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Abstract This study reports an investigation on the effects of process parameters and part-to-part gaps on joint quality when producing fillet edge joint using the novel gap-bridged remote laser welding (RLW) technique. Joint geometries, microstructural characteristics, scanning electron micrographs (SEM), electron backscatter diffraction (EBSD) maps, microhardness and tensile strength behaviours are reported for the autogenous RLW fillet edge welds in an aluminium alloy, AA5182, used extensively for automotive structural applications. It has been found that laser process parameters and part-to-part gap directly influence key geometric features including penetration, leg length and throat thickness of the weld fusion zone, and subsequently, tensile performance. Lap shear test results demonstrate that both laser power and speed greatly influence the maximum mean load at failure and the corresponding tensile extension. Furthermore, both the weld macrostructure sections and lap shear strength confirm that the gap-bridging RLW technique can be successfully applied to close the part-to-part gaps. The microhardness profiles reveal that under zero gap and gap-bridged conditions the AA 5182 alloy base material has lower hardness (5–10%) compared to fusion zone. The EBSD maps exhibit the grain distribution from the base material to fusion zone under different gap conditions. As a result of directional cooling, a plane of weakness was formed at the junction of the horizontal and vertical grain developments when part-to-part gaps were employed. This study shows that the gap-bridging RLW technique is capable of creating good quality performance joints with automotive grade AA5182 aluminium alloy. Highlights • Fillet edge joints were produced in an Al alloy, AA5182, using the novel gap-bridged remote laser welding (RLW) technique. • Relations between RLW process parameters to key geometrical features of weld microstructure were obtained. • Satisfactory joint strength can be achieved by gap-bridging through proper selection of process parameters. • EBSD maps exhibit the grain distribution from the base material to fusion zone under different gap conditions. [ABSTRACT FROM AUTHOR]

Past researches showed that the energy dissipation capacity of the wide beam-column joints was not sufficient. So, two full-scale reinforced concrete interior wide beam-column joints were tested under quasi-static cyclic loads and the performance of the specimens was studied experimentally and numerically. Effect of using wide beams in two directions was investigated and it became clear that the longitudinal reinforcement of transverse wide beam had significant effect on the seismic behavior of the joints. Flexural hinging mechanism in the wide beams occurred instead of torsion brittle mode of failure. Effect of eccentric beams on joints is one of the areas needing research in ACI 352R-02. In the numerical study, it was seen that damage of the joints was concentrated to one side of the joints that the beams shifted to. Besides, concrete grade did not have much effect on behavior of the joint. [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical studies on the ultimate behaviour of K-joints in transmission tubular structures. Tests were conducted on nine connection specimens using high-strength steel to investigate ultimate strength. The material properties and load–displacement responses of nine tubular K-joints are tested and discussed with emphasis on the factors that affect the ultimate strength of the joints. Based on the experimental and numerical results, the failure mode and mechanism of the high-strength steel K-joints are identified. Using energy theory and the virtual work principle, a formula for predicting the ultimate strength of high-strength steel K-joints is developed. In order to verify the validity of the proposed formula, finite element models are built to perform a sensitivity analysis on the parameters that affect the ultimate strength of the connections. The results indicate that the compression ratio of the chord and the thickness and diameter of the chord have significant effects on the ultimate strength of the K-joints with an external annular steel plate. Moreover, the results predicted by the proposed formula correlated very well with the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Overlapped K-joints arise in truss type structures when one diagonal (overlap brace) intersects the other diagonal (through brace). In such joints, part of the through brace is hidden within the overlap brace, and the hidden toe of the through brace may or may not be welded to the chord. This study investigates the hysteretic behaviour of partially overlapped circular hollow section K-joints, with and without hidden welds, under cyclic loading. This study involved nine full-scale specimens, out of which four specimens had hidden welds. One joint was statically loaded and the remaining eight joints were cyclically loaded until failure. Chord plastification, brace local buckling, and cracking of the brace adjacent to welds were observed in these tests. The hysteretic performance indicators, such as ultimate capacity, joint ductility, energy dissipation, ultimate stiffness, etc., were established, which were then used to understand the hysteretic behaviour of overlapped K-joints. Results show that, compared with static loading, brace cracking occurred more easily under cyclic loading with a reduced joint capacity of up to 7% and a severely decreased ductility. Joints with hidden welds may exhibit a higher strength by approximately 10% and an increased hysteretic energy dissipation capacity, but with a reduction in joint ductility. The analysis of strain distributions around the joint zone indicates that, even though the joints with hidden welds experience lower strains, the hidden weld creates an asymmetric strain profile in the joints, which may be a weakness as some locations may become stress raisers leading to crack initiation. [ABSTRACT FROM AUTHOR]

In the present work, a numerical investigation of the effect of the blank holder parameters on material flow and the final geometry of the die-less clinched joint is conducted. Various blank holder designs as well as different process parameters are used to obtain clinched joints. Axisymmetric finite element (FE) model was developed to simulate die-less clinching experiments. A hybrid material model with a weight function between the two common used hardening laws, Swift and Voce, was utilized to better represent the material behavior in the FE model. Another hybrid material model, referred to as extended-Voce model, was also utilized in the FE simulation and the results compared with the weight function approach. The weight function material model resulted in smaller geometric interlock compared with the experiment, whereas, the extended-Voce model led to better prediction of experimental geometric interlock with an error of less than 5%. The results showed that the interlock forms due to a large material flow in the axial and radial directions. The interlock can be maximized by controlling the material to flow in radial direction instead of axial direction, by decreasing blank holder depth. Also, distortion of the bottom of the die-less clinched joint can be avoided by achieving a bottom thickness of at least 10% of the total sheet thickness. Lastly, finite element models were also developed to predict the joint strength in shear and peel failure modes. [ABSTRACT FROM AUTHOR]

