Joint Interface Research Articles

Teachers and Students Attitude and Challenges on Applications of ICT Tools

Online learning environments can be described as online domains that permit synchronous, joint interface with teachers and students; they also provide some asynchronous learning resources for students, according to Siddiqui's information bank of educational technology. Additionally, it offers a crucial understanding of computer-based learning. Online instruction uses technology and the internet to facilitate learning and teaching between faculty and students. The objective of the study is to find out the teachers and students’ attitude and challenges on applications of ICT tools

Influence of Microstructure and Mechanical Properties of Dissimilar Rotary Friction Welded Inconel to Stainless Steel Joints.

The present study aims to evaluate the microstructure, grain size, and mechanical properties of the dissimilar AISI 316L/Inconel 718 (IN 718) rotary friction welded joints under both the as-welded and post-weld heat treatment (PWHT) conditions. Because of reduced flow strength at elevated temperatures, the AISI 316L and IN 718 dissimilar weldments exhibited more flash formation on the AISI 316L side. At higher rotating speeds during friction welding, an intermixing zone was created at the weld joint interface due to the material softening and squeezing. The dissimilar welds exhibited distinctive regions, including the fully deformed zone (FDZ), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and the base metal (BM), located on either side of the weld interface. The dissimilar friction welds, AISI 316L/IN 718 ST and AISI 316L/IN 718 STA, exhibited yield strength (YS) of 634 ± 9 MPa and 602 ± 3 MPa, ultimate tensile strength (UTS) of 728 ± 7 MPa and 697± 2 MPa, and % elongation (% El) of 14 ± 1.5 and 17 ± 0.9, respectively. Among the welded samples, PWHT samples exhibited high strength (YS = 730 ± 2 MPa, UTS = 828 ± 5 MPa, % El = 9 ± 1.2), and this may be attributed to the formation of precipitates. Dissimilar PWHT friction weld samples resulted in the highest hardness among all the conditions in the FDZ due to the formation of precipitates. On the AISI 316L side, prolonged exposure to high temperatures during PWHT resulted in grain growth and decreased hardness. During the tensile test at ambient temperature, both the as-welded and PWHT friction weld joints failed in the HAZ regions of the AISI 316L side.

Correlation of surface and interfacial temperature during differential ultrasonic spot welding

Ultrasonic spot welding (USW) has become an attractive joining method for thermoplastic polymers (TP) and thermoplastic matrix composites (TPMC). In the USW process, the material to be joined is subjected to mechanical vibrations of high frequency, causing intermolecular and surface friction which heat and melt the material at the joint interface. The interface resolidifies, resulting in a joint between two materials. In USW, it is necessary to focus the mechanical vibrations at the required weld location. A common method to accomplish this is to incorporate an energy director (ED) at the interface between materials to melt preferentially. However, incorporating EDs complicates the manufacturing process, particularly for large constant thickness polymer sheets. In this work, differential ultrasonic spot welding (DUS) is used which employs a flat horn and anvil of different diameters to initiate frictional heating between laminates at the desired joint location. This work investigates the effectiveness of DUS compared to a more traditional USW setup. Additionally, by measuring temperature at both the surface and the interface during DUS using infrared imaging and a thermocouple (TC), respectively, the driving factors behind the thermal profile of the welding process are examined. The goal of coupling the thermal profile to physical attributes of the DUS process is to eventually determine if variability present in the thermal profile may be tied to well-known joint area and strength variabilities.

