Conventional Joint Research Articles

Reactive-Element-Free, Silver-Based Brazes for SOFC Applications

The current go-to braze for SOFC applications is the Ag-CuO reactive air braze (RAB). As with other RAB brazes, the ability to use this braze with ceramic materials (such as yttria stabilized zirconia (YSZ) and oxide-protected stainless steel (SS)) is enabled by a braze component (in this case Cu) reacting with the brazing atmosphere to form a surface oxide that facilitates wetting. [1-3]. Although Ag-CuO provides an easy way to join YSZ and SS for SOFC applications, the insufficient ~45° wetting angle of the conventional Ag-4 wt.% Cu braze [1, 2] often leads to braze joint manufacturing defects (Type I pores). Further, the reduction of CuO during dual atmosphere (H2/O2) SOFC operation results in porosity (Type II pores) that: i) mechanically weaken the braze/SS and braze/YSZ interfaces and ii) facilitates H2invasion into the center of the braze, which in turn, hastens the development of gaseous water pockets within the braze (Type III pores) caused by dissolved oxygen and hydrogen meeting. This poster will present a new method for silver brazing YSZ and SS without the need for reactive air elements. As shown in Figure 1, this procedure (which is performed under SOFC electrode compatible oxygen partial pressures ≥ 1x10-10atm) produces a braze that wets both the YSZ and SS. In addition, this procedure also produces Ag-YSZ bonding which has been shown by Kuhn et. al [4] to have a fracture energy two times higher than conventional Ag-CuO braze joints. It is expected that the elimination of Type I and Type II pores enabled by this new brazing method will increase SOFC braze joint lifetimes.

Letter to the Editor: S. Sreenivasan, S.K. Mishra, K. Dutta. Ratcheting strain and its effect on low cycle fatigue behavior of Al 7075-T6 alloy [Mater. Sci. Eng. A 698 (2017) 46–53

Electromigration will induce polarity effects on the formation and dissolution of intermetallic compounds (IMCs) at the electrodes in conventional solder joints. However, the entire solder joint of a microbump may convert to intermetallic compounds after prolonged current stressing. The present study investigated the growth behavior of intermetallic compounds in a 30 μm height Sn1.8Ag microbump plated on a Cu pillar with or without an intermediate Ni layer when the substrate metallization was either Organic Solderability Preservative-Cu (OSP-Cu) or Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG). The progress of the growth of the intermetallic compounds under a current density of 1.0 × 104 A/cm2 was investigated for up to 300 h. The segregation and growth of the intermetallic compounds revealed by a three-dimensional cross section during current stressing was observed and discussed.

Keyhole refilled friction stir spot welding of aluminum alloy to advanced high strength steel

A keyhole refilled Friction Stir Spot Welding (FSSW) process is developed, which consists of two steps. Regular FSSW is performed in the first step. After that, the tool travels along a circular path to refill the original keyhole. The process is applied for joining aluminum alloy 6061 to Transformation Induced Plasticity (TRIP) steel. It increases the joint strength by 56.33% compared with that of conventional FSSW joints. A ductile failure mode is observed. The process can be implemented in any universal CNC machine and needs only one simple FSSW tool. An additional pure circular path welding process shows the enhanced performance of the keyhole refilled FSSW joints relies on three bonding mechanisms: the refilled original keyhole, the increased bonding area between steel and aluminum as well as the hook structure generated from the regular FSSW process. Three distinct layers of grain structures can be observed on the hook, which reveal the material flow pattern during the process.

Encrypted Color Barcode Using Tree-Structure Joint Stereo Coding

In this study, we propose color barcodes using tree-structure joint stereo coding (TJSC). TJSC is a method that combines sets of tree-structure coding channels. Optimum pairs of reference channels are searched by using vector similarity to form channel pairs. TJSC is expected to improve the compression ratio by 6% on average when compared to the conventional joint stereo coding methods. In this study, we propose high capacity color barcodes with bit data arranged in multilayers that provide color information to each layer. As both tree-structural and coding information are generated during coding by TJSC, encrypted color barcodes can be generated by generating a decoding key of the tree-structural information. The color barcodes proposed in this study are expected to be accepted as a new printing medium that employs an information protecting function and uses an electronic medium with a high security function.

Effects of nano-SiC particles on the FSSW welded AZ31 magnesium alloy joints

The microstructure of nano-SiC enhancing friction stir spot welding (FSSW) joint with dwell time of 3 s was characterised by an onion ring structure which consisted of alternate SiC-free zones and SiC-rich zones where SiC particles refined the grains. However, onion ring structure disappeared and SiC particles dispersed homogeneously when dwell time was 5 s. The microhardness of stir zone (SZ) and tensile shear load of SiC enhancing FSSW joint were higher than those of conventional FSSW joints. After heat treatment at 200°C for an hour, grains of the SZ grew substantially and coursed reduction in mechanical properties of joints, while grain size of SZ and tensile shear load of SiC enhancing joint was invariant but the microhardness of SZ increased.

