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The plate-fin heat exchanger (PFHE) is the core equipment used to achieve the high efficiency of solid oxide fuel cell (SOFC), however, the issues of high-performance brazed joints in the manufacturing of the PFHE have been a challenge due to the poor mechanical properties. This study proposes a brazing manufacturing technology of isothermal solidification with the optimized post bonding heat treatment strategy, to synergistically improve the strength-ductility property and homogenize microstructure of brazed joints, aiming at guaranteeing the high energy efficiency of SOFC. The results show that brazing at 1065 °C for 25 min achieves the complete isothermal solidification and an intermetallic-free joint centerline with numerous borides generating in the diffusion-affected zone. Solution treatment then dissolves large quantities of acicular and blocky borides. The uniformity of grain size and kernel average misorientation distribution is also improved due to recrystallization, which becomes more pronounced after solution aging treatment. In addition, solution aging treatment results in an improvement in the ultimate tensile strength of the brazed joint, which is more prominent than that after solution treatment. However, the increase in elongation after solution aging treatment is smaller than after solution treatment, while still much higher than the as-brazed joint due to the dissolution of boride precipitates and growth of twin boundaries. The results demonstrate that the proposed brazing manufacturing technology not only homogenizes microstructure, but also significantly improves strength and ductility, further promoting the long-life operation of SOFC. • A proper brazing technology to fabricate plate-fin heat exchanger of SOFC is proposed. • An appropriate heat treatment strategy to enhance strength and ductility is proposed. • Solution aging gets superior strength but inferior ductility to solution treatment. • Borides dissolution, solid solution and precipitation strengthening enhance strength. • More uniform microstructure, increased recrystallization and twins raise ductility. [ABSTRACT FROM AUTHOR]

• Heat transfer performance of a Lightnin stirred reactor coupled with draft tube has been investigated. • The optimized impeller off-bottom clearance has been obtained in the draft tube stirred tank. • The time-correlation variation of heating rate and synergistic angle has been investigated. • A correlation formula coupled by multifactor for enhancing heat transfer in a stirred tank has been proposed. The heat transfer issue in stirred tanks is a prevalent concern in the industry. This article aims to investigate the fluid flow and heat transfer within a stirred tank equipped with a Lightnin A320 impeller coupled with a draft tube (DT) structure. The heat transfer performance of a 37 L jacket stirred tank is experimentally measured with the rotation speeds of 50 ‒ 300 RPM. The effects of off-bottom clearances and rotational speeds on mixing and heat transfer performance are explored using Computational Fluid Dynamics (CFD) by flow patterns, local velocity, turbulent kinetic energy (TKE), helicity, vorticity, heat transfer coefficient, synergy angle, extensional efficiency, and coefficient of variation (CoV) , respectively. The numerically predicted temperature curves have a good agreement with the experimental results. An optimal off-bottom clearance with C/D = 0.43 is found in this stirred tank. Furthermore, empirical correlations are developed to predict heat transfer performance by analyzing the relationship between wall heat transfer coefficient, power consumption, and heat transfer rate. By evaluating the variation of the temperature gradient synergy angle with time and rotational speed of the stirred tank, it was determined that a stabilization time of 120 s is required for the synergy angle. In the area outside the DT, 80 % of the region exhibits extensional efficiency values greater than 0.5. For 100 ‒ 300 RPM, achieving a CoV of 0.01 requires 48.36 %, 67.26 %, 76.81 %, 82.34 %, and 85.67 % less time compared to that of 50 RPM, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• The cyclic property degradation method considering the anisotropy of the PFRC is proposed. • The fatigue behavior of PFRC obtained by proposed model agrees well with experiment. • The flexural fatigue failure modes of PFRC were found to relate with the load levels. • The delamination and fibre fracture only occur after the matrix crack of the corresponding local area reaching saturation. This study proposes an improved progressive fatigue damage model. The relation between cyclic property degradation and direction is established. The fatigue damage evolution and life of rod-shaped pultruded fibre-reinforced composite (PFRC) under three-point bending are investigated using the proposed progressive fatigue damage model and acoustic emission test. The damage and failure mechanisms of PFRC are elucidated. Results show that the fatigue damage evolution and life can be predicted accurately by the proposed model. For PFRC under high load levels, delamination is the dominant failure mode; by contrast, the failure of PFRC under fatigue load not higher than medium–high level is dominated by matrix cracks and fibre fracture. The area of flat fracture is related to load level. The sequence of each damage mode appearing in each layer differs. Because the stress distribution in each single layer of PFRC under three-point bending load is not uniform, the delamination and fibre fracture only occur after the matrix crack of the corresponding local area reaches saturation, instead of occurring after the matrix crack of the whole specimen reaches saturation. [ABSTRACT FROM AUTHOR]

In order to improve product design efficiency and guarantee the high temperature structural integrity during the long-term creep of solid oxide fuel cell (SOFC), the creep strength design method is studied by using the finite element method (FEM) and the response surface method (RSM) with considering the interaction between the geometric parameters. A multi-regression model representing the correlation between the sealant failure probability and the geometric parameters is established for rapid estimation of creep strength and optimization design of geometric dimensions. The sealant failure probability is decreased from 0.994 to 0.015 by the optimization of SOFC geometrical size. And the error between results predicted by the FEM and results predicted by the multi-regression model is less than 10%. Therefore, the multi-regression model is proven to be an excellent tool for creep failure prediction and structural design optimization, reducing research costs and time, and improving design efficiency. • Correlation between creep failure probability and geometric parameter is established. • Interaction between anode thickness H a , sealant thickness H s and frame thickness H f is considered. • The optimal geometric parameters is obtained through regression equation analysis. • 50,000 h creep life is met by optimizing the thicknesses of the components. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimized 3D-anode-driven EO was coupled with Co 3 O 4 nanoneedle activated PMS. • 3D-SFS + CoNN@SFF system exhibited excellent oxidation capacity and stability. • 1O 2 was the active species that dominated tetracycline degradation. • Initial paths of TC were more prone to •OH addition and H transfer than 1O 2 addition. • 1O 2 played an essential role in subsequent ring cleaving reactions of TC. In this work, a dual three-dimensional porous system (3D-SFS + CoNN@SFF) with anchored Co 3 O 4 nanoneedles for peroxymonosulfate activation (CoNN@SFF) and coating optimized porous electrodes for electrocatalysis (3D-SFS) coupling is constructed based on SiC foam filler for the degradation of high concentrate tetracycline (TC). The results indicate that the coupled system demonstrates favorable synergistic performance. Its reaction kinetic constant (k) is 2.29, 2.45, and 8.47 times that of the single system of CoNN@SFF, 3D-SFS, and conventional BDD-driven electrocatalytic oxidation. Meanwhile, the energy consumption of the coupled system is low at 0.00151 kWh·g−1. Experiments under different operating parameters reveal that the 3D-SFS + CoNN@SFF system exhibits good performance under multiple anion coexistence conditions or over a wide pH range of 2–10. Furthermore, EPR and quenching experiments reveal that active species hydroxyl radical (•HO), sulfate radical (S O 4 ∙ - ), and singlet oxygen (1O 2) are involved in TC degradation reactions. 1O 2 is the most dominant active species, followed by •HO. Based on this, TC degradation mechanisms dominated by 1O 2 and •HO are further calculated via density functional theory (DFT). Results show that the dominant initial reaction channels are •OH abstracting hydrogen atom on the hexatomic ring with dimethylamino group (A-ring, OH-RH9) and the addition reaction to a carbon atom on the adjacent ring (B-ring, OH-RC7) with apparent rate constants (k app) of 2.29 × 109 and 1.52 × 109 M−1s−1. Although it is difficult for 1O 2 to attack TC directly, it plays an essential role in the subsequent ring-cleaving reaction of TC. The three most probable ring cleaving pathways with low energy barriers for the rate-determining step are screened, which include reactions of 1O 2 addition, •HO 2 elimination, ortho -position H-transfer, and •HO addition. This work not only constructs an efficient coupled 3D catalytic system, but also provides a universal reference for the degradation mechanism of TC with •OH and 1O 2 as the main active species. [ABSTRACT FROM AUTHOR]

