Joint Cross-section Research Articles

Investigation into the Effect of Interlock Volume on SPR Strength

During the design of automotive structures assembled using Self-Piercing Rivets (SPRs), a rivet and die combination is selected for each joint stack. To conduct extensive physical tensile testing on every joint combination to determine the range of strength achieved by each rivet-die combination, a great deal of lab technician time and substrate material are required. It is much simpler and less material-consuming to select the rivet and die solution by examining the cross sections of joints. However, the current methods of measuring cross sections by measuring the amount of mechanical interlock in a linear X-Y direction, achieved with the flared rivet tail, do not give an accurate prediction of joint strength, because they do not measure the full amount of material that must be defeated to pull the rivet tail out of the bottom sheet. The X-Y linear interlock measurement approach also makes it difficult to rapidly rank joint solutions, as it creates two values for each cross section rather than a single value. This study investigates an innovative new measurement method developed by the authors called Volumelock. The approach measures the volume of material that must be defeated to pull out the rivet. Creating a single measurement value for each rivet-die combination makes it much easier to compare different rivet and die solutions; to identify solutions that work well across a number of different stacks; to aid the grouping of stacks on one setter for low-volume line; and to select the strongest solutions for a high-volume line where only one or two different stacks are made by each setter. The joint stack results in this paper indicate that there is a good predictive relationship between the new Volumelock method and peel strength, measured by physical cross-tension testing. In this study, the Volumelock approach predicted the peel strength within a 5% error margin.

Failure Analysis of Printed Circuit Board Solder Joint under Thermal Shock

Investigating the failure mechanism of solder joints under different temperature conditions is significant to ensure the service life of a printed circuit board (PCB). In this research, the stress and strain distribution of a PCB solder joint was evaluated by high- and low-temperature thermal shock tests. The cross-section of the solder joint after thermal shock testing was measured using a 3D stereoscopic microscope and SEM equipped with EDS. The microstructure of the lead-free solder joint and the phase of the intermetallic compound (IMC) layer were studied by XRD. The working state of the PCB solder joint under thermal shock was simulated and analyzed by the finite element method. The results show that thermal shock has a great effect on the reliability of solder joints. The location of the actual crack is consistent with the maximum stress–strain concentration area of the simulated solder joint. The brittle Cu6Sn5 and Cu3Sn phases at the interface accelerate the failure of solder joints. Limiting the growth of Cu6Sn5 and Cu3Sn phases can improve the reliability of solder joints to a certain extent.

Evaluation of residual stresses in CO2 laser beam welding of SS316L weldments using FEA

Laser welding is used in critical component production when tight tolerances like minimal distortions and residual stresses are required. Laser beam welding offers a lower heat input, a smaller heat affected zone, lower residual stresses, minimum distortions, and greater mechanical joint characteristics than conventional welding does. In order to simulate the laser welding process used on SS316L plates, the Gaussian heat source model was used. The model is developed and simulated with volumetric heat source model with APDL coding using ANSYS. The thermal profiles at the joint cross sections via welded area, interface across joints is taken for the analysis. The maximum temperature was observed at the fusion zone and associated zones. The residual stresses are analysed in the same path and found the stresses are in safe limits of base material. Predicted and experimentally measured residual stresses are close agreement with 10%.

Effect of material combinations on mechanical properties of flat bottom riveted joint

Flat bottom riveting is a newly developed joining technique. Since the bottom surface of joint is flat, the joint can be applied in areas that need a high degree of smoothness. This article investigated the effect of material combinations on mechanical properties of joints. Four material combinations which involved two kinds of aluminum alloy were produced. Cross sections of joints were observed by metallographic microscope and geometrical parameters of joints were measured. It was found that material combinations exerted significant influence on the geometrical parameters of joints. When the bottom sheet remained the same, with the increase of top sheet hardness, the interlock thickness of joint decreased, while the neck thickness of joint increased. Tensile and shearing tests were conducted on joint to obtain the tensile load and the shearing load of joint. The absorbed energy of joint in shearing test was calculated. Results showed that when joining materials with different hardness values, the joint with high hardness sheet on the top exhibited higher static load than the joint with high hardness sheet on the bottom. In tensile tests, 1060–5052 joint failed in the manner of neck fracture, while other joints failed in the manner of button separation. In shearing tests, 5052–1060 joint failed in the manner of button separation, while other joints failed in the manner of neck fracture.

Effect of the meltdown on thermoplastic joint produced by quasi-simultaneous laser transmission welding

This study aims to investigate the effect of the polymer pair meltdown process and mechanical properties using three different laser transparencies 20%, 30% and modulated, ranging from a minimum 27% to a maximum 47%. The cross-sections of joints were analysed with an optical microscope. Burst pressure was performed to evaluate the strength of welded joints produced with different laser welding process parameters. Welding parameters, scanning speed and meltdown were varied and their influence on the quality of the polymer joint was recorded and evaluated. With the increase of meltdown, a more molten volume of polymer can be seen in the cross-section area. It was shown that with the increase of meltdown, the formation of pores occurred due to the high energy concentration obtained within each laser scan passing across the weld seam. The decrease of burst pressure in all polymer pairs was observed with 0.33 mm and 0.34 mm targeted meltdown. Burn marks and burned lines were observed in joints with 20% laser transparency. Modulated laser transparency influenced non-homogeneous temperature distribution inside the joint, which influenced the formation of heat-affected zones (HAZ) and pores. A study of the influence of cooling time on joint formation showed that it is possible to variate total meltdown while changing cooling time until the joint is solidified. • Within the increase of meltdown, bigger weld flash occurred inside weld seam. • Peak weld strength observed at specific meltdown values. • The decrease of weld strength is influenced by defect formation inside seam. • Non-homogeneous melting, HAZ observed with modulated laser transparency polymers. • Total meltdown can be controlled by modulating cooling time.

Direct microwelding of dissimilar glass and Kovar alloy without optical contact using femtosecond laser pulses

In the current microwelding process using femtosecond (fs) laser between dissimilar materials, surface polishing and pressure assistance, so-called optical contact, are believed necessary. In this paper, direct welding of soda lime glass and Kovar alloy using a fs laser is investigated to overcome the limit of optical contact. The processing of fs laser welding is comprehensively studied by varying the laser power, welding velocity and the number of welding. The shear joining strength is as high as 2 MPa. The cross-section of glass-Kovar alloy joints, the elemental diffusion and the fracture behavior of welded joints were studied. The results show that the fs laser irradiates the surface of Kovar alloy, micron/nanometer-sized metal particles are generated. These particles perform the role as an adhesive part in the welding process. It is believed that the Si atoms diffuses to Kovar alloy from the glass and partially replaces the Fe2+ ions on the surface of Kovar alloy, indicating that the mixing and interdiffusion of materials have occurred during the welding process. Finally, the welded sample was tested and has excellent water resistance and sealing property. Furthermore, to justify that this method can be applied to other stack ups, the glass-copper, the glass-Al6063 and sapphire-ceramic are also welded together. This work greatly simplifies the fs laser microwelding process and promotes its industrial applications, such as optoelectronic devices, medical devices and MEMS.

Laser-joined aluminium–polypropylene sheets: the effect of the surface preparation of aluminium

The aim of this paper is to determine the effect of aluminium surface preparation on the load-bearing capacity of laser-joined aluminium–polypropylene (Al-PP) specimens. The surface of the aluminium is prepared by chemical cleaning and laser engraving. The effect of pulse frequency, engraving speed and repetition number during laser engraving is investigated on the geometric parameters of the structure (straight groove) created on the surface of AA6082 aluminium alloy. Quasi-static shear testing of Al-PP joints is performed to determine how the amount and distance of the grooves affect the load-bearing capacity of the joints. The highest ultimate shear force (1250 ± 35 N) was achieved when many (21) grooves were formed with a laser engraving frequency of 20 kHz, a slow engraving speed (5 mm s−1) and many engraving repetitions (10) in the aluminium specimen. This corresponds to a shear strength of 3.1 MPa, which is 72.5% of the shear strength of the PP material used. Microscopic evaluation of joint cross-sections confirmed that the molten PP completely filled the grooves on the aluminium surface.Graphical abstract

