Ultimate Strength Of Joints Research Articles

Shape optimization of single-pin reinforcement in metal-composite joints

Purpose Utilizing through-the-thickness pin reinforcement in metal-to-composite joints can significantly increase the joint mechanical properties, enabling the introduction to a whole new field of applications in joining technology. However, with the rise of advanced pin manufacturing techniques – such as additive layer manufacturing, little research has been performed on the pin shape optimization and its behavior. The paper aims to discuss this issue. Design/methodology/approach In this study, a numerical shape optimization algorithm is used to produce optimized pin shapes for several initial pin dimension parameters, having as objective to achieve a more uniform stress distribution along the surface of the pin, enhancing the pin strength and joint integrity. Findings Results showed that pin shape is a crucial factor in the mechanical response of the pin. In Mode I, the presence of an undercut feature on the pin head can increase the ultimate load of the pin by +250 percent, while in Mode II, the base diameter is the dominant feature in the joint ultimate strength. Originality/value With these results, the paper aims to utilize commercial available numerical software to explore optimization capabilities in joints strength. These optimization capabilities show that it could be used for the enhancement of metal-to-composite joints response.

Effect of Heat Input on the Microstructure, Strength and Corrosion Behavior of Sheets of Alloy AA6061 After Cold Metal Transfer Welding

The effect of the parameters of welding conducted by the method of cold metal transfer on the geometry of the welding pool, the ultimate tensile strength, and the corrosion rate of welded joints of sheets from aluminum alloy AA6061 is studied. The influence of the current, voltage, and heat input rate during welding on the properties of the welded joints is analyzed. The welding parameters providing maximum ultimate strength and high corrosion resistance of welded joints of alloy AA6061 are determined.

Metallic multi-material adhesive joint testing and modeling for vehicle lightweighting

While adhesive bonding has been shown to be a beneficial technique to join multi-material automotive bodies-in-white, quantitatively assessing the effect of adherend response on the ultimate strength of adhesively bonded joints is necessary for accurate joint design.In the current study, thin adherend single lap shear testing was carried out using three sheet metals used to replace mild steel when lightweighting automotive structures: hot stamped Usibor® 1500 AS ultra-high strength steel (UHSS), aluminum (AA5182), and magnesium (ZEK 100). Six combinations of single and multi-material samples were bonded with a one-part toughed structural epoxy adhesive and experimentally tested to measure the force, displacement across the bond line, and joint rotation during loading. Finite element models of each test were analyzed using LS-DYNA to quantitatively assess the effects of the mode mixity on ultimate joint failure. The adherends were modeled with shell elements and a cohesive zone model was implemented using bulk material properties for the adhesive to allow full three-dimensional analysis of the test, while still being computationally efficient.The UHSS-UHSS joint strength (27.2 MPa; SD 0.6 MPa) was significantly higher than all other material combinations, with joint strengths between 17.9 MPa (SD 0.9 MPa) and 23.9 MPa (SD 1.4 MPa). The models predicted the test response (average R2 of 0.86) including the bending deformation of the adherends, which led to mixed mode loading of the adhesive. The critical cohesive element in the UHSS-UHSS simulation predicted 85% Mode II loading at failure while the other material combinations predicted between 41% and 53% Mode II loading at failure, explaining the higher failure strength in the UHSS-UHSS joint.This study presents a computational method to predict adhesive joint response and failure in multi-material structures, and highlights the importance of the adherend bending stiffness and on joint rotation and ultimate joint strength.

Evaluation of Microstructure, Hardness and Mechanical Properties of Friction Stir Welded Al–Ce–Si–Mg Aluminium Alloy

A vast majority of the research on friction stir welding(FSW) is mainly focused on welding of aluminium alloys. The research studies in this paper are based on one such alloy known as Al–Ce–Si–Mg aluminium alloy, of which, the microstructure and other mechanical properties of the friction stir welded joints are yet to be studied. The plates of Al–Ce–Si–Mg aluminium alloy were friction stir welded using a non consumable, rotating tool with triangular profile pin and circular shoulder, with different combinations of tool rotation speeds and weld speeds. The microstructure, hardness and mechanical properties of the weld were analyzed. The microstructure of the weld zones revealed that, the average grain size at the bottom of the Nugget Zone (NZ) is 5 ± 0.12 μm and gradually increases to 15 ± 0.23 μm at the top of the NZ. In the TMAZ the grain size is 20 ± 0.14 μm and is bigger compared to the NZ. In the HAZ, the grain size is around 37 ± 0.21 μm and is bigger than that in the TMAZ. The maximum Vickers hardness value at the NZ center is 231.9 ± 2 Hv, and uniformly reduces to 100 ± 2.4 Hv in the TMAZ and 65 ± 1.3 Hv in the HAZ and then increases to 98 ± 1 Hv in the base material (BM). The maximum ultimate tensile strength (UTS) of FSW joint was found to be around 102.55 ± 3 MPa with elongation at fracture of 2.5%. The BM UTS was 154 ± 4.5 MPa. For a tool rotation speed of 800RPM and a weld speed of 20 mm/min a maximum joint efficiency of 67%. was obtained. Hence these were chosen as the optimum process parameters to join the alloy Al–Ce–Si–Mg by FSW.

