Determination of the Fatigue Life for the Breech Mechanism Assembly for the Cannon, 175mm Gun: M113 and M113A1

摘要

Because of the increases in the tube service life, testing was performed to validate the original breech mechanism life and to justify the increase to the present 3600 EFC round life. The testing determined that the mode of failure of the breech mechanism was threads shearing from the breechblock which resulted in difficult opening of the breech. In all cases prior to thread shearing, the breech blocks had deformed the bushing threads leaving an impression of the mating breechblock threads. The test also showed that any failure due to fatigue would be non-catastrophic in nature. Of the nine field fired breech mechanisms tested, (four that were used in the 175MM Product Improvement Test and three that were used in the Special Test for Service Life in Vietnam), the minimum life was 16,112 cycles (EFC rounds plus laboratory cycles) with the other eight averaging approximately 27,000 cycles. As a result of this test, it is recommended that the 175MM breech ring be given an increased service life of 7200 EFC rounds. (Author)