Cold Bending Research Articles

Research on the axial elongation and springback law of thick-walled tubes in cold bending forming

Research on the axial elongation and springback law of thick-walled tubes in cold bending forming

Reliability and sensitivity analysis of cold-bent curtain wall glass

Cold bending is widely used in the forming of curtain-wall glass because of its simplicity, low cost and short construction period. However, residual stress is always generated in the glass during the process of cold-bending; if this stress is greater than the strength of the glass, the curtain wall will break. In this paper, an analysis model of cold-bending stress on a glass surface is developed using a finite element method to predict the residual stress of cold-bent glass. An experimental platform for measuring the cold-bending stress of the curtain-wall glass is built to verify the results of the finite element analysis. Considering the influence of random factors, a reliability analysis of cold-bent curtain-wall glass is performed using Monte Carlo simulation method and adaptive Kriging-Monte Carlo simulation method. Furthermore, reliability sensitivity analysis of curtain-wall glass is used to estimate the impact of different parameters’ random variation on the reliability of the curtain-wall. The above studies have important guiding significance for practical applications, and can provide a theoretical basis for the engineering design and construction of glass-curtain walls.

The Development of Log Aesthetic Patch and Its Projection onto the Plane

In this work, we introduce a new type of surface called the Log Aesthetic Patch (LAP). This surface is an extension of the Coons surface patch, in which the four boundary curves are either planar or spatial Log Aesthetic Curves (LACs). To identify its versatility, we approximated the hyperbolic paraboloid to LAP using the information of lines of curvature (LoC). The outer part of the LoCs, which play a role as the boundary of the hyperbolic paraboloid, is replaced with LACs before constructing the LAP. Since LoCs are essential in shipbuilding for hot and cold bending processes, we investigated the LAP in terms of the LoC’s curvature, derivative of curvature, torsion, and Logarithmic Curvature Graph (LCG). The numerical results indicate that the LoCs for both surfaces possess monotonic curvatures. An advantage of LAP approximation over its original hyperbolic paraboloid is that the LoCs of LAP can be approximated to LACs, and hence the first derivative of curvatures for LoCs are monotonic, whereas they are non-monotonic for the hyperbolic paraboloid. This confirms that the LAP produced is indeed of high quality. Lastly, we project the LAP onto a plane using geodesic curvature to create strips that can be pasted together, mimicking hot and cold bending processes in the shipbuilding industry.

Моделирование воздействия грунта на напряженно­деформированное состояние линейного участка трубопровода с отводами холодного гнутья средствами ASYS

he purpose of the article is to consider a local problem associated with deviations from the norm of bends resulting from uneven subsidence of soil under an underground linear section of a pipeline with a cold bend outlet. Modeling and calculation of the linear section of the pipeline was carried out in the ANSYS software environment, which made it possible to identify the maximum possible length of the soil failure, at which the structure will suffer irreversible deformations due to climatic conditions and other natural factors. The data obtained will allow assessing the risks during the laying and operation of the pipeline.

The Influence of anisotropy on the vibration behaviour of S600Mc sheet metal

Sheet metal anisotropy is the directional dependence of mechanical properties. It is a critical factor that must be considered when using numerical simulation to predict any plastic deformation manufacturing process. Sheet metals prove anisotropic plastic behaves due to crystallographic texture caused by progressive rolling steps, Banabic D. et al. (2000). Cold bending of steel sheets is a widely used manufacturing process in the automotive industry due to its cost efficiency. By avoiding line heating, the oxidative process of steel is thus avoided. The automotive industry's primary application of sheet metal includes doors, fenders, bumpers, roof panels, and seat frames. In this paper, test specimens were laser cut at orientations θ = 0°, 45°, and 90° to the rolling direction. The specimens were subjected to forced vibration on an electromechanical shaker, and the frequency response amplitude was measured using accelerometers. Natural frequency and Q-factors were discussed. Experimental data are used for viscous damping coefficients (alpha and beta) for each direction of the specimen. The measured coefficients are then used to validate each type's finite element, numerical models. The results show the level of dependency between the structural damping and anisotropy of the laminated sheet metal and the influence on the high cycle fatigue performance.

