Determination of the critical state during adiabatic process of thermoplastic deformation of metallic materials

ABSTRACT

The adiabatic process of thermoplastic deformation of metallic materials is analyzed in frames of coupled thermoplasticity theory. The problem of pure adiabatic shearing is considered; the critical value of adiabatic plastic strains, critical temperature, critical values of shearing stresses, and the value of internal parameter identified with the plastic strain work are determined. The critical state determines the maximum of the adiabatic curve of hardening; in other words, it indicates when the adiabatic function (adiabatic modulus) of hardening reaches zero. Exceeding the critical values can cause the forming of the localization state of deformations during processes of adiabatic shearing. Such phenomena can appear even under quasi-static and higher rates of plastic strain, for example, when . They can be observed during some technological processes of machining, such as milling, turning, beveling tube edges for welds, cutting out, cutting at the guillotines, punching with the punches, forging, calibration, or dragging with torsion (tubes, bars, etc.). The idea of macroscopic internal parameters was applied for description of thermodynamic state of the thermoplastic body.

KEYWORDS:

• Adiabatic modulus of hardening
• critical state
• shear stress
• thermoplastic deformation