Tailored Profiles Made of Tailor Rolled Strips by Roll Forming – Part 2 of 2

The main scope of the presented work is to demonstrate the potential of load optimized tubes with a varying thickness distribution in circumferential direction produced by roll forming. As initial material a so called Tailor Rolled Strip (TRS) sheet metal coil produced by Strip Profile Rolling (SPR) method was used instead of plain sheet. The TRS sheet metal is manufactured in a continuously working process by rolling one or more groves in transverse direction into the sheet metal coil. In this paper, the secondary forming of the TRS sheet metal to TRS tubes is investigated by means of FE‐simulations and roll forming experiments. To simulate the manufacturing process of the TRS tube by FEM, an integrated consideration of the process is necessary because of the large local strain hardening in the groves of the initial SPR sheet metal. In experimental roll forming operations welded tubes could be manufactured successfully. The geometrical and material properties of these tubes are analyzed. The reprocessing of TRS tubes by hydroforming is investigated by means of tube bursting tests. It has been found that an additional annealing process is necessary to achieve deformations in the grooved area during the hydroforming process.     

Peter Groche

Tube hydroforming (THF) is a relatively new but established technology among metal tube forming processes. It is the technology of forming closed sections, hollow parts with different cross‐sections by applying an internal hydraulic pressure and sometimes additional axial compressive loads to force a tubular blank to conform to the shape of a given die cavity. Material properties have a significant influence on the process stability. Often roll‐formed, non‐heat treated tubular materials made of steel with longitudinally oriented welding lines are used in tube hydroforming. Different production processes involve a change of the material properties from the initial flat sheet to the hydroformable tube. Testing methods such as tensile tests and conventional forming limit diagrams do not accurately reflect the state of stress and strain conditions seen in the tubular blank during the hydroforming process. Thus, inaccuracies in FEA predictions and design failures occur. Test methods were developed to characterize the relevant geometrical and mechanical properties of tubular semi‐finished products.     

厚壁锆合金管材超声波探伤方法研究

分别尝试采用纯横波、横波纵波相结合、双角度纵波斜入射3种超声波探伤方法,对某壁厚与外径比（t／D）为0．25的锆合金厚壁管进行探伤对比实验。结果表明：纯横波法杂波干扰大,且内壁缺陷容易漏检,不适用于该规格锆管的检测;而横波纵波相结合和双角度纵波斜入射的方法均能准确的发现内、外壁缺陷,且杂波干扰小,探伤重复性好;纵波斜入射法简便易行,但探伤效率较低,适合于小批量厚壁管材探伤,而横波纵波相结合法更适用于大批量厚壁管检测,这2种方法同样适用于t／D更大的管材探伤。     

Design of hydroforming process for an automobile subframe by FEM and experiment

Tube hydroforming technology has shown the attention of the automotive industry due to its advantages over conventional stamping and welding methods.In this study,the tube hydroforming process including tube bending,preforming and hydroforming process for an automobile subframe is analyzed and designed by the simulation software AutoForm of a finite element method (FEM) program.A parametric study is carried out to obtain the effect of the forming parameters such as initial tube size and loading path on the forming results.The simulation results are also compared with experiment results.The research indicates that the multiple forming operation of the tube hydroforming process can be simulated accurately by using the implicit code AutoForm,and the formability of tube hydroforming can be improved by designing suitable forming parameters.     

Cr35Ni45钢高温长期服役过程的氧化与渗碳机理

采用扫描电镜、电子探针和X射线衍射等手段对不同服役时间（原始态、1.5a和6a）Cr35Ni45乙烯裂解炉管内壁的氧化与渗碳机理进行了系统分析.结果表明:高温长时服役后炉管内壁出现了氧化层、碳化物贫化区和碳化物富集区三个区域,其氧化行为包括Cr₂O₃外氧化和SiO₂内氧化,且服役过程中外氧化膜发生反复破坏和重建;炉管服役过程的渗碳行为主要由内表面结焦引起,外氧化膜的反复破坏可以加重渗碳,但外氧化膜在破坏后能自动修复,所以服役态两个炉管的渗碳程度较轻;外氧化膜的反复破坏和重建使亚表层贫铬,导致形成碳化物的临界碳浓度增加,在内壁亚表层形成贫碳化物区,多余的碳原子在其内侧析出,形成碳化物富集区.      

