Investigating brittle-to-ductile transition in glassy polymers by multiscale modeling across atomistic and continuum scales

• Applicant: Dr.-Ing. Wuyang Zhao
• Subject Area: Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale ; Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549959345

The aim of this project is to explore the physical mechanisms underlying the brittle-to-ductile transition (BDT) in glassy polymers. These materials, formed by cooling from a liquid state to temperatures below their glass transition point, can transition from ductile to brittle behavior under certain conditions such as aging or decreased temperatures, leading to sudden breakage with minimal energy absorption and potential accidents. Enhancing the toughness of glassy polymers without compromising stiffness is a significant scientific challenge, yet the mechanisms behind the BDT remain poorly understood. In crystalline materials, the BDT is often attributed to the kinetics of dislocations, but this explanation cannot be directly applied to glassy materials due to the absence of well-defined microscopic structures of such plastic carriers like dislocations. Molecular dynamics (MD) simulations have shown that spatial fluctuations of local mechanical properties at the atomistic scale and geometric loading conditions are crucial in the BDT of glassy materials, with higher brittleness associated with larger fluctuations. However, addressing the effects of geometric loading conditions under non-uniform deformations is challenging in pure MD simulations due to computational constraints on system sizes. To overcome this limitation, this project employs a multiscale simulation method by embedding an MD domain into a continuum domain to conduct non-uniform deformation boundaries for the MD system. This approach enables a better understanding of the interactions between plastic carriers and the relationship between local structures and global mechanical properties in glassy polymers. The project consists of four work packages (WPs). WP1 systematically characterizes the main factors influencing the BDT using pure MD simulations. WP2 aims to establish a mean-field constitutive model that accounts for the evolution of plastic carriers in glassy polymers during deformation. In WP3, a multiscale simulation method developed in preliminary work is used to study the effects of non-uniform deformation on the BDT in glassy polymers based on MD systems and constitutive models developed in WP1 and WP2. Finally, WP4 investigates the effects of nanoparticles on the BDT in glassy polymers. The outcomes of this project will provide valuable insights for designing the material properties of glassy polymers by selecting appropriate polymer matrices and incorporating suitable nanoparticles.

• DFG Programme: Research Grants