Various types of solid-state phase transformation (SSPT) occur during the SA508 steel welding process, especially for multi-pass welding. The multiple thermal cycles lead to a more complex microstructure distribution and significantly influence the residual stress distribution. Therefore, to better control the microstructure and residual stress, it is necessary to optimize the process parameters which are closely related to the welding thermal cycles. This study established a thermo-mechanical-metallurgical multi-field coupling model and then validated it using X-ray and neutron diffraction residual stress measurement tests. Furthermore, the influence of welding heat input and preheating temperature on the formation of phase constituents and the ultimate residual stress field were analyzed in detail, concomitantly with a comprehensive discussion on their underlying mechanisms. The results showed that the increase of heat input expanded the domain occupied by the bainite phase, accompanied by the increase of compressive stress region. Moreover, the rise of preheating temperature promoted the bainite phase transformation, thus decreasing the longitudinal compressive stress and the stress gradient. The variation induced by welding parameters was closely related to the welding cooling rates. To obtain a full bainite and low residual stress condition of welded joint, it becomes imperative to exercise control over cooling rates, maintaining them at approximately 1.0 °C/s. • Increase of heat input expands the area of bainite phase and compressive stress. • Increasing preheating temperature magnifies transverse tensile stress. • As Cooling rate increases, bainite content decreases and martensite content increases. • To get welded joints free of martensite, the cooling rate should be below 1 °C/s. [ABSTRACT FROM AUTHOR]

Benefited by its high efficiency and low cost, the narrow gap welding has been widely used in thick wall pressure equipment. Considering the fact that defects in welded joints inevitable, the safety assessments for welding equipment with residual stress are crucial. However, for the thick-wall equipment using narrow-gap welding, the current safety assessment standards specifying the residual stress distribution are not detailed or missing. In this paper, the through-wall residual stress of thick wall girth welds with narrow gap welding is studied. The stress components (bending stress, membrane stress and self-equilibrating stress) at the evaluation point are obtained by stress decomposition. The effects of the heat input, the wall thickness, the radius thickness ratio and the number of welding passes on residual stress are considered, respectively. The results show that the heat input only affects the distribution of bending stress and membrane stress. The axial and hoop bending stresses decrease with the increase of the wall thickness, and the hoop membrane stress is about 0.75 times material yield strength. With the increase of radius thickness ratio, the bending stress decreases while the hoop membrane stress increases. The stress distribution is fluctuating when the number of welding layers is small, which be expressed by trigonometric function. The distribution model of welding residual stress through the wall thickness is proposed. The stress distribution obtained by the proposed prediction model is in good agreement with the finite element calculation results. • >The universal model of residual stress and stress components for girth weld with thick wall was proposed. • The stress components (bending stress, membrane stress and self-equilibrating stress) of the evaluation point are also obtained. • The effects of heat input, wall thickness, radius thickness ratio and number of welding passes on residual stress are considered, respectively. • Heat input only affect the amplitude of bending stress and hoop membrane stress. • The stress on inner surface using narrow gap welding for thick walls is compressive stress. [ABSTRACT FROM AUTHOR]

The measurement of welding residual stress (WRS) is necessary to formulate the stress control strategies, in order to ensure the reliability of engineering structures during their service life. The instrumented indentation technique can detect surface residual stress nondestructively with an acceptable accuracy, making it a desirable option for in-situ applications. However, it is difficult to meet the requirement for stress-free samples, particularly in the case of welded joints with non-uniform mechanical properties. In this work, the impact of stress-free indentation curves on determining WRS is furtherly studied based on the previously proposed indentation energy difference method. The WRS in a mismatched welded plate is measured using single reference method and distributed reference method, respectively. The study suggests that using the single reference method can lead to significant errors in determining the sign and magnitude of WRS in the weld zone. A prediction model combining the continuous spherical indentation (CSI) method and Back Propagation (BP) neural network is proposed to obtain the stress-free indentation curves of local positions nondestructively. And the CSI-BP method is verified through reverse finite element analysis and experiments. • The WRS were measured by indentation energy difference method. • A continuous spherical indentation -BP neural network prediction model was established to estimate the stress-free indentation curves for unknown materials. • A single reference method and two distributed reference methods were compared in the WRS measurement. [ABSTRACT FROM AUTHOR]

In this paper, the effects of dual-cracks on the CCG behaviour of Hastelloy C276-BNi2 brazed joints were investigated. And the effects of inner crack length, inner crack distance and mismatched material coefficients on the creep crack initiation (CCI) time, CCG rate and creep life were also discussed. The results show that the creep crack can across over the inner crack and propagates continuously. The brazing defects can accelerate the CCG rate, thus leading to the decrease in the creep life and CCG length. With the increases in inner crack length and the decreases in inner crack distance, the CCI time, creep life and CCG length decrease. Longer inner crack distance and shorter defect length can suppress creep crack initiation and propagation. Bigger mismatch factor between base metal and filler metal may avoid the weakening effects of brazing defect on creep life. [ABSTRACT FROM AUTHOR]

