On the Delayed Fracture of Pure Copper Wire

Abstract

Observation is made on the time required for pure copper wires to fracture under a given tensile load. In general, the probability of occurrence of fracture increases from zero to a certain value with time. This probability-time curve is assumed to be composed of two lines: the one with the probability being zero up to a critical time and the other a constant thereafter. Then this critical time is interpleted as the mean minimum time for the fracture. The mean fracture time and the mean minimum fracture time are very sensitively affected by surface conditions, but the probability of fracture occurrence remains relatively unaffected. Electrolytical polishing then heating and dipping in 3% HgCl₂ solution weaken the specimen extremely, but electroplating and diffusion of the deposited metal over the surface layer strengthen the specimen. Raising the annealing temperature is another cause of weakening. The specimen, annealed in air, is weaker than the one annealed in vacuum. From these experimental results, it is inferred that cracks originating from microcracks on the surface of the specimen grow rapidly with the deformation of the specimen and end in complete fracture.