Failure Mechanisms

A Fracture Mechanics model for Stage-II fatigue crack growth

· The diagram shows a sample configuration suitable for the measurement of the rate of crack growth in stage-II.

· A constant alternating force, P, acts on the machined slot with a fatigue crack at its apex. The crack length, a, can be measured as a function of time by optical or electrical resistance methods.
· Although the applied force (and hence the alternating stress amplitude) is constant, the increase in the crack length causes the stress at the crack tip to increase as a function of the number of stress cycles.

From: Ashby and Jones, "Engineering Materials I," Pergamon (1986)