As the use of shotcrete (sprayed concrete) to build full-depth structural elements increases in North America, the encapsulation quality of reinforcing bars has become a subject of growing concern. In this investigation, the influence of the mixture consistency and the size of imperfections (created deliberately) behind reinforcing bars on the bond strength of the bars was studied using shotcrete “pull-out” specimens sprayed with the dry-mix process. However, as the desired range of the imperfection sizes could not be obtained, cast-in-place “pull-out” specimens were built with artificially created voids. This strategy allowed to study the reduction of the bond strength by knowing the precise size of the voids. The results suggest that the best bond performance of a bar is obtained, given an appropriate spraying technique, when the optimal combination between the mixture consistency and the airflow rate is used. Moreover, reinforcing bars encased with shotcrete slip less, relative to concrete, than those encased with cast-in-place concrete because of the high compaction with which the mixture is placed. Additionally, a void’s transversal length (in contact with the bar) of about 20% of the bar’s nominal perimeter was found to be the threshold beyond which an important change of the bond performance occurs. [ABSTRACT FROM AUTHOR]

This investigation focuses on the assessment of the residual (after cooling) bond strength between concrete and steel rebars of reinforced concrete elements after exposure to elevated temperature and how to restore the bond strength using different repairing techniques and materials. The bond test was carried out on twenty-four beam end test specimens. The test parameters considered in the current research are the exposure condition, concrete compressive strength, rebar type, rebar size, rebar location, repairing techniques, and repairing materials. The test results indicated a significant reduction in the residual bond strength for heat-damaged specimens with a dramatic change in the bond stress-slip behavior. The deep repair technique is more efficient than the shallow repair technique in restoring a large portion of the original bond strength for heat-damaged specimens. Among the different repair materials used in the current research, the commercially fiber reinforced mortar is the most efficient one. Based on the limited number of specimens considered in this study, simple relationships are proposed to predict the bond strength and characterize the bond stress – slip behavior. The proposed relationships yield good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) is the most popular and efficient method of solid-state joining for similar as well as dissimilar metals and alloys. It is mostly used in applications for aerospace, rail, automotive, and marine industries. Many researchers are currently working with different perspectives on this FSW process for various combinations of materials. The general input process parameters are the thickness of the plate, axial load, rotational speed, welding speed, and tilt angle. The output parameters are joint hardness, % of elongation, and impact and yield strengths. Genetic programming (GP) is a relatively new method of evolutionary computing with the principal advantage of this approach being to evaluate efficacious predictive mathematical models or equations without any prior assumption regarding the possible form of the functional relationship. This paper both defines and illustrates how GP can be applied to the FSW process to derive precise relationships between the output and input parameters in order to obtain a generalized prediction model. A GP model will assist engineers in quantifying the performance of FSW, and the results from this study can then be utilized to estimate future requirements based on the historical data to provide a robust solution. The obtained results from the GP models showed good agreement with experimental and target data at an average prediction error of 0.72%. [ABSTRACT FROM AUTHOR]

The use of composites to repair localized corrosion damage in metallic pipelines has significantly increased in the past years. Repair techniques using polymer-based composites are interesting, since they do not require draining the line and stop operation. However, pipelines conveying liquids may work at elevated temperatures, what can be a limitation for the use of polymeric materials. The adhesion between pipe and composite is the key to the effectiveness of the repair (sleeves or patches), mainly in the case of through-thickness defects. This paper is a preliminary attempt to propose and analyse a global failure criterion for a particular class of adhesively bonded composite-metal joints. Single-lap joints (SLJ) were fabricated with metal and composite adherends bonded with an epoxy resin reinforced with Aramid fibres. The surface treatment adopted in this study was the same used in the field for repairs. The performance of these joints in pure bending and in shear was studied at four test temperatures: 25 °C, 50 °C, 70 °C and 90 °C. The mechanical behaviour is rate and temperature dependent. A global energy criterion for the joint fracture is proposed. It is verified experimentally that, for a given temperature, the critical energy is the same in both kinds of tests and that this energy decreases almost linearly with temperature. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted on empty and grouted stainless steel tubular X-joints with circular hollow section (CHS) chord member under axial compression. A total of 25 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors ( β , τ , grouting and grout strength) on the behaviour of grouted stainless steel tubular X-joints with CHS chord member under axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel tubular X-joints generally increased with the increase of the β and τ values. Furthermore, the ultimate strengths of stainless steel tubular X-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally unconservative for empty and grouted stainless steel tubular X-joints with CHS chord member under axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate. [ABSTRACT FROM AUTHOR]

Under an optimal phosphating time of 30 min, the nanoparticles can be effectively protected from oxidation at temperatures below 300 °C and stored for months in air. The shear strength of the phosphated joint was higher than that of the untreated one while the joint had a better performance in storing and aging tests. The shear strength decreased 23% after storing for 90 days and 17% after aging at 80 °C for 12 h (the figures for the untreated joint were 60% and 44%, respectively). The major oxidation product formed on the surfaces of the nanoparticles was Cu 2 O and the formation of voids in the sintering structure due to oxidation reduced the shear strength of the joints. A joint with a bonding strength of about 20 MPa was achieved even at 250 °C and under a pressure of 8 MPa. [ABSTRACT FROM AUTHOR]

