Strength and Fatigue
Most hard materials testing involves short-term testing, while relatively little is understood about fatigue characteristics. Hardmetals and PM products, however, are frequently used under heavy fatigue loads, yet little is known about their behaviour or the criteria for choosing the optimum materials. However, there can be problems with scatter of test data in brittle materials because of the effects of randomly sized and located defects.
Notched flexural fatigue test
To overcome the problem of scatter NPL has been pioneering test, in which a standard-sized notch is introduced into the material in order to focus the stress into a small region. This avoids the effects of the occasional large strength controlling defect, and thus determines more reliably the fundamental differences between material grades.
Fatigue Elevated temperatures
Fatigue at raised temperature often occurs in practice, especially in applications such as process rollers, dies, drills, cutting tools, valves, etc. With a novel design of furnace, NPL is able to measure fatigue at elevated temperature in controlled atmospheres using the same, and therefore comparable, test technique described for room temperature.
For more information: Ken Mingard