Steel Design Research Articles

Parametric Finite Element Study on FREEDAM Beam to Column Joints with Different Details of the Haunch Slotted Holes

Parametric Finite Element (FE) simulations were performed to investigate the ultimate flexural of different configurations of friction steel beam-to-column joints equipped with FREEDAM (free from damage) dampers. The main aim of this study was to compare the effectiveness of friction dampers featuring either single or multiple slotted holes, examining how these variations influence the behavior of the joint and the devices under seismic loads. In particular, the ultimate behavior of the connection (i.e., when the device reaches its maximum stroke) was investigated to characterize the involvement of the bolts in shear, the bearing of the plates, and the yielding of the supporting components. The analysis of bolt stress states revealed significant differences influenced by the number of bolts and slots. The FE models were calibrated against the experimental results obtained within the FREEDAM RFCS Project. These insights contribute to the design and performance evaluation of steel beam-to-column joints with FREEDAM connections, in particular the detailing of the haunch slots, laying the groundwork for future research and applications.

Exploring the effect of alloying elements on the thermoelasticity and strength of bcc Fe-based alloys by first-principles phonon calculations

Designing compositions for novel alloys requires a fundamental grasp of the role of each alloying element in its properties. This study delves into the influence of alloying elements in Ultra-High Strength Steels on essential high-temperature properties, including thermoelasticity, thermal stress, and strength, utilizing first-principles phonon calculations. These properties are pivotal for steels used in high-temperature applications. Our investigation quantitatively forecasts the impact of alloying elements on elastic properties, providing valuable insights for advanced alloy design in high-temperature environments. The introduction of alloying elements markedly amplifies the elastic modulus of Fe-based alloys. The Ni, Mo, Cr, and C elements significantly enhance the anisotropy of the alloy. While refining elastic modulus and mechanical properties, alloying elements induce thermal stress, posing a potential risk of high-temperature cracking. The quantitative analysis underscores the robust strengthening potential for C, Ni, Mo, and W elements, with interstitial C emerging as pivotal in enhancing mechanical properties. The findings of this study illuminate the diverse roles played by different alloying elements and offer theoretical guidance for the design of advanced Ultra-High Strength Steels.

A high-power-density design method for polymer gear systems via an adaptive non-dominated sorting genetic algorithm III and surrogate sub-models

There is a growing and prevalent trend in the power transmission field of high-performance polymers replacing metallic materials given the strict light-weight requirement. Polymer gears exhibit a low elasticity modulus, high-temperature sensitivity, and increased geometric design flexibility, presenting technical challenges to the straightforward application of metallic design methods to polymer gear systems. This study is centred on the development of a high-power-density polymer gear transmission system for the accessory unit of a gas turbine engine, utilising an adaptive NSGA-III algorithm and surrogate sub-models. A comprehensive assessment indicator for the operating performance of the transmission system is suggested, encompassing gear strength, bearing temperature, and shaft torsional stiffness. The model made it possible to simultaneously optimise forty-six structural parameters, including gear tooth module, web thickness, and bearing clearance. In contrast to the original steel design scheme, the optimised polymer gear transmission system indicated a 49% reduction in weight and a 1.96-fold increase in power density. This presents a method for substituting steel with polymers for effective power transmission.

Multi-scale damage mechanism of hierarchically structured high-strength martensitic steels under shock loading

