Tensile Joint Research Articles

Experimental methods for the analysis of the tensile behavior of concrete joints

AbstractAdhesion plays an important role in the evaluation of hydraulic structures with unreinforced concrete joints. The experimental determination of joint tensile strength as a quantifiable parameter is not standardized, resulting in a variety of test setups found in literature. The present paper highlights advantages and disadvantages of three of the most common tension tests for plain concrete and concrete joints through both theoretical and laboratory experimental analysis on specimens with artificial joints. Splitting tension tests were found to be inexpensive but tend to overestimate the adhesive strength of weak joints. Direct tension tests require an elaborate test setup but may yield information on the tension softening behavior. Pull‐off tests stand out for their ability to yield in‐situ results but deliver inconclusive results.

Friction stir welding of dissimilar aluminum alloys AA7075 to AA2014

The joining of dissimilar Al-Cu alloy AA2014-T651 and Al-Zn alloy AA7075-T651 plates was carried out using friction stir welding (FSW) technique and the process parameters were optimized using Taguchi L9 orthogonal design of experiments. The rotational speed, transverse speed, and axial load were the parameters taken into consideration. The optimum process parameters were determined with reference to tensile strength of the joint. The predicted optimal value of tensile strength was confirmed by conducting the confirmation run using optimum parameters. This study shows that defect free, high efficiency welded joints can be produced using a wide range of process parameters and recommends parameters for producing best joint tensile properties. Analysis of variance showed that the axial load is the most dominant factor in deciding the joint soundness while rotational speed and welding speed also played significant roles.

Effect of heat input modes on microstructure, mechanical properties and porosity of laser welded NiTi-316L joints: A comparative study

Laser welding of NiTi to stainless steel (SS) wires is prospective in biomedical devices. In this work, the influence of different heat input modes, high power density with short welding time (HPDS) and low power density with long welding time (LPDL), on laser welded NiTi-316L wire joints was investigated. The HPDS mode resulted in non-uniform microstructure and hardness distribution in the fusion zone (FZ). On the contrary, a relatively uniform intermetallic compounds (IMCs) network of Fe2Ti + Ni3Ti formed in the FZ welded with LPDL mode. Finite volume modeling (FVM) was used to reveal the flow of molten metals between HPDS and LPDL modes. Different mechanisms for high porosity in the HPDS joint were proposed: processing-induced large pores were caused by the instability/collapse of laser keyhole, while diffusion-induced small pores initiated from the Ni vaporization. A low laser power density and long welding time in LPDL mode could significantly decrease the porosity by weakening laser keyhole, increasing time for pore escaping and uniformizing FZ microstructure. LPDL mode could result in an enhanced joint tensile strength to maximum 290.2 MPa because of the increased effective joining area (by decreasing porosity) and the reduced brittle Fe–Ti IMCs segregation in joints.

Effect of activated fluxes during welding of dissimilar stainless steels using semi-automatic setup

ABSTRACT In the present work, two dissimilar metals austenitic AISI 304 and 316 stainless steels were welded with duplex 2205 using semi-automatic bi-directional GMAW setup to appraise the microstructural and mechanical behavior of the welded joints. Three different activated fluxes i.e. SiO2, TiO2 and CrO3 were used to enhance the depth of penetration during joining of different stainless steels grades. Various process parameters such as welding current, voltage, filler wire, gas flow rate and activated flux were varied to observe their influences on joint tensile, bending strength, microhardness and microstructural properties. The experiments were designed using mixed level L18 orthogonal array of Taguchi method. Tensile strength was observed to be considerably dependent on the low gas flow rate, whereas welding current and activated flux influenced the toughness. The most significant effect on the bending strength and toughness was experienced with the use of SiO2 activated flux.

