■ Fracture dynamics in soft matter – large strain meets dissipation - a model study

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Description of the PhD project

The context
In soft matter (elastomer, gels), fracture (and also adhesion rupture) imply both large strains and extensive energy dissipation over a macroscopic region that may easily become comparable with system size. These mechanisms stand way outside the scope of standard fracture mechanics, which fails to deal with these materials, but at the same time, they are responsible for the specific properties of these materials, and especially a significant strengthening which opens the way to a wide range of innovative applications. There is a strong need for a better evaluation of the impact of dissipation in the large deformation fracture of soft materials. In this project, we propose a strategy to tackle this important issue by a joint experimental and simulation work, in collaboration with Pr. Rong Long (Colorado University, USA).

The project
Rupture of model soft materials with tunable dissipation will be monitored by innovative experiments specifically designed to map the large deformation fields around a running crack. The results will be compared to numerical models of steady-state crack propagation in soft dissipative materials.
The student will first synthetize and characterize his own model soft dissipative materials using associative gels recently developed in the SIMM laboratory at ESPCI. To measure strains around a crack, the standard method (Digital Image Correlation) correlates small area elements in two successive images of a specimen during deformation. Under large deformation, the area elements to be correlated undergo severe stretch and rotation, and the correlation scheme breaks down. This difficulty can be circumvented by a new technique developed in the laboratory of Pr. Rong Long, based on tracking individual tracer dots deposited on the specimen surface. During this project, this method, particularly suited for mapping large deformations, will be developed at SIMM in collaboration with Pr. Long. Two experimental configurations will be set-up, one for fracture and the other one for adhesion rupture. Adhesion will be adjusted through surface modification. Most importantly, the experiments will be complemented by the specific algorithm needed to turn the displacement field into strain fields.
The output of these experiments will be compared to numerical models. There several issues related to modeling fracture with large strains and dissipation, and we are presently developing specific, non standard, numerical schemes intrinsically based on the steady-state assumption to solve this problem. The very stringent steady state condition strongly reduces the numerical cost of the calculation and facilitates convergence.
The project should result in improved understanding of the rupture of soft solids, and also of adhesion. In particular, our aim is to provide guidelines for design of tougher materials/interfaces, by illuminating the interplay between large deformations and dissipative processes in
toughness properties.


Soft matter, fracture, acrylate gels, digital image correlation, dissipation, large deformation, adhesion

Research unit

UMR7615 Soft Matter Sciences and Engineering

Description of the research Unit/subunit

At SIMM, research focuses on soft matter, ranging from rather homogeneous (liquids, bulk polymers or gels) to more complex (self-organization, multiple elastomer networks, nanocomposites, multilayers, emulsions, foams). The areas we are primarily interested in are functional assembly, mechanical properties across lengthscales and interfacial dynamics. Through material chemistry, we exert control over molecular interactions, structural disorder and dynamics to interrogate properties such as polymer toughness and adhesion, complex wetting dynamics and the glass transition, and develop our understanding of their relation to the structure of complex soft systems. For that purpose, SIMM benefits from the complementary expertise of researchers from different fields, ranging from chemistry and physical chemistry to physics and mechanics.

Name of the supervisor
Matteo Ciccotti (matteo.cicotti (arobase) espci.fr)

Name of the co supervisor
Etienne Barthel (etienne.barthel (arobase) espci.fr)

3i Aspects of the proposal

This project is of fundamental nature, but in the long run, the understanding it aims at developing should benefit many applications involving rupture, adhesion or friction of deformable soft solids. In particular, the primary type of materials of technological interest concerned by the present project are elastomers, which are ubiquitous as vibration isolation, bridge bearings, flexible joints, seals, electrical insulators, energy absorption, hoses, belts, tires, in transportation, manufacturing, home appliances and many other areas. Although predominantly oriented towards soft matter physics and mechanics, the project also involves a significant input from chemistry for the elaboration of model systems with tuned dissipation. Our objective is ultimately to link fracture properties and the formulation of the material through understanding the relation between formulation, material structure, dynamical mechanical response, dissipation in the strain field around the crack and ultimately fracture resistance. Both experimental and modeling will be developed in close collaboration with Rong Long, currently an Assistant Professor in the Department of Mechanical Engineering at University of Colorado at Boulder. His research interests include continuum mechanics of soft materials, fracture mechanics, contact mechanics and adhesion. In particular, his laboratory is equipped with an experimental system and associated data processing software to measure large deformation strain fields around cracks in soft materials, which is directly relevant to this project.

Expected Profile of the candidate

Our main requirement is scientific curiosity and enthusiasm for a project which combines material chemistry, advanced optical measurement for the measurement of dissipative processes and mechanical modeling. Also relevent would be a background in experimental methods, typically in physics or mechanics, to set up the experiments, and ideally some degree of familiarity with - or at least some taste for - numerical methods, which will be used both to derive the experimental strain fields from the image kinematics and compute the response from the simulations.

Important dates

Call for applications : from July 16th to September 17th 2018
Eligibility check results : Late September
3i Committee evaluation results : Late October
Interviews from the shortlisted candidates with the Selection Committee : Mid-December (week of December 10th)
Final results : Late December

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