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Austenite and duplex stainless steels are widely used in engineering, and the latter exhibits a more excellent combination of mechanical properties and corrosion resistance due to the coexistence of austenite and ferrite and higher nitrogen. However, fatigue failure still threatens their structural integrity. A comprehensive comparison of their cyclic deformation behavior is a major foundation to understand the role of duplex-phase microstructure and nitrogen in the safety assessment of engineering components. Thus, in this paper, the cyclic deformation behavior of fully-austenitic stainless steel 316L and duplex stainless steel 2205 was studied by a series of low cycle fatigue tests with various strain amplitudes, loading rates and tensile holding. A theoretical mechanism diagram of the interaction between nitrogen and dislocation movements during cyclic loads was proposed. Results show that the cyclic stress response of 2205 was the primary cyclic hardening, followed by a long-term cyclic softening regardless of strain amplitudes and rates, while an additional secondary hardening was observed for 316L at greater strain amplitudes. Cyclic softening of 2205 was restrained under slower strain rates or tensile holding due to the interaction between nitrogen and dislocations. The cyclic plasticity of 2205 started within the austenite, and gradually translated into the ferrite with the elevation of the cyclic amplitude, which lead to a decreased hardening ratio with the increase in amplitude and a shorter fatigue life for a given smaller plastic strain amplitude. [ABSTRACT FROM AUTHOR]

The large-size lattice truss panel structure (LTPS) is continually increasing for higher upsizing, but the roles of its connected structures on the mechanical properties are always ignored during the previous structural integrity assessment. Thus, in this paper, a series of mechanical tests, including the fabricating of panel-to-panel LTPSs, monotonous tensile, and three- and four-point bending tests, were performed to comprehensively understand the mechanical behavior. Furthermore, a theoretical model including the role of connected structures was developed to predict both the elastic and plastic deformation behavior of panel-to-panel LTPS. Results show that the connected structure has a very significant effect on the mechanical properties of panel-to-panel LTPS during the three-bending tests, and I-beam element depresses its carrying capacity. The developed theoretical model was proved to accurately predict the experimental results, and the maximum error was limited within 20%. Finally, the dimensional effects of the connection components on mechanical properties were also analyzed by the theoretical model, and indicated that the panel-to-panel LTPS will present better mechanical performance than the intact structure when the width of I-beam element exceeds 12.2 mm or the its length downgrades to 39.1 mm, which provide a comprehensive guidance for the engineering design of large-size LTPS. [ABSTRACT FROM AUTHOR]

The filter press is one of the most important devices in purified terephthalic acid (PTA) refinement, and it is of great significance to ensure the fatigue strength of the structure in operation. In this study, the fatigue life prediction of the shell structure of the PTA filter press was investigated through numerical and experimental methods. Firstly, the accurate stress at the critical area of the stiffener was obtained based on the thermomechanical model and submodel approach proposed. Subsequently, the fatigue life was evaluated by the fatigue strength reduction method and hot spot stress method. Finally, the shell structure is optimized by increasing the size of the axial stiffener and continuous hoop stiffener. The results unveil that both thermal load and outer structure constraints have little effect on the radial displacement and stress amplitude of the shell structure. Through modifying the fatigue design curve of the fatigue strength reduction method, the shell structure of the PTA filter press has 42.0% and 0.3% failure probabilities in the previous and present cyclic pressure conditions. Furthermore, the hoop stiffener plays an important role in reducing radial displacement and stress amplitude, among which three hoop stiffeners exhibit the most satisfactory optimization. [ABSTRACT FROM AUTHOR]

In this study, the effects of ultrasonic impact treatment (UIT) on the residual stress in a repair welding joint are investigated by experimental and finite element methods. A three-dimensional numerical analysis approach including a thermomechanical-coupled welding simulation and dynamic elastic-plastic UIT simulation is developed, which has been validated by X-ray diffraction measurement and indentation strain method. The results show that longitudinal residual stresses basically turned into the small tensile stress state from the large tensile stress state, and transverse residual stresses have mainly turned into compressive stresses from large tensile stress after the UIT. In the thickness direction, the average decrease of longitudinal residual stress is 259.9 MPa, which is larger than the 149.1 MPa of transverse residual stress. The calculated residual stress distribution after the UIT of the thin plate is compared with that of the thick plate in the literature, with the results showing the stress accumulation layer inside the thick plate. The simulation results show that the elastic strains are decreased slightly and the equivalent plastic strain is increased markedly after UIT, which explains the mechanism of residual stress relaxation. [ABSTRACT FROM AUTHOR]

Shot peening is one of the most famous mechanical surface treatments to improve fatigue performance of metallic components, which is attributed to high amplitude compressive residual stresses. A numerical approach is developed to analyze the residual stresses in 301LN metastable austenitic stainless steel by shot peening. The material behavior is described by a proposed constitutive model in which strain-induced martensitic transformation, isotropic hardening and kinematic hardening effects are taken into account properly. Both single shot and random multiple shots peening were simulated and analyzed. A numerical method is presented with the Python programming language to make the multiple shots follow a random probability distribution. Results demonstrate that the simulated equivalent plastic strains and martensitic volume fractions agree well with the experimental ones, which verify the validity of the constitutive model. Besides, the numerical method is effective at achieving a realistic surface coverage. The maximum compressive residual stress by the Johnson–Cook model is 12% higher than that of the proposed model. Additionally, each hardening effect has an effect on the simulated residual stress. The developed numerical approach can provide a feasible simulation of the shot-peening process and makes an accurate prediction of the residual stress field in 301LN steel. [ABSTRACT FROM AUTHOR]

The strength of brazed joints is of great significance for plate-fin heat exchangers. Although a lot of research on the strength of brazed joints has been carried out, few studies have focused on the whole process of the crack propagation of brazed joints under loading, and no accurate simulation methods have been published. In this paper, the crack propagation of SS304/BNi-2 brazed joints was investigated by both experiments and numerical simulations. The cohesive zone model (CZM) was applied to simulate the crack propagation. The cohesive energy was obtained by the T-type brazed joint peeling experiments. The cohesive strength was determined as 30 MPa by comparing the load–displacement curves from the simulations and experiments. The results showed that the crack propagation process predicted by the CZM was consistent with the experimental results. Furthermore, with the increase of displacement applied on the specimen, the rate of crack propagation of the brazed joints was high at the beginning, and then gradually slowed down in the later stages. Under displacement-controlled conditions, increasing the thickness and the yield strength of the base metal could delay the crack initiation, but it would increase the crack growth rate once the crack was initiated. [ABSTRACT FROM AUTHOR]

A numerical and experimental study of welding temperature distribution and residual stresses in thick welded plates of SA738Gr.B was conducted. Within the framework of numerical investigations, the temperature field of SA738 thick plate welding was simulated and analysed by using 2-D modelling technology. The temperature field was checked by using the thermal cycle curve with the aim of increasing the computational accuracy and efficiency, and the temperature field was verified by using the thermal cycle curve and heat affected zone. The welding stress field was analysed based on the temperature field, and the indentation test method was used to verify the stress field, and the error was controlled to within 12.5%. With the help of a welding model established for SA738Gr.B thick-plate welding the sequence was simulated. Seen from welding sequence 1 to welding sequence 3, transverse stress S11 changed significantly, decreasing by 14% and 17% respectively, adjusting the welding sequence can reduce welding residual stresses. [ABSTRACT FROM AUTHOR]