Volume 2, Issue 3 (May 1974)
High Cycle Fatigue Crack Propagation Rates in Copper
The crack propagation rate was studied on axially loaded specimens of oxygen-free, high conductivity copper tested in the high cycle life region. Fatigue tests were conducted under load control without a mean load. The variables of the test conditions were the engineering stress range, the average grain size, and the atmosphere (air and argon gas). The crack propagation rate during the first 80 percent of the life was determined by using an electropolishing technique. The rate was also measured after final failure of each specimen from the distances of the striations on the fracture surface observed through a scanning electron microscope. The crack propagation rate depended upon the test conditions as well as on the prior stress cycling. The crack propagation was divided into two main stages: the crack nucleation and microcrack development stage, and the crack propagation or macrocrack development stage. Argon gas atmosphere reduced the macrocrack propagation rate, but did not affect the crack nucleation and microcrack development significantly. Increasing the grain size shortened the crack nucleation stage markedly.