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Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the increasing global demand for green and environmentally friendly materials, advanced high-strength steels (AHSS) produced using by cold rolling process are gaining more attention in the construction industry, such as in cold-formed thin-walled structures. To expand their engineering applications, the study of the mechanical behavior and constitutive models of AHSS is particularly important. This paper focuses on DP1180 and Q&P1180, employing experimental research and theoretical analysis to elucidate the patterns at various characteristic points and establish constitutive models for AHSS. The specific conclusions are as follows: 1) For DP1180 and Q&P1180, the average elongation after fracture is 8.9 % and 16.7 %, respectively, with strength-to-yield ratios ranging from 1.24 to 1.34 and 1.14–1.24, respectively. 2) Due to the insignificant nonlinearity exhibited by DP1180 and Q&P1180 near the nominal buckling strength, the modified nominal yield strength and equivalent ultimate strength was defined and adopted as the boundaries to divide the stress-strain curve into three segments. The mathematical expressions and relevant parameter models for each segment are established. Finally, the three-stage AHSS uniaxial tensile constitutive model was established. Compared to existing models, the proposed model demonstrates higher accuracy. • The stress mechanisms of advanced high-strength steels have been clarified. • A modified nominal yield strength model and equivalent strength model were established. • A three-stage AHSS uniaxial tensile constitutive model was established. [ABSTRACT FROM AUTHOR]

• Mechanical properties of titanium-clad bimetallic steel (TCBS) after cold forming revealed. • Cold forming–fire exposure coupling effects on TCBS mechanical properties clarified. • Constitutive model to quantify stress–strain curve of TCBS after cold forming devised. Titanium-clad bimetallic steel (TCBS), composed of a titanium alloy cladding layer and carbon steel substrate layer, has been proposed to mitigate the effects of corrosion and enhance the durability of steel structures. This study conducted tensile coupon test to explore the coupling effect of the cold-forming process and fire exposure on the monotonic mechanical properties of TCBS. Following the cold-forming process and fire exposure, there was no visible cracking observed in either the cladding or the metallurgical bonding layer. Test results revealed a notable enhancement in the strength properties and a decrease in the ductility of the TCBS specimens after cold forming. Moreover, the study elucidated the effects of the exposure temperature and cooling method on the stress–strain curves and fractures of TCBS corner specimens. Three different fracture sequences of the TCBS corner specimens were observed during monotonic tensile test. The key mechanical parameters were concerned in this study, which included the yield and ultimate strengths, yield and ultimate strains, elastic modulus, elongation after fracture, and section shrinkage. Then, the variation trends of key mechanical parameters were clarified. Predictive equations were developed for these parameters of the TCBS corner specimens after fire exposure. Additionally, two constitutive models were developed for the corner TCBS stress–strain curves with and without the yield plateau, enabling their use in numerical and theoretical investigations of the post-fire performance of cold-formed TCBS components. [ABSTRACT FROM AUTHOR]

This paper describes experimental and numerical investigations conducted to characterize the basic material properties and design of YSt–310 cold–formed structural steel sections at Indian Institute of Technology, Guwahati. Square (SHS) and rectangular (RHS) hollow sections with minimum yield strength of 310 MPa manufactured by Tata Steel India, were considered in the study. Initially, results from elemental analysis via optical emission spectrometer (OES) investigation and metallographic examination using optical microscope are presented. Key stress–strain parameters viz., Young's modulus, proof stress, ultimate strength, percentage elongation, strain hardening exponent etc. were generated based on flat, corner and weld coupon tests data. Extent of corner strength enhancement due to cold – forming determined using Vickers's microhardness test are reported. Additionally, cross – section capacity of the stub columns were also investigated experimentally and numerically. The column capacities generated from test and finite element study are compared with the existing design code – EN 1993–1–1 (EN 1993-1-1, 2005) [1] and design rules – continuous strength method (CSM) (Zhao et al., 2017) [2] and direct strength method (DSM) (North American Specifification for the Design of Cold-Formed Steel Structural Members, 2016; Arrayago et al., 2017) [3,4]. Based on the comparison, modifications on the existing design code and rules are suggested to provide a more accurate and reliable compressive design prediction. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the behaviour of cold-formed lean duplex stainless steel for six different sections, among which two are square hollow sections and four are rectangular hollow sections. The test specimens were cold-rolled from flat strips of lean duplex stainless steel. The material properties of high strength cold-formed lean duplex stainless steel square and rectangular hollow sections were determined. Tensile coupons in the flat portions and corners of each section were tested. Hence, the Young''s moduli, 0.2% proof stresses, 1.0% proof stresses, tensile strengths, elongation at fracture and the Ramberg–Osgood parameter (n) of lean duplex material for each section were measured. The material properties of the complete cross-sections in the cold-worked state were also obtained from stub column tests. The initial local geometric imperfections of the six sections were measured, and the profiles of the local imperfections along cross-section were plotted for each section. Residual stresses were measured for section 150×50×2.5 using the method of sectioning. The membrane and bending residual stress distributions in the cross-section were obtained and plotted. Furthermore, finite element model of stub columns was developed and compared well with the test results. The stub column test strengths were also compared with the design strengths predicted by the American Specification, Australian/New Zealand Standard and European Code for stainless steel structures. Generally, the three specifications conservatively predicted the column strengths. The European Code provides the most conservative prediction. [Copyright &y& Elsevier]