The component method incorporated in Eurocodes 3 and 4 is one of the most accepted models for composite semi-rigid beam-to-column joint design. This method explicitly considers the contribution of the components with the most relevant composite action, such as reinforcing bars, concrete and shear connectors. This was the main motivation to further improve the assumptions employed in the structural response of composite joints to surpass the current limits of its adoption in hogging moment regions. However, in hogging moment regions the concrete slab is not under compression forces, leading to extensive concrete cracking, which can influence the actual structural joint response. An alternative set-up, namely, pull-out tests, was developed to better represent composite joints where tension forces act in the concrete slab. The overall results served as the main basis for a better understanding of some of the components present in composite joints, enabling a better formulation for their design capacities. The present paper focuses on a series of pull-out tests that presented failure modes associated with a tensile reinforcing bar rupture or anchorage capacity. The test results enabled a better understanding of the reinforcing bar failure modes and their relevance over the global beam-to-column joints' structural response. [ABSTRACT FROM AUTHOR]

The steel-truss-reinforced composite beam is a type of steel-reinforced concrete structure, in which the concrete beam is reinforced by steel trusses. Unlike traditional reinforced concrete structures, the steel truss works as the main skeleton and takes the main responsibility for the whole structural strength. In order to fulfil energy dissipation requirements, diagonal angle steel crosses are placed at the end of the steel truss. Specimens are designed based on different key parameters, including axial compression ratio and dimensions of chord, web and angle steels. Low-cyclic reversed loading tests are carried out on eight interior joint specimens to simulate realistic reversed loading conditions under earthquake. Load-deflection hysteresis loops and skeleton curves of joint specimens are obtained. Ductility, hysteresis behaviour and seismic-resistant performance are evaluated. Equivalent viscous-damping coefficients and energy dissipation indicators are calculated. The influences of axial compression ratio and steel ratio on the seismic performances are analysed. It is found that a large steel ratio will generally increase the bearing capacity. However, a relatively high axial compression ratio will benefit the bearing capacity of joints, but has adverse effects on hysteresis behaviours. Further, some conclusions are drawn on the overall seismic performances of this type of joint. [ABSTRACT FROM AUTHOR]

In order to evaluate the bending capacity of laminated bamboo lumber (LBL) beams, material performance tests and beam tests have been carried out. A strain-stress relationship is proposed based on compression and tensile tests conducted parallel to the grain. Two failure modes are identified based on the locations of cracks in the beam specimens. Direction of bending and the location of internal joints are shown to influence the mechanical properties of LBL beams. Internal joints have more influence on specimens under tangential bending (where the culms are bent across their width) than that under radial bending (where the culms are bent across their thickness). Irrespective of the bending direction, the strain across the cross-section of the laminated bamboo beam is shown to be linear throughout the test process, following standard beam theory. Based on this theory and the proposed simplified strain–stress relationship for the beam, calculation approaches for the ultimate bending moment and ultimate bending deflection are proposed for three bending failure modes which give a good agreement with the test results. [ABSTRACT FROM AUTHOR]

Splice strength of deformed steel bars embedded in recycled aggregate concrete was experimentally investigated using 24 bottom-cast scaled splice beam specimens detailed with unconfined contact lap splices and tested under four-point bending. The following variables were investigated: concrete grade (normal- and high-strength), recycled concrete aggregate replacement level (0%, 50% and 100%), rebar diameter (12 mm and 20 mm) and rebar surface characteristics. Bond behaviour and failure modes were noted to be similar in the natural and in the recycled aggregate concrete and a regression analysis of the experimental results in an expanded data base shows that f′ c 1/4 provides a good representation of the influence of recycled aggregate concrete grade on splice strength. A descriptive bond strength equation has been proposed for recycled aggregate concrete and it is noted that the ACI Committee 408R-03 model (for conventional concrete) gave relatively the most accurate and conservative bond strength predictions for the recycled aggregate concretes under investigation. [ABSTRACT FROM AUTHOR]

A polymer coating is often used instead of lubricant in order to protect the threaded part of an oil pipe fitting. There are several forms of these coatings of different composition applied by spraying to the threaded element of a pipe. Metal surface preparation before coating application has a considerable effect on polymer coating quality. Conversion coatings that formed on a pipe threaded surface and couplings as an intermediate layer between a metal surface and a polymer coatings are analyzed. The conversion coatings selected are various phosphate coatings and an alternative phosphate-free zirconium coating. Comparative study of these coatings includes an analysis of application technology, a study of conversion coatings physicochemical properties, and comparative tests for a conversion coating - thread lubricant coating system. [ABSTRACT FROM AUTHOR]

Laser welding-brazing process was developed for joining 5052 aluminum alloy and H62 brass in butt configuration with Zn-15%Al filler. Effect of welding speed on microstructural characteristics and mechanical properties of joints were investigated. Acceptable joints without obvious defect were obtained with the welding speed of 0.5–0.6 m/min, while lower and higher welding speed caused excessive back reinforcement and cracking, respectively. Three reaction layers were observed at welding speed of 0.3 m/min, which were Al 4.2 Cu 3.2 Zn 0.7 (τ′)/Al 4 Cu 9 /CuZn from weld seam side to brass side; while at welding speed of 0.4–0.6 m/min, two layers Al 4.2 Cu 3.2 Zn 0.7 and CuZn formed. The thickness of interfacial reaction layers increased with the decrease of welding speed, but varied little at different interfacial positions from top to bottom in one joint. Tensile test results indicated that the maximum joint tensile strength of 128 MPa was obtained at 0.5 m/min, which was 55.7% of that of Al base metal. All the joints fractured along the weld seam/brass interface. Some differences were found regarding fracture locations with three and two reaction layers. The joint fractured between Al 4 Cu 9 and τ′ IMC layer when the interface had three layers, while the crack occurred between CuZn and τ′ phase in the case of two layers. [ABSTRACT FROM AUTHOR]