Twisted Tower – A Feasibility Study for Cold‐Bent Insulating Glass Units with an Elastic Edge Seal

This paper describes a case study of cold bent insulating glass units (IGUs) for use in facades or roofs using the example of a demonstrator called the “Twisted Tower”. Modern designs often try to combine a curved shape with transparency. Cold bending IGUs is a cost efficient method to achieve both. In such applications the bending angles are often limited by the allowable deformations of the primary seal which ensures the gas tightness of the IGU. This investigation shows IGUs with much more acute bending angles than in standard applications were achieved using a flexible yet durable thermoplastic spacer ensuring superior gas tightness. This work investigates the geometry, the deformations and fixing options for the bent IGU form. The results demonstrate the advantages of using such spacer systems for these applications.

An interpretation of creep rupture properties of grade 91 steel service- exposed for 100,000 hours at 600 °C

ABSTRACT Creep rupture data of grade 91 steel used as hot reheat pipes have been reported recently. The data are investigated by comparison with the creep rupture database of the steel in normalised and tempered (NT) states. Four regions H, M, L and G with different values of stress exponent appear in creep of grade 91 steel. The pipes were used in long-term region G (around 600 °C for 100,000 hours) in fossil-fired power plants. Medium- and low-stress regions M and L are confirmed to exist in the service-exposed states. Stress exponents in the two regions are kept unchanged in all the pipes, but the service exposure reduces their remaining creep rupture lives. The reduction is significant in the pipes made by cold bending. The service exposure retards the appearance of long-term region G. Causes of these findings are discussed in this paper.

Experimental Study on Single Corner Cold Bending Mechanical Response of Laminated of PVB Interlayer Tempered Glass Panes and the Coupling Effect with Load.

The cold bending method is a type of curved glass curtain wall construction method that has been used in practical engineering for a short time. It has the advantages of simple operation, high efficiency and low cost. However, the mechanical response and properties of glass panes caused by cold bending have not been solved effectively. To study the mechanical response and the properties of cold formed laminated tempered glass panes after applying with a wind load, cold bending and load tests of 9 laminated tempered glass panes were conducted by the orthogonal experimental design method. The effects of cold bending curvature, glass pane thickness and interlayer thickness were considered. In this paper, the response law of cold bending stress to the curvature and the relationship among the influencing factors were analyzed. The variation process of stress, the deflection of cold-formed glass panes under uniform load and the characteristics affected by cold-formed stress and deformation were studied. The results show that the cold bending stress is distributed in a saddle shape, and the curvature has the greatest influence on the cold bending stress, followed by the thickness of the glass panes. The influence of the interlayer thickness is small. The maximum stress appears near the corner of the short side direction adjacent to the cold bending corner. The cold bending stress increases linearly with increasing cold bending curvature. The cold bending stress and deformation have little effect on the change process of the later stage load effect.

An Experimental Study on Cold-Bending Stress and Its Reverse-Coupling Effect with the Uniform Load on Cold-Bent SGP Laminated Glass

SentryGlas® Plus (SGP) laminated glass is a novel type of safety glass with high strength and stiffness. On the other hand, cold bending is a novel technique to build curved glass curtain walls, and is advantageous in terms of its greater energy efficiency and cost-effectiveness as well as its simple construction processes. The cold bending of SGP laminated glass could result in broad applications for the material and provide huge economic benefits in the field of glass curtain wall construction. To study cold-bending stress and its reverse-coupling effect with the uniform load in SGP laminated glass panels, single-corner cold-bending tests, uniform load tests, and ultimate capacity tests were conducted on eight pieces of such panels with different cold-bending curvatures and interlayer thicknesses. The results revealed that cold-bending stress in the glass panels under single-corner cold bending demonstrated a saddle-shaped distribution, with the maximum and second-largest cold-bending stresses located near the corner of the short side and the long side adjacent to the cold-bending corner, respectively. The cold-bending stress and coupling stress increased nonlinearly as the cold-bending curvature rose and the interlayer thickness became greater. Moreover, cold-bending curvature was a factor that affected the cold-bending stress and coupling stress more significantly than the interlayer thickness. The ultimate capacity and ultimate deflection of the glass panels decreased as the cold-bending curvature and interlayer thickness grew.