The borehole stability is crucial in well-drilling and oil-production operations. Before drilling, the rock at certain depth is in equilibrium state with its surrounding formation. This balance is disturbed when the borehole is created by the drill bit. Although the borehole-related problems are influenced by complex factors, including weak formation properties, tectonic stress state, fluid-related problems and etc., understanding the drill-induced borehole damage is critical before further investigating the borehole instability. In this paper, the damage of the borehole induced by the drill bit is analyzed based on the state-based peridynamics. The damage of the formation is expressed in the form of 'broken bonds'. The bond break criterion, local damage criterion and bit penetration criterion are proposed for the drilling modeling. The heterogeneous properties of the formation rock are modeled stochastically by modifying peridynamic constitutive parameters. The natural discontinuities of rock are represented by the artificially breaking bonds in the initially-cracked region. The geometries of discontinuity, including spacing, orientation, persistence and etc., are modeled by following the particular statistical distributions. Thus, the crack propagation of formation rock under the drilling operation is captured. In this peridynamic model, the borehole damage propagations under the influence of discontinuity surfaces and multi-layer interfaces are analyzed. This research investigates the drill-induced borehole damage, which casts light on the guideline for the borehole instability control and the drilling operations. • The properties of formation, including rock heterogeneities, formation discontinuities and multiple formation layers, are represented within peridynamic framework. • Peridynamic formation damage criteria, including bond break criterion, local damage criterion and bit penetration criterion, are reformulated. • A numerical adaptive peridynamic model is proposed to simulate the process of drill bit penetration and formation damage propagation. • Drill-induced borehole damage characteristics are analyzed by considering the heterogeneities, discontinuities and multi-layers of the formations. The coupling of discontinuous joints with the nonlocal parameter is discussed. [ABSTRACT FROM AUTHOR]

During long term operation at high temperature, creep is inevitable and can cause damages and cracks, which should be decreased to ensure the stack integrity. A strain based creep damage model is used to predict the creep damage behavior of a planar solid oxide fuel cell (SOFC). It demonstrates the maximum creep damage locates at the corner of glass-ceramic (GC) facing the frame after 50 000 h creep. The effect of frame material on the creep is studied. By increasing the creep parameter B of frame, the creep and damage in the cell and GC are decreased. This indicates the frame with a larger creep parameter can alleviate the interaction between components and decrease the deformation of the system. It recommends to use frame materials which have creep parameters larger than 1.3752 × 10−15 MPa-nh−1 besides CTEs closed to the cell to compensate and mitigate the creep and damage of SOFC system. • The creep and damage of cell and GC can be mitigated and compensated by the frame. • This is a new discovered advantage for frame material with a larger creep parameter. • The interaction between components is alleviated and the deformation is decreased. [ABSTRACT FROM AUTHOR]

The brazed joint has been widely used in the plate-fin structure, and the periodic pressure suffering in operation makes it very important to ensure the fatigue strength. This paper investigates the fatigue crack growth of 316 L brazed joint by experiments and simulations. Firstly, the mechanism of the fatigue crack growth behavior is analyzed via the scanning electron microscope (SEM) and the electron back-scattered diffraction (EBSD) techniques. Then, the virtual crack closure technique (VCCT) is adopted to simulate the fatigue crack propagation by developing a user subroutine. Lastly, the effect of filler metal thickness on strain energy release rate is discussed. Results show that the fatigue crack mainly propagates along the interface of the base metal and filler metal. However, the crack is still located at the filler metal and follows a transgranular fracture mode. In addition, the simulated results by VCCT agree well with the experiment, which demonstrates the feasible application of VCCT for brazed joint fatigue crack simulation. Besides, the strain energy release rate of the brazed joint has an intrinsic different mechanism compared with the base metal and the filler metal, and the strain energy release rate decreases with the filler metal increasing. • The fatigue crack shows a trans-granular fracture mode in the filler metal. • The VCCT is successfully applied to the fatigue crack simulation of brazed joint. • The stain energy release rate of brazed joint shows a different mechanism. [ABSTRACT FROM AUTHOR]

Abstract In this study, the cyclic mechanical characters of 316L stainless steel at elevated temperature are extensively investigated by the experimental and cyclic constitutive models. The experiments include the monotonic tensile tests with different loading rates and the low cycle fatigue tests considering the effect of strain amplitudes, strain rates and loading sequences. The evolution of cyclic stress amplitudes, hysteresis loops and elastic modulus under various loading conditions are comprehensively analyzed. The experimental results show that the 316L steel at elevated temperature performs a typical three-stage cyclic mechanical response, i.e., initial hardening, subsequent saturation and final accelerated softening. The cyclic softening in both stiffness and flow stress is mainly caused by the nucleation of micro-voids or micro-cracks, and the subsequent coalesce and propagation. Furthermore, although the nearly rate-independent mechanical behavior is observed at monotonic tensile and first several fatigue cycles due to the DSA effect, the cyclic hardening/softening behavior shows a significant strain-rate and loading history dependence. Finally, inspired by the experimental observations and analyses, a damage-coupled cyclic elastic-viscoplastic constitutive model involving strain-range, strain-rate and loading history dependence is proposed to predict the complex cyclic behaviors of the material at elevated temperature. A hardening factor is incorporated into the Chaboche kinematic hardening equations to model the kinematic-induced hardening behavior. And the plastic strain memory surface and the maximum plastic strain rate are introduced to model the strain-range, strain-rate and loading history dependence of cyclic behavior. The proposed model is proved to effectively describe the complex evolution of not only cyclic stress amplitude but also hysteresis loops for the 316L steel at elevated temperature. Highlights • The cyclic response and fatigue mechanism for the 316L steel at room and elevated temperature were compared. • The various tensile and LCF tests considering the effect of strain range, strain rate and loading sequence were carried out. • The fatigue damage was determined experimentally, and incorporated into the cyclic elastic-viscoplastic constitutive model. • The relationship between strain rate, DSA effect and cyclic behavior were investigated and realized by the proposed model. • The proposed model can predict the evolution of not only cyclic stress amplitude but also hysteresis loops accurately. [ABSTRACT FROM AUTHOR]

Abstract This paper studied the distribution of weld residual stress in a spiral welded pipeline by finite element method (FEM) and experimental measurements, and the effect of helix angle on residual stress has also been investigated. Both the FEM and experiment results show that the residual stresses in HAZ are larger than those in weld. The error between FEM and experiment results is within 14%, proving that our FEM is correct. There is a peak-shape stress distribution through the weld thickness and the residual stresses in the inner surface are larger than those in the outer surface. Different helix angle has a different equivalent weld length along the hoop and axial directions, which generates different hoop and axial plastic strains, leading to different hoop and axial residual stresses. As the increase of the helix angle, both the radial and hoop residual stresses decrease, while the axial residual stresses increase. As the helix angle increases from 20° to 50°, the hoop stresses in HAZ decrease by 65%, while the axial stresses increase by 120%. The residual stresses are influenced by the pipe dimension (pipe diameter, thickness, weld profile), welding technology (heat input, welding speed) and material grade. When the helix angle is between 40° and 45°, both the hoop and axial residual stresses are reduced to the minimum. The most suitable helix angle is suggested to design around 40°–45°. Graphical abstract Image 1 Highlights • Effect of helix angle on residual stress for oil pipelines is investigated. • HAZ is a weakest zone for X70 steel spiral pipes. • The residual stresses are easily influenced by the pipe dimension and welding technology. • The most suitable helix angle is suggested to design around 40°–45°. [ABSTRACT FROM AUTHOR]

