Stress In Steel Research Articles

Experimental investigation of bond and crack behaviour of reinforced concrete ties using distributed fibre optical sensing and digital image correlation

The interaction of reinforcing steel and concrete is decisive for the structural behaviour of reinforced concrete (RC) in the serviceability and ultimate limit state. In the past decade, distributed fibre optical sensing (DFOS) and digital image correlation (DIC) have emerged as valuable tools to investigate and comprehend the mechanics of this interaction in more detail. This paper presents and discusses the results of an experimental campaign comprising 21 RC ties subjected to monotonic and cyclic uniaxial tension, where these refined instrumentation methods were utilised to study the influence of the reinforcing bar diameter, rib geometry and mechanical properties on the structural behaviour. Local strains were measured along the reinforcing bars with DFOS, from which the distributions of steel and bond stresses, as well as slip were derived. The crack pattern and kinematics on the surface were determined through DIC. The results allowed studying the influence of the deformation level, cyclic loading and the rib geometry on splitting and the magnitude of local and average bond stresses. The results indicate that the bond and crack behaviour depend on parameters typically neglected in design standards, such as the relative rib area, elastic steel stiffness, and bar diameter. Moreover, the observed average bond stresses in the elastic range were lower than proposed by design standards for serviceability verifications. These observations allow identifying weaknesses and inconsistencies in common bond models, serving as a starting point for improvements in modelling.

Stress evolution in plastically deformed austenitic and ferritic steels determined using angle- and energy-dispersive diffraction

In the presented research, the intergranular elastic interaction and the second-order plastic incompatibility stress in textured ferritic and austenitic steels were investigated by means of diffraction. The lattice strains were measured inside the samples by the multiple reflection method using high energy X-rays diffraction during uniaxial in situ tensile tests. Comparing experiment with various models of intergranular interaction, it was found that the Eshelby-Kröner model correctly approximates the X-ray stress factors (XSFs) for different reflections hkl and scattering vector orientations.The verified XSFs were used to investigate the evolution of the first and second-order stresses in both austenitic and ferritic steels. It was shown that considering only the elastic anisotropy, the non-linearity of sin2ψ plots cannot be explained by crystallographic texture. Therefore, a more advanced method based on elastic-plastic self-consistent modeling (EPSC) is required for the analysis. Using such methodology the non-linearities of cos2φ plots were explained, and the evolutions of the first and second-order stresses were determined. It was found that plastic deformation of about 1–2% can completely exchange the state of second-order plastic incompatibility stresses.

Influence of preheating on residual stresses in ultra-high strength steel welded components

Preheating is generally required in the welding of ultra-high strength steels (UHSSs) for avoiding cold cracking. The present work systematically explores the influence of preheating on welding residual stresses (WRS) in components made of UHSS by means of both experiments and numerical simulations. The results reveal that, no matter what UHSS is with or without metallurgical phase transformation, preheating has a great influence on the magnitude of transverse residual stress (σT-RS). In general, the higher preheating temperature (TPH) the lower magnitude of σT-RS is. Preheating would change the longitudinal residual stress (σL-RS) sign in the weld area and σL-RS amount obviously diminishes with the increase of TPH for transforming UHSS, while that has nearly no influence on the maximum σL-RS but has an impact on the area of tensile σL-RS for non-transforming UHSS. The effect of entire preheating and partial preheating on WRS in UHSS welded components could be nearly the same. Nevertheless, TPH in the partial preheating case (about 300 °C here) should be higher than that in the entire preheating one (corresponding 100 °C here) for that same effect. The weld dimensions, especially the size of the heat-affected zone (HAZ), and cooling time Δt8/5 significantly increase with TPH. Preheating has almost no influence on the restraint degree of welded components.

Prestress monitoring for prestress tendons based on the resonance-enhanced magnetoelastic method considering the construction process

Monitoring the prestress of prestressed concrete structures is hard but helpful. The resonance-enhanced magnetoelastic (REME) sensor could measure the stress of steel, but the measurement is influenced by the stress history. Thus, after analyzing the principle of the REME method according to the electric circuit theorem, the construction process and stress history of different prestress tendons were discussed. The prestress monitoring experiment showed that the induced voltage–prestress relationship was influenced by the stress history. To evaluate the prestress, a prestress evaluation method suitable for prestress steel strands was proposed. Using the precise calibration method, the monitoring errors in the construction stage and the prestress loss stage were less than 13.26% and 5.97%. The simplified calibration method reduced the workload of the calibration by 50% while the monitoring error increased by less than 4%. In addition, using the self-calibration method can avoid the influence of the differences in steel strands, leading to higher monitoring accuracy.