The influence of hand hole on the ultimate strength and crack pattern of shield tunnel segment joints by scaled model test

With the shield tunnel going deeper and deeper, the circumferential axial force becomes the governing factor rather than the bending moment. The hand hole acts as a weak point and initial damage in the segment joint especially when the circumferential axial force is extremely high. Despite the wide application of steel fiber or synthetic fiber in the tunneling, limited researches focus on the structural responses of segment joint with macro structural synthetic fiber (MSSF). In this paper, a 1:2 reduced-scale experiment was conducted to study the structural performance of the segment joint with different types of hand holes under ultra-high axial force. Special attention is paid to failure mode and structural performance (bearing capacity, deformation, cracking, and toughness). Moreover, segment joints with MSSF are also tested to evaluate the effects of MSSF on the failure mode and structural performance of the segment joints. The experiment results show that the hand hole becomes the weakest point of the segment joint under ultra-high axial force. A \ /-type crack pattern is always observed before the final failure of the segment joints. Different types and sizes of the hand hole have different degree of influences on the structural behavior of segment joints. The segment joint with MSSF shows higher ultimate bearing capacity and toughness compared to segment joint with common concrete. Besides, the MSSF improves the initial cracking load and anti-spallling resistance of the segment joint.

An Optimization of Welding Process Parameters :To Maximize the Ultimate Tensile Strength of Lap Welding Joint by using Orthogonal Array and Taguchi Method followed by ANOVA Techniques

An Optimization of Welding Process Parameters :To Maximize the Ultimate Tensile Strength of Lap Welding Joint by using Orthogonal Array and Taguchi Method followed by ANOVA Techniques

Effects of supporting plate hole and welding force on weld formation and mechanical property of friction plug joints for AA2219-T87 friction stir welds

Friction plug welding (FPW) experiments were performed on 8-mm-thick 2219-T87 FSW welds to investigate the weld formation, microstructure, hardness distribution, mechanical property, and fracture behaviors of FPW joint. The main findings are as follows: geometric size of supporting plate hole and welding force exert great effect on weld formation and mechanical property. Recrystallized zone (RZ) with varied width is observed on the bonding interface between the plug and base metal due to huge friction heat and deformation. Softening is found near the bonding interface due to the disappearance of cold working and transformation of constituent particles. The ultimate tensile strength (UTS) and elongation of FPW joint can reach 336.3MPa and 8%, respectively. The initial fracture of tensile specimen is prone to locate at the lower part of RZ. The tensile fracture morphology of FPW joint is characterized by dimples.

Trustworthiness in Modeling Unreinforced and Reinforced T-Joints with Finite Elements

As required by regulations, Finite Element Analyses (FEA) can be used to investigate the behavior of joints which might be complex to design due to the presence of geometrical and material discontinuities. The static behavior of such problems is mesh dependent, thus these results must be calibrated by using laboratory tests or reference data. Once the Finite Element (FE) model is correctly setup, the same settings can be used to study joints for which no reference is available. The present work analyzes the static strength of reinforced T-joints and sheds light on the following aspects: shell elements are a valid alternative to solid modeling; the best combination of element type and mesh density for several configurations is shown; the ultimate static strength of joints can be predicted, as well as when mechanical properties are roughly introduced for some FE topologies. The increase in strength of 12 unreinforced and reinforced (with collar or doubler plate) T-joints subjected to axial brace loading is studied. The present studies are compared with the literature and practical remarks are given in the conclusion section.

