Nano-scale thermometer at crack tip

Full description

Predicting when, why and how solids break is central to many science and enginnering fields, from materials engineering to seismology. This question is classically addressed using Griffith’s fracture theory: a crack starts to grow when the prying force (stress intensity factor or energy release rate) is greater than a given material constant threshold (fracture toughness or fracture energy). Nevertheless, slow fracture regimes (e.g. creep) exist at lower prying forces, which are generally interpreted by invoking specific dependences of some material properties (viscoelastic moduli, toughness) with the strain rate.
Recently, Toussaint and Vincent-Dospital et al. [1] proposed to consider the crack growth as a thermally activated failure process. In this novel theoretical framework, the heat production due to local damage process at the crack tip is coupled to heat diffusion, which cause the temperature in the surrounding solid to rise. In the slow cracking regimes, this heat has time to diffuse into the solid; therefore, the temperature rise remains low. However, as the crack tip velocity increases, heat is unable to diffuse fast enough, which causes local crack tip heating. This becomes a cyclic process causing the crack tip to move faster by thermal activation and subsequently additional heating, which causes the phenomenon to spiral out of control. This first order transition concerns Griffith’s classical theory of catastrophic failure. This framework now needs to be experimentally tested; in particular, crack tip heating needs to be probed. The area coresponding to the temperature rises is small (nano to micrometer scale, depending on the material) and the crack tip velocity is high (100 to 1000 meters per second). This prevents the use of conventional temperature measurements (e.g. infrared cameras).
SPEC laboratory has hypothesized a novel experimental route to detect and measure post-mortem the highly (time and space) localized temperature elevation. The idea consists in deposing a nanometer thin layer of properly chosen oxyde and detect the thermally-induced changes in its atomistic structure. The internship aims at establising a proof of concept of this novel method. The selected candidate will be involved in all the steps of the method: deposition of the thin oxyde layer with atomic scale control on its structure, running fracture experiments covering several order of magnitudes in crack speed, probing the post-mortem thermally induced changes through adequate near-field microscopy and spectroscopy methods. This project lies at the interface between experimental mechanics, condensed matter physics, and material sciences and the selected candidate will have the opportunity to learn and use first-hand advanced methods from these three domains.
Practical aspects: The intern will work in SPEC, the Condensed Matter Physics Laboratory (SPEC: UMR 3680 CEA-CNRS) of CEA Saclay, located at L’Orme des Merisiers. A CEA bus system provides easy access to L’Orme des Merisiers from various locations in Ile-de-France
Candidate profile: Last year of engineering school, M2 or M1 student with a background in materials science, chemistry or physics with knowledge in condensed matter physics, mechanics of materials and/or surface science. The intern should be curious, motivated by experimental work, and able to work both in a team and independently.

Location

France

Internship conditions

• Internship duration: 6 months
• Level of study: Bac+5
• Training: Master 2
• Continuation in PhD thesis: No
• Application deadline: 1 février 2027

Useful methods and technics:
Experimental mechanics, near-field spectrocopy, thin films

Supervisor

Laure Chomat
Phone: 0169087932
Email :

Head of the laboratory SPEC / SPHYNX

Sawako Nakamae
Phone: