620.178.7

експериментальна методика
дисковий зразок
термошок
розповсюдження та зупинка тріщини
experimental method
disc-shape specimen
thermal shock
crack propagation and arrest

Розроблено експериментальну методику дослідження особливостей розповсюдження та зупинки тріщини у дискових зразках в умовах термошоку. Проведено випробування та отримано дані про зміну температури на поверхні дискових зразків зі сталі 45 та 15Х2НМФА. За допомогою спеціальних розривних датчиків отримані залежності швидкості розповсюдження тріщини від часу.
Searching of an additional durability reserves for guarantee of structural component integrity is one of the most important task of the present science. Investigations of crack propagation and arrest under thermal shock conditions are very important for service possibility justification of reactor plants during a planned lifetime. There were only few experimental investigations of crack propagation and arrest under thermal shock in the world. Thus crack propagation under thermal shock needs to be examined more. Present work describes an exprerimental method of the disk-shape specimen testing under thermal shock conditions. Disk-shape specimen testings are relatively cheap and simple than testings of full-scale specimens and allow to obtain more specific information about crack propagation and arrest features under thermal shock. The method of a crack propagation registration using disruptive gauges was developed and approved. Experimental study of crack propagation consists of the next steps: preparing of specimen, attachment of thermocouples on the specimen surface, gluing of disruptive gauges near crack front, connection of recording system, cooling while -210°C was reached, fast heating of an inner surface of the specimen to 900°C. The influence of a temperature gradient on crack propagation in disc-shape specimens was investigated. A temperature gradient under thermal shock was controlled with thermocouples on three different areas of the specimen surface (inner, outer and cetral section of the work surface). Maximal temperature gradient between two different points of specimen surface during crack propagation was near 200°C. The high-speed recording system was used to obtain crack propagation data with time resolution 0,05 microsecond. Also using of disruptive gauges allow to obtain information about crack propagation and arrest features such as place and time moment of crack initiation, place and time moment of crack arrest, instantaneous velocity of crack propagation in each moment of time. Curves of a crack propagation velocity versus time were obtained. The velocity curve is nonmonotonic function that has a significant peak at the beginning of the crack propagation with consequent decreasing of velocity value.

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