Experimental investigations of spontaneous damage to wet multi-plate clutches with carbon friction linings

Forschung im Ingenieurwesen - Safety and comfort, while ensuring torque transfer capability, are essential for wet multi-plate clutches. The safety of the torque transmission process largely...     

Real-time temperature calculation and temperature prediction of wet multi-plate clutches

Forschung im Ingenieurwesen - Many applications of wet multi-plate clutches are within safety-critical areas since malfunction or failure of the clutch is often equivalent to “loss of...     

滑移速度对铜石墨滑板材料摩擦性能的影响

为研究铜石墨滑板材料在不同滑移速度下的摩擦性能,从摩擦机理角度建立了滑板材料摩擦性能与滑移速度关系的理论模型,假定材料摩擦性能和滑移速度之间存在抛物线型关系,即存在一个最佳滑移速度区域,当滑移速度接近或处于此区域时,摩擦接触面石墨层的形成量和消耗量趋于平衡,材料表面形成了完整的石墨层,铜石墨滑板材料具有稳定的摩擦性能.在不同滑移速度下进行摩擦实验,采用扫描电镜分析磨损表面形貌,结果证明了理论模型的正确性.     

汽车悬架用弹簧钢铁素体全脱碳行为研究

为掌握汽车悬架用60Si2MnA弹簧钢的铁素体全脱碳行为,利用Gleeble1500热模拟机、金相显微镜、扫描电镜和电子探针等研究了加热温度、保温时间、热轧后的冷却速率对铁素体全脱碳层形成的影响.研究结果表明,加热温度对铁素体全脱碳行为影响最大,影响区间为725～925℃,850℃对应的脱碳层厚度达到最大;保温时间和冷却速率对铁素体脱碳行为也有较大影响,脱碳层厚度与时间的平方根呈线性关系;冷却太慢会形成较厚的脱碳层,冷却速率达到0.2℃/s时,实验钢基本不会发生脱碳行为.因此,避开脱碳层峰值温度,减少在(α+γ)两相区停留时间,均可有效阻止60Si2MnA弹簧钢的铁素体全脱碳.     

Fretting fatigue behavior and life prediction of automotive steel bolted joint

Fatigue tests of bolted joints of SAPH400 automotive steel plate were carried out. Effect of groove on fretting fatigue strength was investigated by introducing various geometries of grooves at contact edge. The fretting fatigue strength was improved by introducing groove: the fatigue strength increased with increasing groove depth. As the next step, the applicability of the tangential stress range–compressive stress range diagram to the bolted joints was investigated using the tangential stress range–compressive stress range diagram obtained from conventional laboratory-type SAPH400 steel specimens. The result showed that the fretting fatigue strength of actual component, i.e. the bolted joint could be successfully predicted based on the tangential stress range–compressive stress range diagram.     

多维复合增强汽车摩擦材料

以玻璃纤维、 铜纤维、 矿物纤维、 芳纶纤维、 纳米钛酸钾晶须和片状蛭石等制备多维复合增强非石棉有机汽车摩擦材料, 构成具有“微米和纳米”尺度、 “一维（纤维）和二维（片状）”形态、 “无机和有机”材质的多维复合增强体系。基于材料的力学和摩擦磨损性能测试结果, 通过回归模型分析对复合体系配方进行了优化。通过材料的内部结构和摩擦面的形貌观察, 分析了多维复合增强体系提高材料力学和摩擦磨损性能的内在机制。结果表明, 通过优化配方, 各增强相之间表现出良好的混合和协同效应, 优化多维复合增强汽车摩擦材料的冲击强度为0.54J/cm2、 总磨损率为1.35×10-7cm3/(N·m)、 摩擦系数的变异系数为5.86%。      

