高温灵敏系数标定影响因素分析

高温应变计是高温结构强度测试、疲劳测试和寿命评估的主要测量传感器,其灵敏系数测试的准确性影响高温应变测试中应变修正数据的真实性。对应变计灵敏系数原理进行分析,明确灵敏系数是应变计输出与应变之间的关系,对砝码加载四点式简支梁结构和纯弯矩钢架梁结构灵敏系数测量模型进行分析,确定产生标准应变的影响因素。常温灵敏系数标定的影响因素有试验梁尺寸、试验梁轴向力,实际灵敏系数测试结果表明简支梁灵敏系数略大,分散明显较大。高温下应变计的输出与载荷应变、应变计热输出、试验梁尺寸变化、弹性模量变化和摩擦力变化有关,对热输出消除方法进行探讨,理论上明确温度下简支梁尺寸变化、弹性模量变化误差高达22%,钢架梁的刚性封闭静态力学平衡系统的温度影响误差较小。利用自研框架式高温裸栅应变计、高温陶瓷胶,进一步用简支梁、钢架梁实际测试灵敏系数随温度变化验证了理论分析的正确性。     

蠕墨铸铁焊接温度场、应力场研究

以高温应变片和热电偶为敏感元件，对蠕墨铸铁材料焊接过程中的温度场、应力场进行了测试，分析了焊接电流、焊接速度对温度场、应力场的影响规律，提出了减小焊接应力的基本方法。     

A new method of calibrating strain release coefficients in measuring welding stresses

The measured values of welding residual stresses often exceed material yield strength (σ_y) or tensile strength (σ_t), in measuring welding residual stresses in the welded joints of low carbon steel or stainless steel by drilling a blind hole. It is quite evident that measured values do not represent reality. Local plastic strain caused by residual stress concentrations round the blind hole has a main effect on the measuring error of welding residual stresses. This article presents a new method of calibrating strain coefficients A and B for eliminating influence of local plastic strain. In calibrating strain release coefficients A and B, calibrating stresses applied on the specimen were increased so that material round the blind hole produced local plastic deformation, ie coefficients A and B contained a component of the plastic strain. Numerial values of coefficients A and B were classified into four grades. Every grade coefficient contained a different quantity of the plastic strain for offseting the influence of the plastic strain round the blind hole. Test results have proved that by adopting these coefficients more satisfactory values for residual stresses can be obtained in practical engineering. The measuring average error in stainless steel (1Cr18Ni9Ti) reduces from 109% to 1.52%. The measuring average error in low carbon steel reduces from 54.69% to 3.21%.     

Modeling of resistance spot welding of multiple stacks of steel sheets

Weld quality is a major challenge for resistance spot welding of multiple stacks of steel sheets. Because of the differences in mechanical and physical properties of steel sheets and the sheet gage variation, the contact state between sheets and welding current flow throughout the stack joint is complicated. As a result, discrepant weld sizes at the faying interfaces become an issue. In this study, a coupled thermal–mechanical/thermal–electrical incremental model has been developed to reasonably predict the weld nugget formation process of resistance spot welding of a sheet stack made of 0.6 mm thick galvanized SAE1004+1.8 mm thick galvanized SAE1004+1.4 mm thick galvanized dual-phase (DP600) steel using published thermal, electrical, and mechanical properties. It was found that the weld nugget on the faying interface of DP600 forms earlier than that on the other interface, which agrees well with the experimental results. Based on the coupled model, the effects of the sheet gage combination and steel grade combination were examined. The results show that, for a multiple stacks of steel sheets SAE1004 + SAE1004 + DP600, the critical ratio of sheet thickness between the top and bottom sheets is approximately 1:3. The model could provide an important guidance in the selection of the welding variables, sheet gage and steel grade to meet the weld quality of steel component.     