The multi-scale damage behaviors and underlying mechanisms of hierarchically structured high-strength martensitic steels are investigated via plate-impact recovery experiments, postmortem characterizations. Plate-impact experiments were conducted at compressive peak stresses ranging from approximately 5.5 to 11.0 GPa, and the tensile strain rates are ∼105 s −1. Significant improvement in the spall strength of the heat-treated martensitic steel is achieved (5.4 GPa), about 80% higher compared to the as-received bainite steel. The spall failure of the investigated martensitic steel exhibited a mixed-mode combination of brittle (micro-cracks) and ductile (voids) characteristics, known as quasi-cleavage spallation. As the impact velocity increased, voids nucleated successively at different types of boundaries as follows: boundaries between enriched and depleted zones, prior austenite grain boundaries, packet boundaries, block boundaries and lath boundaries. Shear cracking was found to be an important mechanism to accommodate the severe plastic deformation during spallation, giving the strict geometric constraints due to void nucleation tending to occur at grain boundaries. Additionally, molecular dynamics simulations considering realistic hierarchical structure of martensitic steel have been developed to validate the experimental results. These findings and simulation methods contribute a better understanding of the spall behavior of martensitic steels, as well as guidance for future design of high-strength martensitic steels with exceptional reliability and safety under extreme conditions.

Impact of trace silicon on irradiation hardening and embrittlement of RAFM steel subjected to neutron irradiation

The content of silicon (Si) element in reduced activation ferritic/martensitic (RAFM) steels varies significantly among different candidates of fusion reactor structural materials. Si is not intentionally added to the RAFM steel but rather remains as a residue during the deoxidation process in steel fabrication. To control and reduce the Si content, removing processes and special treatments are required. The additional refining processes significantly increase the cost of steel fabrication. Currently, the role of residual or trace Si in neutron irradiation of steel remains unclear. In the presented study, two 9Cr-2 W RAFM steels with Si contents of 0.1 wt.% and 0.01 wt.% were fabricated and subjected to a neutron irradiation at 563 K with a neutron fluence of 4.8 × 1023m−2. The main results show that 0.1 wt.% Si can contribute to the suppression of irradiation hardening and embrittlement, as evidenced by the reduction in irradiation-increased hardness and yield strength, while maintaining preferable elongation. Microscopic analysis suggests that an appropriate content of Si helps refine the grains in RAFM steel, increases the ductile fracture region of the fracture surface, and effectively reduces the density of dislocation loops induced by neutron irradiation. The findings evidence that retaining a certain amount of trace Si should be an informed and rational choice in the design of RAFM steel.

Influence of fiber orientation on flexural‐based design of steel fiber‐reinforced concrete slabs: Experimental and numerical program

AbstractSteel fiber‐reinforced concrete (SFRC) has proven to be a suitable structural material for constructing elevated flat slabs, and several existing office and residential buildings, in which SFRC was used for these components, highlighted the positive outcomes from both technical and sustainability perspectives. However, research on the influence of fiber orientation on the flexural performance of SFRC slabs is relatively scarce despite the fact that a number of studies revealed that the use of constitutive models derived from three‐point bending tests on notched beams leads to overestimations of the bearing capacity of statically indeterminate slabs. In this context, this study aims at presenting an extensive experimental program that consisted of testing three SFRC slabs (3.0 × 3.0 × 0.1 m3) subjected to point load under a statically indeterminate test configuration. The testing procedure was followed by the extraction of 88 cores in order to analyze both fiber distribution and orientation by means of a non‐destructive inductive method. The results indicate that lower orientation numbers were observed in cylinders drilled from the slabs in comparison with those observed in the 150 × 150 × 600 mm3 notched reference beams tested to characterize the pre‐ and post‐cracking flexural performance of the SFRC produced. Based on these results, a straightforward design‐oriented approach to compute an orientation factor was proposed and considered to develop the constitutive law used to simulate the structural response of SFRC slabs by means of nonlinear finite element model. The numerical simulation results showed a good agreement with the experimental response, this evidencing that the orientation factor may permit to account for the differences caused by geometric and statistical scale‐induced factors between both the beams used for the SFRC flexural properties characterization and slabs produced with the same SFRC.

