The tensile

compressive and equilibrium-state properties of polymer nano-composites (PNC) are studied using molecular dynamics (MD) with coarse-grained polymer-nanoparticle model.The influence of the size and the mass loading of the nanoparticles on PNC's mechanical properties

and the microscopic change of the cross-linked networks of PNC systems are investigated by the tensile and the compression tests of the PNC MD simulations.We find that nanoparticles of relatively smaller size reinforce the mechanical property more

when the surface area or the mass loading of nanoparticles of different sizes are kept still.Secondly

the mechanical property of PNC system increases while the increment becomes smaller

as the mass loading of nanoparticles increases; and there exists an optimised value of the mass loading of nanoparticles for enhancing the tensile property of PNC system.Most important

the microscopic polymer-polymer and polymer-NP cross-linked networks existing in PNC systems compete with each other

and affect the tensile and compression stress with different microscopic mechanisms.Additionally

the equilibration-state MD simulations of varying mass loading of nanoparticles illustrate that the ratio of respective microscopic cross-linked networks determines the mechanical properties of PNC systems

and the aggregation of the nanoparticles induced by overloading weakens such effects.