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This paper reports an experimental investigation of the mechanical properties of cold-formed lean duplex stainless steel after exposure to high temperatures up to 1000 °C. The test specimens were extracted from rectangular and square hollow sections that were cold-rolled from flat plates of lean duplex stainless steel. The mechanical properties, Young's modulus, yield strength, ultimate strength, Ramberg-osgood parameter and strain at ultimate strength of lean duplex stainless steel, are reported. The residual mechanical properties of steel materials are compared with the predicted values calculated by the existing equations. It is shown that the existing equations cannot provide accurate predictions for the post-fire mechanical properties of lean duplex stainless steel materials. Thus, a unified equation is proposed to predict residual mechanical properties for lean duplex stainless steel specimens in post-fire conditions. A constitutive model is also proposed to predict the stress-strain relationship of the test specimens after exposure to high temperatures up to 1000 °C. A reliability analysis was conducted for the proposed equation. The proposed equation compared favourably with the experimental results, and was found to be reliable for predicting lean duplex stainless steel mechanical properties after exposure to high temperatures. [ABSTRACT FROM AUTHOR]

The structural performance of cold-formed lean duplex stainless steel beams at elevated temperatures ranging from 24 to 900 °C was investigated in this study. A finite element model was developed. The numerical analysis covered the specimens of square and rectangular hollow sections. The material properties obtained from tensile coupon tests on lean duplex stainless steel at elevated temperatures were used in the finite element model. A total of 125 numerical flexural strengths were obtained from the finite element analysis. The numerical results were compared with the design values calculated by the existing design rules, including the American Specification, Australian/New Zealand Standard, European Code, direct strength method and continuous strength method. The suitability of these design rules for lean duplex stainless steel beams at elevated temperatures was assessed using reliability analysis. It was shown that the existing design rules are generally quite conservative in predicting the flexural strengths at elevated temperatures, except that the modified direct strength method provides accurate and reliable predictions. Therefore, it is recommended that the modified direct strength method be used for cold-formed lean duplex stainless steel beams at elevated temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Tensile coupon tests are commonly carried out to determine the material properties of metallic materials in research and industry. However, ambiguities are found in the current specifications in determining initial Young's modulus of material, which may lead to different test results. The material properties lay the crucial foundation in research and structural design. Different researchers may interpret coupon test results differently. Therefore, standard procedures of coupon test and the interpretation of test results are important and worth investigating. In this study, a series of tensile coupon tests on metallic materials, such as cold-formed carbon steel, cold-formed stainless steel and aluminum alloy, were carried out using different test and data analysis procedures. Two types of stainless steel materials, namely lean duplex and ferritic, were investigated. The test and data analysis procedures of loading rate on coupon specimens, determination of cross-sectional area of curved coupons and Young's modulus were carefully designed. In this study, tensile coupon test and data analysis procedures are proposed for both flat and curved coupons. The proposed procedures are able to eliminate possible errors and provide clear guidelines for tensile coupon tests. [Copyright &y& Elsevier]

Abstract: This paper describes a test program on cold-formed lean duplex stainless steel members in combined compression and minor axis bending. The test specimens were cold-rolled from flat strips of lean duplex stainless steel grade EN 1.4162. In this study, square and rectangular hollow sections were compressed at different eccentricities, in order to obtain a beam-column interaction curve for each series of tests. Initial overall geometric imperfections of the members were measured prior to testing. The ultimate loads and the failure modes of each specimen were obtained. The observed failure modes include local buckling, flexural buckling and interaction of local and flexural buckling. The test strengths obtained from this study and other available data were compared with the design strengths predicted by the American Specification, Australian/New Zealand Standard and European Code for stainless steel structures. It should be noted that these specifications do not cover the material of lean duplex stainless steel. Therefore, the suitability of the beam-column design rules in these specifications for lean duplex stainless steel is assessed in this study. Generally, these specifications are capable of predicting the beam-column strengths of the lean duplex stainless steel test specimens, and the design rules in the specifications are considered to be reliable. It is observed that the European Code generally provides quite conservative predictions for the beam-column specimens compared to the American Specification and Australian/New Zealand Standard predictions. [Copyright &y& Elsevier]

Abstract: A test programme to examine the material properties of a relatively new cold-formed lean duplex stainless steel at elevated temperatures is presented. A total of 80 tensile coupon tests were carried out by both steady state test method and transient state test method for temperatures ranged from 24 to 900°C. The coupons were extracted from square and rectangular hollow sections. Material properties including thermal elongation, Young's modulus, yield strength, ultimate strength and ultimate strain were obtained. The test results and available data were compared with the design values in the European Code as well as a unified equation by Chen and Young [1] for stainless steel. The lean duplex stainless steel is not covered by these design rules. Reliability analysis was carried out to assess the applicability of these existing design rules. It is shown that the material properties of lean duplex stainless steel at elevated temperatures cannot be well predicted by the existing design rules. Modification to the existing design rules for lean duplex stainless steel at elevated temperatures is proposed. The stress–strain curves of the test specimens under different temperatures were plotted and compared with stress–strain curves predicted by the unified equation using modified coefficients. It is shown that the stress–strain curves and other material properties predicted by the modified design rules agree well with the test results. [Copyright &y& Elsevier]

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]

The behaviour of cold-formed lean duplex stainless steel columns at elevated temperatures was investigated. A numerical investigation on columns of square and rectangular hollow sections were performed at elevated temperatures ranged from 24 to 900 °C. A validated numerical model with material properties obtained from tensile coupon tests at elevated temperatures were used in the finite element analysis. A total of 180 numerical column strengths were compared with design column strengths predicted by existing design rules, which do not cover the lean duplex stainless steel material at elevated temperatures. Reliability analysis was carried out to assess the suitability of the existing design rules for lean duplex stainless steel columns at elevated temperatures. It is shown that the existing design rules are generally not suitable for predicting the column strengths, except for the American Specification and the modified direct strength method for stainless steel. The modified direct strength method for stainless steel provides accurate and reliable predictions with relatively simple calculation procedure. Therefore, it is recommended that the modified direct strength method for stainless steel be used for design of cold-formed lean duplex stainless steel columns at elevated temperatures. • Finite element model of lean duplex stainless steel columns were developed. • Finite element analysis of 180 pin-ended columns was carried out. • The numerical specimens were subjected to temperatures from 24 - 900 °C. • Various existing design rules were assessed by compared with 180 columns. • Design rules are recommended for lean duplex stainless steel columns at elevated temperatures. [ABSTRACT FROM AUTHOR]