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

Abstract

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.