Growth of short fatigue cracks in HY130 steel in 3.5% NaCl solution

6.04 – Environment-assisted Fatigue in Liquid Environments

The effect of corrosion inhibitors on environmental fatigue crack growth in Al–Zn–Mg–Cu

A criterion to predict under what conditions EAC would Initiate In cracks In a high-sulfur steel in contact with low-oxygen water was recently proposed by Wire and U. This EAC Initiation Criterion was developed using transient analyses for the diffusion of sulfides plus experimental test results. The experiments were conducted mainly on compact tension-type specimens with initial crack depths of about 2.54 mm. The present paper expands upon the work of Wire and U by presenting results for significantly deeper initial semi-elliptical surface cracks. In addition, in one specimen, the surface crack penetrated weld-deposited cladding into the high-sulfur steel. The results for the semi-elliptical surface cracks agreed quite well with the EAC Initiation Criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water.

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The initiation of environmentally-assisted cracking in semi-elliptical surface cracks

The environment sensitive fracture under cyclic loading of the white zone of commercial 7017-T651 aluminium alloy weldments was investigated. Fatigue crack growth ratesfor the white zone were obtained by utilising small arc type specimens over a wide range of frequencies from 0·01 Hz to 10 Hz. Fracture mode changes were observed to take place at certain crack velocities and their dependence upon the square root of the reciprocal of the loading frequency are shown to be consistent with an environment enhanced crack growth rate involving hydrogen diffusion ahead of the crack tip during each cycle. An enhancement of crack growth rates observed near the 1 Hz load cycling frequency has been attributed to crack tip solution modification owing to the motion of electrolyte in and out of the crack enclave during fatigue.

Environment sensitive fracture of white zone of AI-Zn-Mg alloy weldments under cyclic loading conditions

There exists in the literature several observations indicating that the electrolyte within corrosion-fatigue cracks can become modified relative to the bulk solution. Since the rate of fatigue-crack growth should depend upon electrolyte chemistry near the crack tip, it is important that the conditions under which such modification occurs and the role of influential variables be recognized. This paper represents an initial analysis of how fatigue variables might influence mixing between the crack and bulk solutions. The rationale considers that such mixing is governed primarily by net momentum of the periodically exhausted and ingested electrolyte. It is shown that this momentum should be directly proportional to the crack opening angle, cyclic frequency, and the cube of crack length. Decreasing mean stress also contributes to a momentum increase, with the latter becoming large for stress functions that result in crack closure during a portion of each cycle. Other factors which are considered include temperature, stress-wave form, specimen geometry, test method, and applied current density. The significance of the projected trends is discussed within the frame of commonly employed corrosion-fatigue test procedures.

WC Hooper

Papers

Solution Chemistry Modification within Corrosion-Fatigue Cracks