Microstructures and mechanical properties of laser-welded TiNi shape memory alloy and stainless steel wires

The Nd ： YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.

Roll System and Stock's Multi-parameter Coupling Dynamic Modeling Based on the Shape Control of Steel Strip

The existence of rolling deformation area in the rolling mill system is the main characteristic which dis- tinguishes the other machinery. In order to analyze the dynamic property of roll system＇s flexural deformation, it is necessary to consider the transverse periodic movement of stock in the rolling deformation area which is caused by the flexural deformation movement of roll system simul- taneously. Therefore, the displacement field of roll system and flow of metal in the deformation area is described by kinematic analysis in the dynamic system. Through intro- ducing the lateral displacement function of metal in the deformation area, the dynamic variation of per unit width rolling force can be determined at the same time. Then the coupling law caused by the co-effect of rigid movement and flexural deformation of the system structural elements is determined. Furthermore, a multi-parameter coupling dynamic model of the roll system and stock is established by the principle of virtual work. More explicitly, the cou- pled motion modal analysis was made for the roll system. Meanwhile, the analytical solutions for the flexural defor- mation movement＇s mode shape functions of rolls are discussed. In addition, the dynamic characteristic of the lateral flow of metal in the rolling deformation area has been analyzed at the same time. The establishment ofdynamic lateral displacement function of metal in the deformation area makes the foundation for analyzing the coupling law between roll system and rolling deformation area, and provides a theoretical basis for the realization of the dynamic shape control of steel strip.

Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Extrusion process of 304L H-shaped stainless steel used in passive residual heat removal heat exchanger

304L H-shaped stainless steel is used as the support frame of the passive residual heat removal heat exchanger(PRHR HX) in a nuclear fission reactor. The extrusion process is adopted to manufacture the 304L H-shaped stainless steel. Finite element method simulation is herein used to analyze metal flow characteristics, optimize the extrusion die, and predict the extrusion force at different temperatures and speeds. A Φ400-mm container and Φ388-mm forging billet are selected, and the 304L H-shaped stainless steel is successfully manufactured using a Germany SMS 60 MN horizontal extruder. The mechanical properties and microstructure of the manufactured 304L H-shaped stainless steel meet the requirements of the PRHR HX, and the surfaces of the product pass the dye penetration test. The H-shaped stainless steels are used in Haiyang nuclear power plant in Shandong Province.

Temperature and stress fields in electron beam welded Ti-15-3 alloy to 304 stainless steel joint with copper interlayer sheet

Electron beam welding of Ti-15-3 alloy to 304 stainless steel （STS） using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding process were numerically simulated and experimentally measured. The results show that the rotated parabola body heat source is fit for the simulation of the electron beam welding. The temperature distribution is asymmetric along the weld center and the temperature in the titanium alloy plate is higher than that in the 304 STS plate. The thermal stress also appears to be in asymmetric distribution. The residual tensile stress mainly exists in the weld at the 304 STS side. The copper filler metal decreases the peak temperature and temperature grade in the joint as well as the residual stress. The longitudinal and lateral residual tensile strengths reduce by 66 MPa and 31 MPa, respectively. From the temperature and residual stress, it is concluded that copper is a good filler metal candidate for the electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel.

Experimental study on box shape steel reinforced concrete beam

Experimental study on the fundamental behavior of box shape steel reinforced concrete （SRC） beams was conducted. Seven 1 ： 3 scale model SRC beams were tested to failure. The experimental results indicate that the flexural strength increases with the increase of the ratio of flexural reinforcement and the thickness of flange of the shape steel; the shear strength increases with the increase in the thickness of the web of the shape steel. Concrete filled in the box shape steel can prevent the early failure of specimens due to the buckling of the box shape steel, and increase the ultimate load. Measures should be made to strengthen the connection and co-work between the shape steel and the concrete. Formulae for flexural and shear strength of the composite beams are proposed, and the calculated results are in good agreement with the experimental results. In general, the box shape SRC beam is a kind of ductile member, and it is suitable for extensive engineering application.