Seismic and structural health monitoring systems for large dams: theoretical, computational and practical innovations

This paper is focused on the study of the dynamic behaviour of two large arch dams, and it presents some innovations for the improvement of Seismic and Structural Health Monitoring (SSHM) systems for dams. The work describes a methodology based on the integrated use of software for automatic monitoring data analysis and of computational 3D finite element (3DFE) models for dam dynamic behaviour simulation. The monitoring data analysis software was developed for automatic modal identification, in order to obtain natural frequencies and mode shapes, for automatic detection of vibrations induced by seismic events, to be distinguished from those caused by other operational sources, and for comparison between results retrieved from measured vibrations and numerical results from 3DFE modelling. The numerical simulations are carried out using a 3DFE program developed for dynamic analysis of dam-reservoir-foundation systems, based on a solid–fluid coupled formulation and considering the dam-water dynamic interaction, including calculation modules for complex modal analysis and for linear and non-linear seismic analysis. The case studies are two large arch dams that have been under continuous dynamic monitoring over the last ten years: Cabril dam (132 m high), the highest dam in Portugal, and Cahora Bassa dam (170 m high), in Mozambique, one of the highest dams in Africa. The SSHM systems installed in both dams have similar schemes and were designed to continuously record accelerations in several locations at the upper part of the dam body and near the dam-foundation interface, using uniaxial and triaxial accelerometers. The most significant experimental results from continuous dynamic monitoring are presented and compared with numerical results for both dams, with emphasis on the evolution of natural frequencies over time, including the vibration mode shapes for various water levels, and on the measured accelerations during low-intensity seismic events. Furthermore, the main results of non-linear seismic response simulations are provided, considering the effects due to joint movements and tensile and compressive concrete damage, aiming to assess the seismic performance of both dams based on the Endurance Time Analysis method.

Z‐pin effect on interlaminar mechanical and ablation performance of quartz‐phenolic composites

AbstractWhen a spacecraft flies at a high speed through a high‐heat flow, the ablative composites suffer from severe delamination and bulging due to their weak interlaminar performance. This will interfere normal operations of spacecraft. To improve the interlaminar performance of ablative composites is of great significance to the ablative structures. This study investigated Z‐pin reinforced quartz‐phenolic composites and reinforcement mechanism. First, a thermogravimetry (TG) test was used to analyze the thermal decomposition process of the phenolic. Second, a series of tests, including a single Z‐pin pull‐out, a single‐lap joint tensile and an oxyacetylene ablation test, were conducted to investigate composites' ablation performance. We also deployed a 3D morphometer and an infrared thermography to reveal the function of Z‐pins. The results demonstrated that Z‐pins can improve composites' ablation performance in both structure and function. In the structure, Z‐pins suppress the interlaminar delamination of composites by enhancing the interlaminar strength. As the ablation time increases, interface bridging between the Z‐pin and laminates contributes increasingly to the interlaminar shear strength of laminates. After 60 s of ablation in a flame of 920°C, the interlaminar shear strength of Z‐pin specimens is 84.66% stronger than that of the normal composites. In the function, the Z‐pins suppress large areas of bulges by providing escape channels for pyrolysis gas, and reduce bulging areas by 60%. Z‐pin technology can effectively suppress mechanical erosion of the ablative surface due to the delamination and bulging. It is an important way to improve ablation performance of ablative structures.

Development of hydro-axial tension method for whole pipe butt-fusion joint tensile test

Assessing the integrity of the thermo-fusion joint in plastic pipes is important as they can appear as a weak link in the piping system. In this work, a hydro-axial tension (HAT) test was developed as a whole pipe axial tensile test and applied to evaluate the polyethylene (PE) pipe butt-fusion (BF) joint containing various flaws. HAT test utilizes hydrostatic pressure to cause axial tension in pipes. The experimental and numerical analysis was carried out to confirm the axial tensile stress as the dominant principal stress, causing axial tension in the pipe. The HAT method was further tested against the whole pipe mechanical axial tensile (AT) test, and the HAT was shown to closely duplicate the AT behavior of the whole pipe and the BF joint. In addition, the HAT test correctly identified PE pipe butt-fusions having no flaws and flawed joints containing cold-fusion and fine particulate contamination.

