•The corrosion kinetics under both testing conditions follow the equation, W = Atn.•The mechanical property degradation is insensitive to differences in rust layer.•Inter-crystalline corrosion is the ...microscopic cause of mechanical property decline.•Relationship between mechanical property and etch pit topography has been clarified.•The accelerated test can simulate natural test to predict the mechanical properties.
Exposure tests in an urban industrial atmosphere and wet/dry cyclic accelerated corrosion tests for Q235B structural steel were performed. The corrosion kinetics under both conditions follow the empirical equation, W = Atn. Inter-crystalline corrosion is the basic cause of mechanical property degradation in both environments. Steel mechanical property degradation is not strongly sensitive to differences in rust layer topographies and corrosion processes; as long as the microscopic mechanisms of corrosion are identical and the topographies of etch pits are similar, the accelerated corrosion test can simulate atmospheric corrosion and accurately predict the degradation pattern of steel mechanical properties in an atmospheric environment.
•This paper presents a state-of-the-art cast-steel connector to be used in HSS modular construction.•This study ensures satisfactory performance of the HSS modular connection under axial design ...loads.•Two significant design improvements are recommended based on a parametric study.•The connector weight can be reduced up to 20% without compromising the design load requirements.•The location of the screws can be adjusted to significantly increase axial tension load capacity.
The popularity of steel modular construction is on the rise. This paper presents a new and innovative modular steel construction which uses state-of-the-art cast-steel connectors and hollow structural steel members. Structural behavior of a typical corner connection of this modular construction to be used in an assisted living facility was studied when the connection is subject to axial tension and axial compression loads. The study was completed using both experimental method and a numerical method. Six full-scale specimens were built and tested under axial compression and axial tension. It was found that this innovative modular connection satisfactorily carries the design loads. Based on the parametric study completed using finite element method, two significant design improvements are recommended. The cast-steel connector can be made 20% lighter without compromising the strength needed to satisfy the design loads. The locations of the connecting screws can be adjusted to achieve a higher stiffness and load carrying capacity of the connection when subjected to axial tension. This paper presents the new modular construction method in brief, the test method and test results, development of finite element model, and parametric study.
Nature has inspired researchers over the past years to address a wide range of engineering challenges by mimicking living organisms due to their unique mechanisms. In structural engineering, ...bio-inspired systems have been utilized in previous studies as energy absorbers; however, their uses as blast-resistant structures are still very limited. The current study proposes three bio-inspired steel blast mitigation systems that can effectively reduce the pressure values behind their panels based on mimicking the structural frameworks of i) falcon's nostril; ii) orca's jaw; and iii) pangolin-armadillo scales. In this respect, the study discusses the morphology of such organisms and their corresponding integrated blast mitigation mechanisms that include interlocking bearings, deviations and reflections, element deformations, and suppressive system interactions. The blast performance of the developed bio-inspired systems is then numerically compared to conventional steel systems (solid and corrugated panels). These comparisons include the pressure values and the transmitted impulse at different distances behind the panels as well as kinetic and internal energy histories. The proposed mitigation mechanisms are also verified through different response parameters such as wave distributions, material strains and panel deformations. Finally, performance charts are presented for each system to illustrate the pressure values behind the panels for different scaled distances (from 0.2 m/kg1/3 to 0.5 m/kg1/3), thus showing different protection levels. The results demonstrate that the developed systems can reduce the maximum pressure values of the explosions relative to the conventional panels by averages of 65%, 59%, and 74%, respectively.
•The study introduces three bio-inspired blast mitigation systems that can reduce the pressure values behind their panels.•The proposed steel panels are based on the mimicry of the falcon's nostril, orca's jaw, and pangolin-armadillo scales.•The blast performance of the three developed bio-inspired systems is numerically compared to conventional steel systems.•Performance charts are presented to illustrate the protection levels of the systems under different explosion scenarios.•The results can be utilized in future studies to address other complex engineering challenges using bio-inspired systems.
