Zusammenfassung
The porous ductile material models accounting for the nucleation
and growth of voids are discussed in some detail, and cell model
studies that are a major tool in understanding material behaviour
are considered. Such model studies have been used to investigate
the nucleation of voids and void coalescence, as well as the interaction
between different size- scales of voids. Applications of the
material model to predict fracture mechanisms in structural components
or test specimens is one of the main purposes of developing these
constitutive relations. Localization of plastic flow in shear bands
leading to final shear fracture by a void-sheet mechanism is one
such application, and ductile crack growth by void coalescence is
another. Extensions of porous ductile material models to account
for the effect of a rounded vertex on the yield surface or material
strain rate sensitivity are presented. The viscoplastic material
model used to represent rate sensitivity is illustrated by analyses
of the fracture mode transition in the Charpy V-notch test. \par
Void growth and coalescence is also the dominant cause of failure
in polycrystalline metals subject to creep at elevated temperatures.
However, at high temperatures the voids appear mainly in the grain
boundaries, and diffusion gives a significant contribution to the
growth rate. Due to the interaction of diffusion and dislocation
creep, the rate of void growth can here be constrained by creep.
This rather different mode of material failure by void coalescence
is described in terms of a material model proposed by the author
Acta Metall. 32, 1977-1990 (1984). Applications of the model to
analyzes of creep rupture in structural components are included in
the discussion.
Nutzer