Mechanical Behavior Of Joints Research Articles

Experimental study on mechanical behavior of joints in precast concrete members by PC-press joint method

Experimental study on mechanical behavior of joints in precast concrete members by PC-press joint method

Microstructure and Mechanical Properties of Welded Joints of Cr18Ni30Mo2Al3Nb Alloy

In this present study, A comparative research on the mechanical properties of the dissimilar welded joints of 800H and Cr18Ni30Mo2Al3Nb was investigated. Butt joints were made using argon tungsten-arc welding (TIG). The TIG joint was made using well established welding parameters (i.e., current ampere of 110~120A, welding rate of 105~115mm/min, argon flow 8~10L/min and voltage of 12V). Mechanical behavior of joints was evaluated by room temperature and high temperature (650°C) tensile testing, and hardness testing, respectively. The microstructure of joint was characterized via optical microscopy, and the morphology of tensile fracture was observed by scaning electron microscopy. As can be seen from the experimental results, clearly shown that Cr18Ni30Mo2Al3Nb has better mechanical performance of welded joint than 800H.

One-sided laser beam welding of autogenous T-joints for 6013-T4 aluminium alloy

Autogenous T-joints for aluminium skin-stringer component performed by one-sided laser beam welding process was conducted using a high power Yb-fiber laser. The influence of the shielding gas, seam angle, beam focal position, and beam positioning relative to weld centerline were investigated regarding to weld microstructural features. The joint mechanical behavior was evaluated concerning to the sheet rolling directions. It was observed that a precise control of the process parameters enabled to obtain weld beads with acceptable dimensional and geometric characteristics and minimizing weld defects. Helium shielding gas produced higher aspect ratio welds than those with pure argon. Although, pores were observed in the fusion zone, they represented only about 5% of the weld bead area. The optimal beam positioning should remain up to 0.2mm relative to junction line, for seam angles between 10° and 15°. The weld mechanical behavior depended on the sheet rolling direction. Joint efficiency up to 85% were obtained after hoop tensile tests when the weld bead longitudinal-section was perpendicular to skin rolling direction and parallel to the stringer rolling direction.

Mechanical Behavior Experimental Study on Lattice Wind Turbine Tower KT-Type Joints of Concrete-Filled Steel Tubular

The mechanical behavior of joints on lattice wind turbine tower of concrete-filled steel tubular(CFST) is very complex, the safety and reliability of joints is very important for the whole structure. To better understand the mechanical properties of the joints, we design a static loading test of 3 KT-type CFST joints. According to the test, we make analysis about the failure progress, equivalent stress of joint intersection and the relation of load-defomation. The results showed that due to the presence of concrete, the failure mode of CFST joints is web members failed. The failure characteristic of overlap joints is the instability of compression web member while the gap joints are the weld tear of tensile web member. With the increase of the overlap ratio, the distribution of the equivalent stress is more uniform. The high stress area is in the gap and the tower wall which between the crown point and saddle point in tensile side.

THE EFFECTS OF FATIGUE ON PEAK TORQUE, MUSCLE STIFFNESS, AND MUSCULOARTICULAR STIFFNESS OF THE KNEE JOINT IN YOUNG MALE ATHLETES

BackgroundAppropriate levels of muscle strength, muscle stiffness (MS) and musculoarticular stiffness (MAS) are important factors linked to athletic performance. Alterations in knee joint mechanical behavior induced by neuromuscular fatigue may...

SiC Die Attach for High-Temperature Applications

Eutectic solders AuIn19 and AuGe12 and nanosilver paste were investigated for SiC die attach in high-temperature (300°C) applications. The soldering or sintering conditions were optimized through die shear tests performed at room temperature. In particular, application of static pressure (3.5 MPa) during sintering resulted in greatly improved mechanical behavior of the nanosilver-based joint. Microstructural study of the eutectic solders showed formation of Au-rich grains in AuGe die attach and significant diffusion of Au and In through the Ni layer in AuIn19 die attach, which could lead to formation of intermetallic compounds. Die shear tests versus temperature showed that the behaviors of the studied die attaches are different; nevertheless they present suitable shear strengths required for high-temperature applications. The mechanical behavior of joints under various levels of thermal and mechanical stress was also studied. Creep experiments were carried out on the eutectic solders to describe the thermomechanical behavior of the complete module; only one creep mechanism was observed in the working range.

