Mechanical Strength Of Joints Research Articles

Active brazing of YAG crystal and Cu using AgCuInTi filler: Microstructure and joint properties

YAG crystal is successfully brazed with Cu using active filler AgCuInTi. The microstructure and mechanical properties of the brazed joints are investigated. The effects of brazing time and holding time on the interfacial microstructure and joint mechanical strength are studied. The joints brazed at 600 °C for 20 min are found to show the highest shear strength of 38.3 MPa, reaching 79.6% of the YAG base material.

The Energy Consumption of the Process of Joining Steel Sheets with the Use of Clinching With and Without an Additional Rivet, and Analysis of Sheet Deformation and Mechanical Strength of Joints

AbstractThis paper presents the results of research on the impact of the use of different tools and the shape of the additional rivet, on the geometric quality of the joint, the energy consumption of the forming process, the distortion of the steel samples, and the load capacity of the joints. The tests were carried out for DX51D steel sheets with a thickness of 1.5 [mm] joined by using three different sets of tools. A steel rivet with a hardness of 400HV1 and various shapes was used for the tests. In addition to the full rivet, two types of rivet were used, the first with a through hole and the second with a depth of hole of 3 [mm]. The holes in the rivet had different diameters: 1.0, 1.5, 2.0 and 2.5 [mm]. The influence of changing the shape of the rivet (hole and its diameter) on the change in forming force and energy consumption of the joining process was analyzed. The lowest forming force was achieved for a rivet with a through hole and a hole diameter of 2.5 [mm]. The lowest joint forming force was obtained for the die with movable segments. For joints made with three tool arrangements and a series with a modified rivet, the amount of sheet metal deviation was analyzed. Of the three cases of arrangement of tools used to form the joint, the largest deviation of the sheets occurred at the clinch joint formed with a solid round die. In the case of a series of clinch-rivet joints with a modified rivet, the greatest deviation of the sheets occurred for the rivet with a hole of 1.5 [mm]. Changes in the geometric structure of the joint were also studied, and changes in the surface of the sheets in the joint area were observed. The highest value of the interlock in the joint was obtained when a solid rivet was used in the clinch-riveting technology. The strength of the joints was also identified in the lap shear test and the energy consumption at failure was determined. The use of a rivet increased the maximum load capacity to almost twice that of the clinch joint. Graphical abstract

Thermographic procedure for the assessment of Resistance Projection Welds (RPW): investigating parameters and mechanical performances.

This study presents a non-destructive testing (NDT) thermographic procedure for assessing the quality and mechanical strength of resistance projection welded (RPW) joints with rectangular embossments. We analysed twelve RPW joints by systematically varying process parameters based on a factorial design. These joints underwent flash thermography followed by mechanical tests to evaluate the maximum breaking force (Fmax). Significant statistical correlations between process parameters (time and force) and Fmax were established. Furthermore, we found a correlation (p-value 0.86) between the optically measured fused region and Fmax. Subsequently, we developed a pulsed phase thermography-based procedure for non-destructively measuring the fused region, resulting in an average difference of approximately 4% compared to optical measurements. An empirical linear relationship was derived to correlate the welded area obtained by thermal data with Fmax, enabling the estimation of mechanical joint strength through non-destructive pulsed thermography. This research offers a promising approach for assessing the mechanical integrity of RPW joints using thermal imaging techniques.

Crack-Free Joining of High-Strength AA7055 Sheets by Friction Based Self-Piercing Riveting with the Aid of Numerical Design

Unique friction-based self-piercing riveting (F-SPR) was employed to join high-strength, low-ductility aluminum alloy 7055 for lightweight vehicle applications. This study aimed to maximize the joint strength of the AA7055 F-SPR joint while avoiding cracking issues due to low ductility at room temperature. A fully coupled Eulerian–Lagrangian (CEL) model was employed to predict the process temperature during F-SPR, and the temperature field was then mapped onto a 2D axisymmetric equivalent model for accelerated numerical analysis. The geometry, dimensions, and material strength of the rivet, as well as the depth of the die cavity and plunging depth, were investigated to enhance joint formation. Also, a static finite-element analysis model was developed to predict and analyze the stress distribution in the rivet under different mechanical testing loading conditions. Overall, the numerical model showed good agreement with the experiment results, such as joint formation and mechanical joint strength. With the aid of virtual fabrication through numerical modeling, the joint design iterations and process development time of F-SPR were greatly reduced regarding the goal of lightweight, high-strength aluminum joining.