Welding of shape memory alloy to stainless steel for medical occluder

Dissimilar metal joining between NiTi shape memory alloy（SMA） and stainless steel was conducted.A cluster of NiTi SMA wires were first joined with tungsten inert gas（TIG） welding process,then the NiTi SMA TIG weld was welded to a stainless steel pipe with laser spot welding process.The microstructure of the welds was examined with an optical microscope and the elemental distribution in the welds was measured by electron probe microanalysis（EPMA）.The results show that TiC compounds dispersively distribute in the NiTi SMA TIG weld.However,the amount of TiC compounds greatly decreases around the fusion boundary of the laser spot weld between the NiTi SMA and stainless steel.Mutual diffusion between NiTi shape memory alloy and stainless steel happen within a short distance near the fusion boundary,and intermetallic compounds such as Ni3Ti＋（Fe,Ni）Ti appear around the fusion boundary.

基础隔震-外挂墙板减震钢筋混凝土框架振动台试验研究

该文提出一种新型的基础隔震-外挂墙板减震混合控制结构(简称“隔震-减震结构”)。该结构采用铅芯橡胶隔震支座作为基础隔震装置,上部结构则采用外挂墙板与U型金属消能器联合构成减震系统。通过减震与隔震混合控制,实现主体结构和围护墙体在罕遇地震下不发生损伤,可用于对韧性性能要求较高的生命线工程中。为对比研究隔震-减震结构与传统隔震结构的抗震性能,设计制作了一个在两方向上完全一致的1/2缩尺基础隔震钢筋混凝土框架结构,并在Y方向附加外挂墙板和U型金属消能器,形成隔震-减震结构,X方向不含外挂墙板,为隔震结构。分别在两个方向输入单向地震动进行振动台试验,试验结果表明:相比隔震结构,隔震-减震结构能进一步降低结构在设防和罕遇地震下的位移响应;隔震-减震结构在罕遇地震下最大层间位移角小于或接近钢筋混凝土框架结构弹性层间位移角限值,主体结构保持弹性,外挂墙板未出现损伤,可以实现预期的性能目标。

T型钢连接方钢管柱-H型钢梁节点抗震性能分析

目的为了研究单边螺栓和T型钢连接的方钢管柱-H型钢梁节点的抗震特性,方法采用室内试验和数值模拟分析方法,对1∶2缩尺的边节点进行拟静力试验,并通过ABAQUS有限元软件进行数值模拟,综合分析边节点的滞回特性、承载力、刚度与耗能等力学特性。有限元分析变量为T型钢加肋、梁翼缘狗骨式和梁腹板开圆孔式。结果试验中,节点试件中连接件T型钢参与耗能且其变形最明显,梁、柱构件变形较小。塑性铰主要集中在连接构件T型钢上,T型钢腹板与翼缘交接处出现应力集中状态。试验弹性阶段,节点构件共同抵抗外部作用力。进入塑性阶段,节点损伤逐渐累积至T型钢,使T型钢最终产生塑性破坏而失效。有限元模拟中,T型钢加肋的形式对节点整体承载力影响最大,其中加3号肋的形式使节点承载力的增长量达到最大;梁翼缘狗骨式的形式对节点整体耗能能力影响最大,为44.01%。结论在T型钢上加肋板对节点的承载力和刚度提升较明显,对耗能能力影响不大;梁翼缘狗骨式和梁腹板开圆孔式均能提高节点的耗能能力,节点承载力和刚度基本不变;梁翼缘做狗骨式对节点抗震性能影响最显著。

