ELFT HÍRADÓ

[Kormányos Andor <andor.kormanyos AT ttk.elte.hu>]

ELTE TTK Fizikai Intézet / ELTE Institute of Physics


ORTVAY KOLLOKVIUM / ORTVAY COLLOQUIUM
(https://physics.elte.hu/ortvayseminar)



Thursday, 23rd January  2025, 15:00h.

Pócza Jenő Lecture Hall, Physics Building 1.71

Pázmány Péter sétány 1/A, 1117 Budapest


Mikko Alava

Aalto University (Finland)

Fatigue and creep crack propagation from elastic interface theory or why 
small loads make cracks faster

Subcritical depinning describes interface propagation as an Arrhenius 
activation process, where the energy barrier diverges as a power law with 
decreasing driving force. This framework has been successfully applied in 
magnets and to fracture under creep loading but its naive extension to 
fatigue fails: in real materials, fatigue crack growth exhibits paradoxical 
behavior: the crack velocity is driven by the driving force (stress intensity 
factor) range so that the velocity increases when the minimum driving 
decreases. This is driven by processes occurring within the fracture process 
zone ahead of the crack front. To investigate this, we perform creep and 
fatigue experiments. By incorporating the history of the crack by an 
additional length scale into the observed crack front position, we reproduce 
the Paris--Erdogan-like fatigue behavior using subcritical depinning. We 
extend this approach to variable loading conditions and show how the approach 
can be used to explain the fatigue behavior in metals, the usual case.

Our results show in fracture the fundamental importance of the crack 
overcoming local barriers by activated avalanches. The crack tip local 
history may be encompassed in a leng thscale, that allows to apply a 
statistical fracture description to the time-dependent crack growth rate. We 
discuss the universal and material-dependent features of the developed crack 
growth theory.



Andor Kormányos

coordinator