Iterative multi-objective design of hydrogen embrittlement resistant high-strength steels using Bayesian optimization

The infiltration of hydrogen can weaken the strength and toughness of materials, especially in high-strength steel. Considering the inherent trade-off between strength and toughness in steel design, balancing these two factors with the material's hydrogen embrittlement sensitivity has become a huge challenge in steel design. The long cycle nature of hydrogen embrittlement testing makes the iteration of traditional trial and error methods infeasible for steel development. This work adopts active learning algorithms based on Bayesian and Pareto optimization to iteratively optimize the chemical composition and processing technology of high-strength steel, in order to simultaneously improve its hydrogen filled tensile strength (UTS_H) and hydrogen filled total elongation (TEL_H). After two rounds of iterative optimization, the iterative optimization algorithm significantly improved the strength prediction of materials after hydrogen charging. The machine learning model found 16 types of steel from over 15 million unknown materials. Eight materials showed better comprehensive performance than known data, with one material having a tensile strength exceeding 1800 MPa and an elongation of 12.6%. Subsequent experiments showed that the optimization algorithm demonstrated an understanding of the impact of austenite content on hydrogen embrittlement sensitivity in multiple experiments, and designed high-strength steel resistant to hydrogen embrittlement through the austenite content of martensitic steel.

Design of carbide free bainitic steels for hot rolling practices

ABSTRACT In this work, we provide with an overview of the main theories, metallurgical and microstructural concepts used for the design of carbide free bainitic steels adapted to industrial hot rolling and coiling practices. The selected alloys were cast and tested at pilot plant scale and the obtained good combinations of properties tend to validate the thorough and careful approach undertaken to predict the microstructures during the alloy design process.

Seismic Response and Design of Steel Multitiered Concentrically Braced Frames Not Specifically Detailed for Seismic Resistance

Seismic Response and Design of Steel Multitiered Concentrically Braced Frames Not Specifically Detailed for Seismic Resistance

Phase Transformation Temperature Prediction in Steels via Machine Learning.

The phase transformation temperature plays an important role in the design, production and heat treatment process of steels. In the present work, an improved version of the gradient-boosting method LightGBM has been utilized to study the influencing factors of the four phase transformation temperatures, namely Ac1, Ac3, the martensite transformation start (MS) temperature and the bainitic transformation start (BS) temperature. The effects of the alloying element were discussed in detail by comparing their influencing mechanisms on different phase transformation temperatures. The training accuracy was significantly improved by further introducing appropriate features related to atomic parameters. The melting temperature and coefficient of linear thermal expansion of the pure metals corresponding to the alloying elements, atomic Waber-Cromer pseudopotential radii and valence electron number were the top four among the eighteen atomic parameters used to improve the trained model performance. The training and prediction processes were analyzed using a partial dependence plot (PDP) and Shapley additive explanation (SHAP) methods to reveal the relationships between the features and phase transformation temperature.

Research on the evolution of corrosion products of 17-4 PH martensitic stainless steel in the tropical marine environment

Deterioration of stainless steel is significantly influenced by the characteristics of corrosion products. Evolution of corrosion products of 17-4 PH martensitic stainless steel (17-4 PH MSS) in the tropical marine environment was systematically studied by field-exposure, combined with morphological observation, compositional characterization and electrochemical testing in this work. The corrosion process of 17-4 PH MSS was divided into three stages: stage I–rapid formation and shedding of corrosion products, stage II–adhesion and transformation of corrosion products and stage Ⅲ–remarkable increase in the protective properties of corrosion products. Corrosion rate of 17-4 PH MSS was maximum in the first stage and then decreased continuously in the second and third stages, which is closely related to the morphology, distribution and composition of the corrosion products. In terms of morphological evolution, corrosion products of 17-4 PH MSS showed the dynamic cycle characteristic of "nucleation-growth-cracking-shedding". In view of compositional transformation, the high content of Cr, Ni, and Cu in stainless steel is involved in the formation of corrosion products, and the production of Cr2O3, Cr(OH)3, FeCr2O4, NiFe2O4, and CuFeO2 after 6 months of exposure was an important shift. Argument from protective properties, increase in coverage percentage and the generation of Cr-containing products are responsible for the enhancement of protective properties of the corrosion products. This work prepares the way for further research on the generation and growth mechanism of pitting under corrosion products and provides technical support for the design, selection, and protection of stainless steel in tropical marine environments.

