دانلود رایگان مقاله مقایسه مقاطع توخالی مستطیلی متشکل گرما و سرما

Abstract

This paper presents a comparative experimental study on the physical, chemical and mechanical properties of indirectly formed hot-formed, hot-finished and cold-formed structural steel rectangular hollow sections. Characteristic geometrical parameters and chemical compositions are examined to investigate the physical and chemical differences. Tensile test and charpy V-notch impact test are employed to evaluate the difference in strength, ductility and toughness. Further, the residual stress distributions in both transverse and longitudinal directions are measured using the sectioning method and hole-drilling technique. It is found out that although the geometrical parameters and chemical composition of the tested hollow sections are similar, the mechanical properties are significantly different, especially for strength, ductility and residual stress distribution. While the hot-finished and hot-formed sections are often treated equally in design, their mechanical properties and residual stresses distribution are actually different.

4. Conclusions

A three-phase comparative experimental study was carried out to investigate the influence of different manufacturing techniques on the properties of cold-formed, hot-formed and hot-finished thick-walled structural hollow sections (SHSs). Phase-1 investigated the differences in the geometrical profiles and chemical composition. Phase-2 analyzed the difference in the common mechanical properties such as yield stress, tensile stress, ductility and impact toughness. Phase-3 evaluated the distribution and effect of residual stress through sectioning and hole-drilling techniques. The test results reveal that although the geometry and chemical composition of the tested SHSs are comparable, the mechanical properties are remarkably different. Although the hot-finished SHS shows yield plateau as the hot-formed SHS does,the ductility in terms of elongation and tensile ratio is not as good as that ofthe hot-formed SHS. While the cold-formed SHS shows much higher strengths, the stress-strain relationship is much worse than the other two SHSs. It is also shown that the residual stresses in the hot-formed SHS is generally compressive and low in stress level in terms of residual stress/yield strength ratio. The cold-formed SHS has lower stress level in the corner areas than that in the flat and welding areas and the distribution pattern is different from that of the well-known cold-formed thin-walled SHSs. Besides, although the hot- finished SHSs are treated equally to the hot-formed SHSs in design, their residual stress distribution pattern is actually similar to that of the cold-formed SHSs but the stress level is much lower than the later due to stress relief heat treatment.