Microstructural characterization and non-destructive testing and of welded joints of duplex stainless steel in flexible pipes

Flexible pipes are complex structures made of different layers and different materials. They are used in the oil and gas production in the off-shore platforms to conduct the oil or gas between different units, such as platforms, Christma's tree and transportation ships. The internal carcass of flexible pipes is made of duplex stainless steels type 2205 (UNS S32205 or S31803). In the production line, sheets of 1.8 mm thickness of this material are submitted to uncoiling and cold bending operations to form “S” profiles which are assembled to form the internal carcass. The end of one coil is welded to the begin of another, to make the process continuous. The welding process is autogenous automatic gas tungsten arc (GTAW). This work analyses the microstructure and corrosion resistance of the weld metal and compares to the base metal. Besides, non-destructive tests and electrical resistance measurements were conducted in the welded joint and base metal. The samples analyzed were from a flexible pipe manufacturer. It was concluded that the joints of this producer were not heat treated, which results in inadequate microstructure and lower corrosion resistance in the weld metal.

Optimal Design of the Shape of a Non-Ball Mandrel for Thin-Walled Tube Small Radius Cold Bending

In the field of cold bending, it is necessary to use ball mandrels, especially to bend thin-walled tubes with a small radius. However, the bending process with a ball mandrel is complex and expensive, and it is easy to jam the core ball inside the tube. To solve these issues, we designed two kinds of hollow non-ball mandrel schemes with low stiffness that were suitable for the small radius bending of thin-walled tubes. We evaluated the forming quality of cold bending numerically and the influence of the hollow section length and thickness on the forming indices. Our results showed that the thickness of the hollow section has a greater influence on forming quality than the length. As the hollow section’s thickness increased, the wrinkling rate first declined by approximately 40% and then increased by above 50%. When the thickness was 11 mm in scheme 1 and 13 mm in scheme 2, the wrinkling rate reached minimum values of 1.32% and 1.50%, respectively. As the hollow section’s thickness increased, the flattening rate decreased by more than 60% and the thinning rate increased by about 40%. A multi-objective optimization of forming indices was carried out by ideal point method and grey wolf optimizer. By comparing the forming results before and after optimization, the feasibility of using the proposed hollow mandrel was proved, and the hollow mandrel scheme of standard cylinder is therefore recommended.

Experimental investigation on fatigue behavior of butt-welded high-strength steel plates

This paper presents an experimental investigation into mechanical properties and fatigue performance of butt-welded high strength steel plates. Four typical high-strength steels (HSSs) were selected, with steel grades of 460, 550, 690, and 960 MPa. Mechanical properties were measured through monotonic tensile tests, cold bending tests, Charpy V-notch impact tests and hardness tests. A total of 114 fatigue tests were conducted on butt-welded high-strength steel plates. Comparisons of mechanical properties and fatigue performance are made among HSSs tested and conventional strength steels (CSSs) with a yield strength around 235 to 355 MPa. The natural slope of S–N curves for HSS butt-welded connections varied from 3 to 5. Two fatigue design approaches are recommended with one based on natural slope and one based on a fixed slope of 3 as for CSSs.

Study on the mechanical response of anticlastic cold bending insulating glass and its coupling effect with uniform load.

