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Research Papers: Materials and Fabrication

Crack Growth Under Moving Temperature Field by the Example of Circumferential Crack in Steel Cylinder Specimen

[+] Author and Article Information
D. A. Tereshin

Applied Mechanics, Dynamics and Strength of Machines Department, Southern-Ural State University, Lenin Avenue, Chelyabinsk 454080, Russiatdenis@sopro.susu.ac.ru

J. Pressure Vessel Technol 130(3), 031406 (Jul 11, 2008) (8 pages) doi:10.1115/1.2937743 History: Received June 16, 2006; Revised March 13, 2007; Published July 11, 2008

High thermally loaded construction exploitation practice has shown that the destruction under the loading with the temperature field caused by a moving heat source can be much more dangerous than the one in case of a stationary heat source. The growth of long cracks in the first case occurs by means of the two main mechanisms specific to the describing loading conditions. They are the codirectional crack growth mechanism when a crack grows jointly with the thermal tension stresses zone and the oppositely directional mechanism realizing when a crack grows in the opposite direction relative to the stress field moving direction. In both cases, the ultimate crack extension will be limited only by the stress moving zone. However, an experimental proof of such a crack growth on ductile specimens was absent. To demonstrate the possibility of crack development under the action of the moving temperature field up to the length essentially greater than the temperature stress tension zone by the mechanisms peculiar to such loading, the experiment on steel thin-walled cylinder was carried out. The specimens were heated in the circular high-frequency current inductor. Cold-water jet falling on the specimen’s surface resulted in high temperature gradients and high local stresses. Automodel movement of the temperature field was achieved by means of the drive rotating the specimen about its longitudinal axis. The fatigue crack arose under the action of cyclically moving temperature field. Thereafter, the near-automodel fatigue crack growth proceeded. After several tens of cycles, the crack length essentially exceeded the thermal tension zone and became greater than half-circumference. The experimentally obtained crack growth rate was in good agreement with the calculated result by the developed calculation technique. It was proved that in addition to the codirectional and oppositely directional quasistatic mechanisms, the high-speed fatigue crack growth is also possible in constructions made of materials having a considerable fracture toughness. It can occur in the same and opposite directions relative to the temperature field moving direction. Although the fatigue crack growth rate is small in comparison with the quasistatic codirectional and opposite directional ones, the final crack length can also reach a great size. That length is limited only by the tensile stress moving region.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Thermal cracks caused by action of fixed heat sources

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Figure 2

Thermal cracks of a large size

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Figure 3

Quasistatic crack growing under moving nominal (as if there was no crack) stresses perpendicular to crack line: (a) codirectional and (b) opposite directional; V is the stress field moving direction

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Figure 4

Sketch of experiment on the specimen with spacer

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Figure 5

Temperature variation depending on hoop angle

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Figure 6

(a) Axial stress dependency on hoop angle, (b) codirectional mechanism of crack growth, and (c) the opposite directional one

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Figure 7

Dependency of the stress intensity factor on crack tip coordinate for crack lengths: (1) 5mm, (2) 35mm, (3) 65mm, (4) 95mm, and (5) 125mm

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Figure 8

Finite element mesh, boundary conditions, and temperature field for opposite directional crack growth: (a) general view and (b) crack tip zone

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Figure 9

Dependency of maximal stress intensity factor on crack length for (a) opposite directional crack growth mechanism and (b) codirectional growth mechanism: Line 1 corresponds to estimation by Eq. 1; Line 2 to finite element calculation

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Figure 10

Fatigue crack growth diagram

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Figure 11

The sequential stages of crack growth

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Figure 12

Circumferential crack in the cylinder specimen: (a) the final crack in the tested sample (b) and FE calculation (axial stresses)

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