Fatigue Performance Of Joints Research Articles

Effect of ultrasonic rolling on the fatigue performance of laser-welded TC4 titanium alloy joints

Effect of ultrasonic rolling on the fatigue performance of laser-welded TC4 titanium alloy joints

Static and fatigue performance of non-circular rivet joints: Comparison between numerical modelling and preliminary testing

Alternative non-circular rivet joint geometries are investigated. An optimum non-circular rivet geometry based on a continuous change in the radius of curvature is proposed to minimise the stress concentration factor on structural components joined by rivets, which is the first time to be proposed to the best author’s knowledge. By-pass and bearing load cases are considered for both numerical analysis and a preliminary experimental programme. For isotropic materials, linear elastic analyses (for the stress concentration factors) and fully elastoplastic analyses are carried out in the numerical simulations. The experimental programme includes static tests (for both by-pass and bearing load cases) and fatigue tests (by-pass loading) for isotropic materials, whereas only static tests (for both by-pass and bearing load cases) are considered for orthotropic composites. The correlation of experimental and numerical results indicates that the reduction of the stress concentration factor plays an important role in improving fatigue behaviour and has almost no influence under static loading. Hence, the life of structural riveted components may increase, improving the life cycle of the entire structure in service.

Effect of Selective Z-Pinning on the Static and Fatigue Strength of Step Joints between Composite Adherends

The z-pinning reinforcement technique, which involves inserting thin pins through the body of a laminate, has proven highly effective in enhancing the strength of various composite joint configurations. This investigation aims to explore the enhancements achievable through selective z-pinning at very low pin contents on both the static and fatigue performance of composite joints. Single-step joints between carbon/epoxy adherends were reinforced using steel pins arranged in two, three, or four rows of pins parallel to the edges of the overlap, resulting in pin contents ranging from 0.2% to 0.4%. Joint panels were manufactured through co-curing, and coupons were extracted from the panels for static and fatigue tensile testing. The experimental tests show that z-pinning improves the static strength (by about 15%) and extends the fatigue lives of the joints. The ultimate failure of both unpinned and pinned joints is due to the unstable propagation of a crack at the bond line. The superior performances of pinned joints are mainly due to the bridging tractions imposed between the crack faces by z-pins, which delay the growth of the debonding crack. The enhancements in static and fatigue strength achieved by z-pinning were essentially independent of the number of pin rows, and the pins positioned near the joint edges were found to play a dominant role in controlling the structural performance of pinned joints.

Influence of corrosion on ultra-low cycle fatigue performance of steel butt-welded joints with various welding methods

Preferential corrosion of welded joints in steel structures has been observed in a wide range of scenarios and should receive enough attention. The current work focuses on the corrosion and ultra-low cycle fatigue (ULCF) behavior of low-alloy steel weld joints. Firstly, 1600 h neutral salt spray (NSS) tests were conducted on welded joints made by different welding methods, and then topography scanning of corrosion pits was carried out. It was found that the welded region is more susceptible to corrosion. Dynamic polarization curves of the welded joints were measured, and the results show that the self-corrosion potential of the welded region is lower than that of the base metal (BM) region, while the corrosion current density is higher than that of the BM region. Subsequently, cyclic tests were carried out on the corroded weld joints. The results show that corrosion can cause a maximum reduction of 11.79% in yield load and 20.87% in ultimate load of the welded joints. Corrosion has slight influence on the energy dissipation capacity of welded joints, but the maximum reductions in ULCF life could reach 77.31% due to corrosion. Fractography analysis further shows that secondary cracks, map cracks, and intergranular brittle fracture, apart from more common fatigue fracture, ductile fracture, and quasi-cleavage fracture, appear on the fracture surfaces. Supplementary numerical simulation was conducted to enable a better understanding of the failure processes. In the simulation, a geometric modeling method using topography scanning data of corrosion surface was proposed. By using the proposed modeling approach, together with Chaboche cyclic plasticity constitutive model and cyclic void growth model (CVGM) for capturing fracture behavior, the predicted results show an acceptable agreement with the experimental ones.

