This paper is the second part in a two-part sequence and presents a stochastic model of fatigue crack propagation in metallic materials that are commonly encountered in mechanical structures and machine components of complex systems (e.g., aircraft, spacecraft, ships and submarines, and power plants). The stochastic model is built upon the deterministic state-space model of fatigue crack growth under variable-amplitude load presented in the first part. Predictions of the stochastic model are in agreement with the exprimental data for speciments made of 2024-T3 and 7075-T6 aluminum alloys and Ti-6Al-4V alloy. The (non-stationary) statistics of the crack growth process under (tensile) variable-amplitude load can be obtained in a closed form without solving stochastic differential equations in the Wiener or Ito setting. The crack propagation model thus allows real-time execution of decision algorithms for risk assessment and life prediction on inexpensive platforms such as a Pentium processor.
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