190 / 352
186
Figure 11: Methodology used for the stretch zone geometry measurement /9/
Figure 12: Typical variation in the measured
w
,
t
and
h
/9/
7. FATIGUE CRACK
Under certain conditions, fatigue crack can also be characterised by the stress intensity
factor. Consider a growing crack in presence of a constant amplitude cyclic stress inten-
sity, Fig. 17. At the tip of a crack subjected to variable load, a variable plastic zone is
formed, which is the largest when the force is the maximal, i.e. when the load is highest,
and smaller for lower loads.
w
,
t
and in
μ
m
Measurement number