Joint Test Research Articles

Development of hybrid bonded-hole hemmed joints: Process design and joint characterization

This study proposes a novel hybrid joining process, called bonded-hole hemming, for joining dissimilar materials. The process combines the hole hemming process, a newly developed joining process by plastic deformation, and adhesive bonding. The suitability of this process for joining AZ31 magnesium and AA6082-T4 aluminium sheets is evaluated through finite element simulations and experimental tests, where single-lap shear testing is carried out to assess mechanical performance. The experimental and numerical analyses of the single lap joint (SLJ) tests are also performed to validate the cohesive zone model (CZM) employed in the finite element models and the phosphate-permanganate treatment (PPT) for the magnesium sheets. The results show that the pre-cured bonded-hole hemmed (BHH) joint is more advantageous than the post-cured BHH joint, due to the presence of defects in the latter, caused by uncured adhesive during the hemming stage. Both the numerical simulations, using cohesive elements, and the experimental data confirm that the hemming stage does not cause damage to the cured adhesive layer in the bonded-hole hemming process. Furthermore, the numerical simulation acceptably predicts the mechanical behaviour of the BHH joint under shear testing. In conclusion, the maximum joint strength of the BHH joints is around 11 kN, which is about 3.8 times stronger than the hole-hemmed (HH) joints (2.9 kN). According to the numerical results, it is believed that the BHH joint would exhibit enhanced strength and elongation if the tested specimens did not contain the holes used for clamping. The results allow to conclude that the bonded-hole hemming process is a viable method for joining dissimilar materials, especially those with significantly distinct mechanical properties.

Non-destructive testing of an aluminum alloy welded joint based on a mathematical model of the thermal welding process and computer microtomography

Strength control of welded joints is used in many industries. X-ray microtomography as a method of non-destructive testing allows not only to detect the presence of defects, but also to classify them and assess the size of cracks and non-crack-like defects (pores). This article discusses the non-destructive testing of welded joints of aluminum alloy 6061 T6 using computer micrototomography and a mathematical model of the thermal welding process implemented in ANSYS Workbench. Experimental results of the X-ray microtomograph are presented, and the size of defects in this sample is estimated. The mathematical model allowed us to obtain the thermal histories at which the faults were formed.

Study on Flexural Performance of Aluminum Alloy Gusset Joints Subjected to Bending Moment and Shear Force

Aluminum alloy gusset (AAG) joints are widely applied in space reticulated shell structures. To investigate the flexural performance of AAG joints under the combined action of shear force and in-plane and out-of-plane bending moments, this analysis was developed by means of finite element (FE) models implemented in the non-linear code ABAQUS, and the accuracy of the FE simulation results based on the existing AAG joint test results was verified. The FE simulation results effectively described the mechanical properties of the AAG joints, including the failure mode, deformation process and bending moment-rotation curves. Furthermore, a parametric study was conducted by varying the height of the member section, the number of bolts, the radius of the joint plate, the thickness of the joint plate, the bolt preload force, and the ratio of in-plane to out-of-plane bending moments. It was found that these parameters had different effects on the bending behavior of the AAG joints.

Multi-Group Generalizations of SIBTEST and Crossing-SIBTEST

ABSTRACT This article presents generalizations of SIBTEST and crossing-SIBTEST statistics for differential item functioning (DIF) investigations involving more than two groups. After reviewing the original two-group setup for these statistics, a set of multigroup generalizations that support contrast matrices for joint tests of DIF are presented. To investigate the Type I error and power behavior of these generalizations, a Monte Carlo simulation study was then explored. Results indicated that the proposed generalizations are reasonably effective at recovering their respective population parameter definitions, maintain optimal Type I error control, have suitable power to detect uniform and non-uniform DIF, and in shorter tests are competitive with the generalized logistic regression and generalized Mantel–Haenszel tests for DIF.

