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Micro‐indentation fracture from flat‐ended cylindrical indenter
Author(s) -
XIE Y. J.,
HU X. Z.,
CHEN J.,
LEE K.Y.
Publication year - 2012
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.2011.01611.x
Subject(s) - indentation , materials science , fracture toughness , stress intensity factor , stress field , composite material , fracture mechanics , fracture (geology) , brittleness , cracking , crack closure , stress (linguistics) , contact mechanics , strain energy release rate , forensic engineering , structural engineering , finite element method , engineering , linguistics , philosophy
Unlike a Hertzian ring crack induced by a spherical indenter in absence of a singular stress field, a ring crack generated by a rigid flat cylindrical indenter can be explicitly linked to a K‐dominant singular stress field at the perimeter of the flat indenter. This means microcrack initiation induced by a flat indenter and relevant properties such as the critical indentation load and fracture toughness can be formulated explicitly using the fracture mechanics approach. It is shown in this paper that the indentation stress intensity factor, , for such a stress field is similar to that of a mode I crack. Based on the energy‐releasing rate and the Griffith's theorem, a flat indentation cracking model has been proposed; the critical load and critical cracking angle for crack initiation are derived. A new concept of fracture toughness for negative mode I singular stress field,, has been defined and a relationship between and the traditional K IC has been derived. The experimental investigation validates the existence of such , from which the K IC value of the glass had been determined to be 0.772 ± 0.003 MPa m 1/2 , agreeing well with the literature data. This analysis for indentation fracture or crack initiation due to surface contact of a flat indenter is particularly useful in determining K IC of brittle materials with dimensions in micro/nanoscales, e.g. thin films and other microstructures as flat micro/nano‐indenters are available and can be used on various nano‐indentation machines.