The quality of the joints produced by means of Laser-Assisted Metal to Polymer direct joining (LAMP) is strongly influenced by the temperature field produced during the laser treatment. The main phenomena including the adhesion of the plastic to the metal sheet and the development of bubbles (on the plastic surface) depend on the temperature reached by the polymer at the interface. Such a temperature should be higher than the softening temperature, but lower than the degradation temperature of the polymer. However, the temperature distribution is difficult to be measured by experimental tests since the most polymers (which are transparent to the laser radiation) are often opaque to the infrared wavelength. Thus, infrared analysis involving pyrometers and infrared camera is not suitable for this purpose. On the other hand, thermocouples are difficult to be placed at the interface without influencing the temperature conditions. In this paper, an integrated approach involving both experimental measurements and a Finite Element (FE) model were used to perform such an analysis. LAMP of Polycarbonate and AISI304 stainless steel was performed by means of high power diode laser and the main process parameters i.e. laser power and scanning speed were varied. Comparing the experimental measurements and the FE model prediction of the thermal field, a good correspondence was achieved proving the suitability of the developed model and the proposed calibration procedure to be ready used for process design and optimization. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this work is to explore the forms of intermetallic phase compounds (IMPCs) in Pt/In/Au and Pt/In/Ag joints by using isothermal solidification. This lead-free technique leads to formation of IMPCs having high-temperature stable joints for platinum-based micro-heater gas sensor fabricated on low temperature co-fired ceramic (LTCC) substrate.Design/methodology/approach Proposed task is to make an interconnection for Pt micro-heater electrode pad to the silver and gold thick-films printed on LTCC substrate. Both Pt/In/Au and Pt/In/Ag configured joints with different interactive areas prepared at 190 and 220°C to study temperature and contact surface area effects on ultimate tensile strength of the joints, for a 20 s reaction time, at 0.2 MPa applied pressure. Those delaminated joint interfaces studied under SEM, EDAX and XRD.Findings IMPCs identified through material analysis using diffraction analysis of XRD data are InPt3, AgIn2, AgPt, AgPt3, Au9In4 and other stoichiometric compounds. The interactive surface area between thick-films and temperature increment shows improvement in the formations of IMPCs and mechanical stability of joints. These IMPCs-based joints have improved the mechanical stability to the joints to sustain even at high operating temperatures. Elemental mapping of the weak joint contact interface shows unwanted oxide formations also reported. Physical inter-locking followed by the diffusion phenomenon on the silver substrate strengthen the interconnection has been noticed.Research limitations/implications Inert gas environment creation inside the chamber to isolate the lead-free joint placed between heating stamp pads to avoid oxide formations at the interface while cooling which adds up to the cost of manufacturing. Most of the oxides at a joint-interface increase minute to moderate resistance with respect to the level of oxides took place. These oxides contributed heat certainly damage the micro-heater based gas sensors while functioning.Practical implications These isothermal solidification-based lead-free solder joints formation replace the existing lead-based packaging techniques. These lead-free interconnections on ceramic or LTCC substrate are reliable and durable, especially those designed to work for heavy-duty engines, even at severe environment conditions.Originality/value Platinum micro-heater-based gas sensors handles over a wide-range of temperatures about 300 to 500°C. The specific temperature level of different oxide films (SnO2) on the micro-heater is capable of detecting various specific gases. This feature of platinum based gas sensor demands durable and mechanically stable joints for continuous monitoring. [ABSTRACT FROM AUTHOR]

Welding-induced residual stress and distortion have detrimental influences on the ultimate strength of ships and offshore structures. Various experimental and numerical studies have been performed to understand the mechanism of residual stress and distortion under different factors, such as boundary condition, welding sequence and so on. In the present study, experimental tests and numerical simulations were performed to investigate the welding-induced residual stress and distortion under different material models. A sequentially coupled thermo-mechanical finite element model which implemented high temperature effects, temperature-dependent material properties and a moving volumetric heat source was developed to investigate the effect of material model on the residual stress and distortion in T-joint welds. The finite element models were validated carefully by the experimental tests. The results show that the material model has significant effects on residual stress and distortion. Considering that the welding process involves substantial plasticity, the material model must be carefully calibrated. [ABSTRACT FROM AUTHOR]

The paper mainly focuses on the study of the effects of Rayleigh damping in the simulations of FRP-concrete bonded joints, thereby proposing an approach to determine the value of its appropriate Rayleigh damping. Specifically, the element tests under Mode I and Mode II fracture modes were first carried out to investigate the effects of the mass proportional Rayleigh damping and the stiffness proportional Rayleigh damping. An FRP-concrete bonded joint is then employed to further investigate the effects of Rayleigh damping on the simulation results under Mode II fracture mode. It is shown that low-frequency vibrations are produced in the simulations of the specimens loaded by Mode I loading and could be damped by the mass proportional Rayleigh damping, while high-frequency vibrations are produced in the simulations of the specimens loaded by Mode II loading and could only be damped by the stiffness proportional Rayleigh damping. It also shows that the stiffness proportional damping is essential to damp out the oscillations in such simulations, thereby improving the convergence. In addition, the procedure proposed in this paper can lead to a proper interval for the value of the stiffness proportional Rayleigh damping, beyond which an unreasonable simulation result may be obtained. [ABSTRACT FROM AUTHOR]

