Stress In Steel Research Articles

Altering the Residual Stress in High-Carbon Steel through Promoted Dislocation Movement and Accelerated Carbon Diffusion by Pulsed Electric Current

Altering the Residual Stress in High-Carbon Steel through Promoted Dislocation Movement and Accelerated Carbon Diffusion by Pulsed Electric Current

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

Experimental study on residual stress of fire-resistant steel welded box-sections

Residual stress is one of the important imperfections should be considered in predicting the ultimate bearing capacity of welded section columns. Extensive experimental and theoretical study on the residual stress of conventional structural steel (CSS) welded sections have been carried out. In order to provide higher resistance under elevated temperature, fire-resistant steel (FRS) is developed. In view of the different mechanical properties at elevated temperatures and post-fire conditions, the residual stresses may be different for FRS welded box-sections. In this study, six welded box-section specimens are fabricated from 10 mm Q345FR and Q460FR FRS plates with varying width-thickness ratios. The sectioning method is adopted to measure the residual stresses. The magnitudes and distributions of residual stresses of FRS are obtained. A simplified residual stress model for welded box-section in Q345FR and Q460FR steel is proposed. The effects of strength and width to thickness ratio on the residual stresses are discussed. In addition, the residual stresses between FRS and CSS welded box-sections are compared and the reasons for the differences are discussed. The test results show that residual stress to yield strength ratios of FRS welded box-sections are lower than those of CSS welded box-sections.

Estimation of contact stresses in EN31 rolling contact bearings for screw compressor using Gauss quadrature & statistical analysis

ABSTRACT The aim of this work is to estimate Hertzian contact stresses in EN31 alloy steel and to obtain the line of best fit using statistical analysis. In refrigerant screw compressors, EN31 is used as a material of construction for cylindrical roller bearings. The Hertzian contact with friction between the outer surface of the inner race of the rolling contact bearing & the outer surface of the cylindrical roller is simulated using pin-on-disk tribometer. Measurement of friction coefficient was carried out by sliding different cylinders of hardened EN31 material against the hardened EN31 disk of the pin-on-disk tribometer. A total 16 tests, each of 1 minute time duration, are performed for the estimation of friction coefficient with varying loads from 20 N to 100 N and speeds in the range of 50 RPM to 200 RPM. The magnitude of Von Mises stress induced in the inner race of the bearing is estimated using Gauss quadrature method with the help of a self-developed MS Excel program. Statistical analysis showed that the stress magnitude increases with the increase in the load & decreases with an increase in speed.

Calculation method for the interface contact stress of steel tube-to-sleeve grouted connections subjected to bending moments

Steel tube-to-sleeve grouted connections (GCs) have been widely used for offshore wind turbine structures due to its excellent structural behaviour. Interfacial contact stress is a crucial indicator for evaluating the ultimate stress state of the GCs. However, the information is still limited regarding the calculation formulas for contact stresses considering the effects of friction coefficient, elastic modulus of grout, and cross-sectional dimensions of steel tube and sleeve. An extensive FE analysis on a total of twenty full-scale grouted connection specimens under bending moments was performed in this paper. Based on the parametric analysis results, the contact stress distribution pattern was obtained and the design formulas were derived for calculating the contact stress. In these formulas, the cross-sectional influence factor (CIF) is proposed to evaluate the effect of cross-sectional dimensions of steel tube and sleeve. The proposed formulas were featured with a reasonable accuracy and could be adopted in the flexural design of GCs.

Mechanical Response of a Buried Pipeline to Permafrost Thawing Based on Sequential Coupling Method

Thawing permafrost has affected the structural integrity of buried warm pipelines in cold regions and poses an ongoing threat in the context of climate change. Therefore, characterizing variation in the engineering properties of pipeline foundation permafrost and its effect on the mechanical behavior of pipeline is important. In this paper, the ground temperature distributions around a buried warm pipeline and mechanical response of the pipeline to differential thaw settlement of foundation permafrost are investigated using thermal–mechanical sequential coupling simulation, based on the observational data collected from a selected monitoring site along the China-Russia crude oil pipelines in northeastern China. The results indicate that the thaw-induced settlement of pipeline foundation permafrost develops quickly with the formation and expansion of the thaw bulb in the first 10 years, and then increases slowly when the thaw bulb extends to the weathered granite. Differential thaw settlement will cause a significant change in the deformation and stress of the pipeline near the interface of strong and weak thaw settlement zones. When the length ratio of strong and weak thaw settlement zones is 1, the maximum stress of the pipeline with a thickness of 16 mm is approximately 45% of the allowable stress of X65 steel, and the pipeline remains safe for 30 years. However, the potential failure of the pipeline should be considered due to the continued ground thawing and warming and pipe material aging. Forthcoming research on this topic is needed to evaluate more carefully the structural integrity of buried pipelines in cold regions.

