Mechanical Performance Of Joints Research Articles

Experiment investigation and theoretical analysis of an improved aluminum alloy gusset joint

This study presents enhancements made to traditional aluminum alloy gusset (AAG) joints, including the integration of a central stiffening (CS) system, an inter-panel stiffening (IS) system, and a peripheral stiffening (PS) system. Three sets of tests on a full-scale specimen are conducted to investigate the improved AAG joint's axial stiffness, in-plane and out-of-plane bending stiffness, as well as ultimate load-bearing capacity. Nonlinear refined finite element models (FEMs) are established and validated through experimental results. Theoretical mechanical models are developed by integrating experiments and FEMs. These models elucidate the contribution of the stiffening systems to the joint's mechanical performance. The CS system is proven to significantly assist in load transfer, particularly in out-of-plane bending conditions. The IS system enhances overall inter-panel integrity, especially during the plastic deformation phase under out-of-plane bending moments. The PS system improves joint stiffness by participating in load transmission under both axial load and in-plane bending moments. Compared to traditional AAG joints, the combined effects of the three stiffening systems enhance overall structural integrity, stiffness, and load-bearing capacity. This enables the full utilization of component material properties and provides excellent ductility before failure occurs.

Assessing the role of friction stir welding tool shoulder profile and parameters on mechanical performance of Al5083 weld joints pre- and post-corrosion exposure

Al5083 alloy sheets were joined by friction stir welding (FSW) by using three different tools having different shoulder profiles (flat, concave and convex) at three different tool rotational speeds. From the cross-sectional microstructures, weld joints obtained at 1120 rpm with three different shoulder profiles were observed as defect free. XRD analysis confirms the development of texture that was dominated with close packed planes. The weld joint mechanical performance was assessed by conducting tensile tests before and after exposing them to 3.5% NaCl solution for 24 h. Combination of concave shoulder profile with 1120 rpm tool rotational speed has given higher strength in the weld joint, compared with base alloy and the other weld joints. The weld joints produced by using flat and concave shoulder profiles exhibited higher mechanical strength even after corrosion attack compared with the base alloy. From the potentiodynamic polarization studies, the three defect free weld joints (processed at 1120 rpm) were measured with lower corrosion current density. The results demonstrate the promising role of FSW to retain the strength against the corrosion initiated mechanical failure of Al5083 alloy by selecting appropriate combination of the shoulder profile and welding parameters.

Influence of tool positions variation on axial force, torque sensitivity, mechanical and microstructure properties of Al/Cu dissimilar FSW

ABSTRACT Study on tool offset must be necessary to minimise IMCs formation and mechanical properties enhancement. Tool offset has a significant variations in the instantaneous force and torque are measures for the welding process. Increasing in the offset means more % of Al. This means softer IMCs formation and so increasing in offset distance decrease on load in the spindle/Z-axis and X-axis torque. A precise critical offset towards Al plate could result in a defect-free joint and superior mechanical performance. 1.5 mm offset gives smooth variations in the peaks, indicating a uniform distribution of the intermetallic compound, smooth weld surface and defect-free weld leads to better mechanical properties. In comparison to the Al base metal, the weld sample had more tensile and yield strength of 95% and 100%, respectively in case of optimised offset of 1.5 mm. 1.5 mm offset give maximum compressive strength (97.5% of the Al BM), maximum tensile properties and micro-hardness (176.2HV) due to fine grain with Al 44 μm and Cu 42 μm. As the grain size decreases so it helps to increase tensile properties and the strength of the joint depends on the offset distance and formation of the suitable amount of the intermetallics.

Intermetallic compound growth behavior and mechanical performance in Sn58Bi/Cu solder joint bearing Mg particles incorporation during thermal aging

The microstructure and intermetallic compound (IMC) growth in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints were examined in this study under varied thermal aging time (6, 12, 18, 24, and 30 h) at 120 °C. The Shear test was conducted to assess the solder joint mechanical performance. The results indicated that the precipitation of the Bi phase in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints was not significantly inhibited by adding Mg as aging time increased. The IMC layer thickness of both solder joints increased as the aging time increased, but the Cu3Sn IMC thickness in Sn58Bi-0.4 Mg/Cu solder joint was consistently thinner than that in Sn58Bi/Cu joint. The temporal evolution of the Cu3Sn IMC layer was investigated, and it was found that the inclusion of Mg particles reduced the diffusion coefficient of Cu3Sn IMC. Furthermore, the shear test revealed that throughout the initial phases of thermal aging, fractures occurred within the solder matrix for both joints. As thermal aging time increased, fractures extended into the IMC layer, accompanied by transgranular and intergranular fractures. Simultaneously, adding Mg particles delayed brittle fracture in the solder joints, enhancing their mechanical properties.

