Joint Resistance Research Articles

Study on magnetic pulse crimping process for joining large-diameter aluminum alloy tube/magnesium alloy shaft

A structure for joining 6061T6 aluminum alloy tube and AZ31B magnesium alloy shaft via the magnetic pulse crimping process was proposed. The forming process, mechanical properties, failure modes, and corrosion behaviors of the joint were studied. The results showed that the enormous Lorentz force drove the wall of aluminum alloy tube to move towards the groove of magnesium alloy shaft at high velocity, thus realized mechanical locking and formed joint. Through torsion tests, it was found that the mechanical properties of the joint with different process parameters varied. There were two failure modes for joint: torsional separation and torsional crack. Specifically, discharge time, groove angle, and discharge energy for torsional crack were, respectively, 1, 90°, and 28 kJ and 3, 90°, and 25 kJ. The maximum torque was up to 961.99 N·m under discharged twice, 90° groove angle, and 25-kJ discharge energy. Through neutral salt spray corrosion tests, it was found that the maximum torque only decreased by 28.03% after corrosion for 192 h. It indicated that the corrosion resistance of joint was good relatively.

Effect of Post-Welding Aging Treatment on the Microstructure and High-Temperature Properties of Inertia Friction Welded GH4065A Joint.

In this study, post-welding aging treatments were applied to a novel Ni-based superalloy GH4065A inertia friction welding (IFW) joint to improve its high-temperature properties. The effect of aging treatment on the microstructure and creep resistance of the IFW joint was systematically investigated. The results indicated that the original γ' precipitates in the weld zone almost completely dissolved during the welding process, and fine tertiary γ' precipitated during the subsequent cooling process. Aging treatment did not significantly change the characteristics of grain structures and primary γ' in the IFW joint. After aging, the size of tertiary γ' in the weld zone and secondary γ' in the base material increased, but their morphology and volume fraction did not change evidently. After 760 °C, 5 h aging treatment, the tertiary γ' in the weld zone of the joint grew from 12.4 nm to 17.6 nm. Correspondingly, the creep rupture time of the joint at 650 °C and 950 MPa increased from 7.51 h to 147.28 h, which is about 19.61 times higher than that of the as-welded joint. The creep rupture was more likely to occur in the base material instead of the weld zone for the IFW joint. This revealed that the creep resistance of the weld zone was significantly improved after aging due to the growth of tertiary γ'. However, increasing the aging temperature or extending the aging time promoted the growth of secondary γ' in the base material, and meanwhile, M23C6 carbides tended to continuously precipitate at the grain boundaries of the base material. It might decrease the creep resistance of the base material.

Process parameters, structure and mechanical properties of dissimilar Nimonic 80 A/AISI 316 L resistance welded joints

Abstract The effects of welding current and welding time on the shear resistance of spot welded joints of dissimilar Ni-base superalloys and austenitic stainless steels are investigated for expanding the limits of their use in automotive, naval and aerospace industries. The macro- and micro-structural characteristics, microhardness, and shear strength of the welded joints were examined in order to characterize the resulting joints. It was found that the shear resistance of the heterogeneous welded joints reaches values of 742–849 MPa, much higher than the one specific of the weaker material, which is the austenitic stainless steel with low carbon content, AISI 316 L. The diameter of the welded cores increased for higher current and welding time. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) were used to evaluate the microstructure of the welded joints from the two dissimilar materials.

Improving the corrosion resistance of friction stir welding joint of 7050 Al alloy via optimizing the process route

The macro-galvanic effect in friction stir welding (FSW) joints is contributive for accelerating the localized corrosion of 7xxx aluminum alloy weldment. A process route, solid solution treating→FSW→T76 ageing (SSW-T76), was developed to weak the macro-galvanic effect. The microstructure and corrosion of joints prepared from SSW-T76 route and the conventional route (T76→FSW, T76W) were comparatively investigated. It was found that both precipitate coarsening and solute segregation were effectively suppressed when the route was changed from T76W to SSW-T76. The discrepancy in microstructure, micochemistry and corrosion potential between the base material (BM), the heat-affected zone (HAZ) and the nugget zone (NZ) was narrowed, leading to suppressed macro-galvanic effect and thereafter to decreased pitting and IGC.

