Search Results (19)

The presence of mixed-mode stresses, combining both opening and shearing components, complicates fatigue life estimation when applying the Paris law. To address this, the crack path, along with Mode-I (opening) and Mode-II (shear) components, was numerically analyzed using Fracture Analysis Code (Franc2D) based on the linear elastic fracture mechanics (LEFM) approach. Accordingly, fatigue life and stress intensity factors (SIFs) under various biaxial loading ratios (λ) were calculated using the Paris law and compared with available data in the literature. The results show that crack growth is primarily driven by the Mode-I component, which exhibits the largest magnitude. Thus, the Mode-I stress intensity factor (K_I) was adopted for the numerical integration of the fatigue life equation. Furthermore, the influence of normal and transverse loads (σ_y and σ_x, respectively) on the crack path plane and SIF was examined for λ. The analysis revealed that lower λ values led to faster crack propagation, while higher λ values resulted in extended fatigue life due to an increased number of cycles to failure. The comparison demonstrated good agreement with reference data, confirming the reliability of the proposed modeling approach over a wide range of biaxial loading conditions. Full article

The very high cycle fatigue (VHCF) strength of welded joints made of high-strength structural materials is generally poor, which poses a serious threat to the long life and reliability of the structural components. This work employs an ultrasonic vibration fatigue testing system to investigate the biaxial fatigue failure mechanism of the welded joints. The results revealed that under uniaxial loading conditions, the propensity for fatigue failure in plate specimens was predominantly observed at the specimen surface. Regardless of whether under uniaxial or biaxial loading, the initiation of fatigue cracks in cruciform joints was consistently traced back to unfused flaws, which were primarily located at the interface between the solder and the base material. Concurrently, it was noted that the fatigue strength of cruciform joints under biaxial loading was merely 44.4% of that under uniaxial loading. The geometric peculiarities of the unfused defects led to severe stress concentrations, which significantly reduced the fatigue life of the material under biaxial loading conditions. Full article

In this paper, the notch effect in weldments has been investigated, and the optimal configuration of different types of welded joints has been analysed using the implicit gradient approach. By considering this implicit gradient method, it is possible to calculate the effective stress related to fatigue damage, with the effective stress being a continuous scalar function of the real stress tensor components, even in the presence of sharp edges. Hence, the search for the optimal configuration that maximises fatigue life can be tackled as the condition of minimum effective stress obtained by changing the weld shape and geometrical parameters. Both load-carrying cruciform joints and spot welds made of steel have been considered. The structural details have been studied by modelling actual shapes without any geometric simplification. Moreover, the same numerical procedure has been considered independently of the size, shape or load condition without imposing restrictive rules on the FE mesh. Full article

This paper deals with the problem of stress concentration at the weld toe of non-load-carrying-type plate cruciform joints under tension, bending, and shear. Theoretical stress concentration factors were derived using the finite element method. Five of the most important geometrical parameters: the thickness of the main plate and the attachments, the weld throat thickness, the weld toe radius, and the weld face inclination angle were treated as independent variables. For each loading mode—tension, bending, and shear—parametric expression of high accuracy was obtained, covering the range used in real structures for cruciform connections. The maximum percentage error was lower than 2.5% as compared to numerical values. The presented solutions proved to be valid for the toe radius ρ tending to zero. Full article

Friction stir welding (FSW) has been considered ideal for aluminum alloy structures. The performance of FSW joints under unidirectional stress state has been widely tested, but there is still a lack of experimental data under a biaxial stress state. For accurate characterization of the mechanical properties of 2219 aluminum alloy FSW joints under a biaxial stress state, this article conducted biaxial tests. The FSW joint was tested using scanning electron microscopy (SEM) to obtain its microscopic properties and obtain the partition results of the welded joint. The stress–strain relationship and yield characteristics of welded joints under different loading ratios were studied using biaxial tensile tests of cruciform specimens combined with digital image correlation technology. By comparing it with the existing yield criteria, the yield criterion suitable for FSW joints of 2219 aluminum alloy under a biaxial tensile load was determined. Full article