Phenolic-based composite tubes are being used in industry due to their high fire resistant and lower yields of heat and toxic fumes. These tubes can be better designed by changing the ply-orientation to meet desired performance requirements. This study aims to numerically evaluate the influence of the winding angle and stacking sequence on the mechanical performance of glass/phenolic composite tubes subjected to tensile and radial compression loadings. An extensive study, using the LS-DYNA finite element software, was employed to obtain the optimal ply angle and layup condition of the tubes. The numerical results were in good agreement with the experimental data. Failure modes, tensile stress versus percentage elongation behavior, load–displacement behavior, and stiffness of the tubes were investigated. The behavior of the tubes was found to be highly dependent on the winding angles and stacking sequence, i.e., the specimens with fibers at ± 75° and ± 80° presented the best radial compressive characteristics, whereas those wound at ± 55° performed better under coupon tensile testing. In addition, following the design guidelines of using balanced, symmetric, and homogeneous stacking sequence with 10% of plies in the ± 45 ° , instead of the classical unidirectional ply [ ± θ ] can lead to significantly improved optimal designs. [ABSTRACT FROM AUTHOR]

As a result of altered chemical composition, multiphase microstructures, and other micromechanical change, advanced high strength steel (AHSS) has three to five times the strength of conventional mild steels. Developed for automotive applications, AHSS has high potential for application in cold-formed steel construction. However, the material properties must be properly understood and quantified for application to structural design with economic efficiency. A series of tensile coupon tests were carried out to determine typical AHSS material properties. Existing stress-strain models, designed for steels with gradual strain hardening, were studied and recalibrated to the AHSS test data. No existing method provided an accurate fit for all cases. An updated two-stage plus linear stress-strain model, based on the Ramberg-Osgood expression, was developed. The predictive equations for the parameters required by the new model were provided based on the statistical analysis of AHSS test data. In addition, from the discussion of the new model, a novel proof stress was recommended to represent the yield strength of AHSS. Energy was used to compare the AHSS experimental stress-strain curves with conventional steel stress-strain models to examine the rationality of the proposed proof stress as the yield strength in design. [Display omitted] • Advanced high-strength steels (AHSS) have different stress-strain behaviors from conventional cold-formed steels. • Existing models based on Ramberg-Osgood expression do not provide accurate fit of AHSS data, thus a new model is developed. • Required properties of the new model cannot be accurately predicted by existing equations, thus new equations are proposed. • 0.2% proof stress may not be used as the yield strength of AHSS while a proposed proof stress shows better rationality. [ABSTRACT FROM AUTHOR]

Steel structures have been increasingly applied in contemporary infrastructures, which always require high loading capacities and strong resistance to disasters such as earthquake actions, fire and environmental corrosion, etc. Recently a superior high-performance (SHP) steel is developed accordingly, possessing combined beneficial features of high-strength, high-ductility, corrosion-resistance and fire-resistance, which may well satisfy the structural requirements. The present study aims to investigate mechanical properties of the SHP steel at elevated temperatures and to propose its constitutive models for further usage in fire design and analyses of structural members. A comprehensive experimental programme including a series of standard tensile coupon tests at both ambient and elevated temperatures is described herein, and key mechanical properties including modulus of elasticity, yield strength, ultimate tensile stress as well as stress-strain curves of the SHP steels are obtained based on the test results. Reduction effects of elevated temperatures on their mechanical properties are quantitatively clarified, and further comparisons with prediction results in accordance with national standards as well as with independent test results reported in literature are made. It is indicated that the mechanical properties of the SHP steels differ significantly from that of conventional mild steel and fire-resistant steel. Specific prediction equations are proposed for evaluating the temperature-dependent mechanical properties of the SHP steel; furthermore, an adapted Ramberg-Osgood model is developed for describing its full range stress-strain relation. The research outcomes of the present research may serve as an essential basis for better understanding mechanical performance of the SHP steel at elevated temperatures as well as for further investigations on its structural members' behaviour; and it is helpful to promote its application in practice. Unlabelled Image • 60 tensile coupons of superior high performance steel are tested. • Mechanical properties at ambient and nine elevated temperatures are obtained. • Reduction factors of material properties at elevated temperatures are clarified. • Prediction equations are proposed for elevated-temperature material properties. • Constitutive model of full-range stress-strain relation is proposed. [ABSTRACT FROM AUTHOR]