Effect of pad surface finish and reflow cooling rate on the microstructure and the mechanical behavior of SnAgCu solder alloys

The microstructure of Pb-free solder joints fabricated with SnAgCu alloys possesses a complex morphology owing to nonequilibrium solidification of Sn. The microstructure also depends on variables such as pad surface finish as well as process conditions during solder reflow. Specifically, the Ag3Sn intermetallics formed during the assembly vary in composition and structure due to pad finish as well as reflow cooling rate. An understanding of the behavioral impact of the microstructural changes due to pad finish and reflow cooling rate on micron-scale SnAgCu joints is an important need at the present time. In this paper, we study the impact of pad finish and cooling rate on three alloys formed by the mixing during assembly of Sn3.0Ag0.5Cu paste with Sn1.0Ag0.5Cu, Sn3.0Ag0.5Cu or Sn3.5Ag balls (with 33% of paste material and 67% ball material by volume). We examine the effect of pad finish on the microstructural disintegration near the pad and correlate the microstructural change to the observed behavior under constant strain rate loading. For this, a comprehensive series of constant strain rate tests, 24 in all, on all the three alloys with Electroless Nickel Gold (NiAu), Organic Solderability Pad (OSP) and Solder on Pad (SOP) pad finishes were conducted. We also investigate the role of faster reflow cooling rate by evaluating the mechanical behavior of the solder joints resulting from 1°C/min or 6°C/min reflow cooling profiles. The NiAu–OSP pad finish yielded the highest saturation stress during constant strain rate tests while the saturation stresses of OSP–OSP, SOP–OSP combinations were comparable to each other. Also, joints formed using reflow profiles with higher cooling rates exhibited a greater resistance to deformation. In particular, the cooling rate has a significant effect on mechanical behavior of a joint with OSP–OSP pad finish.

The temporomandibular joint : from classical anatomy to modern functional assessments

The temporomandibular joint (TMJ) is a complex synovial articulation, made by the mandibular condyles and the squamous surface of temporal bones. The skeletal surfaces are highly incongruent and are separated by a fibrous disc, that reduces joint incongruence, increases joint stability, and allows mandibular movements with six degrees-of-freedom. In mammals, TMJ characteristics are so unique that are used to define the class Mammalia. TMJ development is strictly related to that of the middle ear, and it represents a complex modification of a phylogenetically older articulation found in non-mammalian vertebrates [1]. In particular, human TMJ possesses several differences from that of the other mammals, and animal models cannot be easily used to investigate its dynamic and kinematic characteristics. Several hypotheses have been proposed to describe TMJ movements and intra-articular force, but a major limitation lies in the difficulty in the actual assessment of condylar movements. Indeed, no current imaging system can provide a complete three-dimensional evaluation of TMJ motion: conventional radiographic images lack the third dimension and cannot inform about the behaviour of soft tissues; CT provides all three spatial planes but still cannot image the disc and related structures; magnetic resonance (MR), while providing adequate details of soft tissue structures, lacks the necessary dynamic information. Therefore, most of these studies are based on biomechanical models, where TMJ motion is recorded with three-dimensional motion analyzers, and mathematical and geometrical calculations provide the necessary background for the hypotheses about joint mechanical behaviour [2].

