Compression fatigue crack growth behavior of metallic alloys: Effect of environment

Abstract

Many structures are subjected to cyclic compressive loading and corrosive atmosphere. However, research on environmentally-assisted compression fatigue of metallic materials has not yet been undertaken. In the present paper, the behavior of fatigue cracks under compressive cycling in laboratory air, mineral oil and 3.5% NaCl was studied on circumferentially notched cylindrical specimens of an Al-alloy and CrNi stainless steel. Fatigue tests were supplemented by fractographic observations. In oil and air, the non-catastrophic character of the compression fatigue crack growth process was confirmed for both materials. The saturation depth of the crack was found to depend on the material as well as on the nominal stresses, but was insensitive to the load frequency in a range of 2–110 Hz. In the case of the aluminum alloy tested at low load frequency in 3.5% NaCl, continuous growth of fatigue crack was observed. The role of hydrogen embrittlement and anodic dissolution in promoting fatigue damage under compressive cycling is discussed and the mechanism rationalizing observed behavior is proposed. The detrimental influence of corrosive environment is attributed to the crack tip blunting via anodic dissolution and concomitant development of the tensile residual stresses ahead of the crack growing under compressive cycling. If operative in service, the above mechanism may cause a catastrophic failure even under fully compressive cyclic loading.