Effect of High-Temperature Tempering on Microstructure and Mechanical Strength of Laser-Welded Joints between Medium-Mn Stainless Steel and High-Strength Carbon Steel

The strengthening effect due to high-temperature tempering (HTT) at 700 °C on the microstructure and mechanical properties of welded joints between medium-Mn stainless steel (MMnSS) and high-strength carbon steel (CS) was studied. The microstructure of the weldments was investigated using Laser and scanning electron microscopes. An Electron probe microanalyzer (EPMA) was used to assess quantitatively the elemental distribution profiles of alloying elements within the weld zone. The strengthening precipitates induced during welding and HTT were characterized by transmission electron microscopy (TEM). Uniaxial tensile tests and microindentation hardness (HIT) measurements of the weld joints were conducted to evaluate the strengthening effect. Fully fresh-martensite and fine-tempered martensitic structures were promoted in the as-weld and HTT processes, respectively. The HTT structure exhibited a remarkable improvement in mechanical properties (a better combination of yield and tensile strength together with moderate ductility) compared to its weld counterpart. TEM investigation revealed that various types of precipitates have been promoted in the structures of the weld and HTT, e.g., nanosized vanadium and chromium carbides. It is apparent that the proposed HTT of the joints is an effective treatment for improving the mechanical properties due to inducing the formation of fine interphase precipitates, resulting in enhanced mechanical strength of the joints.

Enhancement of strength in laser-joined Al-TRIP and Si-TRIP steels: Microstructural insights and deformation analysis

This study highlights the strengthening mechanisms observed during the metal joining of high-strength grade steels (Al-TRIP and Si-TRIP) by providing a concise investigation of microstructural features, mechanical strength evaluation, and employing Finite Element Method (FEM) analysis to understand the deformation behaviour in the joint. The base metals (BMs), Al-TRIP and Si-TRIP are cold-rolled sheets with thicknesses of 0.9 mm and 1.3 mm, respectively. Al-TRIP contains 2.4 wt% Al, while Si-TRIP contains 1.5 wt% Si. The Al-/Si-TRIP joint was processed by laser welding at low energy input 24 J/mm. Electron backscattering diffraction and transmission electron microscopy extensively characterized the microstructural features in the fusion zone (FZ) and heat-affected zone (HAZ) to study strengthening mechanisms induced by welding. Uniaxial tensile tests examined joint mechanical strength, while microindentation hardness (HIT) measurements evaluated mechanical response in the weld zones. The FZ showed a fully martensitic structure, while the HAZs displayed refined grains. Ultrafine-grained structures with an average size of 1 μm were observed in the HAZs, resulting in higher HIT hardness values (∼6.7 GPa) compared to the FZ (∼6.3 GPa). Interestingly, the mechanical tensile properties of the joint were unaffected as failure occurred in the thinner Al-TRIP steel. Finite Element Method (FEM) analysis simulated the tensile testing, revealing localized plasticity in the thinner Al-TRIP and explaining the observed fracture.

Experimental investigation of the loading speed effects on the performances of ultrasonically welded PA66/glass fabric composites

These past decades, the ability of thermoplastic composites to be welded has been of great interest, with numerous studies investigating the process and mechanical strength of joints for quasi-static loadings. The present study aims to determine the loading speed influence on the behaviour of these structures, as crashworthiness is of tremendous interest in the transport industry for safety issues. The polyamide-based composite used in this work is sensitive to strain rate, which may influence the interface and the entire structure's behaviour. Tensile tests were performed on single lap joint specimens for loading speeds from 1.2 mm min−1 to 7 m s−1, considering several substrate orientations. Loading speed influences the lap shear strength for the different configurations: increasing loading speed induces a performance enhancement of 11.2%–22.9%. This phenomenon is caused by the matrix strain rate sensitivity, which stiffens and strengthens the substrate shear behaviour and the welded joint behaviour. Finally, the fractography analysis confirms that fracture mechanisms observed are similar for each loading speed tested with primarily fibre/matrix debonding. Therefore, improvement in the welded structures' performance is due to the mechanical performance of its constituents and their influence on the interfacial strength.

