Fatigue Crack Paths 2003

T A B L E1. Fracture process scales

Scale (mm) Feature

10-6

Ions, electron cloud

10-5

Dislocations

10-4

Subgrain boundary precipitates

10-3

Subgrain slip band

10-2

Grains, inclusions, voids

10-1

Large plastic strains

1

Elastic-plastic field

10

Stress intensity factor

Component or specimen

100

Figure 1. Network of surface fatigue cracks in a chilled cast iron rolling mill roll [6].

Magnification: x 12.5.

Macroscopic aspects of fatigue crack paths have been of industrial interest for a very

long time. For example Figure 1 shows a network of surface fatigue cracks in a chilled

cast iron rolling mill roll. This was published in 1930 [6]. The same Ref. includes a

primitive example of the use of a critical plane approach in fatigue design calculations.

The book by Cazaud published in 1948 includes an analysis of fatigue crack paths in

both laboratory specimens and industrial components. An English translation of his

book, including additional material, was published in 1953 [7]. At about the same time,

the metallurgical microscope was being used by Forsyth in the examination of fatigue

crack paths at microscopic scales [8, 9]. By 1962 the use of quantitative fractography in

the reconstruction of crack path information was well developed [10].

In the intervening four decades there have been substantial advances in the

understanding and prediction of fatigue crack paths, largely through developments in

fracture mechanics and in the application of modern computers and microscopes. See

for example the handbook edited by Carpinteri [3] and a recent summary [11]. At

microscopic scales there has been interest in the use of fractals [12] and random process

theory [11, 13] in the characterisation of fatigue crack paths. At macroscopic scales

differential geometry has been used in the interpretation of some features of crack paths

[11, 14].