Characterization of galvanized steel-low alloy steel arc stud welded joint

This paper investigates the possibility of successfully welding a Low Alloy Steel (LAS) stud to Galvanized Steel (GS) plate.Arc Stud Welding (ASW) was performed on joining LAS studs to GS plates. Welding parameters were selected based on weld trails. The first tests of the welded joints were based on visual inspection for welding defects such as lack of fusion and undercut welding defects. The good quality should be free of these defects and have full weld reinforcement. Other weld qualifications included torque strength test, microhardness test, and microstructure examination.The LAS studs have been successfully welded to a galvanized steel plate using the arc stud welding process. Higher welding current with adjusted welding time (800 A, 0.3 s) gave full weld reinforcement, the best joint appearance, and strength. Martensite phase was detected in the weld area and heat affected zone (HAZ), affecting the joint mechanical properties. Hardness property varied across the welded joint, and maximum hardness was recorded at the HAZ at the stud side. Hardness increased with the increasing welding current. At 800 A, welding current hardness was 10% higher than at 400 and 600 A. Torque strength was affected by weld reinforcement, and 800 A gave the best weld reinforcement that produced the highest torque strength.The main research limitation is the difficulty of welding LAS studs and GS plates. In conventional welding methods, such as gas metal arc welding, it is hard to get full weld penetration due to the geometry restrictions of the joint, which results in partial weld penetration between the studs and the plates. Furthermore, the issue of zinc evaporation during welding can be reduced by the advantage of the very high welding speed (in milliseconds) of ASW that overcomes the problem of continuous welding that usually results in the formation of harmful porosities and poor weldability.In this research, galvanized steel plates were successfully welded to LAS studs using the ASW process. The welding parameters for this dissimilar welding joint were carefully selected. Microstructure changing due to the welding process was investigated. The joint mechanical properties were evaluated.

Changi Airport To Operate Aurrigo’s Autonomous Ground-Handling Vehicles

Aurrigo International has signed an agreement with Changi Airport Group (CAG) for the continued joint development and testing of the company’s autonomous Auto-Dolly and Auto-DollyTug vehicles, plus its Auto-Sim airport simulation software.

Design and testing of multischeme horizontal joints for prefabricated two-walls-in-one diaphragm wall

There are obvious technical defects and resource wastage related to cast-in-situ diaphragm walls. To overcome these problems, this study presents a novel prefabricated two-walls-in-one diaphragm wall (PTDW) and a horizontal joint design method. First, full-scale experiments on multischeme PTDW horizontal joints and prefabricated walls were conducted. Second, a design method for PTDW horizontal joints was developed. Finally, the key design parameters for the joints were determined through a parametric analysis. The main conclusions are as follows. First, the mechanical properties of the welded joint (WJ) were better than the prefabricated wall. Bolted joints and grouted joints (BJ and GJ) may be damaged before the prefabricated walls. Second, the proposed design method promoted an excellent performance of WJ far superior to that of the BJ and GJ. Third, one compressive interface is the core factor and most efficient for the joints' bending resistance. Small-tenon joints with a maximized compressive interface achieved maximum performance. Finally, fasteners are the core factors of the joints' bearing capacity and stiffness properties. Therefore, WJ are recommended to easily form a rigid joint with a small-tenon scheme. This study provides a parameterized joint design method, which has high application value for green construction.

On the static failure behaviour of co-cured composite joints with enhanced interlaminar fracture energies via multiscale toughening

