Behaviour of cold-formed stainless steel beams at elevated temperatures

A study of the behaviour of constructional cold-formed stainless steel beams at elevated temperatures was conducted in this paper. An accurate finite element model (FEM) for stainless steel beams was developed using the finite element program ABAQUS. Stainless steel beams having different cross-sections were simulated in this study. The nonlinear FEM was verified against the experimental results. Generally, the developed FEM could accurately simulate the stainless steel beams. Based on the high temperature stainless steel material test results, a parametric study was carried out on stainless steel beams at elevated tem- peratures using the verified FEM. Both high strength stainless steel EN 1.4462 and normal strength stainless steel EN 1.4301 were considered. A total of 42 stainless steel beams were simulated in the parametric study. The effect of temperatures on the behaviour of stainless steel beams was investigated. In addition, a limiting temperature for stainless steel beams was also proposed.

Investigation on Electron Beam Welded Copper to AISI 316 Stainless Steel Joints

Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a nd mechanical properties. Electron Beam Welding (EBW) process has been found to be especially well suited in this area. Selection of the appropriate welding par ameters needs thorough investigations. These parameters include: preheat tempera ture (℃), welding current (I w), focusing current (I F), welding spee d (V), height between the gun and workpiece surface (H), scan width (S w) and shift distance (S). The present work aims firstly, setting the pr oper welding conditions to get sound joint between commercially pure copper (C10 200) and AISI 316 stainless steel plates 8 mm thickness. Secondly, investigate t he effect of Electron Beam (EB) shift, single-sided and double-sided welds on the mechanical, metallurgical and chemical properties of the weld bead. Due to t he high difference in thermal conductivity between copper and stainless steel, E lectron Beam (EB) was shifted towards copper with different values. These values were ranged from 0.3 to 0.9 mm in welding without preheating of copper plate an d from 0.1 to 0.4 mm with preheating. Number of joints were welded using variabl e EBW parameters in view to obtain the sound weld bead. These parameters are as follows: gradual reduction I w=51 to 49 mA, I F=845 mA, V=8 mm/sec , H=130 mm, S w=500 μm and S=0.4 mm. The investigation has shown t hat, the copper (C10200) plate must be preheated to get sound welded joint with AISI 316 stainless steel using the EBW process. The tensile fracture in all wel ded samples occurred in copper plate away from the weld bead. This reflects that the weld bead tensile strength is greater than the copper strength. The EB shif t has slight effect on hardness distribution through weld bead. The hardness val ue (H v) reduces in gradual manner from stainless steel hardness to copper one. The EB shift distance has no significant effect on the impact toughness.

Influence of high-intensity pulsed ion beams irradiation on oxidation behavior of 316L stainless steel at 700℃

316L stainless steel samples, as a widespread used material, were irradiated with HIPIB at the beam parameters of ion energy 300 keV, current density 100, 200 and 300 A/cm2, shot number 10 and pulse duration 75 ns. The surface morphology and the phase structure in the near surface region of original and treated samples were analyzed with scanning electron microscopy (SEM) and X-ray diffractometry (XRD). It is shown that the HIPIB irradiation can smooth the surface of the samples, and the preferred orientation is present in the surface layer of irradiated coupons. The influence of HIPIB irradiation on the oxidation behavior of 316L stainless steel at 700℃for up to 100 h was investigated. Electron probe microanalysis (EPMA) was used to study the distribution of elements in the oxidation products. It is found that the oxidation behavior of the irradiated coupons depends greatly on the ion current density of HIPIB. HIPIB irradiation with ion current density of 100 A/cm2 slightly reduces the oxidation rate with respect to the unirradiated coupon. The improvement of the oxidation resistance can be attributed to more oxide of Cr that forms on the surface of the irradiated coupons. In contrast, HIPIB irradiation with ion current density of 200 or 300 A/cm2 is proved to be detrimental, causing a higher oxidation rate.

Effect of Laser Beam Welding Parameters on Microstructure and Properties of Duplex Stainless Steel

The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.

Electron beam braze-welding of vanadium alloy to stainless steel with electroplated Cu/Ag coatings

Cracks may easily occur in the fusion weld between vanadium alloys and stainless steel due to the brittle intermetallics and welding stress. The high vacuum electron beam braze-welding has been successfully used to join vanadium alloy（V-5Cr-STi） to stainless steel （HR-2） with electroplated Cu and Ag coating. To investigate the effects of electroplated coating on the weldability, the joint appearaace, the microstrueture and the mechanical properties of the joints have been thoroughly analyzed. The results show that the joint surface configuration was good and root reinforcement was full and smooth. A reaction zone （RZ） was gained on the interface between the V-5 Cr-5 Ti alloy and HR-2 stainless steel base metals. The width of reaction zone at the top of the joint was up to O. 65 mm, wider than that in the bottom of the joint （ 0.46 mm）. The reaction zone consisted of considerably smaller dendritic structures with an average grain size of less than 10μm. Element Ag and Cu almost enriched the interface between V-SCr-5Ti alloy substrate and RZ, serving as a physical barrier which decreases or avoids the formation of intermetallics. The maximum tensile strength of vanadium alloy^stainless steel dissimilar alloy joint was more than 300 MPa. The joint was defects free.

Low Temperature Nitriding of 304 Austenitic Stainless Steel Using RF-ICP Method: the Role of Ion Beam Flux Density

The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage was inserted. A milliammeter is used to detect tile current of ions which collide with the sample and optical emission spectroscopy is used to discern the reactive species included in the nitrogen plasma. The nitriding efficiency is indicated by X-ray diffraction and the microhardness test. The reported data reveal that the ion beam flux density as well as the deposition pressure, bias voltage and time can strongly affect the nitriding of stainless steel via tile expanded multiphase microstructure inside the nitrided layer. The increase in the density of ion flux results in an ascent in the intensity of the expanded peak and a simultaneous decline in the intensity of the 3＇ austenite peak. The evolution trend of ion beam flux density is described as a function of tile operating pressure and the bias voltage. The maxinmm ion flux density has been achieved at 10 Pa pressure and 500 V bias voltage. A reasonable nitriding region has been, consequently, suggested after comparing this work with previously reported results.

Finite element analysis on electron beam brazing temperature and stresses of stainless steel radiator

Based on thermal-elasto-plastic finite element theory, a two-dimensional finite element model for calculating electron beam brazing temperature and residual stress fields of stainless steel radiator are presented. The distributions of temperature and residual stress are studied. The resuhs showed that temperature distribution on brazing surface is rather uniform, ranging from 1 026 ℃ to 1 090 ℃. The residual stresses are varied from initial compressive to tensile , and the variation of residual stress is very little in total zone of brazing surface.

Characterizing modified surface layer of 316L stainless steel treated by high current pulsed electron beam

High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material within a short pulse time,coupled thermal and stress processes would lead to the formation of metastalbe microstructure with improved properties.In the present work,HCPEB treatment of 316L stainless steel(SS) was carried out and the microstructural changes in modified surface layer were characterized with optical microscopy,X-ray diffractometry and electron backscatter diffractometry(EBSD) techniques.The corrosion resistance of modified surface was measured in a 5wt.% salt solution.The evolution regularity of surface craters and grain refinement effect,as well as the preferred orientation of(111) crystal plane occurring in the HCPEB treatment under different working parameters were discussed along with their influence on corrosion resistance.

Metallurgical and Mechanical Properties of Underwater Laser Welds of Stainless Steel

In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steel were investigated. JISY308L type filler wire was used as filler wire during welding. A gas-shielding nozzle was used to form a local dry cavity surrounding the welding zone. The main results are summarized as follows: (1) The shielding condition of the local dry cavity severely affects the oxygen content of the weld, the worst shielding condition leading to the oxygen content of 800×10-6, which largely increases the oxide inclusions and somewhat reduces the ferrite content. (2) The increase of oxygen content reduces the elongation rate and reduction of area in tensile test, but has no influence on the tensile strength. (3) In appropriate shielding condition, the mechanical properties of the underwater laser welds can be as same as that in the air.

基于连续强度法的不锈钢梁抗剪切性能研究

不锈钢结构因具有良好的耐腐蚀性、容易维护等优点,逐渐成为工程建设领域中广泛使用的高性能绿色建筑材料。但不锈钢具有应变强化特性,现有设计规范计算工字形截面梁的抗剪切承载力结果较为保守,基于连续强度法,对不锈钢工字形截面梁的剪切屈曲承载性能进行研究,考虑了不锈钢材料几何非线性和几何初始缺陷的影响。基于试验验证的有限元数值模型,开展不锈钢梁抗剪切承载力影响的参数分析,探究各关键参数对其的影响规律,并与现行规范(中国、美国、欧洲)的计算结果进行对比。结果表明,在腹板厚度等参数不变的情况下,不锈钢工字形梁腹板的极限承载力会随着腹板宽高比的增加而降低。中国规范计算结果较为保守,低于构件的实际抗剪切承载力。连续强度法可以对不锈钢工字形截面的抗剪切承载力进行较为准确的计算。