窄翼缘异形柱-波纹钢板剪力墙体系的抗震性能

针对钢结构住宅凸梁、凸柱和抗侧刚度不足的问题,提出一种新型窄翼缘异形柱-波纹钢板剪力墙体系;通过与传统H形钢柱-平钢板剪力墙体系进行对比,确定内嵌波纹钢板布置方式,采用ABAQUS软件建立所提出体系的有限元模型,对所提出体系的抗震性能进行分析,探讨外部框架截面形式与布置方式、波纹钢板厚度与剪跨比等对所提出体系的抗侧承载力、耗能能力和塑性变形能力的影响。结果表明:所提出的体系具有较大的抗侧承载力和较强的耗能能力、塑性变形能力,极限抗侧承载力为设计值的1.73倍,具备一定的安全储备;横向布置的波纹钢板能有效减小其作用于框架梁柱的荷载;采用十字形异形柱使所提出的体系有更强的塑性变形能力;所提出体系中的异形柱偏肢宜沿剪力墙面内方向布置,内嵌波纹钢板厚度宜取为3~5 mm,剪跨比宜控制在1.25左右。

Fe-SMA主动加固钢桥面横隔板弧形切口疲劳裂纹实桥应用研究

为确定铁基形状记忆合金(Fe-SMA)主动加固正交异性钢桥面板横隔板弧形切口疲劳裂纹的可行性,以某在役钢箱梁斜拉桥为背景进行实桥加固研究。根据现场横隔板弧形切口的开裂特征,在对裂纹钻孔止裂的基础上,提出利用Fe-SMA材料对横隔板弧形切口裂纹进行粘贴加固的方案,并进行加固施工。通过现场测试得到Fe-SMA板条热激活过程的应变和温度变化,分析Fe-SMA板条和钢板之间的相互作用及加固机理。结果表明:粘贴Fe-SMA板利用Fe-SMA热驱动形状记忆效应可有效便捷地为结构施加预压应力,实现对受损部位的主动加固;经过Fe-SMA联合止裂孔修复后,热驱动作用下的Fe-SMA可以产生200~240 MPa的预拉应力,并在钢板止裂孔边缘施加43~90 MPa的压应力,可有效阻止裂纹进一步扩展;加固体系在加热激活过程完好可靠,当控制一侧加热区域中部温度为200℃时,热传导作用下非加热区域中部的温度为60℃以下,而背面总体温度基本在90℃以下。

Microstructures and properties of capacitor discharge welded joint of TiNi shape memory alloy and stainless steel

Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.

C型外包花纹钢-混凝土界面粘结强度推出试验研究

为探究带拉条式C型外包花纹钢-混凝土的粘结强度及粘结滑移性能,考虑钢板的花纹高度、混凝土强度、拉条间距、截面宽度和翼缘截面形式对试件粘结强度的影响,设计制作了12个带拉条的C型外包花纹钢-混凝土推出试件。分析各试件的破坏过程、荷载-滑移曲线、钢板应变沿纵向分布规律及特征粘结强度;综合考虑各影响因素,统计回归得出特征粘结强度的计算公式。研究结果表明:增大花纹高度是改善粘结性能最有效的途径;特征粘结强度随着混凝土强度的增大呈增大趋势,随着截面宽高比和拉条间距的增大呈减小趋势;在同等条件下,翼缘内翻试件的粘结性能优于翼缘外翻试件;特征粘结强度的回归公式能够较好地拟合试验结果。

Effects of electrode configuration on electroslag remelting process of M2 high-speed steel ingot

The electrode configuration determines the thermophysical field during the electroslag remelting(ESR) process and affects the final microstructure of the ingot. In this work, ingot with a diameter of 400 mm was prepared with two electrode configuration modes of single power ESR process, namely one electrode(OE) and two series-connected electrodes(TSCE). Finite element simulation was employed to calculate the electromagnetic field, flow field and temperature field of the ESR system. The results show that the temperature of the slag pool and the metal pool of the TSCE process is lower and more uniform than that of the OE process.The calculated temperature distribution of the ingot could be indirectly verified from the shape of the metal pool by the experiment. The experimental results show that the depth of the metal pool in the OE ingot is about 160 mm, while the depth of the TSCE ingot is nearly 40 mm shallower than that of the OE ingot. Microstructural comparisons indicate that coarse eutectic carbides are formed in the center of the OE ingot, whereas more even eutectic carbides appear in the center of the TSCE ingot. In general, compared with the OE process, the TSCE process is preferred to remelt high speed steel ingots.