The study presents an analysis of S355J2+N steel and AA5083 aluminum alloy welded structural joints using explosion welded transition joints of reduced thickness. The transition joint thickness reduction significantly hinders the welding of the joints due to the risk of damage to the Al/steel interface as a result of the high temperatures during welding. In the previous article, the strength of the transition joint was analyzed but ship structures, apart from static loads, are subjected to many different cyclical loads. Welded structural joints are analyzed to determine the welding influence on the fatigue life and fracture type of the transition joints. The results of the fatigue tests show that the fatigue damage in the specimens occurs in the aluminum welded joint, and not in the explosively welded joint. The damage obtained was characteristic of cruciform welded joint specimens and both types of root and toe damage occurred. Based on the obtained results, fatigue curves for the joint were determined and compared to the fatigue curves for the AA5083 base material. The experimental fatigue curve was also compared with the design curve for welded aluminum structures from Eurocode. The conducted analysis showed the possibility of using Al/steel explosion welded transition joints of reduced thickness to transfer cyclical loads. Full article

Welding is prone to several defects. To test the fatigue properties of the welded defective joints of high-speed rail bogies, SMA490BW steel cruciform welded joints were employed with artificial defects treatment. Consequently, fatigue tests were conducted on the specimens. Fatigue fracture morphology was studied via scanning electron microscopy. The ABAQUS (version 2022) finite element software was used to calculate the stress distribution and concentration factor of cruciform welded joints with defects. The results show that the fatigue limits of 1 and 2.4 mm defect specimens were approximately 57.2 and 53.75 Mpa, respectively. Furthermore, the stress concentration factor of no, 1 mm, and 2.4 mm defects were 2.246, 4.441, and 6.684, respectively, indicating that the stress concentration factor of 1 and 2.4 mm defects increased by 98 and 198%, respectively, with respect to the no-defect case. Full article

Fatigue damage accumulation under variable amplitude loadings is vital for the life prediction of welded structures. An approach based on damage distribution mapping is presented. S-N curves of welded joints are utilized to construct fatigue damage zones, and a corresponding polynomial fitting function is derived from the heat transfer FEA solution. Experimental results for cruciform and T joints under tensile and three-point bending are employed for validation. Compared with four existing damage models, the proposed approach shows greater accuracy and provides a better description for the early stage of fatigue. Full article

Articular cartilage injuries are a common source of joint pain and dysfunction. As articular cartilage is avascular, it exhibits a poor intrinsic healing capacity for self-repair. Clinically, osteochondral grafts are used to surgically restore the articular surface following injury. A significant challenge remains with the repair properties at the graft-host tissue interface as proper integration is critical toward restoring normal load distribution across the joint. A key to addressing poor tissue integration may involve optimizing mobilization of fibroblast-like synoviocytes (FLS) that exhibit chondrogenic potential and are derived from the adjacent synovium, the specialized connective tissue membrane that envelops the diarthrodial joint. Synovium-derived cells have been directly implicated in the native repair response of articular cartilage. Electrotherapeutics hold potential as low-cost, low-risk, non-invasive adjunctive therapies for promoting cartilage healing via cell-mediated repair. Pulsed electromagnetic fields (PEMFs) and applied direct current (DC) electric fields (EFs) via galvanotaxis are two potential therapeutic strategies to promote cartilage repair by stimulating the migration of FLS within a wound or defect site. PEMF chambers were calibrated to recapitulate clinical standards (1.5 ± 0.2 mT, 75 Hz, 1.3 ms duration). PEMF stimulation promoted bovine FLS migration using a 2D in vitro scratch assay to assess the rate of wound closure following cruciform injury. Galvanotaxis DC EF stimulation assisted FLS migration within a collagen hydrogel matrix in order to promote cartilage repair. A novel tissue-scale bioreactor capable of applying DC EFs in sterile culture conditions to 3D constructs was designed in order to track the increased recruitment of synovial repair cells via galvanotaxis from intact bovine synovium explants to the site of a cartilage wound injury. PEMF stimulation further modulated FLS migration into the bovine cartilage defect region. Biochemical composition, histological analysis, and gene expression revealed elevated GAG and collagen levels following PEMF treatment, indicative of its pro-anabolic effect. Together, PEMF and galvanotaxis DC EF modulation are electrotherapeutic strategies with complementary repair properties. Both procedures may enable direct migration or selective homing of target cells to defect sites, thus augmenting natural repair processes for improving cartilage repair and healing. Full article

This paper provides data on stress concentration factors (SCFs) from experimental measurements on cruciform tubular joints of a chord and brace intersection under axial loading. High-fidelity finite element models were generated and validated against these measurements. Further, the statistical variation and the uncertainty in both experiments and finite element analysis (FEA) are studied, including the effect of finite element modelling of the weld profile, mesh size, element type and the method for deriving the SCF. A method is proposed for modelling such uncertainties in order to determine a reasonable SCF. Traditionally, SCF are determined by parametric formulae found in codes and standards and the paper also provides these for comparison. Results from the FEA generally show that the SCF increases with a finer mesh, 2nd order brick elements, linear extrapolation and a larger weld profile. Comparison between experimental SCFs indicates that a very fine mesh and the use of 2nd order elements is required to provide SCF on the safe side. It is further found that the parametric SCF equations in codes are reasonably on the safe side and a detailed finite element analysis could be beneficial if small gains in fatigue life need to be justified. Full article

