Comparison of Shock Test Methods of MIL-S-901 Derived from Tests on a Circuit Breaker & Switchboard

Abstract

For shipboard equipment to qualify as shock-hardened, it must pass a shock test in accordance with the U.S. military shock test specification, MIL-S-901 [1]. The test methods prescribed by MIL-S-901 have gone essentially unchanged since 1963. All equipment is divided into three test categories, depending on weight, and a different shock test machine is specified for each weight category. The heavy weight category is further subdivided depending on the method of mounting within the ship, namely deck mounted or hull mounted. The authors have observed cases when equipment passing MIL-S-901 shock qualification testing using one method (e.g., the medium weight) failed when tested on another method (e.g., the floating shock platform). Concern about this difference in shock phenomena between the approved equipment performance stimulated the authors to perform the testing and analysis presented in this paper. The thirty year old test methods which have contributed significantly to shock survivability may not always simulate adequately the actual shipboard installation during shock qualification testing, thus leading to a false confidence level that all qualified equipment will perform well in combat. To explore the possible variations in shock phenomena from the different methods, an extensive testing program was conducted whereby a 100 ampere circuit breaker was subjected to shock testing under the four methods outlined in MIL-S-901 D, namely, lightweight, medium weight, heavy weight deck, and heavy weight hull. The data gathered during the testing, and the performance of the equipment under test, were both evaluated and analysed to observe differences in shock phenomena from each of the four different test methods. The shock testing methods, the equipment which was subjected to test, the test procedures, and the results of the investigation are described in this paper. The recommendations suggest improvements to the U.S. Navy shock testing methods and procedures.