Electrochemical behavior of friction stir welded joint of ultra-low carbon steel

In this study, friction stir welding of ultra low carbon steel was performed at tool rotational speeds in the range from 300 to 750rpm with 150rpm increments at 60mm/min fixed traverse speed. Throughout study was performed on macro and micro structures in order to determine the several welded zones for example stir zone, thermo-mechanically affected zone, and heat-affected zone. Microhardness profiles were performed along the welded joint's cross section and the utmost hardness was obtained at stir or nugget zone as compared to the other zones of the welded joints. The hardness values on the stir zone decreases with rise in tool rotating speed. Electrochemical study was investigated in 3.5%NaCl electrolyte solution. Corrosion rate is maximum (~27MPY) at 300 rpm stir zone and minimum value (~0.3 MPY) obtained at heat affected zone at 750rpm welded sample.

Determining the Charred Layer of Wooden Beams with Finite Element Analysis Based on Enthalpy Approach

In the process of computer modeling the formation of a charred layer in wood materials, it is important to implement the correct material data. In thermal analysis, there exist two different approaches of implementation: the temperature-dependent material data properties, heat capacity approach and enthalpy approach, which is not commonly used but which has a few advantages. This approach should be examined in more detail because it can solve the problem associated with inaccurate results at temperatures around 100 °C. This scientific paper deals with the assessment of the computer-aided fire modeling and simulation suitability based on the enthalpy approach for determining the charred layer of structural elements. The structural elements selected for testing were spruce wooden beams with rectangular and circular cross-sections. A finite element model (FEM) was created in ANSYS software. The model was validated by medium-scale fire tests data of the spruce wooden beams loaded with a radiation panel. Boundary conditions were identical to the medium-scale fire test. Due to the enthalpy approach, the temperature curves from the simulations also faithfully simulated the section with a constant temperature around 100 °C. Within the temperature profiles, the accuracy of simulations averaged 91.7%. The accuracy of the simulations describing the total area of the charred layer was 93.0% on average. Presented FEM can be used in the search for new construction solutions for wooden elements and modifications to the design of cross-sections of wooden beams or wooden joints so that they can better withstand fire conditions.

Development of anti-oxidation Ag salt paste for large-area (35 × 35 mm2) Cu-Cu bonding with ultra-high bonding strength

In this paper, by proposing a novel and low-cost Ag salt paste, a robustly and large-area (35 × 35 mm2) bare Cu to Cu bonding was realized under a low sintering pressure of 0.8 MPa and a low sintering temperature of 300 °C in air atmospheric conditions. The relationship between the bonding strength and microstructure changes of sintered Ag under various bonding conditions was investigated in detail. The large-area bonded plate exhibits low porosity about 10% and low percentage of voids, which result in ultra-high bonding strength over 58 MPa. More importantly, the introduction of reducing agent formic acid (CH2O2) and the low porosity successfully improve the anti-oxidation of novel Ag salt paste during sintering process, result in pure Cu-Ag-Cu bonding. The cross-section of the Ag joints was obtained to explain the bonding pattern, in which Cu was oxidized only at the edge of the sintering interface, and no Cu oxide generated in middle bonding section. The development of novel Ag salt paste successfully addresses the energy-intensive process and low bonding strength faced by large-scale sintering, which greatly promotes the high-temperature applications of power device.