Flexural Behavior of Hybrid FRP-Concrete-Steel Double-Skin Tubular Members

This paper presents the results of an experimental study on the flexural behavior of a new type of hybrid FRP-concrete-steel member as well as results from a corresponding theoretical model based on the plane section assumption and the fiber element approach. This new type of hybrid member is in the form of a double-skin tube, composed of a steel inner tube and an FRP outer tube with a concrete infill between the two tubes, and may be employed as columns or beams. The parameters examined in this study include the section configuration, the concrete strength, and the thicknesses of the steel tube and the FRP tube, respectively. The results presented in this paper show that these hybrid beams have a very ductile response because the compressive concrete is confined by the FRP tube and the steel tube provides ductile longitudinal reinforcement. The beams' flexural response, including the flexural stiffness, ultimate load, and cracking, can be substantially improved by shifting the inner steel tube toward the tension zone or by providing FRP bars as additional longitudinal reinforcement. The predictions from the theoretical model are in reasonably close agreement with the test results. Differences between the test and predicted results arise from factors not considered in the theoretical model, including the existence of a strain gradient in the confined concrete, concentrations of cracks and the slips between the concrete and the two tubes; these are issues to be accounted for in the development of a more accurate model in the future.     

Microstructure and Mechanical Properties of Al Tube Processed by Friction Stir Tube Back Extrusion (FSTBE)

Friction stir tube back extrusion is presented as a method to produce fine-grained tubes based on friction stir back extrusion process. In this method, a tubular aluminium alloy specimen whose inner diameter is less than the diameter of the rotating tool, is placed on a cylindrical die and penetrated by a rotating tool. Mechanical properties and microstructural evaluation of the processed tube have been investigated. The optical micrographs of the microstructure demonstrate strain gradient along the tube wall. Reduction in grain size and grain refinement occurs across the inner wall of the formed tube as well. Hence, the grain size with an initial value of ~100 µm is decreased to ~39 µm in the inner side of the formed tube wall. The obtained results from tensile tests illustrate that the ultimate strength and elongation at failure increases from the initial value of 183–225 MPa and 19–22 %, respectively. Microhardness assessments represent an increase in initial value from 74 to 86 Hv. Moreover, the microhardness values of the inner surface of the formed tube are more than the outer surface. The results show that this method is suitable for fabricating a kind of ultrafine-grained tube which possess an acceptable combination of strength and ductility.     

DP590/DP780高强钢管液压成形的性能

为对生产进行指导,研究了DP590/DP780高强钢焊管在液压成形过程中的变形行为;使用场发射扫描电镜观察管材周向的横截面以确定基体的组织,通过VMHT30M显微硬度计确定管材的焊缝及热影响区的大小,以便研究液压成形破裂行为;采用液压成形试验机对两种管件进行液压成形研究。实验结果表明:管材在胀形过程中的破裂压力比理论计算公式得到的破裂压力大,破裂位置全部位于靠近焊缝及热影响区的母材区域;随着管径的增大和长径比的增大,管材的极限膨胀率呈现下降趋势;在自由胀形过程中,管材的焊缝区域基本上不发生减薄,最小壁厚位于管材的热影响区和基体的过渡区域,并且壁厚的减薄率在胀形最高点所在截面最大,越靠近管材夹持区,壁厚的减薄率越小。最终得到以下结论:管材液压成形实验是准确获得管材力学性能参数的途径;提高焊接质量有助于控制失效破裂位置;合理选择管材的长径比有利于管材性能的充分发挥;通过合理控制各处的减薄有利于降低液压成形件的破裂风险。      

Controlled Material Flow in Hydroforming by Multipoint Drawing Technology

Sheet hydroforming, which is based on an active working medium, results in advantages over conventional forming techniques that make this technology interesting for the production of components with a large surface area. In order to expand the range of applications for this method, the current limits must be extended and the obstacles eliminated. One important aspect here is finding a solution to the conflict between a reliable tool sealing and a controlled material flow, particularly in the filling and preforming phases of the hydroforming process. One way of achieving progress in this area is to employ multipoint technology. In order to exploit multipoint cushion technology ‐ the potential of which has been proved in conventional deep‐drawing operations ‐ to extend the limits of sheet hydroforming, this technology has to be developed further, similarly to the multipoint cushion systems used in deep‐drawing, and adapted to the process‐specific conditions of sheet hydroforming.     