The optimization of the information flow from the initial design and through the several production stages plays a critical role in ensuring product quality while also reducing the manufacturing ...costs. As such, in this article we present a cooperative welding cell for structural steel fabrication that is capable of leveraging the Building Information Modeling (BIM) standards to automatically orchestrate the necessary tasks to be allocated to a human operator and a welding robot moving on a linear track. We propose a spatial augmented reality system that projects alignment information into the environment for helping the operator tack weld the beam attachments that will be later on seam welded by the industrial robot. This way we ensure maximum flexibility during the beam assembly stage while also improving the overall productivity and product quality since the operator no longer needs to rely on error prone measurement procedures and he receives his tasks through an immersive interface, relieving him from the burden of analyzing complex manufacturing design specifications. Moreover, no expert robotics knowledge is required to operate our welding cell because all the necessary information is extracted from the Industry Foundation Classes (IFC), namely the CAD models and welding sections, allowing our 3D beam perception systems to correct placement errors or beam bending, which coupled with our motion planning and welding pose optimization system ensures that the robot performs its tasks without collisions and as efficiently as possible while maximizing the welding quality.
•BIM (Building Information Model) processing and vertical information flow.•Enables streamlining production by optimizing poses, configurations and placements.•Provide immersive human machine interface for helping human operators perform their tasks, via spatial augmented system.•Fixes gaps, correct deviation and automatically proceeds to an efficient beam welding operation.
The ductile fracture characteristics of Chinese Q460 high strength structural steel under quasi-static condition were studied by using mechanical tests of four types of notched specimens. The ...influence of stress state on fracture mechanism of the material was investigated by observing the fracture surfaces of all test specimens using the Scanning Electron Microscope. Meanwhile, corresponding numerical simulations were conducted to collect the critical stress and strain at notch for all test specimens. The effects of stress triaxiality and Lode angle parameter, which were found to be the key parameters governing the ductile fracture of metallic material in many studies, on fracture strain of the Q460 structural steel were investigated. The analysis results show that different fracture mechanisms were observed in different stress triaxiality regions. At high stress triaxialities, Q460 steel exhibits a typical mechanism of “void nucleation, growth and coalescence”. When stress triaxiality equals to zero, a shear fracture mechanism was observed. At low stress triaxiality values, fracture develops as a combination of shear and void growth modes. In addition, the ductility of Q460 structural steel under pure shear or plane strain is lower than that under axisymmetric tension, especially at low stress triaxiality.
•The notch has an “embrittling and strengthening” effect on Q460 structural steel.•The stress triaxiality controls the ductility and fracture mechanism of the steel.•The ductility of Q460 steel is different under different Lode angle parameter.•The results can be used to calibrate micromechanical fracture models for Q460 steel.
The mechanical properties of high strength structural steel (HSSS) at elevated temperatures are the basis for fire-resistant design of HSSS members and structures. Previous studies on the mechanical ...properties of HSSS at elevated temperatures were mainly conducted on QT (Quenched and Tempered) HSSS, while few studies were conducted on TMCP (Thermo-Mechanical Controlled Process) HSSS. In order to identify the effect of manufacturing process on the mechanical properties of HSSS at elevated temperatures, an experimental study was carried out by steady-state method on TMCP Q690 HSSS, considering nine elevated temperatures ranging from 200 to 800 °C. Results showed that the elastic modulus and strength of TMCP Q690 HSSS decreased significantly as the temperature increased over 400 °C, while the ultimate elongation increased as the temperature increased above 500 °C. Formulas for calculating the reduction factors of mechanical properties of TMCP Q690 HSSS at elevated temperatures were proposed. Comparing the results of TMCP Q690 HSSS with those of QT Q690 HSSS previously studied, it can be found that the reduction on elastic modulus and strength was more severe for TMCP Q690 HSSS than QT Q690 HSSS in most cases, which was explained in the microstructure level of HSSS.
