Stress In Steel Research Articles

Flexural behavior of high-strength square concrete-filled steel tube members subjected to cyclic loadings

This paper investigated the flexural behavior of high-strength concrete-filled steel tube (HSCFST) members subjected to cyclic loadings. Nine cyclic tests of square HSCFST members were conducted. The investigated parameters were the height of steel tube, thickness of steel tube wall, yield stress of steel, and compressive cylinder strength of concrete. A finite element (FE) model was developed and validated. Results from the experimental tests and FE analyses indicated that: (i) the failure modes of HSCFST members were characterized by local buckling and fracture of the steel tube, both occurred earlier with increasing height or yield stress of steel, or with decreasing thickness of steel tube wall, but were delayed when higher strength concrete was used; (ii) using high-strength steel significantly improved the flexural strength, had no obvious influence on the flexural stiffness, but significantly reduced the ductility; (iii) using high-strength concrete improved the flexural strength, stiffness, and ductility; and (iv) the limits by AISC 341-16 on the slenderness coefficient is conservative for HSCFST members subjected to cyclic flexural loadings.

Experimental investigation on creep behaviors and life prediction across phase-transformation of thermal aged 16MND5 steel

Reactor pressure vessel (RPV) is one of the key equipment for nuclear power plant, and long-term exposure to high temperature is an important factor causing its performance deterioration. Under core meltdown conditions, RPV steel experiences high temperature creep due to the In-Vessel Retention (IVR) mitigation measures. This paper aims to investigate high-temperature mechanical properties, especially for the creep behaviors of 16MND5 steel after thermal aging at 650 °C for 2000 h. The results showed that the yield stress and ultimate tensile strength of the 16MND5 steel are decreased, and the creep rupture time is rapidly shortened after thermal aging. The microstructure was analyzed by scanning and transmission electron microscopy (SEM, TEM). 16MND5 steel showed a typical bainitic phase before thermal aging. After 2000 h of thermal aging, the micro-grains were coarsened, and finally changed into a ferritic microstructure. Based on Larson-Miller (LM), Orr-Sherby-Dorn (OSD) parameters methods and Kachanov-Rabotnov (K–R) model to predict uniaxial creep life after thermal aging, the prediction results are satisfactory, and all within the double tolerance band. This work reveals the creep damage mechanism of 16MND5 steel after thermal aging, and provides basic data for the implementation of IVR strategy in nuclear power plants after long-term service.

Study of magnetoelastic demagnetization of locally magnetized steel

To improve the accuracy of determining mechanical stresses in steel by the method of magnetoelastic demagnetization (magnetoelastic memory), the magnetoelastic sensitivity of the material to elastic stresses is additionally measured by applying or removing an additional load of a known value. We present the results of studying the magnetoelastic demagnetization of locally magnetized steel by varying stresses of the uniaxial tension or compression against a background of the base load. The magnetoelastic sensitivity of the steel in a loaded state to variable stresses has been assessed. It is shown that the determination of the magnetoelastic sensitivity of the steel to variable loads makes it possible to improve the accuracy of estimating base stresses in the steel structure using magnetoelastic methods. It is revealed that a decrease in the strength of the magnetic scattering field of the local residual magnetization (LRM) of the steel after variable loading (or unloading) exponentially depends on the magnitude of the base stresses. The possibility of controlling the uniaxial mechanical stresses in steel structures in the magnetoelastic memory mode which is based on the dependence of the strength of magnetic scattering field of the local residual magnetization of the steel on the uniaxial stresses is shown. A method for monitoring uniaxial stresses in the elements of steel structures by the method of magnetoelastic memory is proposed using the measured magnetoelastic sensitivity of the material. The results obtained can be used in the development of a method for monitoring the stress-strain state of steel structures during operation under the simultaneous effect of static and dynamic loads.

Development of Rhombus Hanging Basket Walking Track Robot for Cantilever Casting Construction in Bridges

For enhancing the efficiency of cantilever casting construction in a bridge, a novel rhombus traveling track for a hanging basket was developed and optimized. The business-oriented software called MIDAS was applied to analyze the mechanical properties of the hanging basket with a full load and a control load. The strength and distortion of the walking mechanism are within the specified range when the maximum beam unit internal force is 149.69 MPa, which is less than the allowable stress of steel of 175 Mpa, and the anti-overturning safety factor of the hanging basket is 2.5, which meets the requirements. Through the comparative analysis of the key components and the finite element calculation, it was found that there is about a 30% redundancy in the structure performance. Therefore, further optimization of each structure was carried out, and the front elevation of the main truss of 20° was achieved. It obtained the best performance in all aspects.

