Article,
Modeling damage and deformation in impact simulations
METEORITICS & PLANETARY Science, 39 (2): 217--231 (2004)
Abstract
Numerical modeling is a powerful tool for investigating the formation
of large impact craters but is one that must be validated with observational
evidence. Quantitative analysis of damage and deformation in the
target surrounding an impact event provides a promising means of
validation for numerical models of terrestrial impact craters, particularly
in cases where the final pristine crater morphology is ambiguous
or unknown. In this paper, we discuss the aspects of the behavior
of brittle materials important for the accurate simulation of damage
and deformation surrounding an impact event and the care required
to interpret the results. We demonstrate this with an example simulation
of an impact into a terrestrial, granite target that produces a 10
km-diameter transient crater. The results of the simulation are shown
in terms of damage (a scalar quantity that reflects the totality
of fragmentation) and plastic strain, both total plastic strain (the
accumulated amount of permanent shear deformation, regardless of
the sense of shear) and net plastic strain (the amount of permanent
shear deformation where the sense of shear is accounted for). Damage
and plastic strain are both greatest close to the impact site and
decline with radial distance. However, the reversal in flow patterns
from the downward and outward excavation flow to the inward and upward
collapse flow implies that net plastic strains may be significantly
lower than total plastic strains. Plastic strain in brittle rocks
is very heterogeneous; however, continuum modeling requires that
the deformation of the target during an impact event be described
in terms of an average strain that applies over a large volume of
rock (large compared to the spacing between individual zones of sliding).
This paper demonstrates that model predictions of smooth average
strain are entirely consistent with an actual strain concentrated
along very narrow zones. Furthermore, we suggest that model predictions
of total accumulated strain should correlate with observable variations
in bulk density and seismic velocity.
Tags
- chicxulub
- collapse;
- compression;
- crater;
- failure;
- formation;
- friction;
- mechanics;
- peak-ring
- rock;
- shear
- strength;