Fluid-Fluid Interaction Problems at High Reynolds Numbers: Reducing the Modeling Error with LES-C

We consider a fluid-fluid interaction problem, where two flows (with high Reynolds numbers for one or both of these flows) are coupled through a joint interface. A nonlinear coupling equation, known as the rigid lid condition, creates an extra level of difficulty, typical for atmosphere-ocean problems. We propose a novel turbulence model, NS- -C, from the recently introduced family of LES-C (large eddy simulation with correction) models. Combining it with the so-called geometric averaging (GA) partitioning method, we obtain the NS- -C-GA model that is shown to possess several key properties. First, the preexisting solvers for the subdomains can be used, which is critical, e.g., for atmosphere-ocean applications. Second, the LES-C turbulence models use defect correction to efficiently reduce the modeling error of the corresponding LES models; we demonstrate numerically that the NS- -C model outperforms its LES counterpart, the NS- model. It has also been shown recently that it is favorable for an LES model to have the nonfiltered velocity in the interface terms. The NS- -C-GA model possesses this important property; we also show it to be stable and have optimal convergence properties.

Dislocation behavior in Cu single crystal joints under the ultrasonically excited high-strain-rate deformation

• The interfacial evolution for ultrasonically welded joints was used to clarify the coupling effects of ultrasonic excitation and high-strain-rate deformation. • Transmission Kikuchi diffraction and transmission electron microscopy were used to analyze grain orientation and deformed microstructures simultaneously. • Ultrasonic excitation dramatically weakened the constraint of high-strain-rate and characteristic orientations on dislocation motion. • The first-principle calculation and applied strain-rate analysis were conducted to discuss the preferred deformation mechanism to accommodate the imposed plastic strain. The coupling effects of ultrasonic excitation and high-strain-rate deformation are the core factors for weld formation during ultrasonic welding. However, interfacial deformation behavior still shrouds in uncertainty because of the contradictory features between mutual dislocation retardation caused by severely frictional deformation and ultrasonic-accelerated dislocation motion. [101] and [111]-oriented Cu single crystals which tended to form geometrically necessary boundaries (GNBs) were selected as the welding substrates to trace the uniquely acoustoplastic effects in the interfacial region under the ultrasonically excited high-strain-rate deformation. It was indicated that for a low energy input, micro-welds localized at the specific interface region, and equiaxed dislocation cells substituting for GNBs dominated in the initial single crystal rotation region. As the welding energy increased, continuous shear deformation drove the dynamic recrystallization region covered by equiaxed grains to spread progressively. Limited discrete dislocations inside the recrystallized grains and nascent dislocation cells at the grain boundaries were observed in [101] and [111] joints simultaneously, suggesting that the ultrasonic excitation promoted motion of intragranular dislocation and pile-up along the sub-grain boundaries. The interfacial morphology before and after expansion of recrystallization region all exhibited the weakening of orientation constraint on dislocation motion, which was also confirmed by the similar micro-hardness in joint interface. The first-principle calculation and applied strain-rate analysis further revealed that ultrasonic excitation enhanced dislocation slipping, and enabled dislocation motion to accommodate severe plastic deformation at a high-strain-rate.

Anisotropic AE Attenuation in Mapping of Composite Specimen Progressive Failure under Unconfined Loading

The mapping of failure that uses acoustic emission (AE) is an advanced approach when tracking the location of cracks in rock materials under progressive stress. However, attenuation of the acoustic wave significantly affects the identification of the acoustic source. The isotropic attenuation model suggests a constant attenuation in all rock material directions, which provides unrealistic failure mapping for anisotropic rocks. This study investigated the impact of high attenuation on the mapping failure of a composite (sandstone–shale–sandstone), intact sandstone, and shale specimens that used AE under axile stress. The results proved that wave attenuation is the primary obstacle when obtaining a compatible failure map to the real specimen failure. Multiple setups of AE sensors were implemented to quantify the attenuation values for a wave that propagated across composite joints and shale bedding planes. The amplitude and energy attenuation (EA) values increased by 85% and 47%, respectively, when the bedding plane of the shale was from 0° to 90°, which reflected anisotropic behavior. The energy and amplitude reduction reached 99% and 39%, respectively, by propagating across a single joint. In addition, behind a double joint, no signal was received. However, the application of a load perpendicular to the joint interface improved the acoustical–wave characteristics. Therefore, when the rock material anisotropy was increased, there was lower accuracy when mapping specimen failure, because the attenuation varied at each angle between the source and sensor. In addition, the EA method suggested in this study presented hits location more precisely compared with the P-velocity (Vp) method. These findings could contribute to the development of an anisotropic attenuation model for field and laboratory application of AE.