Strength prediction of adhesively bonded joints under cyclic thermal loading using a cohesive zone model

Structural adhesives are being widely adopted in aerospace and automobile industries. However, in many cases, hostile environments cause non-ignorable degradation in joints mechanical performance. In this work, a combined experimental–numerical approach was developed to characterise the effect of cyclic-temperature environment on adhesively bonded joints. The environmental degradation factor, Deg, was introduced into a cohesive zone model to evaluate the degradation process in the adhesive layer caused by the cyclic-temperature environment and the stress states in adhesive layer before and after temperature exposure treatment were investigated. Carefully designed experimental tests were carried out to validate the simulation results and help the numerical procedure to predict joint mechanical behaviour after environmental exposure. A response surface method was utilised to provide a better visualisation on the relationship between selected factors and response. Finally, the scanning electron microscopy was carried out to investigate the micro fracture mechanisms of adhesively bonded joints.

Experimental Study on the Static Performance of Joints in the Castellated Portal Frame of Light-Weight Steel

In order to study the mechanical behavior of joints in the castellated portal frame of light-weight steel under static loads, a static loads experiment has been performed for these new joints in this paper. The experiment members include four castellated joints and one solid-web joint of original steel, considering three vary parameters which are connection form of joints, joint region with setting stiffener and the distance from the center of hole to joint region. Experiment shows: the stiffness of castellated joints is higher than the one of solid-web joint. The parameters have a great influence on the mechanical behavior of joints, except the connection form of joints.

Research on the Strength Degradation of Unbalanced Adhesive Joints Subjected to Cyclic-temperature Environment

With the development of automobile lightweight technology,the structural adhesion technique is being widely adopted in the connecting process of dissimilar materials in vehicle body.An experimental-numerical approach is developed to investigate the influence of cyclic-temperature environment on adhesive joints.The finite element model is set up to evaluate the degradation process in the adhesive joints through ABAQUS software and the peel and shear stress states in the adhesive layer are analyzed through cohesive zone modeling.Carefully designed experiment is carried out to validate the simulation results and help the numerical procedure to predict joint mechanical behavior after environmental exposure.The scanning electron microscopy is performed on the failure surface to investigate the micro fracture mechanisms in the adhesive layer.

Improved measure of beam-to-column joint rotation in steel frames

The behavior of beam-to-column joint rotation in a steel frame has been shown to have significant effects on the internal force distribution and the global deformation response. However, approaches to experimentally quantify the joint rotation are not well established. This fact impairs the applicability and comparability of research results on joint mechanical behavior. This paper compares different measurement methods in the research literature on beam-to-column joint rotation in steel frames, and proposes improved approaches for the experimental quantification of the rotation of welded joint and welded-flange-bolted-web (WFBW) joints. The feasibility and accuracy of the proposed methods are demonstrated by the comparison of results from simplified frame analysis with those from finite element analysis on both partial and complete structural levels.

Analysis of Mechanical Performance Considering Damage Accumulation of Intersecting Joints in Steel Structures

The mechanical behaviors of intersecting joints considering damage accumulation in steel tube structures is analyzed through the FE-program ABAQUS. The stress characteristic and failure modes of these joints are concluded. Especially, it has been analyzed influence of the change of geometric parameters to mechanical behavior of joints. Finally, the results indicate the joints have a good mechanical performance and good plastic deformation as to excessive local buckling of chord under the loads.

The role of rotation speed on intermetallic compounds formation and mechanical behavior of friction stir welded brass/aluminum 1050 couple

In this paper, the intermetallic compounds formation during dissimilar friction stir welding of brass to aluminum 1050 and its effect on the mechanical behavior of joint were studied. Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy analysis (EDS) and X-ray Diffraction analysis were used to characterize intermetallics. In addition, tensile tests and microhardness measurements were performed to evaluate mechanical properties. The results showed that utilizing rotation speeds higher than 400 rpm leads to gradual formation of intermetallic compounds in the stir zone and at the interface. CuAl2 is the dominant compound in the composite structure of the stir zone, whereas four intermetallic bands are detected at the interface. From aluminum to brass, two middle layers were formed. Then, CuAl2, Cu9Al4 and CuZn were detected. The increase in rotation speed is accompanied by thickening and development of interfacial intermetallic compounds. The optimum rotation speed of 450 rpm yielded a narrow interfacial intermetallic compound and a lamellar composite structure within the stir zone which enhances the tensile strength of the weld. On the other hand, further increase of rotation speed lowers the tensile strength of the weld which is accompanied by disappearance of lamellar composite structure, increment of weld defects and thickening of interfacial intermetallic layer.