Cold bending is a characteristic of significance for the beautiful curved glass curtain walls, because it affects them in terms of energy-efficiency and cost-efficiency. The increasing engineering projects call for more special studies on the mechanical properties of cold-bent glass panels, especially when the walls are built by insulating glass that is currently widely used while its relevant research is very scarce. This paper is devoted to studying the mechanical properties of anticlastic cold-bent insulating glass while taking different factors into consideration, including glass thickness, cold-bent torsion rate and cavity thickness. 9 pieces of insulating glass were manufactured for anticlastic cold-bending test and their coupled effect with identical load is also studied, and numerical finite element analysis sessions were carried out to simulate the experimental results for each one of them. Further, we analyzed the stress distribution performance of the sample pieces under cold bending and a uniform load, followed by discussions about stress transfer controls in glass plates. The results showed that the cold-bent control stress is on the surface with direct loads from cold bending and close to the cold-bent corner on the short edge, and it is transferred from the parts around the corner to the center when the uniform load plays a leading role in generating stress. This transfer could occur under a relatively small load with a small cold-bent torsion rate. A higher cold-bent torsion rate in cold bending contributed mostly to greater center stress in the glass, and as the glass thickness grows, stress and deflection at the plate center would significantly drop. However, the effect of cavity thickness on the anticlastic mechanical response of insulating glass was found to be trivial.

Experimental Study on Cold Bending and Temperature Change of Toughened Glass

In order to study the temperature strain of the insulating tempered glass under certain cold bending test, cold bending test and temperature test were carried out on the glass plate. Taking the self-made cold-formed steel frame as the tool and the hollow laminated tempered glass as the object, the cold bending test of the glass was carried out. The results show that the stress of each measuring point increases linearly with the increase of cold bending displacement, and the maximum principal stress appears at the end of the loader near the loading point of the outer sheet glass. The temperature changes test of the glass shows that the stress of each measuring point is linear with the increase in temperature difference. The results show that the maximum principal stress appears near the constrained angle steel on the displacement side of the upper edge of the outer sheet glass; the stress changes greatly during the short-term cooling test, and the tensile and compressive stresses transform each other. The internal stress produced by cold bending is coupled with the maximum principal stress produced by temperature load, and the maximum principal stress appears at the lower edge constraint of the loading displacement side.

Advances and Trends in Forming Curved Extrusion Profiles.

Curved profiles/sections have been widely used for manufacturing lightweight structures with high stiffness and strength due to aerodynamics, structural properties, and design reasons. Structural components fabricated using curved aluminum profiles satisfy the increasing demands for products used in many high-technology industries such as aerospace, shipbuilding, high-speed rail train, and automobile, which possess the characteristics of lightweight, high strength/stiffness relative to weight, superior aerodynamics performance, and aesthetics. In this paper, the advances and trends in forming techniques of curved extrusion profiles of metal alloys have been reviewed. The curved profile forming techniques are classified into three major categories: conventional cold bending technique, stress/moment superposed cold bending technique, and extrusion-bending integrated forming technique. Processes for innovative development in the field of forming curved profiles are identified; the extrusion-bending integrated technique which can directly form the billets into curved profiles by one single extrusion operation possesses the full potential for further innovation. Due to the nature of the research to date, much of the work referred to relates to hollow circular and rectangular tube cross-sections.

Distortion Control and Prevention by Fabrication Techniques in Cold Bent Steel Frame with Perforated Web

Cutouts are widely used in ships and offshore structures. Cutouts of big size are used mainly for inspection, passing pipes, and weight reduction. Some cutouts of small size may be used for various purposes, such as water hole in the web of stiffeners. The stiffeners with perforated web are the most commonly adopted structure members in the shipbuilding industry, and they are mainly fabricated by cutting and bending the frame to meet the requirements of desired design configuration. In ship production, the manufacture of the curved stiffener with holes is desirable to perforate first and then to bend the frame. This fabrication procedure is adopted for efficient production because of the layout of the production line. However, structural distortion and damage may occur during cold bending of the frames with perforated web, such as necking, wrinkling, and even crack initiation. This problem should be solved in ship production. In this study, cold bending experiments and finite element simulations were performed to analyze the deformation characteristics of curved frames with cutouts. A fabrication method is proposed to control the deformation in the cutouts during the bending process. In this method, the block cut out during the first step is filled in the hole and afterward the frame is bent. The results show that this method can control well the deformation localized around the hole during the bending process. It offers an important guidance for cold bending steel frames in ship production.

