Session: MF-02-03 Materials for hydrogen service III (Joint with C&S)

Paper Number: 61740

Start Time: Tuesday, July 13, 2021, 08:00 PM

61740 - Fatigue Crack Growth Retardation After Single Overloading, as an Indicator of Hydrogen-Effect on the Extension of Crack-Tip Plastic-Zone 

Hydrogen embrittlement of metallic materials has been a concern to design pressure vessels exposed to high-pressure hydrogen gas. It has been reported that hydrogen triggers the loss of ductility and the acceleration of fatigue crack growth (FCG) in various materials although none of several proposed mechanisms can comprehensively explain the whole events. It is well-known that FCG is influenced by various types of crack closure, for which crack-tip plastic-zone evolution can be the important factor dominating the plasticity-induced crack closure. However, the influence of hydrogen on the crack-tip plastic deformation and its role on the FCG acceleration have not fully been understood. In this study, with aforementioned research interest as well as the practical importance, we focused on the effect of single overloading on the subsequent FCG in a low-alloy, martensitic steel.

During the ΔK-constant FCG tests using compact-tension specimens in ambient air and 90 MPa hydrogen gas, a single overload was applied and the subsequent FCG rates were monitored. Substantial crack blunting was observed in air upon overloading, whereas, in hydrogen gas, the crack tip retained a sharp configuration and propagated a short distance. Nevertheless, in both the cases, the growth rates in the subsequent FCG exhibited a great retardation as compared with those before overloading, for which the recovery distances (i.e., distance for FCG rate to revert to its original level) were nearly equivalent in the two test environments. The results inferred that, in the overloading process, a large plastic-zone possessing the size comparable to that in air, was formed ahead of the crack tip even in 90 MPa hydrogen gas.

Presenting Author: Keiichiro Iwata Kyushu University

Authors:

Keiichiro Iwata Kyushu University
Yuhei Ogawa Kyushu University
Masami Nakamura Kyushu University
Saburo Okazaki Kyushu University
Osamu Takakuwa Kyushu University
Hisao Matsunaga Kyushu University