Use of Modern High Strength Steels in Load Adapted Hydroformed B‐Pillars

The increase of legal and insurance demands on B‐pillars calls for high strength steels and new process chains. Therefore, the hydroforming of high strength close‐to‐contour tailored tubes to load adapted B‐pillars was investigated. Modern high strength steels were identified for the use in B‐pillars. Their forming and crash behaviour was predicted with the aid of validated numerical models. The accuracy of the numerical models was increased significantly by taking the forming history into account. The design of the hydroformed B‐pillar considered a product concept catalogue (i.e. package, functional areas, crash performance) close to a reference B‐pillar. As a reference the deep drawn B‐pillar of the Mercedes‐Benz W203 was chosen. Using high strength materials in the close‐to‐contour tailored tubes led to a significant reduction of the number of parts and the weight of the B‐pillar compared to the reference.     

分区分级燃气辐射管模型验证及仿真研究

本文首先对双P型辐射管进行实验和数值研究,发现除NO_x含量的误差偏大外,其他参数的偏差都在1%以内,证明该模型具有一定的可靠性.在此基础上,将空气分级的理念应用于双P型辐射管,提出一种带支管喷口的分区分级燃气辐射管,并建立相应的数学和物理模型.对比双P型辐射管和分区分级辐射管的模拟结果显示:分区分级燃气辐射管和双P型辐射管内气体的平均流速分别为25.8m·s-1和21.0m·s-1,热效率分别为65.9%和64.2%;分区分级燃气辐射管壁面最高温度为1047℃,壁面最大温差为73℃,比双P型辐射管降低15℃,分区分级后气体平均流速增大,提高了直管和回流管管段的烟气温度和壁面温度,具有更好的温度均匀性.      

Properties and Mechanism of Al/St Bimetal Tube Bonding Produced by Cold Spin-Bonding (CSB) Process

Spin-bonding is a novel tube cladding method for fabrication of bilayer tubes based on flow-forming process. The bimetal Al/St tubular components have extensive application in different industries. In this paper, an Al/St bimetal tube was successfully produced at different thickness reductions from 35 to 65% and mechanical and metallurgical aspects of the joint were investigated. Peeling tests were done to investigate the strength of the bond. The results showed that an increase in the thickness reduction led to a significant increase in the bond strength. Besides, the bonding mechanism between Al as inner tube to St as an outer one resulting from spin-bonding process was investigated. The results showed that an excellent bonding of Al and St tubes could be achieved from this process. The results showed that the bonding process consisted of three stages. First, removal of surface layers resulting in contact between the virgin metals of two bond surfaces and then an unstable bond was formed that stabilized as deformation proceeded. Finally the bond strengthening occurred. The SEM micrographs of the peeled surfaces showed that removing surface films in aluminum and steel in the first stage was based on different mechanisms. Also, SEM back-scatter images of bond interface showed that no intermetallic phases were formed.     

Tests and Analysis of Cantilevered GFRP Tubular Poles with Partial Concrete Filling

In this study, six glass fiber-reinforced polymer (GFRP) cantilevered tubular poles were tested in flexure. Four poles were filled with varying amounts of concrete; within 13, 30, 51, and 72% of their lengths, from the fixed point. Two poles, namely, a hollow and a totally concrete-filled tubes, were also tested as control specimens. The filament-wound prismatic tubes were 3,660 mm long, including a 700 mm clamped length at the fixed end, with a 220 mm outer diameter, and 4.15 mm wall thickness. The study aims at increasing flexural strength of thin-walled GFRP tubular poles by using a small amount of concrete at the vicinity of maximum moment near the base. Test results showed that flexural strength increases as the length of concrete fill is increased, until it reaches a plateau corresponding to about double the strength of the hollow tube, when the concrete fill is about one third of the clear length. This is considered the optimal condition for this tube that provides the largest strength-to-weight ratio. Poles with a shorter filling length failed prematurely, by a combined local buckling and crushing of the hollow part, while poles with a longer filling length failed at the base by rupture of the tube in tension. An analytical model was developed, validated, and used in a parametric study. The correlations between the optimal filling length ratio and both “diameter-to-thickness” ratio, and laminate structure of the tube, have been demonstrated for both angle-ply and cross-ply tubes.     

