Fatigue striation morphology

1
Fatigue striation morphology
(a) Ductile specimens high stresses
(b) Ductile specimens high stresses
common also for small cracks
(c) Specimens cycled at lower stresses
(d) Specimens cycled at lower stresses
(Source Campbell Laird The influence of
Metallurgical Structure on the Mechanisms of
Fatigue Crack Propagation, Fatigue Crack
Propagation, ASTM STP 415, ASTM, 1967, p. 131)
2
Stage II crack - Crack tip plastic blunting and
fatigue striation formation

1. Zero load
2. small tensile load
3. Maximum tensile load
4. Small compressive load
5. Maximum compressive load
6. Small tensile load

(Source Campbell Laird The influence of
Metallurgical Structure on the Mechanisms of
Fatigue Crack Propagation, Fatigue Crack
Propagation, ASTM STP 415, ASTM, 1967, p. 131)
3
Crack tip profile in a copper single crystal
cycled in tension-compression with a stress axis
parallel to 001 (x250)
(Source Campbell Laird The influence of
Metallurgical Structure on the Mechanisms of
Fatigue Crack Propagation, Fatigue Crack
Propagation, ASTM STP 415, ASTM, 1967, p. 131)
4
Changes occurring at the crack tip during a
fatigue cycle

1. Compression
2. Maximum tension
3. Compression
4. Crack tip in an annealed nickel specimen after
   360 cycles at a strain range of 0.017 (N 465)
   (x850)
5. Crack in a fully compressed aluminum specimen
   cycled at 0.02 (x350)

5
Fracture surface of a cold-worked copper specimen
cycled at high strain showing striations and
inter-striations (x4500)
(Source Campbell Laird The influence of
Metallurgical Structure on the Mechanisms of
Fatigue Crack Propagation, Fatigue Crack
Propagation, ASTM STP 415, ASTM, 1967, p. 131)
6
Stage I FCG plastic blunting
(a) Zero stress
(b) Maximum stress
(c) Compressive stress
(Source Campbell Laird The influence of
Metallurgical Structure on the Mechanisms of
Fatigue Crack Propagation, Fatigue Crack
Propagation, ASTM STP 415, ASTM, 1967, p. 131)