• Effects of loading mode on mechanical properties of high strength steel (HSS) Q690 were studied. • Stress relaxation has negligible effect on dynamic ultimate strength and strain on HSS Q690. • Suggestions on tensile coupon test to obtain static mechanical properties of HSS Q690 were proposed. • Parameters of the Cowper-Symonds model were calibrated for strain rate effect of HSS Q690. The coupon test methods specified in the current specifications do not satisfactorily address the strain rate effect on mechanical properties of materials, which may cause some deviations in the results. Therefore, there is a demand for alternative loading modes of coupon test. In this paper, effects of loading mode on the mechanical properties of high strength steel (HSS) Q690 were tested, considering monotonic tensile coupon test, tensile coupon test with displacement-controlled holds, and tensile coupon test with strain-controlled holds. Parameters such as pre-strain, loading rate, hold times, and hold duration were considered. Results show that the yield strength, ultimate strength, and ultimate strain of steel Q690 were hardly affected by the stress relaxation induced by holds, while increase with the increase of loading rate. The largest difference of the ultimate strength induced by loading mode was 6.2 MPa which is less than 1% of the ultimate strength of the material, and that of the ultimate strain was 5.8E-3. The stress drop during stress relaxation increases with the increase of pre-strain and strain rate. The normalized stress drop at the pre-strain of 0.04 could be 37.4% larger than that at the pre-strain of 0.01. The normalized stress drop of specimen with strain rate of 0.001/s could be 27.7% larger than that with strain rate of 0.0001/s. Tensile coupon test with two displacement-controlled holds is proposed to obtain the static mechanical properties of HSS Q690. Based on the test results, the values of parameters of the Cowper-Symonds model were calibrated to consider the effect of strain rate on the dynamic yield strength and ultimate strength, respectively, of steel Q690. [ABSTRACT FROM AUTHOR]

• The pre-fatigue damage reduces tensile strength and ductility of Q690 steel. • The ductility of Q690 steel sharply decreases with increasing pre-fatigue damage. • The influence of pre-fatigue damage on the elastic modulus of Q690 steel is negligible. • The proposed equation can predict the residual mechanical peroperties of Q690 steel. This paper investigates the residual strength of Q690 high-strength steel previously damaged by fatigue. Pre-fatigue damage was induced by subjecting the specimens to nine different loading cycles without causing fracturing under three initial cyclic loadings, and then subsequent tensile tests were performed on these pre-fatigued specimens to obtain their stress-strain curves and associated mechanical properties (yield strength, ultimate strength, elastic modulus and ultimate elongation). Systematic comparative analyses for the evolution of residual mechanical properties of Q690 high-strength steel with different pre-fatigue damages were carried out. Significant differences are observed in the fracture position and the morphological features of fractures of Q690 high-strength steel with different pre-fatigue damages. Meanwhile, pre-fatigue damage also exerts distinct influences on yield strength, ultimate strength and ultimate elongation of Q690 high-strength steel. Specifically, the dramatic reduction is especially noted in ultimate elongation of Q690 high-strength steel due to pre-fatigue damage. In contrast, the influence of pre-fatigue damage on the elastic modulus of Q690 high-strength steel is negligible. When pre-fatigue damage is ranging from 0 to 0.6, the maximum decrease of ultimate elongation reaches up to 49.3% and the maximum reduction of yield strength is 11.1%, however the decline of elastic modulus is less than 4.0%. According to the experimental results, a new set of predictive equations were proposed to determine the mechanical properties of Q690 high-strength steel with pre-fatigue damage and to provide the fundamentals for appropriate pre-fatigue damage evaluation of Q690 high-strength steel structures. [ABSTRACT FROM AUTHOR]

Current guidelines stipulate a sample size of five for a tensile coupon test of fiber reinforced polymer (FRP) composites based on the assumption of a normal distribution and a sample coefficient of variation (COV) of 0.058. Increasing studies have validated that a Weibull distribution is more appropriate in characterizing the tensile properties of FRP. However, few efforts have been devoted to sample size evaluation based on a Weibull distribution. It is not clear if the Weibull distribution will result in a more conservative sample size value. In addition, the COV of FRP's properties can vary from 5% to 15% in practice. In this study, the sample size based on a two-parameter Weibull distribution is compared with that based on a normal distribution. It is revealed that the Weibull distribution results in almost the same sample size as the normal distribution, which means that the sample size based on a normal distribution is applicable. For coupons with COVs varying from 0.05 to 0.20, the sample sizes range from less than 10 to more than 60. The use of only five coupons will lead to a prediction error of material property between 6.2% and 24.8% for COVs varying from 0.05 to 0.20. [ABSTRACT FROM AUTHOR]