Achieving Exceptional High Ductility in Binary Mg–6Zn Alloy Wire by Grain Boundary Strengthening and Twinning‐Induced Plasticity

Mg–6Zn alloy wires are prepared by the combination of hot direction extrusion and multi‐pass hot drawing. The tensile results show that this technology achieves an exceptional tensile elongation of about 18%, as well as the yield strength of 175 MPa and the ultimate tensile strength of 310 MPa when the drawing temperature is 350 °C. Meanwhile, it also exhibits the highest strain‐hardening data compared with the other wire samples. The microstructure characterizations show that the near single‐phase α‐Mg microstructure with the MgZn2 nanoprecipitates on grain boundaries and it can significantly produce twin intersections and stacking faults under cold bending deformation. The exceptional high elongation can be attributed to the grain boundary strengthening of nanoprecipitates and twinning‐induced plasticity.

Finite Element Modeling of Cold Curved Steel Rolled Beams Under Service Loads

Cold bending is an efficient method recommended by steel fabricators for curving structural steel beams. It relies solely on mechanical forces to curve the beam into the required shapes without heating. While extensive research has been conducted on fabrication processes, data on the structural performance of cold bent steel girders in service is scarce which limits its use specifically in bridge structure applications. This paper investigates the effects of cold bending on the service load capacity of steel rolled shapes. An experimental and analytical program was developed for this purpose. The experimental program consists of cold curving a rolled IPE section about its weak axis and then bending it about its strong axis by applying vertical static loads that simulate service loads. Numerically, finite element analysis was conducted and validated based on experimental results. A parametric study was then conducted to identify structural parameters that can adversely affect the resistance capacity of cold bent steel rolled beams. Results show that the reduction in resistance capacity of the cold curved steel beam depends on the configuration of the applied loads and that its structural behavior can be improved by adding stiffeners, bearing plates, modifying the end boundary conditions and introducing load eccentricities. Recommendations are finally made to improve the efficiency of cold curved steel beams in service.

Bending and Welding of New High Oxidation Material - Thor™ 115

Development of materials used in the power industry for the production of USC boilers poses new challenges. The introduction of new alloying agents intended at obtaining the best possible mechanical properties, including creep resistance, affects the fabricability of new steel grades. All new materials have to undergo a lot of tests, particularly as regards bending and welding processes, with the aim of enabling the development of technologies ensuring failure-free production and assembly of boiler components. Martensitic steels containing 9% Cr, used in the production of steam superheaters shall have good creep resistance and, at the same time, low oxidation resistance at a temperature above 600°C. In turn, steels with a 12% Cr content, for example, VM12-SHC or X20CrMoV12-1 are characterized by significantly higher oxidation resistance but have lower strength at higher temperatures, which translates to their limited application in the production of modern USC and A-USC boilers.X20CrMoV12-1 was withdrawn from most of the power plants across Europe and VM12-SHC was supposed to replace it, but unfortunately, it failed in regards of creep properties. To fulfill the gap a new creep strength-enhanced ferritic steel for service in supercritical and ultra-supercritical boiler applications was developed by Tenaris and named Thor™115 (Tenaris High Oxidation Resistance). This publication covers the experience obtained during first steps of fabrication which includes cold bending and TIG welding of homogenous joints.

Cross-Section Deformation and Bending Moment of a Steel Square Tubular Section.

When bending thin-walled profiles, significant distortion of the cross-section occurs, which has a significant impact on the course of the bending moment characteristics and on the value of allowable bending curvatures. This paper presents the results of experimental and numerical modeling of the box profile bending process, which was carried out in order to determine the dependence of the cross-sectional shape and bending moment of bending curvature. Extensive numerical calculations were used to model the process of shaping a square pipe from a circular tube and to model the bending process, especially when taking into account the effects of such a deformation path. The pure bending moment characteristics and the deformation of the cross-section were performed for a 25 × 25 × 2 mm square tube made of S235JR structural steel. The innovative approach for determining the parameters of cold bending square tubes pertained to considering the stress state in the preserved material in individual areas of their cross-section. The results of numerical modeling—after considering the history of deformation (i.e., the process of forming a square pipe from a pipe with a circular cross-section)—gave a satisfactory agreement with the results of experimental tests, both in terms of the degree of pipe wall deflection and the characteristics of the bending moment.