Reduced Plastic Dilatancy in Polymer Glasses

Abstract

Amorphous solids in general exhibit a volume change during plastic deformation due to microstructure change during plastic relaxation. Here the deformation dilatancy of alkane polymer glasses upon shearing is investigated using molecular static simulations at zero temperature and pressure. The dilatancy of linear alkane chains has been quantified as a function of strain and chain length. It is found that the system densities decrease linearly with respect to strain after yield point. In addition, dilatability decreases considerably with increasing chain length, suggesting enhanced cooperation of different deformation mechanisms. An analytic model is introduced for dilatability based on the atomistic study. The entanglement chain length is predicted as 43 for alkane polymers from the model, agreeing well with experiments. The study provides insights of correlations of the physical properties and chain length of polymers which might be useful in material design and applications of structural polymers.

Examining the Quasi-Static Uniaxial Compressive Behaviour of Commercial High-Performance Epoxy Matrices

“…The highly crosslinked networks produced in CYCOM ® 890 (A), CYCOM ® 977-2 (B), and PRISM EP2400 (D) will all produce significant concentrations of hydrogen bonds to restrict molecular mobility and limit segmental motion. Molecular dynamics simulations show that polymer networks bound by stronger interchain associations will exhibit smaller volume dilation [15]. The more open the network produced in cured PR520 (C), with a lower crosslink density, offers more molecular freedom to undergo molecular rotation; hence, the apparent lower dilation angle but higher K IC value.…”

“…Furthermore, to date, little effort has been devoted to exploring the potential links between compression properties and dilation angle [15][16][17], although the volumetric change during plastic deformation of the matrix is likely to be important. These questions form the basis of the current systematic study, carried out on a series of chemically related epoxy resins, sourced from a unique supplier.…”