Dynamic instability in adiabatic thermoplastic shear

Conference · Sat Jan 01 04:00:00 EST 1983

OSTI ID:5927400

Burns, T J

The formation of adiabatic shear bands in ductile metals under dynamic loading conditions is generally thought to result from a material instability which is associated with a peak in the curve of engineering plastic flow stress vs engineering shear strain. This instability rises from the effect of thermal softening, caused by irreversible adiabatic heating, which counteracts the tendency of the material to harden with increasing plastic strain. Asymptotic analysis of a one-dimensional rigid-thermoviscoplastic model, based on data taken from dynamic torsion experiments on thin-walled tubes of mild steel, shows that shear band formation in this situation can be interpreted as a bifurcation from a homogeneous shearing deformation which occurs near the peak in the homogeneous stress-strain curve. It can be shown that the growth rate of small perturbations on the homogeneous deformation is controlled by the ratio of the slope of the homogeneous stress vs strain curve to the material viscosity, i.e., the rate of change of the plastic flow stress with respect to the strain-rate. In addition, it can be shown that this growth rate is essentially independent of the wavelength of the small perturbation. Numerical methods can be used to show that this growth rate beyond the bifurcation point may not be sufficiently large for the model to account for the experimental data.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 5927400
• Report Number(s): SAND-83-0801C; CONF-830719-7; ON: DE83015206
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ADIABATIC PROCESSES
ELEMENTS
HEATING
INSTABILITY
METALS
SHEAR
STRAINS