372595877

JPRS-UMS-92-003 16 March 1992

ANALYSIS, TESTING

15

of sequential loading, the amount of damage incurred by minerał ores subjected to two instances of loading is additive. In the case of simultaneous loading, the equa-tion used must contain an additional term AR. This additional term represents the product of the probabili-ties of two independent events, i.e., no destruction at a given point due to the separate effect of each of two loads and destruction at the said point when the two loads act simultancously. A formula was also derived to describe the size distribution of the cracks formed. The proposed model was used as a basis for deriving additional for-mulas for use in determining the energy intensity of the destruction of monolithic and cracked minerał ores. A probability model of the spalling of a ledge is also developed. On the basis of their proposed model, the authors showed that the destruction of minerał ore occurring in the case of simultaneous loading of one space with several loads is morę intensive (by a factor of 1.7 to 2.3) than in the case of sequential loading by the same load. Figures 2; references 9 (Russian).

The Link Between Critical Embrittlement Temperaturę and Stress Concentrator Geometry and Loading Ratę

927D0066D Kiev PROBLEMY PROCHNOSTI in Russian No 12, Dec 91 (manuscript received 27 Dec 90) pp 35-39

(Article by M. Mishin, I.V. Kislyuk, and V.I. Sarrak, Metal Science and Metal Physics Scientific Research Institute, and Central Scientific Research Institute of Ferrous Metallurgy imeni I.P. Bardin, Moscow]

UDC 539.4:620.178

[Abstract] The authors of the study worked to develop the physical principles of a method to determine the critical embrittlement temperaturę of a Steel specimen or component with stress concentrators. Specifically, they set out to develop a method that would make it possible to tie the values of critical embrittlement temperaturę with the characteristics of local rupture strength, yield, and overstress and that would give consideration to the geometry of the specimen and the notch. Specimens (8.00 mm in diameter) of 10KP Steel smelted in an open induction fumace were selected for the study. Three types of specimens were studied: smooth specimens; specimens containing annular grooves with a depth of 2.00 mm and a radius of curvature of 0.50 mm and with groove angles of 30, 60, and 120°; and specimens with a U-shaped notch. The specimens were heat-treated at 1,000°C for 60 minutes and cooled in air. The tensile strength tests were conducted on an Instron testing machinę at loading rates of 2 and 20 mm/min at tem-peratures ranging from 77 to 293 K. The process of determining embrittlement temperaturę consisted of establishing the temperaturę at which the total-yield load equaled the breaking load. The experiments performed confirmed that critical embrittlement temperaturę (defined as the temperaturę at which local fracture at the apex of a structural stress concentrator occurs) is directly linked to the characteristics of strength, yield. and over-stress. The studies further confirmed that critical embrittlement temperaturę may be calculated by using the known critical maximum local tensile stress, the temperaturę dependence of the yield strength, and the over-stress of the total yield. Finally, the authors concluded that their proposed calculation method may be used in developing a method of determining the critical embrittlement temperaturę of components with structural stress concentrators. Figures 4, tables 2; references 8: 7 Russian, 1 Western.

The Arrest and Propagation of a Brittle Crack in Construction Steels. Communication 1

927D0066A Kiev PROBLEMY PROCHNOSTI in Russian No 12, Dec 91 (manuscript received 25 Jan 89) pp 15-21

[Article by Z. Bilek and M. Chemy, Brno, Czech and Slovak Federated Republic]

UDC 539.4

[Abstract] The authors of the study examincd the fracture toughness of three construction steels used in nuclear power plants (11.373, 11.483.1, and 15.313.5) in the stage of crack arrest at different temperatures. They measured the fracture toughness of the said steels by using the standard method of determining the critical coefficient of stress intensity in the stage of a running crack’s arrest (K_la) as described in several other publi-cations. The value of K,_a of the individual construction Steel was determined by loading a test specimen mea-suring 270 mm long x 100 mm wide x 24 in diameter x 20 mm thick or 270 x 100 x 52 mm in diameter x 30 mm thick with a wedge with an angle of 11° at its tip. The test temperaturę was varied from -196 to -60°C (nitrogen vapors were used to achieve these temperatures). The data obtained for all three construction steels tested demonstrated that their capability to arrest a running crack was below their rupture strength during initiation of the crack. The difference between these two indica-tors, which was found to inerease with temperaturę, was interpreted as a rcflection of the different micromecha-nisms of the initiation and arrest of fractures. Fracto-graphic and metallographic studies of the specimens at the site of the end of the arrested cracks in the direction parallel to their propagation and perpendicular to the fracture surface revealed the presence of microdamage before the apex of the main crack. This was espccially true in the cases of the ferrite-perlite steels 1 1.373 and 11.483.1, in which the growth of the main crack was determined to be due to the merger of individual microdamage. The values of K,_a that the authors determined by using a statistical approach were determined to reflect the capability of the test materials to arrest propagating brittle fractures. The studies performed led the authors to conclude that the planned American Society for Testing and Materials [ASTM] standard