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Micro Pitting
Micro pitting is a fatigue failure of the surface of a material commonly seen in rolling bearings and gears. It is also known as grey staining, micro spalling or frosting. Pitting and micropitting The difference between pitting corrosion and micropitting is the size of the pits after surface fatigue. Pits formed by micropitting are approximately 10-20 μm in depth, and micropitted metal often has a frosted or gray appearance. Normal pitting creates larger and more visible pits. Micropits are originated from the local contact of asperities produced by improper lubrication. Causes In a normal bearing the surfaces are separated by a layer of oil, this is known as elastohydrodynamic (EHD) lubrication. If the thickness of the EHD film is of the same order of magnitude as the surface roughness, the surface topography is able to interact and cause micro pitting. A thin EHD film may be caused by excess load or temperature, a lower oil viscosity than is required, low speed or water in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fatigue (material)
In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure. Fatigue has traditionally been associated with the failure of metal components which led to the term metal fatigue. In the nineteenth century, the sudden failing of metal railway axles was thought to be caused by the metal ''crystallising'' because of the brittle appearance of the fracture surface, but this has since been disproved. Most materials, such as composites, plastics and ceramics, seem to experience some sort of fatigue-related failure. To aid in predicting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elastohydrodynamic
Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubricated systems are designed so that the applied load is partially or completely carried by hydrodynamic or hydrostatic pressure, which reduces solid body interactions (and consequently friction and wear). Depending on the degree of surface separation, different lubrication regimes can be distinguished. Adequate lubrication allows smooth, continuous operation of machine elements, reduces the rate of wear, and prevents excessive stresses or seizures at bearings. When lubrication breaks down, components can rub destructively against each other, causing heat, local welding, destructive damage and failure. Lubrication mechanisms Fluid-lubricated systems As the load increases on the contacting surfaces, distinct situations can be observed wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pitting Corrosion
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation reaction) while an unknown but potentially vast area becomes cathodic (reduction reaction), leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with a limited diffusion of ions. Another term arises, pitting factor, which is defined as the ratio of the depth of the deepest pit (resulting due to corrosion) to the average penetration, which can be calculated based on the weight loss. Development and kinetics of pitting According to Frankel (1998) who performed a review on pitting corrosion, it develops in three successive steps: (or nucleation) by breakdown of the passive film protecting the metal surface from oxidation, (2) growth of metastable pits (growing up to the micron scale and then repas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ISO 25178
ISO 25178: Geometrical Product Specifications (GPS) – Surface texture: areal is an International Organization for Standardization collection of international standards relating to the analysis of 3D areal surface texture. Structure of the standard Documents constituting the standard : * Part 1: Indication of surface texture * Part 2: Terms, definitions and surface texture parameters * Part 3: Specification operators * Part 6: Classification of methods for measuring surface texture * Part 70: Material measures * Part 71: Software measurement standards * Part 72: XML file format x3p * Part 600: Metrological characteristics for areal-topography measuring methods * Part 601: Nominal characteristics of contact (stylus) instruments * Part 602: Nominal characteristics of non-contact (confocal chromatic probe) instruments * Part 603: Nominal characteristics of non-contact (phase-shifting interferometric microscopy) instruments * Part 604: Nominal characteristics of non-contact (coher ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Metrology
Surface metrology is the measurement of small-scale features on surfaces, and is a branch of metrology. Surface primary form, surface fractality, and surface finish (including surface roughness) are the parameters most commonly associated with the field. It is important to many disciplines and is mostly known for the machining of precision parts and assemblies which contain mating surfaces or which must operate with high internal pressures. Surface finish may be measured in two ways: ''contact'' and ''non-contact'' methods. Contact methods involve dragging a measurement stylus across the surface; these instruments are called profilometers. Non-contact methods include: interferometry, digital holography, confocal microscopy, focus variation, structured light, electrical capacitance, electron microscopy, photogrammetry annon-contact profilometers Overview The most common method is to use a diamond stylus profilometer. The stylus is run perpendicular to the lay of the surface. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Embrittlement
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement. The essential facts about the nature of hydrogen embrittlement have been known since the 19th century. Hydrogen embrittlement is maximised at around room temperature in steels, and most metals are relatively immune to hydrogen embrittlement at temperatures above 150 °C. Hydrogen embrittlement requires the presence of both atomic ("diffusible") hydrogen and a mechanical stress to induce crack growth, although tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. However, the dependence on some of these properties ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Roughness
Surface roughness, often shortened to roughness, is a component of surface finish (surface texture). It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. In surface metrology, roughness is typically considered to be the high-frequency, short-wavelength component of a measured surface. However, in practice it is often necessary to know both the amplitude and frequency to ensure that a surface is fit for a purpose. Roughness plays an important role in determining how a real object will interact with its environment. In tribology, rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities on the surface may form nucleation sites for cracks or corrosion. On the other hand, roughness ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lubricant
A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity. In addition to industrial applications, lubricants are used for many other purposes. Other uses include cooking ( oils and fats in use in frying pans, in baking to prevent food sticking), bioapplications on humans (e.g. lubricants for artificial joints), ultrasound examination, medical examination, and sexual intercourse. It is mainly used to reduce friction and to contribute to a better and efficient functioning of a mechanism. History Lubricants have been in some use for thousands of years. Calcium soaps have been identified on the axles of chariots dated to 1400 BC. Building stones were slid on oil-impregrated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bearing (mechanical)
A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may ''prevent'' a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. Rotary bearings hold rotating components such as shafts or axles within mechanical systems, and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the '' plain bearing'', consists of a shaft rotating in a hole. Lubrication is used to reduce friction. In the ''ball bearing'' and ''roller bearing'', to reduce sli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lubrication
Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubricated systems are designed so that the applied load is partially or completely carried by hydrodynamic or hydrostatic pressure, which reduces solid body interactions (and consequently friction and wear). Depending on the degree of surface separation, different lubrication regimes can be distinguished. Adequate lubrication allows smooth, continuous operation of machine elements, reduces the rate of wear, and prevents excessive stresses or seizures at bearings. When lubrication breaks down, components can rub destructively against each other, causing heat, local welding, destructive damage and failure. Lubrication mechanisms Fluid-lubricated systems As the load increases on the contacting surfaces, distinct situations can be observed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
