Corner material properties of cold-formed lean-duplex stainless steel sections at elevated temperatures

Material properties at corner parts of cold-formed sections are different from their flat counterparts. Currently, there is lack of investigation into corner material properties of cold-formed stainless steel sections at elevated temperatures. This paper presents a careful experimental study on corner material properties of cold-formed lean-duplex stainless steel (LDSS) sections at elevated temperatures. The corner coupons were extracted from rectangular hollow sections (RHS) cold-formed from grade EN 1.4162 LDSS strips. Tensile corner coupon tests were conducted by using steady state test method for temperatures up to 850 degrees C. The full-range stress-strain curves at 12 different temperatures were obtained with key material properties derived. The corner coupon test results were compared with flat coupon test results previously reported in the literature. The comparison results demonstrated that the material strengths at corner parts of cold-formed RHS generally deteriorated more severe than their flat counterparts at elevated temperatures, especially for temperatures exceeding 550 degrees C. The obtained reduction factors were compared with design values codified in current EN 1993-1-2. New design curves to predict the deterioration of corner material properties of cold-formed LDSS RHS at elevated temperatures were proposed. A constitutive model was proposed to predict the stress-strain relationship of the corner coupon specimens. It is shown that the proposed reduction factors and stress-strain model can be used to predict the corner material properties of cold-formed LDSS RHS at elevated temperatures. The impact of elevated temperature history on corner material properties of cold-formed LDSS RHS was also explored.