Comprehensive design and analysis of a 300L steel fuel tank for heavy off-road vehicles: numerical and experimental insights

Introduction: This study presents a comprehensive design and analysis of a 300L steel fuel tank intended for heavy off-road vehicles. The design process integrates numerical simulations and experimental investigations to optimize the tank's performance and durability under various operating conditions.Methods: The design methodology involves CAD model optimization, numerical analysis setup, and experimental validation. CAD model optimization simplifies the tank geometry while retaining structural integrity. Numerical analysis setup includes defining boundary conditions, meshing strategies, and simulation parameters. Experimental validation entails testing the tank under dynamic loading conditions to assess its structural response.Results: Numerical simulations reveal insights into stress distribution, deformation behavior, and fluid dynamics within the tank. Experimental tests confirm the numerical predictions and provide valuable data for model validation. Key results include stress concentrations in critical areas, deformation patterns under different loading conditions, and fluid flow characteristics.Discussion: The integrated approach combining numerical simulations and experimental tests offers a comprehensive understanding of the fuel tank's behavior. Findings highlight areas for design improvement, such as reinforcement of stress-prone regions and optimization of fluid flow dynamics. The study contributes to enhancing the performance, reliability, and safety of fuel tanks for heavy off-road vehicles.

Fretting fatigue of cast iron and aluminium – A strength assessment method based on a worst-case assumption

Many components made of cast iron (e.g., in combustion engines) and aluminium (e.g., in aircraft construction) are subject to fretting fatigue. This results in a need for a method for assessing the strengths of the aforementioned materials that takes into account the reduction in fatigue strength due to fretting as well as the accompanying reduction in service life. In a first paper, the authors already presented a calculation method for the fail-safe design of steel–steel contacts subject to fretting fatigue. This enables the engineer or designer to perform a strength assessment for any component connection made of steel. The calculation method is based on a tribological worst-case assumption and can be integrated into the analytical strength assessment of the internationally known FKM Guideline. The strength reduction is taken into account by use of empirically determined fretting factors. The frequent failures of component connections made of cast iron and aluminium in the field made an extension of the calculation method became necessary. This work therefore includes experimental investigations into the materials EN-GJS-700, EN-GJS-400 and EN-GJL-300 (cast iron), as well as EN AW-7075 T651, EN AW-6082 T651 and EN AW-5083 (aluminium). Since the main parameters determining fretting fatigue strength are slip amplitude and contact pressure, the worst-case combinations of these parameters (resulting in the lowest friction fatigue strength) were first determined for each of the two material groups using a laboratory test setup. These parameters could be found at sa=10μm;p=40MPa for cast iron and sa=5μm;p=10MPa for aluminium. Based on these worst-cases, the fretting fatigue limits of the aforementioned materials were determined, as well as the effect of mean stress. The fretting factors of the materials were derived from the experimental results. Additional experimental investigations using a connecting-rod-like geometry served to validate an application typical of the industry. Using the calculation method, the degree of utilisation of the connecting rods could be determined with good accuracy (maximum error: 18.7%).