This paper is focused on the multiscale toughened co-cured composite interfaces of carbon/epoxy laminates using vacuum infusion and out-of-autoclave curing—with an emphasis on the role of enhanced interlaminar fracture energies on the static failure of laminate joints. To toughen co-cured interlaminar regions, three toughening routes are used: (i) epoxy matrix toughening with 10 wt% core–shell rubber (CSR) nanoparticles, (ii) 10 g/m2 polyphenylene sulfide (PPS) non-woven micro-fibre veil toughening, and (iii) multiscale toughening by combining epoxy matrix toughening with 10 wt% CSR nanoparticles and 10 g/m2 PPS veils. Double cantilever beam and end-notch flexure tests are conducted with the toughened interfaces for mode-I and mode-II fracture energies. Moreover, three co-cured joint configurations (viz. double-notch single lap, stepped scarf and skin-stiffener joints with the three toughening routes) are tested to characterise the role of enhanced interlaminar fracture energies on the static failure of laminate assemblies. The results show that the three toughening routes have significantly altered the R-curve behaviour and interlaminar fracture energies and that the degree of enhancement in mode-I and mode-II fracture energies is sensitive to the type of toughening route. Based on the material systems tested, the mode-I fracture initiation energy is enhanced by ∼150% with multiscale toughening, ∼65% with particle toughening, and ∼60% with veil toughening; whereas, the mode-II fracture initiation energy is enhanced by ∼85% with veil toughening and ∼35% with multiscale toughening—but reduced by ∼20% with particle toughening. The joint tests show that the toughening routes affect the static failure of the three joint configurations and that the strength and damage evolution of the co-cured joints depend on the interlaminar fracture energies. The strength of the co-cured single lap joints is increased by ∼50% with multiscale toughening and ∼40% with veil toughening; whereas, the strength of the co-cured skin-stiffener joints is enhanced by ∼35% with multiscale toughening and ∼45% with veil toughening. The failure mechanisms observed on the fracture surfaces indicate that the strength/failure behaviour of the co-cured joints depends on the dominant interlaminar fracture mode and the corresponding fracture energies. Overall, it is shown that the multiscale interlaminar toughening routes that are used to address the issue of delamination can also be effectively explored to enhance the static failure of co-cured laminate assemblies by toughening the co-cured interfaces/bondlines.

Binocular Rivalry Impact on Macroblock-Loss Error Concealment for Stereoscopic 3D Video Transmission

Three-dimensional video services delivered through wireless communication channels have to deal with numerous challenges due to the limitations of both the transmission channel's bandwidth and receiving devices. Adverse channel conditions, delays, or jitters can result in bit errors and packet losses, which can alter the appearance of stereoscopic 3D (S3D) video. Due to the perception of dissimilar patterns by the two human eyes, they can not be fused into a stable composite pattern in the brain and hence try to dominate by suppressing each other. Thus, a psychovisual sensation that is called binocular rivalry occurs. As a result, undetectable changes causing irritating flickering effects are seen, leading to visual discomforts such as eye strain, headache, nausea, and weariness. This study addresses the observer's quality of experience (QoE) by analyzing the binocular rivalry impact on the macroblock (MB) losses in a frame and its error propagation due to predictive frame encoding in stereoscopic video transmission systems. To simulate the processing of experimental videos, the Joint Test Model (JM) reference software has been used as it is recommended by the International Telecommunication Union (ITU). Existing error concealing techniques were then applied to the contiguous lost MBs for a variety of transmission impairments. In order to validate the authenticity of the simulated packet loss environment, several objective evaluations were carried out. Standard numbers of subjects were then engaged in the subjective testing of common 3D video sequences. The results were then statistically examined using a standard Student's t-test, allowing the impact of binocular rivalry to be compared to that of a non-rivalry error condition. The major goal is to assure error-free video communication by minimizing the negative impacts of binocular rivalry and boosting the ability to efficiently integrate 3D video material to improve viewers' overall QoE.

Experimental Study of the Impact of Notches Made in the Front Edge of Adherends on the Properties of Static and Fatigue Strength of Adhesive Joints

This paper presents the effect of simple structural changes consisting in making notches on the edge of adherends on the static and fatigue properties of adhesive joints. The study is based on the set of experimental static strength tests of the single lap shear adhesive joints. It has been shown that a slight increase in load capacity is possible by using adhesive-filled notches. However, this structural modification leads to an increase in the standard deviation of test results. Based on the fatigue strength tests done at the limit number of cycles equal to 2×106, it was shown that the use of notches on the front edge of adherends, which are filled with adhesive, can significantly increase the fatigue lifetime of the joint. The effect is shown in the area of low-cycle fatigue, where for fatigue stress with a maximum value of 11.5 MPa, an increase in the average value of fatigue lifetime by 481.5% was shown for joints with notches. On the basis of fractography analyses using SEM microscopy, it was shown that the positive effect of the notches is caused by the absorption of some energy by the adhesive filling the notches, due to the increased susceptibility of the adhesive in this area to elastic deformations.