Highlights • A new model was proposed to reasonably predict creep life. • The notch weakening effect was found in the brazed joint. • The creep life increases with notch angle increases while it decreases with notch radius increases. • The brazed joint under multiaxial stress was mainly fractured by intergranular brittle mode. Abstract The brazed components operating at high temperature inevitably suffer from multiaxial creep under multiaxial stress. In this study, the creep strain, fracture and failure mechanisms of HastelloyC276-BNi2 brazed joint under multiaxial stress were studied by experiment and finite element modeling (FEM). A new damage evolution model was put forward to estimate the creep fracture behavior of brazed joint under multiaxial stress. And the influences of notch angle and radius were also discussed. The notch weakening effect was exhibited in the brazed joints. The creep life is not only dependent on the creep fracture strain but also on notch type. The proposed creep damage evolution model can reasonably reflect the relationship between creep fracture ductility and multiaxiality. The predicted creep life by proposed model agrees very well with the experimental results. Most importantly, the fracture mechanisms of brazed joint under multiaxial stress were revealed and the creep damage evolution was well interpreted by FEM. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • The equivalent thermophysical properties are calculated analytically. • The equivalent properties are applied to creep-fatigue design. • The equivalent method is verified by finite element analysis. • Equivalent thermophysical properties are dependent on geometrical parameters. • The result of creep-fatigue design satisfies the design criteria. Abstract Creep-fatigue life prediction is essential to plate-fin heat exchangers (PFHE) work at high temperatures and pressures in addition to thermal cycles. As the core of PFHE, the plate-fin structure is a complex pore structure and it is pretty difficult to carry out the stress analysis by conventional finite element method. Thus in this paper, a homogeneous method is proposed to do the strength design for plate-fin structure. This method treats the pore structure as an equivalent solid structure, and the key is to calculate the equivalent material properties and the equivalent stress. The equivalent mechanical properties have been obtained in our previous work [1], and in this paper the equivalent thermophysical properties including thermal conductivity, coefficient of thermal expansion, specific heat and density have been derived. This equivalent method is also verified by the three-dimensional finite element method. Besides, creep and fatigue tests of plate-fin structure are applied to calculate the stress and strain magnification factors. Basing on the equivalent material properties, a full scale stress analysis of PFHE by the equivalent finite element model has been carried out successfully to calculate the equivalent stress. After that, we multiply the equivalent stress-strain by the stress and strain magnification factors to calculate the local stress and strain. Then the creep and fatigue damages are predicted according to design curves of base metal. The result of equivalent model agrees well with that of the classical model, which concludes that this homogeneous method is effective to predict the macroscopic performance of plate-fin structure. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • CCG behaviors of Inconel 625 at 650 °C are studied by test and numerical method. • Intergranular fracture is the dominated failure mechanism of Inconel 625. • The obtained α can reasonably predict the CCG behaviors of Inconel 625. • Single C ∗ can well be used to describe the CCG rate of Inconel 625. • Constraint effect is not obvious for the C ∗ to characterize CCG rate of Inconel 625. Abstract Creep crack growth behaviors of the Inconel 625 superalloy at 650 °C are investigated through experimental and numerical methods. The simulated data agree well with the experimental results, reflecting that the multi-axial creep performance parameter α obtained by present paper can reasonably predict the creep crack growth behaviors of Inconel 625 superalloy. The crack initiation time takes up the most proportion of the whole life for all the load levels, and intergranular fracture is the dominated failure mechanism. Creep constraint effect is not obvious for the C ∗ to characterize the creep crack growth of Inconel 625 superalloy. [ABSTRACT FROM AUTHOR]

• The corrosion on the sealing surface of the valve body was related to the galvanic corrosion in the spent acid. • Intergranular corrosion along the interface of the weld deposit for the gate and seat was derived from carbides. • The formation of carbides was induced by the C element diffusion from alloy deposits during the spray weld. The different types of corrosion behavior occurred on a 13Cr gate valve using weld deposited gate and seat after about sixteen months of service in an oilfield in China, resulting in the leakage failure. In this study, the corrosion causes were investigated through visual inspection, mechanical performance testing, scanning electron microscopy, energy dispersive spectrometer and electrochemical analysis. The results demonstrated that the corrosion on the sealing surface of the valve body was related to the galvanic corrosion between the 304 SS ring gasket and 13Cr SS ring groove, which presented a significant potential difference in the spent acid environment. In addition, due to the C element diffusion from deposits during the spray weld on the surface of the gate and seat, a large amount of Cr enrich carbides were formed at the prior austenite grain boundaries in the 13Cr SS matrix side, which further induced the intergranular corrosion and cracking along the interface in service. [ABSTRACT FROM AUTHOR]

In this study, the weld residual stresses (RS) in a 25 mm thick ferrite steel plate with newly developed low-temperature transformation (LTT) welding wire were investigated by finite element method and neutron diffraction (ND) measurement. A thermo-elastic–plastic finite element model coupled with solid-state phase transformation (SSPT) was developed to investigate the distribution and formation mechanism of RS, which has been verified by ND measurement. The results demonstrate that the developed LTT alloy can significantly reduce the RS and even generate compressive RS in the weld zone, due to the interrupted cooling shrinkage caused by the LTT. The higher inter-pass temperatures related to the microstructure evolution result in an increased region of compressive stress within the weldment. Moreover, the longitudinal RS in the weld zone gradually changes to tension as the initial temperature of martensitic transformation increases. Notably, the relaxation effect of transformation-induced plasticity on RS and its influence on model accuracy were discussed. [ABSTRACT FROM AUTHOR]

The creep failure lives of a pyramidal lattice truss panel structure at compressive and tensile loads have been investigated by theoretical and finite element methods. Two analytical models are derived to calculate the life of creep-rupture and creep-buckling. The results reveal that the creep-rupture life is highly sensitive to the geometry dimensions. With the decreases of the stamping angle, cutting angle, truss length and the increases of the truss width and thickness, the creep-rupture life decreases significantly. The creep-buckling model presents that the creep-buckling life can be improved by increasing the width and thickness of truss and decreasing the length of truss. A synthetically analytical model combines the creep-rupture and creep-buckling is proposed to predict the creep failure time accurately. The transition mechanism from creep-buckling to creep-rupture is also extensively studied. Creep-buckling is the dominant failure mechanism as the applied stress approaches the critical stress. The solid truss is inclined to creep-rupture when the compressive stress is smaller than the critical stress. [ABSTRACT FROM AUTHOR]