Influence of sutures configuration on the strength of tendon-patch joints for rotator cuff tears treatment

PurposeMassive rotator cuff tears are common in the aging population. The incidence of failed rotator cuff repairs is still quite high, especially in the treatment of full-thickness tears or revision repairs. In this context, natural and synthetic meshes can be used as augmentation scaffolds or as devices to close the gap between a retracted tendon and the bone.The purpose of this work is to evaluate the ultimate tensile strength of different tendon-patch joints in order to consider their use in the treatment of massive cuff tears. Materials and methodsPorcine tendons and a synthetic low-density polypropylene mesh have been used. A preliminary study on the tensile strength of tendons and patches has been performed. Different patch-tendon joints have been studied by modifying the number and the layout of the sutures. For every joint, the tensile test, performed through an electromechanical machine, has been repeated at least twice to obtain reliable data. ResultsExperimental tensile tests on tendons and patches have given good results with very low dispersion data. Mean values of the calculated ultimate tensile stresses are, respectively, about 34 MPa and 16 MPa for tendons and patches. As regards the sutures arrangement, the staggered layout gave, for all joints, a higher tensile strength than the regular (aligned) one. Different ultimate tensile stress values, depending on the sutures number and layout, have been calculated for the joints. ConclusionSynthetic patches could be an interesting option to repair massive cuff tears and to improve, in a significant way, pain, range of motion and strength at time 0, so reducing the rehabilitation time. Obtained results demonstrated that joints with a suitable number and layout of sutures could ensure very good mechanical performances. The failure load of the tendon-patch joint, in fact, is higher than the working load on a healthy tendon.

Application of an artificial neural network model to predict the ultimate tensile strength of friction-welded titanium tubes

This paper presents an investigation to establish the link between friction welding process parameters and the ultimate tensile strength (UTS) of friction-welded titanium joints by application of an artificial neural network (ANN) technique. The experimental matrix is based on a central composite design with parameters varied at five levels. The UTS of the joints was modeled by the application of the response surface method (RSM). The joint UTS was also simulated by the application of a feed-forward back-propagation ANN with a single hidden layer composing of 20 neurons. The ANN was tested against and trained with the experimental data. The influence of the various parameters on the UTS was assessed by performing a sensitivity analysis. Lastly, the predictions of both the RSM model and the ANN were compared with one another. The results indicate that ANN is indeed a feasible technique for modeling and predicting the effect of process parameters on the UTS for friction welding of titanium tubes. When compared to RSM, ANN displayed a closer agreement with the data. In both cases, however, prediction errors were within 5%. Moreover, the link between the various process parameters and the UTS of the weld joints was also examined and commented upon.

Model for the evaluation of the beam-column joint ultimate strength -a more simplified version

In this study, a well-established model and a new simplified version of it, that help avoid collapses in reinforced concrete structures during strong earthquakes, are presented and discussed. Using this model, the initial formation of plastic hinges and the final concentration of the damages only in beams are accurately assured. The model also assures that the columns and the beam-column joints can remain intact. This model can be applied for the design of modern R/C structures, as well as for the design of strengthening schemes of old R/C structures by the use of reinforced concrete jackets. The model can also predict the form of earthquake damages in old structures but also earthquake damages in the modern structures.

Optimization of FSW parameters for maximum UTS of AA6082/SiC/10P composites

Friction stir welding (FSW) offers significant advantage when compared with fusion joining process such as no shield gas or flux are used, no harmful gases are produced, thereby making the FSW environmentally friendly. In this work, an experimental approach has been used for studying and optimizing the FSW process, applied on AA6082/SiC/10P composite plates. In particular, the effect of process parameters on ultimate tensile strength (UTS) of FSW joint has been investigated. The UTS of FSW joints is affected by FSW parameters. The FSW of the AA6082/SiC/10P composite plates was carried out with different combinations of FSW parameters. The experiments were conducted according to the Taguchi’s L9 orthogonal array. Taguchi method of designing the experiments was used for optimization of the FSW parameters. The signal to noise ratio and analysis of variance were used to determine the effects of FSW parameters on the UTS of the welded joints. The optimum FSW parameters for the maximum UTS were found to be the tool rotation speed of 1800 r/min, the welding speed of 100 mm/min and the tool tilt angle of 2°. UTS increased by 24.5% when FSW was carried out at optimum process parameters as compared to initial FSW parameters. Results have shown good agreement between the predicted and experimental values of UTS. High tensile strength is required for use of FSWed AA6082/SiC/10P composite joints in aerospace industry.