A comprehensive study on CFRP rapid portable bridge: Design, experimental investigation and finite element analysis

For military and emergency applications, there is the high demand for bridges that are light-weight, high-strength, and easy to transport and install. Carbon fiber-reinforced polymer (CFRP) composites are promising for rapid portable bridges due to their excellent performance. A CFRP rapid portable bridge (CRPB) with a box beam profile was designed in this study, and a 1:2.5 scaled model of the CRPB was manufactured and tested under track loads to evaluate its structural performance. The failure mode of the CRPB was crushing of the bridge upper deck, and the ultimate load was 6.5 times the design strength. Tensile joints performed well in the test without obvious damage and were an effective connection strategy. The mechanical behavior of the shear keys and tensile joints were studied by finite element methods. The numerical results from the finite element analysis of CRPBs show good agreement with the experimental results.

Experimental study on the tensile behavior of ultra‐high performance concrete fiber continuous joints

AbstractThe application of ultra‐high performance concrete (UHPC) in the bridge deck effectively increases the strength, ductility, and durability of the deck system, while the problem of fiber discontinuity at the joint‐deck interface remains unsolved. This study proposes an innovative UHPC joint to create steel fiber continuity at the interface and experimentally investigates its tensile behavior. Test parameters include fiber content, fiber length and diameter, fiber shape, and fiber strength. Test results indicate that the joint tensile strength increases with fiber content, fiber length, and fiber strength. The specimen with hooked end fibers also develops higher joint tensile strength compared with the specimen with straight fibers. It is recommended to use fibers with a smaller diameter to increase the interfacial bonding area between the fibers and the matrix. High‐strength fibers are also recommended to achieve the best efficiency in a high‐strength matrix, like UHPC. The tensile performance of the joint with a fiber content of no less than 0.5%, and an embedment length of 15 mm (with a fiber length/diameter ratio of 50), and a diameter of 0.3 mm is similar to the performance of the specimen cast as one piece. Therefore, a properly designed UHPC fiber continuous joint is recommended in engineering practice to improve the integrity of the joint‐deck system.

Microstructure and Mechanical Properties of Aluminum Alloy/Stainless Steel Dissimilar Ring Joint Welded by Inertia Friction Welding

In recent years, studying the weldability of a dissimilar metal hybrid structure, with the potential to make full use of their unique benefits, has been a research hotspot. In this article, inertia friction welding was utilized to join Φ130 forged ring of 2219 aluminum alloy with 304 stainless steel. Optical observation (OM), electron back scattering diffraction (EBSD), and scanning electron microscopy (SEM) were utilized to examine the joint microstructure in depth. Depending on the research, a significant thermal–mechanical coupling effect occurs during welding, resulting in inadequate recrystallization on aluminum-side thermo-mechanically affected zone (TMAZ) and forming zonal features. The crystal orientation and grain size of each TMAZ region reflect distinct differences. On the joint faying surface, the growth of intermetallic compounds (IMCs) is inhibited by a fast cooling rate and metallurgical bonding characteristics were found depending on the discontinuous distribution of IMCs. The average joint tensile strength can reach 161.3 MPa achieving 92.2% of 2219-O; fracture occurs on aluminum-side base metal presenting ductile fracture characteristics.

Al-steel dissimilar joining: Challenges and opportunities

Al-steel joining has a lot of use in the automotive and aerospace industries since it saves a lot of weight. The materials' physical, thermal, and metallurgical qualities differed significantly, making connecting this combination difficult. This article provides a comprehensive overview of the Al-steel joining processes. The fundamental reason for the problem in fusion joining operations is the formation of a thick intermetallic compound (IMC) layer and additional difficulties related to solidification. The effects of heat input, wettability, and IMC layer on joint formation are summarised in this article. To achieve a good joint, numerous elements like heat generation, IMC formation, and process parameters must be critically balanced in solid-state joining processes. The effects of process parameters in friction stir welding (FSW) techniques on joint's mechanical and metallographic soundness are explored in this work. Because of the steel's higher strength, there have been various attempts to soften it and make it easier to deform in order to improve weld amalgamation. The use of tungsten inert gas (TIG) welding and electrical resistance heating to achieve heat-assisted hybrid friction stir welding has been documented in the literature. The hybrid joining processes are found to be improving the joint's tensile properties.

