Heterogeneous deformation model for the high pressure strength of aluminum

Conference · Thu Jan 01 04:00:00 EST 1987

OSTI ID:6376529

Swegle, J W

Recent data from a series of reshock and unloading experiments on 6061-T6 aluminum have provided values of both yield strength and deviatoric stress in the initial shocked state. The data indicate that the stress state lies inside the yield surface after passage of the first shock wave. This is also supported by the appearance of an elastic precursor with the second shock in the reshock experiments. Standard elastic-plastic theories are unable to predict this anomalous behavior and postulated mechanisms have involved high temperature transients in regions associated with shear banding. Heat conduction normally occurs on time scales which are long compared to shock risetimes, but shear bands are so thin that they can be expected to thermally equilibrate with surrounding material in times comparable to shock risetimes. However, shock risetimes have been found to be a strong function of shock stress, and this effect must be included along with heat conduction in order to correctly calculate shear band temperatures. A recently developed viscous model provides correct shock wave risetimes in finite-difference wavecode calculations and has thus allowed the first capability for modeling the phenomenon of thermal trapping in shear bands. At low stresses, risetimes are long compared to thermal diffusion times and shear bands stay in thermal equilibrium with surrounding material, but at high stresses risetimes are very short, and shear band temperatures greatly exceed bulk temperatures before thermal equilibrium occurs. Decreasing yield strength with increasing shear band temperature followed by yield strength recovery due to thermal quenching as the shear bands cool produces good agreement with the experimental data on aluminum.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6376529
• Report Number(s): SAND-87-0774C; CONF-870753-38; ON: DE87011063
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALUMINIUM
DEFORMATION
DYNAMIC LOADS
ELEMENTS
MECHANICAL PROPERTIES
METALS
SHEAR
SHOCK WAVES
TEMPERATURE GRADIENTS
TRANSIENTS
YIELD STRENGTH