四点接触球转盘轴承许用接触应力试验

42CrMo钢具有良好的淬硬性,被广泛用做转盘轴承套圈材料。首先对42CrMo钢采取不同热处理工艺进行表面感应淬火,以获得不同的淬硬层深度;然后通过电子万能试验机进行压痕试验;最后对试验数据进行分析研究。研究发现:决定转盘轴承许用接触应力的因素除了材料的机械性能外,还包括材料热处理后的表面硬度、淬硬层深度以及轴承的结构参数等因素。     

磨削用量对65Mn钢磨削淬硬层深度及其均匀性的影响

采用刚玉砂轮在普通平面磨床上对65Mn钢进行磨削淬硬,研究磨削深度和工件进给速度对65Mn钢磨削淬硬层深度及其均匀性的影响。结果表明:试件淬硬层由完全淬硬层、过渡层组成;淬硬层最大深度随磨削深度的增大而增大,随工件进给速度的增加而减小;在本试验条件下,磨削深度ap0.4mm时,试件表层全部淬硬,均匀性较好。     

液氮冷却磨削淬火后42CrMo钢的组织与硬度

用液氮作为冷却液对调质态42CrMo钢进行磨削淬火试验,之后对试验钢进行空冷和深冷处理,研究了淬硬层的组织、硬度和表面粗糙度,并将其组织与乳化液冷却磨削淬火试验钢的淬硬层组织进行对比。结果表明:与乳化液冷却磨削淬火相比,液氮冷却磨削淬火后,淬硬层中的马氏体更加细小;深冷处理后,淬硬层中的的马氏体和碳化物增多;随着磨削深度增加,液氮冷却磨削淬火试验钢淬硬层的厚度、峰值显微硬度和表面粗糙度均增大。     

42CrMo钢磨削淬硬加工中磨削力的研究

磨削力对磨削淬硬层的形成及其质量具有重要影响。本研究在MKL7132X6/12型数控强力成形磨床上对42CrMo钢进行磨削淬硬加工试验。试验结果表明,磨削深度、磨削速度和工件进给速度都是影响切向和法向磨削力的因素,且磨削深度的影响程度最大,工件进给速度最小。切向和法向磨削力会随着磨削深度和工件进给速度的增加、磨削速度的降低而增大。对磨削力比影响程度最大的是磨削深度,最小的是磨削速度。磨削力比会随着磨削速度、磨削深度的增加或工件进给速度的降低而增大。本研究为提高磨削淬硬加工质量提供了依据。     

磨削条件对45钢最大磨削淬硬层深度的影响

以磨削淬硬实验为基础,研究了单程磨削淬硬过程中磨削深度、工件进给速度对淬硬层深度的影响;同时通过建立最大磨削淬硬层深度的计算模型并结合Matlab软件的数值仿真功能,对45钢最大磨削淬硬层深度进行模拟仿真。结果表明:最大磨削淬硬层深度随着磨削深度的增加或者工件进给速度的减小而增加;采用Matlab对最大磨削淬硬层深度进行数值仿真得到的结果与实验结果吻合度较高,通过建立适当的数学模型可以有效地预测最大磨削淬硬层深度。     

磨削用量对40Cr钢磨削淬硬层的影响

以平面磨削淬硬试验为基础，研究了磨削用量对40Cr钢磨削淬硬层组织与性能的影响。结果表明，在磨削淬硬加工中的热、力耦合作用下，磨削用量对磨削淬硬层的马氏体组织形貌及其高硬度区硬度值无显著影响，其高硬度值均在HV630～HV680之间。随着磨削速度的提高、磨削深度的增加或工件进给速度的降低，磨削淬硬层表面残余压应力值相应减小，但淬硬层深度以及应力作用深度相应增加。     

感应淬火硬化层深度超声波检测方法的适用性

对42Cr Mo钢和50Mn钢进行感应淬火,采用硬度法及超声波无损检测法检测2种材料的淬火硬化层深度,研究超声波无损检测法对2种材料的适用性。结果表明:42Cr Mo钢淬透性好,淬硬层与基体界面明显,适用超声波无损检测法;50Mn钢淬透性较差,淬硬层与基体间存在大的过渡区,界面不明显,不适宜采用超声波无损检测方法。即超声波检测法测量感应淬火硬化层深度不适用于淬透性差的钢。     

高频感应淬火工艺研究

我单位中频感应淬火机床电源系统发生故障,需要中频感应淬火的长又轴、短又轴和摆销外委热处理加工费用很高,且生产周期无法得到保证。故想到在高频感应淬火机床上调试。用一次连续加热淬火的方法来试制,硬度达到了技术要求,但淬硬层深度不够;如果继续放慢加热速度,易造成零件表面加热温度过高,加之两种零件的材料都是42CrMo钢,淬火时容易在零件表面产生淬火裂纹,易导致成批报废。为此,采用先预热后加热的淬火法,对该类零件的淬火工艺进行了研究与改进。     