Pressure Measurement in the Cervical Spinal Facet Joint

A novel noninvasive approach to measure facet joint pressure in the cervical spine was investigated using a tip-mounted transducer that can be inserted through a hole in the bony lateral mass. This technique is advantageous because it does not require resection of the joint capsule, but there are potential issues regarding its applicability that are addressed. The objective was to evaluate the effect of a tip-mounted pressure probe's position and orientation on contact pressure measurements in biomechanical experiments. Measurements of direct contact pressure in the facet joint of cadaveric spines have been obtained via pressure-sensitive films. However, that method requires the resection of the facet capsule, which can alter the overall joint's mechanical behavior and can affect the measured contact pressures. Influence of position and orientation on probe measurements was evaluated in companion surrogate and cadaveric investigations. The probe was placed in the facet of an anatomic vertebral C4/5 surrogate undergoing sagittal bending moments. Pressure-sensitive paper was used to map contact regions in the joint of the surrogate and cadaveric cervical segments (n = 3) during extension. The probe also underwent uniaxial compression in cadaveric facets to evaluate the effect of orientation relative to the contact surface on the probe signal. Although experimental and theoretical pressure profiles followed the same trends, measured maximum pressures were half of the theoretical ones. In the orientation study, maximum pressures were not different for probe orientations of 0° and 5°, but no signal was recorded at orientations greater than 15°. This approach to measure pressure was selected to provide a minimally-invasive method to quantify facet joint pressures during clinically relevant applications. Both the position and orientation of the probe are critical factors in monitoring local pressure profiles in this mobile synovial joint.

Nonlinear Analysis of Mechanical Behavior of the Eccentric In-Plane Beam-Wall Joint

On the basis of previous experimental research, the nonlinear finite element analysis of the eccentric in-plane beam-wall joint is made with nonlinear bond-slip constitutive relation between steel and concrete. The mechanical behavior of the joint is studied in detail, and parametric analysis is carried out for mechanical behavior of the joint. Results of experiment and nonlinear analysis proved that: the important guarantee for mechanical behavior of the eccentric in-plane beam-wall joint is macro resistance capability, which is a precondition of local force transmission of the joint. In addition, the length of beam plunging wall, eccentricity of the joint and the stirrup ratio of beam within wall are the main factors influencing on mechanical behavior of the joint.

Numerical Study on Progressive Failure of the Marble Plate Based on the Thin-Layer Tri-Node Jointed Element

In order to model the mechanical behavior of joints efficiently, a thin-layer tri-node joint element is constructed. The stiffness matrix of the element is derived in the paper. For it shares the common nodes with the original tri-node triangle element, the tri-node joint element can be applied to model the crack propagation without remeshing or mesh adjustment. Another advantage is that the cracked body is meshed without consideration of its geometry integrity and existence of the joints or pre-existed crack in the procedure of mesh generation, and then the triangular element intersected by the crack or joint is automatically transformed into the tri-node joint element to represent pre-existed cracks. These make the numerical simulation of crack propagation highly convenient and efficient. After CZM is chosen to model the crack tip, the mixed- energy simple criterion is used to determine whether the element is intersected by the extended crack or not, the extended crack is located in the model. By modeling the marble plates with two edge cracks subjected to the uniaxial compressive loads, it is shown that the numerical results are in good agreement with the experimental results, which suggests that the present method is valid and feasible in modeling rock crack propagation.