Slip Coefficient and Ultimate Strength of High-Strength Bolted Friction Joints with Compact Bolt Spacing and Edge Distance

In current design codes, the minimum bolt spacing and edge distance for high-strength bolted friction joints are specified based on the bolt diameter, regardless of the plate thickness or steel strength. However, the mechanical performance of joints with a more compact bolt spacing than that given in the current design specifications has been little examined. In this study, the slip and ultimate strength of high-strength bolted joints with a compact bolt spacing and edge distance were investigated. Tensile tests were conducted on friction-type joints with various bolt arrangements. The use of a compact bolt arrangement was not observed to have a negative influence on the slip strength in these tests. The estimated strengths corresponding to the experimentally observed failure modes were found to agree fairly well with the experimental results within a 10% error. A parametric finite element analysis was also conducted to investigate the influence of the bolt arrangement on the slip coefficient. It was concluded that the bolt spacing and edge distance have little influence on the slip coefficient.

Fabrication of AA6061-T6/Al<sub>2</sub>O<sub>3</sub> Reinforced Nanocomposite Using Friction Stir Welding

In the present work, attempts were made to join AA6061-T6 sheets by Friction Stir Welding (FSW) process. Al₂O₃ nanoparticles were added into the aluminum matrix for refining the microstructure of the nugget zone (NZ) and to restrict the growth of granularly in the heat-affected zone (HAZ). In order to illustrate the influence of Al₂O₃ nanoparticles on mechanical properties, namely ultimate tensile strength, micro-hardness distribution, and wear resistance of the welded joints, FSW was conducted with and without nanoparticles at a constant rotating velocity of 2000 rpm and transverse velocity of 70 mm/min. For characterization of microstructures, optical and scanning electron microscopes were employed. The findings revealed that Al₂O₃ nanoparticles addition along the joint line resulted in remarkable refining of grains structure in the weld nugget zone. This was due to the pinning effect produced by nano-sized Al₂O₃ particles which prevent the grain growth followed by recrystallization during FSW, leading to a remarkable reduction in grain size. Also, the sample with nanoparticles joined at rotating and transverse velocities of 2000 rpm and 70 mm/min showed higher tensile properties than the sample without nanoparticles. However, the employment of single FSW pass resulted in an unusual Al₂O₃ nanoparticles distribution and void initiation at the interface between Al-matrix and Al₂O₃ nanoparticles in the heat-affected zone resulted in the early fracture of welded joints during tensile loading. Moreover, Al₂O₃ nanoparticles addition results in the reduction of frictional coefficient and increment in wear resistance due to fine small grains size and large distribution of hardness in NZ of friction stir welded specimens.

Optimization of Process Parameters on Friction Stir Welding of AA 6082-T6 Butt Joints Using Taguchi Method

Abstract Friction Stir Welding (FSW) was carried out on Aluminum Alloy 6082-T6 plates with dimensions of 200 × 70 × 2 mm. Design of Experiment (DOE) was applied to determine the most important factors which influence the Ultimate Tensile Strength (UTS) and Hardness (HV) of AA 6082-T6 joints produced by Friction Stir Welding (FSW). Effect of two factors which include tool rotational speed and welding speed on (UTS, HV) were investigated by Taguchi method using L9 orthogonal array to find the optimum process parameters. An analysis of variance (ANOVA) was carried out to determine which of the selected factors are more significant on both of responses, the optimum parameters for the higher UTS it found by using a rotational speed of 1400 rpm and 125 mm/min for the welding speed, also 1400 rpm and 160 mm/min to maximize Hardness (HV).

Improving microstructural and tensile properties of AZ31B magnesium alloy joints by stationary shoulder friction stir welding

Sound AZ31B magnesium alloy welds with glossy surface appearance and little flash were achieved for the first time by lower heat input stationary shoulder friction stir welding (SSFSW) at different rotational speeds (700–1500 rpm) and a constant welding speed (50 mm/min). Results show that a bowl-shaped stir zone (SZ) with fine equiaxed grains is present, and its grain size increases as increasing the tool rotational speed. The lowest Vickers hardness appears in the thermo-mechanically affected zone (TMAZ) on the advancing side. As the rotational speed increases, the ultimate tensile strength of joints also increases, while the yield stress and elongation at fracture decrease. An exceptionally high joint efficiency of 97% has been achieved at the rotational speed of 1500 rpm. In addition, the SSFSWed joints show higher strain hardening capacity due to dynamic recrystallization in the SZs. The fracture locations of joints shift from TMAZ to SZ with the increase of rotational speed. Fracture morphologies of the SSFSWed joints are characterized as the mixture of shear and ductile fracture modes.