In the present paper, the mechanical properties of hybrid bonded bolted joints between Fiber metal laminate (FML) and stainless steel adherends are investigated using experimental tensile tests. Three and five layered FMLs were fabricated using 430 stainless steel sheets and fiberglass prepreg layers. The adherends were bonded by AD-314 resin mixed with HA-34 hardener as adhesive and steel bolt was used for the mechanical fastening. The specimens were immersed into the sea water for 30 days and degradation of the mechanical strength of the joints was studied. Thermal cycles including heating (40 °C to100 °C) and cryogenic (−100 °C to −40 °C) cycles were applied in order to study their effects on the strength of the degraded joints. The failure mode for the adhesive bond was mixed failure and that of the bolted joint was the net-tension failure. The results showed 52% strength recovery in hybrid joints subjected to heating cycles. Cryogenic cycles also caused a 50% improvement in the tensile strength of the hybrid joints. In addition, the joint stiffness and absorbed energy of the specimens were improved significantly for both heating and cryogenic cycles. Moreover, the effect of FML stacking sequence on the results was also investigated. The results revealed that the mechanical fastening failure load for 5 layered FML joint is more affected by thermal cycles in comparison with 3 layered FML joint. [ABSTRACT FROM AUTHOR]

Scaffolds are temporary structures commonly used in construction to support various types of loads. Recently their collapse is becoming more common as shown by the number of accidents and injuries reported. The paper analyzes the main flaws and imperfections that could lead to the collapse of the scaffoldings. The study has been focused at the numerical level on three different types of steel scaffoldings: (i) joint tubes, (ii) multidirectional and (iii) prefabricated systems, which are commonly used in Italy. Several finite element simulations under different loading conditions on three types of steel scaffoldings have been performed, taking into account the imperfections during the assembly at the construction site, the base boundary conditions and the effects of lateral restraint arrangement. Finally, the study proposes an empirical formula to identify the critical load of different types of steel scaffoldings based on the number of story levels and the type of boundary conditions. [ABSTRACT FROM AUTHOR]

This article presents a mechanical model, based on thin plate theory and which incorporates the thermal degradation of material properties, to investigate the behavior of T-stub assembly, in terms of resistance, stiffness, deformation capacity, and failure modes at different temperatures. Also, a three-dimensional finite element model is developed to simulate the performance of T-stub. The proposed two models are validated against T-stub experiment available in other literature, and it is shown that the models proposed in this article satisfactorily predict the behavior of a T-stub assembly exposed to fire. Then, a thorough parametric study is conducted. The key variables include flange thickness, bolt grade, the distance from bolt line to flange root, and the temperature of the T-stub. Two kinds of loading paths, namely, “loading under constant temperature” and “heating under constant load,” are also adopted. The parametric study provides some valuable suggestions to improve the performance of T-stub and to refine the T-stub configurations. [ABSTRACT FROM AUTHOR]

This article presents the static tests on bare and concrete-filled circular hollow section X-joints with curved chord under in-plane bending. A total of 16 specimens were fabricated by hot-rolled bending the chord members into curvature with three different radii to apply in-plane bending to the brace members, in which six specimens were tested with bare curved chord, six specimens were tested with concrete filled in the curved chord only, and four traditional bare and concrete-filled circular hollow section X-joints with straight chord were also tested for comparison. The effects of curvature radius of chord member, concrete filled in the chord member and cross-section dimension of brace member on the joint strength, and behaviour under in-plane bending were evaluated. The curvature radius of chord member generally has insignificant influence on the in-plane flexural behaviour of circular hollow section X-joints with large radius. However, the ultimate strengths of circular hollow section X-joints under in-plane bending are greatly weakened by hot-rolled bending the chord members into curvature with small radius. Furthermore, the reinforcement of filling the concrete in the chord member has insignificant influence on the in-plane flexural behaviour of circular hollow section X-joints. On the other hand, the cross-section dimension of brace member has significant effect on the ultimate strengths of circular hollow section X-joints under in-plane bending. In addition, the current design rules are quite conservative for the design of bare and concrete-filled circular hollow section X-joints with curved and straight chord under in-plane bending loading. [ABSTRACT FROM AUTHOR]

The behaviour of different steel beam to column connections has been studied intensively against static and seismic loading regimes. However, there is a lack of knowledge on the response of such connections against impact and blast. In order to close this gap, the most common connections with partially depth end plate (PDEPCs), as a simple connection, and flush plate (FPCs), as a moment resisting connection, were investigated under both quasi-static and impact loads. Here, eight specimens were tested under those loading conditions with different locations. 3 D finite element models were then developed and validated against the corresponding experimental results. Full range analyses of the connection responses under both loading regimes are then carried out using the validated FE models to examine the internal forces of the connections. Finally, the results of full analyses under both loading regimes were compared and dynamic increase factors (DIF) were proposed to assist predicting the impact response of these types of connections using the static analysis. The results showed that failure modes under both loading regimes were similar, but with the larger fracture on the PDEPC under quasi-static load than that under lateral impact. The DIFs were found to be between 1.02 and 1.21, 1.03 and 1.36 and 1.22 and 1.45 based on the bolt tensile strength, axial resistance and bending resistance of the connections, respectively. However, if based on the energy approach, the range of DIFs was recorded between 1.25 and 1.38 using the experimental results and between 1.19 and 1.34 using the finite element analysis results. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigation and numerical investigation on seismic behavior of special-shaped concrete-filled steel tubular (CFST) column to steel beam joints. Exterior diaphragm and vertical rib are respectively introduced as joint stiffeners. A pseudo static experiment was conducted to investigate load transmission mechanism, failure mode and seismic performance index based on load-deformation curves and strain curves. The seismic behavior of the two kinds of joints were compared and evaluated. The classification of the joints by stiffness is conducted according to Eurocode. Inter-story drift of the specimens was calculated with data from laboratory apparatus and verified with test results. A design formula of joint shear resistance based on internal load transmission was proposed for engineering application. A finite element model of special-shaped CFST to steel beam connections was established as a supplement to analyze load transmission mechanism. [ABSTRACT FROM AUTHOR]