Study on the mechanical properties and acoustic emission signal characteristics of freezing pipe

The increase in freezing depth requires thicker, stronger, and colder freezing walls, and various complex factors in deep strata greatly increase the risk of freezing pipe fracture. To address the phenomenon of freezing pipe fracture, this paper designs freezing pipe and joint mechanical performance experiments based on acoustic emission (AE) technology, mainly testing the deformation of freezing steel pipes and composite joints at normal and low temperatures, changes in load bearing capacity, and corresponding AE characteristics of the process. Additionally, the associated AE characteristics throughout the process will be analyzed. The ultimate goal is to establish a discriminative pattern for identifying the critical fracture of freezing pipes based on the analysis of AE signal characteristics in conjunction with mechanical properties. The sensitivity of the AE system under low-temperature conditions and the reliability of the test were tested through pencil lead break experiments, and saltwater noise detection experiments were conducted to prevent noise interference from low-temperature saltwater flow and pipe wall friction in the identification of crucial signals for freezing pipe fracture. This study provides a basis for identifying the deformation mechanics and fracture warning of freezing pipes through dynamic analysis of AE monitoring information.

Analysis of mechanical performance of modular steel-concrete composite joints considering floor slab composite effects

This study establishes and verifies the finite element models (FEM) of MSCCJs to analyze the mechanical performance of modular steel–concrete composite joints (MSCCJs) under monotonic static load without considering the floor slab composite effect (FSCE). Subsequently, 12 MSCCJ models incorporating the FSCE are constructed using ABAQUS. The study evaluates the effects of varying column axial compression ratios (n = 0.15, 0.25, 0.4, 0.6), floor width (w = 800, 1200 mm), floor thickness (t = 90, 110, 120 mm), and floor reinforcement ratio (r = 6 %, 8 %, 12 %) on the bending moment, initial stiffness (k0), ductility, and stress transfer of the joints. The results indicated that as n increases, the shear stress concentration in the joint core module (JCM) and the steel framework at the lower column end become more pronounced. Concurrently, the bearing moment and k0 of the joint also increase. However, once n surpasses 0.4, the joint's plastic properties diminish upon damage. With an increment in w, the k0 and ductility deformation of the joint remain stable and then decline. At w = 1000 mm, the joint's bearing capacity, stress distribution, and deformation performance reach their optimum. Since it significantly impacts stress distribution, its effect on the joint's mechanical performance is minimal. Lastly, the value of r enhances the ductility of MSCCJs and the stress concentration in the reinforcement. It is advisable to maintain r between 1.1 % and 1.7 %.

Microstructure and texture evolution of friction stir lap welded dissimilar multi‑aluminum stack

This work investigates the microstructural evolution of a dissimilar multiple‑aluminum alloy stack (AA7055, AA7055, AA6022) produced by friction stir lap welding (FSLW). A through-thickness analyses of grain orientation map, grain size and distribution, strain distribution, and texture evolution by electron backscattered diffraction-based characterization technique were performed. Two different welding parameters (combination of tool rotation and traverse speed) were used to study the effects of the welding parameters on these microstructural characteristics. The study shows that higher welding speed and higher rotation speed of the FSLW tool yield finer grains. FSLW resulted in shear texture formation in the weld regions due to high welding speeds. This texture development in the nugget zone is consistent with shear deformation, and (111) pole figures show ideal shear texture components. The Stir Zone (SZ) exhibits shear texture (A/A ̅ and B/B ̅ components), consistent with other shear-assisted processes. Recrystallization mechanisms observed are CDRX in SZ and DDRX in TMAZ (Thermo-Mechanically Affected Zone). Interface analysis reveals the presence of oxide layers between different aluminum sheets, affecting joint mechanical performance. The mechanical property of the lap welded joints was presented in terms of microhardness distribution across the weld cross section. Slightly higher hardness in higher speed welding setup was observed throughout the SZ and AA6022 layer, indicating greater grain refinement and uniform grain structure distribution.

