The thermal shock phenomena induced by a rapidly propagating crack tip: experimental evidence

Abstract

For a crack tip rapidly propagating in a solid medium, the temperature field in the near-tip region obtained by Tzou is compared with the recent experimental result obtained by Zehnder and Rosakis. For a crack propagating at a speed of 900 m s −1 in a specimen of 4340 steel, the temperature wave solution at the transonic stage is found to preserve several unique features in the experimental results. They include: (1) a family of parallel isotherms behind the crack tip, (2) a constant temperature gradient in the vicinity of the crack tip, and (3) an intensified thermal energy cumulated in the immediate vicinity ahead of the crack tip. For a higher crack speed of 980 m s −1, moreover, the parallel isotherm evolves into a hyperbolalike pattern which is strong evidence for the wave behavior of temperature in the near-tip region. Coincidence between the theory and the experiment reveals two important aspects: (1) the threshold value of the thermal wave speed in the 4340 steel is 900 m s −1, and (2) the wave behavior resulting from the phase lag between the temperature gradient and the heat flux under high-rate response is an important mechanism for modelling the process of heat conduction in the near-tip region.