How heat controls fracture: the thermodynamics of creeping and avalanching cracks

While of paramount importance in material science, the dynamics of cracks still lacks a complete physical explanation. The transition from their slow creep behavior to a fast propagation regime is a notable key, as it leads to full material failure if the size of a fast avalanche reaches that of the...

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Bibliographic Details
Published in:Soft matter 2020-01, Vol.16 (41), p.959-962
Main Authors: Vincent-Dospital, Tom, Toussaint, Renaud, Santucci, Stéphane, Vanel, Loïc, Bonamy, Daniel, Hattali, Lamine, Cochard, Alain, Flekkøy, Eirik G, Måløy, Knut Jørgen
Format: Article
Language:eng ; nor
Subjects:
Condensed Matter
Crack propagation
Crack tips
Creep (materials)
Dynamic mechanical properties
Energy release rate
Fracture surfaces
Goodness of fit
Materials failure
Mechanical properties
Mechanical tests
Morphology
Parameter sensitivity
Peeling
Physics
Polymethyl methacrylate
Polymethylmethacrylate
Pressure sensitive adhesives
Propagation
Propagation velocity
Rupture
Sublimation
Temperature
Thermodynamics
Velocity
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Summary:While of paramount importance in material science, the dynamics of cracks still lacks a complete physical explanation. The transition from their slow creep behavior to a fast propagation regime is a notable key, as it leads to full material failure if the size of a fast avalanche reaches that of the system. We here show that a simple thermodynamics approach can actually account for such complex crack dynamics, and in particular for the non-monotonic force-velocity curves commonly observed in mechanical tests on various materials. We consider a thermally activated failure process that is coupled with the production and the diffusion of heat at the fracture tip. In this framework, the rise in temperature only affects the sub-critical crack dynamics and not the mechanical properties of the material. We show that this description can quantitatively reproduce the rupture of two different polymeric materials (namely, the mode I opening of polymethylmethacrylate (PMMA) plates, and the peeling of pressure sensitive adhesive (PSA) tapes), from the very slow to the very fast fracturing regimes, over seven to nine decades of crack propagation velocities. In particular, the fastest regime is obtained with an increase of temperature of thousands of Kelvins, on the molecular scale around the crack tip. Although surprising, such an extreme temperature is actually consistent with different experimental observations that accompany the fast propagation of cracks, namely, fractoluminescence ( i.e. , the emission of visible light during rupture) and a complex morphology of post-mortem fracture surfaces, which could be due to the sublimation of bubbles. Fast fractures and the brittleness of matter are explained by statistical physics and by thousands of degrees hot rupture fronts, the blackbody radiation of which elucidates fractoluminescence.
ISSN:1744-683X
1744-6848
DOI:10.1039/d0sm01062f