Multiscale model-based simulation of multi-phase (solid-fluid-gas/hard-soft) interactions involving failure evolution is challenging due to the limitations in experimental characterization and validation. As continuous approaches, nonlocal elastoplasticity and elastodamage models, in terms of strain gradients or integrals, have been proposed to predict the interactions among material points (particles) during the evolution of failure, for which the size effect is the key to calibrate these constitutive models based on available experimental data. The size effect in continuous approaches is similar to the cut-off radius in discontinuous approaches such as molecular dynamics (MD) simulation, but the quantitative analysis of the relationship between continuous and discontinuous approaches remains to be lacking. With the development of the material point method (MPM) [1,2], an effort is being made to understand the spatial discretization effects on evaluating failure evolution such that the multi-phase interactions could be better predicted to optimize the structural responses to extreme loading conditions. In this conference, the recent findings [3,4] with the use of MD, MPM and other particle methods will be presented, followed by the discussion of future research directions.