Roles of microstructures in high-cycle fatigue behaviors of 42CrMo high-strength steel under near-yield mean stress

In this study, high-cycle S-N characteristics and fatigue cracking behaviors under near-yield mean stress of 42CrMo steel with two different fine/coarse-grain tempered sorbite/bainite microstructures (FGM/CGM) were investigated. The results show that fatigue strength is greater for FGM than for CGM as expected, but fatigue crack growth (FCG) threshold is higher for the latter. Compared to FGM with a single crack source, CGM has multiple fatigue sources together with higher-degree ratchetting-fatigue damage, i.e., plastic-strain, dislocation cells and sub-grains, thus accelerating fatigue crack initiation. In the near-threshold regime, roughness-induced crack closure in coarse-microstructures of CGM leads to FCG retardation behavior, which increases FCG threshold. In the Paris regime, CGM presents a similar FCG rate to FGM. Microstructure barriers (i.e., crystal interfaces, carbides and interfaces with different orientations), secondary cracks, crack-path fluctuations, ratchetting and plastic strain jointly result in severer crack-tip stress shielding effects in CGM than in FGM. However, fatigue crack tends to propagate through the high Schmid factor region with {110}<111> slip system with lower slip resistance in FGM but not in CGM, which facilitates fatigue cracking of the former. Under the combined effects of the above factors, similar FCG rates are thus exhibited in both steels with different tensile strengths.

Effect of Local Combined Thermal Action on Value and Distribution of Residual Stresses in Steel 20 Plate

Effect of Local Combined Thermal Action on Value and Distribution of Residual Stresses in Steel 20 Plate

Effects of thermo-chemical treatment and grinding process of external cylindrical surfaces on residual stresses in 13CrMo4-5 steel

This paper presents a study aimed at determining the effect of the carburizing treatment process and the subsequent grinding process on the residual stresses occurring in ring-shaped specimens made of 13CrMo4-5 steel.During the tests, vacuum carburizing was used, achieving an effective case depth ECD = 0.5 mm. Subsequently, the cylindrical outer surfaces of the samples were ground by conventional plunge grinding and with innovative kinematics using a test stand based on a conventional flat-surface grinding machine. As part of the study, microhardness and residual stresses were measured before and after grinding. Measurements were carried out to a depth of 1 mm. The main component of the stand is an original special device that allows the cylindrical specimen to be clamped. Then the angle between its axis of rotation and the axis of rotation of the grinding wheel is set with respect to the plane of the grinding machine’s magnetic table. In the described tests, the axis of rotation of the cylindrical specimen was deviated from its original position by 15 and set at an angle of 75 to the axis of rotation of the grinding wheel. The specimens were ground with a grinding wheel of noble electro-corundum marked 38A60K8V. In both kinematic cases of the grinding process, a machining allowance of 0.01 mm was removed.Grinding using innovative kinematics did not cause any significant changes in the microhardness distribution, either for vacuum or conventional carburizing. In addition, residual stress measurements using the Dawidenkov-Sachs method showed that innovative grinding enables a more favourable distribution than those obtained after conventional plunge grinding.Further research will focus on, among others, selecting the angular settings of the workpiece axes relative to the grinding wheel axes depending on their dimensions. Grinding guidelines should include coverage ratio, infeed value, grinding time, and peripheral speeds. In addition, the plan for future research includes measuring the components of the grinding force and the geometric structure of the surface.Grinding process is a crucial stage of steel treatment in almost every industrial branch. In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers’ health.The proposed test stand, together with the authors’ device, makes it possible to conduct machining of the external surfaces of cylindrical workpieces on a flat surface grinder. In this case, the innovation of the grinding process consists of the non-parallel alignment of the cylindrical rotational axis of the specimen and the rotational axis of the grinding wheel with respect to the plane of the magnetic grinding table.

High-strength rectangular concrete-filled steel tube long columns: Parametric studies and design

High-strength steel and concrete materials (i.e., steel with yield stress Fy > 525 MPa and concrete with compressive strength f'c > 70 MPa) have been applied in various types of structures because they can increase the resistance and space efficiency of the structure. However, the AISC Specification (AISC 360-16) does not permit the use of high-strength materials in concrete-filled steel tube (CFT) members due to a lack of adequate research. This paper aims at investigating the behavior of high-strength CFT long columns and evaluating the applicability of current design equations for high-strength rectangular CFT long columns. Firstly, an experimental database including 74 tests of high-strength rectangular CFT long columns was compiled and gaps in the database were identified. Then, finite element (FE) models were developed and benchmarked for parametric studies. The effects of width-to-thickness ratio of the steel tube, yield stress of steel, compressive strength of concrete, and length-to-depth ratio of the member were investigated. Finally, new design equations for high-strength rectangular CFT long columns were proposed based on the modified slenderness reduction factor in AISC 360-16.

