Crazing Of Glassy Polymers: Coarse-grained Bead-spring Molecular Dynamic Study

The damaging process of glassy polymers crazing is simulated and analyzed by molecular mechanics method based on coarse-grained bead-string model, using the large-scale atomic/molecular massively parallel (LAMMPS) program.A periodic unit cell model is established firstly. Crazing is simulated under different tensile strain rates. The distribution and the process of generation, extension and fracture of the crazing micro-voids in unit cell structure are obtained. Combining with the critical stresses related with strain rates, microscopic configurations of initiated crazing are obtained by use of criterion for crazing initiation. With the introduction of non-affine displacement field, participation evolution with tension strain is calculated, which proved the existence of linear viscoelasticity in polymer crazing.Secondly, Restraint ratioλof the model deformation is defined referencing the macroscopic poisson ratio effect of the materials, in accordance with different transversal compressive strain configurations, with the same longitudinal extension displacement imposed on the structure of cyclic unit cell. At differentλ=1/12, 1/6, 1/4 and 1/3, crazing processes of polymers are conducted. Initializing, extending and fracture process as well as spatial distribution of the crazing micro-voids are analyzed. With the introduction of non-affine displacement field, participation evolution with tension strain is calculated, which proved the existence of linear viscoelasticity in polymer crazing of different restraint ratios. Microscopic configuration of the initiated crazing are verified with criterions considering the critical stress and stress-strain relations, which agree with the experimental possion ratio 0.2~0.3 of polymer.