Dynamic compressive behaviours of stainless-clad bimetallic steel under high temperatures

To study the dynamic performance of stainless-clad (SC) bimetallic steel under coupling actions of high temperature and strain rate, a total of 72 compression experiments were designed and conducted at four strain rates (0.001, 1000, 2000 and 3000 s−1) and four temperatures varying from 20 °C to 600 °C. The deformation patterns, stress versus strain responses, as well as strain rate and temperature effects were obtained and analyzed. Experimental results indicated that the dynamic compression performances of SC bimetallic steel were sensitive to both temperature and strain rate. The dynamic yield strength at 3000 s−1 was approximately 1.7 times than that under quasi-static conditions, while reduced by 24–35%, 37–50% and 52–62% when temperatures rose from 20 °C to 200 °C, 400 °C and 600 °C, respectively. Moreover, the strain rate sensitivity increased with the growing strain rate and temperature. The observation of microstructures showed that the grain dimensions declined with increase in strain rate or a decreased temperature. According to test data, a modified Johnson-Cook model was developed for predicting the stress versus strain response of the SC bimetallic steel subjected to combined actions of high strain rate and elevated temperature (20–600 °C), in which the influences of temperature softening, strain-rate strengthening and strain hardening were considered.

Prediction of residual stress, surface roughness, and grain refinement of 42CrMo steel subjected to shot peening by combining finite element method and artificial neural network

Prediction of residual stress, surface roughness, and grain refinement of 42CrMo steel subjected to shot peening by combining finite element method and artificial neural network

Interplay between hierarchical microstructure and graded residual stress in a stainless steel fabricated by laser powder bed fusion

Interplay between hierarchical microstructure and graded residual stress in a stainless steel fabricated by laser powder bed fusion

Constitutive modeling for elevated temperature flow behavior of a novel Cr-Si alloyed hot stamping steel

The flow behavior of a novel Cr-Si alloyed hot stamping steel (Cr-Si steel) at elevated temperature was investigated via isothermal compression tests on a Gleeble-3500 thermomechanical simulator with a temperature range of 600 ∼ 900 °C and a strain rate range of 0.1 ∼ 10 s−1. Subsequently, the Arrhenius-type constitutive model, comprising strain compensation, was established in accordance with the friction and adiabatic heating corrected stress-strain curves. Furthermore, the predictability and prediction accuracy of the constitutive model were verified. The results reveal that at a constant strain rate, the flow stress of the Cr-Si steel initially increases as the strain increases before tending to stabilize, owning to the combined effects of work hardening and dynamic recovery. The peak flow stresses decrease as the temperatures increase and the strain rates decrease. The constitutive model can accurately predict the elevated temperature constitutive relationship of the Cr-Si steel during the hot stamping process.

Influence of Several Heat Treatments on Residual Stress in Laser Powder Bed-Fused Maraging 18Ni-300 Steel

In laser powder bed fusion, process-inherited thermal residual stress is developed due to the thermal strain misfit between each layer. Detailed analysis and a prediction of the residual stress are needed because it can induce distortions of the components and, in some serious cases, stress-induced defects such as cracking. In this work, the effects of heat treatment conditions on residual stress in maraging 18Ni-300 steel, fabricated by laser powder bed fusion, were investigated. Cantilever-shaped specimens were used to experimentally analyze residual stress caused by the distortions of the specimens while cutting them from the supporters. The cantilever samples showed complex distortion behavior in the as-built state. They bent downward while cutting them from the supporter when the thickness was relatively thin, and the bending deformation became upward instead of downward with increasing thickness. Interpreting this behavior by finite element simulation showed that the downward bending was due to the compressive stress state at the top layer of the maraging steel. When the cantilever specimens were aging heat treated, the distortions were significantly reduced, implying that the process-inherited residual stress was diminished.

Bainite transformation under the effect of large stress in a carbide-free bainite steel

The effects of large stress on bainite transformation and microstructure were investigated by dilatometry, SEM and EBSD. The results show that the effect of large stress on bainite transformation includes two parts: mechanical driving force and prior deformation. A new finding is that bainite transformation is inhibited by large stress when the negative effect of prior deformation surpasses the positive effect of mechanical driving force. In addition, the bainite transformation kinetics model established by van Bohemen and Sietsma is modified to describe the bainite transformation under the effect of stress more accurately. Moreover, significant variant selection occurs under the effect of large stress, but the selected bainite variants in adjacent austenite twins are different. Furthermore, the hardness of the steel increases with the stress because of the increase in dislocation density and martensite amount.