Refined simulation of bond-slip behavior between ribbed steel and concrete: Effects of initial stress and temperature

The bond performance between steel and concrete exposed to fire is influenced by many factors, including the presence of an initial load before the temperature increase. To investigate such effect, a 3-D refined simulation model is presented accounting for the heterogeneity of concrete at the mesoscopic level and the external geometry of ribbed steel bars. The rationality and validity of the refined simulation model and of the multi-step analysis were verified by comparison with existing experimental data. Subsequently, the effects of aggregate gradation and distribution, initial loading level and temperature on the bond behavior were analyzed. The load transfer mechanism at the steel–concrete interface as a function of temperature under different loading levels is captured and discussed. It is found that the influence of aggregate grading and distribution on the bond-slip curve can be ignored under the aggregate volume fraction set in this work. Additionally, results show that the damage initially concentrates at the rib tip of the deformed steel bars, with an increase across the concrete section as the slip increases, as it could be expected. However, the bond stress and both stress and strain of steel at the same position decrease as the temperature increases. Finally and most importantly, it is found that the heating and loading sequence induce a different damage evolution inside the specimen, with a significant effect on the bond stiffness, the plateau portion of the bond stress-slip curve and the bond strength associated to a given critical temperature.

Experimental Investigation of Monotonic and Cyclic Behaviour of High-Performance Steels

As a new trend in modern structural design, the high-performance steels are increasingly used in steel structures, due to their superior mechanical properties, which could have decisive impact on the resistance and deformation capacity of structural components. High-performance steels include stainless and high-strength steels. The higher proof stress of the high-strength steels allows using thinner sections and material economy for those structural elements that do not experience stability problems. Austenitic stainless steel shows a series of advantages, including low maintenance costs and an excellent toughness at low temperatures. But the main characteristic which matters especially in seismic design, is the higher ductility, larger strain hardening and elongation at fracture in comparison with carbon steels. In this paper, the analysis of the behaviour of 1.4404 austenitic stainless steel and of S690 high-strength steel, in comparison with a reference S235 mild carbon steel is presented. This paper presents the assessment of the monotonic and cyclic performance of these steel grades, as well as the failure pattern, in order to assess the potential use in structural applications.

Stress and shear of steel reinforced floors with prefabricated units and steel beams

Steel-reinforced concrete floors with prefabricated reinforced concrete slabs are industrial quickly erectable structures. The use of such structures makes it possible to reduce construction time, save metal, obtain efficient structures without beam projecting up to 20 m for loads produced by buildings and car parks. Codes and foreign norms do not include prefabricated reinforced concrete floor slabs in the operation of combined structures, as designers try to avoid complex connections (welding, bolts) during construction. Of obvious interest is the inclusion of precast slabs in the operation of combined steel and reinforced concrete beam as well as grouted joints between steel and slabs in the absence of additional anchors and connections.Experimental results of structural models and 6×10 m floors with precast slabs are considered to identify the concrete shear. The effective shear deformation up to 0.5 mm is detected even without additional anchors. Simplest anchors significantly increase the joint operation of cast concrete and steel profile. The operation mechanism is determined for steel-concrete and steelconcrete-anchor contact zones, and respective diagrams are plotted for numerical calculations.Floor testing shows that the use of the simplest joining, cast reinforced concrete combining steel and precast elements involves precast slabs at a distance from the beam axis of at least two thicknesses of the floor for two different ways of the beam support.Numerical modelling, including the contact zone operation, shows good agreement with the experimental data. It is recommended to clarify the width of compressed concrete flange in normative documents for the structural analysis.

