Fatigue Strength Of Joints Research Articles

Effect of Ni interlayer on interfacial microstructure and fatigue behavior of friction stir lap welded 6061 aluminum alloy and QP1180 steel

In this work, the interfacial microstructure and fatigue properties of friction stir lap welding (FSLW) joint of 6061 aluminum (Al) alloy and QP1180 steel with a Ni interlayer were characterized, and the effects of Ni on the intermetallic compounds (IMCs) evolution and fatigue behavior were revealed. The results show that an Al-Ni transition layer with a thickness of ∼ 200 nm appears at the interface of Al-Ni-Fe joint. No Al-Fe IMC is formed in the joint, because the Ni interlayer effectively blocks the reaction between Al alloy and steel. The fatigue strength of Al-Ni-Fe joint is 50 % higher than that of Al-Fe joint. The failure modes of Al-Fe joints are affected by the load levels. The joint breaks at the interface at high load levels, while the joint tends to break along the thickness direction of Al plate at low load levels. After adding Ni interlayer, the joint breaks along the thickness direction of Al plate at both high and low load levels. Based on the theoretical calculation, all Al-Fe IMCs exhibit brittleness, and most of Al-Ni IMCs exhibit toughness. Hence, Al-Ni phases effectively prevent crack propagation by enhancing the interface bonding strength of Al alloy and steel, and improve the fatigue strength of joint.

Investigation of corrosion behavior, tensile and cyclic fracture mechanism of EH36 steel welded joints

This work systematically revealed the static-dynamic corrosion failure behavior of EH36 joints under air, simulated seawater and cathodic protection in seawater. The result indicated that the seawater environment affected tensile performance slightly but acted a critical role in the fatigue behavior. Specifically, the corrosion pit and cyclic stress would respectively induce high-stress concentration and corrosion current density, significantly decreasing the fatigue strength of joints. The application of cathodic protection on joints in seawater would decrease the tensile behavior, but would continuously provide electrons for the surface and crack tip to prevent corrosion damage, improving fatigue performance of EH36 joints.

Fatigue strength of self-piercing riveted joints of carbon fiber reinforced composite and Al5052 alloy plates

Self-piercing riveting (SPR) is an alternative to the conventional spot-welding method when joining sheets of dissimilar materials. In this study, the static and fatigue strengths of the SPR joints of carbon fiber composite laminate and an Al5052 aluminum alloy plate under various loading conditions were evaluated. Fatigue test results show that the load amplitudes, corresponding to the fatigue endurance limit, based on a lifetime of one million cycles, were 680 N, 323 N, and 305 N for loading angles of 0°, 45° and 90°, respectively, with corresponding fatigue ratios of the joints of 33%, 23% and 24%. The fatigue strengths at the loading angles of 45°, and 90° in terms of the equivalent stress intensity factor were found to be much higher than those at a loading angle of 0°. This is partially due to the difference in the fatigue failure modes. Regarding the fatigue strength designs of SPR joints consisting of composite laminate and aluminum alloy plates under various loads, it can be suggested that the tensile-shear strengths dominate the SPR fatigue strengths of the joints because they are highly vulnerable to tensile-shear loading.

Fatigue life improvement of similar and dissimilar aluminum friction stir welds by deep rolling

At the moment, high production costs prevent the friction stir welding (FSW) process from further industrial applications even if comparable high fatigue strength of the joints can be reached. Higher welding speed may reduce the production costs but decrease the fatigue strength of the manufactured FSW joints. A potential solution is a mechanical post weld treatment directly after welding to increase the fatigue strength of the FSW joint again. In this study, hydrostatic deep rolling was applied for fatigue strength improvement of similar and dissimilar FSW joints made of EN AW 5083 and EN AW 6082 alloys manufactured with different welding speed. Additionally, the fatigue strength was directly compared to conventional joints manufactured by metal inert gas (MIG) welding and to base material specimen made of EN AW 5083. The surface state in as-welded condition was characterized by surface roughness and residual stress measurements. Fatigue tests were performed to quantify the fatigue strength of the FSW joints. Similar compressive residual stresses were determined after deep rolling for similar and dissimilar joints. No fatigue life improvement was determined for deep-rolled similar joints made of EN AW 5083. However, in this condition, the fatigue life of the specimen was within the range of the base material. Thus, significant lower fatigue life and a high fatigue life improvement by deep rolling were reached for dissimilar joints. An increase of the welding speed from 300 to 800 mm/min strongly decreased the fatigue strength of dissimilar welded joints in the investigated case.

