Fatigue crack formation and propagation behavior of 30Cr3WVE bearing steel

The fatigue characteristics of a high cleanliness bearing steel(30Cr3WVE)produced by double vacuum melting and the effect of non- metallic inclusions on fatigue properties were studied by mechanical analysis and SEM analysis of microstructure and fatigue fracture morphology.The results show that the 30Cr3WVE bearing steel achieves excellent mechanical properties after being quenched at 870?? and tempered at 550??, and its ultimate rotating bending fatigue strength reaches 732MPa.Through observing SEM results of fatigue fracture,the fatigue crack originates from the surface defects and internalnon- metallic inclusions. Surface defects are caused by the abscission of non- metallic inclusions and machining marks. The internal non- metallic inclusions are mainly oxides of Al, Mg, Si and Ca. The influence of inclusions on the ultimate bending fatigue strength of 30Cr3WVE bearing steel is closely related to its size and distance to the surface. The model of influence of the size and distribution of inclusions on the rotating bending fatigue strength of 30Cr3WVE bearing steel is constructed. The rotational bending fatigue strength of the steel can be improved remarkably by controlling the size and quantity of inclusions.     

薄壁管材连续矫直截面扁化动态仿真分析

薄壁管材在连续矫直过程中会在大弯曲变形阶段发生截面扁化（即Bazier效应）,截面最大扁化量和残留扁化量作为重要工艺参数,用以控制截面变形程度和管材的圆度。而目前现场仍沿用经验图表结合人工经验和反复试矫对其进行估定,为此运用ANSYS/LS-DYNA对薄壁管材弯曲扁化的过程进行动态仿真,得到了最大扁化量和残留扁化量数据,并通过现场实验证明了分析结果的正确性和可信性,为现场矫直过程相关工艺参数的合理设置提供有效手段。     

Deformation behavior of metallic composites with brittle fibers during bending

Conclusions The aluminum-boron system was chosen for studying the mechanism and conditions of deformation of metallic composite materials reinforced with brittle fibers. It was established that, unlike that of an orthodox metallic material, the bending of a composite is accompanied by displacement of a neutral layer in the direction of compression. The causes and character of the displacement of this layer in the course of deformation were determined. The role of processing pads in bending was examined. A study was made of the fracture of fiber-reinforced composites on the attainment of critical values of strain.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 80–85, November, 1982.     

Effect of plastic deformation and high pressure working on the structure and microhardness of metallic glasses

The effects of rolling, bending and high pressure working on the structure and microhardness of Fe, FeNi and Co based metallic glasses have been investigated. Some special methods of specimen deformation and microhardness measurement were used. The structure has beeninvestigated by X-ray analysis and positron annihilation methods. A large importance of structural relaxation process occurring at room temperature during some hours after deformation has been established. The correlation between structural changes and those of mechanical properties after deformation has been found. The strain hardening and strain softening of metallic glasses has been found to depend upon the pattern of stressed state under the deformation.     

Numerical Solution of Thin‐walled Tube Bending Springback with Exponential Hardening Law

The process of manufacturing thin‐walled tubes which show exponential hardening is investigated. The analysis is based on the feedback analysis of bending springback tests. The springback angle is calculated using a formula which is derived from numerical methods. The experiments and finite element calculations prove that the formula agrees well with the test results. However, for tubes with strong hardening characteristics, certain discrepancies exist. The springback angle increases linearly with the ratio of plastic and elastic modulus, and decreases nonlinearly with increasing hardening index. The larger the ratio of plastic and elastic modulus, the greater the amount of reduction as the hardening index increases. The amount of increment in the springback angle incurred by the increase of the normalized bending radius is greater for smaller hardening index values. For thin‐walled tubes, after unloading, the elastic component takes a higher percentage in the total deformation as the relative wall thickness increases, causing the springback angle to increase slightly. However, when the growth rate of the cross section inertia moment is greater than that of the proportion of elastic deformation, the springback angle tends to decrease slightly as the normalized wall thickness increases. The formula will be applied to promote the technical development in springback prediction, control and compensation.     

