Crack Propagation Test and Analyses of CH-47 Swashplate Rotating Ring

In response to field inspections that revealed fatigue cracks in the forward swashplate rotating ring of the H-47 fleet, a comprehensive inspection, test and analyses program is conducted. The incidence of anomaly is approximately 15 percent in the field. A significant analytical effort combining classical techniques and numerical simulation examined the stress state and crack geometry of the field cracks. To replicate the cracks a full-scale test fixture was developed and applied to flight articles. Although the test results did not produce cracks representative of the field cracks, it is shown that the resultant thumbnail cracks are a result of fretting. Due to the geometry and loading of the cracks, standard fatigue codes are not capable of predicting their propagation and arrest.