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From measurements of Luder's band-front velocities it is concluded that hydrogen does not affect the activation energy for separating a dislocation and its atmosphere and thereby the delay-time for yielding. Suppression of the upper yield point by hydrogen seems rather to be caused by local stresses surrounding inclusions of molecular hydrogen, which contribute to the stresses at the specimen shoulder, and thus facilitate the initiation of the first Luder's band. Hydrogen raises the flow stress, which seems to be due to dragging of hydrogen along nith moving dislocations.
A LA LIMITE ELBSTIQUE DE L'ACIER DOCS De mesures de vitesses de d&placement du front des bandes de Liiders, l'auteur con&t que l'hydrogene ne modifie pas l'energie d'activation necessaire pour &parer une dislocation de son atmosphere, et d&s lors que cet element n'intervient pas sur le temps d'incubation lie l'apparition du crochet a la limite Blastique. La disparition du crochet en presence d'hydrogene parait plutot Btre due It des tensions locales autour d'inclusions d'hydrogene molerulaire qui s'ajoutentaux tensions dues au systeme d'attache de l'eprouvette et facilitent ainsi l'apparition de la premiere bande de Liiders. L'hydrogene augumente la limite elastique par suite. semble-t-il, de l'entrainement de l'hydrogene par les dislocations en mouvernant. DER EINFLUSS VON WASSERSTOFF AUF DA8 FLIESSEN VON FLUSREISEN Aus Messungen der Geschwindigkeit einer Liiders-Bandfront folgt, dass Wasserstoff die Aktivierungsenergie zur Trennung einer Versetzung van ihrer Wolke und damit die Verzugszeit, des Fliessens nicht beeinflusst. Die Unterdrtickung der oberen Streckgrenze durch Wasserstoff scheint vielmehr van lokalen Spannungen in der Umgebung van Einschhissen molekularen Wasserstoffs herzuriihren, die zu den Spannungen an der Probenschulter beitragen und so den Beginn des ersten Liiders-Bands erleichtern. Wasserstoff erhoht die Fliessspannung, dies srheint auf dem Rlitschleppen van Wussersmff nut bemegten Versetzungen zu beruhen.
๐ SIMILAR VOLUMES
Results of dynamic and impact tests on mild steel are reviewed, and a criterion for dynamic yield is proposed, based on Cottrell and Bilby's theory of yielding. The criterion is applied to some of the published experimental data and a comparison is made with theory. The need for further experimental
Abrasion of mild and stainless steel on a 3 M Company 120-grade silicon carbide paper has been shown to increase the hydrogen content by 0.0049 and 0.0034 ml. per sq. cm. of apparent abraded area, respectively. The application of the results to the determination of hydrogen in steel is discussed an
T, is the temperature at which the surface tension is measured. The density p must also be corrected, using the bulk coeilicient of expansion. Using a factor o = 9 and without making any temperature corrections, relatively good predictions are made for the surface tension of many metals. Table 1