Effect of Ni in pure Cu/304 stainless steel induction brazing joints

The joints of pure Cu and 304 stainless steel are widely used industrially as heat exchangers. Brazing joints between pure Cu and 304 stainless steel using AgCuZnMnNi as the filler metal were investigated herein. The brazing experiments were carried out in the temperature range of 710–810 °C for 15 s. Microstructural analysis showed the primary components of the joints were Ag-based (ss.) (where “ss.” indicates a solid solution) and Cu-based (ss.). Energy dispersive X-ray spectroscopy revealed a violent interdiffusion at the Cu interface during brazing, where Ni accumulated at the Cu interface at higher brazing temperature and the Ni content in the α-Cu (ss.) of the Cu interface increased with brazing temperature. Under tensile deformation, fracture initiated at the Cu and propagated along the α-Cu (ss.) of the Cu side, but the tensile rupture location transformed from the α-Cu (ss.) to the HAZ of the Cu side as the temperature increased. A maximum joint tensile strength of 210 MPa was obtained at 810 °C. Nanoindentation matrix testing indicated that the hardness of the α-Cu (ss.) was proportional to the content of elemental Ni in the α-Cu (ss.). The accumulation of Ni at the Cu interface induced an enhancement of nanoindentation hardness, which caused the transformation of the fracture location.

Experimental and numerical study on the screw connection strength of bamboo-oriented strand board compared with wood-oriented strand board

The utilization of resourceful bamboo can alleviate the wood shortage problem. Bamboo-oriented strand board (BOSB) with the highest utilization of bamboo ratio and excellent mechanical properties was considered as a good engineering and furniture material. The strength of joints affects the safety of BOSB structure. This study aims to investigate the effect of screw spacing on the tensile and compressive stiffness and strength of corner joints from BOSB by experimental method combined with finite element method (FEM) compared with wood-oriented strand board (WOSB). The results showed that (1) the strength and stiffness of the corner joint was significantly affected by the screw spacing, and it affected the compressive strength and stiffness of WOSB more significantly; (2) the bending moment and stiffness coefficient of BOSB compressed joint decreased with the increase of spacing, while that of tensile joint increased first and then decreased, and it reached the maximum value, when the spacing was 48 mm; (3) compared with WOSB joint, BOSB joint had higher strength and stiffness, and the failure of the joint was due to the yielding of self-drilling screws. This was also verified by numerical analysis results; (4) the bending moment of BOSB joints was about 2.5 times that of WOSB joints, while the difference between stiffness coefficient was small; (5) the elastic deformations resulted from experimental tests and FEM are similar. It was shown that when the screw spacing is 48 mm, the Von Mises stresses on the BOSB joint were smaller, and the bending strength and stiffness were larger, which was the most suitable screw spacing.

Tensile Characteristics of Mechanical Lap Joints Between Commercial ReBCO Tapes With Various Interlayer Materials

In this work, the mechanical lap joint of commercial ReBCO tape from SHSC is prepared. The tape is reinforced with stainless steel bar in both side to reduce the effect of bending moment in the joint tensile test. We use Indium and GaInSn as interlayer material, respectively, and different pressures are applied on the joint by jig during testing. The relationship between joint resistance and applied tensile stress was measured at 77 K. The results shows that for all measured joints under pressure, the voltage rise duo to tensile stress is small at first and then sharply grows until a certain value of stress is reached. The maximum tensile stress is higher for the joint which has lower resistance. Comparing two types of mechanical lap joints with Indium and GaInSn, the former joint shows smaller dispersion on joint resistance than the latter under pressure above 40 Mpa. It is also shown that the joint with Indium can tolerate higher tensile stress than the joint with GaInSn by using the Weibull distribution function analysis.

