  Shrinkage strains measured from microstructural simulations using the
mesoscale kinetic Monte Carlo (kMC) model for solid state sintering are
discussed. This model represents the microstructure using digitized discrete
sites that are either grain or pore sites. The algorithm used to simulate
densification by vacancy annihilation removes an isolated pore site at a grain
boundary and collapses a column of sites extending from the vacancy to the
surface of sintering compact, through the center of mass of the nearest grain.
Using this algorithm, the existing published kMC models are shown to produce
anisotropic strains for homogeneous powder compacts with aspect ratios
different from unity. It is shown that the line direction biases shrinkage
strains in proportion the compact dimension aspect ratios. A new algorithm that
corrects this bias in strains is proposed; the direction for collapsing the
column is determined by choosing a random sample face and subsequently a random
point on that face as the end point for an annihilation path with equal
probabilities. This algorithm is mathematically and experimentally shown to
result in isotropic strains for all samples regardless of their dimensions.
Finally, the microstructural evolution is shown to be similar for the new and
old annihilation algorithms.
