  Ion beam plays a pivotal role in ion implantations and the fabrication of
nanostructures. However, there lacks a quantitative model to describe the
residual stresses associated with the ion-beam radiation. Radiation-induced
residual stress/transformation strain have been mostly recognized in the
hydrostatic sub strain space. Here, we use molecular dynamics (MD) simulations
to show that the response of a material to irradiation is generally anisotropic
that depends on the ion-beam direction, and should be described using tensorial
quantities. We demonstrate that accelerator-based ion beam irradiation,
combined with the intrinsic lattice anisotropy and externally induced
anisotropy (such as anisotropic mechanical loadings), causes radiation-actuated
shear transformation strains in addition to hydrostatic expansion. We map out
these complex correlations for several materials. Radiation-induced defects are
shown to be responsible for residual shear stresses in the manner of Eshelby
inclusion transformation. We propose such tensorial response model should be
considered for accurate nanoscale fabrication using ion-beam irradiation.