Mechanical Characteristics of an Open-Buried Double-Arch Tunnel during Construction

The open excavation and concealed construction method is widely adopted for the construction of bias double-arch tunnels. However, the mechanical behavior of the tunnel during the whole construction period by using the open excavation and concealed construction method is not well understood, and the basis for construction organization and optimization is lacking. Based on an open-buried double-arch tunnel on Xiajuan Road, Changsha City, China, on-site monitoring was carried out in terms of the deformation of the steel arch in the primary lining, the stress of reinforcement in the secondary lining, and the deformation of the surrounding rock during the construction process. The correlation between the vault settlement rate and the steel arch strain was analyzed. The results show that the maximum vault settlement and settling rate of the left and right caverns occur at different locations due to different supporting conditions. The peripheral displacement experiences a process of convergence inward and extension outward. The compressive steel stress in the secondary lining of the right cavern is greater than that in the left cavern, except for the points at the arch waist. The backfill above the left cavern reduces the loading on the lining of the right cavern, but it increases the loading on the left cavern. The bias effect of the open-buried double-arch tunnel is well controlled and balanced when the open excavation and concealed construction method is adopted.

A comprehensive and reliable investigation of axial capacity of Sy-CFST columns using machine learning-based models

The literature on predicting the load-carrying capacity of symmetrical concrete-filled steel tube (Sy-CFST) columns using different machine learning methods has mainly focused on a single method or cross-section type in each study. Sy-CFST column has been widely used in the engineering field because of its several benefits such asincreased strength due to confinement generation, better ductility due to high steel ratio, and less construction cost and time as compared to the encased reinforced concrete. This study attempted to evaluate the load-carrying capacity of these columns with circular and square cross-sections based on the simultaneous use of the two gene expression programming (GEP) and artificial neural network (ANN) approaches. The database required for extracting GEP and ANN models was based on the empirical results of 993 specimens. Variables considered here include the compressive strength of concrete (fc), yield stress of steel (fy), cross-sectional areas of concrete (Ac) and steel (As), diameter to thickness ratio of the steel tube (D/torB/t), and slenderness ratio of Sy-CFST columns (λ). Moreover, parametric and sensitivity analyses were conducted separately to assess the contribution of each effective parameter to the axial capacity. To validate the efficiency of the models, prediction values of GEP and ANN were compared with the predictions of existing codes (6 codes) and different studies (8 studies). The results indicated that the developed models provide accurate predictions for the load-carrying capacity of Sy-CFST columns. In addition, the variation of parameters in the proposed models is consistent with experimental trends observed in other studies, which confirms the consistency of the proposed numerical models with physical observations.

Experimental and numerical analyses of residual stress redistributions in large steel dies: Influence of tempering cycles and rough milling

The aim of the present research was to study the residual stress variations induced by heat treatment and rough milling operations of large forged steel blocks. The heat treatment process includes quenching and tempering operations. An efficient strategy based on a size sensitivity analysis (SSA) was proposed to reach the actual values of residual stresses in large-size steel blocks by using small-size workpieces in laboratory scale without damaging the blocks. The residual stresses were measured and compared after the first and second tempering and the rough milling. A 3D finite element (FE) model was developed to predict superficial residual stresses and was then calibrated experimentally. The results showed that the residual stresses after the first and second tempering were highly compressive on and near the surface. In addition, the resultants of the residual stresses after double tempering processes were almost equal. Therefore, the second tempering could be omitted from the manufacturing process. It was also found that both surface and sub-surface hoop and radial residual stresses were highly tensile after the rough milling. Finally, the 3D FE model can be used as a predictive tool to predict residual stresses for rough milling to avoid conducting expensive, time-consuming experimentations and measurements.

Structure Integrity Analysis Using Fluid–Structure Interaction at Hydropower Bottom Outlet Discharge

Dam reliability analysis is performed to determine the structural integrity of dams and, hence, to prevent dam failure. The Chenderoh Dam structure is divided into five parts: the left bank, right bank, spillway, intake section, and bottom outlet, with each element performing standalone functions to maintain the overall Dam’s continuous operation. This study presents a numerical reliability analysis of water dam reservoir banks using fluid–structure interaction (FSI) simulation of the bottom outlet structures operated at different discharge conditions. Three-dimensional computer-aided drawings were used to view the overall Chenderoh Dam. Next, a two-way fluid–structure interaction (FSI) model was developed to explore the influence of fluid flow and structural deformation on dam systems. The FSI modeling consists of Ansys Fluent and Ansys Structural modules to consider the boundary conditions separately. The reliability and performance of the reservoir bottom outlet structure was effectively simulated and recognised using FSI. The maximum stress on the bottom outlet section is 18.4 MPa, which is lower than the yield stress of mild steel of 370 MPa. Therefore, there will be no structural failure being observed on the bottom outlet section when the butterfly valve is fully closed. With a few exceptions, the FSI models projected that bottom outlet structures would be able to run under specified conditions without structural collapse or requiring interventions due to having lower stress than the material’s yield strength.