Barkhausen Noise Emission as a Function of Tensile Stress in Low-Alloyed Steels: Influence of Corrosion and Steel Strength

Components of civil buildings are frequently made of low-alloyed steel, which can suffer from corrosion damage. This damage reduces their bearing capacity and/or redistributes the load to neighboring regions with the potential risk of their collapse. For this reason, this study deals with the non-destructive monitoring of bodies made of these steels based on Barkhausen noise emission. The superimposing contribution of corrosion extent and exerted tensile load is investigated on samples of variable yield strength in the range from 235 to 1100 MPa. It is found that the presence of a corroded layer attenuates Barkhausen noise and makes the body harder from a magnetic point of view. The reduced effective thickness of the samples as a result of corrosion damage increases the true stress. Barkhausen noise grows along with the tensile stress in the direction of exerted stress at the expense of decreasing Barkhausen noise in the perpendicular direction. The evolution of Barkhausen noise versus tensile stress is mostly shifted to the lower values of Barkhausen noise, along with the increasing degree of corrosion damage. The evolution of Barkhausen noise versus tensile stress is also affected by the initial microstructure and the corresponding yield strength of the low-alloyed steel. Corrosion attack results in the growth of FWHM, which is compensated by the decreasing evolution along with the tensile stresses. The effective values drop down with the higher extent of corrosion damage. However, the response with respect to the tensile stress is asymmetric in RD and TD due to the realignment of DWs into RD. Finally, PP tends to increase with the corrosion attack as well as the tensile stress and this parameter only exhibits the systematic behavior in RD as well as TD. On the other hand, MBN-extracted parameters as well as their combination provide no exclusive values on which the pure contribution of corrosion and tensile stress can be distinguished.

Study on failure mechanism and treatment measures of floor heave of high-speed railway tunnel in the interbedded surrounding rock with high geostress

The tunnel floor heave is easy to occur in the interbedded surrounding rock with high geostress, which has a serious impact on the safety of the tunnel structure and the normal operation of the tunnel. Through field investigation, numerical simulation, and in-situ monitoring, this paper studies the failure mechanism and corresponding treatment measures of the floor heave of a high-speed railway tunnel from various aspects such as geostress, surrounding rock structure, and bottom structure. The results show that the high horizontal geostress, the structure of interbedded surrounding rock, and the weak inverted arch are the reasons for the tunnel floor heave failure. Under the condition that high horizontal geostress acts on the structure of interbedded surrounding rock mass, the underlying rock layer under the tunnel will undergo cyclic deformation or failure, and the tunnel will show floor heave failure. Based on the research results, treatment measures such as removal and replacement of the inverted arch, anchor cable and anchor bolt anchoring were taken to treat the foundation and overall track bed of the tunnel. After the treatment, an automated monitoring system was established to monitor the displacement of the inverted arch, surrounding rock pressure, and steel stress for three years. Based on the analysis of monitoring results, this treatment plan can effectively control the tunnel floor heave. The research results can provide reference for the prevention and control of other tunnel floor heave failures.

Experimental and analytical assessment of fatigue damage in reinforced concrete tension members

In this paper, the effects of bond deterioration due to fatigue loading on the structural response of reinforced concrete tension members are studied. A comprehensive experimental campaign on reinforced concrete ties and pull-out specimens was carried out under monotonic and repeated loading. The use of distributed fibre optical sensing to assess the local strains allowed the bond deterioration mechanism under repeated loading to be observed. Previously applied load cycles caused a reduction in tension stiffening for load levels below the maximum cyclic load but did not significantly influence the deformation behaviour of the member near the ultimate load. The bond stresses at the maximum cyclic load decreased fairly linearly with the logarithm of load cycles, with the most pronounced reduction in bond stresses near the cracks. At the minimum cyclic load, the bond stress distribution along the tie changed and bond stresses reversal occurred close to the cracks. This caused negative tension stiffening in some cases, i.e., the mean strains exceeded those occurring in a bare reinforcing bar at the same load. The mean steel stresses and the steel stress amplitudes between the cracks increased with the number of load cycles due to the gradual reduction of the concrete contribution and bond degradation. Bond degradation occurred linearly on a semi-logarithmic scale, as expected for the generated bond stresses, which were below the fatigue bond strength. The test results highlight that accounting for shrinkage-induced strains is essential for a realistic evaluation of tension stiffening and residual deformations in particular.Based on the experimental observations and previously developed models for monotonic and cyclic loading, two approaches were used to predict the response of reinforced concrete tension members under repeated loading: the Local Fatigue Damage Model (LFDM), based on the local bond stress-slip relationship, and the adapted Tension Chord Model (TCM) which assumes constant bond stresses and mean strains. The results of both approaches agree well with the test results at the maximum load but yielded less satisfactory predictions at the minimum loading level where only the LFDM was able to be applied successfully. Further research is required to validate the negative bond stresses occurring upon slip reversal in the LFDM and the reduction factor proposed in the adapted TCM.