超塑焊接接头变形特点分析

本文以结构钢 (4 0Cr)与工具钢 (T1 0A)为研究对象 ,探讨了两种压前组织超细化预处理工艺 (整体循环淬火和高频淬火 )及压接工艺因素对恒温超塑焊接头变形的影响。试验结果表明 :恒温超塑焊接属小变形焊接 ,其接头变形主要表现为应变的时间积累。压前组织越细 ,其接头变形越大 ,与 4 0Cr侧相比 ,T1 0A侧接头变形均较大     

高精度检测系统在合拢焊缝焊接变形中的应用

介绍了水工大型钢结构的一种高精度检测系统的组成及其工作原理,利用该系统对大型水轮机蜗壳与引水压力钢管合拢焊缝接头焊接过程中座环上变位进行实时监测,同时采用游标卡尺和百分表对焊缝收缩及钢管轴向变位进行监测,测量结果满足设计和工程要求。     

Impact surface fractures of glass-fiber/epoxy lamina-coated glass plates by small steel-ball

Fiber orientation effects on the impact surface fracture of glass plates coated with a glass-fiber/epoxy lamina layer were investigated using a small-diameter steel-ball impact experiment. Four kinds of materials were used: soda-lime glass plates, unidirectional glass-fiber/epoxy layer (one ply, two plies) coated glass plates, crossed glass-fiber/epoxy layer (only two plies) coated glass plates. The maximum stress and absorbed fracture energy of these plates were measured by a single-grid strain gage bonded to the back surface of the glass plates during the impact of the steel ball. With increasing impact velocity, various surface cracks, such as ring, cone, radial and lateral cracks, occurred near the impact sites of the uncoated glass plates. Plates with glass-fiber coating had a plastic deformation zone between the fiber layer and the glass plate that formed around the impact site while the surface cracks in the plates drastically diminished. The principal direction of this plastic deformation and delamination followed the fiber orientation. The impact surface-fracture index expressed in terms of the maximum stress and the absorbed energy could be used as an effective evaluation parameter for surface resistance.     

Practical strain extensometry for biaxial cruciform specimens—Part 1

Of a number of methods for testing materials under biaxial stress conditions, the cruciform specimen with tension/compression loading of the arms allows exploration of the whole in-plane failure envelope. This paper highlights the problems arising in the measuring, monitoring and control of strains in cruciform specimens subject to static and cyclic biaxial loading. Three extensometers are described which have been used respectively for testing high strain fatigue in steels, fatigue crack propagation in steels and fatigue and fracture of a glass reinforced polyester composite. Each extensometer uses a full bridge resistance strain gauge circuit; two are based on bending of a beam and the third on deformation of a thin ring. Examples are shown of stress/strain loops for equibiaxial and shear conditions from fatigue tests on a steel and g.r.p.     

TIG电弧热丝对铜、钢堆焊的工艺研究

针对某产品铜带焊接工艺,提出了一种电弧热丝方式应用于TIG堆焊铜、钢工艺的研究。电弧热丝可有效预热低电阻率的焊接材料,如铜;传统的电阻热丝只能加热具有高电阻率的焊接材料,如钢。采用电弧热丝系统,热丝电流小于50A时即可有效预热焊丝,与电阻热丝电流400A相当。在相同焊接电流下,能够大大提高焊接熔敷速度;在相同送丝速度下,降低焊接电流,大大降低焊接设备功率。同时证明2种热丝加热方式对钢基体、铜合金的影响相同,特别是对堆焊层铜合金中泛铁量的影响相当。     

An optical device for measuring bending strain to 5000 microstrain and compatible with optical fiber installations

An optical sensor is described which can be attached to a structure and used as a gage for measuring bending strain. This device can be adjusted to maximize the gage factor for predetermined strain ranges. The sensor consists of glass capillaries coated on the outer surfaces with an optical absorbing layer followed by a reflecting layer. A mechanical strengthening layer can be included to extend the range of strain response. A source laser beam from an optical fiber is injected into one end of the gage. The light remaining in the beam after traveling through the gage is collected via another optical fiber. The optically active layer is adjusted during manufacture to provide a predetermined gage factor. For a given thickness of the absorber layer, the detected light is proportional to the amount of bending. Thus, by rigidly affixing the sensor to a structural member, the strain experienced by the member can be monitored.     