不锈钢车体激光焊连接的模拟方法及强度评估

采用有限元分析方法研究不锈钢车体侧墙激光焊连接的模拟方法与强度分析问题。首先,分别建立实体单元、薄壳单元及梁单元模拟半熔透搭接激光焊连接强度的分析模型,以及梁单元模拟不同焊缝长度的分析模型,并在相同计算条件下,通过对比分析确定了适用于复杂结构激光焊连接强度分析的焊缝单元类型;其次,基于GB/T 37778—2019和接头疲劳试验数据及不同焊缝长度模型的分析结果,总结适用于复杂结构激光焊连接静强度与疲劳强度的评估方法;再次,建立某弧焊-点焊-激光焊的不锈钢车体结构强度分析模型;最后,在EN 12663-1:2010+A1:2014规定的静态与动态载荷工况作用下,分析不锈钢车体侧墙激光焊连接强度。结果表明:AW3状态车钩压缩工况的车体侧墙中部上边梁区域的激光焊梁单元的最小安全系数为1.03;车体侧墙激光焊区域的梁单元的计算剪应力变化范围均远低于106次和107次的疲劳强度值,侧墙激光焊连接疲劳强度冗余大。

不锈钢复合钢H形截面钢梁受剪承载性能

基于复合钢本构模型,明确了复合比β对不锈钢复合钢应力-应变性能的影响。通过试验结果的承载曲线和破坏模式验证了数值模拟方法的准确性,进而以β、腹板宽高比a/hw和腹板高厚比hw/tw为变量开展300个数值模型的参数分析,系统分析了各变量对不锈钢复合钢H形截面钢梁受剪承载曲线和极限承载力的影响。研究结果表明:随着β的增加,不锈钢复合钢应力-应变曲线中的屈服平台逐渐消失,复合钢应力-应变性能逐渐由碳钢转变为不锈钢。当β较小时,不锈钢复合钢应力-应变曲线存在明显的屈服平台,这削弱了复合钢的应变强化对H形截面钢梁受剪承载性能的有利影响。随着β的增加,不锈钢复合钢的非线性应变强化性能逐渐增强,导致H形截面钢梁的延性性能逐渐提高,强度性能逐渐降低。经过验证,既有的欧洲规范设计公式对不锈钢复合钢H形截面钢梁受剪极限承载力的预测过于保守。基于参数分析结果,建立了考虑β影响的腹板贡献系数计算方法。研究结论有助于推广不锈钢复合钢的工程应用。

冷弯薄壁折叠翼缘C形不锈钢构件受弯性能分析

为了在同成本下获得更高效的截面形式,利用ABAQUS对前期六组V形加劲C形截面奥氏体304不锈钢受弯构件建立有限元简化数值分析模型,将得到的结果与试验结果进行了对比验证。对应上述六组受弯构件设计了四组与其用钢量相同,但尺寸分布不同的折叠翼缘不锈钢受弯构件,共24组;探讨了折叠翼缘截面不锈钢受弯构件在四点受弯作用下的构件承载性能,并将其与C形截面不锈钢受弯构件的承载性能进行了对比。利用现有的设计计算方法计算了24组折叠翼缘截面受弯构件的极限承载力,并将其与有限元得到的结果进行了比较。对比发现:相同用钢量的情况下,当折叠翼缘截面腹板高度与斜翼缘在腹板平面内的投影长度值之和较C形截面腹板高度提升12%以上时,折叠翼缘截面不锈钢梁的极限承载性能比C形截面更优异,截面形式更加高效。现有的计算方法计算腹板V形加劲的折叠翼缘受弯构件得到的结果比较理想,误差较小;而对于平翼缘V形加劲且宽度较小的构件,计算得到的结果偏大,不能准确地预测构件的极限承载能力。

近断层连续梁桥支座与不锈钢U形阻尼器组合减震控制研究

强震下多跨连续梁桥可能会发生邻梁碰撞,导致伸缩缝以及过渡墩的破坏,甚至出现落梁问题。针对传统减震装置的局限性,本文提出了一种高阻尼隔震橡胶支座与不锈钢U型阻尼器联合使用的组合减震体系,在耗能的同时有效控制梁体位移。以强震区临近断层的一座预应力混凝土连续梁桥为工程案例,采用有限元软件Midas Civil建立了空间动力分析模型,通过输入不同的近断层地震动进行非线性动力时程分析,对比研究了桥梁采用不同减震体系时的地震响应。结果表明:仅采用高阻尼隔震橡胶支座的桥梁在近断层地震作用下支座变形过大,桥梁有落梁风险;当增设不锈钢U型阻尼器后,可有效控制墩梁间的相对位移以及过渡墩的地震响应,各工况下减震率均在70%以上,减震效果显著。