Explainable machine learning models for probabilistic buckling stress prediction of steel shear panel dampers

Steel shear panel dampers are widely used as passive energy-dissipation devices in earthquake-resistant structures. The out-of-plane buckling stress of the core plate included in the steel shear panel damper is critical for obtaining the desired lateral force-resistant and hysteretic energy-absorbing capacities. However, the existing calculation method of buckling stress of the steel shear panel damper cannot well address the effects of the steel material’s and geometries’ inherent uncertainties. This paper intends to develop the probabilistic buckling stress prediction models of steel shear panel dampers using machine learning methods considering the steel material’s and geometries’ uncertainties. To this end, the nominal buckling stress prediction models are first developed using different machine learning algorithms based on finite element analysis results where the efficiency of the finite element models has been validated through test results. The analysis results confirm the highest accuracy of the artificial neural network (ANN) model. The SHapley Additive exPlanations (SHAP) and feature importance analysis methods are adopted for interpreting the developed prediction models. The analysis results indicate that the yielding stress of steel (fy), the height-to-width ratio (α), the width-to-thickness ratio (β), and the initial imperfection (δ) show significant influences on the nominal buckling stress of the steel panel damper while the thickness of the core plate (t) shows negligible effects. The probabilistic buckling stress prediction models are further developed based on the trained ANN model considering the combined uncertainties of steel materials and geometries by the Latin hypercube sampling method. The efficiency of the developed probabilistic buckling stress prediction models is confirmed by capturing the probability density of the numerical simulation results. The global sensitivity analysis (GSA) method is introduced for investigating the influence of the design parameters on the discreteness of the probabilistic buckling stress. It has been found from the analysis results that the uncertainties of the yielding stress of steel (fy) and the initial imperfection (δ) have significant influence, that of the height-to-width ratio (α) have limited influence, and that of the width-to-thickness ratio (β) and the thickness of the core plate (t) have negligible influence on the buckling stress of the steel panel damper. For practical application, the interactive software named “PBSSD” is developed and provided for predicting the probabilistic buckling stress by inputting the nominal design parameters of steel material and geometries.

Study on surface residual stress of 42CrMo steel treated by ultrasonic rolling extrusion

To obtain the distribution law of residual stress of 42CrMo steel processed by ultrasonic rolling extrusion process (UREP), according to the characteristics of the material treated by ultrasonic rolling extrusion process, 42CrMo steel quasi-static experiment and dynamic experiment are carried out, the improved Johnson–Cook model was proposed. Based on the 42CrMo constitutive equation, the ultrasonic rolling extrusion process finite element method and experiment of 42CrMo steel were carried out. The results show that the simulation value and experimental value of the residual stress distribution after ultrasonic rolling extrusion process of 42CrMo steel have good consistency, with the increase of static pressure and amplitude, the residual stress increases, and with the increase of rotational speed and feed speed, the residual stress decreases, a more accurate residual stress distribution law of ultrasonic rolling extrusion of 42CrMo steel is obtained.

Electromagnetic (EM) sensor measurement for residual stress characterisation in welded steel plates

ABSTRACT Residual stresses can cause compromise in structural integrity; it is desirable to assess residual stresses using non-destructive testing so that effects on structural properties can be predicted. Electromagnetic (EM) sensors can be used to characterise residual stresses in steels accounting for, microstructure and geometry effects. Residual stress characterisation in welded EN S275 steel plates using EM sensors is reported. Low-frequency, low-magnetic field EM sensors were used to assess residual stresses in the plates. A finite element model for the sensor and sample was generated in COMSOL software so the influence of weld bead geometry and microstructure could be predicted and accounted for. This allowed residual stresses to be determined from EM sensor measurements, excluding the geometry and microstructure effects, XRD was used to verify EM sensor measurements. The highest residual stresses were found adjacent to the weld fusion zone, with magnitudes of, 170±5MPa, 120±20MPa and 42±10MPa for X-ray diffraction (XRD), a small EM sensor (U-12.7) and a big EM sensor (U-31) types, respectively. The differences are due to the volume of the material measured by each measurement type. It was shown that EM sensors are capable of measuring residual stress in welded plates to a good level of accuracy.