Static performance and design of cold-formed high strength steel rectangular hollow section X-joints

Cold-formed high strength steel (CFHSS) X-joints made of square and rectangular hollow sections (SHS and RHS) brace and chord members were investigated in this study. The steel grades of tubular members were S900 and S960 with the nominal 0.2% proof stresses of 900 and 960 MPa, respectively. The authors carried out tests on cold-formed S900 and S960 steel grades RHS X-joints. The test results were used to develop accurate finite element (FE) models in this study. Using the validated FE models, a comprehensive FE parametric study was then performed. The validity ranges of critical geometric parameters were extended beyond the current limits mentioned in international codes and guides. The nominal resistances predicted from existing design rules given in European code and Comité International pour le Développement et ĺEtude de la Construction Tubulaire (CIDECT) were compared with a total of 726 test and FE joint resistances, including 684 numerical data generated in this study. Chord face failure, chord side wall failure and a combination of these two failure modes were reported. It is shown that design rules given in European code and CIDECT are not suitable for the range of cold-formed S900 and S960 steel grades RHS X-joints investigated in this study. Therefore, user-friendly, accurate and reliable design equations are proposed in this study. Moreover, reliability analysis was also performed for the existing and proposed design equations.

Modelling and Multi-Objective Optimisation of Finger Joints: Improving Flexural Performance and Minimising Wood Waste

The wood industry faces the dual requirements of improving the quality of timber products and minimising waste during the manufacturing process. The finger joint, which is an end-to-end joining method for timber boards, is one of the most important aspects of engineering wood products. This study presents a numerical and optimisation investigation of the effects of finger-joint design parameters on the flexural behaviour of finger-jointed timber beams. A numerical model based on advanced three-dimensional finite element analysis was developed to model the behaviour of finger-jointed beams. Using the validated finite element (FE) model and automated parameterisation, a parametric study was conducted to assess the impact of each design parameter of the finger joint, including finger length, tip thickness, and the number of finger joints. The results indicate that the number of fingers and finger length significantly influence the maximum load capacity, while the tip thickness has a marginal effect on performance. This study identifies a design threshold of five fingers and a 14 mm finger length for achieving efficient, high-performance finger-joint designs. In addition, the multi-objective modified firefly algorithm (MOMFA) was proposed to maximise the finger joint resistance while simultaneously minimising the material waste. The optimisation shows that there will be a significant amount of wood waste when using traditional single-objective optimisation that only focuses on structural performance. In contrast, the proposed method achieves comparable load capacity while significantly reducing waste (up to 53.31%) during the joining process. The automated finite element modelling framework and holistic optimisation developed in this study can be used to design and optimise engineering wood products for construction applications.

Influence of structural timber fibre orientation on the strength capacity of dowel-type joints