Influence of the WAAM process and design aspects on residual stresses in high-strength structural steels

Wire arc additive manufacturing (WAAM) enables the efficient production of weight-optimized modern engineering structures. Further increases in efficiency can be achieved by using high-strength structural steels. Commercial welding consumables for WAAM are already available on the market. Lack of knowledge and guidelines regarding welding residual stress and component safety during production and operation leads to severely limited use for industry applications. The sensitive microstructure of high-strength steels carries a high risk of cold cracking; therefore, residual stresses play a crucial role. For this reason, the influences of the material, the WAAM process, and the design on the formation of residual stresses and the risk of cold cracking are being investigated. The material used has a yield strength of over 800 MPa. This strength is adjusted via solid solution strengthening and a martensitic phase transformation. The volume expansion associated with martensite formation has a significant influence on the residual stresses. The focus of the present investigation is on the additive welding parameters and component design on their influence on hardness and residual stresses, which are analyzed by means of X-ray diffraction (XRD). Reference specimens (hollow cuboids) are welded fully automated with a systematic variation of heat control and design. Welding parameters and AM geometry are correlated with the resulting microstructure, hardness, and residual stress state. Increased heat input leads to lower tensile residual stresses which causes unfavorable microstructure and mechanical properties. The component design affects heat dissipation conditions and the intensity of restraint during welding and has a significant influence on the residual stress.

Rectangular filled composite members made from high strength materials: Behavior and design of columns and beams

The AISC Specification limits the use of steel and concrete materials in filled composite members to concrete strength (fc′) less than or equal to 69 MPa and steel yield strength (Fy) less than or equal to 517 MPa. This paper presents the results of comprehensive analytical investigations conducted using benchmarked numerical models to evaluate the behavior of rectangular filled composite members made from one or both materials exceeding the AISC Specification strength limits. The numerical models are developed and analyzed using the displacement-based formulation of the fiber-based finite element in OpenSees. Prior research has developed effective (phenomenological) stress–strain curves for steel and concrete materials that implicitly account for the effects of steel yielding, local buckling, concrete cracking, crushing and confinement, and the interaction between the two materials in the composite cross-section. This paper first benchmarks the modeling approach and then uses the benchmarked model to conduct analytical parametric studies covering a wide range of parameters, including: member slenderness, section slenderness, section aspect ratio, steel yield stress and concrete compressive strength. The results from the parametric studies are used to evaluate behavior and develop new design equations based on nominal stress distributions over the composite section. The nominal steel stress in compression (Fcr) is expressed as a continuous function of the section slenderness and yield strength, thus eliminating the current AISC Specification’s need for section classification (compact, noncompact and slender). The new design equations are recommended for relaxing the material strength limitations in the next version of the AISC Specification.

Effect of Tempering Temperature on the Microstructure and Mechanical Properties of 42CrMo4 Steel

This paper investigated the effects of tempering temperature (200°C, 400°C, 600°C or 800°C) on microstructures, mechanical properties, and residual stress of 42CrMo4 steel. Microstructures were characterized by OM and SEM techniques. The results show that the change in tempering temperature leads to a change in austenite, resulting in a change in hardness and toughness. The specimen showed the best combination of mechanical properties under the heat treatment condition of a tempering temperature of 600°C. The hardness, yield strength, tensile strength, area shrinkage, and elongation reached 312.74HV, 759MPa, 898MPa, 60%, and 18%, respectively. The experimental results provide a reference for the selection of the heat treatment process of 42CrMo4 steel.

Design of calculation model of residual stress in austenitic stainless steel during plastic deformation

In the process of processing, the residual stress in the deformed component will play a crucial role in the assembly and future use. This paper analyzes the deformation behavior of martensite phase transition induced by deformation through unidirectional stretching. The martensite phase variables and residual stress distributions after stretching were measured. The calculation model of residual stress distribution is established considering the phase change factors. It provides a theoretical basis for the calculation of phase transition behavior and residual stress distribution in the complex deformation process. A dynamic model based on stress and strain was established under different conditions, and the realization of martensite transformation was added to the finite element software with the help of secondary development subroutine. By comparing with the test data, the results show that the distribution pattern of residual stress can better reflect the residual stress after deformation under the consideration of the phase transformation of martensite.