Microstructure evolution and mechanical property strengthening mechanisms of Cu/Cu NPs/Cu joint fabricated by ultrasonic spot welding

Ultrasonic spot welding, as a high strain rate plastic deformation process, utilizes the high frequency sliding between the metal sheets to generate a solid-state joining. For the ultrasonic spot welded Cu/Cu joint, even with the good metallurgical bonding at the welding interface, it couldn't obtain high T-peel strength and maintain quite high T-peel load bearing capacity before failure. In order to enhance the T-peel strength and bearing capacity, Cu nanopaticles (NPs) interlayer was screen-printed on the Cu sheet surface that was to be welded. It was beneficial to enhance the temperature at the welding interface and the degree of dynamic recrystallization, obtain the nano-scaled equiaxed grains with random orientations at the welding interface, and change the microstructure evolution pattern along the weld thickness. These results are key factors to the improvement of the joint mechanical strength. In comparison with the Cu/Cu joint, the T-peel strength of the Cu/Cu NPs/Cu joint (471.7 N) was increased by 69.4%, the displacement (0.97 mm) corresponding to the T-peel strength was enhanced by 42.7%, the obviously increased fracture energy was achieved, and quite high T-peel load bearing capacity could be maintained after exceeded the T-peel strength. The mixed failure modes of brittle cleavage and quasi-cleavage as well as shallow dimples fracture occurred in the Cu/Cu joint. However, the failure mode for the Cu/Cu NPs/Cu joint was turn into the micro-void coalescence.

Joining of SiC ceramics by combining NITE-SiC interlayer and its thickness control

Combined with the thickness control of interlayers (∼10 µm and ∼60 µm), SiC nano-powders with Al2O3-Y2O3-MgO-CaO additive (NITE-SiC) were used as the joining materials to achieve the low-temperature joining of SiC ceramics. Some residual pores were observed in the interlayer with a thickness of ∼60 µm after joining at 1650 ℃, and the shear strength of SiC joints measured was 39.3 ± 5.5 MPa. Observations showed the fracture of joints occurred at the interlayer. When the thickness of the interlayer decreased to ∼10 µm, no cracks or porosity were observed at the interface region after joining at 1650 ℃. The shear strength of SiC joints increased to 69.5 ± 8.9 MPa, and the fracture originated from the matrix. The results demonstrated using NITE-SiC with Al2O3-Y2O3-MgO-CaO additive as the joining layer and reducing the thickness of the interlayer could lower the joining temperature and significantly improve the mechanical strength of joints.

Joining of Al2O3 ceramic to Cu using refractory metal foil

Joining of Al 2 O 3 ceramic to Cu has been conducted with Ag-26.7Cu-4.5Ti braze and refractory metal (W or Ta) foil. The interfacial microstructure in the joint with W foil is similar to that with Ta foil. The joining region in the joint consists of a reaction zone, braze zone I, refractory metal layer and braze zone II. The reaction zone of Cu 3 Ti 3 O with a thickness of about 5 μm develops close to Al 2 O 3 side due to the reactions of Ti and Cu in the braze with Al 2 O 3 substrate. The braze zones I and II are mainly composed of Ag- and Cu-based solid solutions. For the joint with W foil, the adsorption of Ti at the braze/W interfaces followed by the Ti diffusion into W foil occurs, whilst slight dissolution and diffusion of Ta into the brazes take place in the joint with Ta foil. The average shear strengths of joints with W and Ta foils are much higher than those without refractory metal foil, indicating the contribution of the refractory metal foil to the improvement of joint mechanical strength. Introduction of refractory metal foil in Al 2 O 3 /Cu joining is beneficial for the shift of joint residual stress distribution and the decrease of stress concentration in the joint since the coefficient of thermal expansion (CTE) of refractory metal layer approximately approaches that of Al 2 O 3 . Furthermore, a slight thickness increase of the Cu 3 Ti 3 O reaction zone in the joint with refractory metal foil may also give rise to the joint strength promotion.

Retracted: “Evaluation of the Structural Integrity of Bell–Spigot Joints in Steel Gas Pipelines” [ASME Journal of Pressure Vessel Technology, 2022, 144(2), p. 021801; DOI: 10.1115/1.4052210

Abstract The most common joining method in steel gas pipelines is welding; however, this method involves time-consuming, expensive manufacturing and assembly processes to ensure quality in operation. Bell–Spigot joints, which work by mechanical interference, have started to be used as an alternative joining method in steel pipes. Its use has increased due to its reduced assembly time and fewer postassembly inspection requirements. In this paper, the structural performance of Bell–Spigot joints in 16-in. steel pipe API 5 L X70 with fusion bonded epoxy coating for Natural Gas transmission pipeline are evaluated experimentally and by modeling. Test pieces were taken from the gas pipeline after 3 years of operation. Then, tensile pull-out and bending with hydrostatic pressure tests were performed to replicate operating conditions. Deformations, displacements, and the potential presence of leaks were monitored. Experimental results were compared with a finite element method model. Finally, an analytical model for the calculation of stresses and strains in the joint system's components was developed. It was determined that the tightness of the joint depends mainly on the radial interference and the interference length. A higher safety factor can be obtained at the Bell–Spigot joint than the base pipeline by optimizing the selection of joint design variables and the service loading conditions. If the interference pressure is lower than half of the operation pressure, the joint's mechanical strength will be higher or equal that the base pipe. Under interference pressure at operating pressure conditions, the most vulnerable component is the Bell due to the increased stresses acting on it, while the operating pressure relieves the stresses on the Spigot due to the interference pressure acting in the opposite direction. Under combined loading of internal pressure and external bending force, the base pipeline is the most susceptible component to fail. Therefore, the use of Spigot–Bell joints reduces assembly times and costs in steel gas pipelines while providing a safe and reliable joint under operating conditions.