L形钢管混凝土柱-钢梁节点的抗震性能试验研究及有限元分析

为了研究异形钢管混凝土节点的抗震性能,按照1∶2缩尺比例制作了6根L形钢管混凝土柱-钢梁节点试件。通过低周往复试验,探讨了轴压比、梁柱线刚度比和是否带楼板等因素对节点抗震性能的影响。试验结果表明:试件滞回曲线饱满,试件展现出较好的抗震性能;随着梁柱线刚度比的增大,试件的强度、刚度和延性均有所提高;随着轴压比的增大,其耗能能力也增加,但延性有所下降;此外,混凝土楼板的存在对节点承载力的影响较大。利用ABAQUS有限元软件建立有限元模型进行仿真模拟分析,结果显示,有限元计算结果与试验结果符合度较好,从而验证了有限元建模的准确性,为参数分析提供依据。

Effect of Aging Temperature on Erosion-Corrosion Behavior of 17-4PH Stainless Steels in Dilute Sulphuric Acid Slurry

The effect of aging temperature on erosion corrosion （E-C） behavior of 17-4PH stainless steels in dilute sulphuric acid slurry containing solid particles was studied by using self-made rotating E-C apparatus. The effect of impact velocity on EC behavior of 17 4PH steels at different aging temperatures was analyzed. Surface micrographs of the specimens after E C test were observed by using scanning electron microscope （SEM）. The results showed that under the condition of the same solution heat treatment, when aging temperature ranged from 400 ℃ to 610℃, the hardness reached the highest value near the temperature 460℃. The characteristics of E-C for 17-4PH stainless steels at different aging temperatures were as follows： pure erosion （wear） was dominant, corrosion was subordinate and at the same time corrosion promoted erosion. The effect of aging temperature on E-C rate of 17-4PH steels was not significant at low impact velocity, but it was found that E-C resistance of 17-4PH steels aged near 460℃ was the most excellent due to the best precipitation strengthening effect of fine and dispersed e-Cu phase. With a prerequisite of appropriate corrosion resistance, the precipitation hardening could significantly improve the E-C resistance of the materials.

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

书夹型钢-混组合结构在桥梁加宽中的应用研究

为避免桥梁加宽时下部结构拓宽,减少新旧桥面纵向裂缝及铺装层损伤,提出一种以钢结构立柱及护栏、书夹式钢板、高强度螺栓为主要构件,超高性能混凝土(UHPC)为铺装层的书夹型钢-混组合结构进行桥梁加宽。为评估该组合结构在运营条件下的安全性,以厦门官浔溪大桥加宽工程为背景,通过实桥现场静载试验研究水平荷载作用下书夹型钢-混组合结构的力学性能,并与数值仿真结果进行对比,验证试验结果的可靠性。结果表明:实测结果与数值仿真结果吻合良好;书夹型钢-混组合结构关键部位荷载~位移曲线、荷载~应力曲线呈线性变化,钢结构最大拉应力约为材料屈服强度的75%,整体结构处于弹性工作阶段;螺栓预紧力有效减少了高强度螺栓的直剪作用,降低了剪切疲劳破坏风险;采用书夹型钢-混组合结构进行桥梁加宽可有效避免下部结构拓宽,改善新旧桥面纵向裂缝及铺装层损伤,具有较好的加宽效果。

Effect of rare earths on mechanical properties of plasma nitrocarburized surface layer of 17-4PH steel

The aim of this investigation is to reveal the influence of rare earths(RE) addition on mechanical properties of plasma nitrocarburized 17-4PH steel.The nitrocarburized layers were characterized by optical microscope,scanning electron microscope equipped with energy dispersive X-ray analyzer,X-ray diffractometer,microhardness tester and pin-on-disc tribometer.The results showed that RE atoms could diffuse into the surface layer of 17-4PH steel plasma nitrocarburized at 500 °C for 4 h and did not change the ...

Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel

The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595℃, the bulk hardness of samples attains its peak value （42.5 HRC） for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M23C6 precipitated from the lath martensite matrix. Both precipitations of copper and M23C6 are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases.