Tensile Shear Loading Conditions Research Articles

Experimental and numerical research for the failure behavior of the dieless clinching joints

In this work, the failure behavior of dieless clinching joints for AA5052-H32 aluminum alloy under cross tension and tensile shear loading conditions was investigated by experimental and simulation methods. Firstly, The VUMAT subroutine for the N–H shear-modified GTN model (Proposed by Nahshon and Hutchinson, a modified GTN model considering hole shear effects) was written. Subsequently, the conventional and shear parameters calibration was accomplished. A finite element model (FEM) for the failure process of dieless clinching joints based on the N–H shear-modified GTN microscopic damage model, elimination of large deformation mesh distortion and consideration of the material hardening history was established. In addition, the deformation, damage and destruction processes of the joint under two loading conditions were analyzed. And macro/microfracture analysis of the failed joints was performed to further reveal the failure behavior. The results show that the established FEM of the failure process agrees well with the experimental results and failure modes are consistent. The model accuracy in predicting the tensile and shear loads is 91.9% and 92.7%, respectively. This provides a reference for the process design and joint arrangement of the dieless clinching joints in practical applications.

Resistance spot welding of NiTi shape memory alloy sheets: Microstructural evolution and mechanical properties

Resistance spot welding was used for welding superelastic NiTi shape memory alloy sheets. The microstructure of the welded sample showed a fully austenitic NiTi nugget without any visible weld defect due to the insignificant change in the transformation temperature during the welding process. Additionally, the fusion zone has a homogenous microhardness distribution with an average hardness value of ~340 HV, which is below the average hardness value for NiTi base material (~410 HV) because of the large grain size in the weld nugget. The perseverance of the superelastic response as a main functional property of NiTi alloy after the RSW procedure is significant. The welded sample failed via pullout failure mode during tensile shear loading conditions. Face digital image correlation imaging confirmed that strain is localized in the area around the nugget. The dominant fracture mode of the sample during tension-shear loading was ductile, and the EBSD results of the fracture area revealed the excessive deformation around the HAZ resulted in a transgranular fracture. Therefore, resistance spot welding is highly capable of providing a sound, straightforward and reliable joint between NiTi sheets.

RETRACTED ARTICLE: An investigation on mechanical and metallurgical properties of 2024-T3 aluminum alloy spot friction welds

In this study, the spot friction welding of 2024-T3 aluminum alloy with 1.6 mm in thickness has been investigated. The effects of the tool rotational speed (630, 1000, and 1600 rpm), shoulder penetration depth (0.3 and 0.7 mm), and pin geometry (cylindrical and triangular shape) have been discussed on the metallurgical and mechanical properties. Results indicated that the pin geometry has a considerable effect on the shape of the stir zone. The results of tensile shear tests showed that the tensile shear load increased with increasing rotational speed in the shoulder penetration depth of 0.3 mm, while high shoulder penetration depth had a bilateral effect on the tensile shear load. In addition, the results showed that the tensile shear load of welds made with the triangular pin at a low rotational speed, and a low shoulder penetration depth was more than of welds made with the cylindrical one, which was attributed to a finer grain size generated in the stir zone. Observation of the failed specimens indicated two types of failure modes under tensile shear loading conditions including the fractures that occurred in the vicinity of keyhole (shear fracture) and the fractures that occurred in shoulder indentation (tensile shear-mixed fracture mode). The microhardness tests with both pins showed that the minimum hardness was measured in the heat-affected zone.

Characterization of microstructure and deformation behaviour of resistance spot welded AZ31 magnesium alloy

Resistance spot welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy. The microstructure and composition analysis of weld nugget, heat affected zone (HAZ) and base metal were examined using optical and scanning electron microscopy (HR-SEM and EDS/X). The resistance spot welded magnesium alloy joints consist mainly of weld nugget and HAZ. The nugget contains two different structures, i.e. the cellular-dendritic structure at the edge of the nugget and the equiaxed dendritic structure in the centre of the nugget. The structure transition is attributed to the changes of solidification conditions. In the HAZ, grain boundary melting occurred and grain boundaries became coarse. It has been shown that hardness reduction in the weld nugget and HAZ compared with base metal is evident due to dendritic microstructure and grain growth, respectively. The results showed that spot welded joints have failed in interfacial mode under torsion and tensile–shear loading conditions. Digital image correlation during tensile–shear testing showed that low surface strains occur in the interfacial failure mode, because fracture and deformation happened primarily in the nugget area.

