Research Studentship in Solid Mechanics
3.5-year D.Phil. studentship
Project: Micromechanics of Soft Materials
Supervisor: Prof Laurence Brassart
Traditional engineering applications mostly use hard materials, such as steel, concrete or fibre-reinforced composites. In contrast, materials found in plant and animal tissues are soft. Softness imparts attractive characteristics to materials, such as the ability to deform in response to external stimuli (force, pH, temperature). Softness is also desirable for applications where materials interact with the human body. Inspired by nature, there has been a fast-growing interest in developing soft materials for emerging applications in engineering and medicine, such as artificial cartilage and soft robots [1,2].
This general objective of this project is to develop micromechanics-based modelling techniques for soft materials in order to elucidate their complex structure-property relationships. The project will focus on hydrogels, which consist of a polymer network swollen in water. Some possible research directions are listed below. The specific orientation of the research will be fine-tuned based on the candidate’s interest and background.
1. Mesoscale simulations of polymer networks
The aim of this project is to elucidate the relationships between network parameters and mechanical properties using a Random Network model, in which polymer chains are represented by nonlinear springs connected at crosslinking points . The role of network topology, reversibility of the crosslinks and chain length distribution will be investigated in relation to strain-rate dependency, damage and crack propagation resistance. Mesoscale simulations will serve as reference for the formulation of macroscale “mean-field” estimates useful for large-scale simulations.
2. Modelling viscoplasticity, damage and self-healing in hydrogels
This project aims at developing a novel physics-based constitutive model for highly-stretchable and tough hydrogels. The exceptional properties of these gels is attributed to the reversible crosslinking mechanism at microscale, enabling efficient energy dissipation and self-healing . The model will be developed in a continuum thermodynamics framework at finite strains, and will be implemented as a user subroutine in the Finite Element software ABAQUS. The model will be further extended to simulate damage and self-healing in view of guiding the design of soft structures.
3. Micromechanics of fibre-reinforced hydrogels
An efficient technique to improve the mechanical strength of hydrogels is to reinforce them with stiff fibres, thereby mimicking natural tissues such as muscles and cartilage. This project aims to develop a micromechanical approach for fibre-reinforced polymer gels, inspiring from homogenisation techniques previously developed for filled elastomers, e.g. . Mean-field predictions will be validated against full-field simulation results on Representative Volume Element of the microstructure. The effect of fillers on the mechanical and diffusion properties will be investigated.
Prospective candidates will be judged according to how well they meet the following criteria:
• A first class honours degree in Engineering, Physics or Applied Mathematics
• Excellent English written and spoken communication skills
• Strong interest for mathematical modelling and numerical simulations in Mechanics of Materials
• Strong background in Solid Mechanics
• Good programming skills (e.g. Matlab, Python, C/C++)
The following skills are desirable but not essential:
• Basic knowledge of polymer physics or soft matter physics
• Basic knowledge of the Finite Element Method
Informal enquiries are encouraged and should be addressed to Prof Laurence Brassart ([email protected]
Candidates must submit a graduate application form and are expected to meet the graduate admissions criteria. Details are available on the course page of the University website.
Please quote 20ENGMM-LB in all correspondence and in your graduate application.
Application deadline: 24 January 2020
Start date: October 2020
 Calvert, P., 2009. Hydrogels for soft machines. Adv. Mater. 21, 743-756.
 Suo, Z., 2012. Mechanics of stretchable electronics and soft machines. MRS Bull. 37, 218-225.
 Alame, G., Brassart, L., 2019. Relative contributions of chain density and topology to the elasticity of two-dimensional polymer networks. Soft Matter 15, 5703.
 Sun, J.-Y., Zhao, X., Illeperuma, W.R.K., Chaudhuri, O., Oh, K.H., Mooney, D.J., Vlassak, J.J., Suo, Z., 2012. Highly stretchable and tough hydrogels. Nature 489, 133.
 Goudarzi, T., Spring, D.W., Paulino, G.H., Lopez-Pamies, O., 2015. Filled elastomers: A theory of filler reinforcement based on hydrodynamic and interphasial effects. J. Mech. Physics Solids 80, 37-67.