Deduction of the bond law from test on short RC tie in service conditions

AbstractBond between ordinary steel bars and concrete plays a fundamental role in the behavior of the reinforced concrete. It is associated to the slip between steel and surrounding concrete and determines the variation in the steel and concrete stresses of cracked RC members. The need to formulate simple constitutive bond laws has led the international standards, such as fib Model Code 2010, to adopt an average bond stress versus slip relationship obtained from an extensive experimental campaign based on pull‐out tests. However, in pull‐out tests bond is substantially influenced by the state of stress, deformation and cracking of the concrete. Moreover, in‐service conditions of RC members, in order to study the cracking behavior or the tension stiffening, an ascending distribution of the bond stress is usually considered as it corresponds to an ascending distribution of the slip from the zero slip section to the cracked section and in the literature the bond law is applied as it is. In particular, at the cracked section, the bond stress is maximum. But, this distribution of the bond stress is not confirmed by the experimental results available in the literature concerning the behavior of an RC tie with a length equal to the crack spacing, where close to the cracked sections a descending distribution of the bond stress is observed while the distribution of the slip remains ascending, with null bond stress at the cracked section. The modeling proposed here does not claim to be exhaustive due to the limited albeit accurate experimental data. However, it does indicate the opportunity to abandon bond laws based on experimental works that do not represent the real situation or are far from it.

Effect of Shapes on Concrete Filled Steel Tubes under Static Axial Load

In this study, the mechanical properties of different CFST column shapes, including circular, rectangular, square, square with rounded corners, and triangular, are all analyzed and compared using the ANSYS R2 2021 software. Total deformation, equivalent stress in concrete and steel, equivalent elastic strain in concrete and steel, and mechanical characteristics of the various CFST column shapes are also compared. axial load as well as the highest load that CFST columns can support. Comparing the circular model to other models, it was discovered that it is more resilient to stress and strain and deforms less.13.648% total deformation and decreases in stress and strain of 41.66%, 25.93%, 42.06%, and 24.99% for concrete and steel, respectively. Key words: steel tubes with concrete filling, deformation, maximum load, stress-strain, and ANSYS software.

Analysis of hydrogen-induced delayed cracking and hydrogen trapping behavior in plastically deformed quenching and partitioning steel

Plastic deformation is an important factor affecting the critical condition of hydrogen-induced delayed cracking (HIDC) of quenching and partitioning (Q&P) steels. The study established a clear relationship between pre-strain, threshold stress, and critical hydrogen concentration of QP1180 steel. Furthermore, the reversible and irreversible hydrogen trap densities were determined, and the distribution characteristics of hydrogen were studied using Hydrogen Microprinting (HMT) and Scanning Kelvin Probe Force Microscopy (SKPFM) tests. The results provide valuable insights into the behavior of Q&P steels under hydrogen exposure, which can facilitate the development of safe and reliable components in various industrial applications.

Physical metallurgy guided machine learning to predict hot deformation mechanism of stainless steel

This study proposes a novel approach to address the limitations of traditional experimental and mathematical statistical methods in predicting the deformation mechanism of materials. Specifically, a physical metallurgy-guided machine learning method is proposed to achieve fast and accurate prediction of the thermal deformation mechanisms of antibacterial stainless steels with varying Cu contents. First, the Arrhenius and the dynamic recrystallization model were developed utilizing experimental data for the preliminary prediction of the effect of Cu content on the thermal deformation behavior of antibacterial stainless steel. Then, the calculated intermediate parameters were incorporated into the original data set as additional input features to construct a physical metallurgy (PM) guided least squares support vector machine (LSSVM) prediction model, and the optimization of the prediction model is performed through utilization of a particle swarm optimization (PSO) algorithm. The results indicate that the addition of Cu content influences the rheological stress of antibacterial stainless steel at low temperatures and high strain rates. Furthermore, the increase of Cu content reduces the thermal deformation activation energy, inhibiting the dynamic recrystallization of antibacterial stainless steel, while an increase in deformation temperature or a decrease in strain rate promotes recrystallization. The proposed PM-PSO-LSSVM model is in good agreement with experiments, providing theoretical guidance for optimizing the composition and process parameters of antibacterial stainless steel.

Effect of Alternated Multiaxial Stress State on Fatigue Strength and Relaxation of Residual Stress in Welded S355 Steel with Nonlinear and Combined Hardening

This work aims to analyse the effect of the alternated multiaxial stress state on the relaxation mechanisms of residual stresses and the integrity of welded S355 steel, presenting a nonlinear and combined hardening behaviour. The first part of this work proposes a model to predict the residual stresses introduced by the thermal effect of the welding process. The stresses resulting from the thermal cycle were integrated into a second model in which the material was subjected to a cyclic load to analyse the relaxation process. To ensure a good accuracy of the relaxation results, the kinematic and isotropic hardening were combined in a nonlinear model. In the last part of this paper, a multiaxial fatigue strength analysis was carried out, taking into account the effect of residual stresses and the relaxation process. The results show a considerable relaxation of the residual stresses if they are subjected to low load levels applied under specific conditions. The relaxed residual stresses can have a considerable effect on fatigue strength. Also, the importance of the consideration of the relaxation process on the accuracy of the fatigue strength results is illustrated.

