Exploring the mechanical response of a discrete-based heuristic molecular model with nonlinear constitutive response for impact problems

The mechanical response of an auxetic material obtained by an original periodic microstructure is investigated when loaded by a concentrated loading. This is intended to provide an initial insight for applications to localised impact problems. The unit cell is designed using a plane heuristic molecule approach which is based on a Rigid-Body-Spring-Model (RBSM) that includes both centred and non-centred bond-springs between specifically shaped heuristic atoms. A linear static analysis is firstly presented, then this is extended to include non-linear constitutive laws for the bonds. Bond elastic stiffness is calibrated through energy equivalence with a macro-scopic elastic and isotropic Cosserat continuum. Non-linear bond laws are proposed to model potential bond-atom contact under compression and elastic-perfectly plastic behaviour under tension. Parameters that govern the contact onset are explored to assess its influence on the macro-scale mechanical response of the material layer under concentrated loading. While this parametric study is exploratory, we discuss the advantages of the proposed microstructure for impact applications, by observing its ability to disperse tension-induced damage away from the impact zone conditioned by the bond deformation for contact onset.