Study of the effect of the combination of protective gases on the structure of the weld bead for the GMAW process using pulsed arc and short circuit

A weld bead's geometry directly influences the welded joint's physical characteristics and mechanical performance. The composition of the shielding gas directly affects the form of metal transfer during the welding process and, therefore, modifies the geometry of the weld seam obtained. In addition, metal transfer methods also influence the configuration of the weld bead profile. The objective is to analyze the geometry of the weld bead with different combinations of shielding gases and metal transfer modes in the continuous wire electric arc welding process with gas shielding (GMAW). To achieve this objective, a methodology is proposed to analyze the weld bead's penetration and other geometric parameters. This is achieved by varying the percentages of the gas mixture between Ar and CO2 and by employing different types of metal transfer, such as short circuit, pulsed, and PMC multi-control pulsed. Generally, when using only CO2 as shielding gas, a wide, round weld bead is obtained. If Ar alone is used, the weld bead profile has a very thin shape and deep penetration. With the mixture of Ar and CO2, a bead is obtained with good penetration and sufficient width to cover the two test tubes without empty spaces between the base and filler materials. The macrographic analysis of the chords with their respective measurements is presented, and the geometric parameters of the obtained chords are tabulated. The penetration of the bead is directly proportional to the percentage of CO2 present in the mixture. In a comparison between the three transfer modes used with the same gas composition, it is found that the pulsed spray mode produces greater penetration.

Formation mechanism and mechanical strength evaluation of hybrid riveted/solid-state bonded aluminium alloy joint

In this research, an improved friction self-piercing riveting (F-SPR) process with internally threaded rivet and flat die was proposed to achieve hybrid riveted/solid-state bonded connection for low-ductility aluminium alloys. Instead of relying on rivet shank flaring to form mechanical interlock in the existing F-SPR process, a reliable threaded connection was established between the rivet shank and sheets by rapid filling of sheet material into the rivet thread grooves. A perfectly flat joint bottom was formed without inducing large-scale sheet distortion. A series of experimental tests were performed to clarify the joint quality characteristics, formation mechanism and mechanical performance. The results revealed that the quality of newly formed five aluminium threads demonstrated a decline trend from bottom to top. Two kinds of thread formation mechanisms were identified: The mechanism I is solely composed of Filling step and applied to upper four threads; The mechanism II consists of Filling-Fracturing-Welding steps and is applied to the lowest thread. Discontinuous solid-state bonding was formed at the sheet interface around the rivet shank periphery, whilst a bowknot-liked solid-state bonding zone with a weak welded zone and an unwelded zone was formed at the joint centre. Rivet pull-out failure from the bottom sheet was observed for the studied AA7075-T6 joints under both lap-shear and cross-tension loads. The peak loads reached 9.79±0.23 kN and 5.41±0.15 kN in the lap-shear and cross-tension tests, and the corresponding energy absorption was 13.82±0.59 J and 16.42±0.87 J.

Study on the joint formation mechanism and performance of resistance rivet welding of Mg/steel dissimilar materials

In this paper, a new resistance rivet welding process (RRW) is used to achieve the joining of Mg alloy and steel. A rivet is utilized to pierce the upper Mg plate during the welding process and then welded to the lower steel plate. It realizes a metallurgical bond between the rivet and the steel plate, and a hybrid rivet-welded joining between the steel plate and the Mg plate. The joint morphology, forming mechanism, microstructure, and mechanical performance of RRW joints were investigated. And the role of welding current variations on the failure mode and mechanical properties of the joint was studied. The results showed that at welding currents between 11 kA and 13 kA, the main bearing area of the joint was primarily the Mg plate base material. As the welding current increased, the bonding location between the Mg refilled into the rivet cavity and the Mg plate could also be subject to more load, significantly affecting the mechanical properties and failure mode of the joint. The RRW joints achieved a tensile-shear load of 6.08 kN and an energy absorption value of 8.95 J at the optimum parameters.