Threaded-dowel type timber joints with free ends and with nut-washer end fixings were experimentally investigated, modifying the orientation of the timber beams and the evolution in the deformation of their fibres as the structure was loaded, with the objective of quantifying their contribution to the strength in relation to displacement. The work is based on an analysis of the equations for the dimensioning of dowels, compiling the original models developed by Johansen in comparison with the superimposition extensions of Eurocode 5. This provides the basis for carrying out the experimental tests to compare the load capacity established in the dimensioning of structures with the experimental results. This work focuses on dowels-type joints that fail in plastic mode, which improves the distribution of stresses and optimizes the resistant capacity of the joint while analysing the crushing regions in the contact areas of the timber dowel which contain the dowel and redefine the angle of the hinge joint in successive flat planes perpendicular to the axis of the hole where the dowel is housed, which allows analysing the dominant stresses related to the repositioning of the timber fibres exposed to crushing. The tests with nut-washer fastening show a behaviour that notably improves the resistant capacity when the degree of displacement increases. This research shows how the capacity of the structural joints is linked to the effects of crushing, provoking a reorientation of the fibres. This work raises the need to study in detail the resistance of the structural joint, limiting the displacement, when comparing the analytical results against the displacement curves of the experimental tests. It can be seen that increases in the angle of orientation of the fibre of the beams are penalized by the analytical equations with load capacity losses greater than 10% for fibre angles located at 90°, however the tests show an improvement in the progressive resistance capacity with the displacement. The load capacity in the joint improves by 7% and 11% for fibre orientations at 45° and 90°, if no fixing is established at the ends of the joint. These values reach improvements of 13% and 28% when there is fixing at the ends of the dowel.

Comparison of RSW technologies on DP steels with modified instrumented Charpy impact test

In recent decades the toughness of welded structures becomes more and more important. This trend is particularly valid for the advanced high-strength steels (AHSS), which have reduced toughness comparing to the low-strength structural steels. Dynamic characteristics of the welded joints of the newly developed high-strength steel sheets required by the automotive industry have been neglected, with welding procedures being optimized on the static joint properties, mainly on the tensile-shear force. Up to the present time, testing of dynamic properties of the spot-welded joints has been performed by increased testing speed during tensile testing. The authors have developed a new dynamic testing method and designed new testing equipment for impact bending, which can give a numeric result to characterize the resistance of spot-welded joints against dynamic load. In this paper, this method will be used to evaluate resistance spot-welded joints made on DP600 and DP800 steels with three different technological parameters, comparing long-time welding, short-time welding, and two-pulse welding. The different parameters cause different weld nugget sizes, failure modes, impact energies, and force–time diagrams. All test results show that bigger weld nugget diameters cause better impact energies and impact forces, but the differences are not perfectly correlated.

Study on water resistance improvement of wood dowel rotation welding joints

Rotation welding of wood dowels has the advantages of high bonding strength, fast processing speed and green environmental protection, and is suitable for jointing nodes in furniture and wood products. However, most wood friction welding specimens have poor water resistance where the welded joints are more likely to be damaged in wet environments, which greatly limits their wider application. Previous studies focused on using natural and green materials or methods to enhance bonding strength and water resistance of friction-welded joints. This paper reveals an innovative chemical pretreatment method to improve the water resistance of rotary friction welded joints by treating the substrate blocks or dowels with reagents that successively oxidize and sulfonate the wood, and spraying the dowels with Zinc acetate alcohol solution that has a lubricant effect, followed by friction welding. The findings show that both the dry bonding strength of friction welded joints and the wet bonding strength after impregnation with cold, hot, and boiling water of dowels pretreated with oxidation and sulfonation reactions were higher than those without pretreatment and significantly superior to the traditional polyvinyl acetate (PVAc) adhesive bonding.

Tele-Snap: a joint impedance estimation system using snap motor and openPose for remote rehabilitation diagnosis

We propose a remote joint impedance estimation system called Tele-snap for a rehabilitation diagnosis under the COVID-19 pandemic. Dynamic resistance of the human joint is essential physical information reflecting the motor function. The resistance is assessed based on the touching sensation of the doctor (physiotherapist), but the pandemic restricts such an in-person manner. Our proposing system aims to provide this physical information quantified by the joint impedance for a diagnosis in the telerehabilitation context. The proposed system employs a compact impulsive perturbation generator called the snap motor and a marker-less motion capture technology called the OpenPose. The subsystem installed in the patient's place is then simplified remarkably, which consists of the wearable snap motor and Raspberry Pi with a built-in camera module. The proposed system can collect the dataset for impedance estimation through the examiner's teleoperation of the snap motor and camera via a virtual private network, with no need for the operation by the patient. We verify the proposed system through an in-person experiment and then demonstrate the remote impedance estimation scheme.

