The Interaction of Test Methods and Failure Criteria

摘要

Two examples are given in which test methods interact with failure criteria. One involves self-pressurized products and their containers, or aerosols, which are regulated by the Department of Transportation (DOT) with respect to acceptable temperatures and pressures of their contents as well as their minimum burst pressures for transportation. Experiments have shown that the burst pressures of the containers are a function of the test methods used to measure the burst pressures. The second example concerns the relationship between proof testing of gun barrels and delayed failures. Such failures are due to fatigue, many of which are related to the presence of microstructural discontinuities. If such discontinuities are small enough, immediate failure may not occur during the proof test, but the flaws may grow during the proof test and subsequent service to a critical size causing a fracture (or crack) at a normal service stress. While focusing on the specific examples of aerosols and gun barrels, the broader issue being addressed is the relationship between test methods and the results achieved, with the ultimate goal of safer engineering outcomes. The nature of various test methods and their relationships to how a mechanical system is likely to stop functioning properly in the real world are also discussed. Aerosols and gun barrels present interesting case studies as they involve several disciplines and concepts, while also being familiar to most ordinary people.