Effects of the exposure to corrosive salts on the frictional behavior of gray cast iron and a titanium-based metal matrix composite

The introduction of increasingly corrosive road-deicing chemicals has created significant and costly problems for the trucking industry. From a tribological perspective, corrosion of the sliding surfaces of brakes after exposure to road salts can create oxide scales that affect friction. This paper describes experiments on the effects of exposure to sodium chloride and magnesium chloride sprays on the transient frictional behavior of cast iron and a titanium-based composite sliding against a commercial brake lining material. Corrosion scales on cast iron, whose compositions were analyzed by several methods, initially act as abrasive third-bodies. Then they become crushed, spread out, and behave as a solid lubricant. Owing to its greater corrosion resistance, the titanium composite remained scale-free and its frictional response was markedly different. No corrosion scales were formed on the titanium composite after aggressive exposure to salts; however, a reduction in friction was still observed. Unlike the crystalline sodium chloride deposits that tended to remain dry, hygroscopic magnesium chloride deposits absorbed ambient moisture from the air, liquefied, and retained a persistent lubricating effect on the titanium surfaces.     

Modeling Wear Traces of Automotive Friction Materials by Cantor Set

Grooves parallel to the disc rotation direction were observed on the surface of non-metallic organic (NMO) friction materials after Friction Assessment Screening Test (FAST). Grooves are traces of wear and formed by abrasive mechanism. Grooves have fractal nature and they can be described by Cantor set. Two equations, one is time coordinate (x-axis) “matheqn” and the other one is wear ordinate (y-axis) “matheqn”, were proposed based on Cantor set to model the linear relationships among wear, time and sliding speed.     

汽车制动鼓内表面温升计算

介绍了一种计算制动鼓内表面制动温升的方法,并根据实际车型进行了计算和试验验证。     

RELIABILITY ANALYSIS OF CRANE BRAKE PARAMETERS

The high failure rate of crane brake results from improper choice of braking torque. The mathematical model of reliability for the crane brake parameters is introduced. Based on large amount of actual data the parameter reliabilities of 5-50 t general overhead travelling cranes are calculated, the probabilities that the braking torque is less than the static torque acting on the axle when the load moves down are obtained. Moreover, the ways to improve the reliability of brake parameters are discussed, the most reasonable values of braking safety coefficient are given.     

Composite friction materials based on metallic fillers: Sensitivity of μ to operating variables

Variation in μ during braking with operating variables is of major concern to the composite manufacturers, since it is composition specific. The frictional response of a multicomponent NAO friction composite is highly complex under a set of dynamically variable pressure and speeds. This paper discusses the sensitivity of friction (μ) towards braking pressure and sliding speed of selected composites based on variation in an inclusion of metallic fillers, viz. brass, copper and iron. Among metallic fillers, copper powder proved very effective in reducing μ-sensitivity to dynamic variations in pressure and speed. Regression analysis of μ values was also carried out.     

SiC particle reinforced Al matrix composites brazed on aluminum body for lightweight wear resistant brakes

Aluminum alloys are well known light-weight alloys and very interesting materials to optimize the strength/weight ratio in order to reduce automotive vehicle weight, fuel consumption and CO₂ emissions; unfortunately, they are also relatively soft and therefore cannot be used for high wear applications.The aim of this work was to develop an aluminum alloy brake disc with wear-resistant SiC particle reinforced aluminum matrix composites (SiC/Al) joined on to its surface.Different approaches based on brazing or shrink fitting joining technologies were used to join SiC/Al to the aluminum alloy surface.A functional graded structure was built by brazing thin layers of aluminum matrix composites reinforced with progressively higher amount of SiC particles by using a Zn–Al based alloy as joining material. Several samples were prepared by shrink fitting and brazing: 40 mm x 40 mm x 10 mm samples and a 100 mm diameter brake disc with 68% SiC particle reinforced Al matrix surface and aluminum alloy A365 body. Tribological tests demonstrated that an aluminum alloy brake disc with wear-resistant SiC particle reinforced aluminum matrix composites (SiC/Al) brazed on its surface is a promising technical opportunity.     

Frictionally excited thermo-elastoplastic instability

A transient finite element simulation is used to solve the two-dimensional contact problem involving thermo-elastoplastic instability (TEPI) in frictional sliding system. The existence of plastic deformation below the critical speed for thermoelastic instability is independent of the size of initial perturbation. For the simulation of the first/second partial contact, the amount of initial perturbation affects only the time interval of the first partial contact and the second partial contact is reached earlier, regardless of the initial perturbation. In addition, it shows that the locations of hot spots after cooling are changed.     

进口非标主机用盘式制动器主体结构优化的数学模型

:针对起重运输机械等行业进口主机所用标准的不同 ,提出了为其配置盘式制动器的主体结构优化。根据使用时的一般状况 ,分析了制动器工作时的力学和热力学特性 ,建立了以制动时间和外形尺寸最小为目标的结构优化数学模型 ,并对结构优化的软件设计进行了简单描述     

电动轮自卸车制动性能计算及摩擦副热机耦合分析

通过对行车制动性能标准的分析得到了性能要满足的最低要求,即行车制动性能要求为制动距离最长114 m,计算并确定了相应的制动力矩,实现方案初定。根据制动器的具体方案进行各种工况的校核,确定了最终的性能计算结果。针对100 t矿用自卸车车型进行制动盘热机耦合分析,从盘体材料的性能和载荷方面对摩擦副进行了温度场、应力场及热膨胀量的分析,并通过全周期制动性能验证。结果表明:该制动系统完全符合要求,从而确保了整车的制动性能。     

Surface characterisation by parameter-based technique, slicing method and PSD analysis

An effort has been made to compare the capability and results of three different surface roughness characterisation methods (parameter-based technique, slicing method and power spectral density analysis). Although all of these surface characterisation techniques are well-known such a comparison has not been made yet. It was found that 3D surface roughness parameters widely used in practice do not show any correlation with the surface finishing technique applied because of the inhomogenity of investigated surfaces. Contrary to this, based on parameters provided by the slicing method, such as width and orientation of asperities, ratio of major and minor axis of asperities, the different surface finishing techniques can be distinguished clearly. Additionally, it was found that the different machining technologies cannot be properly separated, in every case, by the fractal dimension. In other words, fractal dimensions may be very similar even if they belong to two different surface finishing techniques.