Finite element analysis of the effect of welding heat input and layer number on residual stress in repair welds for a stainless steel clad plate

Stainless steel clad plate is widely used in petroleum, chemical and medicine industries due to its good corrosion resistance and high strength. But cracks are often formed in clad layer during the manufacture or service, which are often repaired by repair welding. In order to ensure the structure integrity, the effects of residual stress need to be considered. The objective of this paper is to estimate the residual stress and deformation in the repair weld of a stainless steel clad plate by finite element method. The effects of heat input and welding layer number on residual stresses and deformation have been studied. The results show that large residual stresses have been generated in the repair weld. The heat input and layer number have great effects on residual stress distribution. With the heat input and welding layer number increasing, the residual stresses are decreased. Using multiple-layer welding and higher heat input can be useful to decrease the residual stress, which provides a reference for optimizing the repair welding technology of this stainless steel clad plate.     

Fatigue performance of butt welds between cast steel joint and steel tubular members

Cast steel joints have gained increasing popularity for use in engineering. The fatigue performance of butt welds between cast steel joint and steel tubular members, however, is not yet well characterized. A series of fatigue tests were conducted on a new type of welding detail, cast steel joint with sloped end and integrated backing ring (Type C), for butt welds between cast steel joint and steel tubular members. Fatigue failure mechanism and S–N curves obtained from the tests were compared with those of Type A connection with backing ring and Type B cast steel joint with integrated nose obtained in literature. Fatigue behaviours of all three welding details were successfully predicted by local strain approach, the results of which are consistent with test results, especially for Types A and B welding details. According to the results of tests and analysis, fatigue cracking of butt welds between cast steel joint and steel tubular members always initiates from the bottom of the weld root, and the fatigue performance of Type C welding detail is better than those of Types A and B because of its lower stress concentration level. A simplified fatigue design equation was then proposed based on the results of local strain approach, in which the fatigue notch factor was adopted in fatigue behaviour evaluation. The accuracy of this simplified fatigue design equation was verified for Type C welding details with various geometry configurations.     

含裂纹钢试样在拉伸过程中的声发射特性

对于带有I型裂纹的SM490A钢和SUS304钢试样,通过测量其在拉伸断裂过程中的声发射特征参数及裂纹尖端特定点的温度,分析了裂纹尖端和塑性变形区域的力学特征.结果表明:声发射能量计数、振铃累积计数在裂纹扩展的各个阶段都有着明显的曲线特征,且曲线特征和屈服、强化阶段的应力-应变曲线基本吻合,因此可以用声发射能量计数、振...     

Cr12MoV钢焊接区表面高频淬火后的超塑性焊接

对Cr12MoV钢进行表面高频淬火后超塑性焊接,选用的工艺参数为:加热温度为800℃,焊接时间t=5min,预压应力σ0=56.6MPa,初始应变速率ε0=2.5×10-4s-1。对接头组织进行了观察和分析。试验结果表明,焊接区局部高频淬火后的Cr12MoV钢在其超塑变形温度及应变速率范围内,经短时间超塑焊接,其接头抗拉伸强度可以达到母材值。     

Mechanical and corrosion properties of P/M-HIP super duplex stainless steel after different industrial heat treatments as used for large components

Abstract

Mechanical tensile and impact toughness tests and critical pitting corrosion temperature (CPT) tests were performed on samples of Duplok 27, a P/M-HIP duplex stainless steel containing copper, after heat treatments simulating industrial heat treatments of large components. It was shown that copper alloying has positive effects on mechanical tensile properties leading to hardening and more uniform deformation. No negative effects of copper alloying on corrosion resistance properties were found. A drastic drop in impact toughness values and CPT of samples cooled at controlled cooling rates is explained by the precipitation of intermetallic secondary phases or their precursors. Lower CPT of a NG-GTAW (narrow gap gas tungsten arc welding) welded joint is explained by the lower level of alloying than that of the base material. The high temperature region of precipitation of intermetallic secondary phases is shifted towards higher temperatures than assumed for Duplok 27 P/M-HIP duplex stainless steel.     