Ultrasonic Welding of Aluminum to Steel: A Review

As a solid-state bonding technology, ultrasonic welding (USW) has the characteristics of green energy saving and environmental friendliness. It is more suitable for joining dissimilar metals than other welding technologies. The aluminum-to-steel USWed joint has been widely used in the automotive and aviation industries. Currently, there is no review literature report on aluminum-to-steel USW. The main physical phenomena of the USW process include interface temperature increase, ultrasonic softening, plastic deformation, formation and growth of the IMCs, and dynamic recrystallization. Hence, the microstructures and mechanical properties of aluminum-alloy-to-low-carbon-steel, aluminum-alloy-to-stainless steel, and aluminum-alloy-to-galvanized-steel-joints by USW are reviewed. Moreover, the effect of interface temperature, interface plastic deformation, and interface macrostructure and microstructure is explored. Lastly, tensile-shear and fatigue strength of joints and numerical simulation of the USW process are also discussed. In addition, some new application types of aluminum-to-steel USW are introduced. Finally, the future trends of aluminum-to-steel USW with guidance are provided.

Use of seawater to improve the static strength and fatigue life of bonded coated steel joints

Shipbuilding industry is demanding adhesive solutions for joining components to painted substrates, as traditional welding technologies require costly and time consuming processing operations. However, this topic is rarely considered in the literature. The aim of the current study is to investigate the influence of sodium chloride solution on the static strength and fatigue performance of adhesively bonded painted steel joints. To achieve this, a brittle two component epoxy adhesive was used to manufacture single lap adhesively bonded painted steels. Static and fatigue tests were performed after ageing the joints by immersion in chloride solutions for different periods of time. The results surprisingly show that both the static and fatigue mechanical properties of the joints increase significantly with ageing during the first month of the exposure. The water diffusion taking place for the first month at the single lap joints improved more than 30% both the static and fatigue strength of joints manufactured with this relatively rigid adhesive. The water absorption rate of the adhesive was also calculated using Fick's law relations. The results were used to numerically simulate the humidity level within the adhesive layer in bonded joints.

Effect of abrasive blasting and atmospheric plasma treatment on static and fatigue strength of SPCC adhesive joint

For greater fuel efficiency and increased safety, shifts to design of car body using multi-material such as ultra-high strength steel, aluminum alloy and carbon-fiber-reinforced plastic (CFRP) in addition to conventional steel are accelerated. Therefore, effective joint methods for dissimilar materials are required. Adhesive bonding has attracted attention from this point of view. The strength of adhesive bonding joints is affected by the surface conditions of the adherend. Therefore, in this study, the effects of abrasive blasting and atmospheric plasma treatment on the static and fatigue strength of SPCC (steel plate cold commercial) adhesive joint were evaluated. It was found that abrasive blasting increased the surface roughness and waviness due to the collision of particles and improved both static and fatigue strengths of the joints due to anchor effect. On the other hand, atmospheric plasma treatment created hydrophilic surface of SPCC, however, only fatigue lives of the joints increased and the static strength was not improved.

Properties of welded joints of casting aluminum VAL8 alloy and wrought 1151T alloy

The results of the formation of the butt joint of 3 mm thickness plates made of VAL8 and 1151T aluminum alloys in different combination are presented. The ultimate strength of VAL8 and 1151T alloy welded joints during melting welding is 87...88 % of ultimate strength of the VAL8 alloy. The strength coefficient of joints of similar combinations of alloys made by friction stir welding is 0.92...0.93 of the strength coefficient of the VAL8 alloy. The fatigue strength for joints of VAL8 and 1151T alloys is 140 MPa. Joints made by friction stir welding at higher values of fatigue strength (160...200 MPa), withstand approximately 1.5...1.8 times more test cycles than joints obtained by automatic argon-arc welding.

Precipitation-dependent corrosion analysis of heat treatable aluminum alloys via friction stir welding, a review

Although the various advantages of novel Friction stir welding (FSW) process; the weld surfaces are subjected to various serious problems such as lower corrosion resistance, high susceptibility to stress corrosion cracking and poor joint fatigue strength due to complex material flow and severe plastic deformation during the welding process. Corrosion behaviour of friction stir welded (FSWed) precipitate strengthening Al alloys have significant impact on metallurgical and electrochemical properties of structures. In FSW of precipitate strengthening Al alloys the localized heat input and severe plastic deformation creating appreciable changes in microstructure and modifies the microchemistry and metallurgical characteristics of precipitates. The heterogeneous distribution of precipitates and precipitate free zones (PFZs) along the grain boundaries leads to variation in electrochemical behaviour across the weld zones and hence increasing the susceptibility of weld surface to various corrosion attacks such as intergranular corrosion, pitting corrosion, exfoliation corrosion, stress corrosion cracking and galvanic corrosion. However, the corrosion resistance of FSWed joints can be improved either by reducing the size or redissolve the coarsened precipitates within the joint or modifying the microchemistry by controlling the size, location and distribution of precipitates which largely determine the corrosion rate of the weld surfaces. Consequently, it is imperative to address the influence of material modifications during FSW on corrosion behaviour of weld surface. This review paper addresses the precipitate dependent corrosion behaviour of FSWed joints of heat treatable/precipitate strengthening Al alloys and the various effective methods either to reduce or eliminate the effect of corrosion attack in FSWed joints of heat treatable Al alloys.

Fatigue Modeling and Numerical Analysis of Re-Filling Probe Hole of Friction Stir Spot Welded Joints in Aluminum Alloys.

In the present study, the fatigue behavior and tensile strength of A6061-T4 aluminum alloy, joined by friction stir spot welding (FSSW), are numerically investigated. The 3D finite element model (FEM) is used to analyze the FSSW joint by means of Abaqus software. The tensile strength is determined for FSSW joints with both a probe hole and a refilled probe hole. In order to calculate the fatigue life of FSSW joints, the hysteresis loop is first determined, and then the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted. The results were verified against available experimental data from other literature, and a good agreement was observed between the FEM results and experimental data. The results showed that the joint’s tensile strength without a probe hole (refilled hole) is higher than the joint with a probe hole. Therefore, re-filling the probe hole is an effective method for structures jointed by FSSW subjected to a static load. The fatigue strength of the joint with a re-filled probe hole was nearly the same as the structure with a probe hole at low applied loads. Additionally, at a high applied load, the fatigue strength of joints with a refilled probe hole was slightly lower than the joint with a probe hole.

A research on the fatigue strength of the single-lap joint joints bonded with nanoparticle-reinforced adhesive

Nano-technological developments, which have made significant progress in recent years, have significant impact on the science of adhesives. Therefore, in our study, the static and fatigue strengths of single-lap joints (SLJs) incorporating nanoparticles were compared to those without nanoparticles. Steel plates were used in the adhesive joints. The results revealed that average damage load increased significantly in nanoparticle-reinforced adhesive joints. The highest damage load was obtained with 4 wt% nano-Al2O3 in epoxy adhesive. As the average damage load increased, the locus of damage changed from interfacial to the mixture of interfacial and cohesive. Also, fatigue strengths of the joints increased when the adhesive joint had nano-Al2O3 and nano-SiO2, and decreased when the adhesive joint had nano-TiO2.

Fatigue assessment of cruciform joints: Comparison between Strain Energy Density predictions and current standards and recommendations

The main aim of the present work is to investigate the effects of different design parameters on the fatigue strength of cruciform welded joints through an energy based approach, the Strain Energy Density. The most important design parameters taken into account in the present work for investigating the fatigue strength are the plates dimensions, the scale effect, the lack of welding bead penetration and the weld leg length.The results of the numerical analysis carried out have been also compared with the fatigue strength predicted by the most known design guidance for the fatigue assessment of steel welded joints: Eurocode 3; British Standard; International Institute of Welding; DNV-GL.The attached plate thickness severely affects the fatigue strength of the joint compared to the transverse plate one, as well as the weld leg length. The scale effect for this joint class can be predicted adopting the mode I Williams’ eigenvalues. The welding bead penetration, besides the codes provide fragmented information, has been predicted and the optimal design dimensions have been found. Several differences between the codes, with overestimation or underestimation of the cruciform joint fatigue strength, have been found due to their lack of consideration of the aforementioned design parameters.

An investigation of the fatigue performance of adhesively bonded step-lap joints: An experimental and numerical analysis

Adhesively bonded joints are used in many engineering applications and are manufactured by joining various materials together. Static and dynamic analysis of adhesively bonded joints is very important in both scientific and sector studies on these joints. In this study, the static and fatigue strengths of single-lap joints (SLJs) and three-step-lap joints (TSLJs) that were subjected to tensile and four-point bending tests were examined experimentally and numerically. Adhesively bonded joints were produced using DP460 toughened type adhesive and AA2024-T3 aluminum alloy was used as the adherent. Fatigue tests were performed at a loading ratio (R) of 0.1 and a frequency of 10 Hz. As a result, applying a step-lap to the overlap area of adhesively bonded joints considerably increased the tensile static and fatigue strength of the joint. For the single-lap joint, both the static tensile and the tensile fatigue lifetime limit value of the three-step-lap joint increased approximately 100%. One of the reasons for that increase was that the moment effect formed in single lap joints due to the eccentric loading is minimized and the other is that a step-lap applied to the overlap area retards the formation of damage. However, static bending and fatigue strength values of TSLJs significantly decreased compared to those of SLJs. In addition, the results of the experimental and numerical analyses were found to be highly compatible with each other.

Effect of welding wires on fatigue property of 7N01-T4 aluminium alloy joints

The effect of ER5356 and ER5087 welding wires on fatigue property of MIG-welded 7N01-T4 aluminium alloy joints was investigated. The microstructure of ER5087 welded joint is similar to that of ER5356 joint. However, the fusion zone of the welding joint with ER5087 has a smaller grain size than that of the joint with ER5356. The fatigue strength of joints welded with ER5356 and ER5087 is 105.9 and 103.2 MPa at 107 cycles. During the fatigue process, the crack initiation for joints welded using ER5087 is due to porosity while for ER5356 is due to microcracks from eutectic melting in the heat-affected zone.

Fatigue strength assessment of ground fillet-welded joints using 4R method

In the present paper, a fatigue analysis for welded joints made of mild, and high- and ultra-high-strength steel grades and post-weld-treated with grinding and combined grinding and peening methods is carried out using literature data. The 4R method was used to re-analyze the data points considering material strength, residual stress, applied stress ratio, and weld toe radius. The use of the 4R method, instead of local fatigue strength assessment approaches, enabled residual stresses to be taken into consideration and accurately predicted the fatigue strength of joints in the as-welded and post-weld-treated conditions, including grinding and combined grinding and peening methods.