Dancing with Counterpreservation

The Tabacalera is a 30,000 sq m building located in Madrid city centre. Erected at the end of the eighteenth century, it originally functioned as a state-run tobacco factory until its closure in 2000. After ten years of abandonment, the Ministry of Culture leased part of the property to a series of local collectives to use as a “self-managed social centre”. Here, in an atmosphere characterised by repurposed decay and new informal accretions, all kinds of cultural and communal activities are held every day, including those of the Centro Revolucionario de Arqueología Social (CRAS, Revolutionary Centre for Social Archaeology). Between 2018 and 2020, I engaged with the social and organisational dynamics of the centre, exploring the motivations and aspirations of its various collectives and of other actors involved. Deploying Daniela Sandler’s notion of “counterpreservation” – the purposeful embracing of decay as a social and aesthetic act – this article suggests that, in just a decade, the centre has become an icon of free culture and libertarianism, acquiring a consistent heritage identity that is indissociable from its decaying materiality. This article also aims to examine how both social and aesthetic dimensions forge a joint resistance to potential institutional plans that may jeopardise the centre’s continuity.

New proposal for the bending moment capacity of tubular T-joints in carbon steel and stainless steel structures

The expected failure mode of T-joints between rectangular hollow sections subjected to bending moment with a ratio of the brace width (b1) over the chord width (b0) below 0.85 (i.e., β=b1/b0≤0.85) is the chord face failure, produced by yielding. This paper presents the development of a numerical model to reproduce this phenomenon, calibrated against experimental laboratory tests, which is then used to carry out a large parametric study, where the influence of the main geometric parameters involved in the joint resistance –the chord width (b0), the chord thickness (t0), the chord radius (R0), the brace width (b1), the brace height (h1) and the weld thickness (a)– is assessed for two different materials: S275 carbon steel and EN 1.4301 austenitic stainless steel. The results derived from the parametric study suggested that a different yield line mechanism may develop for higher β-values (β≥0.45) than that considered in current European and American codes. Hence, a new formulation for estimating the bending resistance of T-joints exhibiting chord face failure modes is presented based on a different yield line mechanism developed in this paper. This formulation includes additional geometric parameters that are dismissed in the current formulation, such as the chord radius and the weld thickness, which are found to have a non-negligible influence on the joint resistance. Moreover, the proposed formulation is adjusted in order to be used for joints with lower β-values without losing accuracy. Additionally, the new proposed formulation is adapted for stainless steel joints by combining it with the Continuous Strength Method (CSM) formulation with promising results. Finally, the soundness and safety of the proposed formulation is statistically demonstrated.

Experimental investigation of the effect of induction preheating on the microstructure evolution and corrosion behaviour of dissimilar FSW (IN718 and SS316L) joints

The present work investigates the microstructure and electrochemical behaviour of the joints formed with and without induction-assisted friction stir welds (FSW) between SS316L and Inconel 718. For this purpose, conventional and induction preheating assisted friction stir welding (I-FSW) was carried out at a rotational speed of 300 rpm and traverse speed of 140 mm/min with 300 °C preheating. The microstructure and phases of the nugget zone were analyzed. The corrosion behaviour of the welded joint and the base metal was investigated in 1 M HCl solution and 3.5 wt% NaCl solution using immersion test and electrochemical techniques. The results show that the induction preheated friction stir welding process produces defect-free joints than the conventional FSW with little increased grain size. Intermetallic compounds (IMCs) at the interface of the nugget zone were not detected due to insufficient heat input. The corrosion result revealed that the corrosion resistance of the I-FSW weld joint was better than the FSW weld joint, and it was lowest in the case of base SS316L, which was confirmed with the immersion test, potentiodynamic polarization test (PDP), and electrochemical impedance spectroscopy (EIS). The presence of blocky carbide particle M23C6 was responsible for the pitting corrosion in the steel region.

