By D. A. Hills, D. Nowell (auth.)
Failures of many mechanical parts in provider outcome from fatigue. The cracks which develop may perhaps both originate from a few pre-existing macroscopic disorder, or, if the part is of excessive integrity yet hugely under pressure, a quarter of localized pressure focus. In flip, such concentrators can be because of a few minute illness, similar to a tiny inclusion, or inadvertent machining harm. one other resource of floor harm that could exist among notionally 'bonded' elements is linked to minute relative movement alongside the interface, caused often be cyclic tangential loading. Such fretting harm is sort of insidious, and will result in many forms of difficulties resembling put on, however it is its effect at the merchandising of embryo cracks with which we're involved right here. whilst the presence of fretting is linked to reduced fatigue functionality the impact is named fretting fatigue. Fretting fatigue is a topic drawing both on fabrics technological know-how and utilized mechanics, however it is the purpose during this e-book to pay attention realization totally at the latter elements, in a look for the quantification of the impact of fretting on either crack nucleation and propagation. there were only a few past texts during this region, and the current quantity seeks to hide 5 valuable parts; (a) The modelling of touch difficulties together with partial slip below tangentialloading, which produces the skin harm. (b) The modelling of brief cracks by means of rigorous equipment which deal successfully with steep rigidity gradients, kinking and closure. (c) The experimental simulation of fretting fatigue.
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Additional info for Mechanics of Fretting Fatique
2 Indentation by a rigid ftat-ended punch The classical complete contact of interest in fretting is that involving indentation by a 'punch' having a square end, fig. 7. It might be thought that the solution to be presented has relevance to the standard 'bridge' geometry fretting fatigue test, but it should be emphasised that this would only be so if the feet of the bridge were very stiff in comparison to the stiffness of the specimen, so that the latter accommodated all of the imposed displacement.
108) This interesting result expresses the most general physically acceptable solution for the contact pressure between two spheres. It gives explicitly a solution for p( r) only if both ~, the approach, and a, the radius of contact, are specified. It also indudes a singular tension term, which varies as (a 2 - r 2 t, corresponding to the existence of cohesive or adhesive tensions. 2). Analytically, the extra generality of the solution is because the formulation is cast in terms of displacements rather than displacement gradients; this, in turn, is because in non-planar geometries the absolute displacement of partides is known.
48) Fretting causes surface damage, so that the surface stress and displacement are of particular importance. 56) 24 CHAPTER 2. BASIC CONTACT MECHANICS The relative surface displacement for normal contact between cylinders is useful in calculating partial slip, and may be deduced from the stress field by using Hooke's law and integrating (Poritsky (1950), Hills, Nowell and Sackfield (1993)). The results quoted below are exact if the two bodies are elastically similar. 16), so that they are only approximately true under these circumstances.