Digital image correlation study on tensile properties of high strength quenched and tempered steel weld joints prepared by K-TIG and GMAW

The aim of this investigation was to compare the strength, ductility and strain distribution during tensile testing of High Hardness Armour (HHA) and Rolled Homogenous Armour (RHA) in a welded configuration, using a range of different welding procedures. Gas metal arc welding (GMAW) using austenitic filler, GMAW using ferritic filler and Keyhole-Tungsten Inert Gas (K-TIG) were investigated. The results of cross weld joint tensile tests exhibited both lower strength and lower ductility compared to the base metals. Among the three welding techniques, K-TIG resulted in the highest weld metal hardness, the highest strength and the largest ductility. GMAW using an austenitic filler resulted in the lowest strength and the smallest ductility. Digital image correlation (DIC) observation revealed strain localisation within the weld metal for specimens welded by GMAW using the austenitic filler. For specimens welded by GMAW using ferritic filler, the strain localisation occurred within the weld metal and at the interface of heat affected zone and over tempered base metal. For K-TIG welded specimens, the strain localisation was more extended to base metal. It can be concluded that among the three welding techniques used, the K-TIG resulted in the highest strength and ductility. Comparison of HHA and RHA revealed that the starting material had little influence on the tensile performance of the weld for this configuration.

Interfacial reaction and microstructure investigation of 4J36/Ni/Cu/V/TC4 diffusion-bonded joints

Diffusion bonding of 4J36 invar alloy and TC4 titanium alloy was carried out by inserting Ni/Cu/V multi-layer metal interlayer. The results showed that temperature had a significant effect on microstructure and mechanical properties of welded joints. At 890 °C, the joint tensile strength reached maximum value of 249.3 MPa. Fe-Ni solid solution ((Fe,Ni)ss), Cu-Ni solid solution ((Cu,Ni)ss), V-Cu solid solution ((V,Cu)ss) and Ti-V solid solution ((Ti,V)ss) were produced at interfaces of 4J36/Ni, Ni/Cu, Cu/V and V/TC4, respectively, and fracture surfaces of all joints showed dimples of different sizes, which showed that the application of Ni/Cu/V interlayer was an effective method.

Plasma arc welding-brazing of aluminum to copper with SiO2 nanoparticles strengthening

Dissimilar metal of T2 copper and 1060 aluminum alloys were welded by plasma arc welding-brazing method with a lap joint, and SiO 2 nanoparticles were added in the welding pool to control the interfacial intermetallic compounds (IMC). The interfacial microstructure and phase composition of the weld joint were identified by scanning electron microscope (SEM) and electron probe microanalysis (EPMA). IMC formation mechanism, weld joint tensile strength, and IMC nanohardness was also discussed. The results show that after adding SiO 2 nanoparticles, due to the adsorption of the nanoparticles on the copper surface, the total interface energy between the aluminum liquid and the copper substrate would be reduced, and the wetting angle would be reduced. So that the aluminum melts can have better wetting ability, and the barrier effect of SiO 2 nanoparticles formed prevents the further diffusion and reaction of copper atoms and aluminum atoms, and inhibits the growth of the IMC layer to a certain extent. The weld fracture occurred at the aluminum-based material added with nano-SiO 2 , showing typical dimple morphology. The phase with the highest hardness in the IMC layer is CuAl 2 . SiO 2 nanoparticles exist in the CuAl 2 intermetallic compound layer due to the adsorption of nanoparticles.