Effect of the Weld Deposit Thickness on the Impact Strength of Heat-Affected Zone of the Welded Joint

The methodology has been developed to show the functional connection of the impact strength of the heat-affected zone metal of welded joints with weld deposit thickness and, accordingly, with the consumption of welding materials during electric arc welding while constructing and repairing various metal structures and pipeline systems operating in conditions of low climatic temperatures. To reach the objective of the paper, rational intervals of cooling rates of the HAZ metal during welding low-alloy pipe steels were used, and the calculated dependences from the existing works were modified. The methodology allows increasing cold resistance of welded joints of steels of mass use by regulating the weld deposit thickness and welding consumables during electric arc welding while constructing and repairing various metal structures and pipeline systems operating in extreme conditions of the North.

A Comparative Study of the Influence of Volumetric Joint Counts (Jv) and Resistivity on Rock Quality Designation (RQD) Using Multiple Linear Regression

A Comparative Study of the Influence of Volumetric Joint Counts (Jv) and Resistivity on Rock Quality Designation (RQD) Using Multiple Linear Regression

Experimental study on seismic behavior of a new precast shear wall system with angle steel connectors

The mechanical behavior of the connections between the wall panels and the foundation determines the seismic performance of precast concrete shear walls. The post-tensioned connection, sleeve connection, lap-spliced connection, welded connection, and bolted connection are the most common today. However, they frequently have some shortcomings, such as the need for skill-trained workers, concealed work, engineering precision, high cost, and remarkable damage to horizontal joints. In order to overcome the shortcomings, a new precast reinforced concrete shear wall system with angle steel connectors was proposed and designed. Angle steel connectors were used to improve the shear resistance of the horizontal joints between the precast RC shear wall and the foundation, as well as to provide temporary support for specimen positioning and installation. Meanwhile, the angle steel connector can provide tensile resistance under extreme conditions such as a typhoon or strong earthquake. In order to investigate the seismic behavior of the new precast shear wall system, a full-scale precast RC shear wall specimen with angle steel connectors was built. Meanwhile, three full-scale precast RC shear walls with integral cast-in-place connections, grouting sleeve connections, and lap-spliced connections were designed and built to compare and investigate their seismic performance and mechanism. The results showed that the new precast shear wall system with angle steel connectors had improved seismic performance and deformation capacity. At the same time, the upward movement of the main crack was conducive to improving the bearing capacity of the shear wall. When compared to the grouting sleeve connection, it significantly reduced the amount of concealed work and made the construction quality easy to ensure. The seismic performance of the specimen with lapped steel bars and angle steel connectors was better than that of the specimen with grouting sleeve connection and cast-in-place specimen. The new precast shear wall system with angle steel connectors proposed in this study is well suited for use as a seismic resistance of building structures.

Low-velocity impact response of self-piercing riveted carbon fiber reinforced polymer-AA6061T651 hybrid joints

Self-piercing riveting (SPR) is an effective method to join dissimilar materials, such as composite and aluminum alloy. In this paper, the dynamic loading response and the impact damage mechanism of carbon fiber reinforced polymer (CFRP) laminates and AA6061-T651 self-piercing riveting joints were investigated using the drop weight tests at energy levels between 7.5 J and 20 J at room temperature. The effect of diverse damage mechanisms on the impact resistance and quasi-static mechanical properties of the SPR joints were evaluated. The results showed that the low-velocity impact position has a great influence on the strength of SPR joints, and the strength of the joints is seriously decreased when impacted at the center of the rivet. There are two impact damage mechanisms. One was the internal damage of CFRP laminates and it was the dominant damage mechanism before the impact energy of 10 J. Another one is the plastic deformation of aluminum alloy when the impact energy was above 10 J. The composite damage played a leading role in the absorption of the impact energy. Moreover, the impacted joints present residual strengths of 83 % (5 J), 76 % (7.5 J), 71 % (10 J), 57 % (12.5 J), 51 % (15 J), 48 % (17.5 J), 38 % (20 J) of the non-impact SPR joints. The axial impact resistance was more sensitive to the plastic deformation of aluminum alloy, while the quasi-static mechanical properties were more sensitive to the internal damage of CFRP.