圆盘拉拔紫铜管杂物压入类缺陷研究

随着市场竞争的加剧,空调生产厂家对铜管材的质量,尤其是对表面质量的要求渐趋严格。杂物压入是紫铜管加工过程中经常出现的一种表面缺陷,这种表面缺陷不仅会降低铜管的质量,而且还有可能在紫铜管拉拔过程中发生管材断裂,造成产品报废。通过跟踪铜盘管的拉拔过程,分析杂物压入处的形貌和成分,结果发现：圆盘拉拔三道次后,铜管内外表面均有杂物压入,进而导致断管发生。而引起铜盘管拉拔过程出现杂物压入类缺陷的主要原因是外部杂质铁（Fe）,硅（Si）,氧（O）和其他异物微粒的压入,这些杂物压入点在拉拔力的作用下形成裂纹源并逐渐扩展,最终导致在铜管拉拔过程中出现断管。根据分析结果,通过加强铜原料成分管控和有效控制熔铸铸坯中氧含量,以及提升熔铸、轧制、盘拉等工序环节的5S管理等方面入手,有效减少此类缺陷的产生,进一步提高产品质量。     

Failure in internally pressurized bent tubes

The analysis and modeling of tube-hydroformed components is more complicated than that employed for sheet-metal panels, due to the lengthier process sequence and variable strain path—from flat-rolled sheet to tube; from straight tube to bent tube; and from bent tube to hydroformed component. These additional process steps make it difficult to determine whether post mortem analyses of tube failure during hydroforming can, and should, be conducted with the same tools and databases as used for simple stampings. To provide a partial answer, the properties of commercially fabricated welded straight tubes were evaluated using a free-expansion internal pressure test and compared with those of free-expansion internal pressure tests on bent tubes. The results demonstrated that the behavior of the bent tube was consistent with the mechanical properties of the as-received tube, provided due notice was accorded to the complex strain history of the bent tube. However, due to the strain-path changes occurring at the failure location, conventional approaches for monitoring strain history would yield (apparently) anomalous results.     

Failure in internally pressurized bent tubes

The analysis and modeling of tube-hydroformed components is more complicated than that employed for sheet-metal panels, due to the lengthier process sequence and variable strain path—from flat-rolled sheet to tube; from straight tube to bent tube; and from bent tube to hydroformed component. These additional process steps make it difficult to determine whether post mortem analyses of tube failure during hydroforming can, and should, be conducted with the same tools and databases as used for simple stampings. To provide a partial answer, the properties of commercially fabricated welded straight tubes were evaluated using a free-expansion internal pressure test and compared with those of free-expansion internal pressure tests on bent tubes. The results demonstrated that the behavior of the bent tube was consistent with the mechanical properties of the as-received tube, provided due notice was accorded to the complex strain history of the bent tube. However, due to the strain-path changes occurring at the failure location, conventional approaches for monitoring strain history would yield (apparently) anomalous results.     

Microstructure Evolution and Nitridation in an As-Cast 25Cr-35Ni-1Mo Radiant Tube After Long-Term Service

The microstructure evolution of 25Cr-35Ni-1Mo radiant tubes was investigated after approximately two years of service in a continuous annealing furnace. The inner and outer tube walls were exposed to N₂-containing combustion environment and protective atmosphere, respectively. The decarburization feature analysis indicated that carbon content decreased toward the tube surface. However, precipitates at the inner and outer walls were coarser, their content increased and the microhardness value also increased compared to that in the central area. X-ray diffraction illustrated that M₂(C,N) and M₆(C,N) were the dominant carbide at the inner and outer walls, and precipitates in the central area were mainly M₂₃C_6?and M₆(C,N) phases. The results were assumed to be associated with the nitridation phenomenon that occurred in the N₂-containing environment at elevated temperatures.     

Impact of aging on gastrointestinal mucosal immunity

More than two million tympanotomy tubes are placed annually in the United States, making this operation the most common performed on children. This article provides an overview of the applications of tympanotomy tubes for the treatment for otitis media in childhood. The indications for tube placement are discussed; a visual guide for managing children with tympanostomy tubes is presented; an approach to dealing with tube complications is outlined; and guidelines for referral to a pediatric otolaryngologist are suggested.