Corrosion fatigue behavior of friction stir processed interstitial free steel

In this study, interstitial free (IF) steel plates were subjected to double-sided friction stir processing (FSP). The fine-grained structure with an average grain size of about 12 μm was obtained in the processed zone (PZ) with a thickness of about 2.5 mm. The yield strength (325 MPa) and ultimate tensile strength (451 MPa) of FSP IF steel were significantly higher than those of base material (BM) (192 and 314 MPa), while the elongation (67.5%) almost remained unchanged compared with the BM (66.2%). The average microhardness value of the PZ was about 130 HV, 1.3 times higher than that of the BM. In addition, the FSP IF steel showed a more positive corrosion potential and lower corrosion current density than the BM, exhibiting lower corrosion tendency and corrosion rates in a 3.5 wt% NaCl solution. Furthermore, FSP IF steel exhibited higher fatigue life than the BM both in air and NaCl solution. Corrosion fatigue fracture surfaces of FSP IF steel mainly exhibited a typical transgranular fracture with fatigue striations, while the BM predominantly presented an intergranular fracture. Enhanced corrosion fatigue performance was mainly attributed to the increased resistance of nucleation and growth of fatigue cracks. The corrosion fatigue mechanism was primarily controlled by anodic dissolution under the combined effect of cyclic stress and corrosive solution.     

Influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank

This work investigated the influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank. The results indicate that the corrosion rate of three ferrite-pearlite steels increased with extending the immersion time due to the continuous accumulation of the residual Fe_3C. However, the addition of Sn or the combined addition of Sn and Mo could reduce the corrosion rate of Sn containing steel and Sn-Mo containing steel to 37.5% and 20% of that of carbon steel, respectively. Moreover, the cathodic reaction of Sn containing steel and Sn-Mo containing steel was always controlled by the charge transfer step during the whole immersion test, while that of carbon steel was gradually transformed into the diffusion-controlled process. These results were mainly related with the deposition of metallic Sn and Mo on the steel surface. The metallic Sn and Mo with uniform distribution restrained the galvanic effect through suppressing both the anodic dissolution of ferrite and cathodic hydrogen evolution reaction on the residual Fe_3C.     

Influence of dynamic load on friction behavior of human articular cartilage,stainless steel and polyvinyl alcohol hydrogel as artificial cartilage

Many biomaterials are being developed to be used for cartilage substitution and hemiarthroplasty implants. The lubrication property is a key feature of the artificial cartilage. The frictional behavior of human articular cartilage, stainless steel and polyvinyl alcohol (PVA) hydrogel were investigated under cartilage-on-PVA hydrogel contact, cartilage-on-cartilage contact and cartilage-on-stainless steel contact using pin-on-plate method. Tests under static load, cyclic load and 1 min load change were used to evaluate friction variations in reciprocating motion. The results showed that the lubrication property of cartilage-on-PVA hydrogel contact and cartilage-on-stainless steel contact were restored in both 1 min load change and cyclic load tests. The friction coefficient of PVA hydrogel decreased from 0.178 to 0.076 in 60 min, which was almost one-third of the value under static load in continuous sliding tests. In each test, the friction coefficient of cartilage-on-cartilage contact maintained far lower value than other contacts. It is indicated that a key feature of artificial cartilage is the biphasic lubrication properties.     

A combinatorial approach for automotive friction materials: Effects of ingredients on friction performance

Raw materials used in automotive friction formulations were classified using a combinatorial approach into two groups in accordance with their ability to improve the wear properties of the mixture by two-phase friction composites. Components of group one, which improved the wear resistance, include softer additives (graphite, MoS₂, and Twaron), harder additives (Al₂O₃ and steel wool), and organic binder (benzoxazine). Softer additives have low friction coefficient (μ), low wear, and easily transferred debris to the surface of disc. Harder additives have intermediate wear, intermediate μ, and formed iron-containing surface layer transferred from cast iron disc to friction material pad. Benzoxazine has high wear and high μ and there is no transferred layer formed either on disc or pad in the case of benzoxazine used as pad. The wear of two-phase friction materials can be improved by adding Al₂O₃, graphite, MoS₂, steel wool, and Twaron to benzoxazine and four wear improvement mechanisms were proposed: (1) lubrication mechanism (graphite and MoS₂); (2) abrasive mechanism (Al₂O₃); (3) friction layer mechanism (steel wool); (4) reinforced mechanism (Twaron). Components of group two, which produced poor wear resistance, include BaSO₄, BN, B₂O₃, brass chips, CaCO₃, Ca(OH)₂, cashew, copper chips, CuS, Cu₂S, H₃BO₃, iron powder, MgO, oxidized PAN fiber, PMF (SiO₂ + CaO), Sb₂S₃, Ultrafibe (CaSiO₃), and ZrSiO₄.     

