Thursday December 18, we will have the pleasure to host Didier Long (INSA Lyon) for a SIMM Seminar entitled « Theory of brittle-to-tough transition in polymer materials ». The seminar will take place at 2 pm in the Nobelium room (please note the unusual place).
Theory of brittle-to-tough transition in polymer materials
Polymer materials of different types break under applied strain with the remarkable feature that the fracture energy can increase by several orders of magnitudes when the rupture behavior changes from brittle to ductile. We show that this brittle-to-ductile transition in these different materials is underpinned by a phase transition regarding rupture mechanisms on a network that has been discovered recently [Fusco et al J. Stat. Phys. 2019]. The key ingredient of this theory is the distribution of the local stress rupture thresholds of the sites. If this distribution is narrow, a crack propagates as soon a cavity appears as a result of stress concentration in the vicinity of the crack tip. Then, a negligible damage 𝛟 at break is observed. Above a critical a value of the disorder, cracks do not propagate in an initial stage because they are blocked by stronger sites. Eventually, once the sample has been weakened by a sufficiently large accumulation of small damage, one of the cracks propagates and final rupture takes place. In this case, the sample accumulates a very large fraction of damage smaller than but of order 1 before catastrophic failure takes place [1]. We show how the theoretical network model of Fusco et al can be transposed to real materials by studying in detail breaking mechanisms in three different polymer materials : 1) neat glassy polymers, for which the brittle-to-ductile transition is induced by increasing the temperature; 2) high impact glassy polymers toughened with rubbery inclusions; 3) interpenetrated hydrogels. In these three different systems a brittle-to-ductile transition is observed beyond which impact or tear energy increases by up to 2 or 3 orders of magnitudes. Our transposition of the network theoretical model to these systems allow to describe each specific failure mechanism and to explain quantitatively these effects, which has eluded research for many decades [2].
[1] C. Fusco, D. R. Long, and L. Vanel, Brittle-to quasibrittle transition in creep rupture of 2d disordered elastic materials, J. Stat. Mech.: Theory and Experiment, 053301 (2019). DOI10.1088/1742-5468/ab11de
[2] C. Fusco, T. Lamy, L. Vanel and D.R. Long, Theory of brittle-to-tough transition in polymer materials, submitted (2025)
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