Severe Plastic Deformation of Copper Pipes Using Integrated Extrusion-Equal Channel Angular Pressing (Ex-ECAP)

In the present study, copper tubes were subjected to severe plastic deformation through integrated extrusion-equal channel angular pressing (Ex-ECAP). Plastic deformation characteristics were analyzed using finite element simulation and resultant microstructures were characterized by optical microscopy. Also, X-ray diffraction patterns were utilized to calculate crystallite size. Results showed that integrated Ex-ECAP could be successfully applied on metallic tubes. Meanwhile, the resultant sub-grain size was measured to be in the range of 360–550 nm by Williamson–Hall method. Optical micrographs taken from the cross section of deformed sample demonstrated that initial grains in the plane perpendicular to flow direction remained equiaxed after deformation by Ex-ECAP and their sizes were decreased from 16 to 4 μm after deformation.     

一种2000 MPa级中碳高强度弹簧钢的疲劳破坏行为

 研究了一种2 000 MPa级中碳高强度弹簧钢的疲劳破坏行为。升降法得出实验钢的旋转弯曲疲劳极限σ-1为810 MPa，此值明显高于传统弹簧钢；这主要得益于实验钢具有良好的强度和塑韧性配合及均匀细小的奥氏体晶粒。用SEM对疲劳断口的分析表明，实验钢的疲劳破坏均起源于试样表层的非金属夹杂物，其主要成分为含Ti和V的碳氮化物，平均尺寸为(50±10)μm，且呈“鱼眼”断裂。相对于试样心部的夹杂物，表层夹杂物对实验钢的疲劳性能的危害性更大。     

32Cr3MoVE轴承钢旋弯疲劳特性及裂纹萌生扩展行为

摘要：采用光滑漏斗状试样对32Cr3MoVE轴承钢进行旋转弯曲疲劳测试，研究了32Cr3MoVE轴承钢旋转弯曲疲劳性能及裂纹萌生扩展行为。采用升降法测得其疲劳极限为860MPa，疲劳断口SEM观察并统计破断试样结果表明：疲劳破坏68.7%是由于非金属夹杂起裂，18.8%由表面加工缺陷起裂，125%为表面粗糙度起裂。当加载应力低于980MPa时，疲劳断裂主要是由于内部非金属夹杂引起的，高于980MPa时，疲劳断裂主要是由于表面粗糙度引起的。表面加工缺陷和表面粗糙度引起的最大应力强度因子分别为3.05和2.97MPa·m1/2，容易引发疲劳裂纹。非金属夹杂物尺寸在5.30～5.90μm范围内，局部应力从859.35MPa升至977.75MPa时，疲劳寿命从1.96×105降低到1.58×105；非金属夹杂物局部应力在840～900MPa范围内，夹杂物尺寸从2.28μm升至5.83μm时，疲劳寿命从1.10×106降低到1.96×105。     

Investigation into the surface damage of pure metals allowing for the cyclic loading frequency

The results of an investigation into the surface damage of pure metals after fatigue tests are described. Mathematical dependences of the variation in the fatigue resistance index on the cyclic loading frequency under the bending deformation of the rotating samples are derived. The equations of fatigue curves are presented and the microstructural variations under cyclic loading are presented.     

Metal-on-metal friction plating

The most expedient method of applying metallic coatings is friction plating with the use of rotating wire brushes (RWB). The coating metal is pressed against the bristles of the RWB and heated to high temperatures in the contact region. Particles of the coating metal are then captured by the ends of the bristles and transferred to the surface of the product being coated. The surface layer is simultaneously subjected to plastic deformation. The article presents the main parameters of the process and describes its ranges of application.     