Tightening torque effect on fatigue performance of single-lap joints

Tightening torque effect on fatigue performance of single-lap joints

Fatigue performance of root-to-throat cracks repaired by bonding steel: experimental and numerical investigations

Root-to-throat cracks are one of typical fatigue cracking modes in rib-to-deck welded joints of orthotropic steel bridge decks (OSDs). An efficient technique of non-destructive bonding steel plates (BSP) was proposed to address the cracking issue. A series of local full-scale test specimens with and without strengthening were performed under different loading cases. Meanwhile, the typical failure modes and fatigue performance of welded joints were evaluated. Subsequently, fracture mechanical models were developed to deepen the understanding on crack propagation behavior and strengthening effectiveness. Finally, a parametric study was carried out to explore the effects of various parameters on stress intensity factors (SIFs) at the crack tips. The results showed that fatigue cracks dominated the crack propagation of the welded throats in the case of rib bending. External BSP on rib-to-deck welded joints contributed greatly to the extended in-service life of existing cracked structures. To be more specific, the fatigue stress range response at the cracked region was reduced by an average of 90.6% by means of the BSP method. By comparing SIFs, it was found that the BSP retrofit method led to a reduction of at least 78%. The predicted directions of crack propagation agreed well with the observations from fatigue tests. Moreover, the thickness of bonded plates exerted more significant effects on fatigue improvement.

Fatigue performance assessment of thick TIG-Dressing cruciform welded joints made by Q355D structural steel

TIG-Dressing treatment is often used for steel welded joints in construction machinery manufacturing as an effective and reliable method for post-weld fatigue strength improvement. This paper investigates the fatigue performance of thick Q355D cruciform joints in heavy load-carrying steel structures under different TIG-Dressing treatments. Two TIG-Dressing treatments for the full-penetration welded joints were used for fatigue tests considering filling metal during this post-welded processing. Experimental tests studied the fatigue strength of TIG-Dressing cruciform welded joints of Q355D structural steel. The geometric parameters and relevant statistical analyses were performed by actual 3D optical measurement. Moreover, the stress concentration factors are calculated according to the actual geometrics of the welded joint. On the other hand, the effective notch stress and hot spot stress methods were employed to evaluate the fatigue data of Load-Carrying Welded joints (LCWJs) under different notch radius. The collected fatigue data from the literature was compared with the tested data by the above methods. The results show that the fatigue strength of LCWJs under TIG-Dressing processing without filler metal is higher than those under the same TIG-Dressing treatment with filler metal. The effective notch stress method with a fictitious notch radius r = rtrue + 1 mm (rtrue is the actual notch radius at weld toe) could obtain smaller scatter bands for the tested fatigue data.

Stress Distribution Prediction of Circular Hollow Section Tube in Flexible High-Neck Flange Joints Based on the Hybrid Machine Learning Model.

The flexible high-neck flange is connected to the circular hollow section (CHS) tube through welding, and the placement of the weld seam and corresponding stress concentration factor (SCF) are crucial determinants of the joint's fatigue performance. In this study, three hybrid models combining ant colony optimization (ACO), a genetic algorithm (GA), and grey wolf optimization (GWO) with a random forest (RF) model were developed to predict the stress distribution on the inner and outer walls of the CHS tube under different flange parameter combinations. To achieve this, an automated finite element (FE) analysis program for flexible high-neck flange joints was initially developed based on ABAQUS 2020 software. Parameter combinations were randomly selected within a reasonable range to simulate the nonlinear mechanical behavior of the joint under uniform tension, generating a dataset comprising 5417 sets of data. The accuracy of the FE model was validated through experimental data from the literature. Based on this, feature importance analysis was conducted to reveal the influence of different variable parameters on the stress distribution in the tube of the joint. The flange parameters and tube stress distribution are considered as inputs and outputs, respectively. Three hybrid RF models, specifically ant colony optimization-based random forest (ACO-RF), genetic algorithm-based random forest (GA-RF), and grey wolf optimization-based random forest (GWO-RF), are trained for regression prediction. The results demonstrate that the three hybrid models outperform the original machine learning model in predictive accuracy. The ACO-RF model achieved the highest accuracy with average coefficients of determination (Rmean2) of 0.9983 and 0.9865 on the testing and training sets, respectively. Building upon this foundation, the study developed a corresponding open-source graphical user interface (GUI) as a tool for facilitating computations and visualizing results. Finally, a case study on fatigue damage assessment of a flexible high-neck flange joint in a wind-turbine tower is presented to demonstrate the application of the proposed model in this study.

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.