Bellows joint is a critical part of an underground pipeline system, which can undergo severe damage such as breaking, crushing, and bending under a strong earthquake. In our research work, finite element analysis (FEA) of the bellows joint was studied using LS-DYNA. Single convolution and multi-convolution bellows joints applied with different loadings were investigated. Force – displacement curve, plastic strain distribution and bending moment – angular displacement curve were obtained. Furthermore, low frequency cyclic experiment on 4-convolution bellows joints was conducted and the results from the experiment were compared with the results from FEA. The load capacity of the multi-convolution bellows joint was almost the same as the single convolution bellows joint, and the energy absorption increased with the number of the convolution linearly. [ABSTRACT FROM AUTHOR]

Steel-plate composite (SC) walls used in the containment internal structures of safety-related nuclear facilities intersect each other at corners of compartments to form wall-to-wall corner or L-joints. This paper focuses on joint shear behavior and strength of wall-to-wall corner L-joints, the understanding of which is imperative for the design of wall-to-wall joints irrespective of the failure mode. This paper presents the results of a large-scale test conducted on an SC wall-to-wall corner or L-joint. The test specimen was designed to undergo joint shear failure prior to flexural yielding of the connected SC walls. The test specimen did not include any tie bars in the joint shear region, which would represent the lower bound case for these joints. The specimen was subjected to cyclic loading until failure, and the test results included the joint shear force-displacement and joint shear force-shear strain responses of the specimen along with observations of concrete cracking and crushing in the joint region. The results and observations were evaluated to establish the joint shear strength and governing failure mode. The experimentally measured joint shear strength was compared with the ACI 349-06 code equation for calculating the joint shear strength of comparable reinforced concrete beam-to-column joints. A detailed nonlinear finite element model was developed to gain additional insight into the observed behavior. The model was benchmarked using experimental results. The experimental and analytical results were compared with ACI 349-06 code provisions for calculating the joint shear strength of reinforced concrete beam-to-column joints. The results from experimental and analytical investigations indicate that the ACI 349-06 code equation could be used for estimating the joint shear strength of steel-plate composite wall-to-wall L-joints with γ of 8. [ABSTRACT FROM AUTHOR]

The determination of unactuated structural joint axes within a compliant structure by external measurements is a subject of interest in many areas. Most eminently, the issue arises for example in the identification of a human joint axis by non-invasive measures, as is needed in robotics rehabilitation and surgery planning procedures. While most existing non-invasive approaches rely here on external optical tracking systems and/or inertial measurement units (IMU) attached to the skin and hence induce large artifact errors, identification of joint axes through tactile control has not yet been addressed in the literature. This paper presents a novel approach to determine an unknown unactuated joint axis in a compliant embedding serial kinematic chain using robot force-controlled motion. The approach consists in iteratively imparting a load increment according to the Krylov power iteration method until convergence to the force eigenscrew with largest impedance eigenvalue is achieved. The novelty of the approach consists in applying the Krylov steps directly on the target system, hence avoiding the need to explicitly identify the impedance matrix, which is difficult to obtain. The paper validates the proposed procedure by a mimicry mechanical device of the upper limb, composed of a revolute joint representing the elbow joint and a compliant wrist suspension imitating the local movements of the soft tissue at the wrist. The experiments show a promising perspective of the approach. [ABSTRACT FROM AUTHOR]

Low density foam core sandwich composites are recerving increasing attention and application in marine engineering. In order to solve the damage failure problem of sandwich L-joints for ship structures, the ultimate strength and fatigue properties of full scale L-joints were researched by experimental method. On the basis of the research on the static strength, the fatigue life and failure mode of this kind of connection were analyzed in different load amplitudes by a series of fatigue tests. The generation and development of cracks in the whole process were revealed and S-N curves were also drawn. The results show that fatigue life and stiffness of sandwich L-joints are decreased with the increase of load levels, and the major failure modes are in the form of sandwich debonding, sandwich face/core delamination, and gelcoat damage. Finally, a fatigue life model has been developed with stress level r and crack length a i and validated with test results. [ABSTRACT FROM AUTHOR]

The effects of Cu concentration ( x ) on the interfacial microstructure between a molten Sn-3Ag- x Cu alloy and an electrolytic Au/Ni/Cu multilayer and its mechanical reliability were investigated via transmission electron microscopy (TEM) and high-speed ball shear (HSBS) testing. The x values were 0, 0.3, 0.4, 0.5, 0.7, and 1.0 (wt%). An increase in x caused an interfacial intermetallic compound (IMC) transition from a dense (Ni,Cu) 3 Sn 4 layer ( x = 0 and 0.3) to the coexistence of (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 ( x = 0.4 and 0.5), and to a dense (Cu,Ni) 6 Sn 5 layer ( x = 0.7 and 1.0) after soldering reaction at 250 °C for 2 min. An increase in the reaction time enhanced the IMC growth and induced the nucleation of a (Ni,Cu) 3 Sn 4 nanolayer beneath (Cu,Ni) 6 Sn 5 in the high x case. The TEM and HSBS characterizations showed that a single, thin (Ni,Cu) 3 Sn 4 layer grown at the interface possessed better shear resistance than a single (Cu,Ni) 6 Sn 5 layer, and the presence of a dual layer structure of (Cu,Ni) 6 Sn 5 /(Ni,Cu) 3 Sn 4 substantially degraded the mechanical properties of the joint interface. These observations indicated that the Cu concentration in Sn-3Ag- x Cu alloy plays a crucial role in the interfacial reaction, which, in turn, dominates the mechanical reliability of microelectronic joints. [ABSTRACT FROM AUTHOR]