Investigation of microstructure characteristics and work hardening behaviour of water-cooled FSW dissimilar aluminium alloys

The present study investigates the microstructure characteristics, tensile properties and work hardening behavior of friction stir welding (FSW) AA5083-AA6061 dissimilar aluminium alloys under different cooling conditions (naturally air-cooled and water-cooled). Microstructure evolution and tensile test of FSWed joints were investigated through Optical Microscope (OM), Electron Back Scattered Diffraction (EBSD), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Universal Testing Machine (UTM). EBSD results showed that the grain size obtained at the stir zone was 7.6 µm for air-cooled FSW (ACFSW) and grain growth restricted to 3.2 µm using water-cooled FSW (WCFSW). Brass [{110} <112>] and Goss [{110} <001>] were the two texture components that primarily evolved in FSW samples. The study suggests that joints produced with water cooling exhibited higher UTS at all distinct microstructure locations of the FSW joint and whereas the WCFSW-L sample exhibited higher UTS (271 MPa) than compared to ACFSW-L (246 MPa). Moreover, in the WCFSW, the strain hardening coefficient and work hardening rate enhanced by 6.3 % and 18.7 %, respectively, than ACFSW. The fracture surface morphology analysis of ACFSW and WCFSW samples was consistent with the tensile strength results.

Fatigue &amp; Fracture of Engineering Materials &amp; Structures Virtual Special Issue: Data science and machine learning for fatigue and fracture assessment

<scp>Fatigue &amp; Fracture of Engineering Materials &amp; Structures Virtual Special Issue</scp>: Data science and machine learning for fatigue and fracture assessment

Safety of Steel Arch Support Operation During Rock Bursts Under Explosive Atmosphere Conditions

Abstract Methane and coal dust explosions are among the most common causes of disasters in hard coal mining. Therefore, it is important for occupational safety in hard coal mines operating under methane and coal dust explosion hazards to identify possible ignition sources, whether due to natural or technical factors. One technical source of ignition can be mechanical sparks generated during operation of mechanical equipment and high surface temperatures of equipment components during operation. This paper presents the methodology and results of thermal imaging and strength testing of roadway support elements under dynamic loading. The goal of the tests was to identify the potential explosive atmosphere ignition sources during the operation of the support under the conditions of rock bursts. The scope of testing encompassed the temperature measurements by means of thermal camera of friction prop and yielding support frame sliding joint elements at yield under dynamic impact loading (simulating a burst). Significant joint element heating and mechanical sparking was observed during the testing of arching yielding support frame sliding joints and straight friction prop joints as a result of friction at yield. Some of the aspects defined in standard PN-EN ISO80079-36:2016 include the maximum temperature T max =150°C for a surface that can accumulate a layer of coal dust. Tests of the friction joints have shown that during impact loading, numerous mechanical sparks are produced at the friction joints of sections of the steel prop, with the surface temperature of the sections starting from 169.6°C and reaching up to 234.1°C. During tests it was also to determined emissivites of the tested sliding joints constructed from V29-V32 secrions depending on corrosion products which consist in range 0.842–0.873. Such a high temperature can initiate an explosive mixture consisting of methane, air and coal dust.

Analysis of Residual Stresses for Underwater Wet Welding of High Strength Steel

This study describes a perspective using non-destructive testing of stress-strain state joints in underwater wet welding and air. High residual stresses after underwater wet welding may be a possible cause of arising corrosion processes and cold cracking in structures. Assessing residual stresses can introduce additional changes in the technological welding process and subsequent reducing stresses. Analysis of application magnetic anisotropy and X-ray diffraction methods are shown for discovering residual tensile stresses after surfacing on high strength steel. Two complementary methods make it possible to determine the magnitude and features of the distribution of residual welding stresses after underwater wet surfacing and air surfacing.

Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars

In this research, methods of increasing the corrosion resistance of reinforced concrete were experimentally investigated. The study used silica fume and fly ash at optimized percentages of 10 and 25% by cement weight, polypropylene fibers at a ratio of 2.5% by volume of concrete, and a commercial corrosion inhibitor, 2-dimethylaminoethanol (Ferrogard 901), at 3% by cement weight. The corrosion resistance of three types of reinforcements, mild steel (STt37), AISI 304 stainless steel, and AISI 316 stainless steel, was investigated. The effects of various coatings, including hot-dip galvanizing, alkyd-based primer, zinc-rich epoxy primer, alkyd top coating, polyamide epoxy top coating, polyamide epoxy primer, polyurethane coatings, a double layer of alkyd primer and alkyd top coating, and a double layer of epoxy primer and alkyd top coating, were evaluated on the reinforcement surface. The corrosion rate of the reinforced concrete was determined through results of accelerated corrosion and pullout tests of steel-concrete bond joints and stereographic microscope images. The samples containing pozzolanic materials, the corrosion inhibitor, and a combination of the two showed significant improvement in corrosion resistance by 7.0, 11.4, and 11.9 times, respectively, compared to the control samples. The corrosion rate of mild steel, AISI 304, and AISI 316 decreased by 1.4, 2.4, and 2.9 times, respectively, compared to the control sample; however, the presence of polypropylene fibers reduced the corrosion resistance by 2.4 times compared to the control.

Post-fire seismic performance of concrete-filled steel tubular column to steel beam joints with blind-bolted connections: Experiment and simulation

During the life-cycle of a building, the structure might be subjected to multiple hazards such as fire, earthquake and impact. Compared with the traditional structure design methods based on a single type of disaster load, the structure subjected to multiple and coupled disaster loads would be more dangerous and worth to be investigated. In this paper, the post-fire seismic behavior of concrete-filled steel tubular (CFST) column to steel beam joints with blind-bolted connections subjected to coupled fire and cyclic loads were investigated. A total of ten post-fire hysteresis joint tests were designed and conducted, and the testing parameters included heating time, post-fire column load ratio and thickness of fire protection layer. The test results indicated that the joint failure mode changed from column failure to connection failure when the post-fire column load ratio ranged from 0.3 to 0.6. Generally, the blind bolts in the panel zone of this joint specimen showed acceptable working performance in fire, but gap between the stee tube and beam end plate might be formed during the post-fire cyclic loading process. Finite element analysis (FEA) models were established to simulate and discuss the post-fire seismic performance of this type of blind-bolted CFST joints under the coupled fire and loading process. Finally, a simplified post-fire hysteretic relationship model for this type of joint was proposed.

Quasi-static test loading protocols for modular steel construction joints

Owing to the different structural configuration of modular steel construction (MSC) joints compared with those in conventional structural frames, the existing loading protocols might not be applicable to MSC joints. Suitable loading protocols for MSC joints are therefore required for use in quasi-static cyclic tests, which is the focus of the present study. A representative three-dimensional MSC building was adopted in the numerical simulation programme. Dynamic analyses were carried out using the developed numerical model under a selection of seismic waves, from which the inter-storey displacements were obtained. The rainflow counting method was employed to process the obtained displacement–time histories, and the key parameters for the loading protocol, including the total number of cycles and maximum amplitude etc. were derived accordingly. A quasi-static cyclic loading protocol dedicated to MSC joints was subsequently established. The proposed loading protocol was compared with the existing loading protocols specified in ATC-24 and in FEMA-461 through numerical simulations. The examined loading protocols were applied to two typical MSC joints, and the numerical results indicated that the proposed protocol led to a small increment in the energy consumption, ductility and bearing capacity, in comparison with the two existing loading protocols. The results show that the existing and the proposed loading protocols are all deemed suitable for use in quasi-static cyclic testing of the MSC joints, and the proposed loading protocol with 37 cycles and 0.0158 rad loading peak value could provide a new and alternative loading program for the quasi-static test of MSC joint.