Study on Microstructure and Mechanical Properties at Constant Electromigration Temperature of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu Solder Joints

To solve the electromigration problem of micro-electronic connection solder joints, an ideal electromigration tester was designed, and the thickness of the intermetallic compounds (IMCs), average void diameter, grain orientation, failure, shear strength, and fracture path of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu solder joints under constant-temperature electromigration were studied. The results indicate that the solder joints show evidence of typical electromigration polarity in the asymmetric growth of interfacial IMCs on the anode and cathode sides under the conditions of a current density ≥7 × 103 A/cm2 and an included angle between the c-axis of the β-Sn grains and the current direction θ ≤ 53.2°. The anode-side interfacial IMC is dominated by a Cu6Sn5 phase with a gradually increasing thickness, forming a Cu3Sn phase and showing evidence of microcracks. The Cu6Sn5 phase of the cathode-side interfacial IMC is gradually completely dissolved, and the growth of the Cu3Sn phase is accompanied by the formation of Kirkendall voids. The anisotropic diffusion of Cu atoms in the β-Sn of the micro-solder joints causes increased solder joint resistance and reduced shear strength. The shear fracture path of the solder joints moves from the cathode side near the IMC solder seam to the Cu3Sn interface. The shear fracture mechanism changes from ductile transgranular fracture dominated by β-Sn dimples to brittle fracture dominated by interfacial IMC cleavage and slip steps.

Design of partial height web stiffeners in beam-to-column joints and influence of residual stresses induced by welding

Fixed beam-to-column joints in steel portal frames with bolted connections typically present stiffeners to ensure proper load bearing resistance and stiffness to the joint. Executing the same stiffeners with a reduced height (e.g. partial height web stiffener) allows for cost saving during manufacturing but must be paid off by considering its effects in the design verification of the joint. The usual gap size of the partial stiffener has a height of 10%–30% of the concerned element web depth. Based on the Astron product example, this study analyzes the effects of the partial stiffener on the concerned knee joint resistance components according EN1993-1-8. A numerical parametric study is performed based on an advanced 3D FEM model to determine and compare the structural behavior of the beam-to-column joints with full and partial stiffeners. Comparison of the calculation results prove, the partial stiffener influences only the shear panel resistance component, and it has no effect on other components of the joint. The failure mechanism of the shear panel using different slenderness ratios are analyzed in the paper and an enhanced design method is developed, which allow to consider the geometrical gap between the flange and stiffeners. The effect of residual stresses resulting from the manufacturing processes of the plated elements is also analyzed and introduced in the paper using advanced weld simulation technique.

Experimental study on fire resistance of traditional timber mortise-tenon joints with damages

This paper presents the experimental results on the fire resistance of traditional timber mortise-tenon joints with looseness, decay and cracking in the jointing area. Static loading test and fire resistance tests were conducted on six full scale joint specimens. The development of the temperature, the charring depth and rate, and the degradation of the rotational stiffness of the joints with fire exposure time was quantified. It was found that the service damage can have significant influence on the fire resistance of the traditional timber mortise-tenon joints. The charring rate calculated from the beam and column cross-sections is close to the recommended value in design code for softwood. The displacement of the damaged joints with wood decay and cracking increased by 69% and 90%, respectively, with respect to that of the undamaged joint after 30 min of dire exposure. The rotational stiffness of a damaged joint after 30 min of fire exposure can drop down to 11.4% of the initial rotational stiffness of a sound joint at ambient temperature. The influence of the stiffness degradation of joints on the moment redistribution and fire endurance of neighbouring beams and columns is worth of further investigation.