Seismic behaviour of the non-straight steel beams in the structural plans

Purpose This research study focuses on investigating the seismic performance of non-straight beams in steel structures and exploring the mechanism by which plastic hinges are formed within these beams. The findings contribute to the understanding of their behaviour under seismic loads and offer insights into their potential for enhancing the lateral resistance of the structure. The abstract of the study highlights the significance of corners in structural plans, where non-coaxial columns, diagonal elements or beams deviating from a straight path are commonly observed. Typically, these non-straight beams are connected to the columns using pinned connections, despite their unknown seismic behaviour. Recognizing the importance of generating plastic hinges in special moment resisting frames and the lack of previous research on the involvement of these non-straight beams, this study aims to address this knowledge gap.Design/methodology/approachThis study examines the seismic behaviour and plastic hinge formation of non-straight beams in steel structures. Non-straight beams are beams that connect non-coaxial columns and diagonal elements, or deviate from a linear path. They are usually pinned to the columns, and their seismic contribution is unknown. A critical case with a 12-m non-straight beam is analysed using Abaqus software. Different models are created with varying cross-section shapes and connection types between the non-straight beams. The models are subjected to lateral monotonic and cyclic loads in one direction. The results show that non-straight beams increase the lateral stiffness, strength and energy dissipation of the models compared to disconnected beams that act as two cantilevers.FindingsThe analysis results reveal several key findings. The inclusion of non-straight beams in the models leads to increased lateral stiffness, strength and energy dissipation compared to the scenario where the beams are disconnected and act as two cantilever beams. Plastic hinges are formed at both ends of the non-straight beam when a 3% drift is reached, contributing to energy damping and introducing plasticity into the structure. These results strongly suggest that non-straight beams play a significant role in enhancing the lateral resistance of the system. Based on the seismic analysis results, this study recommends the utilization of non-straight beams in special moment frames due to the formation of plastic hinges within these beams and their effective participation in resisting lateral seismic loads. This research fills a critical gap in understanding the behaviour of non-straight beams and provides valuable insights for structural engineers involved in the design and analysis of steel structures.Originality/valueThe authors believe that this research will greatly contribute to the knowledge and understanding of the seismic performance of non-straight beams in steel structures.

Effectiveness of repairing yielding anchor rods in exposed column bases in steel structures

AbstractOne of the features of Japanese structural steel design is an economical design option for yielding exposed column bases before first‐story columns, namely weak‐base/strong‐column design, which is unlike the strict capacity design for column bases. This study aims to develop a repair methodology that identifies damage states of the yielding column bases and anchor rods, and selects appropriate repair/retrofit methods. As a standard repair method for damaged exposed‐type column bases, the applicability and effectiveness of the re‐tightening process of anchor rods need to be examined. This study first reviews the literature on standard retrofit techniques for column bases and required deformation capacity of ductile anchor rods. The threaded anchor rod deformation capacity with different steel grades and screw threads commonly used were tested to clarify the required ductility. To clarify the reparability of exposed column bases, numerical models of four‐ and six‐story steel moment resisting frame buildings were developed and validated by shaking table test results. The results show that this simple repair method was proven to be effective through the test program and numerical analysis and it's not always applicable for standard anchor rods assumed for pin or fixed column bases designed to remain elastic. Finlly, a repair methodology and flow chart that identifies the damage states of anchor rods and selects appropriate repair/retrofit methods for the exposed steel column base was suggested and applied to the simulation results.

Effect of Mo on the Corrosion Resistance of Cr-Containing Steel in a Simulated Tropical Marine Atmospheric Environment

In this manuscript, the effect of Mo addition on the corrosion resistance of the low-alloy steel in a simulated tropical marine atmospheric environment has been studied through microstructure characterization, corrosion immersion experiments, electrochemical measurement, and a series of microscopic characterization methods. The results show that Mo has the ability to reduce the corrosion rate of low-alloy steel in a marine atmospheric environment, with a more pronounced reduction effect observed over longer corrosion periods. The addition of Mo enhances the corrosion product film’s compactness when coupled with Cr, subsequently improving corrosion resistance. Simultaneously, MoO42−, acting as a slow-release ion, can effectively suppress localized corrosion in low-alloy steel. The research findings can offer data support and a theoretical foundation for the design of low-alloy steels with enhanced corrosion resistance in a tropical marine atmospheric environment.

Heterogeneous plastic deformation and HDI strengthening of the heterostructured dual-phase steels investigated by in-situ SEM-DIC

Heterostructured dual-phase (DP) steels comprising different martensite volume fractions (HS740 steel, VM:41 %; HS780 steel, VM: 54 %) were produced by cold rolling and intercritical annealing. HS780 steel produces a near-ideal heterostructure where the grains are mostly isolated by the F/M interfaces, resulting in a superior combination of strength-ductility (ultimate tensile strength, UTS: 1064 MPa; uniform elongation, UE: 9.8 %). The excellent mechanical properties is primarily attributed to the stronger hetero-deformation induced (HDI) strengthening and hardening of HS780 steel. The relationships between HDI hardening and the heterogeneous plastic deformation of the heterostructured DP steels were elucidated based on the in-situ tensile tests and digital image correlation analysis. The insights from these results will improve our understanding of the deformation behavior of heterostructured materials and guide the design of low-carbon steels with outstanding mechanical properties.