Optimization of vibratory welding process parameters using response surface methodology

The current investigation was carried out to study the effect of vibratory welding technique on mechanical properties of 6 mm thick butt welded mild steel plates. A new concept of vibratory welding technique has been designed and developed which is capable to transfer vibrations, having resonance frequency of 300 Hz, into the molten weld pool before it solidifies during the Shielded metal arc welding (SMAW) process. The important process parameters of vibratory welding technique namely welding current, welding speed and frequency of the vibrations induced in molten weld pool were optimized using Taguchi’s analysis and Response surface methodology (RSM). The effect of process parameters on tensile strength and hardness were evaluated using optimization techniques. Applying RSM, the effect of vibratory welding parameters on tensile strength and hardness were obtained through two separate regression equations. Results showed that, the most influencing factor for the desired tensile strength and hardness is frequency at its resonance value, i.e. 300 Hz. The micro-hardness and microstructures of the vibratory welded joints were studied in detail and compared with those of conventional SMAW joints. Comparatively, uniform and fine grain structure has been found in vibratory welded joints.

Method for inverse synthetic aperture radar imaging of space debris using improved genetic algorithm

Due to the rapid spinning of space debris, its radar echoes have serious migration through range cells and highly non-stationary, time-varying Doppler. With low pulse repetition frequency (PRF) and data missing, conventional joint time–frequency imaging methods such as the Wigner–Ville distribution and the short-time Fourier transform cannot obtain well-focused image. To tackle this problem, this study proposes a novel method for inverse synthetic aperture radar imaging of rapidly spinning space debris using the improved genetic algorithm (GA). Firstly, the authors derive the analytic model of the scattering centres and convert the imaging problem to a parametric optimisation problem. Then, an improved GA method combined with the CLEAN technique is introduced to estimate the model parameters and construct the range and cross-range history of each scattering centre. Finally, high-resolution images at different time instants are obtained. Simulation results have shown that the proposed method achieves high resolution with low computational burden, and it is robust to low PRF and data missing.

A proposal of a beam-to-column joint using shear studs: Finite element methods and experiments

The main aim of this work is to propose an alternative beam-to-column joint for use in building structures. This novel solution consists of a group of headed studs, and has been conceived to connect reinforced concrete floors to steel columns. It is a primary structural joint and it can be used both in conventional concrete beams and in slabs. The alternative approach presented in this work offers significant benefits compared to conventional joints. Some of these advantages are regarding simplicity, industrialization possibilities, shear strength capacity, as well as the excellent weld safety due to the use of headed studs.

Propuesta de unión viga-pilar mediante pernos conectores: Análisis por método de elementos finitos y ensayos experimentales

The main aim of this work is to propose an alternative beam-to-column joint for use in building structures. This novel solution consists of a group of headed studs, and has been conceived to connect reinforced concrete floors to steel columns. It is a primary structural joint and it can be used both in conventional concrete beams and in slabs. The alternative approach presented in this work offers significant benefits compared to conventional joints. Some of these advantages are regarding simplicity, industrialisation possibilities, shear strength capacity, as well as the excellent weld safety due to the use of headed studs.

KITECH-Hand: A Highly Dexterous and Modularized Robotic Hand

This paper presents an anthropomorphic robotic hand named “KITECH-Hand,” along with its kinematic analysis and detailed mechanical features. From a kinematic perspective, the authors particularly focus on the structure of the metacarpophalangeal (MCP) joints of the fingers. The KITECH-Hand adopts a new “roll–pitch”-type MCP structure to replace conventional “yaw–pitch” structures. The proposed structure provides benefits such as enhanced kinematic performance and ease of the mechanical design. Through the kinematic analysis, it is shown that the KITECH-Hand shows remarkably high dexterity, well surpassing that of existing robotic hands with conventional MCP joints. The unique MCP structure also helps modularize the robot at the joint level, which simplifies its mechanical structure and enables the production cost to be reduced. The performance of the KITECH-Hand, including its dexterity feature, was experimentally verified through a series of experiments, which included object in-hand manipulation and a Cutkosky taxonomy test.