Ultimate strength of tubular T-joints reinforced with doubler plates after fire exposure

Two doubler-plate-reinforced tubular T-joint specimens were tested to failure under axial loading. One specimen was tested at ambient temperature and the other was tested after a heating and cooling process. The failure mode for both specimens was the overall flexural failure of the chord. Load-displacement curves revealed that the heating and cooling process did not exert any negative influence on the stiffness of the joints but did slightly diminish their ultimate strength. A finite element (FE) method was then developed to simulate the structural response of the joint during a complete fire process, including ambient-temperature, heating, cooling, and post-fire stages. The results of the FE simulation were compared with the experimental data and that from previous literature. The comparison illustrated that the FE method reliably and accurately predicted the structural response of the joints. The FE method was then used in a parametric study, which revealed that the ultimate strength of the joint increased with β, ξ, and ε, but did not change with τ ranging from 0.4 to 0.8. Statistical analysis of the FE results indicated that the “twice elastic slope method” was more general and efficient than the 3% deformation limit for determining the ultimate strength of tubular joints. A simple approach to evaluate the post-fire strength of tubular T-joints reinforced with doubler plates is discussed.

Microstructure, mechanical properties and stress corrosion behavior of friction stir welded joint of Al–Mg–Si alloy extrusion

Microstructure, mechanical properties and stress corrosion behavior of friction stir welded (FSWed) Al–Mg–Si alloy were investigated. The average grain sizes of shoulder-affected zone (SAZ), nugget zone (NZ), heat-affected zone (HAZ) and base material (BM) are 6.03, 4.80, 168.30 and 127.24 μm, respectively. The thermo-mechanically affected zone (TMAZ), which is generated on the edge position between HAZ and weld nugget zone, has a narrow width of 400 μm. The ultimate tensile strength (UTS) of FSWed joint is 232.20 MPa, about 91.04% with respect to that of base material of 255.06 MPa, and the joint fracture occurs at HAZ on advancing side (AS). The FSWed joint is more susceptive to stress corrosion cracking (SCC) than base material, and the SCC susceptibility increases with the rise in temperature. The residual UTS of FSWed joints in constant loaded tests at the load levels of 90, 105 and 120 MPa is 89.97%, 67.50% and 54.75% of the UST of FSWed joint in air, respectively. The increase of the load in constant loaded tests and four-point beam-bent tests accelerates the SCC of FSWed joints.

Optimization of mechanical and microstructural properties of friction stir spot welded AA 6061-T6 reinforced with SiC nanoparticles

The aim of this study is to improve weld characteristics employing a new proposed method in adding SiC reinforcement nanoparticles to friction stir spot welds (FSSW). 6061-T6 aluminum alloy plates 3 mm in thickness and SiC nanoparticles 45 to 65 nm in diameter were used in FSSW. Design of experiments, S/N ratio analysis and optimization of joint ultimate strength were conducted using Taguchi method. In this way, the amount of nanopowder, tool rotational speed and dwell time were considered as input parameters to optimize joint ultimate strength. A confirmation test was also conducted which validated optimal measure predicted by Taguchi. The fracture mode of each examined specimen was specified by an investigation of their force-displacement graphs and failed nugget surfaces. The specimen microstructures were examined next and grain size and nanoparticles distribution in weld region were evaluated. Achieved results justified the effect of design parameters on ultimate strength and microhardness of the joint. Energy dispersive x-ray spectroscopy (EDS) indicated that nanoparticles assembled in grain boundaries during dynamic recrystallization and prevented the growth of grain size. Incorporation of SiC nanoparticles in FSSW increased joint ultimate strength and average hardness in stir zone (SZ) up to 28% and 24%, respectively.

Mechanical behavior of 7085-T7452 aluminum alloy thick plate joint produced by double-sided friction stir welding: Effect of welding parameters and strain rates

Mechanical behavior of double-sided friction stir welding (DS-FSW) aluminum alloy thick plate joints under various rotational rates and welding speeds tested at different strain rates were investigated. The results show that both the yield stress (YS) and the elongation to failure of DS-FSW joints increase, but the ultimate tensile strength (UTS) of defect-free joints decrease with the decrease of strain rate from 10−2 s−1 to 10−5 s−1. A remarkable reduction in the YS, UTS and elongation to failure presents, particularly at the top slice of 950/60 joint, reaching approximately 65%, 68% and 25% of the BM tested at a strain rate of 10−4 s−1and fails through brittle fracture. The top slice presents the highest strength and the middle slice has the largest ductility, the same as change laws of joint efficiency and strain hardening behavior among three slices. The best welding parameters is the rotational rate of 300 rpm and welding speed of 60 mm/min due to the higher and the smaller fluctuation of strength and ductility for different slices.