Mechanisms of spalling of metals in the fast space-heating regime in submicrosecond and submillimicrosecond ranges of durability

Abstract

It is known [1, 2] that fast heating of materials by pulsed flows of penetrating radiation gives rise to compressive stresses whose amplitude in the solid-phase region is proportional to the concentration of the absorbed energy.The time lag of the absorbing medium causes a motion in the form of compression waves (or shock waves) and expansion waves. The interaction of two counter waves of the latter type gives rise to tensile stresses in the material with duration rt "-" A/c (A is the thickness of the heated layer and c is the speed of sound). The amplitude of these stresses depends, in the general case, on the absorbed energy, the heating rate (the rate of energy supply), the distribution of the absorbed energy in mass, and the physicomechanical properties of the medium. The appearance of tensile stresses produces conditions for the development of failure. When critical amplitude-time characteristics of the impulse of tensile stresses are reached in a cross section of the sample, failure of the normal separation (spalling) type occurs in it.Investigation of the dynamic effects caused by fast heating of a material is very important for applications, because the capabilities of modern high-energy pulsed facilities are largely determined by the mechanical strength of elements, units, and constructions.The thermal-shock method used in studies of failure allows a considerable extension of the range of the material states studied as compared with conventional methods (shock-wave and explosion loadings [3, 4]). Thus, the results of these investigations provide new information on the behavior of specific materials and are of independent importance for the physics of failure, in particular, in developing models of failure under high-speed deformation that fit the process well.Materials Can be fast heated by impulsive penetrating radiation (in particular, by a nuclear explosion [5]) and by pulsed beams of charged particles [3,[6][7][8][9][10]. The spalling of some solid media (colored ice and polyvinyl chloride plastic) under absorption of the laser-radiation energy is considered in [1, 8, 10]. The spalling of some metals upon fast space heating by high-current electron beams is described in [3, 5,[7][8][9] 10].Sources of impulsive radiation allow one to investigate the behavior of materials in the region of extreme loading parameters and over a wide range of initial temperatures.In studies of the failure of metals under laboratory conditions, high-current accelerators of relativistic electrons are the most widely used sources of pulsed pressure. Use of these accelerators offers unique possibilities and new avenues of attack on the problem of failure of solid bodies in the submicrosecond range of durability for the following acting parameters: rate of energy supply dE~dr of up to 10 al J/(g 9 sec), concentration of the absorbed energy E ~ 1-103 J/g, initial temperatures To = 4K-0.8Tmelt, and electron energy Ee "~ 1-10 MeV. The experimental methods developed to date in combination with mathematical modeling make it possib...

Dynamic fracture of copper under the action of a relativistic high-current electron beam

“…To study the dynamic (spall) fracture of materials on the submicrosecond scale of loading, along with the highspeed impact of plates [1], shock waves are currently used that are generated under the action of high-current ion [2][3][4] and electron beams [5][6][7] of power density 10 10 -10 11 W/cm 2 . The generation of a shock wave is associated with fast heating and intense evaporation of the surface layer of the target under the action of the beam.…”

Fracture of metals samples under conditions of fast heating by intensive X-ray radiation

“…The results obtained under X-ray irradiation for low-carbon steels, copper, titanium, tungsten, molybdenum, cadmium, lead and zinc [5], and the results obtained under electronic irradiation for copper, titanium, cadmium, lead and zinc [8], and for aluminum, 6061aluminum alloy, copper and titanium [11,12] were used. In whole the consistent picture of influence of loading conditions, first of all loading time and temperature, on the fracture conditions under fast heating by penetrating radiation was noted for all examined materials.…”

“…Mention may be made of some of the works of this group in which rather numerous results were published for a number of metals [6][7][8]. For the first time such results were published for tin, lead and cadmium [6].…”

“…For the first time such results were published for tin, lead and cadmium [6]. Then these data were added by the results for copper, nickel, iron, titanium, tantalum and tungsten [7]. The results of executed calculations and experiments showed that spall fracture took place in the middle plane of a sample or in its neighbourhood even in the case of some deviations from the uniformity of a heating profile.…”

“…It was also shown that in a range of heating time up to 20 ns the calculated amplitude and duration of tensile stress in the middle plane of a sample did not depend practically on heating time. Ultimate generalisation of all the results obtained by this group was made in work [8], where the time dependences of critical tensile stresses were given for all examined metals and all the used research methods were described in detail. It also should be noted that studying fracture of metal samples under fast heating by a high-current electron beam was conducted earlier and the results were presented in the works of various authors.…”