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Existing agitator paddles in material feeders were failing in fatigue. An experimental evaluation was undertaken to assess the fatigue strengths of the existing agitator paddles and the newly designed replacement paddles. As in most typical industrial situations, the study was constrained by budget and time limitations. After considering several options, it was decided to strain gage and test the paddles in their own feeder frame and drive motor with minimum mock-up fixturing to achieve several load levels. While using real-time test speeds, the test durations were accelerated by using higher than normal operating loads. Results were analyzed using strain-based cumulative fatigue damage-analysis techniques and component fatigue-life curves were developed to project the long life fatigue strengths. The investigation showed that while the newly designed replacement paddles would have significantly improved fatigue strengths, the actual improvements may be limited by other built-in weld discontinuities in the paddle stiffeners.
steel, torsional fatigue, cumulative damage analysis, fatigue test, rainflow histogram data analysis
Principal engineer, Fatigue and Fracture Mechanics, Siemens Power Corporation, Milwaukee, WI