficient of linear thermal expansion, and thermal conductivity. The joint properties of copper to stainless steel welds are in great demand for various mechanical components of the international thermonuclear experimental reactor, ultra-high vacuum system, plan wave linear-accelerator or linac structure, and heat exchanger. These dissimilar-metals joints offer excellent flexibility in design and production, leading to a robust structure for many cutting-edge applications. Hence, the present article reviews the copper to stainless steel joining mechanism under different solid-state processing conditions. The present understanding says that defect-free strong joints between the dissimilar metals are systematically possible. Apart from this understanding, the authors have identified and highlighted the gaps in the research exploration to date. Moreover, a sustainable methodology to achieve a desirable weld of copper to stainless steel depends on favorable processing conditions.

Dynamic performance and cross-level damage criteria of strengthened reinforced concrete frames with VE energy dissipation braces

Based on the low cost and superior damping performance of viscoelastic dampers, the new structural system strengthened with viscoelastic energy dissipation braces (VEDB) is proposed to upgrade the reinforced concrete frame structures with insufficient seismic capability. For the dynamic performance researches and damage evolution predictions of this structure system during earthquakes, the dynamic performance of six RCFs (reinforced concrete frames) and six VEFs (another six special reinforced concrete frames with VEDB) are studied under sinusoidal wide frequency range loading excitation horizontally. On this basis, the qualitative and quantitative relations on the damage growing at the material-level and the member-level performance deteriorating about the frame structures are conducted. Furthermore, the empirical calculation model on the cross-level damage evolution of VEFs are established and verified. Finally, a set of useful and robust cross-level judgment criteria for damage performance rates is proposed. The research found that, the installation of VEDB can significantly improve the load bearing capacity, the lateral stiffness and the energy dissipation capacity of the structures. The damage pattern of the structures is improved by VEDB, and it ensures the design criteria of “strong joints and weak members.” The empirical calculation model on the cross-level damage evolution and judgment criteria for damage performance rates proposed in this paper are useful and stable in practical engineering.

Investigation of Friction Stir-Welded B4C Particles-Reinforced Copper Joint: Mechanical, Fatigue, and Metallurgical Properties

Solid-state friction stir welding (FSW) is a sophisticated technique that can join materials that are similar and different without significantly affecting the properties of the base materials. The purpose of this study is to enhance the tensile strength, micro-hardness, and fatigue strength of the copper (C1100) butt-joints reinforced with B4C nanoparticles. The effects of B4C nanoparticle inclusion on the mechanical properties of the fabricated joints are studied in correlation with the microstructural features of the welded joints using optical microscopy. The joints are fabricated on a specialized friction stir welding machine (VMC-TC-1200) with a square pin-profiled tool. Defect-free joints of 3 mm copper plates are produced at the constant tool rotational speed of 1100 rpm, welding speed of 30 mm/min, plunge depth of 0.25 mm, and constant axial stress of 5 kN. B4C particles of 1, 2, 3, and 4wt% are added to the joints and their properties are compared with the joints produced without the inclusion of B4C particles to study the effects of the addition of nanoparticles. The joints attained a maximum micro-hardness of 123 HV, fatigue strength of 159 MPa, and tensile strength of 203 MPa with the addition of 3% B4C. Microstructural investigations performed through an optical microscope and scanning electron microscope (SEM) indicated the presence of homogeneously distributed B4C particles engulfed by finely refined grains. The thermal conductivity of the B4C particles facilitated the smooth flow of copper around the particles by forming a thin lubricating layer, thus improving the properties of the joints. Furthermore, this study has established that the addition of B4C particles is an effective and eco-friendly method of producing strong joints which could be used for industrial and defense applications.

A specific analytical study of friction stir welded Ti-6Al-4V grade 5 alloy: Stir zone microstructure and mechanical properties

The light metal titanium alloys find extensive usage is in industries where weight is a significant factor. Research in friction stir welding (FSW) aimed at producing strong joints without adding extra weight since machines like aircraft and automobiles must have as little weight as possible to improve their fly-to-buy ratio. This study reports 10 mm thick titanium alloy plates that are FSWed by varying rotational speed and tool traverse speed using the W-La2O3 tool. Due to the heat produced during the welding process, each material region experiences a different thermal cycle, which significantly affects microstructural changes. The peak temperature during FSW exceeded the β-transition temperature, causing phase transformations in the stir zone (SZ). A lamellar structure was observed in the SZ, and a transition line region (TLR), Bimodal, or duplex microstructure obtained consists of (α + β) phase. The SZ grain size decreases along the thickness direction, tensile strength increases, and reaches 89–102% of the base material. A lower hardness value is found in the SZ than in the base material (BM). The tensile fracture surface is observed to have a honeycomb-like structure or dimples, representing ductile fracture.

Determining the effective slab width of composite joint with the weak-axis connection for ultimate bearing capacity

Extensive brittle failures on the weld zone of beam bottom flange in composite joints of SMRFs were observed during the Northridge earthquake. One of the main reasons is the sizeable tensile strain demand generated at the beam bottom flange zone under sagging bending. The key to accurately understanding the mechanical properties of composite joints is the effective width of the slab. However, the previous research is all aimed at the I-section composited joints with column strong-axis connection or CFST column connection. Therefore, the research conclusions may not suit the composited joint with the weak-axis connection. Beam column weak axis connection is as universal as the strong axis connection. Therefore, this paper used ABAQUS software to investigate the effective width of the slab in composited joints with the weak-axis connection. Firstly, it defines the ultimate state of bearing capacity corresponding to the analysis in this paper. Secondly, it investigates the influence factor on the effective width of the slab under the ultimate sagging moment and hogging moment. Thirdly, it uses Gray Correlation Theory and MATLAB to fit the calculation formula of the effective width of the slab under the ultimate sagging moment and hogging moment. Fourthly, it compares the slab's effective flange width in the previous experiment and the formula presented in the paper. Finally, analyze the applicability of the fitting formula to the strong axis rigid composite joints and T-shaped rigid composite joints of the I-shaped column and H-beams.