Comparative experimental study of hot-formed, hot-finished and cold-formed rectangular hollow sections

دسته: , تاریخ انتشار: 30 فروردین 1400تعداد بازدید: 307
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جزئیات بیشتر

انتشار

۲۰۲۱

پایگاه داده

نشریه الزویر

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مقاله پژوهشی

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scopus – master journals – JCR

ایمپکت فاکتور

۴٫۲۷۶ در سال ۲۰۲۰

شاخص H_index

۲۶ در سال ۲۰۲۱

شاخص SJR

۰٫۹۰۱ در سال ۲۰۲۰

شاخص Quartile (چارک)

Q1 در سال ۲۰۲۰

مدل مفهومی

ندارد

پرسشنامه

ندارد

متغیر

ندارد

رفرنس

دارد

قوانین استفاده

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Comparative experimental study of hot-formed, hot-finished and cold-formed rectangular hollow sections


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Comparative experimental study of hot-formed, hot-finished and cold-formed rectangular hollow sections

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 signifi- cantly 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.

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  1. Introduction

Structural Hollow Sections (SHS),  especially rectangular hollow sections, are  widely used in  construction due to  the recognition of the inherent aesthetic and structural advantages. Currently, SHSs of steels are classified into two major groups based on the manufacturing methods: cold-formed and hot-finished, in which hot-finished hollow sections consist of another two types, i.e. hollow sections formed hot and formed cold  with subsequent heat treatment (hot-formed and hot-finished, respectively) [1,2].  Although these three types of SHSs are  manufactured by either direct or  indirect forming techniques, the rolling condition/subsequent heat treatment processes lead to significant differences in properties [3]. Through decades of study and practice, the importance of physical, chemical and mechanical properties for  designing and analyzing steel structures has  been well recognized. Based on the preference on these properties, hot-formed sections are  widely favored as the first choices, while cold-formed hollow sections are  often misunderstood and treated unfavorably although they are actually easier to  manufacture and more economical [4].  As for  hot-finished sections, they are  often treated the same as hot-formed sections in mechanical properties, provided that the sections formed cold  are  fully  annealed in the subsequent heat treatments [5,6].

Among the differences among the three types of SHSs, residual stress is the most frequently concerned, as  it is often associated with issues such as brittle fracture, fatigue, stress corrosion, buckling and post-buckling strength reduction [7–۹]. In practice, the SHSs produced by hot-forming techniques are  considered to be residual stress free  and have no  change in mechanical properties from base metal [10].  The  concerns for  locked-in residual stresses are  mainly for  cold-formed and hot-finished SHSs, as they are  formed cold  by bending in the beginning. For residual stress contained in cold-formed  SHSs, numerous work has  been done. Detailed studies of through thickness residual stresses in the longitudinal and transverse directions of square and circular cold-formed thin-walled SHSs can  date back to 1980s by stripping method [10].  Later,  the through thickness residual stress distribution in cold-formed thin-walled SHSs by panel removal method is also  reported [11]. Nowadays, it is well recognized that for cold-formed thin-walled SHSs, the longitudinal residual stresses are  in tension at outer surface and in  compression at inner surface, and the distribution is assumed to  be  linear through the thickness [12]. However, studies on the cold-formed thick-walled plate subjected to bending [13,14] show that the through thickness residual stress distribution pattern is not linear. Tong  et al. measured the longitudinal residual stress distribution of cold- formed thick-walled SHS and found out the through thickness distribution was different from that of the thin-walled and dependent on  the geochemical profile [15].  On the other hand, different from the cold-formed SHS, the concern with the hot-finished SHS is that it is difficult to  make sure the sections formed cold  are  subsequently “properly” heat treated and successfully get  rid  of the issues associated with cold-forming techniques [16].  Currently, common design standards have taken the effect of residual stresses in consideration  implicitly [17–۱۹]. However, there is still  few  specific guidelines on designing and evaluating the distribution and amount of the residual stress itself in a given SHS, especially for thick-walled cold-formed and hot-finished SHSs.

In this study, the influence of different manufacturing processes on the physical, chemical and mechanical properties of popular thick-walled SHSs including hot-formed and hot-finished square SHSs manufactured to Grade S355J2H of EN 10210 [2] and cold-formed square SHS complying EN10219 [1] Grade S355J2H is investigated experimentally. The aim is to provide useful data for the EN Standards and engineers as reference. This comparative study is carried out in three phases. Firstly, physical and chemical properties are  examined to  investigate the difference in  the geometry and chemical composition. Secondly, tensile test and chapry V-notch impact test are  conducted to analyze the difference in the mechanical properties such as yield stress, tensile stress, ductility and impact toughness. Thirdly, sectioning test and hole-drilling test are employed to evaluate the locked-in residual stress in the SHSs qualitatively and quantitatively. By comparing the performance of the tested SHSs in the above three phases, the differences among the tested SHSs are  evaluated.

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