Thermal Conductivity Measurement Method for the Thin Epoxy Adhesive Joint Layer

Epoxy adhesives, particularly for non-conductive pastes, are used in 3D chip-stack flip-chip packages to reinforce the mechanical strength of joints. Although the thickness of the adhesive layer is relatively small, its thermal conductivity is known to have a major effect on the heat dissipation behavior of chipstack packages. Because conventional thermal conductivity measurement methods such as the laser flash method are based on the bulk specimens having thicknesses greater than several mm, they are limited in their ability to measure the thermal conductivity of thin adhesive layers between silicon dies. In this study, a modified guarded hot-plate method is proposed using standard joint layer samples of known thermal conductivity, and the measurement results are compared with those of the laser flash method. Results showed that, based on a constant heat flux from heat source to heat sink, the temperature difference at both sides of the joint layers was proportional to the thermal resistivity of the joint layer materials. The thermal conductivity of the under-test joint layer could therefore be determined from the thermal conductivity spectrum of the known samples using a graphical method. Although the measured values by the modified guarded hot-plate method were slightly higher than those derived from the laser flash method due to the thickness effect, it was concluded that the modified guarded hot-plate method could be a practical method in measuring the thermal conductivity of thin adhesive joint layers.

Mechanical Properties of Adhesive Joints Made with Pressure-Sensitive Adhesives

The paper aims to determine the mechanical properties of the adhesive joints made with acrylic pressure-sensitive adhesives. Two types of double-sided acrylic pressure-sensitive adhesive tapes are used. Three construction materials are used to prepare the adhesive joints: structural steel sheet (C45), aluminium alloy sheet (EN-AW 5754), and titanium sheet (Grade 2). Strength tests of adhesive joints made with the pressure-sensitive adhesive tapes are carried out both after conditioning time at room temperature (23 °C) and subjected to thermal shocks (500 cycles: +60 °C / –40 °C). Strength tests are carried out based on the DIN EN 1465 standard on a Zwick/Roell Z150 testing machine. The main conclusion from the tests carried out was the positive effect of thermal shocks on the mechanical strength of joints bonded with pressure-sensitive adhesive tape.

不同复合材料机械连接强度性能对比分析

不同复合材料机械连接强度性能对比分析

Comparison between traditional and alternative biocompatible welding techniques used in orthodontic devices.

To compare the mechanical strength of joints made by conventional soldering with those made by alternative, more biocompatible, methods (spot, tungsten inert gas [TIG] and laser welding), and to compare the microstructural morphology of wires welded with these techniques. In vitro, laboratory study. Forty stainless-steel wire segments with 0.8-mm diameter were joined by silver soldering, spot, laser and TIG welding. Ten specimens were produced for each one. Tensile strength test was performed 24 h after welding on the Emic DL2000™ universal testing machine, using a load cell of 1000 N with a crosshead speed of 10 mm/min. The highest tensile strength mean values were obtained with silver soldering (532 N), next were laser (420 N), spot (301 N) and TIG (296 N) welding. Statistically significant differences were observed between the groups; the Dunn post-hoc test revealed differences between laser and spot welding (p=0.046), laser and TIG (p = 0.016), spot and silver (p <0.001), and silver and TIG (p <0.001). Laser welding strength is high, and comparable to silver welding. Spot and TIG techniques present comparable and significantly lower strengths. The four methods presented resistance values compatible with orthodontic use. The microstructural morphology is different for each technique. The association between the mechanical performance and the microstructure evaluation shows that laser presented the highest quality joint.

Enhanced strength and ductility in dissimilar friction stir butt welded Al/Cu joints by addition of a cold-spray Ni interlayer

Abstract In this study, commercially pure Cu plate was cold sprayed with a 90 μm thick Ni coating and friction stir welded to an Al 6061 alloy plate in a butt joint configuration. The joint interface was characterized by optical microscopy and scanning electron microscopy and was compared to the joint without a Ni coating. The results show that the joint mechanical strength was significantly improved with a Ni interlayer. The average peak stress and the elongation of the joint with Ni coating reached 190 MPa and 14 %, respectively. The formation of intermetallic compounds at the interface was clearly suppressed with a Ni coating compared to the directly welded sheets.