Failure Analysis of Resistance Spot-Welded Structure Using XFEM: Lifetime Assessment

Due to their effective and affordable joining capabilities, resistance spot-welded (RSW) structures are widely used in many industries, including the automotive, aerospace, and manufacturing sectors. Because spot-welded structures are frequently subjected to cyclic stress conditions while in service, fatigue failure is a serious concern. It is essential to comprehend and predict their fatigue behavior in order to guarantee the dependability and durability of the relevant engineering products. The analysis of fatigue failure in spot-welded structures is the main topic of this paper, along with the prediction of fatigue life (Nf) and identification of failure mechanisms. Also, the effects of parameters such as the amount of cyclic load applied, the load ratio, and size of the spot-welding on the Nf were investigated. To achieve this, the fatigue performance of spot-welded joints was simulated using the extended finite element method (XFEM). The XFEM method is particularly suited for capturing intricate crack patterns in spot-welded structures because it allows for the modeling of crack propagation without the need for remeshing. It was observed that when the cycling load was decreased by 20%, Nf increased by around 250%. On the other hand, the fatigue life of the structure, and, hence, the crack propagation rate, was significantly affected by the load ratio and diameter of the spot-welding. This paper presents the details of the novel approach to studying spot-weld fatigue characterization using XFEMs to simulate crack propagation.

An experimental investigation on the influence of environmental ageing on strength and fatigue behavior of different single lap joints

It is essential to examine the performance of CFRP and aluminum specimens after being exposed to environmental aging and to develop a technique that can predict their mechanical function. However, there is limited research on the static and fatigue strength of adhesive, mechanical, and hybrid joints (adhesive/mechanical) after environmental ageing. The study aims to examine the effect of thermal and hygrothermal ageing on the static and fatigue performance of three-point bending joints. Three groups of samples were prepared: I) unaged, II) thermally aged, and III) hygrothermally aged. The bending performance of three different types of joints (bonded, bolted, and bonded/bolted) was evaluated by conducting bending tests using three distinct types of adherends: ATA (Aluminum-to-Aluminum), CTC (Composite-to-Composite), and ATC (Aluminum-to-Composite). Also,the strength of the joints was measured and assessed for both static and fatigue (at three different levels of loading using the new fixture) loading. Static tests showed that bonded/bolted CTC specimens had the highest strength, and hygrothermal and thermal conditions significantly affected the static performance of the three types of joints and substrates. Under fatigue load, the highest fatigue life was observed in bonded, bolted, and bonded/bolted specimens for ATA, ATC, and CTC, respectively. In a bonded/bolted single lap joint, the static and fatigue strength consists of two steps: the initial step corresponds to the strength of a bonded specimen, and the next step starts when the bonded joint fails and fits the strength of a bolted joint. Finally, both ageing and static load percentage reduced the fatigue life and shifted the failure mode of the joints.

Experimental Study of Hot Spot Stress for Spatial CHS KK-Joints

In offshore structures such as offshore wind turbine jacket foundations, prolonged exposure to wind and wave loads can lead to fatigue failure, especially at the joint connections. Currently, international codes primarily evaluate the fatigue performance of tubular joints using the hot spot stress (HSS) method, with stress concentration factor (SCF) being the most crucial parameter. Numerous studies have investigated the SCF of tubular joints and proposed corresponding calculation formulas. However, most of these studies have focused on simple basic loading cases. To comprehensively understand the distribution pattern of the HSS method at spatial tubular joints, this study selects the spatial CHS KK-joints as the research subject and performs the HSS testing on spatial KK-joints. The research indicates that, in CHS joints, the distribution of the HSS on the chord side remains consistent under tensile or compressive loading conditions along the brace axis. Additionally, within spatial joints, the loading conditions of neighboring braces near the reference brace significantly affect the distribution of HSS on the chord side and exhibit varying spatial effects on the SCF. Furthermore, this study applies recommended calculation formulas from codes to analyze the experimental results. The findings reveal significant discrepancies between the SCF calculation formulas recommended by CIDECT and the test results, rendering it inadequate for accurately calculating the SCF of spatial KK-joints. Therefore, further research is required to develop suitable calculation formulas for SCFs in spatial KK-joints.

Effect of Residual Stress on Mode-I Stress Intensity Factor: A Quantitative Evaluation and a Suggestion of an Estimating Equation

An extensive literature review was conducted primarily to develop a comprehensive understanding of the quantitative behavior of residual stress (RS) distribution in weld joints. Based on prior data, various levels of the peak RS and distribution profiles were applied to a finite element analyses (FEA) model as an initial loading to evaluate the effect of RS on the Mode-I stress intensity factor (SIF), KI. The RS was not found to have a significant effect on the SIF values when the peak RS was less than 300 MPa. The enhanced effect of RS on the KI values was found to be more pronounced at a lower crack ratio, while the analytical form of the RS distribution had a minor effect. The effective boundary corrections function, FResidual, was derived under the effect of RS for 1T CT specimen for various crack geometries of the crack ratio, (a/W) of 0.2, 0.40, 0.50, 0.60, and 0.75, and with peak RS varying from 100 MPa to 600 MPa. The obtained effective function of KI can be employed to quantitatively evaluate the effect of RS on the fatigue performance of welded joints.