紫铜纤维对汽车摩擦材料性能的影响

以一种成熟的树脂基摩擦材料配方为基础,研究紫铜纤维质量分数对摩擦材料物理性能、力学性能、摩擦磨损性能及制动噪声的影响.结果表明:随紫铜纤维质量分数增加,摩擦材料的密度、硬度、内剪切强度逐渐增大,气孔率、压缩量逐渐降低,pH值则随紫铜纤维质量分数的变化没有明显的区别;通过执行SAE J2521和SAE J2522程序进行台架实验,发现紫铜纤维的添加对摩擦材料名义摩擦因数的影响较小;添加适量紫铜纤维有利于改善摩擦材料与对偶件表面的接触状态,稳定摩擦因数,提高摩擦材料的抗衰退性能;随紫铜纤维含量增加,摩擦材料的磨损率先降低后略微上升,紫铜纤维质量分数为9％时,磨损率最低;当紫铜纤维质量分数在7％时,摩擦材料具有最佳的噪声性能.     

稀土渗碳对GCr15钢激光熔凝层摩擦行为的作用

为了提高在航空航天和民用等领域中广泛使用的GCr15钢的表面强度及耐磨性能,采用激光熔凝方法对GCr15钢表面稀土渗碳层进行改性处理,研究了稀土渗碳对激光熔凝改性层摩擦系数及磨损量的影响.结果表明:稀土渗碳使GCr15钢表面激光熔凝改性层的摩擦系数有所下降且在整个摩擦过程中波动较小,磨损失重为未经改性处理的基体材料失重的14%(质量分数);随着摩擦时滑动距离的增加及载荷的加大,稀土渗碳激光熔凝改性处理降低磨损失重的作用也显著增大;稀土渗碳层的磨损形式为犁沟磨损,而稀土渗碳激光熔凝处理的改性层则属于局部擦伤型;稀土渗碳在钢表面激光熔凝处理中的作用主要表现为细化晶粒、微合金化、净化和改善组织致密性.     

Influence of deep cryogenic treatment on internal friction behavior in the process of tempering

This paper investigated the influence of deep cryogenic treatment on the internal friction behaviors in the process of tempering. The internal friction indicates the carbon atoms segregated to nearby dislocations and produced strong interactions, including interstitial carbon atoms themselves and between the interstitial carbon atoms with time-dependent strain field of dislocations. It is made clear that the cluster of carbon atoms nearby the dislocations in the DCT either acts as or grows into nuclei for the formation of carbide on subsequent during tempering. Thus the improvement of wear resistance due to more carbides precipitation after DCT treating has been observed indirectly by using internal friction.     

A methodology for data-driven modeling and prediction of the drag losses of wet clutches

In wet clutches, load-independent drag losses occur in the disengaged state and under differential speed due to fluid shearing. The drag torque of a wet clutch can be determined accurately and reliably by means of costly and time-consuming measurements. As an alternative, the drag losses can already be precisely calculated in the early development phase using computing-intensive CFD models. In contrast, simple analytical calculation models allow a rough but non-time-consuming estimation. Therefore, the aim of this study was to develop a methodology that can be used to build a data-driven model for the prediction of the drag losses of wet clutches with low computational effort and, at the same time, sufficient accuracy under consideration of a high number of influencing parameters. For building the model, we use supervised machine learning algorithms. The methodology covers all relevant steps, from data generation to the validated prediction model as well as its usage. The methodology comprises six main steps. In Step 1, the data is generated on a suitable test rig. In Step 2, characteristic values of each measurement are evaluated to quantify the drag loss behavior. The characteristic values serve as target values to train the model. In Step 3, the structure and quality of the dataset are analyzed and, subsequently, the model input parameters are defined. In Step 4, the relationships between the investigated influencing parameters (model input) and the characteristic values (model output) are determined. Symbolic regression and Gaussian process regression have both been proven to be suitable for this task. Lastly, the model is used in Step 5 to predict the characteristic values. Based on the predictions, the drag torque can be predicted as a function of differential speed in Step 6, using an approximation function. The model allows a user-oriented prediction of the drag torque even for a high number of parameters with low computational effort and sufficient accuracy at the same time.