Quenching induced residue stress in M50 steel ring: a FEM simulation

A finite element method (FEM) combined with subroutines was established and used for tracing the evolution of stresses in M50 steel in quenching. The constitutive relation and thermal physical properties of M50 steel were tested and integrated into the modeling. The finite element analysis, taking into account of thermal stresses and martensitic phase transformation, predicts accurately the high-velocity nitrogen (HNQ) induced residual stresses in the M50 steel bulk. The simulation results suggested that the residual stresses in M50 steel is compressive at the surface while tensive at the center, along with very strong residual stresses at edges. The residual stress reaches to the high level of −810.3 MPa and −1436 MPa in the case of HNQ and water quenching, respectively. The evolution of stress is found to be jointly driven by the thermal stress and phase transformation stress. The thermal stress dominates the evolution at the initial stage while the phase transformation stress becomes dominating once the martensite transformation begins.

Effect of Nb-induced microstructure on pipeline steel corrosion and stress corrosion cracking performance in acidic environment

The corrosion and stress corrosion cracking response of two steels were examined in acidic environment. The surface microstructure and texture of the steels were significantly affected by a one-order-of-magnitude difference in Nb content. The Nb-containing steel had a refined microstructure, with more {110}-oriented grains, whereas the Nb-deficient steel had an irregular microstructure, containing both fine and large polygonal ferrite grains, with a strong {001}<110> component. When compared to the Nb-containing steel, the Nb-deficient steel had lower corrosion resistance, more delamination cracks, and a higher tendency for embrittlement. This disparity in performance was clearly related to the microstructural characteristics of the steels.

Axial compressive behavior and design of high-strength square concrete-filled steel tube short columns with embedded GFRP tubes

This paper proposed a hybrid column by embedding glass fiber-reinforced polymer (GFRP) tube into high-strength square concrete-filled steel tube (CFT), named as high-strength square steel-concrete-GFRP concrete (SCFC) column. A total of 13 high-strength square SCFC short columns were tested. The test parameters included diameter and thickness of GFRP tube, width and thickness of steel tube, yield stress of steel, and compressive strength of concrete. Results showed that high-strength square SCFC short columns exhibited post-yield strengthening behavior and stable residual strength. The axial strength, confining effect, and ductility were improved because of the embedded GFRP tube. Detailed finite element models were developed and benchmarked to investigate the strength contribution of each component and conduct parametric studies. It was shown that: (i) the concrete infill and the steel tube contributed >90% to the overall compressive strength and (ii) the strength improvement by embedding GFRP tube was closely related to the section size ratio, confinement ratio of the GFRP tube, and confinement ratio of the steel tube. Evaluation of the current equations showed that they were not accurate enough to estimate the axial compressive strength of high-strength square SCFC short columns. New equations were then proposed.

Flexural behavior and design of rectangular ultra-high performance concrete-filled high-strength steel tube members

This study investigated the flexural behavior of rectangular ultra-high performance concrete-filled high-strength steel tube (CuFTh) members. A total of 11 tests were conducted. The influence of yield stress of steel (Fy), steel fiber volume content of UHPC (ρ), height (H) of steel tube, and thickness of steel tube wall (t) was investigated. 3D finite-element models were developed and benchmarked to conduct parametric studies. Results from the experimental tests and FEM analyses indicated that: (i) Fy, t, and H have a significant influence on the flexural strength, while the compressive strength of concrete has a negligible impact; and (ii) increasing ρ slightly improves the flexural strength, but obviously reduces the ductility. Additionally, results from the experimental tests and FEM analyses were compared with the strength estimated using AISC 360-16, GB 50936-2014, Eurocode 4, and AIJ. The comparisons showed that Eurocode 4 and AISC 360-16 can reasonably estimate the flexural strength of rectangular CuFTh members. AIJ is recommended for predicting the service-level flexural stiffness of rectangular CuFTh members.