Half-Cycle Crack Growth software offers a reliable method for calculating theoretical fatigue crack growths that could lead to catastrophic structural component failures. The program builds upon and integrates Armstrong’s proven half-cycle and closed-form aging theories, and considers every half-cycle of loading spectra for specific structural components. The program works by reading test data files and determining maximum and minimum loads of each half-cycle of random loading spectra in order to calculate theoretical crack growth. The innovation is an improvement on traditional prediction software (and in particular, on visual inspections) because it considers mini-amplitude stress loading and half-cycles based on the duty cycle of a particular component or structure. Developed to calculate the number of operational life flights for B-52B pylon hooks at Armstrong testing facilities, the program and underlying theories can be applied to estimate the service life of any critical structural component, making it suitable for use in other industries, especially for construction and petrochemical firms.

The software is a powerful and practical tool for visualizing crack growth curves associated with critical stress points. It was designed to determine the number of safe operational flights an aircraft can make without structural component failures due to fatigue crack growth. By improving fatigue and failure predictions, the software provides safer flights and lower maintenance costs. Additionally, these predictions allow engineers to determine the critical points during operation that the majority of stress is placed on a particular component, which could allow for better component design that takes those specific forces into account.

This work was done by Van Fleischer and William Ko of Armstrong Flight Research Center. DRC-010-044


NASA Tech Briefs Magazine

This article first appeared in the January, 2015 issue of NASA Tech Briefs Magazine.

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