     

Analytical modeling and dimensionless characteristics of open wet clutches in consideration of gravity

Forschung im Ingenieurwesen - Wet clutches are widely used in power transmission, but lack of the fact of an energy loss in open state condition. The flow conditions in the fluid flow of an open...     

Influence of conical projectile diameter on perpendicular impact of thin steel plate

A numerical study of conical projectiles for perpendicular impact on a thin steel plate is reported. The target material considered, Weldox 460 E steel, is frequently used for this kind of application and several results of experiments are available in the international literature to verify numerical simulations. The Johnson-Cook constitutive relation coupled with the Johnson-Cook failure criterion have been applied to analyse penetration of the target and also the failure process. The analysis has been focussed on the influence of the projectile diameter on the perforation process, assuming the same projectile mass. The aim was to preserve the same initial kinetic energy and identical nose angle. The goal is to estimate the ballistic limit, the residual velocity, the plastic work, and the temperature levels produced during the penetration process. The analysis has shown a linear increase of the ballistic limit with the projectile diameter.     

Thermomechanical processes in the friction heating of disk brakes

Thermomechanical processes are studied at the contact area of a metal brake disk and brake block during braking. Expressions are obtained for both the temperature and the thermal displacement in the center of the contact area caused by the effect of the friction heat source, whose power is a linear function of time. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 70, No. 1, pp. 111–116, January–February, 1997.     

Investigation on thermomechanical behavior of a HSLA steel circular plate under impact load

Based on the von Karman equation and classical thin plate theory, thermomechanical behavior of a high strength low alloy (HSLA) steel circular plate under impact load is investigated. Firstly, when the HSLA steel circular plate is impacted by a rigid impactor, the relation of the contact radius and the instantaneous relative displacement is obtained by using the modified nonlinear Hertzian contact law, and the contact force is solved by using the time increment method. Secondly, the nonlinear governing equations in the form of displacements for the HSLA steel circular plate under the impact load are obtained by using the Hamilton variational principle. Finally, the unknown variable functions are discretized in space and time domains by utilizing the finite difference method and Newmark method, and the whole problem is solved by the iterative method. Numerical results denote that the geometrical parameters, boundary conditions of the HSLA steel circular plate and the initial velocity of impactor have great influences on deformation, the contact force and stresses of the HSLA steel circular plate.     

Effect of heat-input on pitting corrosion behavior of friction stir welded high nitrogen stainless steel

In this study, different welding parameters were selected to investigate the effects of heat-input on the microstructure and corrosion resistance of the friction stir welded high nitrogen stainless steel joints. The results showed that, the welding speed had major influence on the duration at elevated temperature rather than the peak temperature. The hardness distribution and tensile properties of the nugget zones (NZs) for various joints were very similar while the pitting corrosion behavior of various NZs showed major differences. Large heat-input resulted in the ferrite bands being the pitting location, while tool wear bands were sensitive to pitting corrosion in the low heat-input joints. Cr diffusion and tool wear were the main reasons for pitting. The mechanisms of pitting corrosion in the NZs were analyzed in detail.     

纸基摩擦材料的研究现状

简要评述了纸基摩擦材料组成、工艺和性能的研究进展.重点阐述了纸基摩擦材料的增强纤维、粘结剂树脂、摩擦性能调节剂和填料的研究现状,介绍了纸基摩擦材料多次漫渍、双层结构和孔隙控制制备技术,以及纸基摩擦材料的物理力学性能、摩擦磨损性能的研究方法.提出了纸基摩擦材料多元组合改性、性能协同研究、交互规律认识的热点课题.