Surrounding rock pressure calculation based on time functions and stress release rate determination of deep soft rock tunnel: taking Zhonghe Tunnel as an example

On the basis of the Zhonghe Tunnel project of the An-Lan Expressway, the objective of this study was to determine the appropriate method of calculating the steel arch load and stress release rate during numerical simulation. First of all, based on the monitoring results of six similar tunnel sections where the surrounding rock exerts pressure on the steel arch, using time functions, the rock pressure time history curve could be fitted, two formulas for calculating stable rock pressure in deep tunnels were compared, and the calculation model suitable for the Zhonghe Tunnel project was constructed. Then, a simulation of the Zhonghe Tunnel was performed using Flac3D, and stress release was simulated using the Mana method. By comparing the surrounding rock characteristic curves and the initial support characteristic curves under different stress release rates, the impact pattern of the stress release rate on the support load was summarized, and an appropriate excavation stress release rate was determined based on the stable rock pressure value calculation. It was found that the Zhonghe Tunnel rock pressure calculation model could better depict the change in rock pressure over time based on the empirical formula and Weibull time function. A prediction of the steel arch load of the Zhonghe Tunnel could be made using this method, and the stress release rate of the numerically simulated rock excavation was determined to be 0.5. This study thus provides a basis for the future internal force analysis and support parameter design of support systems.

Relationship between microstructure, and residual strain and stress in stainless steels in-situ alloyed by double-wire arc additive manufacturing (D-WAAM) process

In the field of welding, assembly of thick parts requires the base metal to be chamfered, followed by multipass welding. The process generates thermal, mechanical, and metallurgical phenomena resulting in the formation of residual strains and stresses. Strains must be limited, as they can cause misalignments during welding and leads to geometrical defects. Residual stresses are especially problematic in structural assemblies, as they add to the external stresses applied to the part during service, often reducing its in-service lifetime and increasing the risk of failure.The objective of this study is to use two stainless steel filler metals with different coefficients of thermal expansion (austenitic 304 L and ferritic 430) to reduce residual stresses and strains in the context of deposits produced by the Double-Wire Arc Additive Manufacturing process on 304 L baseplates. To achieve such a goal, the two filler are mixed in various proportions. After deposition and cooling, residual stresses are determined using neutron diffraction and contour method, strains are studied with profilometry. Microstructure is analyzed via EBSD, free dilatometry tests and XRD.We were able to reduce strains and stresses with a three-phase microstructure (austenite, ferrite, and martensite). The part that offers the best compromise (50% 430 - 50% 304 L filler on 304 L baseplate) exhibits a 67% reduction in strain, and stresses are reduced down to 40%, as compared to the 100% 304 L filler on 304 L baseplate part. The results obtained from neutron diffraction and contour method exhibit a close agreement, with a discrepancy standing below 100 MPa.

A novel smart steel strand based on optical-electrical co-sensing for full-process and full-scale monitoring of prestressing concrete structures

ABSTRACT As the main load bearing component, the steel strand has a significant impact on the safety of civil infrastructure. Real-time monitoring of steel strand stress distribution throughout the damage process is an important aspect of civil infrastructure health assessment. Hence, this study proposes an optical-electrical co-sensing (OECS) smart steel strand with the DOFS and CCFPI embedded in. It can simultaneously measure small strains in the initial damage phase with high accuracy and obtain information in the large deformation phase with relatively low precision. Several experiments were carried out to test its sensing performance. It shows both DOFS and CCFPI have good linearity, repeatability and hysteresis. In comparison to DOFS, CCFPI has a relatively lower accuracy and resolution, but a large enough measurement range to tolerate the large strain in the event of a steel strand failure. To verify the reliability of the proposed smart steel strand in real structures, the strand strain distribution in the full damage process of bonded prestressed beams under four-point bending loading was monitored using the smart steel strand as a prestressing tendon. The strain measured by the OECS steel strand is shown to reflect the deformation and stiffness variation of prestressed beams under different load.

A Way to Determine the Maximum Inducible Residual Stresses in Steel by Mechanical Surface Treatment

A Way to Determine the Maximum Inducible Residual Stresses in Steel by Mechanical Surface Treatment