Automatic system design for flange surface quality inspection with a bionic motion-vision paradigm

ABSTRACT Flanges are used to make connections. Their surface quality determines the joint mechanical strength and characteristics, while their defects lead to device failure. Complex surfaces and surface flaws pose challenges to automatic optical inspection (AOI) and conventionally, visual and manual inspection is employed. The aim of this study is to develop an automatic defect detection system for the flange surface, an operational pipeline with a bionic motion-vision mechatronic system, which mimics manual detection. Three methods are proposed as part of the system. The visual-detection-simulating sensing method, mimicking humans defect detection under horizontal light, is proposed to produce images of the defects on multifaceted reflective-metal surfaces. The human-operation simulation method, mimicking human defects detection under different light angles, is designed to optimize the visual perspective angles. The intelligent decision mechanism, mimicking the way human attention is focused, is proposed to solve complex pattern recognition problems. Based on this approach, an automated inspection machine, including posture adjustment, lighting, and imaging, for flange surface quality is developed. An intelligent inspection system with defect recognition algorithms is deployed. The smallest width of surface defects detected is 0.1 mm. The proposed apparatus design paradigm provides a general solution for flaw-detection on non-planar, complex surface workpieces.

Numerical and Experimental Analysis of Stacking Sequences Effects in Composite Mechanical Joints under Impact Loadings

Composite structures in the field of advanced and modern structures in engineering design and according to high specification of composite materials such as high strength to weight ratio use in various industries such as aerospace, marine. One of the most important fields that Researchers have paid less attention to that is to investigate the effect of stacking sequence on the strength of mechanical joints under impact loading. In view of changing the mechanical properties of composite materials by changing the arrangement of layers, in this study, the effect of different orientation of layers on the strength of pin joints in glass-epoxy composites under low-velocity tensile impact has been investigated. Using the Abaqus software and the finite element method, the impact simulation and the force applied to the mechanical joint were analyzed. To evaluate the simulations, the results of the finite element method have been compared with the experimental results. By observing the results, the introduced finite element model is well-considered and is well-matched with the result of the experimental dataset, which made it a valuable tool for predicting the strength of multi-layer composite materials under impact loadings. Using the results of the model, one can analyze the distribution and type of stress and strain in each layer of composite.

Investigations on the strength of mechanical joints prepared from carbon fiber laminates with addition of carbon nanotubes

The present work is to examine the failure modes and failure loads in pin joints prepared from carbon/epoxy composite laminates with addition of multiwalled carbon nanotubes (MWCNT) as nanofillers. The effect of MWCNT in the carbon/epoxy composites was studied by adding 0.1 to 0.5 wt.% content in the epoxy resin. The maximum tensile strength was observed upto 0.3 wt.%, which is due to the enhanced interfacial bond strength and the efficient stress transfer between the stiff MWCNT and soft polymer matrix through refined polymer/MWCNT interface. The nanocomposite laminates for pin joints were prepared using optimised 0.3 wt.% of MWCNT. The different geometric combinations of width to diameter (W/D) and edge to diameter (E/D) ratios were varied from 2 to 5, respectively. The numerical analysis was performed using Hashin damage criteria along with progressive damage analysis to compare the predicted failure loads with the experimental results.

Joint properties enhancement for PbTe thermoelectric materials by addition of diffusion barrier

PbTe-based alloys are potential mid-temperature thermoelectric materials due to their excellent thermoelectric properties. Formation of intermetallic deteriorates mechanical joint strength and thermoelectric performance as well. In the present work, interfacial reaction, electrical and mechanical behaviors for both p- and n-PbTe joints with an addition of diffusion barrier layer are investigated. The results show that Co–P is a suitable barrier layer for PbTe-based thermoelectric devices with Cu or Ni electrode to inhibit the growth of massive intermetallic compound formation caused by fast interdiffusion in Cu/p-PbTe joints and melting of the joints in Cu/n-PbTe joints. Directly bonded Ni electrode induced formation of needle-like IMCs and disintegration of the electrodes in p- and n-PbTe modules respectively. Severe interfacial problems were overcome by adding a Co–P diffusion barrier, mechanical strength was improved. In addition, the Co–P layers enhanced the thermoelectric properties of the joints. The addition of the barrier layer increased 27% and 109% of the zT for p- and n-type joints, respectively.