Studies on the micro-laser spot welding of an NdFeB permanent magnet with a low carbon steel

In search of high speed and miniaturization, the welding of NdFeB permanent magnet material is currently of increasing interest. Previous studies have shown that dissimilar material joining between magnet and steel sheets can be realized by laser irradiation, but it is still not clear how the welding parameters affect the weld quality. In this paper, the results are reported of experiments studying effects of laser pulse power, pulse duration, and defocusing distance on joint dimensions and mechanical behavior in laser spot welding of an NdFeB magnet (N48) with a low carbon steel (AISI 1006). Both conduction mode and keyhole mode welding were performed in the present study. The welding modes can be altered by changing peak power or defocusing distance, but not by changing pulse duration. Three fracture modes were found in shear tests, i.e., ‘nugget pullout’, ‘through nugget’ and ‘magnet crush’, while in peel tests, only ‘nugget pullout’ fracture mode was observed. The different fracture modes under different loading conditions were attributed to the mechanical locking effects present under shear testing but not under peel testing. For ‘nugget pullout’ mode fracture, the metallurgical quality of joints is the controlling factor of fracture forces; for ‘nugget through’ and ‘magnet crush’ mode fractures, the controlling factors are the size and strength of the nugget and base magnet. Certain nugget penetration should be achieved to avoid ‘nugget pullout’ fracture, while excessive growth of nugget should be limited to avoid ‘magnet crush’ fracture by appropriately adjusting process parameters.

Preliminary study on the mechanical behavior of friction spot welds

The Friction Spot Welding - FSpW is a solid-state process that allows joining two or more metal sheets in lap configuration with no residual keyhole as occurs in the Friction Stir Welding - FSW process. The present work reports part of the efforts made at GKSS Research Centre to better understand the complex phenomena that take place during FSpW of aluminum alloys and establish the mechanical response of the resulting joints. Over the recent years the research on modeling friction based welding processes has increased considerably. Most of the works related to this subject deal with the process mechanics. On the other hand, some investigations have shown how the process variables affect the mechanical properties of the joints, but it is very difficult to find quantitative results that can be readily used for mechanical design purposes. The aim of this work is to develop an analysis procedure based on the process characteristics that allows evaluating how the resulting geometry and microstructure affect the joint mechanical behavior. For this, the results of the mechanical tests obtained on AA2024-T3 aluminum alloy were used to calibrate and validate a numerical model that was used to predict the joint failure mode. The model reproduced the specimen geometry and load conditions adopted in the lap-shear and cross-tensile tests. The joint was considered as formed by three main regions (SZ - stir zone, TMAZ - thermo mechanically affected zone and HAZ - heat affected zone) whose properties and dimensions were based in microhardness evaluation and macrographic analysis of welded specimens. It was observed a good agreement between the simulation results and experimental data. The numerical modeling of the joints allows the prediction of the joint mechanical properties, as well as to understand how a change in geometry and property of each region affects the final mechanical behavior. Based in the obtained results, the analysis procedure can be easily extended to the related friction based spot processes as Friction Stir Spot Welding - FSSW.

Normal and osteoarthritic hip joint mechanical behaviour: a comparison study

The assessment of contact areas within the hip joint during activities of daily living is of critical importance to understand why degeneration mechanisms are sometimes initiated. A generic finite element model is developed and constrained with experimental personalized conditions to locate contact areas and determine pressure distribution, both during walking and stair climbing. Bony structures are positioned in relation to each other by using experimental kinematical data. Implemented loading conditions are computed from an inverse dynamic approach coupled with an optimization method. The mechanical behaviour of a healthy hip joint is first simulated. This model is then used as a reference for the evaluation of a pathological mechanical behaviour. Thus, experimental data are collected for a patient presenting a coxarthrosis. The comparison of the pathological and normal behaviours emphasizes that the contact area swept within the osteoarthritic hip joint is limited both during walking and stair climbing.