Secondary‐Emission signal for weld formation monitoring and control in eletron beam welding (EBW)

The process of emission of term electrons from the zone of effect of the electron beam are analyzed. During the experiments, the samples of stainless steel and titanium alloy were welded. Experiments were conducted to examine the spectrum of oscillations of the secondary current at various values of the specific power of the electron beam. The conducted research showed that the signal spectrum of the secondary current in electron beam welding contains a characteristic high‐frequency (15…?25 kHz) component. It was established that the described frequency spectrum is not created by some control system in the electron beam machine and reflects the oscillations in the system – «keyhole‐plasma». Empirical density distribution of the high‐frequency signal was constructed in the amplitude range. It was shown that the parameters of the density distribution is closely linked with the nature of interaction between the beam with the metal and can be used for remote control of technology process.     

Residual stresses in binder-fiber filler systems

A method of measuring residual stresses in polymer binder-fiber filler systems is developed. A distinguishing feature of this method is that residual stresses are determined by measuring the strain of a 15--diameter constantan wire embedded in a polymer binder, the wire performing the dual function of a reinforcing fiber and a resistance strain gage.The authors wish to thank A. L. Rabinovich for his valuable advice in planning this investigation and interpreting its results.     

Cyclic strain rate effect on martensitic transformation and fatigue behaviour of an austenitic stainless steel

In this study, the effect of strain rate on the cyclic behaviour of 304L stainless steel is investigated to unveil the complex interrelationship between martensitic phase transformation, secondary hardening, cyclic deformation and fatigue behaviour of this alloy. A series of uniaxial strain controlled fatigue tests with varying cyclic strain rates were conducted at zero and non‐zero mean strain conditions. Secondary hardening was found to be closely related to the volume fraction of strain‐induced martensite which was affected by adiabatic heating due to increasing cyclic strain rates. Tests with lower secondary hardening rates maintained lower stress amplitudes during cyclic loading which resulted in longer fatigue lives for similar strain amplitudes. Fatigue resistance of 304L stainless steel was found to be more sensitive to changes in strain rate than the presence of mean strain. The mean strain effect was minimal due to the significant mean stress relaxation in this material.     

Surface Yielding of Metals by X-ray Diffraction

Surface yielding of metallic material was measured with strain gage and X-ray diffraction methods.The results show that.when the residual stress in the transverse direction is involved,the surface yieldstrength should be evaluated with biaxial Mises criterion.For a medium carbon high strength steel,the yield strength of the bulk material is 581 MPa and the surface yield strengths for 0.05% and0.1%plastic strain are about 436 MPa and 463 MPa respectively.The 0.05% yield strength willapproximately increase to 788 MPa after shot peening.In the early stage of plastic deformation,strain hardening in the surface layer is quite different from that of the bulk sample.     

Schweißverhalten von Aluminium und seinen Legierungen

Weldability of Aluminium and Al Alloys Aluminium is behind steel the most used metal. Advantages of Al-materials are the low weight, the favourable strength and deformation properties, the good corrosion resistance and the good electrical and thermal conductivity. Welding of aluminium encounters difficulties due to high melting oxide layer at the surface, the strong heat dissipation from the welding region, the tendency to form craters or pores and the high heat extension. This contribution describes the basic facts and special features of arc welding and weld properties of aluminium and Al-alloys during welding.