Damage tolerance analysis requires the capability to assess the damage, usually measured by incremental crack growth, accumulating in a given piece of structure under flight-by-flight spectrum loading. This requirement implies the need to process this damage accumulation over thousands of flights consisting of millions of load cycles. Many models have been developed to analyze the process of damage accumulation under spectrum loading. All these models have been computerized to permit timely cost-effective damage tolerance analyses to be performed.

This paper examines the techniques used to perform the damage accumulation process within these computerized models. Techniques range from simple closed-form numerical integration to sophisticated equivalent damage techniques based on statistical representation of the flight-by-flight spectrum. Recommendations for applications to various types of spectra are offered.