This paper investigated the fatigue life of a dissimilar welded joint between SAF2205 duplex stainless steel and 304 austenite stainless steel. A nonlinear fatigue damage model based on continuum damage mechanics (CDM) is used to estimate the fatigue life, and the effect of the residual stress is studied. The results show that large residual stresses were generated in the dissimilar welded joint and agree well with the indentation measurement results. The fatigue test specimens were cut from the welded sample, and the residual stress relaxed significantly after longitudinal cutting, especially for longitudinal residual stress. Considering the transverse residual stress, the estimated fatigue life is more consistent with the experiment. The residual stress mainly affects the mean stress, rather than the stress amplitude. As the longitudinal residual stress relaxed significantly after cutting, the effect of welding residual stress on fatigue life can be seriously overestimated. The width of fatigue test specimen should be at least 30% of the as-weld sample for fatigue design in consideration of the residual stress relaxation. [ABSTRACT FROM AUTHOR]

Wire mesh is a high strength/stiffness material with versatility and little defect. This paper proposed a theoretical model to calculate the anisotropic effective elastic constants of a wire mesh material, and finite element method (FEM) is also carried out to validate the proposed model. Considering the effect of wire waviness and the discontinuity between the warp and weft wires, the analytic expressions of effective elastic modulus, shear modulus and Poisson’s ratio were obtained. The results show a good agreement between the theoretical and FEM, revealing that the theoretical method gives a reliable prediction. The in-plane effective elastic modulus is higher about one order of magnitude than the out-of-plane modulus. Conversely, the out-of-plane shear properties are superior to the in-plane properties. The effective modulus are significantly affected by wire radius R , opening length L and the ratio R / L . With the increase of R / L , the effective modulus of variant directions increases with different modalities. The wire waviness leads to much more in-plane stiffness-knockdown of wire mesh with thicker wires. Meanwhile, the out-of-plane stiffness is found to be weakened by the tiny contact area between the warp and weft wires. Stiffness reduction factors were proposed to describe the in-plane and out-of-plane stiffness-knockdown. [ABSTRACT FROM AUTHOR]

This paper studied the creep rupture behavior of Hastelloy C276-BNi2 brazed joint by experimental. Based on a series of creep rupture tests at 600 °C under 110–250 MPa, a relation between the stress and rupture time was achieved to evaluate the creep life of brazed joint. The results show that all the brazed joints were fractured in brazed seam immediately after the second creep stage. The creep model, fracture behavior and failure mechanism are dependent on the level of applied stress. The creep behavior of the brazed joint should be depicted by two-regime Norton (2RN) creep model rather than single Norton model. The creep damage tolerance factor was used to identify the cause of creep damage. From low to high stress level, the failure mode is changed from intergranular brittle to transgranular ductile fracture due to the increases of damage tolerance factor with applied stress increases. [ABSTRACT FROM AUTHOR]

Creep crack growth behavior of the 9Cr-1Mo steel under multi-axial stress state at 600 °C was investigated by a modified creep damage model. Firstly, a modified creep damage model was proposed and incorporated into the finite element software ABAQUS by the CREEP subroutine. And then the creep and damage behaviors of the 9Cr-1Mo steel were simulated by the notched bar and CT specimen. The results indicate that the multi-axial creep ductility and the life of the high temperature components calculated by the modified model are corresponding well with the experimental data, and the life prediction precision has been greatly improved compared to that from the K-R model. This demonstrates that the proposed model can be used to accurately predict the creep crack growth behaviors of the high temperature materials. The creep crack growth rate a ̇ presents a linear relationship with the crack driving force parameter C * in log-log coordinate system. Based on the established relationship between the a ̇ and C *, the creep crack growth rate of the 9Cr-1Mo steel components working at high temperatures can be predicted. [ABSTRACT FROM AUTHOR]

The reduction and re-oxidation of anode have significant effects on the integrity of the solid oxide fuel cell (SOFC) sealed by the glass-ceramic (GC). The mechanical failure is mainly controlled by the stress distribution. Therefore, a three dimensional model of SOFC is established to investigate the stress evolution during the reduction and re-oxidation by finite element method (FEM) in this paper, and the failure probability is calculated using the Weibull method. The results demonstrate that the reduction of anode can decrease the thermal stresses and reduce the failure probability due to the volumetric contraction and porosity increasing. The re-oxidation can result in a remarkable increase of the thermal stresses, and the failure probabilities of anode, cathode, electrolyte and GC all increase to 1, which is mainly due to the large linear strain rather than the porosity decreasing. The cathode and electrolyte fail as soon as the linear strains are about 0.03% and 0.07%. Therefore, the re-oxidation should be controlled to ensure the integrity, and a lower re-oxidation temperature can decrease the stress and failure probability. [ABSTRACT FROM AUTHOR]

The plate-fin structure with high efficiency of heat transfer is a type of periodic pore material. The equivalent homogenization method has been proposed to design the strength of plate-fin structure, and it is essential to calculate homogenized elastic constants of the pore structure. This paper proposed an analytical model to calculate homogenized elastic constants of the plate-fin structure including the elastic modulus, shear modulus and Poisson's ratio. These proposed equivalent formulas have considered the effects of geometrical parameters. The finite element method and experimental study have also been performed to verify the analytical method. In addition, the effects of geometrical parameters on homogenized elastic constants have been fully studied. The results show that homogenized elastic constants by the proposed analytical model show a good agreement with results by FEM and experimental. It has been proved that the stretching deformation is the dominating deformation mechanism of the fin in Z -direction and only the fin paralleled to Y -direction can influence the tensile deformation in Y -direction. The homogenized elastic constants are strongly dependent on the geometrical parameters. This work provides theory formulas to calculate basic mechanical constants for conducting the full-scale design of plate-fin structure by equivalent homogenization method. [ABSTRACT FROM AUTHOR]

In this study, we present a creep analysis for an anode-supported tubular solid oxide fuel cell (SOFC). The effects of tube radius on creep and stress are also studied. The as-sintered residual stress is measured by an X-ray diffraction instrument. Simulated result is consistent with the measurement data. The finding shows that the fracture starts in the electrolyte for the big tube radius after 50 000 h because of the mismatch creep properties between SOFC layers. As tube radius increases, the hoop stress in the electrolyte also increases because the growth of elastic strain is dominant compared with creep relaxation. Hoop stress in the electrolyte exceeds the tensile strength when the tube radius is larger than 30 mm for our SOFC system. The tube radius should be designed to be in millimeter level or sub-millimeter level to decrease the growth of hoop stress in the electrolyte and ensure long-term reliability at high temperatures. [ABSTRACT FROM AUTHOR]