하이브리드 강화재 적용을 통한 FRP 선박 V 스카프 접합 보수면의 기계적 특성

This paper aims to identify the mechanical properties of the hull plate of fiber reinforced plastics, which occupies 95.5% of the registered domestic fishing vessels for strength improvement after a repair by changing reinforced materials. Under the present legislations, in case of repairing the hull plate of fiber reinforced plastics, localized repair using only V- and X-scarf methods are acknowledged. The existing glass fiber reinforced material was replaced with the hybrid laminated method of carbon and aramid fiber before being applied to repair surface of scarf-processed parent material and by comparing the strength with the existing glass fiber mat and roving combination. The use effect when repairing the hull made of hybrid fiber rather than glass fiber was found. As a result of the repaired hull plate, the hybrid joint type exhibited an overall reduction in tensile joint efficiency rather than the existing resin and glass fiber roving and mat combination. However, in flexural joint efficiency improved in specimen applying aramid fiber hybrid compared to the existing joint method improved by up to 77.4%. A 1:12 scarf joint had a high effect in flexural strength rather than tensile strength. When carbon-aramid fiber was used partially appropriately by replacing the existing glass fiber, joint efficiency improved.

Investigation of Shoulder diameter to Sheet Thickness (D/T) Ratio on Tensile Properties Friction Stir Welded AA2014-T6 Aluminum Alloy Joints

ABSTRACT 2xxx and 7xxx high strength alloy are well suited for components and structures that include a greater strength ratio and are typically used in the fabrication of fuselage, wing skins. AA2014 is hard to join using a fusion welding process because of its good thermal conductivity, oxidation behaviour and low fusion point, which can easily lead to burn through and porosity. To overcome the above difficulty, friction stir welding (FSW) is used. The formation of sound weld depends on process and tool parameters. The tool shoulder is the most predominant factor. About two-third of heat is generated at the interface of tool and sheet. Hence, in this investigation, the influence of the tool shoulder diameter (D) to sheet thickness (T) ratio on the tensile properties of FSW AA2014 joints was analysed. Five tools with varying D/T ratios (2.0, 2.5, 3.0, 3.5 and 4.0) were used. Microstructure and hardness measurement were performed to correlate strength properties of FSW joints. It is found that the joint welded with a D/T ratio of 3.0 disclosed superior joint tensile properties compared to other D/T ratios. It is mainly due to the development of fine-grained structure in stir zone of D/T 3.0 joints.

Investigation of interface microstructure and mechanical properties of rotatory friction welded dissimilar aluminum-steel joints

The objective of this work is to analyse the effect of variations in IMC thickness and microstructure at interface on the mechanical properties, for the RFW joints of Al6061 and mild steel. Rotary friction welding is a solid-state joining process which is advantageous towards joining of dissimilar materials. The rotary friction welding of Al6061 and mild steel is performed at combinations of two rotational speeds (1200 rpm and 1400 rpm) and three feed rates (10 mm/min, 20 mm/min and 30 mm/min). The microstructural characterization, tensile and hardness testing of the joints is performed. A concave joint interface is noticed due to inhomogeneous plastic deformation along the radial direction from center to workpiece periphery. Similarly, inhomogeneous intermetallic compounds formation along the radial direction at the joint interface is observed, with higher intermetallic compound thickness near the workpiece periphery. The grain refinement on Al6061 side of the interface is attributed to the continuous dynamic recrystallization. Dynamic recovery is noticed at the mild steel side. The crack initiates at the IMC rich region near the periphery and follows the IMCs to grow radially inwards. Along the radial direction from periphery to the center, the reduction in IMC thickness and increase in DRX region thickness resists the growth of the crack. Brittle failure is observed in the IMC rich regions near the periphery and ductile failure is noticed near the center. An increase in IMC thickness reduces the joint strength and wider DRX region improves the joint strength. This combination led to the maximum tensile strength for the joints prepared with intermediate feed rate of 20 mm/min. A maximum joint tensile strength of 136 MPa is achieved, which corresponds to 65 % joint efficiency.