Localized attack can negatively affect the mechanical properties and durability of high strength low alloy steels. The present work investigates the effect of inclusions on the susceptibility to ...pitting attack of 42CrMo4 QT steel (quenched and tempered condition). A detailed characterization of the microstructure of the steel was performed by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy in order to evaluate the morphology and chemical composition of the inclusions. The initiation of pitting corrosion at the inclusion sites was investigated with a localized approach combining topographic and surface potential maps obtained by means of the scanning Kelvin probe force microscopy technique and the morphology of inclusion sites after the immersion in an aggressive electrolyte. The effect of different inclusion types (clusters combining Al2O3 and MnS and containing Ca and Mg or single MnS based inclusions) is discussed in the present work taking into account their galvanic coupling with the surrounding steel matrix and the existence of gaps at the periphery of the inclusions promoting the formation of an occluded cell.
High strength structural steel (HSSS) can be divided into TMCP (Thermo-Mechanical Controlled Process) and QT (Quenched and Tempered) types according to the manufacturing process. Most previous ...studies on the post-fire mechanical properties of HSSS were conducted on QT HSSS, while few studies were conducted on TMCP HSSS. In order to identify the effect of manufacturing process on the post-fire mechanical properties of HSSS, experimental studies were carried out on TMCP Q550 and TMCP Q690 HSSS and the results were compared with the previous studies on corresponding QT Q550 and QT Q690 HSSS. The static tensile tests were conducted at ambient temperature on TMCP Q550 and TMCP Q690 HSSS specimens heated up to nine pre-selected temperatures ranging from 200 to 900 °C and then cooling in air and water respectively to simulate various post-fire situations. It can be found that the heating and cooling process had little influence on elastic modulus but significant effect on strength and ultimate elongation once the heated temperature exceeded 600 °C, and the cooling way and manufacturing process became critical once the heated temperature exceeded 700 °C. In general, the post-fire strength and ultimate elongation was always less for TMCP HSSS than QT HSSS.
Deep cryogenic treatment (DCT) is believed to have superior performance in coordination with traditional heat treatment. In present work, the effect of DCT combined with inter-critical quenching ...treatment on the mechanical properties and microstructure of 30CrMnSi alloy structural steel was investigated. Before DCT employed, quenching treatment was conducted at different austenitizing temperatures (780 °C, 820 °C and 900 °C) to obtain diverse initial states of microstructure. The influence of different sequence between DCT and tempering was also studied. The results showed that compared to quenching-tempering (QT) treatment, the impact toughness of 30CrMnSi alloy austenitized at all the three temperatures was improved by conducting DCT after quenching and tempering (QTC). The strength and toughness were concurrently improved by quenching-tempering-cryogenic (QTC) treatment at the austenitizing temperature of 820 °C. Microstructural characterizations were carried out by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). Strip ferrite and lath martensite were refined, as well as high-angle grain boundaries increased after 820-QTC. Deep cryogenic treatment has also promoted the dispersed precipitation of stable carbides in the boundaries of ferrite and martensite, through constricting the martensite lattice and increasing the nucleation energy under ultra-low temperature.
Laser cutting represents an appealing solution for high machining speed and precision in steel constructions. To control the efficiency of laser cutting, the effects of laser heating must be ...understood; and to investigate thermal effects on a steel workpiece, a methodological approach for analytical modeling of laser cutting heat source is proposed herein. The proposed model takes into account laser source geometry variation along the cut edge thickness. Given the complexity of the analyzed process, there is no accurate mathematical formulation capable of modelling both heat flux and temperature distribution. Therefore, to model heat flux with an accurate temperature distribution field and both calibrate and validate solid phases of a cut specimen, the paper proposes a modified heat source based on a Gaussian distribution. The study focuses on mild structural steel S235N and relevant commonly used laser cutting parameters for structural applications. More precisely, the model allows the laser cutting process to be simulated as a function of laser beam diameter, cutting speed, laser power and element thickness. Thus, to simulate the thermal process by means of a proper heat source, a model was implemented in the FE software Abaqus. Model parameters were both calibrated and validated through experimental results provided by online monitoring of laser cutting process with a thermal camera and location of microconstituents. In particular, the temperature profiles obtained from the proposed FE model, exhibit a good agreement with experimental results. Finally, the distribution of microconstituents along the depth agrees with predicted temperature profiles.
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