Fatigue performance of Q420C steel fillet-welded joints at low temperatures

This paper focuses on the fatigue performance of Q420C steel fillet-welded joints at low temperatures. The tensile tests and Charpy V-notch tests were first performed to evaluate the mechanical properties of Q420C steel fillet-welded joints under room and low temperatures. It reveals that the yield and ultimate strengths increased with reducing temperature from 20 °C to −50 °C. The Charpy impact energy transition temperature (ETT50) was –33.67 °C. Subsequently, the fatigue test was conducted on the fillet-welded cruciform joint specimens of Q420C steel at 20 °C, 0 °C, −15 °C, −30 °C, 40 °C and −50 °C considering three stress ranges (i.e., 0.0–0.5 ftw, 0.0–0.7 ftw and 0.0–0.9 ftw), where ftw was the design strength of fillet weld. The micro-morphologies of fatigue fracture surfaces were observed by scanning electron microscope (SEM), and the river patterns indicating brittle fracture occurred at −50 °C. The S-N curves and P-S-N curves with a survival probability of 95% were fitted from experimental fatigue life. With decreasing temperature from room temperature (20 °C) to −40 °C, the fatigue life increased at low-stress range (0.0–0.5 ftw), while shrank at high-stress range (0.0–0.9 ftw). Then, the fatigue life presented a declination trend at −50 °C for these three stress ranges, compared with that at −40 °C.

Fatigue Behaviors of Joints between Steel Girders with Corrugated Webs and Top RC Slabs under Transverse Bending Moments

Steel-concrete composite box beams are widely used in bridge engineering, which might bear transverse and longitudinal bending moments simultaneously under vehicle loads. To investigate the fatigue performance of joints between the steel girders and the top reinforced concrete (RC) slabs under transverse bending moments, a reduced scale joint between the weathering steel girder with the corrugated steel web (CSW) and the top RC slab was designed and tested under constant amplitude fatigue loads. Test results show that the joint initially cracked in the weld metal connecting the CSW with the bottom girder flange during the fatigue loading process. The initial crack propagated from the longitudinal fold to the adjacent inclined folds after the specimen was subjected to 7.63 × 105 loading cycles and caused the final fatigue failure. Compared with the calculated fatigue lives in the methods recommended by EC3 and AASHTO, the fatigue performance of the details involved in the joint satisfied the demands of fatigue design. Meanwhile, finite element (FE) models of joints with different parameters were established to determine their effect on the stress ranges at the hot spot regions of the joints. Numerical results show that improving the bending radius or the thickness of the CSW helps to reduce the stress ranges in the hot spot regions, which is beneficial to enhance the fatigue resistance of the investigated fatigue details accordingly.

Experimental study on fatigue behavior of trapezoidal rib-to-deck welded joints in orthotropic steel decks strengthened with CFRP sheets

Due to the unavoidable stress concentrations and welding defects, the trapezoidal rib-to-deck welded joints of Orthotropic Steel Bridge Decks (OSBD) are prone to fatigue cracking. It is a new exploration to apply Carbon Fiber Reinforced Polymer (CFRP) sheets to strengthen the complex welded joints to improve the fatigue strength. In this paper, the comparative tests of un-strengthened and CFRP strengthened welded joints were carried out. The hot spot stress distribution under static load and fatigue behavior under cyclic load were studied, considering the influence of the number of CFRP sheet layers. The experimental results indicate that CFRP reinforcement can effectively reduce the stress concentrations at weld toe of the deck, and three-layers reinforcement has a greater effect than one-layer reinforcement. There was no significant difference in failure modes between the un-strengthened and CFRP strengthened welded joints. The fatigue cracks of all joints originated from weld toe of the deck, and then expanded along the width and thickness of the deck which caused the deck to break. CFRP reinforcement can significantly improve the fatigue life of trapezoidal rib-to-deck welded joints under the same nominal stress range and three-layers reinforcement presented a longer fatigue life. The S-N curve [Formula: see text] based on the hot spot stress range at weld toe of the deck was established, which can be applied to the fatigue strength design of un-strengthened and CFRP strengthened rib-to-deck welded joints. The mechanism that CFRP reinforcement can significantly improve the fatigue performance of welded joints can be concluded to less stress concentrations and slower growth rate of the crack.

