Title:
Size Effect in Fatigue Fracture of Concrete
Author(s):
Zdenek P. Bazant and Kangming Xu
Publication:
Materials Journal
Volume:
88
Issue:
4
Appears on pages(s):
390-399
Keywords:
concretes; crack propagation; cyclic loads; fatigue (materials); fracture properties; loads (forces); tests; Materials Research
DOI:
10.14359/1786
Date:
7/1/1991
Abstract:
Crack growth caused by load repetitions in geometrically similar notched concrete specimens of various sizes is measured by means of the compliance method. The Paris law, which states that the crack-length increment per cycle is a power function of the stress intensity factor amplitude, is valid only for one specimen size (the law parameters being adjusted for that size) or asymptotically for very large specimens. To obtain a general law, the Paris law is combined with Bazant's size-effect law for fracture under monotonic loading. This leads to a size-adjusted Paris law that gives the crack-length increment per cycle as a power function of the amplitude of a size-adjusted stress intensity factor. The size adjustment is based on the brittleness number of the structure, representing the ratio of the structure size d to the traditional size d0, which separates the responses governed by nominal stress and by stress intensity factor. Experiments show that d0 for cyclic loading is much larger than d0 for monotonic loading, which means that the brittleness number for cyclic loading is much less than the brittleness number for monotonic loading. The crack growth is also alternatively characterized in terms of the nominal stress amplitude. In the latter form, the size effect vanishes for small structures, while in terms of the stress intensity factor amplitude, it vanishes for large structures. The curves of crack length versus the number of cycles are also calculated and are found to agree with data.