• >Synthetical effect of material inhomogeneity and welding defect on fatigue behavior. • >New structure strain method including heterogeneous plasticity and stress singularity. • >Evolution of fatigue mode with geometric configurations and cyclic amplitudes. • >A damage tolerance-based fatigue design concept to guide manufacture of welded joints. This paper performed experimental and analytical investigations on the synthetical effect of material inhomogeneity and welding defects on the fatigue behavior of 2205 duplex stainless steel cruciform welded joints. A series of experiments were performed, including microstructure characterization by the electron back-scattered diffraction, fatigue mechanical tests assisted by digital image correlation technique and fracture morphology observations by scanning electron microscope. Results show that fatigue life and failure location of cruciform welded joints depended heavily on their geometric configurations for lower cyclic amplitudes. However, with the elevation of loading, material inhomogeneity played a greater roles, leading to the change of fatigue failure mode with both geometric configuration and cyclic stress amplitude. To quantize the effects of welding defects and material inhomogeneity, a modified structure strain method was proposed by considering the heterogeneous plastic properties, to accurately predict both fatigue lifetime and failure location of cruciform welded joints at both low and high cycles fatigue. Lastly, a damage tolerance-based fatigue design method was discussed to guide the highly-reliable manufacture and damage detection of duplex stainless steel cruciform welded joints in the engineering. [ABSTRACT FROM AUTHOR]

Neutron diffraction measurement, contour method and finite element method have been combined together to study the distribution of weld residual stresses in a thick plate considering the effect of back chipping. The comparison among the three methods, the effect of back chipping and the formation mechanism of the residual stresses in the thick plate were analyzed. The results show that the residual stress distribution exhibits an “M” shape across the specimen width. Large tensile residual stresses were generated in the back weld and top weld layer. Back chipping has a great influence on the residual stress profile. It can change not only the distribution shape of residual stress but also the position of the peak value. The residual stresses increase with the increase in back chipping thickness. The residual stress distribution is mainly formed in the welding of back weld. As the layer number increases, the residual stress distribution in the main weld does not change obviously and only the stress values change. [ABSTRACT FROM AUTHOR]

Lattice truss panel structures (LTPS) have been widely used in engineering structures because of their high strength/density ratios. It is very essential to propose a precise method to calculate the effective elastic modulus (EEM). This paper presented a stretching model and a stretching-bending model to calculate the EEM, which have been compared with experimental results. The stretching-bending model considers the effects of seven geometrical parameters and it shows a good agreement with the experimental results, while the stretching model overestimates the results by approximately two orders of magnitudes. It has been also proved that the stretching-bending model is superior to the models expressed by the relative density. The EEM is strongly dependent on the geometrical parameters rather than the relative density only. At the same relative density, the dip angle, included angle and truss length have more considerable influences on the EEM, followed by truss thickness, truss width and node length successively. [ABSTRACT FROM AUTHOR]

In this paper, the relaxation of weld residual stress in a 316L stainless steel weld joint under cyclic loading was researched by experimental and finite element method (FEM). Initially, the as-weld residual stresses were calculated by a sequential coupling thermo-mechanical FEM. Subsequently, a cyclic plasticity constitutive model was proposed to study the redistribution of the residual stress by the cyclic load. Significant residual stresses are released during the first few cycles. Especially, about 45–60% of the maximum residual stresses are released during the first cycle because of the plastic deformation caused by the superposition between the as-weld residual stress and the applied load. More residual stresses are released with the increase of the stress amplitude and cyclic number. An analytical model, which considers the effects of the initial residual stress, yield stress, stress amplitude, and number of cycles, was proposed to predict the relaxation of the weld residual stress by the cyclic load. In addition, experimental measurements were also performed to validate this model. Experimental results prove that the proposed model can be used as a valid tool to predict the relaxation of residual stress by the fatigue load. [ABSTRACT FROM AUTHOR]

This study explored the microstructure evolution of 2205 duplex stainless steel (DSS) and further probed its effects on microhardness and corrosion performance. The results show that the dislocation multiplication, strain-induced martensite generation and grain refinement resulted from pre-stain increase the microhardness of DSS. Compared with the degradation of corrosion resistance at 7% pre-strain, the improved corrosion resistance at 14% and 21% pre-strain is related to the smaller surface energy difference, more strain-induced martensite and more low-angle grain boundaries. The changed pitting nucleation sites with the rise of pre-strain strongly depend on the increased dislocation density and strain-induced martensite. • Effect of pre-strain on the microstructure evolution of 2205 DSS is unraveled. • Strain-induced microstructural changes notably affect the microhardness of DSS. • The corrosion disparities derived from different pre-strain in DSS is determined. • The correlation between microstructure and corrosion performance is unmasked. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of notch position on creep damage for Hastelloy C276-BNi2 brazed joint. Three different types of notches locate in edge of base metal (base notch), edge of filler metal (surface notch) and center of filler metal (inside notch) were compared, and the influence of notch geometric parameters on creep damage was also investigated. The results show that the different notch position and dimension generate different creep damage distributions and have a great influence on creep life. The creep failure is the easiest to occur in surface notch, then the base notch, and the last is inside notch. The brazed joint with higher maximum principal stress and von Mises stress generates creep failure easier. For the base notch, the failure time increases with the increase of base notch distance and the creep failure location moves gradually from the center of filler metal to notch tip. The notch locating away from filler metal is beneficial to reduce the creep damage in filler metal and enhance the creep life. For the inside notch, the failure time decreases with notch length increases and the maximum creep damage locates at notch tip. With the increase of inside notch width, the failure time increases first and then keep steadiness, and the failure location moves away from notch tip. The effects of notch position and dimension should be fully considered in creep failure analyses and life assessments of brazed joints. [ABSTRACT FROM AUTHOR]

In this study, the evolution of microstructure and its correlation with hardness and pitting corrosion resistance in duplex stainless steel (DSS) welded joints were investigated. The results showed that the precipitation of chromium nitride, refined grain size and large residual deformations contributed to the increase of microhardness in the heat affected zone (HAZ) and weld metal (WM). Poor pitting corrosion resistance was found in the HAZ, especially in the high temperature heat affected zone (HT-HAZ). The chromium nitride precipitates and secondary austenite were the main pitting nucleation sites. • The evolution of microstructure in DSS welded joints was analyzed. • The microhardness and its correlation with microstructure was discussed. • The pitting corrosion resistance of different welded zones was determined. • The HT-HAZ had the worst pitting corrosion resistance. • The relationship between microstructure and pitting corrosion was unraveled. [ABSTRACT FROM AUTHOR]