Improvement of microstructure and mechanical properties of Sapphire/Kovar alloy joints brazed with Ag-Cu-Ti composite filler by adding B powders

The brazed joint of sapphire transparent ceramic and Kovar alloy was prepared using AgCuTi and AgCuTiB composite filler, and the main focus was the effect of B element on the wetting behavior, interface composition and joint mechanical performance. The reliable joint of sapphire transparent ceramic and Kovar alloy was obtained by vacuum brazing with AgCu28-6Ti-0.45B (wt%) composite filler. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as sapphire/Ti3Cu3O/Ag(s,s) + Cu(s,s) + disperse TiB/TiFe2 + TiNi3/Kovar. The results showed that the addition of B could contributed to an optimized interfacial structure via (i) in-situ forming fine TiB whisker reinforcement phase and refining the interface structure and (ii) reducing the diffusion degree of alloy side elements to inhibit the generation of brittle phase, and the maximum shear strength of the joint with AgCu28-6Ti-0.45B (wt%) reached 125 MPa more than twice the joint without B additive. On the other hand, the wetting experiment showed that the addition of B as a solid particle decreased the fluidity of the composite filler, and when the addition of B was excessive, no dense TiB whiskers were produced in the interface. This study provides ideas for the optimization and improvement of sapphire composite connection, and points out that the generation of reinforcing phase is accompanied by the reduction of fluidity, so it is necessary to reasonably control the proportion of reinforcing phase.

Critical effect of heat input on joint quality in resistance element welding of Al and steel

Resistance element welding (REW) has recently attracted increasing interest, especially in the joining of high-strength steels and aluminum alloys. However, the intensity of heat input is a critical factor for the joint quality due to the possibility of excessive melting of the aluminum sheet around the element shank, which often degrades the joint's performance. This study evaluates the influence of heat input on the joint formation and mechanical performance of REW joints between ultra-high strength steel and aluminum alloy. In addition to the experimental investigations, a finite element method (FEM) was used to analyze the temperature distribution, nugget formation, and aluminum sheet melting characteristics as a function of heat input. The results show that the nugget dominates the joint's strength if the heat input is comparatively low. When heat is increased, however, the aluminum sheet plays a significant role in the joint's strength. Excessive melting of aluminum sheets reduces the load-bearing area of the joint. The competition between the weld nugget and aluminum sheet determines the joint's strength. The failure mode changes from interfacial to aluminum sheet failure as the heat input increases. The combined effect of aluminum sheet thickness and heat input on the joint strength was also evaluated. The results indicate that determining the appropriate heat input level is crucial to achieving an excellent performance of the REW joints.

On the feasibility of joining additively-manufactured 316L stainless steel and poly-ether-ether-ketone by ultrasonic energy

• The joining of additively manufactured metal-polymer parts via U-Joining was proven. • Through-the-thickness reinforcements improved the joint mechanical performance. • Ultimate lap-shear forces up to 3.2 ± 0.2 kN were achieved by the produced joints. • Polymer penetrated metal surface cavities, improving micromechanical interlocking. • Fractography analyses showed a mixture of cohesive and adhesive failure. Ultrasonic Joining (U-Joining) process is a friction-based joining technique capable of producing through-the-thickness reinforced (TTR) hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. Previously, the process feasibility has been demonstrated to join injection-molded Ti-6Al-4V and extruded unreinforced and laminated glass-fiber-reinforced polyetherimide structures, resulting in joints with improved out-of-plane strength and fatigue performance. However, there is an unexplored field concerning the joinability of additively manufactured (AM) metal and polymer parts via U-Joining. AM allows the production of structures with complex designs, but joining AM parts can represent a challenge as defects might appear along the process, such as delamination. In this work, the feasibility of joining laser powder bed fusion (LPBF) 316L stainless steel and fused filament fabricated (FFF) poly-ether-ether-ketone (PEEK) via U-Joining is demonstrated. Optical and scanning electron microscopy showed that TTRs were fully inserted into the polymer and that molten PEEK could flow around and penetrate metal surface cavities, thereby improving the macro- and micromechanical interlocking between the parts. Finally, quasi-static lap shear tests were performed, showing an improvement in the ultimate lap shear force up to 2.8 times (from 1.1 ± 0.2 kN to 3.2 ± 0.2 kN) and the displacement at break up to 2.1 times (from 0.7 ± 0.1 mm to 1.45 ± 0.2 mm) when compared to unreinforced (flat pinless) reference joints produced with the same energy input.

