Development of a Navy Standard Test Method for Fatigue Crack Growth Rates in Marine Environments

Abstract

Fatigue crack growth rate testing of metallic materials under conditions which involve a corrosive environment is currently an active field of investigation throughout many of the industrialized nations. This research activity is stimulated by important demands for materials utilization in defense, energy, and transportation applications. A recent survey conducted by ASTM Task Group E24.04.05 on Fatigue Crack Growth Rate Testing in Aqueous Environments identified more than 40 laboratories in nine non-communist countries which are engaged in corrosion-fatigue studies using precracked specimens. Virtually all contemporary corrosion-fatigue crack growth rate testing is conducted using fracture mechanics test methods. ASTM Test for Constant-Load-Amplitude Fatigue Crack Growth Rates Above 10−8 m/Cycle (E 647) provides widely followed procedures for the mechanical aspects of this type of testing. The aforementioned ASTM E24.04.05 survey reported few problem areas in applying the requirements of ASTM E 647 to tests involving corrosive environments. Despite the reported success in applying ASTM E 647 to corrosion-fatigue crack growth rate testing, however, significant questions concerning this type of testing remain to be addressed. Corrosion-related experimental factors can strongly influence test results. Both Navy and nuclear power industry research programs have recognized interlaboratory variability in corrosion-fatigue crack growth rate data to be a potentially serious problem. The Navy has drafted a proposed Standard Method of Test for Constant-Load-Amplitude Fatigue Crack Growth Rates in Marine Environments. This paper describes the key provisions of this test method, the philosophy underlying its approach, and efforts to verify its provisions.