Mechanical properties of aluminum to steel dissimilar spot joints produced by cold metal transfer weld-brazing

Spot joints between aluminum and steel sheets were produced by cold metal transfer arc welding using an AlSi3Mn alloy low melting point filler wire. The current study found that by using optimal welding conditions, the thickness of the joint interface was significantly reduced compared to previous studies. The interface thickness increased from a few nanometers at the center of weld to 1.7 micrometers (1.2 mm from center of weld) at periphery of weld. The reduction in joint thickness helped to achieve better joint properties. The tensile shear and fatigue properties of the spot joints were evaluated in conjunction with interrupted mechanical tests to determine the fracture mechanisms. This study investigates the fatigue properties and fracture mechanisms of cold metal transfer arc spot joints, which has not been done previously. The tensile shear fractures exhibit primarily interfacial fracture passing through an intermetallic compound layer at the joint interface. However, three different modes of fractures are observed during fatigue tests, including interfacial fracture, sheet fracture, and mixed-mode fracture. Interrupted fatigue tests reveal numerous crack initiation in pores/particles in the deposited weld metal and coagulation of those cracks leads to sheet fracture during the fatigue tests. Sheet fracture mode fractures are mainly observed during high cycle fatigue conditions.

Effect of Spindle Speed of Bar-Plate Rotary Friction Welding Machine on Joint Interface Area and Hardness Value

This study aims to determine the effect of the rotational speed parameter on the joint interface weld area and the value of hardness on similar materials. Welding parameters used the rotational speed of 2,484 rpm, 2,613 rpm and 4,335 rpm. Test method used in this research was liquid penetrant, macro and micro-observation and hardness test. The results of the liquid penetrant test showed no defects on the surface of the connection. In macro-observation, where there is a fairly large void at rotational speed of 2,484 rpm, which has length is 2,69 mm, then shrinks at 2,613 rpm to 1,52 mm, then at 4,335 rpm there is no visible void. In micro-observations showed that the weld metal area had a finer grain structure than the HAZ (Heat Affected Zone) and base metal areas this affect hardness value. The results of the hardness test are that the higher the rotational speed the higher the hardness value produced.

Microstructural Evolution and Deterioration of Shear Properties of Sn3.0Ag0.5Cu/Cu Solder Joints after Long-Term Storage at Cryogenic Temperatures

In deep space exploration the exploration equipment will inevitably experience the harsh environment of cryogenic temperature. Solder joints belong to the most vulnerable parts of electronic equipment, and the harsh environment of extreme cryogenic temperature will seriously threaten the reliability of solder joints. In this paper, Sn3.0Ag0.5Cu/Cu solder joints were prepared and stored at cryogenic temperatures (−50 °C, −100 °C, and −196 °C) for up to 960 h, whilst studying the microstructural evolution and deterioration of shear properties. The results showed that the influence of cryogenic temperature on microstructure deterioration was greater than that of storage time. With the decrease of storage temperature and the extension of storage time, the Ag3Sn intermetallic compounds (IMCs) were uniformly dispersed in the β-Sn matrix; the size decreased and the number increased. After being stored at −196 °C for 960 h, some microcracks appeared at the interface of the solder joints. Meanwhile, the shear force of the solder joints was reduced by 19.02%, and the fracture mode changed from ductile fracture to ductile–brittle mixed fracture. Therefore, it is of great scientific significance to reveal the microstructural evolution and deterioration of shear properties of the solder joints under long-term storage at cryogenic temperatures.