Calibration procedure and biomechanical validation of an universal six degree-of-freedom robotic system for hip joint testing

PurposeAmong various test methods for different human joints, the use of robot systems has attracted major interest and inherits the potential to become a gold standard in biomechanical testing in the future. A key issue associated with those robot-based platforms is the accurate definition of parameters, e.g., tool center point (TCP), length of tool or anatomical trajectories of movements. These must be precisely correlated to the physiological parameters of the examined joint and its corresponding bones. Exemplified for the human hip joint, we are creating an accurate calibration procedure for a universal testing platform by using a six degree-of-freedom (6 DOF) robot and optical tracking system for recognition of anatomical movements of the bone samples.MethodsA six degree-of-freedom robot (TX 200, Stäubli) has been installed and configured. The physiological range of motion of the hip joint composed of a femur and a hemipelvis was recorded with an optical 3D movement and deformation analysis system (ARAMIS, GOM GmbH). The recorded measurements were processed by automatic transformation procedure (created in Delphi software) and evaluated in 3D CAD system.ResultsThe physiological ranges of motion were reproduced for all degrees of freedom with the six degree-of-freedom robot in adequate accuracy. With the establishment of a special calibration procedure by using a combination of different coordinate systems, we were able to achieve a standard deviation of the TCP depending of the axis between 0.3 and 0.9 mm and for the length of tool between + 0.67 and − 0.40 mm (3D CAD processing) resp. + 0.72 mm to − 0.13 mm (Delphi transformation). The accuracy between the manual and robotic movement of the hip shows an average deviation between − 0.36 and + 3.44 mm for the points on the movement trajectories.ConclusionA six degree-of-freedom robot is appropriate to reproduce the physiological range of motion of the hip joint. The described calibration procedure is universal and can be used for hip joint biomechanical tests allowing to apply clinically relevant forces and investigate testing stability of reconstructive osteosynthesis implant/endoprosthetic fixations, regardless of the length of the femur, size of the femoral head and acetabulum or whether the entire pelvis or only the hemipelvis will be used.

Estimation and testing of the factor-augmented panel regression models with missing data

Abstract This paper focuses on the factor-augmented panel regression models with missing data and individual-varying factors. A so-called CCEM estimator for the slope coefficient is proposed and its asymptotic properties are investigated under some regularity conditions. Furthermore, a joint test statistic is constructed for serial correlation and heteroscedasticity in the idiosyncratic errors. Under the null hypothesis, the test statistic can be shown to be asymptotically chi-square distributed. Monte Carlo simulation results show that the proposed estimator and test statistic have desired performance in finite samples.

Numerical and Experimental Analysis of Lap Joints Made of Grade 2 Titanium and Grade 5 Titanium Alloy by Resistance Spot Welding

The paper presents the evaluation of the load capacity of lap joints and the distribution of plastic deformations. The influence of the number and arrangement of welds on the load capacity of the joints and the method of their failure was investigated. The joints were made using resistance spot welding technology (RSW). Two combinations of joined titanium sheets were analyzed: Grade 2-Grade 5 and Grade 5-Grade 5. Non-destructive and destructive tests were carried out in order to verify the correctness of the welds within the given parameters. All types of joints were subjected to a uniaxial tensile test on a tensile testing machine, using digital image correlation and tracking (DIC). The results of the experimental tests of the lap joints were compared with the results of a numerical analysis. The numerical analysis was performed using the ADINA System 9.7.2 and was based on the finite element method (FEM). The conducted tests showed that the initiation of cracks in the lap joints occurred in the place as the maximum plastic deformations. This was determined numerically and confirmed experimentally. The number of welds and their arrangement in the joint affected the load capacity of the joints. Depending on their arrangement, Gr2-Gr5 joints with two welds reached from approximately 149 to 152% of the load capacity of joints with a single weld. The load capacity of the Gr5-Gr5 joints with two welds ranged from approximately 176 to 180% of the load capacity of joints with a single weld. Observations of the microstructure of RSW welds in the joints did not show any defects or cracks. The microhardness test in the Gr2-Gr5 joint showed that the average hardness of the weld nugget decreased by approximately 10-23% when compared to a Grade 5 titanium alloy and increased by approximately 59-92% compared to Grade 2 titanium.