Regulation of performance of laser-welded socket joint of Mo–14Re ultra-high-temperature heat pipe by introducing Ti into both weld and heat affected zone

Fusion welding of molybdenum (Mo) alloys faces problems including grain coarsening and embrittlement, so that the obtained joints have poor mechanical performance. The research took the socket joints of a novel Mo–14Re ultra-high-temperature (UHT) heat pipe as research objects. Pre-heating, titanium (Ti) microalloying and brazing were adopted for coordinated regulation of defects, microstructures, and mechanical performance of joints. Results show that Ti added can be uniformly mixed with metals in the molten pool and solidly dissolved in the matrix to achieve solid-solution strengthening. Ti entering the weld zone distributes on grain boundaries and in grains, thus decreasing the relative content of Mo oxides on the surface of grain boundaries in the meanwhile of grain refinement, playing a role in purifying grain boundaries. Ti alloying in the weld zone to some extent can inhibit occurrence of pore defects and improve the bearing capacity of joints. Moreover, the brazing layer formed in the heat affected zone (HAZ) not only enlarges the bonding and bearing area of joints, but also shifts the position of the stress concentration point of joints from the near weld zone with poor performance to the area with favorable performance much farther from the weld. Under the joint action of Ti microalloying and brazing, the tensile strength of joints is improved from 140.8 to 399.8 MPa. The fracture mode changes from intergranular fracture to transgranular cleavage-like fracture. The research results can promote the development of technologies for manufacturing novel UHT heat pipes and welding Mo–Re alloys.

Effects of bolted connections’ properties on natural dynamic characteristics of corner-supported modular steel buildings

Corner-supported modular steel building, made of volumetric units, is an efficient construction system for the next generation of industrialised building construction. The mechanical performance of joints, including inter-modular connections and beam-to-column connections, or so-called intra-modular connections, and their effects on the dynamic behaviour of these structures have remained a research hotspot in the design of modular buildings. This paper studies the effect of bolted vertical inter-module and intra-modular connections’ characteristics on the dynamic properties of a corner-supported modular steel frame using an experimental program and numerical simulations. To that end, a half-scaled vertically stacked 3-storey modular building, instrumented with highly sensitive accelerometers, is used to scrutinise the effect of different configurations of inter- and intra-modular connections on the dynamic characteristics of the structure. The acceleration responses of the system under randomly generated artificial vibrations and pure ambient vibrations are synchronously recorded. Then, dynamic characteristics of the modular building are extracted by employing the Operational Modal Analysis (OMA). Finally, finite element models are developed, and a comprehensive parametric study is conducted to verify the experimental results and evaluate the influence of connections’ behaviour on the frequencies of the structure. The results indicate that while the behaviour of inter-connection has no significant effect on the natural frequency of the building, variation of intra-connections’ properties and their configurations can lead to a change in fundamental frequency of modular buildings. Shear stiffness of connections was found to be the most effective factor influencing the frequencies of modular structures.

Simulation-based parameter optimization of friction forge riveting for AA6061-T6 and TA2 with TA2 titanium rivet

Friction forge riveting (FFR) has been developed for connecting titanium alloy and aluminum alloy with titanium rivets, although the weak formation of rivet during this process is still a key issue that should be solved properly. In this study, a thermomechanical coupling model was established in DEFORM-3D based on the practical thermal cycle of rivet during FFR process. Furthermore, the temperature and stress fields were also revealed in detail. The results showed that by reducing the loading speed of friction tool in the first 1 mm stroke, the flash defects and root defects caused by insufficient filling of the driven rivet head can be effectively avoided, and the joint mechanical performance including strength and service life was also improved. With the optimized FFR parameters, perfect joints were obtained without surface flash, holes or tunnels.

