Speaker
Dr
Aleksey Arakcheev
(Budker INP SB RAS)
Description
Transient events in large plasma devices lead to significant heat loads to plasma-facing components. The experimental simulations of pulsed heat loads on tungsten demonstrate crack formation [1]. The failure is caused by mechanical stresses in a material with non-uniform temperature distribution. In the case of a thin heated surface layer the stress is oriented parallel to the surface and is proportional to the local temperature rise [2]. The heating leads to compressive stress only. The tensile stress causing the crack formation appears during the cooling stage due to plastic deformation [3]. The yield strength and ultimate tensile strength for tungsten manufactured according to ITER specification are both of the same order at any temperature [4]. Therefore the correct theoretical simulation of crack formation requires taking into account both the plastic and the elastic deformation.
The data on tungsten from the ITER Materials Properties Handbook [4] were used for the numerical calculations. First, the temperature dependence of the thermal conductivity and the thermal capacity were used to calculate the one-dimensional temperature distribution. Then the temporal behaviour of mechanical stress and deformation were calculated with respect to the temperature dependence of mechanical properties. The plastic deformation and strain hardening were described by the Hollomon’s equation [5]. The same parameters were used for both the compressive and the tensile deformations. The simultaneous changes of elastic and plastic deformations allows numerical modeling of smooth growth of stress up to the ultimate tensile stress during the ductile-to-brittle transition. The calculations for stress-relieved tungsten demonstrate the threshold of crack formation near 0.4 GW/m$^2$ for 1 ms irradiation and the crack formation even at temperatures above 1000°C.
[1] A. Huber, A. Arakcheev, G. Sergienko, et al., Phys. Scripta T159, 014005 (2014)
[2] A.S. Arakcheev, A. Huber, M. Wirtz, et al., J. Nucl. Mater, doi:10.1016/j.jnucmat.2014.10.090 (2014)
[3] Ph. Mertens, V. Thompson, et al. J. Nucl. Mater. 438 (2013) S401
[4] ITER Materials Properties Handbook (MPH-IV1)
[5] J.H. Hollomon, Transactions of the American Institute of Mining, Metallurgical and
Petroleum Engineers, 162, 268 (1945)
Primary author
Dr
Aleksey Arakcheev
(Budker INP SB RAS)
Co-authors
Dr
Aleksandr Burdakov
(Budker INP SB RAS)
Alexander Vasilyev
(Budker INP SB RAS, Novosibirsk State University)
Mr
Alexandr Kasatov
(Budker INP SB RAS)
Dr
Andrey Shoshin
(Budker INP SB RAS)
Dr
Dmitry Skovorodin
(Budker INP SB RAS)
Dr
Leonid Vyacheslavov
(Budker INP SB RAS)