高硬度淬硬钢高速铣削过程的切削温度研究

通过设计在不同加工工艺参数条件下高速铣削高硬度(48HRC～68HRC)淬硬钢试验,研究了切削温度信号的特征,分析了切削温度与淬硬钢材料硬度、切削工艺参数的关系。结果表明:随着淬硬钢材料硬度的增大,切削温度呈现递增趋势,4种淬硬钢的切削温度随材料硬度变化顺序为:PM60SKD11S136P20,其中,PM60材料的切削温度远高于其余3种淬硬钢材料;随着切削工艺参数(切削速度、每齿进给量、轴向铣削深度和径向铣削深度)的增大,4种涂层铣刀的切削温度基本呈现出逐渐增高的趋势,其中TiSiN和TiAlN涂层铣刀的切削温度增高幅度大于AlCrN和CrSiN涂层铣刀。建立了4种涂层铣刀高速铣削淬硬钢S136的切削温度多元回归预测模型,可应用于淬硬钢S136的切削温度预测。     

基于ANSYS的等离子弧表面淬火过程温度场的数值模拟

用ANSYS软件建立并模拟了等离子弧表面淬火过程的温度场,由此得出工件任意点的温度分布和淬硬层的分布,根据淬硬相变温度预测离子束淬火的最大硬化深度和各节点到达最高温度时间,并通过45钢的淬火试验验证了模拟结果与试验结果的一致性.     

Finite element analysis of spherical indentation to study pile-up/sink-in phenomena in steels and experimental validation

The ball indentation technique based on deforming a material with a spherical indenter is an useful non-destructive tool for evaluating mechanical properties from a very small volume of material. In this work, the indentation test carried out using a 1.0 mm diameter tungsten carbide ball to penetration depths of around 100–200 μm is modeled using finite element (FE) method and analyzed for three steels having different yield stress and strain hardening exponent. The FE generated load–depth curve is compared and verified with the experimental load–depth data for the three materials. The role of the contact friction at the indenter–specimen interface on both the load—depth plot and indentation profile are examined. The development of pile-up/sink-in during indentation and its dependence on strain hardening characteristics of the material, contact friction and indentation depth are analyzed using the FE model. The indentation profiles obtained from simulation are compared with experimental profiles and the implication of pile-up phenomenon on accurate evaluation of stress–strain values from the experimental indentation load–depth data is discussed.     

Deformation analysis of plastic strain rate hardening material using stress function under plane strain condition

The two-dimensional plane strain equation of plastic flow in accordance with the Levy-Mises constitutive relation is expressed in terms of stress functions of complex variables. Expressions for the stress, strain rate and velocity are derived for plastic flow in a non linear viscous medium assuming the stress function in the form of both the summation and product of conjugate stress functions. The plastic states are derived, also using a mixed mode solution expressed in terms of non-seperable, independent conjugate complex variables.The analysis of the block indentation associated with a nonlinear viscous (strain rate hardening) material under plane strain condition using the product form solution is performed. The effect of the variation in the strain-rate hardening exponent on the contact stress is investigated. The predicted behavior of the vertical component of the contact stress suggests the possibility of the development of a specially instrumented plane strain block indentation tests, for the rapid determination of the strain-rate sensitivity of the real material. The vertical contact stress and strain-rate obtained from the product of the complex conjugate stress function are compared with those obtained from the summation form of the complex conjugate stream function.     

硬度影响压痕弹塑性行为的有限元分析

以具有不同硬度40Cr为研究对象,根据集中载荷下的接触模型和赫兹理论,计算了压痕接触半径和压痕附近弹性区域的表面局部接触应力,并采用有限元法,分析硬度物理量对压痕弹塑性行为、局部接触应力、卸载后保留在内部的残余应力的影响,探讨压痕参数、压痕接触应力、残余应力与硬度之间的关系以及载荷增加时它们的发展.结果表明,相同载荷下塑性隆起量、压痕接触半径、压痕量和塑性区范围随着硬度值的提高而减小,弹性回弹量、最大接触应力和残余应力随硬度提高而增加;压痕周围处接触应力和残余应力、其分布范围和塑性区域随载荷的增加而增加.     

MoS2/Ti复合固体润滑膜的力学性能与摩擦特性

采用非平衡磁控溅射法在9Cr18轴承钢基底上制备了厚度约3μm的MoS2/Ti复合固体润滑膜,基于球形压头纳米压痕试验,采用连续刚度法对MoS2/Ti复合固体润滑膜的力学性能进行研究,探究MoS2/Ti复合固体润滑膜力学性能随压痕深度的变化规律;根据压痕试验载荷-位移曲线,采用Hertz接触理论计算MoS2/Ti复合固体润滑膜的弹性模量并与试验结果进行对比;利用CSM摩擦试验机对低速、低载下MoS2/Ti复合固体润滑膜的摩擦特性进行研究;基于压痕试验提出了一种能够更准确计算钢球加载时MoS2/Ti复合固体润滑膜接触应力的方法,并计算了摩擦试验不同载荷下的接触应力。结果表明:MoS2/Ti复合固体润滑膜的力学性能和摩擦特性都会受到表面形貌的影响;除表面初始压入阶段外,MoS2/Ti复合固体润滑膜的弹性模量和接触刚度都随着压痕深度的增大而增大;滑动速度和载荷共同影响MoS2/Ti复合固体润滑膜的摩擦特性。     

