On-Line Fatigue Analysis to Detect Damage as it Occurs
S. M. Price, IMAC XVI, Santa Barbara, CA, February 2-5, 1998. 

In industrial environments, failures of system components can lead to unsafe operation, environmental damage, and significant loss of revenue. When specific components of the system are critically designed, analysis and instrumentation can be combined to assess operation. After analyzing the potential strain fields in a structure, strain gages may be installed at key locations to measure dynamic strain during operation or use of the structure. Fatigue analysis can be performed on the acquired data to determine if failures are likely. From these data, operational parameters and/or system design can be altered to maintain safe and reliable operation.

This procedure can result in high channel counts, producing large amounts of data and can quickly overwhelm the analyst. Furthermore, one is not always assured of obtaining data during time of high strain. Therefore, a system to continuously acquire and evaluate the data while presenting only the most useful information is required.

Such a system using off-the-shelf acquisition and PC hardware has been developed and has been in use for a number of years in oil pipeline service in an environmentally sensitive area. Critical features of this system will be discussed. A method for counting stress-cycles in real-time will also be presented. A procedure for estimating the amount of damage (usage) that has already occurred will be shown. The concept of a “Fatigue Concern Indicator” will be introduced. To best illustrate these methods, a specific application will be discussed.