Surface fatigue

The main causes of failure in gear couplings are wear or surface fatigue caused by lack of lubricant, incorrect lubrication, or excessive surface stresses. Component fracture caused by overload or fatigue is generally of secondary importance. 

The importance of amplitude of slip is emphasised above. In recent years, the area of very low amplitudes and very carefully controlled amplitudes has been investigated. These researches confirm that the specific wear rate (volume removed, per unit distance of sliding per unit applied load) increases dramatically in the region 30-70 /xm and then becomes constant, as would be expected in reciprocating or unidirectional sliding . Damage is produced at amplitudes of 1 /xm or less", but it tends to be characteristic of surface fatigue rather than wear. 

The second basic problem is known as ball-cup friction and wear. It results from frictional wear between the hemispherical bearing and the polished spherical ceramic or metal ball attached to the stem. The third problem is addressed to as sub-surface fatigue. It results from the brittleness of the UHMWPE bearing and the tendency of the UHMWPE bearing to fail under reciprocating applied loads. 

Surface fatigue is usually the result of high periodic loads in the contact zone that lead to changes of the material structure and finally to material failure at the surface. 

PG-2 is the development of a category intended for final drive axles with performance beyond GL-5. In this case, the performance needs are thermal stability, seal compatibility, surface fatigue, copper corrosion, and maintaining GL-5 tests. PG-2 is now known as GL-8. After 1994, most automotive gear oils have been rated as GL-5, GL-7, and GL-8, all in one product. 

Exoelectrons are known to be emitted from nascent or fresh solid surfaces by mechanical action such as abrasion, cutting, surface fatigue, wear, forming and so on. There are two types of EE associated with dark emission termed "triboemission and after emission" (Kajdas, 1985a, 1989 and 1994 Nakayama and Hashimoto, 1991 and 1992 Nakayama et al., 1992 and 1995 Thiessen, 1965). 

Percussion is a repetitive solid body impact, such as experienced by print hammers in high-speed electromechanical applications and high asperities of the surfaces in a gas bearing. Repeated impacts result in progressive loss of solid material. Percussive wear occurs by hybrid wear mechanisms, which combine several of the following mechanisms adhesive, abrasive, surface fatigue, fracture, and tribochemical wear.75... 

The nanotheory implies that cyclic saturation is a thermally activated process of PSB plasticity by repeated avalanches of slip producing intense surface fatigue damage at the nanoscale. The relevant activation energy for recovery... 

If the particle is relatively smooth and spherical wear to the polymer surface occurs by the formation of deformation flakes, fracture and sub-surface fatigue. Where the particle have sharp edges the wear process is dominated by cutting analogous to an abrasive grit. 

The wear of PET with a low crystallinity as small as 8% was mainly due to transfer. On the other hand, wear of high crystallinity PET is different from that of the low crystallinity PET and seemed to be mainly due to. a surface fatigue during sliding. The differnce between the mechanisms in PET of low and high crystallinity was essentially due to the differnce in morphological structures. 

Surface fatigue wear occurs during repeated sliding or rolling over a track. Surface or subsurface crack formation leads to breakup of the surface. 

In the contact area between part and counter part elementary friction and wear mechanisms such as adhesion, abrasion, surface fatigue, deformation, elastic hysteresis and damping, tribochemical reactions etc. may occur. These mechanisms are overlapping in the temporal and spatial undetectable real material contact area. In addition highly formulated lubricants, which are mainly used with highly stressed engine elements, exert influence on tribochemical reactions inside and outside of the tribological contact. ... 

Catastrophic decay is the result of severe wear when large fragments are lost due to surface fatigue. 

In relation with the functional properties of a part, such as fatigue and static strength, or wear and corrosion resistance, are the basis for specifying the proper process and steel as illustrated in Fig. 2 (T. Bell, 2005). The functional part properties that essentially depend on the compound layer are wear resistance, tribological properties, corrosion resistance and general surface appearance. Both abrasive and adhesive wear resistance increase with hardness and with minimised porosity of the compound layer. Porosity can be positive in lubricated machinery parts as the pores act as lubricant reservoirs. The compound layer depth has to be deep enough not to be worn away. The diffusion layer (depth, hardness and residual stress) determines surface fatigue resistance and resistance to surface contact loads. 

Should pitting occur, a heterogeneous mechanism for metal dissolution defines a localized attack that may involve metal penetration in thin stmctural sections, hi the case of massive stmctural sections, pitting is usually of little significance. On the other hand, surface fatigue failures due to pitting mechanism are weU documented in the literature. Hence, pitting develops with surface microcracks. 

In the study of strain-hardening, micro cracking, and surface fatigue, a 245pN normal force was applied to the tip, as the tip moved laterally to mar the surface. 

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