MM504 Lecture 27b Moore's test and S-N diagram

Moore's test of fatigue is a common laboratory test used to determine the fatigue strength of a material by subjecting it to repeated cyclic loading. In this test, a specimen of the material is loaded with a cyclic stress that varies between a maximum and a minimum stress level. The number of cycles required for failure is then recorded, and the results are plotted on an S-N diagram, which is a graph of stress amplitude (S) versus the number of cycles to failure (N). The S-N diagram allows engineers to determine the fatigue limit of a material, which is the stress level below which no fatigue failure occurs after an infinite number of cycles. The S-N diagram also provides information on the endurance limit, which is the stress level below which no failure occurs after a specific number of cycles. This information is crucial in designing structures that are subjected to cyclic loading, as it enables engineers to select materials with appropriate fatigue properties and to determine the expected lifespan of a structure under cyclic loading.