Mapping the Strain Distributions in Deformed Bulk Metallic Glasses Using Hard X-Ray Diffraction

The deformation behavior of Cu₄₅ Zr_46.5 Al₇Ti_1.5 bulk metallic glass (BMG) under bending was investigated in-situ using high-energy X-ray synchrotron diffraction. Samples were bent using two different benders with radii of 10 and 20 mm. The components of the strain tensor were determined from the change of positions of the first maximum of the diffracted intensity in reciprocal space. The procedure of data treatment was improved by the introduction of direct beam off-center correction. Comparing results for the two different bending radii, we found that the zero stress region does not necessarily lay within the central part of the specimen. Bending with smaller radius resulted in symmetric strain distribution, whereas a larger bending radius revealed strong asymmetry. Furthermore, bending with a smaller radius (10 mm) shows steeper strain gradients as compared with the situation in which the larger bending radius (20 mm) was used. Using a smaller bending radius implies reaching higher tensile/compressive stresses and reveals the signs of the plastic deformation, which are demonstrated as a saturation of elastic strains.     

Effects of tungsten fiber on failure mode of zr-based bulk metallic glassy composite

The authors systematically investigated the effects of tungsten fiber on failure mode as well as deformation and fracture mechanisms in tungsten fiber-reinforced Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 bulk metallic glassy composite under uniaxial compression at room and high temperatures. At room temperature, the failure mode of the composite changes from shear fracture to longitudinal splitting failure with increasing fiber volume fraction. Similar to the observations in monolithic metallic glasses, the shear fracture angle of the composite is approximately equal to 39∼40 deg, indicating that the Mohr-Coulomb criterion is suitable to give the critical shear fracture condition of the composite. When the compression tests were performed below the glass transition temperature of Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 metallic glassT _g, the deformation behavior of the composite strongly depends on the strain rates and the test temperature, which is quite similar to the deformation behavior of monolithic metallic glasses in the supercooled liquid region. The corresponding failure mode of the composite changes from shear or splitting fracture to bending failure with decreasing strain rate or increasing test temperature. The failure modes at the temperature nearT _g are mainly controlled by the metallic glass matrix due to the decrease in its viscosity at high temperature. Based on these multiple failure modes, the effects of test temperature and tungsten fiber volume fraction on deformation and fracture mechanisms are summarized.     

CT20钛合金薄壁管材数控冷弯成形行为研究

薄壁管材的小弯曲半径数控弯曲成形十分困难,外侧壁厚减薄是弯管成形中的加工缺陷之一,对于钛合金薄壁管尤为严重。采用模拟与实验相结合的方法,对规格为58 mm×1.5 mm的CT20钛合金管材数控弯曲成形过程中弯曲段的壁厚减薄进行了研究,得到相对弯曲半径对壁厚减薄的影响规律。结果表明,CT20钛合金管材冷弯成形时的极限相对弯曲半径(R/D)为2。     

Investigation of Deformation Behavior of Ring-Tensile Specimens Machined from Pressure Tubes of Indian PHWR

Specimens machined in the form of circular rings directly from the nuclear reactor pressure tubes and tested in a ring-tension test-setup offer great simplicity in evaluating the transverse mechanical properties of the as-manufactured as well as those of the service-exposed tubes. However, the state of stress in the specimen cross-section is not purely uni-axial due to the effect of bending and the presence of lateral pressure due to the loading mandrel. This requires the use of 3-D finite element (FE) analysis for simulation of deformation behavior of the specimens in the ring-tension test-setup. In this work, we have analyzed the deformation behavior of ring-tension specimens machined from two different types of zirconium alloy pressure tubes as used in the Indian pressurized heavy water reactors. The effect of geometry of the loading mandrel (i.e., 2-piece vs. 3-piece type of mandrel) on the load-deformation behavior of the test-setup has been studied. It was observed that the values of maximum load as well as the deformation behavior in the post-necking region differ significantly when only the geometry of the loading mandrel is changed keeping all the other parameters same. FE analysis has been able to correctly predict these variations as it takes into account of the effect of geometry, material properties as well the interaction between the mandrel and the specimen. Hence, the use of FE method is essential in the inverse analysis procedure where the material properties can be determined from these complex test-setups.     

