comment on a recent Nature paper on nucleation of sliding by Fineberg's group

Dear colleagues  As fellows in fracture mechanics, you may be interested in these comments on a recent very nice Nature paper by the group of Jay Fineberg, making clever experiments to measure nucleation of small cracks in frictional interfaces of PMMA, and their propagation velocity during nucleation and later rapid acceleration.   Fineberg derives a threshold shear stress for nucleation which depends on the specimen width which seems new in fracture mechanics to me, but does not entirely convince me, see in the text.   If you have any comments please let me know, I would be glad to discuss... https://www.researchgate.net/publication/388153106 regardsmike