Forming Quality and Microstructure Evolution of AA6061‐T6 Aluminum Alloy Joint during Flow Drill Screwing Process

Flow drill screwing (FDS) is the optimal process to realize the single‐side connection of metal sheets. However, the plastic deformation and high fractional temperature during the plate connection process significantly impact the mechanical properties and microstructure of the metal sheets. Herein, the AA6061‐T6 sheet is connected by the FDS process, and the forming quality and microstructure evolution of the alloy are studied. The results show that the plate and the screw are mechanically connected. Obvious plastic deformation and recrystallization occur in the aluminum alloy around the screw, resulting in a fine‐grained zone near the joint interface. The recrystallization phenomenon in the central bushing region promotes the intermolecular fusion between the plates. The high temperature in the connection process partially promotes the dissolution of the strengthening phase, resulting in a decreased strength of the alloy matrix near the screw. The softening zone and hardening zone appear in the plates after the connection, and the hardness values are 55.8% and 105.7% of the alloy matrix.

Phenomenon and mechanism of ion diffusion at Co-fired joint interface of NiZn Ferrite/MCT ceramic heterostructure

Nickel-zinc ferrite (NZF) discs and magnesium calcium titanite (MCT) dielectric ceramic discs were laminated and co-fired to prepare NZF/MCT bi-layer laminated heterostructure samples. The sintering shrinkage of NZF and MCT was matched well via adjusting the sintering temperature. Ion diffusion curves at the co-fired joint interface were derived by electron-probe microanalysis (EPMA) and fitted basing on infinite diffusion coupling model. Ion diffusion mechanism at the co-fired joint interface was investigated in detail. The results show that Zn2+ ions have the highest diffusion coefficient because of the smaller ion radius which is benefit for interstitial diffusion, while Ca2+ ions have the lowest diffusion coefficient and segregate along the interface of MCT side. Fe3+ ions have the biggest diffusion width because of the interstitial diffusion in the incompletely densified MCT. Sintered at 1260 °C, the maximum interdiffusion width is narrow to be about 102 μm. With increasing temperature, ion diffusion coefficient and diffusion distance both go up obviously.

Nonlinear vibration analysis for bolted CFRC plates based on displacement-dependent surface spring-damping model of bolted joint

Under the effect of external excitation, bolted structures are prone to stiffness weakening and damping energy dissipation at the bolted joint, which makes the structures show nonlinear vibration behavior. In this paper, the displacement-dependent surface springs and tangential surface damping expressed by the S-curve model are proposed to simulate the nonlinear mechanical properties of the bolted joint. The non-uniform distribution of the mechanical parameters for the bolted joint is given to simulate the actual joint interface pressure distribution. Based on these, a nonlinear semi-analytical model for bolted carbon fiber reinforced composites (CFRC) plates considering the nonlinear mechanical characteristics of the bolted joint is established. Combined with the experimental results for a bolted CFRC beam, the specific S-curve expressions for the relevant mechanical parameters of the bolted joint are obtained by the inverse identification technology and numerical fitting method. After that, the bolted joint model is transplanted to the dynamic model of a bolted CFRC plate for numerical calculation. The comparison with the corresponding measured results shows that the proposed modeling method can well reproduce the soft nonlinear vibration of the actual bolted CFRC plate, which verifies the correctness and applicability of the proposed modeling method.

Heat distribution simulation and effects of ultrasonic welding amplitude on carbon fiber/polyetherimide composite joint properties

This work focuses on the effects of ultrasonic welding amplitudes on carbon fiber reinforced polyetherimide (CF/PEI) composite joint properties. The interface temperature measurement, single-lap shear tests and fracture morphology observation were used to evaluated on welding specimens with different welding amplitude. The accuracy of the temperature measurements was verified by the temperature field simulation of COMSOL. The analysis of mechanical strength and fracture morphology of joints were performed by tensile testing machine and SEM. The results indicated that PEI resin of the joint interface fully melted and the joints with good quality were formed under the appropriate welding amplitude. However, the excessive welding amplitude resulted in the extreme melting of PEI resin of the joint interface, which deteriorated the mechanical properties of joints.

