Contact Fatigue under Oscillatory Normal Load

Abstract

URTON ,~and P . 1\1. K U ( ASLE) :\ E x perim en tal st udies we re made w herein co nt act fatigue w as brought about by a cy clic variatio n of norm al load ap plied to t he colltact betuieen a ball and a jlat specimen, Cu rv es of jlat -specim ell t em perat ure v ersus tim e showed t hat a rapid tem perat ure rise occurred ill t he init ial stage of crack f ormation rat her t han aft er t he a ppearan ce of f ully dev eloped spalls ; t hus t he t em perature crit erio n a p peared to pr ov ide all early indication of fat igue. Fati gue failure w as observe d in unl ubricai ed as w ell as lubricated co ntact , bu t w it h mu ch longer life uihen un lubricat ed .T oroidal rings of hardened and sojte ned mat erial w ere not ed both all and below th e co nt act surface. T hese hardn ess uariation s bore sy mm et rical relationship t o th e conta ct geo m etry am! w ere apparently relat ed t o th e st ress patt ern .It w as [ound that t he f atig ue cracks did not initia t e ill th e most seve rely harden ed material bu t in th e mat erial ad jacent t o it . Further, t he slope of th e cracks t ended to fo llow th e bounda ry of t he hard ened region ill general direct ion, Prop agat ion of mi crocracks ill t his general directi on a ppeared t o be infi nenced by t he prior au st enit ic grain boundaries. Th ese microcrack s at time s a ppeared to propa gat e along carbide stringers.

Standing contact fatigue

“…(1). Tyler et al 17 performed cyclic loading with a spherical indenter on steel that was not hardened to the same extent as those used in this investigation. Therefore, Tyler et al 17 do not report ring/cone cracks.…”

Radial Fretting Behavior of Cortical Bone Against Titanium

“…This theory provides a new method to prevent the initiation of radial fretting. According to Tyler et al [15], the maximal shear stress is in the slip region. This is corresponding to the areas suffering the severe fretting damages.…”

“…It extends for about 10 lm and encounters the Havers' canal, and then the crack propagates along the direction of central canal. Tyler et al [15] has pointed out that, after a 7.5 9 10 8 cycles the metal sample is analyzed by cross section, in the edge area of the contacting region, the crack, and the contacting surface formed a 30°angle. The observation of the section suggests that the crack on the cortical bone is extending in a larger angle of 40°against the normal line of contacting surface and changes its direction toward the …”

Alkaloid Screening of Fungi

“…The incidence of alkaloids in 254 species of higher fungi studied by TYLER and STUNTZ was only 2.8OIo [3,4]..However, MASSINGILL and HODGKINS have reported at 47.6010 incidence of alkaloids in a limited study of bacteria [SI.…”