冷間成形角形鋼管の塑性ひずみ履歴と残留応力

概要

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Cold-formed square steel tubes (STKR 41) with 6 sizes of section are examined to clarify plastic strain history along the cold-forming pass. By comparing the thickness of tube with the corresponding sheet coil, the flat part of square steel tube is estimated to receive plastic strain of 3〜5 % approximately. As the matter of fact, yield stresses of tube rise up 1.1〜1.5 times higher than those of the sheet coil. The tensile strengths, however, are independent of the plastic strain history. Therefore, it makes the yield ratio increase up to 0.85〜0.95. Released strains are measured by saw cutting method. Compressive strains of 1500〜700μ are observed along the longitudinal direction at the outer surface. On the contrary, tensile strain of 200〜500μ are obtained to the circumferential. These released strains are converted to the corresponding elastic stress approximately 35〜15 (kgf/mm^2), which is 80〜40 % of the yield stress at the flat part of tube. Assuming the plastic strain pass during the cold-forming process, elastic-plastic two-dimensional numerical analysis is carried out. As the results, complex distributions of residual stresses locked in the section are obtained. Considering the influence of plastic strain history and residual stresses, the global behaviors of square steel tubes are discussed by comparing with the experimental results under stub column test.
1988-03-30