The effects of anode porosity on thermal stress and failure probability of a planar solid oxide fuel cell (SOFC) are investigated by finite element method (FEM). The thermal stress and failure probability in planar SOFC with and without considering porosity (CP) were compared. The results show that the compressive stresses are generated in the electrolyte layer, while tensile stresses are generated in Ag–CuO and BNi2 layer because of the compatibility of deformation. In the case of considering anode porosity, the compressive stresses in anode and electrolyte layer and the tensile stresses in cathode layer are all decreased. Comparing to without CP, the thermal stress with CP in electrolyte and cathode layer decreases by 33.2% and 46.9%, respectively. The anode layer has a large risk of failure (5.6489 × 10 −4 ) than that of cathode and electrolyte layer at as-fabricated state. And the failure probability at cathode layer at start-up reaches 0.998. The failure probability decreases gradually in the period of creep. The failure probability in anode, cathode and electrolyte layer with CP all decrease comparing to without CP. The porosity of anode could lead to the decrease of tensile thermal stress, resulting in the decrease of failure probability in cathode layer. The reduction speed of failure probability at creep stage with CP is bigger than that without CP. As the increase of porosity, the failure probability decreases due to the decrease of the tensile stress. [ABSTRACT FROM AUTHOR]

We developed an analytical model to predict the equivalent creep strain rate of a lattice truss panel structure. The model, which takes into account the effects of the bonded node and the intersection node of the trusses, is well validated by finite element analysis. Compared with Hodge and Dunand model, this model obtains a more accurate prediction result. The creep deformation of the panel structure is controlled by the creep of vertical trusses parallel to the applied load. The equivalent creep strain rate is determined by five key parameters including punching angle, cutting angle, truss thickness, width and length. A slight change of truss dimension can lead to a big variation of the creep rate by orders of magnitude. With the increase of punching angle and cutting angle, the relative density decreases and the stresses in the trusses increase, leading to an increase of creep rate. With the increase of truss thickness and width, the creep rate decreases because the relative density increases and the stresses in the truss decrease. As the truss length increases, the creep rate increases due to the decrease of relative density and the increase of stresses in the truss. [ABSTRACT FROM AUTHOR]

Nickel-based brazed joints are widely used at high temperatures, and it is very important to ensure the creep strength. Using three-dimensional finite element method, this paper presents a study on the creep damage and creep crack initiation (CCI) in P92–BNi2 brazed compact tension (CT) joint specimen, and the effect of brazed residual stress on CCI has been investigated. Firstly, the as-brazed residual stress is simulated. Then the effect of residual stress on creep and damage is calculated by an uncoupled Norton equation and the ductility exhaustion approach. The results show that the CCI is a function of residual stress, load level, joint thickness and notch radius. The brazed residual stress has a great effect on creep damage, and it can lead to the initiation of creep crack lonely without any mechanical load. The combination of applied load not only accelerates the creep damage and decreases the CCI time, but also determines the creep crack propagation rate. The CCI time decreases with the increase of applied load and joint thickness. As the notch radius increases, the CCI time increases. [ABSTRACT FROM AUTHOR]

Planar solid oxide fuel cell (SOFC) operates at high temperature and requires a good creep strength to ensure the structure integrity. This paper presents a creep and damage analysis of a bonded compliant seal (BCS) structure of a planar SOFC considering the effect of as-bonded residual stress and thermal stress, as well as the effect of filler metal and foil thickness. A modified continuum creep-damage model is used in the finite element simulation. It demonstrates that the BCS structure meets the requirement of the long-term operation at the high temperature of 600 °C with an appropriate braze bonding process. The results show that the failure location is not in the region of maximum creep deformation due to the effect of high level multi-axial stress which drastically decreases the multi-axial ductility. Reasonably reducing the thickness of filler metal and foil can decrease the damage of the BCS structure. Based on the consideration of creep and damage, it is proposed that the thickness of filler metal and foil should not exceed 0.1 and 0.05 mm, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Residual stress reduction in penetration weld nozzle by overlay welding was studied. [•] The overlay weld can decrease the residual stress in the weld root. [•] Long overlay welding is proposed in the actual welding. [•] Overlay weld to decrease residual stress is more suitable for thin nozzle. [ABSTRACT FROM AUTHOR]

In this study, a wavelength-dependent neutron diffraction method used to measure the residual stress in thick duplex stainless steel (DSS) welded plate was proposed, which was validated by contour method. By choosing appropriate wavelength, the penetration capability of neutron was improved. The neutron with appropriate wavelengths was then applied to investigate the through-thickness volume fraction, macroscopic and phase-specific residual stress in a 55 mm thick DSS welded plate. The results showed that a wavelength at 2.395 Å had more superiorities than the conventionally-used wavelength at 1.593 Å in the measurement of longitudinal and transverse stresses of a thick DSS plate. In general, high tensile stresses were generated in austenite while high compressive stresses were found in ferrite. For elastic mismatch residual stresses, their maximum values in austenite and minimum values in ferrite were located near the mid-thickness region. Reasons for the formation and characteristics of the phase-specific stresses were also discussed. Besides, large tensile macroscopic stresses were found near the surface whilst significant compressive stresses were found to generate in the mid-thickness of weld metal. • A wavelength-dependent neutron diffraction method for measuring stress is developed. • Altering wavelength enhances the penetrability of neutron in duplex stainless steel. • Macroscopic, phase-specific residual stresses and volume fraction are obtained. • High tensile stress is found in austenite while compressive one is found in ferrite. [ABSTRACT FROM AUTHOR]

• Fracture toughness of X80 steel is tested by nanoindentation method. • Relationship of the nanoindentation load-depth is established. • Elastic modulus is modified by introducing radial displacement correction factor γ. • Nanoindentation fracture toughness constitutive model of X80 is proposed. • The proposed model can well characterize the fracture toughness of the X80 steel. Fracture toughness of X80 steel is investigated and characterized by the nanoindentation technique and a modified constitutive model. Firstly the load–displacement of the X80 steel is tested by nanoindentation technique. Based on the load–displacement, the relationship of the nanoindentation load-depth is established. Secondly, the elastic modulus calculation equation was modified by introducing the radial displacement correction factor γ considering the pile-up phenomenon. At last, based on the strain energy density and indentation fracture energy theory, the nanoindentation fracture toughness constitutive model of X80 is proposed combined with the modified elastic modulus and the critical plastic depth. The fracture toughness calculated by the proposed method locates in the dispersion band range tested by the standard three point bending specimen, while the result calculated by the original method is far away from the dispersion band range. The comparison results illustrate that the proposed method can well characterize the fracture toughness of the X80 steel. The present work is of great significant for ensuring the long term and safety operation of the petroleum and natural gas transporting pipeline. [ABSTRACT FROM AUTHOR]

