Molecular Dynamics Simulation Of The Effect Of Crosslinking Networks And Nanofillers On Mechanical Fatigue Failure Of Elastomer Materials

Understanding the elastomer fatigue mechanism under a cyclic loading is of vital importance in fabricating elastomer nanocomposites with high performance.The crosslinking network of elastomers and filled nanoparticles have important effects on the structure and fatigue properties of materials.In this thesis,coarse-grained molecular dynamics simulation method was used to investigate the molecular mechanism about the effects of crosslink density and crosslink agent type on the cross-linked network,and the effects of cross-linked network,spherical nanoparticle size and packing fraction on the bond breaking and fatigue resistance under dynamic periodic loads was examined by using coarse-grained molecular dynamics simulation.(1)The effects of crosslinking agent type and crosslinking density on fatigue properties of elastomer composites were studied.The results show that in the case of the same number and the bonding capacity of crosslinker molecules,the elastomer molecular chains were more prone to disentangle and orientate in the polysulfide system,compared to those monosulfide and disulfide systems.Rubber molecular chains uniformly sustained the external tensile stress in the polysulfide system,which was beneficial to avoid the rapture of rubber molecules;With the increase in the crosslink density,the cross-linked network size which was indicated as the chain average net molecular weight increase to a plateau.In the presence of saturated network size,an optimum crosslink density and distribution for rubber nanocomposites appeared,avoiding the possibilities of rubber molecule rupture.(2)The effects of particle size and filler fraction on fatigue performance of elastomer composites were studied.The results showed that the decrease of particle size of nanoparticle fillers and the increase of filler fraction enhanced the fatigue properties of composites,which was manifested in the decrease of the total number of broken bonds and the increase of tensile stress under cyclic fatigue.However,too high filler content promoted the fracture of matrix bonds between crosslinking points.In this case,the loss factor increased under large strain,and the damage effect of packing network was obvious,which was not conducive to the maintenance of mechanical properties under cyclic shear.This work provides some insights on understanding the relationship between the cross-linked network and the fatigue performance of the rubber composites at the molecular level,and explores the mechanism of bond breaking at the microscopic level,so as to provide some guidelines for preparing elastomeric materials with high fatigue resistance.