Experimental investigation of high impact polystyrene/metal self‐piercing riveted joint

AbstractSelf‐piercing riveting was adopted to join high impact polystyrene (HIPS) and metal sheets which had huge difference in material properties. Three kinds of metal sheet (AA1060, AA5052, and HC340LA) were joined to HIPS sheet. The effect of polymer sheet thickness on mechanical properties of joints was investigated. The static loads of joints were measured in tensile and shearing tests. The failure modes of joints were analyzed. The cross sections of joints were observed by metallographic microscope. Results showed that self‐piercing riveting could effectively join HIPS and metal sheets when polymer sheet was placed as top sheet. All joints failed in the manner of polymer fracture in both tensile and shearing tests. For joints with different sheet material combinations, though the cross sections and geometrical parameters of joints had great difference, the static loads and absorbed energy values of joints were nearly the same. When AA5052 sheets were joined to HIPS sheets with different thickness values, with the increase of polymer sheet thickness, the flaring degree of rivet decreased, while static loads and absorbed energy values of joints increased. This was because the strength of interlock structure was higher than that of polymer sheet and the strength of joint was determined by the strength of polymer sheet.

Riv-Bonding of Aluminum Alloys with High-Strength Steels against the Favorable Joining Direction

In order to exploit the advantages offered by multi-material design, this work studies the feasibility of joining aluminum alloys with high-strength steels (HSS) against the favorable joining direction by using self-piercing riveting (SPR) combined with adhesive bonding, so-called riv-bonding. Therefore, riv-bonding of four joint configurations including different aluminum alloy sheets (AW-6014-PX, AW-6451-T4), HSS sheets (HC420LA, HC450X) and rivet types (C5.3×8.0-H4, U5.5×5.0-H6) was experimentally investigated. Moreover, riv-bonding of two joint configurations was exemplarily modeled using the Simufact Forming finite element (FE) software. The viscoelastic properties of the liquid adhesive layer between the sheets were substituted with “equivalent” elastoplastic properties to model the adhesive as solid with strain rate-dependent flow behavior. Good agreement of joint cross sections and force-displacement curves between experiments and simulations confirms that the presented numerical model of riv-bonding is suitable for predicting both the joinability of aluminum alloys with HSS and the final quality of hybrid joints.

MECHANICAL PROPERTIES OF REPAIR WELDING HIGH YIELD STRENGTH STRUCTURAL STEEL S690Q

Repeated welding caused by welding defects in the weld joint will result in changes in the mechanical properties of the weld joint, especially in the Heat Affected Zone (HAZ). Significant changes will occur when welding on steel materials that have undergone special treatment during the manufacturing process, such as quenched and tempered S690Q steel. S690Q steel is a structural steel with high yield strength with quenched and tempered conditions. The research was conducted by doing repeated welding as a simulation of the repair process using the GMAW process. Macro observations as well as tensile, bending, hardness, toughness tests were carried out on cross sections of welded joints. From the results of all the tests carried out the results meet the requirements of the BS EN ISO 15614-1 standard, but the results of the hardness test can identify significant changes in mechanical properties in the HAZ, especially in the bottom or root pass and hot pass areas. The average hardness value decreased from 334.07 HV at the top (face) to 209.55 HV and 198.88 HV at the bottom (hot pass and root pass) on the left side of the HAZ. While on the right side of the HAZ, the hardness value is 337.40 HV to 254.34 HV and 208.64 HV.
 Keywords: HAZ, S690Q, Structural Steel, Quenched and Tempered Steel

Pre and post-welding annealing influence on the microstructure of a 7475-T7351 aluminum alloy joining by friction stir welding / Influência do recozimento pré e pós-soldagem na microestrutura de uma liga de alumínio 7475-T7351 que se une por fricção

Friction Stir Welding (FSW) promotes the joining of sheets due to localized plastic deformation and heating by displacing a non-consumable tool. This work aimed to verify the influence of an annealing heat treatment performed at 300 and 500 ºC with 15 minutes of soaking times, before and after the FSW of a 7475-T7351 aluminum alloy. The macrographs of the welded joint (top and cross section) and micrographs of the cross section was obtained by a stereoscope and optical microscope were analyzed and the mechanical behavior was characterized by uniaxial tensile tests. It was concluded that the annealing heat treatments did not influence significantly the nugget grain size, but there are indications that the realization of these before the FSW, provide a homogeneity in the mechanical properties of the welded joint and the base material.