An evaluation method is proposed for determining the full fatigue life of aluminum alloy cruciform joint, including the crack initiation and propagation with welding residual stress. The results of simulations have shown that the boundary between the initiation and propagation stage is not constant, but a variable value. The residual stress leads to a significant reduction in both stages, which is more severe on initiation. With considering residual stress, the ratio of crack initiation to total life is below 7%. The effect of residual stress varies with external loading; when external load is lower, the residual stress has a greater effect. Full article

The existing parametric formulae to calculate the notch stress concentration factor of fillet welds often result in reduced accuracy due to an oversimplification of the real weld geometry. The present work proposes a parametric formula for the evaluation of the notch SCF based on the spline weld model that offers a better approximation of the real shape of the fillet weld. The spline model was adopted in FE analyses on T-shape joints and cruciform joints models, under different loading conditions, to propose a parametric formula for the calculation of the SCF by regression analysis. In addition, the precision of parametric formulae based on the line model was examined. The magnitude of the stress concentration was also analyzed by means of its probability distribution. The results show that the line model is not accurate enough to calculate the SCF of fillet weld if the weld profile is considered. The error of the SCF by the proposed parametric formulae is proven to be smaller than 5% according to the testing data system. The stress concentration of cruciform joints under tensile stress represents the worst case scenario if assessed by the confidence interval of 95% survival probability. Full article

This paper describes a study of welded steel plate joints using experimental and numerical methods. The objectives of this study are to observe the mechanical behavior of welded plate joints under monotonic and cyclic loads, identify their damage degradation processes, and provide useful test data for future damage analysis of beam-column connections in steel frame structures. Six specimens were designed, of which three were tested under monotonic loads, and the other three were tested under cyclic loads. The test setup consisted of three plates arranged in a cruciform and connected by two groove welds. The monotonic and cyclic loads were applied to the free end of the two outstanding plates, inducing a pulling force on the welded joint. Because the only element studied in the present work is the weld, the sizes of the three plates were kept constant. The responses of these welded plate joints are discussed in terms of their experimentally and numerically obtained mechanical parameters, hysteretic behavior, strain variations, stiffness degradation, damage process, and failure modes. The results show that the energy damage model outperforms the displacement damage model in terms of indicating the degree of damage. Furthermore, if designed according to code, all these welded plate joints perform satisfactorily. Full article

As the development of the polar region continues to increase, the fatigue properties of structures at low temperature are increasingly receiving researcher attention. This study aimed to investigate the fatigue properties of T-welded and cruciform welded joints at −60 °C. Logarithmic S–N curves based on the hot-spot stress of the T-welded and cruciform welded joints at 50% and 95% confidence levels were obtained at −60 °C. The test results showed that the fatigue properties of T-welded joints were almost 2–7% better than those of the cruciform welded joints at −60 °C. Factors that affected the fatigue properties of welded joints, such as the stress concentration factor, microstructure, Vickers hardness profiles, and fractography, were also studied and the test results showed that the fatigue properties of cruciform welded joints at −60 °C were 57.215% better than at room temperature. Full article

The multiaxial fatigue critical plane method can be used to evaluate the extremely-low-cycle fatigue (ELCF) damage of beam-to-column welded joints in steel frameworks subjected to strong seismic activity. In this paper, fatigue damage models using structural detail parameters are studied. Firstly, the fatigue properties obtained from experiments are adopted to assess ELCF life for steel frameworks. In these experiments, two types of welded specimens, namely, plate butt weld (PB) and cruciform load-carrying groove weld (CLG), are designed according to the structural details of steel beam and box column joints, in which both structural details and welded factors are taken into account. Secondly, experiments are performed on three full-scale steel welded beam-to-column joints to determine the contribution of stress and/or strain to damage parameters. Finally, we introduce a modification of the most popular fatigue damage model of Fatemi and Socie (FS), modified by us in a previous study, for damage evaluation, and compare this with Shang and Wang (SW) in order to examine the applicability of the fatigue properties of PB and CLG. This study shows that the modified FS model using the fatigue properties of CLG can predict the crack initiation life and evaluate the damage of beam-to-column welded joints, and can be subsequently used for further investigation of the damage evolution law. Full article