Equivalent Dynamic Modeling for the Relative Rotation of Bolted Joint Interface Using Valanis Model of Hysteresis

Dynamic modeling of the joint interface is critical to the performance analysis of bolt-jointed structures. In this work, an equivalent modeling method was presented for modeling the relative rotation of the joint interface in bolt-jointed beam structures. As the transverse vibration of the studied structure is closely related to the rotation of the joint, which is different from previous studies that focused on the tangential slip of the joint interface, the Valanis model is used to model the relative rotation of the joint. In addition, the shear deformation and rotational inertia of the beam were considered in the modeling, using a finite element method that employed Timoshenko beam elements. The parameters of the Valanis model were determined by fitting a series of hysteresis loops obtained from the transient nonlinear analysis of a 3D FEM model. The results show that the proposed equivalent modeling method can accurately simulate the dynamic response and dissipation of the jointed beam structure with a significantly high computational efficiency. The maximum errors of the dynamic response amplitude and the energy dissipation are 5.5% and 8.3%.

Superhydrophobicity‐mediated enhanced enzymatic kinetics and high‐performance bioassays

AbstractAs a typical superwettability behavior, superhydrophobicity can provide an appropriate strategy to enhance the mass transport in multiphase chemical reactions. In the oxidase‐based enzymatic reactions, the elaborately regulating of reactant oxygen are critical to the development of an oxidase‐based high‐performance biosensor. In solid–liquid diphase condition, however, the kinetics of oxidase‐catalyzed reactions is inhibited by delayed mass transport and poor solubility of oxygen. To address this limitation, the design of the solid–liquid–air triphase interface is proposed according to the binary cooperation of superhydrophobicity and hydrophilicity. On the triphase joint interface, oxygen required for the oxidase‐catalyzed reactions can diffuse directly to the reaction center from the air phase through the micro/nanostructured superhydrophobic substrate, thus improving the kinetics of the oxidase‐catalyzed reactions. In this minireview, we summarize recent advances in the fabrication of triphase reaction system based on different superhydrophobic substrate for oxidase‐based biosensors. Common substrates including fibrous network, nanowire arrays, 3D porous framework, and hollow sphere structures are outlined in categories.

Interface microstructure and mechanical properties of copper-steel joints with nickel transition layer prepared by ultrasonic additive manufacturing

In order to suppress the problems of intergranular copper infiltration, liquid phase separation and thermal cracks in the process of fusion welding between copper and 304 stainless steel, UAM technology was used to consolidate the nickel transition layer on the surface of stainless steel to achieve surface modification, and then obtained copper-304 stainless steel overlap joints by pulse TIG process. Through the study of the joint interface configuration, microstructure, microhardness distribution and room temperature tensile strength of the control group, it was found that the introduction of the nickel interlayer can realize the metallurgical isolation between copper and steel and relieve the interfacial stress. Stainless steel and copper form the high-quality brazed joint with a nickel interlayer of 0.1 mm thickness, and the ultimate tensile strength of the joint at room temperature reaches 165 MPa. The joint fracture occurred near the fusion line near the copper side, and the fracture showed a ductile fracture mode.