Influence of laser power on microstructure and mechanical properties of laser welded TWIP steel butted joint

The twinning-induced plasticity (TWIP) steel is a newly developed which possesses fantastic mechanical properties and high potential for anti-crash weight-optimized structural applications. In this study, the weldability of 2 mm thick TWIP steel plate by laser welding method was investigated. The welded joint exhibited fully austenitic structure, and the weld seam consisted three types of solidification structures: columnar dendrite, cellular crystal and equiaxed dendrite. The microsegregation of C and Mn elements occurred in the interdendritic regions during the solidification of the weld seam. The toughness of the heat-affected zone (HAZ) was higher than that of the weld seam. The microhardness diagram of cross-section of welded joints presented V-shaped under different laser power. The microhardness of equiaxed dendrite zone was higher than that of the weld seam and coarse grain heat affected zone (CGHAZ). The average strain and tensile strength increased first and then decreased with the rising of laser power. Further study demonstrated that the fracture of the laser welding TWIP steel joints during tensile test presented ductile mode characteristics. The results show that the appearance and performance of the welded joint are optimal with laser power of 1800 W in present study, and the tensile strength and total elongation are 915 MPa and 48%, respectively.

Detailed characterizations of microstructure evolution, corrosion behavior and mechanical properties of refill friction stir spot welded 2219 aluminum alloy

2.0 mm thick 2219-O (upper plate) and 8.0 mm thick 2219-C10S (lower plate) were successfully fabricated using refill friction stir spot welding (RFSSW), and the microstructure evolution, corrosion behavior and mechanical properties of the joints were investigated. The results indicated that the stir zone (SZ) is characterized by refined and equiaxed grains due to dynamic recrystallization, whose grain size gradually increases, and the texture intensity decreases with the increase of the distance from the upper plate top surface. Tangled dislocations and dislocation cells are observed in the SZ, while rod-like precipitates with 20 nm–100 nm length are found in the base material (BM) of the lower plate. Also, numerous Al 2 Cu particles are observed in the upper plate BM, while only a few particles are aggregated in the lower plate BM. However, Al 2 Cu particles are fragmented and uniformly distributed in the SZ. The hardness of the upper plate and the lower plate is approximate 50 HV and 160 HV, respectively. The hardness increases gradually from top to bottom of the cross-section. The self-corrosion potential and corrosion current density of the SZ are −0.45 V and 5.62 × 10 −5 A/cm 2 , respectively. In comparison, those of the BM of the upper plate are −0.49 V and 3.16 × 10 −3 A/cm 2 , and those of the lower plate BM are −0.68 V and 7.94 × 10 −3 A/cm 2 . The electrochemical experiment indicated that the SZ presents excellent corrosion resistance, followed by upper plate BM and then lower plate BM. The corroded area has mainly occurred at the lower plate BM when the joint cross-section is immersed in the EXCO solution for one hour. However, upper and lower plate BMs are eroded seriously when the immersion time increases to two hours. Nevertheless, no obvious corrosion can be observed in the SZ. The mechanical analysis indicated that the tensile load decreases from 7.25 to 4.10 kN, and the tear load decreases from 3.20 to 1.78 kN after being immersed in the 3.5% NaCl solution for 48 h. • Refill friction stir spot welding technology has great advantages in joining aluminum alloys with unequal thickness. • The grains above the lap interface are equiaxed, while those below the lap interface are elongated. • The hardness increases gradually from the top to the bottom of the joint cross-section. • The corrosion resistance of SZ is the best, followed by upper plate BM and lower plate BM. • The tensile force decreases from 7.25 to 4.10 kN, and the tear force decreases from 3.20 to 1.78 kN after being immersed for 48 h.

Experimental study of the explosive welding process applicability for train weight decreasing

For the weight decreasing of the trains, it needs to use a new construction conception. For the weight decreasing of the trains, it needs to use a new construction conception, which means a hybrid material construction. The new conception (steel and aluminium for the vehicle construction) requires a suitable welding process for joining the steel with aluminium. Explosive welding is a suitable process to realize this idea. The authors attempt to examine this possibility by experimental methods and suggest a suitable solution for the reduction of the train’s weight. The authors made explosive welding experimental tests to join aluminium (EN-AW-6082) and low carbon steel (EN 10025 S235J2). The cladding of the test samples was made by an explosive welding process. The welded joint suitability was tested by destructive and non-destructive tests. It was tested the joint cross-section microstructure by microscopy. Based on the results it can declare that explosive welding is a suitable process to realize hybrid train construction.

The visual research of changes in the geometry of a rivet joint for material model effect for simulation riveted joints made of EN AW 5251

The paper presents the results of a numerical analysis of a single-lap joint with a blind rivet and its geometrical verification by inside views from the experiment. The research aimed to determine how the results of numerical analyses (FEM) were influenced by the method of modeling the material model and how it relates to the experimental results. As part of the analyses, a discrete riveted model and material model: linear and nonlinear were constructed. The analyses took into account various load cases (500, 800, and 900 N) to better illustrate the relationship between the numerical and experimental results. A new methodology of visualizing changes in a riveted joint's geometry was used to validate the results. The technology of making riveted joint cross-sections was developed during a static tensile test. Samples of a single lap joint with blind rivets made of aluminum sheets were subjected to a shear load. Deformations were "frozen" during the test, and sections were prepared. The microscope photos allowed for the development of a method for visualizing the deformation of the hole and rivet. The numerical results (for various loads and various material configurations) were compared with the experimental results of geometric parameters (i.e. angles between sheets or other dimensions) on the riveted joint cross-sections. The obtained results help to understand the mechanism of failure of the blind rivet under load and the complex state of loads in various stages of deformation.

Low cycle fatigue properties of friction stir welded dissimilar 2024-to-7075 aluminum alloy joints

Low cycle fatigue (LCF) tests, uniaxial symmetrical (R = −1) push-pull, were performed on the friction stir welded dissimilar 2024-to-7075 aluminum alloy joints at various strain amplitudes, focusing on the effect of base material (BM) positioning during friction stir welding (FSW). The microstructures and microhardness distribution mapping across the joint cross-section were characterized. It was observed that the BM positioned on the retreating side (RS) was dominant in the upper part of stir zone (SZ), while the middle and lower parts of SZ consisted mainly of the BM on the advancing side (AS). A larger low-hardness zone was present when 2024 aluminum alloy was placed on the AS. Cyclic hardening occurred in both types of dissimilar joints at strain amplitudes higher than 0.4%, below which cyclic stablization sustained during cyclic deformation. BM positioning during FSW affected the fatigue resistance of joints at a higher strain amplitude. Longer fatigue life was obtained when 7075 aluminum alloy was located on the AS. All of the fatigued specimens of joints fractured at the location of softer heat-affected zone on the 2024 side because of the coarsened precipitates, with crack initiation from the specimen surface and crack propagation characterized by typical fatigue striations.

Media-expressed tone, option characteristics, and stock return predictability

We investigate the informational content of a huge assortment of NASDAQ articles about a joint cross-section of S&P 500 stock return data and related single-stock option data. Splitting the articles into a trading-time and an overnight archive, we distill tone from each of them. We show that media-expressed tone is informative about option markets and that both option data and tone predict stock returns. The predictive power of option variables is robust to partialling out tone, but varies depending on whether tone is from the overnight or the trading-time archive. A potential reason is that the archives differ in terms of their thematic content. Overall, we conclude that the informational content of option data for predicting single-stock returns extends beyond the information summarized in tone and traditional market factors.