Abstract
Fatigue crack growth (FCG) behavior of a Fe-3wt.%Si ferritic alloy under different environmental conditions using in-situ electrochemical (cathodic) hydrogen (H) charging has been investigated. Three frequencies have been applied. Results clearly show that the FCG rate increased by a factor spanning from 20 to 1000 times, depending on the loading frequencies, when compared to the reference test in air. Lower frequency leads to higher FCG rate. A comprehensive fractographic analysis was carried out: the area fraction of different fracture surface features was measured and taken into statistical analysis. Based on these investigations, the possible mechanisms of H-enhanced FCG are discussed. Similar tests in high-pressure H gas from other studies were also compared and discussed. These results give a preliminary understanding of H effect in fatigue crack propagation procedure in ferritic alloys.
Highlights
It is generally acknowledged that engineering structures are normally experiencing different loads such as static load, cyclic load, impact load or a combination of several loads from the above-mentioned category
The purpose of this study is to study the mechanism in the degradation of structural materials that serve in the condition with cyclic loading and H environment and try to correlate the physical mechanism with engineering aspects
With the highest frequency (10 Hz) in the present study, the Fatigue Crack Growth Rate (FCGR) increased by about 20 times with respect to the test in lab air, while the lowest frequency (0.1 Hz) made the FCGR increase by about 1000 times
Summary
It is generally acknowledged that engineering structures are normally experiencing different loads such as static load, cyclic load, impact load or a combination of several loads from the above-mentioned category. A very common condition is cyclic loading combining a static loading. Researches regarding the fracture behavior from repeated loading have been published over a century and continue increasing. According to the data from Battele Laboratory under contract to United States Government agencies in 1983, the costs of fractures and efforts to prevent fracture amounted to 119 billion US dollars per year, which occupied a considerable part of the gross national product at that time [1]. It can be expected that this number becomes different today due to a faster development in industry. The classical fatigue crack growth behavior can be simplified by a logarithmic linear relation, which is called the Paris’ law (or Paris-Erdogan law), as shown in Eq (1): da/dN = C·ΔKm (1)
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