Volume 2, Issue 5 (September 1974)
The Dynamic Response of Metals in Evaluating Stress Corrosion Cracking
An experimental investigation of stress corrosion cracking in metals is reproted for several alloy-corrodent systems. Internal damping measurements are made on the metals in the as-received condition and after they have been exposed to a corrosive environment. Data curves are reported for different grain sizes of 2024-T4 aluminum in a mercury-corrodent environment and for 304 stainless steel in boiling MgCl2. Considerable changes in the diffusion peaks of these alloys are observed following their exposure in a stressed state to the environment in which they are known to be susceptible to stress corrosion cracking. Corroborative tests on electrolytic copper stressed in a corroding environment of air-saturated synthetic seawater indicate no changes in its internal damping characteristics. This material is immune to stress corrosion cracking in the seawater environment.
This study is developed from the idea that metals which are susceptible to stress corrosion cracking exhibit changes in their damping properties after environmental exposure. From the experimental evidence obtained, susceptibility to stress corrosion cracking is associated with decreases in the peak amplitudes of the internal damping curves. The decrease occurs across either the thermal diffusion peak associated with the specimen thickness or with the grain size of the metal. Moreover, for alloys immune to stress corrosion cracking, it is shown that the peak amplitudes remain unchanged after environmental exposure and when compared to the same data curve for the as-received material.
From these studies it is concluded that the decreased amplitudes of the internal friction peaks indicate the susceptibility to stress corrosion cracking. This decrease results from the thermal diffusion effects associated either with the specimen thickness or with the grain size. For nonsusceptible systems, the peak amplitudes remain unchanged after environmental exposure.
The specific aluminum alloy and stainless steel are used in order to demonstrate a basic phenomenon. It should not be construed that neither aluminum alloys nor stainless steels are useful marine alloys.