Effect of long‐term stress aging on aluminum‐BFRP hybrid adhesive joint's mechanical performance: Static and dynamic loading scenarios

AbstractComposite‐aluminum hybrid adhesive joints represent an ideal solution for designing lightweight structures for the marine industry. However, seawater aging is a serious concern, limiting the safe service life of the joint. Notably, efforts to understand the impact of aging have largely focused on the short‐term periods without considering actual operating conditions. Here, we report the mechanical performance of hybrid joints subjected to the long‐term stress aging. Besides, we modified the epoxy adhesive with halloysite nanotubes (HNTs) to limit the aging driven adhesive degradation and improve the adhesive's rigidity. We evaluated mechanical performances of hybrid joints by performing tensile, flexural, and drop‐weight impact tests. While we increased the load‐carrying capacity by over 25% with the HNTs modification before the stress aging process, modified adhesive withstood almost 55% higher tensile load than the neat epoxy adhesive after six‐month stress aging. The modified adhesive also absorbed 41% less impact energy, indicating the efficiency of HNTs on limiting the degradation due to the stress aging. Furthermore, the damage mode transformed from adhesion to cohesion, thanks to the improved adhesive‐composite interface performance. We envisage that these exciting results will pave the way for designing robust hybrid joints for the marine industry.

Dissimilar laser welding of NiTi to Ti6Al4V via Zr interlayer

ABSTRACT The ability to integrate multiple distinct properties into a single structure is the driving force behind the development of NiTi to Ti6Al4V dissimilar joints. However, differences in thermophysical properties and the subsequent development of brittle Ti2Ni and Ni3Ti intermetallic compounds (IMCs) make fusion welding of these alloys rather challenging. The solidification of brittle IMC causes cracking upon solidification and a significant reduction on the joint mechanical properties. In this study, two strategies were used concurrently to reduce the formation of brittle IMC: zirconium (Zr) interlayer was introduced alongside with the laser beam being offset to the Ti6Al4V side. The influence on microstructural evolution was investigated using various characterization techniques. Scanning electron microscopy aided by energy dispersive spectroscopy and micro-X-ray diffraction supported by Rietveld refinement revealed that the volume fraction of the Ti2Ni brittle phase was drastically reduced from 90 to 9%, leading to improvements on the joint mechanical performance. A joint with a lower hardness of 392 HV was obtained, compared to 515 HV for the conventional NiTi/Ti6Al4V joint. The strength and ductility of the Zr-interlayered joint were improved to 320 MPa and 1.7%, respectively, compared to 148 MPa and 0.8% for the Zr-free joint.

The Effects of Postweld Processing on Friction Stir Welded, Additive Manufactured AlSi10Mg

Given the limited build volumes for most current additive manufacturing (AM) machines, a method for taking advantage of the unique capabilities offered by AM while combining it with traditional manufacturing methods is needed. Welding of AM-produced components is a solution to this challenge. The objective of this study was to determine the feasibility of using friction stir welding (FSW) to join AlSi10Mg melted with laser powder bed fusion (PBF-L) and examine the effects of postweld heat treatment (HT) and hot isostatic pressing (HIP) on overall joint quality and mechanical performance. Samples were examined using optical microscopy, scanning electron microscopy, hardness testing, and tensile testing. Examination of the samples that underwent a postweld annealing HT revealed cracking along the stir zone and the thermomechanically affected zone (TMAZ) boundary. Examination of the crack revealed evidence of liquation near single-phase silicon precipitates in the TMAZ despite the annealing temperature being 27°C (81°F) below the solidus temperature of the material according to the material specification. Using a calculated pseudobinary phase diagram of AlSi10Mg, the annealing HT was determined to be in the partial liquation regime for AlSi10Mg. The voids and crack formation mechanisms were determined to be caused by constitutional liquation coupled with the unique TMAZ microstructure and stress state. The as-welded and HIP coupons were void and defect free, and FSW was determined to be a feasible method of joining PBF-L aluminum alloys with minimal knockdown in tensile strength.

Publisher Correction to: A review of advances in resistance spot welding of automotive sheet steels: emerging methods to improve joint mechanical performance

Publisher Correction to: A review of advances in resistance spot welding of automotive sheet steels: emerging methods to improve joint mechanical performance