水下电弧锯切割质量影响因子的研究

海洋、船舶、石油等领域有大量结构部件需在水下拆解。现有的水下切割方法存在效率低、结构复杂、工具或电极损耗大等局限,亟需探索新的切割方式。高速电弧放电加工具有加工效率高、电极损耗率低等优势,在难切削材料的加工中取得了良好效果。基于高速电弧放电加工原理,设计水下电弧锯切割实验装置,并对该装置极间流场进行仿真,得到不同主轴转速下极间流体流动情况。在此基础上,设计系列实验开展电流形式、主轴转速和电流值等因素对切割质量影响的研究。实验结果表明,采用高速电弧放电切割可实现工件的高效水下切割。此外,使用脉冲电流切割时的切缝质量优于直流,增大电流会改善出口处切缝宽度;主轴转速过低会影响极间排屑效果,加工中宜采用较高转速。

Evaluation of Microstructure and Mechanical Properties of Laser Beam Welded AISI 409M Grade Ferritic Stainless Steel

The microstructure analysis and mechanical properties evaluation of laser beam welded AISI 409M ferritic stainless steel joints are investigated. Single pass autogeneous welds free of volumetric defects were produced at a welding speed of 3 000 mm/min. The joints were subjected to optical microscope, scanning electron fractographe, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into dendritic grains as a result of rapid solidification of laser beam welds. Tensile testing indicates overmatching of the weld metal is relative to the base metal. The joints also exhibited acceptable impact toughness and bend strength properties.

新型不锈钢螺栓连接件疲劳后力学性能退化研究

为探究装配式组合梁中新型不锈钢螺栓连接件疲劳后的力学性能,开展螺栓连接件疲劳后力学性能仿真方法研究。首先,基于当前螺栓连接件存在的问题与不足,设计了一种耐锈蚀、方便拆卸的新型螺栓连接件。其次,进行1组静载推出试验,4组不同疲劳加载次数后的静载推出试验,分析了试件破坏特征以及力学性能退化规律。最后,基于材料剩余强度理论,引入考虑疲劳损伤的混凝土和螺栓连接件的材料退化本构模型,建立不同疲劳加载次数后的螺栓连接件力学性能退化仿真计算流程,并对仿真结果进行了验证。结果表明:新型螺栓连接件疲劳加载270万次后剩余承载力退化了12.1%,且疲劳后破坏模式为螺栓剪断。采用的材料本构退化模型的仿真计算值与试验结果吻合较好,能够合理地反映螺栓在疲劳后的力学性能退化状况。

超薄不锈钢端接接头微束TIG工艺特性

针对0.2 mm超薄1Cr18Ni9Ti奥氏体不锈钢端接接头进行微束TIG焊,采用连续焊和脉冲焊两种形式,研究焊接电流和焊接速度对焊缝成形及接头的影响。结果表明,接头宽度随着焊接电流的增加而增大,熔透深度也随之增大,有效电流相同的情况下,采用脉冲焊接能够获得更小的接头宽度和更大的熔透深度。接头抗拉力随着焊接电流的增加先增大后减小,采用脉冲焊接有利于提高接头的抗拉力,接头抗拉力最大达到1 070 N,高于连续焊接的950 N。奥氏体晶粒的母材经过焊接后出现了较多的δ铁素体,采用脉冲焊接方法的接头被熔合线分为多层,熔合线处的组织为奥氏体晶粒上分布黑色带状的δ铁素体。

不锈钢与钛合金电子束熔覆增材焊接工艺分析

不锈钢与钛合金的双金属结构已在化工、航天、航空等领域得到了广泛的应用。基于对异种金属构件焊接技术的研究,分析了异种金属焊接在熔点、膨胀系数、热导率、比热容等方面的性能特点。基于电子束异种金属的焊接工艺及特点,进一步讨论了不锈钢-钛合金电子束熔覆增材焊接技术。采用电子束熔覆增材焊接技术对不锈钢和钛合金进行焊接时,需要考虑过渡层的设置、焊接的强度与耐腐蚀性工艺、气体环境保护等重要的环节。

不锈钢地铁车体底架边梁MAG焊接变形控制浅析

不锈钢车体底架边梁通常采用钢板辊弯成形工艺,为了加强边梁本身结构,同时考虑与牵枕缓的装配结构,底架边梁在枕梁周边区域通常采取补强板+封板的结构进行补强。不锈钢材料具有热导率低、线膨胀系数大的物理特性,导致底架边梁在采用MAG焊接方法焊接补强板及封板时变形较大,影响后工序底架组装。通过对底架边梁的结构焊接模拟仿真及焊接顺序优化进行分析,为不锈钢地铁底架边梁焊接变形的控制提供参考。