Abstract :
Attention is given to the study of those properties of materials which determine the fracture of electronic valves from mechanical causes. The fracture behaviour, together with the time-dependence or fatigue behaviour, of glass, metal and mica is discussed. The influence of (a) continuously applied static stresses partly residing within the valves and partly applied externally, (b) continuously applied cyclic stresses, and (c) transient shock stresses on fracture behaviour, is described. The approximate time dependence of the probability of static-fatigue fracture is established empirically. This relationship permits the prediction of the probability of static-fatigue fracture. The concept of safe amplitude under vibration is applied to the observed fatigue fractures, and the design and manufacturing features which determine the most dangerous stress amplitudes under vibration are explained. It is shown that static-fatigue fractures, which are the primary cause of mechanical failure in early life, and vibration-fatigue fractures, which generally appear later in life, may be reduced in numbers to a level which is insignificant in comparison with valve failures from other causes.