In a fully mechanized coal-mining face, the positioning and attitude of the shearer and scraper conveyor are inaccurate. To overcome this problem, a joint positioning and attitude solving method that considers the effect of an uneven floor is proposed. In addition, the real-time connection and coupling relationship between the two devices is analyzed. Two types of sensors, namely, the tilt sensor and strapdown inertial navigation system (SINS), are used to measure the shearer body pitch angle and the scraper conveyor shape, respectively. To improve the accuracy, two pieces of information are fused using the adaptive information fusion algorithm. It is observed that, using a marking strategy, the shearer body pitch angle can be reversely mapped to the real-time shape of the scraper conveyor. Then, a virtual-reality (VR) software that can visually simulate this entire operation process under different conditions is developed. Finally, experiments are conducted on a prototype experimental platform. The positioning error is found to be less than 0.38 times the middle trough length; moreover, no accumulated error is detected. This method can monitor the operation of the shearer and scraper conveyor in a highly dynamic and precise manner and provide strong technical support for safe and efficient operation of a fully mechanized coal-mining face. [ABSTRACT FROM AUTHOR]

This paper presents the investigations on joining 10-mm Al metal matrix composite plates with particles of SiC and BC as reinforcement using friction stir welding (FSW) process. This study majorly focuses on the metallurgical characterizations to explore the microstructural behavior of the welded specimen subjected to constant load of 10 KN, rotational speed of 1000 rpm, and traveling speed of 75 mm/min of the FSW tool. Further, tensile and hardness properties of the welded specimens are investigated and related to the microstructural variations. The results reveal vital information on the distribution pattern of the elements in the Al metal matrix composite (MMC) in the weld region leading to variation in the mechanical strength. The feasibility of joining Al MMC with FSW is also established through this study. [ABSTRACT FROM AUTHOR]

combining composite-brazing with transient liquid phase bonding (TLP), a novel process named composite-diffusion brazing was introduced to join C f /SiC composite and Ti-6Al-4V at 930 °C for 30–120 min using (Ti-Zr-Cu-Ni)+16 vol%TiC. The added TiC particles distribute uniformly in the joints, which contributes to relax the residual stresses in the joints. The composition homogenization between interlayer and TC4 leads to the decrease of Cu and Ni contents in the interlayer, thereby the heat-resistance of joints has been improved significantly. When the dwelling time is 120 min, the melting-point of joints is raised to 1217 °C, which is 300 °C higher than that of filler. Besides that, the joints exhibit excellent high-temperature mechanical properties. The shear strengths of the joints at 800 °C reaches to 137.4 MPa, when the dwelling time is 90 min. Thus, the new composite-diffusion brazing process has the superiorities of both composite-brazing and TLP. [ABSTRACT FROM AUTHOR]

By combining a parallel mechanism with integrated flexible joints, a large measurement range and high accuracy sensor is realized. However, the main errors of the sensor involve not only assembly errors, but also deformation errors of its flexible leg. Based on a flexible joint 6-UPUR (a kind of mechanism configuration where U-universal joint, P-prismatic joint, R-revolute joint) parallel six-axis force sensor developed during the prephase, assembly and deformation error modeling and analysis of the resulting sensors with a large measurement range and high accuracy are made in this paper. First, an assembly error model is established based on the imaginary kinematic joint method and the Denavit-Hartenberg (D-H) method. Next, a stiffness model is built to solve the stiffness matrix. The deformation error model of the sensor is obtained. Then, the first order kinematic influence coefficient matrix when the synthetic error is taken into account is solved. Finally, measurement and calibration experiments of the sensor composed of the hardware and software system are performed. Forced deformation of the force-measuring platform is detected by using laser interferometry and analyzed to verify the correctness of the synthetic error model. In addition, the first order kinematic influence coefficient matrix in actual circumstances is calculated. By comparing the condition numbers and square norms of the coefficient matrices, the conclusion is drawn theoretically that it is very important to take into account the synthetic error for design stage of the sensor and helpful to improve performance of the sensor in order to meet needs of actual working environments. [ABSTRACT FROM AUTHOR]

Strengthening of steel structures with adhesively bonded carbon fibre reinforced polymer (CFRP) materials have become increasingly popular in the last decade. However, uncertainties regarding the durability and long-term performance of CFRP/steel joints is a major obstacle for their growing application. Previous research indicates the deleterious effects of moisture and thermal cycles on the mechanical performance of these joints. To the authors' knowledge, the combined effects of moisture and thermal cycles have been scarcely investigated. This paper presents the results of extensive experimental investigations at material- and joint-level subjected to various cyclic environmental scenarios. Special consideration is given to the role of moisture, i.e. distilled- or salt-water, when combined with freeze-thaw cycles. Moreover, the possibility of providing a predictive modelling platform for residual strength prediction of environmentally aged joints using sequentially coupled moisture diffusion-fracture analysis is explored. The results show 11% and 47% strength reductions for the CFRP/steel joints after a complete wet-dry cycle in distilled- and salt-water, respectively, which are significantly larger than those observed after only the wet exposure. In addition, 125 and 250 freeze-thaw cycles were found to have no unfavourable effects on the strength of dry or preconditioned joints. [ABSTRACT FROM AUTHOR]

Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck. A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment. [ABSTRACT FROM AUTHOR]

Vibro-acoustic modulation ( VAM ) – one of the prevailing nonlinear methods for material characterization and structural damage evaluation – is based on the effect of modulation of a low-frequency vibration (pumping vibration) on a high-frequency acoustic wave (probing wave). In this study, the contact acoustic nonlinearity ( CAN ), associated with changes in the solid-solid interface of a bolted joint under VAM , due to bolt loosening, is explored analytically and experimentally, on which basis a VAM -inspired approach is developed for monitoring structural integrity of bolted joints. Numerical simulation based on a theoretical model with structural nonlinear contact stiffness is implemented, to achieve insight into CAN induced by a loose bolt. A quantitative correlation between vibro-acoustic nonlinear distortion and degree of bolt loosening is ascertained. The developed approach is applied to detect bolt loosening in a composite bolted joint and to evaluate the residual torque of the loose bolt quantitatively. Take a step further, the VAM -based nonlinear approach is compared against an elastic wave-based linear method, underscoring a higher sensitivity to bolt loosening. From early awareness of bolt loosening to continuous evaluation of the bolt loosening progress, this VAM -based approach has provided a cost-effective framework for monitoring the health and integrity of a composite bolted joint. [ABSTRACT FROM AUTHOR]

Ni/Sn–xZn/Ni (x = 1, 5, 9 wt%) joints were used to investigate the effect of Zn content on interfacial reactions during reflow under a temperature gradient. Asymmetrical growth and transformation of intermetallic compounds (IMCs) occurred between the cold and hot end interfaces. Faster IMC growth at the cold end and a more prompt IMC transformation at the hot end in a lower Zn content solder joint were identified due to the more thermomigration-induced Zn and Ni atomic fluxes toward the cold end. The main diffusion species into IMC layers changed from Zn atoms at the early stage to Sn and Ni atoms at the later stage. As a result, the IMC evolution followed (Ni,Zn)3Sn4 → Ni3Sn4 in the Ni/Sn–1Zn/Ni joint, Ni5Zn21 → 𝛕 phase → Ni3Sn4 in the Ni/Sn–5Zn/Ni joint, and Ni5Zn21 → 𝛕 phase in the Ni/Sn–9Zn/Ni joint along with the reflow time. A higher Zn content could effectively inhibit the dissolution of the hot-end Ni substrate and restrain the growth rate of the cold-end interfacial IMCs. [ABSTRACT FROM AUTHOR]

Experimental simulation of long-distance shield tunnels is difficult due to the enormous volumes of segments and complexity of joints. In this paper, a multi-scale method is proposed to simulate the test model of shield tunnels, which discretizes the entire model structure into the segmental equivalent ring portion (SER) and the equivalent uniform tube portion (EUT). The EUT model is employed to capture seismic response characteristics of the entire tunnel system, whereas the SER model is employed to describe in detail the deformation responses in lining segments and joints at positions of potential damage or interest. The proposed multi-scale physical model for shield tunnels is validated through shaking table tests, in which a full refined model is set as benchmark for comparison. Results show that: 1) the multi-scale physical model demonstrates the same macroscopic dynamic response, such as acceleration responses of model linings, as the full refined model; and 2) dynamic responses such as the extension of joints in the central zone of SER portion of the multi-scale model is consistent with those in the full refined model. The proposed multi-scale method provides an effective way for the design of complex segmental tunnel models applied in shaking table tests. [ABSTRACT FROM AUTHOR]

The laser welding of aluminium alloys is an important industrial technology but many challenges remain. The objective of this research is to investigate the effect of laser welding parameters on the quality of the fiber laser lap welded AA5182 aluminium alloy. The influences of the laser power, welding speed and focal point position on the mechanical and microhardness properties of the joints were experimentally investigated. The mechanical properties of the joints were evaluated by performing tensile tests. From the experimental results, optimum process parameters were determined, and microstructural examination and microhardness tests were conducted to better understand the performance of the joints. It was found that there is a correlation between the tensile shear loads of the joints and heat input per unit length. At the optimized parameters, the welded joint showed good weld appearance without macro defects, and the joint had an adequate tensile shear load. [ABSTRACT FROM AUTHOR]

Beam-column joints in existing concrete buildings might not satisfy the design requirements for seismic reinforcement details specified in current seismic design codes. Thus, in this study, various retrofit solutions for existing exterior beam-column joints with non-seismic details were developed: head re-bars anchoring, carbon fiber reinforced polymer (CFRP) wrapping, haunch retrofit element, and steel jacketing with various shapes and sizes. To investigate the seismic performance of exterior joints strengthened with the proposed retrofit solutions, seven half-scale exterior reinforced concrete beam-column joints including one control specimen and six retrofitted specimens were fabricated and tested under cyclic loading simulating earthquake loading. The test results showed that the proposed retrofit solutions could partially enhance the seismic capacity of the beam-column joints: steel jackets could increase deformation and load-carrying capacities; steel haunch elements could increase the load-carrying capacity, stiffness, and dissipated energy; and head re-bar anchoring and CFRP wrapping did not significantly effect on the seismic capacity of the beam-column joints. [ABSTRACT FROM AUTHOR]