Thermomechanical dynamic behavior of a disk subject to an impulsive thermal load at the center

Abstract

The dynamic coupled thermoelastic problem formulation and the thermodynamically consistent theory of inelastic behavior of materials are used to solve an axisymmetric problem for a steel disk subject to a heat pulse at the center. The temperature dependence of the physical and mechanical properties of the disk is taken into account. The problem is solved by the FEM. The evolution in time and features of the strain-stress and thermal states of the disk and the dynamic effects accompanying the processes of heating and gradual cooling are studied Keywords: impulsive thermal irradiation, coupled thermomechanics, dynamic effects, pulse propagation, inelastic behavior Introduction. One of the distinctive features of modern engineering is the reduced dimensions and weight of articles and mechanisms. Miniaturization is invoked to enhance the quality, reliability, and life of parts manufactured. Such trends are dictated by the material-and energy-saving requirements and new opportunities for creating advanced cars, mechanisms, and devices based on the recent scientific achievements. In this connection, a great deal of effort is going into the development of test and diagnostic aids and into microengineering, which owes its development to micro and nano materials-processing technologies. Of extreme interest are nonconventional methods such as laser-shock or pulsed electron-beam processing [12,[16][17][18].Promising fields for use of short laser or electron-beam pulses are (i) strength enhancement, wear prevention, and performance improvement [4]; (ii) micro-and nanodiagnostics [21,22]; (iii) surface cleaning and precision nesting [4]; and (iv) micro-and nanoforming and quasistatic and dynamic molding [4,13]. In all cases, the process is based on optimal and precisely metered power supply to the workpiece and, hence, extremely precise and localized load on the stress-strain, thermal, or aggregate state of a structural element.By localizing laser or electron-beam energy in space and time, it is possible to produce highly concentrated irradiation power and, thus, to implement various energy-deposition mechanisms for various types of material processing [4]. Radiation is localized in space by means of various optical systems and in time by reducing the pulse duration. The ordinary laser power supplies produce pulse durations from several milliseconds (10 -3 sec) to several tens of microseconds (10 -6 sec). Special mechanical, optoelectric, or acoustoelectric Q-switches make it possible to generate so-called giant pulses (with very high peak power) lasting from several nanoseconds (10 -9 sec) to several hundreds of nanoseconds [4]. Recently, researchers have managed to generate even shorter pulses of picosecond (10 -12 sec), femtosecond (10 -15 sec), and even attosecond (10 -18 sec) duration [14,20].There are two main thermomechanical effects produced by laser or electron-beam radiation on an object. One is partial evaporation of the surface material and production of plasma. Expanding away from the irradiated surface, the plas...

Viscoplastic microstructural processes in solids under impulsive thermal loading

“…The physical and mechanical properties along with the parameters of the Bodner-Partom model for this material as well as their temperature dependencies are taken from the previous article [25]. The technique for determining the model parameters over the wide range of temperatures is described in [34,35] in detail.…”

“…This plasma induces shock waves during expansion from the irradiated surface, and mechanical impulses are transferred to the target. This mechanism dominates for the irradiation by the short pulses of high intensity [22,23,25]. Second, the irradiation induces rapid heating with high-temperature gradients accompanied by the generation of thermal stresses and shock waves as an inertia effect along with the following gradual cooling.…”

“…This scenario occurs for prolonged or less intensive pulses. Under these circumstances, the mechanical properties can be changed significantly both on the surface and in the near-surface region resulting in large residual stresses and strains [25][26][27], which, in turn, can influence the strength, endurance, and fatigue life of the structure element. It is worth mentioning that this influence can be either positive (enhancing material response in the case of compressive stresses) or negative (compromising structural strength in the case of tensile stresses).…”

“…Consequently, the volume increase upon martensitic transformation is the main cause of straining, distortion, hogging, and crack initiation [28,31]. Dynamic processes generated by the non-steady thermal and mechanical loadings applied to metallic solids possessing fixed microstructural composition were studied in the previous studies [25,26,33]. In the present article, these processes are investigated taking in to account microstructural phase transformations.…”

“…It is assumed that during the thermal loading the temperature of the material does not exceed the melting point. To attack the problem, the dynamic problem statement is used [25,26]. The nonlinear material response under complex thermomechanical conditions for a wide range of temperature is simulated by the generalized unified BodnerPartom model [34,35], which is consistent with the thermodynamics of irreversible processes and is improved to allow for phase transformation [36].…”