Modeling surface roughness for polishing process based on abrasive cutting and probability theory

The surface roughness is a variable used to describe the quality of polished surface. This article presents a surface roughness model based on abrasive cutting and probability theory, which considers the effects of abrasive grain shape, grit and distribution feature, pressure on surface roughness. The abrasive grain protrusion heights are thought to close to Gaussian distribution, and then the relationship between the indentation depth and the pressure based on Hertz contact theory is obtained. Surface roughness prediction model is established by calculating indentation depth of the abrasive grains on workpiece surface. The maximum surface profile height (R_y) is approximately equal to the maximum indentation depth of the abrasive grain. The arithmetic average surface roughness (R_a) is equal to the average indentation depth of the abrasive grain. The effects of process parameters such as pressure and grit on R_y and R_a were simulated and analyzed in detail.     

含多粗糙峰涂层等效应力的有限元分析

研究刚性平面与含粗糙峰涂层在二维与三维模型下的弹性接触问题,采用有限元法分析涂层弹性模量比、涂层厚度、粗糙峰间距、刚性平面压下深度对涂层粗糙峰表面、涂层/基体界面分布及基体等效应力分布的影响。计算结果表明压下深度对三维涂层粗糙峰表面最大应力的影响最大,涂层厚度、涂层/基体弹性模量比、粗糙峰间距的变化对应力值影响逐渐减小;增大涂层厚度、减小压下深度和粗糙峰间距、降低弹性模量比会使得三维接触模型最大等效应力值显著降低;增加涂层粗糙峰数和涂层厚度、同时降低涂层弹性模量有助于提高涂层/基体界面结合强度。相对于二维接触模型来说三维接触模型在粗糙峰表面的等效应力增大,造成这种变化的主要原因是由于涂层表面粗糙峰之间的等效应力叠加引起的。该研究为涂层粗糙峰及涂层/基体界面强度的应力分析提供依据。     

The influence of strain hardening on steel erosion wear studied by analytical modelling of impeller testing

ABSTRACT

Abrasive wear of steel is a common problem in the mining industry. It was tackled by many researches using analytical and numerical approaches. Despite the advantages of the analytical models to provide quick and elegant solutions, they were derived using several assumptions limiting their applicability, such as e.g. rigid-plastic flow. However, the consideration of strain hardening during impact is crucial to depict a real behaviour of tool material, which changes its mechanical properties during collision. In this research, a new analytical model is invented describing the impact of steel plate with a solid rock, while the material of the steel plate is hardening during penetration and scratching. The model provides a frame of analytical equations based on the second Newton law and equations of motion in vertical and horizontal directions. The motion in vertical direction is considered as an indentation problem and the motion in the horizontal direction as a scratch problem. This model incorporates the most general Holloman representation of strain-hardening law to capture the relationship between microstructural characteristics of steels and wear resistance. It was shown that the indentation depth, the pile-up height, length of the scratch and erosion ratio directly dependant on the strain-hardening parameters in Holloman equation. The model predicts the maximum indentation depth and scratch length as a function of strength coefficient and strain hardening exponent, but also of impact angle, mass of the rock, position of impact at the surface of steel plate and coefficient of friction during metal movement. The model was tested qualitatively by comparison with impeller-tumbler experiments using different steel plates. The solution obtained from this model could be used for quick and easy evaluation of the steel for mining tools in an industrial environment.     

非对称齿形下的压痕问题分析

非对称齿形的压痕问题要比分析轴对称压头情况复杂得多。受压基体中的应力一应变分布、塑性硬化面的发展方向等力学特性，都随着齿形非对称程度和角度不断变化。通过量纲分析，文中建立了受压基体中的位移随外力变化的函数关系式，计算分析这个关系式随齿形的变化趋势；并利用数值模拟结果分析压头齿形变化对应力和能量产生的影响。对工业应用的预应力锚片齿形提出了优化方案。     

An attempt to determine the true stress-strain curves of amorphous polymers by nanoindentation

We have made an attempt to identify the true material stress-strain curves of some amorphous polymers (PC, PMMA, CR39 (diethylene glycol bis(allyl carbonate)) from nanoindentation experiments by using non-self similar tip shapes, i.e. tips promoting an increasing strain with an increasing indentation depth. We firstly found that, for a defined strain rate, the relationship linking the contact pressure to the ratio between the contact depth and the contact radius is intrinsic to the material, i.e. it doesn’t depend on the tip shape used. From this relationship, for each material, we calculated the evolution of the average stress with the average strain beneath the tip, by using the theoretical background developed for elasto-perfectly plastic materials. By comparing to compression test results, we concluded that this approach works well for PC and PMMA only for an average strain below 12%. This approach is inapplicable for the CR39 material even at low strains. We assumed that this is mainly due to the occurrence of a significant strain hardening, that doesn’t allow us to neglect the strain gradient existing beneath the tip.