Nanoparticle/solder hybrid joints for next-generation power semiconductor modules

The properties of hybrid joints between SiC chips and direct-bond Cu (DBC) plates, which were composed of Cu nanoparticles and eutectic Bi-Sn solder particles, have been examined. The produced bonding layer contained metallic Cu, Cu-Sn compounds, and metallic Bi species. The interfacial region of the bonding layer along both the SiC chip and DBC plate was formed by wetting of Bi. The hybrid joint exhibited >30MPa of bonding strength without applying high pressure. The bonding strength is higher than that of conventional Cu nanoparticle joints, and exhibited a lower dependence on the need for additional pressure during firing. The bonding strength was also higher than that of Pb-based solder joints measured at temperatures as high as 498K, although it decreased with the testing temperature. The obtained results indicate that the proposed hybrid bonding method enables a low pressure process of soldering and results in a high heat resistance of nanoparticle joints, which is required for packaging next-generation power semiconductor modules.

Compliant thin-walled joint based on zygoptera nonlinear geometry

This paper introduces a Compliant thin-walled joint (CTWJ) that expands the group of existing compliant joints. The CTWJ design is based on the nonlinear geometry of the zygoptera animal. With a thin-walled structure, the CTWJ allows a considerably large range of motion in the x-and-y axes. In addition, the thin-walled structure is then filled by polydimethylsiloxane material to reinforce the stiffness of the CTWJ. First, design of experiment methodology is used for the sensitive analysis of the width and the thickness to the strain of joint. The range of motion, the strain, the buckling behavior, and the first natural frequency of CTWJ are investigated via finite element analysis and experiments. The behavior of the CTWJ is subsequently compared with the conventional compliant joints to realize the efficient performance of the CTWJ. The results revealed that the CTWJ has a range of motion and strain energy larger than those of traditional compliant joints. Finally, an example of vibration isolator is modeled by using the CTWJ as planar spring. It is believed that the CTWJ has a great potential for the development of compliant mechanisms in terms of large range of motions in mutliple axes.

Verification of Strength of the Welded Joints by using of the Aramis Video System

Abstract In the paper are presented the results of strength analysis for the two types of the welded joints made according to conventional and laser technologies of high-strength steel S960QC. The hardness distributions, tensile properties and fracture toughness were determined for the weld material and heat affect zone material for both types of the welded joints. Tests results shown on advantage the laser welded joints in comparison to the convention ones. Tensile properties and fracture toughness in all areas of the laser joints have a higher level than in the conventional one. The heat affect zone of the conventional welded joints is a weakness area, where the tensile properties are lower in comparison to the base material. Verification of the tensile tests, which carried out by using the Aramis video system, confirmed this assumption. The highest level of strains was observed in HAZ material and the destruction process occurred also in HAZ of the conventional welded joint.

Experimental behavior of beam-column joints made with EAF concrete under cyclic loading

This paper presents the results of an experimental campaign carried on exterior beam-column joints made with recycled concrete, containing Electric Arc Furnace (EAF) slag as full replacement of coarse natural aggregates. Three real-scale joints, one made with a conventional mix and two with EAF slag concrete, were tested under horizontal reversed cyclic loading, applied in quasi-static conditions. The three joints exhibited the same failure mode, which involved shear failure of panel joint and yielding of beams steel bars. This failure mode is indeed mainly influenced by concrete strength and was chosen to better highlight the influence of EAF slag use. Similar hysteresis response, stiffness decay, dissipated energy and ductility were obtained both with the conventional and EAF concrete joints. Results demonstrate that the specimens made with EAF concrete are able to attain higher loads than the conventional specimen at the same imposed displacement, and that the panel joint is less damaged.

Design and analysis of a 3-link micro-manipulator actuated by piezoelectric layers

The purpose of this paper is to design and analyze a 3-link micro-device proposed as a micro-manipulator. This micro-manipulator includes 3 micro-beams as links connected to one another with no conventional or flexural joints. While the structure of the micro-manipulator is monolithic, end-effector workspace is achieved through deflection of links which is actuated by piezoelectric layers. By combining static analysis of the links through a multilayer piezoelectric beam model and kinematic analysis of the micro-manipulator, inverse kinematic has been solved utilizing the Taylor series expansion technique and the perturbation method. The obtained results through the present model reveal that the end-effector can provide a workspace of several microns with nano-accuracy. The required piezoelectric voltage for certain end-effector displacement was evaluated, and the error of inverse kinematic was investigated. A finite element model was also constructed to evaluate micro-manipulator behavior. The results show there is a good agreement between the analytical model and the finite element method. Avoiding complex geometry, the micro-manipulator offers a simple structure with a more feasible manufacturing process while it provides acceptable workspace for the end-effector with high accuracy.