Setting and realizing process plan for straightening thin- walled tube by multiple cross rolls of equal curvature

Since it was difficult to setting the plan and the unifying curvature- radius precisely when the thin- walled tubes were straightened continuously by the rolls of equal curvature. Therefore, based on the mechanism of unifying- straightening for the multiple cross- rolls straightening machine, the judgment method of the unifying curvature- radius was presented firstly in view of the bending and springback equation of the thin- walled tube, and then the searching method of the minimum unifying curvature- radius was presented subsequently, finally the straightening plans were drawn up for different thin- walled tubes with different initial curvature radii, especially for the thin- walled tube with the large initial deformation which could not be unified by the two cross rolls, the new method was pre- bending, unifying, and straightening, and it was also presented whether a thin- walled tube could be straightened. Some procedures were developed by VB to calculate the example, which is shown that the methods are effective, meanwhile it is found that if the unifying curvature- radius exist for an initial curvature- radius, it will not be sole and will be within a scope, and it is also found that there must be a scope of the initial curvature- radius within which the thin- walled tubes can??t be unified by the two cross rolls.     

The collapse of square section tubes in bending

The effect of changes in material properties and of geometry upon the load to initiate collapse, and also upon the energy to produce extensive plastic deformation during the three point bending of square section steel tubes, was examined. Over a wide range of material characteristics studied, the tensile strength gave the best correlation with the collapse load and energy characteristics. The geometric contribution to the effectiveness of the tube in resisting collapse was found to depend upon two factors, the relative density of the tube and the side dimension of the tube.     

Springback Analysis of Two-Layer Strips in Clad Cold Bimetal Bending

Recently, multi-layer metallic materials are increasingly being employed in a wide variety of industrial applications in order to create materials with combined functions and higher performances. Based on a nonlinear finite element analysis, the present study aims to develop a model for investigating the effects of sheet thickness and position on the springback of a stainless-steel clad aluminum sheet. It addresses three different types of strain hardening models, namely isotropic, cyclic, and Johnson–Cook (JC). A purely empirical approach, JC considers strain, strain rate, and temperature in elastic–plastic deformation. Good agreements are seen between the obtained results and the experimental verification data, therefore it is concluded that the bending behavior of a bi-layer metallic sheet/strip can be accurately predicted by the proposed model.     

大型回转窑传动功率的确定

对Φ5.5 m×115 m大型焙烧回转窑的传动功率进行计算分析,综合考虑窑内物料运动功率消耗、轴承的摩擦消耗、、表面间滚动摩擦消耗、窑体弯曲变形功率消耗、窑体回转时矫直功率消耗、传动效率以及运转特点等诸多因素,使回转窑传动功率的确定更加科学、合理、准确。     

Q值及变形量对中强钛合金冷轧管材表面质量的影响

针对TA18、TA22两种中强钛合金,对比了轧制Q值及轧制变形量对再结晶退火后管材质量的影响.结果表明,TA18和TA22管材获得内外表面均光洁、无缺陷的最适宜的工艺参数为:TA18变形量ε≤57％,且Q≤1.17;TA22变形最ε≤52％,且Q≤1.02.当TA18和TA22管材的变形量分别大于57％和52％、Q值分别大于1.17和1.12,则在其内表面或外表面产生微裂纹,且裂纹随变形量和Q值的增大而加深.     

圆管无模弯曲加工极限及断面扁平化实验

进行了圆管无模弯曲的基础实验研究。在无模弯曲实验研究的基础上,研究了变形区宽度等参数对圆管材极限弯曲半径的影响,分析了弯曲成形诸因素对圆管扁平化的影响。研究结果表明:在变形宽度一定的情况下,圆管扁平化随着相对弯曲半径的增加而减小;在弯曲半径一定的情况下,随着变形宽度的减小,圆管扁平化减小;圆管加工极限值随着变形宽度的增加而增加;加工极限值与相对变形宽度基本呈线性关系。