Fatigue failure analysis of riveted fibre-metal laminate lap joints

The fundamental aspects of fatigue fracture mechanisms (crack onset and propagation) in riveted single shear lap joints of fibre-metal laminate have been disclosed through extensive failure analysis of double-riveted 2/1 Glare™ laminate layup. Three fatigue fracture mechanisms, namely, rivet fracture, Glare laminate cracking and fretting fatigue have been determined as function of the peak stress. The roles of the joint elements and fibre-metal laminate constituents on the fatigue strength have been determined. Aligned riveting has shown more fatigue resistant than non-aligned rivets due to its higher restriction to secondary bending moments, so that potential fracture mechanisms were postponed and/or prevented. It has been discovery that, more than damage tolerance capacity, damage resistance capability determines the joint fatigue strength. The obtained results can provide insights in designing multi-rivet Glare joints with superior fatigue performance.

The influence of mode mixity and adhesive system on the fatigue life of adhesive joints

AbstractIn real applications, adhesive joints are commonly subjected to fatigue and mixed mode loading conditions. The aim of the current work is to experimentally analyse the influence of mode mixity on the fatigue strength of joints with an epoxy‐based adhesive. Different adhesive systems (acrylic and epoxies) were considered for pure mode I fatigue loading conditions. To achieve this, Arcan joints with an epoxy adhesive were manufactured and tested at different mode mixities. Based on stiffness degradation, monitored during the tests, damage evolution was calculated for different loading conditions and for all the tested adhesives. Finally, fatigue envelopes were constructed for different fatigue life regimes. Results show that a shear loading component reduces both the static strength and fatigue life of the joints. A small reduction rate of the stiffness was found throughout the most part of the life until a sudden drop was observed, indicating a smooth damage evolution.

Effect of jig constraint state during welding process on fatigue properties of Al/CFRP dissimilar welds and fatigue life evaluation based on singular stress

AbstractManufacturers have been promoting multimaterial designs. So the dissimilar material welding methods are being developed. Especially, heat welding technology, which is a direct joining by local heating, has been focussed. Therefore, this study used a heat welding technology for friction stir spot welding of aluminium alloy and carbon fibre‐reinforced plastic. This study investigated the effect of changes to jig constraint of joined members on the fatigue properties of joints. Also, the fatigue life estimation was carried out by considering the singular stress at the welding joint interface. As a result, the fatigue strength of joint in a less constrained state is higher than that in a more constrained state. The singular stress intensity at the slit tip was uniformly predicted by the differences in welding parameters of joints.

Fatigue strength of friction-welded joints of aluminum bronze to stainless steel

Friction welding of C6191 aluminum bronze to SUS304L stainless steel was carried out to examine its weldability. Joint strength was evaluated by fatigue strength. The C6191 and the SUS304L at the weld interface were hardened, while the heat affected zone of the SUS304L was slightly softened. A reaction layer of 1–5 μm that consisted of component elements of the base metals was observed at the weld interface. The fatigue limit of the joint welded under the optimum welding condition was higher than those of the base metals because of the hardening of C6191 and SUS304L, and the fatigue limit of joints decreased as the friction time or the upset pressure varied. In particular, the fatigue strength of joints welded under the conditions varied the upset pressure which was lower than that of the C6191 base metal.

Numerical Study for the Effect of Shape of Additional Weld on Fatigue Strength in Out-of-Plane Gusset Welded Joint

Fatigue crack is often initiated around weld toe, mainly caused by high stress concentration. Various techniques for improving the fatigue strength of joints have been proposed up to the present. Additional welding is known to be one of the effective techniques to improve the fatigue life of welded components. Recently, the authors have conducted fatigue tests on joints with additional weld. The tested welded joints were fabricated with different additional welding conditions. The tests revealed that smaller flank angles and bigger weld toe radii were obtained under certain additional weld conditions and the fatigue tests indicated that fatigue strength of out-of-plane gusset was remarkably improved by additional welding. In this study, 3D finite element (FE) analyses were conducted based on the in-house experimental campaign carried out to characterize the effect of additional welding on fatigue life. The crack initiation and crack propagation simulations were conducted using elastoplastic and linear fracture mechanics analyses, respectively. The results show that an additional weld treatment reduced remarkably the stress concentration at weld toe, leading to longer fatigue life.