✍ Scribed by Gunnar Härkegård
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Thickness-direction specimens have been produced from a number of steel forgings differing mainly with respect to inclusion characteristics. After heat treatment specimens are fatigued and fracture surfaces are examined by means of scanning-electron microscopy in order to determine the site of fatiguecrack nucleation. Experimental observations are evaluated and discussed in the light of fracture mechanics. 2 C ,: 21 A% AK AK* r* G N N, x F(xi; Wk) k NOMENCLATURE minor axis of elliptic defect major axis of elliptic defect distance from defect boundary to specimen surface dist~~~ce from defect center to specimen surface diameter of test specimen minor axis of elliptic crack nominal applied stress-range range. of stress-intensity factor (= K, -K&) arbitrary value of AK crack-propagation rate corresponding to AK * exponent of crack-propagation equation number of load cycles experimentally determined number of cycles to failure theoretically determined number of cycles of propagation dimensionless crack-length (=1/t) dimensionless number of cycles of propagation finite-width-correction factor complete elliptic integral of the second kind modulus of @
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The effect of rest periods on fatigue life was investigated. Small size specimen and constant load amplitudes were used with a new developed fatigue testing machine in alternating bending. Rest periods of 1.5 min were introduced after each half cycle. The cycling rate was 0.25 cpm. Comparative test
## Abstract For some applications in surgical implants a rough surface is desired, since the jagged surface structure assists the adhesion of bone material or surface coatings. Some implants are peened with coarse and sharp edged peening media. In order to avoid a distinct loss of fatigue strength,