Numerical study and design of S35657 stainless steel welded stub columns

As a new type of austenitic stainless steel with high nitrogen and low nickel, S35657 stainless steel has the characteristics of high strength and low price, and it has a good application prospect in the field of construction. To supplement the relevant research on S35657 stainless steel structures and to evaluate the applicability of existing specifications and design methods, a finite element model was established using ABAQUS software and calibrated using existing test results. Furthermore, a series of parametric analyses were carried out, focusing on the effects of width-to-thickness ratio, initial geometric imperfection, and welding residual stress on the local buckling of S35657 stainless steel welded section columns. On this basis, the critical width-to-thickness ratio limit of the compression plate was proposed. Finally, the test results and the simulation results were compared with the calculation results of load-carrying capacities for local buckling in the European code (EN1993-1-4), the American code (SEI/ASCE8–02), the Chinese specification (CECS410:2015), the direct strength method (DSM) and the continuous strength method (CSM). Based on the effective width method and DSM, two new approaches to calculate the load-carrying capacity for local buckling were proposed and demonstrated to obtain reasonable accuracy.

Behaviour and design of duplex stainless steel bolted connections failing in block shear

Duplex stainless steel (DSS) is an emerging construction material for structural engineering, which is featured with high mechanical strength and superior corrosion resistance. Compared with considerable research on DSS structural members, available research is relatively limited for structural joints/connections between these members. In line with this concern, this paper presents a comprehensive experimental and numerical study of duplex stainless steel bolted connections (DSSBCs), focusing on the behaviour and design related to block shear failure. Eleven specimens are tested to investigate the effect of different bolt arrangements on the block shear behaviour. Furthermore, a detailed numerical study was performed as a supplement to the experimental tests, where the anisotropic mechanical properties of DSS are considered in the finite element modelling. Based on the test and analysis results, it is found that the block shear failure mode of DSSBCs resembles that of carbon steel bolted connections, which can be characterised as necking of the tensile section and yielding of the shear sections. Using the experimental and numerical data obtained in this and previous studies, the applicability of various block shear design methods to stainless steel bolted connections is assessed. An updated design method is proposed for predicting the block shear capacity of duplex and austenitic stainless steel bolted connections. A proper partial safety factor/resistance factor is suggested for the proposed method based on the results of reliability analyses.

A Combined Microscopy Study of the Microstructural Evolution of Ferritic Stainless Steel upon Deep Drawing: The Role of Alloy Composition

Ferritic stainless steel (FSS) is widely used to manufacture deep-drawn products for corrosion resistance applications, being the alloy drawability strongly affected by its microstructural anisotropy. This study combines a variety of microscopy techniques enabling in-depth analyses of the microstructural evolution of two different FSSs correlated to their deep drawing performance. One of the steels has a good correspondence with the standard EN-1.4016 (AISI 430). The other is a modified version of the previous one with higher contents of the ferrite-stabilising elements Si and Cr, and lower contents of the austenite-stabilising elements C, N, and Mn. Electron Backscatter Diffraction results confirm that the microstructural properties and drawability of FSS in the deep drawing process are improved in the modified steel version. Scanning transmission electron microscopy under low-angle annular dark field conditions evidences that the deformation mechanism of FSS during deep drawing follows a microstructural distortion model based on the grain size gradient and shows a variation of the deformation texture depending on the alloy composition. This work demonstrates the potential of advanced microscopy techniques for optimising the processing and design of ferritic stainless steels, with slight variations in the alloy composition, for deep drawing applications.