Evaluation of Fatigue Performance of Press Hardening Steel Joints Welded by GMAW-CSC and PAW Processes

The application of press hardening steels is spreading from automobiles, where crashworthiness demands are critical, to other segments, such as the agricultural and road transport industries. However, the operational conditions to which such equipment is exposed requires the application of heavier sheet gages and adapted joining processes. In this context, fatigue is recognized as the critical failure mode. The present article describes the procedures and results of fatigue testing performed on GMAW-CSC and PAW butt-welded specimens of 1500 MPa press hardening steel. Both methods are suitable alternatives to laser welding when joining relatively heavy-gaged components. The obtained fatigue results are also related to heat-affected zone characteristics and weld bead surfaces. Additionally, some ground-flush GMAW-CSC specimens were tested. The test results indicate that both welding procedures provide suitable fatigue performance. As-welded GMAW-CSC joints on this ultra-high strength steel accomplished a fatigue performance similar to welds of conventional steel. However, a remarkable performance increase was observed after flush grinding the weld beads. The plasma welding process presented less good results due to the more extensive manufacturing and geometric variability. The results indicate that adopting a suitable arc welding process, in association with post-weld geometry improvement, provides a fatigue performance that is competitive with laser-welded press hardening steels.

Effect of frequency on the fatigue performance of bolted joints under axial excitation

In a vibration environment, bolted joints may loosen or even fatigue fracture. In this study, fatigue tests of bolted joints were carried out under axial excitation. The effect of loading frequency on fatigue performance was studied. Additionally, the wear mechanisms of bolted joint were revealed. Results show that the wear mechanisms are fatigue wear, oxidation wear and abrasive wear on threads. The fracture morphology presents the characteristics of multi-fatigue cracks and dimples. With the increase of loading frequency, the damage of threads becomes slight, and the self-loosening degree of bolted joint decreases. Moreover, the fatigue life of bolted joint increases because of the decreasing stress amplitude on the section of screw. Numerical simulation was further performed by ABAQUS. The FE results are in agreement with the experimental observations.

Influence of resin asphalt pavement on stress behaviors of double-side welded rib-to-deck joints in orthotropic steel decks

Resin asphalt is one of the best choices for steel deck pavements owing to its excellent performance characteristics, such as high rigidity, excellent high-temperature stability, and convenient construction. Recently, resin asphalt has been increasingly used in orthotropic steel decks (OSDs), significantly influencing their stress levels. To determine the effect of a resin asphalt pavement on the stress behaviors and fatigue performance of double-side welded rib-to-deck (RTD) joints, experimental and numerical approaches were combined. A full-scale OSD specimen with a steel deck pavement was fabricated and tested under different temperature conditions. The experimental results indicated that the transverse bending rigidity of the deck could be improved by laying the resin asphalt pavement, and the stress ranges of the double-side welded RTD joints were significantly reduced. The stress behaviors of double-side welded RTD joints are sensitive to the pavement temperature. Thus, the stress ranges of the double-side welded RTD joints increased significantly with the temperature of the resin asphalt pavement. Furthermore, the numerical results showed that the maximum equivalent stress range of the double-side welded RTD joints occurred at crack type T2, under the transverse loading location of e = −150 mm. The equivalent stress range of the four crack types in the double-side welded RTD joints decreased significantly as the thickness of the resin asphalt pavement increased. The findings of this study suggest that the influence of resin asphalt pavements and their temperature effect must be considered to accurately evaluate the fatigue performance of RTD joints.

Crack extension analysis and fatigue life assessment of single lug and yoke joints containing initial defects

To investigate the impact of initial cracks on the fatigue performance of single lug and yoke joints, fatigue testing was performed for defective welding joint models. The crack extension behaviors were investigated based on the theories of fracture mechanics using ANSYS-FRANC3D interactive technology, and the effects of the initial crack location, morphology pattern, and surface angle on fatigue performance were determined. The results showed a fatigue failure mode in which the crack extended along the welding line for single lug and yoke joints. The fatigue life was shorter when the initial crack was in the corner of the single lug plate. Moreover, the crack growth rates during the early stage of crack extension varied significantly with different initial crack morphology patterns. However, the crack growth rates during the later stages were similar to one another. The remaining fatigue life increased with the shape ratio for the same crack depth. Finally, the crack growth rate was the fastest, and the remaining fatigue life was the shortest when the initial crack surface angle was inclined toward the stress concentration area.