Susceptibility to interfacial failure mode in similar and dissimilar resistance spot welds of DP600 dual phase steel and low carbon steel during cross-tension and tensile-shear loading conditions

Abstract The paper investigates the failure mode transition from interfacial to pullout in similar and dissimilar combinations of DP600 dual phase steel and low carbon steel (LCS) under tensile-shear (TS) and cross-tension (CT) loading conditions. In both CT and TS loading conditions, a transition in the failure mode from interfacial to pullout was observed with increasing fusion zone size beyond a critical value (DC). The tendency to fail in interfacial mode during the CT loading was increased in the order of LCS/LCS, DP600/LCS and DP600/DP600. It was shown that interfacial to pullout failure mode transition during the CT test is governed by the fracture toughness of the fusion zone and strength of the pullout failure location (i.e. heat affected zone). It was shown that increasing carbon equivalent of the fusion zone promoted interfacial failure mode in CT loading condition. The high carbon equivalent of DP600 steel led to formation of hard and brittle martensite, which in turn promotes crack propagation through fusion zone. In DP600/LCS combination, decreased carbon equivalent and fusion zone hardness through dilution with the LCS promotes pullout failure at smaller weld sizes. DC during the TS loading is increased in the order of DP600/LCS, LCS/LCS and DP600/DP600. No correlation between fusion zone carbon equivalent and the tendency to fail in IF mode during TS loading was found. Failure mode transition during the TS loading is controlled by hardness of fusion zone and stiffness of the joint. The lowest DC for DP600/LCS is a function of its high fusion zone hardness (in comparison to LCS/LCS combination) and its low stiffness (in comparison to DP600/DP600 combination).

Mechanical Properties and Fracture Behavior of Friction Stir Spot Welded AZ61 Magnesium Alloys

In this study, the tensile shear strength and the fracture behavior of friction stir spot welded AZ61 joints in lap-shear configuration were investigated. The heat input was measured in FSSW to help analyze the effect of welding parameters on the strength. The tensile shear failure test was performed in a material testing system. The cross section of the joints and the fracture surface of the failed specimens were analyzed using optical microscopy and scanning electron microscopy. Results show that the weld diameter and the tensile shear load increase with increasing the input heat. The path of the material flow formed during FSSW process would provide a good way for crack propagation. All failed specimens in this study appear the same fracture features and show a circumferential failure mode under tensile shear loading conditions. The failure is initiated from a notch tip in the upper sheet loading side, and then propagates along the interface of the upper and lower sheets, then through the stir zone circumference; finally, a small portion of the lower sheet in the lower sheet loading side is torn off with some part of the stir zone.

Effects of welding parameters on microstructure and mechanical properties of resistance spot welded magnesium alloy joints

Effects of welding parameters on spot welded magnesium alloy joints have been investigated. With increasing welding time, the weld nugget diameter increased and the nugget microstructure became coarser. The joint strength (shear load at failure) of 2930–3050 N was obtained when welding time was longer than six cycles. Increasing welding currents from 15 to 23 kA resulted in an increase in the joint strength due to an increase in the nugget diameter. In the range of 1˙5–4˙5 kN electrode force, lowering the electrode force favours increasing the weld nugget diameter and improving the joint strength, but too low electrode force (1˙5 kN) easily causes metal expulsion. The joints have two failure modes (interfacial failure and button pullout failure) under tensile shear loading conditions. For the button pullout failure, the crack initiates at cellular dendritic structure of nuggets and propagates along the cellular dendritic structure, heat affected zone (HAZ) and base metal in sequence.

On the Shear Strength and Mixed-mode Fracture Toughness of a Lead-Tin and a Tin-Silver Solder

ABSTRACTThe increasing demands on solder joints have made it imperative that they perform not only their traditional role of electrical connection but also possess good mechanical integrity. One such key mechanical property is the shear strength of the solder. A number of specimen geometries can be used to evaluate the shear strength of solders, each with its advantages and limitations. This study uses a modified double lap shear geometry to measure the shear strength of the solders as a function of strain rate. It is ahown that the shear strength measured this way is truly reflective of the complex composite formed by the copper, solder and intermetallics and may be more representative of actual conditions of use rather than measurements of the shear strengths of the bulk solder. The study also uses a modified compact tension specimen to measure the fracture of the solder under combined tensile-shear loading conditions. It is shown that the solder fracture under these conditions follows the general principles of a mixed-mode fracture mechanism map.