In this paper, an energy difference method is proposed to estimate biaxial stress components based on indentation technique. The indentation energy is chosen as an analytical parameter, which can be calculated directly from the load-depth curve. The presence of residual stress in a material causes the change of indentation energy. The mapping relationship between uniaxial stress and indentation energy difference was established by finite element analysis. Meanwhile, the Knoop tip was applied since the indentation response varies according to the indenter orientation. Using this feature, a biaxial stress state can be transformed into two equivalent uniaxial stress states by indentation energy conversion. Finally, the biaxial residual stress components can be solved by the energy difference functions of two orthogonal indentations. A portable indentation instrument was developed to implement this approach, which is suitable for in-site measurement. The obtained results show good agreements with the artificial stresses applied by cross-shape sample experiment. • A new methodology is proposed to estimate biaxial stress components based on indentation method. • The Knoop indenter is applied to correlate the stress direction. • A biaxial stress state can be transformed into two equivalent uniaxial stress states by indentation energy conversion. • An indentation testing instrument was developed to validate this approach. • The biaxial stress components can be solved from the load-depth curves, without the need for contact area. [ABSTRACT FROM AUTHOR]

Abstract: Bonded compliant seal is a new sealing design for planar solid oxide fuel cell. During brazing, large residual stresses are generated which have a great effect on failure of the brazing connection. Therefore, how to decrease the residual stresses is a critical issue for structure integrity. This paper presents a study on decreasing residual stresses by using short-time creep relaxation effect. A sequential-coupled calculation model is developed based on finite element method. The brazing temperature field is firstly obtained by simulating the convection and radiation heating, and then the residual stress is calculated by a thermal-elasto-plastic-creep model. The calculated results are verified by neutron diffraction measurements. During cooling, a short holding time at 600 °C is designed to relax the residual stress by creep effect. The results show that this effect has a remarkable impact on decreasing the residual stress. The stresses in cell, Ag–CuO and foil have been reduced by about 26.9%, 13.6% and 22.1%, respectively, as the holding time increases up to 40 h. When the holding time exceeds 40 h, the residual stresses remain almost unchanged. It is thus suggested that the holding time should be reasonably determined to allow sufficient stress relaxation. [Copyright &y& Elsevier]

Abstract: Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located. [Copyright &y& Elsevier]

Highlights: [•] Effect of multiple repairs on residual stress, microstructure and hardness for a clad plate has been studied. [•] A diffusion layer with martensite is generated around weld-base metal interface. [•] Along the weld–clad metal interface, short ferrite is generated in the fusion zone. [•] As the repair times increase, the content of short ferrite is increased. [•] It is proposed that the stainless steel clad plate cannot be repaired more than 2 times. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stress relaxation by cutting is studied by neutron diffraction and simulation. [•] It is correlated to the cutting length exponentially based on St. Venant’s principle. [•] The critical length to avoid relaxation is proposed as 0.3 of the initial length. [ABSTRACT FROM AUTHOR]

The localized defects, including the ruptured truss and debonding joint, have been severely threatening the structural integrity of the pyramidal lattice truss panel structure (PLTPS). In this paper, a series of analytical models, i.e., equivalent elastic modulus, plastic and creep strain rate models, were developed to study the effects of localized defects on the mechanical properties and creep performance of the PLTPS, which have been verified by the experiments and finite element (FE) simulation. Based on the experimental data, the equivalent elastic modulus model was modified when the defect fraction exceeds the threshold value. The complete stress–strain curve was plotted by the proposed analytical models. At elevated temperature, both the analytical model and finite element results indicate that the equivalent creep rate increases exponentially with the increase of the defect fraction. In addition, for the long-term service, the total equivalent strain is the superposition of the steady-state creep strain and the saltatorial strain stimulated by the inconsecutive stress once the truss or joint fails, which is more susceptible to the effective stress comparing with the servicing time. The proposed analytical model which considering the effect of localized defects of the PLTPS provides an efficient criterion to justify whether the structure with certain defects satisfies the engineering requirements. • The creep properties of PLTPS with defects were studied by analytical methods. • The analytical models have been verified by the experiments and FE simulation. • An efficient criterion for sample test is proposed. [ABSTRACT FROM AUTHOR]

The cruciform welded joint is a weak position of filter press to cause fatigue failure under cyclic conditions. In this study, cavitation jet peening (CJP) treatment is proposed to improve the fatigue life of SAF2205 cruciform welded joints. The effects of different CJP treatment positions on the residual stress, microstructure, and microhardness were studied. The results show that different CJP treatment positions have different on residual stresses and fatigue life. The order of the residual stress in fracture position from large to small is the fully treated specimen, untreated specimen, one‐sided treated specimen, and diagonal treated specimen, which is exactly opposite to the order of fatigue life from large to small. After the diagonal CJP treatment, the fatigue life is increased by up to 242.19%, and the residual stress at the weld toe is reduced by more than 80%. A strengthening layer with thicknesses of about 400 μm is formed. [ABSTRACT FROM AUTHOR]

Abstract: A 3-D sequential coupling finite element simulation is performed to investigate the temperature field and residual stress in the repair weld of a stainless steel clad plate. The effect of repair length on residual stress has been studied, aiming to provide a reference for repairing the cracked clad plate. The results show that large tensile residual stresses are generated in the repair weld and heat affected zone (HAZ), and then decrease gradually away from the weld and HAZ. The residual stresses through thickness in the clad layer are relative uniform, while they are non-uniform in the base metal. A discontinuous stress distribution is generated across the interface between weld metal and base metal. The repair length has a great effect on transverse stress. With the increase of repair length, the transverse stress is decreased. When the repair length is increased to 14cm, the peak of transverse stress has been decreased below yield strength, and the transverse stress in the weld and HAZ has also been greatly decreased. But the repair length has little effect on longitudinal stress. [Copyright &y& Elsevier]

Abstract: 316L type stainless steel is widely used in chemical industries due to its excellent resistance to corrosion. But the welding residual stresses have a great effect on stress corrosion cracking. This paper used finite element method to study the effect of heat sink on residual stress. The effects of contact length and the average heat transfer coefficient on residual stress have been investigated. It is found that the heat sink technology can decrease the residual stress greatly. Compared to the model without heat sink, 20% of the peak longitudinal stress has been reduced. The heat sink decreases the dwell time during cooling from 850 °C to 400 °C, which is helpful to decrease the risk of sensitization of 316L stainless steel. With the contact length increase, the transverse stress is decreased. Further increase of the contact length has no positive effect on reducing the longitudinal stress. With the average heat transfer coefficient increase, the transverse stress is decreased greatly while the longitudinal stress decreases slightly, and some tensile residual stresses have been changed to compressive in some zone. [Copyright &y& Elsevier]