Microstructure, residual stress, and nanoindentation properties of GCr15-bearing steel by cryogenic treatment and laser-peening composite strengthening

Microstructure, residual stress, and nanoindentation properties of GCr15-bearing steel by cryogenic treatment and laser-peening composite strengthening

Reduction of Residual Stresses in Cold Drawn Pearlitic Steel by a Soft Secondary Wire Diameter Reduction

In this paper, the effects of the skin pass technique on the residual stress and plastic strain fields generated in cold drawn pearlitic steel wires are analyzed. The aim is to find out the optimal conditions to be used in the design of a manufacturing process for obtaining more reliable structural components in terms of the main cause of failure: the hydrogen embrittlement (HE). To achieve this goal, diverse numerical simulations were performed by using finite elements (FE) and considering, on one hand, the first step of a real cold drawing chain, using (i) a conventional drawing die and (ii) modified drawing dies with different soft diameter reductions, and, on the other hand, numerical simulations by FE of the hydrogen diffusion assisted by stress and strain states to estimate the hydrogen distributions. Obtained results revealed the secondary reduction degree as a key parameter in the die design for reducing the drawing-induced residual stress. According to the results, low values of the reduction ratio cause radial distributions of residual stress with significant reductions at both the wire core and at the wire surface. In addition, the hydrogen accumulation at the prospective damage zone (near the wire surface) given by FE simulations is lower in the wires drawn with modified drawing dies including a skin pass zone.

Peak Cyclic Stress and Ratcheting Response of a Low Alloy Steel for Reactor Pressure Vessel Applications

Peak Cyclic Stress and Ratcheting Response of a Low Alloy Steel for Reactor Pressure Vessel Applications

On the possibility of fabricating fully austenitic sub-micron grained AISI 304 stainless steel via equal channel angular pressing

The paper concerns possibility of increasing yield and ultimate stress of austenitic stainless steels by equal channel angular pressing (ECAP). To this end, an AISI 304 stainless steel subjected to eight passes of ECAP in a 105◦ die at 350◦ C. The evolution of microstructure as a function of induced plastic strain (number of passes) was studied in different length scales using light and scanning transmission electron microscope (STEM). An insight into fine details of dislocation structure was possible via X-ray diffraction profile analysis. Changes in the structure of processed samples were correlated with their mechanical properties as determined by tension tests and microhardness measurements. Light microscopy revealed a shear banded microstructure. STEM observations demonstrated co-existence of three types of grain structure: (a) short elongated grains/subgrains of 71 nm average width formed within the shear band regions, (b) a mixture of coarse (200–350 nm in size) and nanocrystalline (15– 70 nm) equiaxed grains developed outside the shear bands, and (c) nano-twin lamellae of 3–20 nm width inside nanocrystalline grains. XRD peak profile analysis using modified Warren–Averbach approach yielded dislocation density as ρ = 4.71 × 1015 m−2 after eight passes. ECAP-induced changes in the microstructure led to a remarkable increase in yield strength of the alloy (YS=1498 MPa, about 3.5 times the initial amount). At the same time, a moderate ductility of εf = 12% was maintained, primarily due to a large post-necking elongation. This behavior was explained by an increase in the strain rate sensitivity of ECAP-ed material in combination with the contribution from transformation induced plasticity, TRIP effect, caused by formation of ∼ 22 vol% martensite during room temperature straining.

Electrochemical Behavior of Reinforced Concrete Beams with Different Flexural Tensile Stresses in the Steel Reinforcement

In this work, the electrochemical and structural behavior of reinforced concrete beams subjected to flexure is studied. Eight beams with and without corrosion were considered. The study variable was the tensile stress in the longitudinal steel reinforcement. Stresses of 40% and 80% of the yielding stress of steel were considered. The beams were subjected to sustained loads using a post-tensioning system. Corrosion in the steel reinforcement was induced by chloride contamination of fresh concrete and wet and dry cycles. The corrosion rate of the steel, as well as the resistivity and concentration of chlorides of the concrete, were measured. The beams were tested two times using a four-point loading system. The first one before that corrosion was induced; a load associated with the target tensile stress in the steel reinforcement was applied to determine the initial structural parameters of the beams: crack pattern, crack resistance, and initial and postcrack stiffness. The second time after the corrosion was induced; incremental loads were applied until the failure of beams to determine the change in yielding and maximum strength, as well as the postyielding stiffness of the beams. It was found that the electrochemical behavior of the beams with corrosion was similar regardless of the tensile stress in the steel considered (40% or 80%). The measured electrochemical parameters indicated a high level of corrosion in accordance with Mexican standards; however, from the structural point of view, the strength and stiffness were not significantly affected by the corrosion status. Beams with electrochemical parameters associated with a higher level of corrosion are needed to study the initial degradation of the structural parameters, for example, strength degradation.

Automated Calculation of Strain Hardening Parameters from Tensile Stress vs. Strain Data for Low Carbon Steel Exhibiting Yield Point Elongation

Automated Calculation of Strain Hardening Parameters from Tensile Stress vs. Strain Data for Low Carbon Steel Exhibiting Yield Point Elongation