ISSN:
0933-5137
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Description / Table of Contents:
Fracture Mechanical Considerations on the Effect of Hot Cracks.There exists a lot of literature (1, 2) concerning the mechanisms of the origin of hot cracks. Something essential about the effects of hot cracks on the mechanical behaviour of components hardly can be found. These hot cracks can be valuated only by a quantification of the cracks and by an estimation of their behaviour under operational loadings.It is shown how by means of fracture mechanic material laws and calculation methods the growth of hot cracks under operational conditions can be evaluated. By a simple example of a fatigued vessel the systematic procedure is demonstrated and the results of calculation are explained. This procedure can be applied on the most technical problems as the operational stresses generally are below the yield point. For the region of the yield point and above it neither experimental nor theoretical results are available at the moment.The possibility of simplified calculations of burst stress of vessels is mentioned, which is derived from experiments. Experimental data (11) confirm the chosen hypothesis in so far as the burst stress can be realistically or rather conservatively evaluated by this method.It is concluded: With regard to the fact of unavoidable hot cracks for some certain austenitic steels the authors are convinced that basing on the examples and using the well known data of an austenitic steel as well as modified fracture mechanical rules the up to now empirically assumed stability of hot cracks is practically existent against intolerable crack growth. The given examples make it quite significant that the tolerable defect can be rather big without any critical consequences.If the operational conditions are at or above the level of the tolerable stresses, then safety precautions exist in so far as by means of non destructive - for instance during inservice inspections - volumetric examinations can be carried out. This will enable the detection of a critical defect or of one which becomes critical. Whilst the classic hot crack ranges in a micro dimension and therefore remains undetectable for the non destructive testing methods available at present the increased defect is detectable. Furtheron it should be pointed out that this detectable defect will surely be below the critical size and therefore will not be dangerous.
Notes:
Es wird gezeigt, wie mit Hilfe bruchmechanischer Werkstoffgesetze und Berechnungsmethoden das Wachstum von Heißrissen unter betrieblichen Beanspruchungen berechnet werden kann. Anhand eines einfachen Beispiels wechselbelasteter Behälter, die mit konstanter Amplitude be- und entlastet werden, wird das systematische Vorgehen demonstriert und das Resultat der Berechnung erläutert.Unter Berücksichtigung der Tatsache unvermeidbarer Heißrisse bei bestimmten austenitischen Werkstoffen wird auf Grund der gewählten Beispiele, d. h. bezogen auf einen benannten Werkstoff und modifizierten bruchmechanischen Betrachtungen, dargelegt, daß die bislang mehr oder weniger empirisch angenommene Beständigkeit gegen unzulässiges Rißwachstum tatsächlich weitgehend gegeben ist. Die hier aufgezeigten Beispiele lassen deutlich erkennen, daß der zulässige Fehler ziemlich groß sein kann, ohne kritische Folgen zu bewirken.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mawe.19790100409
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