Effects of curvature direction on friction stir welding lap joint of aluminum alloy “S” curved surface

In this paper, the friction stir welding (FSW) of single curvature and double curvature “S” curved surface lap joints were realized using split-type pressing blocks fixture and robotic system with welding parameter 1400 rpm, 150 mm/min. By finite element method (FEM) and axial force analysis, the effects of curvature direction on friction stir welding lap joint of 5083 aluminum alloy “S” curved surface is explored. The results show that Z-axis curvature direction has important influence on joint forming. Z-axis positive curvature makes the actual axial compressive force smaller than the device input, which decreases the interface stress of the lap joint and increases the tendency of upper plate weld edges bending deformation and the probability of interface defects. So the joint mechanical properties are reduced, and the tensile load can be as low as 1.5 kN. Z-axis negative curvature makes the actual axial compressive force greater than the device input, which increases the interface stress of the lap joint. Meanwhile, it decreases the tendency of upper plate weld edges bending deformation and leads to the interface defects disappearing. So the joint mechanical properties are good, and the tensile load can be more than 2.4 kN. For Y-axis curvature direction, its impact is mainly shown in changing the direction of resultant force FR. The inclination of force FR is helpful to eliminate the interface defects of the joint. At the same time, it will cause inconsistent stress between the advancing side (AS) and the retreating side (RS) of the joint interface, which is the reason that the double-curvature lap joint welding process is unstable.

Effect of curing degree on forming of clinch-adhesive joint

ABSTRACT The clinch-adhesive joint has good mechanical properties and the curing degree of the adhesive during the clinching process shows significant impacts on the joint forming and its mechanical performance. During the clinching process, the interface of the cured adhesive layer restricts the flow of the metal thus shows a negative influence on the forming quality of the clinch-adhesive joint. This paper focuses on the interface layers change during the clinching process and the infulence of curing degree on the forming of clinch-adhesive joint by the finite element simulation model. Firstly, the constitutive model and interfacial failure criterion of Araldite 2015 epoxy adhesive considering curing degree were fitted through tensile tests for adhesive dumbbell specimens and bonding joints. Then, the forming process of the clinch-adhesive joints with fully cured adhesive were simulated. Finally, the effects of curing degree on the joint shape and interface failure were investigated. The results show that interface damage occurs at the location of the self-locking, and the curing degree mainly shows influences on the sizes of adhesive pocket and undercut, the damaged width of the interface layers, and the maximum damage of the interface layers.

Mechanical performance of dissimilar friction stir welded lap-joint between aluminium alloy 6061 and 316 stainless steel

The dissimilar lap-joint of the AA6061 to 316 stainless steel was produced by friction stir welding. Changing microstructure, joint interface, and mechanical performances via welding rate were revealed. A wave interface pattern was found at the low welding rate with a free oxide layer. The interface became flat at the high welding rate with the oxide film formation. The diffusion and intermetallic compounds (IMCs) layers were formed on the interface and their thickness decreased via increasing the welding rate. The highest joint strength was obtained at the welding rate of 75 mm/min but strongly reduced with growing the welding rate. The strength was dramatically correlated with the bonding area, diffusion thickness and interface morphology instead of the IMCs layer thickness. At the low welding rate, the joint was fractured via ductile behaviour with a lot of dimples found on the fracture surface of 316 stainless steel.

A methodology for energy dissipation prediction of the bolt group with non-uniform preload

The bolted joints exhibit typical nonlinear hysteresis under tangential loading, and the deviations of the preload in the bolt group add to the complexity of the model describing this behavior. In this paper, based on the mechanical analysis of the bolt group, a new methodology for predicting hysteresis behavior under non-uniform preload was proposed. Firstly, based on the moment equilibrium within the framework of material mechanics and the tangential stiffness model of the joint interface, a new coordination equation of displacement and force between the bolted joints was deduced, which could realize the calculation of the bolt group loading curve. Then, the PCOM (Preload Co-Occurrence Matrix) was constructed considering the arrangement of the joints, and the indices related to the spatial distribution of the preload were extracted from PCOM. The results of GCA (Grey Correlation Analysis) showed that the indices of PCOM were closely related to the hysteresis behavior of the bolt group. Finally, the prediction of energy dissipation could be realized by using the indices extracted from PCOM and the SVM(Support Vector Machine) regression model. The prediction results were in good agreement with the simulation and experiment, which verified the validity of the methodology proposed in this paper.