The paper implements a method for analyzing the stress-strain state of rectangular hollow sections (RHS) by finite-element modeling (FEM) of tests for three-point bending and torsion. Design schemes, 3-D solid-state and deformable models have been developed using the automated analysis and CAD/CAE system software, made it possible to obtain equivalent stress distributions and displacements in models. A simulation of tests for RHS with a cross section of 40 mm × 50 mm, manufactured in two ways, was carried out: (a) by direct-forming of galvanized steel strips on roll-forming mill in a semi-closed section with a longitudinal gap of 0.5 mm between the edges formed on a 40 mm web (DF-RHS); (b) similar direct-forming to the closed section and next welding the edges to a longitudinal weld along the web middle of 50 mm (DFW-RHS). RHS with various wall thicknesses (t = 1.93 mm, 1.84 mm and 0.7 mm) was investigated, given the design features that depend on the manufacturing processes of structural sections. It was found DFW-RHS is stiffer by at least 50% compared to DF-RHS, which allows to savings the metal by reducing the RHS wall thickness by 62% while maintaining the same stiffness and ensuring high strength of structural section.

Steel hollow sections are common for transport engineering, vehicles, highway guardrails. The special requirements for strength and stiffness are determined by tests. The three-point bending test experimental and FEM research were carried out on steel rectangular hollow sections (RHS) with a cross section of 40 mm × 50 mm, manufactured in two ways: (a) by cold bending of steel strips on roll-forming mill in semi-closed section with a longitudinal gap of 0.5 mm between the edges formed on a 40 mm web (B-RHS); (b) similar cold roll-forming to the closed section and welding with a longitudinal weld along the web middle of 50 mm (BW-RHS). As a result, the graphs and analytical equations for relating the force (P) and deflection (f) at load on 50 mm and 40 mm webs were obtained, and revealed the advantages of bent-welded sections (BW-RHS) by stiffness and strength. FEM was performed using the SolidWorks CAD/CAE system for various RHS wall thicknesses (t = 1.93 mm, 1.84 mm and 0.7 mm). It is shown that the BW-RHS design increase the stiffness by at least 50%, reduce the wall thickness by 61.9% while maintaining the same stiffness and ensuring the high strength indices for the case of least loading on the larger web, i.e. the maximum stresses in the RHS webs will be 2.33 times less than the yield stress of low-carbon steel.

The paper implements a method for analyzing the stress-strain state of rectangular hollow sections (RHS) by finite-element modeling (FEM) of tests for three-point bending and torsion. Design schemes, 3-D solid-state and deformable models have been developed using the automated analysis and CAD/CAE system software, made it possible to obtain equivalent stress distributions and displacements in models. A simulation of tests for RHS with a cross section of 40 mm × 50 mm, manufactured in two ways, was carried out: (a) by direct-forming of galvanized steel strips on roll-forming mill in a semi-closed section with a longitudinal gap of 0.5 mm between the edges formed on a 40 mm web (DF-RHS); (b) similar direct-forming to the closed section and next welding the edges to a longitudinal weld along the web middle of 50 mm (DFW-RHS). RHS with various wall thicknesses (t = 1.93 mm, 1.84 mm and 0.7 mm) was investigated, given the design features that depend on the manufacturing processes of structural sections. It was found DFW-RHS is stiffer by at least 50% compared to DF-RHS, which allows to savings the metal by reducing the RHS wall thickness by 62% while maintaining the same stiffness and ensuring high strength of structural section.

A significant factor, which leads to the discrepancy of the final sizes of the bent sheet parts to their drawings is the springing of the sheet blank during bending. At the same time, the springing during multi-pass bending is not sufficiently studied. The purpose of the work is to obtain the graphical and mathematical dependencies for descriptions of the resultative spring-back angle of the blanks at the multi-pass bending, taking into account the width of the blank, number of passes, and pre-bending angle at each preliminary pass. The paper describes the basic information about the difference between the spring-back angle for one-pass or multi-pass bending. In the course of the study it is shown that during calculations of forming and preventive prediction of the geometric quality of bending shapes it is necessary to take into account properties of the blank material, as well as the angles of the prebends and the width to thickness ratio of the blank. A methodology of experimental research was developed for determining the spring-back angle during multi-pass bending in three bending dies with 109°, 91° and 72° pass-by-pass reducing angles.

The paper implements a method for analyzing the stress-strain state of rectangular hollow sections (RHS) by finite-element modeling (FEM) of tests for three-point bending and torsion. Design schemes, 3-D solid-state and deformable models have been developed using the automated analysis and CAD/CAE system software, made it possible to obtain equivalent stress distributions and displacements in models. A simulation of tests for RHS with a cross section of 40 mm × 50 mm, manufactured in two ways, was carried out: (a) by direct-forming of galvanized steel strips on roll-forming mill in a semi-closed section with a longitudinal gap of 0.5 mm between the edges formed on a 40 mm web (DF-RHS); (b) similar direct-forming to the closed section and next welding the edges to a longitudinal weld along the web middle of 50 mm (DFW-RHS). RHS with various wall thicknesses (t = 1.93 mm, 1.84 mm and 0.7 mm) was investigated, given the design features that depend on the manufacturing processes of structural sections. It was found DFW-RHS is stiffer by at least 50% compared to DF-RHS, which allows to savings the metal by reducing the RHS wall thickness by 62% while maintaining the same stiffness and ensuring high strength of structural section.