Current induced segregation of intermetallic compounds in three-dimensional integrated circuit microbumps

Electromigration will induce polarity effects on the formation and dissolution of intermetallic compounds (IMCs) at the electrodes in conventional solder joints. However, the entire solder joint of a microbump may convert to intermetallic compounds after prolonged current stressing. The present study investigated the growth behavior of intermetallic compounds in a 30 μm height Sn1.8Ag microbump plated on a Cu pillar with or without an intermediate Ni layer when the substrate metallization was either Organic Solderability Preservative-Cu (OSP-Cu) or Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG). The progress of the growth of the intermetallic compounds under a current density of 1.0 × 104 A/cm2 was investigated for up to 300 h. The segregation and growth of the intermetallic compounds revealed by a three-dimensional cross section during current stressing was observed and discussed.

On the Process-Related Rivet Microstructural Evolution, Material Flow and Mechanical Properties of Ti-6Al-4V/GFRP Friction-Riveted Joints

In the current work, process-related thermo-mechanical changes in the rivet microstructure, joint local and global mechanical properties, and their correlation with the rivet plastic deformation regime were investigated for Ti-6Al-4V (rivet) and glass-fiber-reinforced polyester (GF-P) friction-riveted joints of a single polymeric base plate. Joints displaying similar quasi-static mechanical performance to conventional bolted joints were selected for detailed characterization. The mechanical performance was assessed on lap shear specimens, whereby the friction-riveted joints were connected with AA2198 gussets. Two levels of energy input were used, resulting in process temperatures varying from 460 ± 130 °C to 758 ± 56 °C and fast cooling rates (178 ± 15 °C/s, 59 ± 15 °C/s). A complex final microstructure was identified in the rivet. Whereas equiaxial α-grains with β-phase precipitated in their grain boundaries were identified in the rivet heat-affected zone, refined α′ martensite, Widmanstätten structures and β-fleck domains were present in the plastically deformed rivet volume. The transition from equiaxed to acicular structures resulted in an increase of up to 24% in microhardness in comparison to the base material. A study on the rivet material flow through microtexture of the α-Ti phase and β-fleck orientation revealed a strong effect of shear stress and forging which induced simple shear deformation. By combining advanced microstructural analysis techniques with local mechanical testing and temperature measurement, the nature of the complex rivet plastic deformational regime could be determined.

Fatigue performance of adhesively bonded single lap joints with non‐flat sinusoid interfaces

AbstractThe role of a sinusoid interface shape on the load bearing capacity and fatigue life of adhesively bonded single lap joints (SLJs) was investigated numerically and experimentally. Aluminium adherends with wavy interfaces were tested under both quasi‐static and fatigue loading conditions. The experimental results showed that the non‐flat SLJs were indeed much stronger than the conventional flat joints. In order to fully demonstrate the advantage of the non‐flat sinusoid SLJ over the conventional SLJ, comparative fatigue tests with different loading levels were performed to determine the durability performance of the SLJs with non‐flat interfaces. The experimental results revealed that the non‐flat SLJ had considerably higher fatigue life than the conventional lap joint.

FSW of aluminum AA5754 to steel DX54 with innovative overlap joint

An innovative overlap joint concept was tested to evaluate the quality improvement of welds between aluminum alloy AA5754-H22 (2 mm) and steel DX54 (1.5 mm). The innovation is a wave-shaped interface produced on the steel being directly processed by the tip of the probe, generating localized heat, extensive chemically active surfaces, and additional mechanical interlocking. Welds with different parameters were evaluated by metallographic analysis and mechanical tests. The best set of parameters was then implemented in a conventional overlap joint, plus in two- and three-passes welding, with the innovative overlap joint concept, to evaluate the effect on microstructure and mechanical efficiency. With a single-pass weld, the new concept presented lower strength in tensile shear tests, but higher strength in peeling tests. The main mechanism governing this behavior was the reduction of effective thickness in the aluminum alloy sheet, due to the flow of steel into the aluminum alloy. The characterization and distribution of the intermetallic compounds were evaluated via SEM-EDX. The two-passes weld resulted in the best strength values in tensile shear tests, reaching about 50% of the ultimate tensile strength of the aluminum alloy base material.

誘発材に異形鉄筋を用いたRC造耐震壁縮小試験体の長期ひび割れ性状

This paper describes the result of long-term crack-inducing experiment on half-scaled four RC wall specimens. Compared to conventional crack control joints, the proposed crack control joints with crack-inducing bars could contribute to inducing shrinkage cracks within the joints more uniformly. As a result, the maximum crack width in the joints with crack-inducing bars was smaller than that in the conventional joints. A crack width estimation method proposed by Ohno et al. could accurately estimate the maximum crack widths of the specimens.