Yasuji Oda

AFM and SEM observation on mechanism of fatigue crack growth in an Fe-Si single crystal

Fatigue crack growth tests are carried out on sheets of an Fe-3.2% Si single crystal with a crystallographic orientation appropriate for striation formation. The behaviour of slip near a crack tip during the loading and unloading parts of a fatigue cycle is observed using an Atomic Force Microscope and a Scanning Electron Microscope. The fracture surfaces are also analysed with an AFM and an SEM. The mechanism of fatigue crack growth is discussed based on the observations, and a fundamental kinematic model for fatigue crack growth is proposed. The model gives a reasonable explanation for both the crack growth and striation formation.

Observation of small fatigue crack growth behavior in the extremely low growth rate region of low carbon steel in a hydrogen gas environment

To investigate the effects of hydrogen on crack propagation in the extremely low growth rate range, fully reversed bending fatigue tests were performed on low carbon steel (JIS S10C) in hydrogen and in nitrogen gas environments at a low pressure. A crack showed almost the same non-propagation behavior in nitrogen as that in air. However, a crack in hydrogen continued to propagate even near

Influence of Testing Frequency on Fatigue Crack Growth of 6061-T6 Aluminum Alloy in Hydrogen Gas Environment

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An Investigation of Hydrogen Environment Effect on the Strain Aging of Low-Carbon Steel through Vickers Hardness Test

107 cycles in the same testing strain range as that in nitrogen. In hydrogen gas, a crack grew intermittently by coalescing with a new micro-crack generated by slip behavior. This implies that hydrogen could inhibit the action of any factor affecting non-propagation.

Effects of Hydrogen Environment on Fatigue Characteristics of 18Cr-8Ni Stainless Steel

In order to investigate the hydrogen effect on fatigue crack growth (FCG) behavior in a few kinds of practical alloys; austenitic stainless steels (solution-treated metastable type 304 and stable type 316L), an aluminum alloy (age-hardened 6061) and a low carbon steel (annealed 0.13%C-Fe), FCG tests were carried out in hydrogen gas and in nitrogen gas. The FCG rates of these materials are enhanced by hydrogen, though the acceleration degrees are different. A crack grows across grains by slip-off in 316L stainless steel and in age-hardened 6061 aluminum alloys even in hydrogen. Faceted area increases in 304 stainless steel and in low carbon steel in hydrogen. In 304 stainless steel, the ratio of facets to the entire fracture surface was not so large. Thus, the FCG rate is not significantly affected through the facets in 304 stainless steel. In low carbon steel, facets were increased considerably, though a crack grows step by step or after a large number of loading cycles even along grain boundaries. Anyhow hydrogen enhances the FCG rate of these materials through the influence on slip behavior. Based on above-mentioned results, the effect of loading frequency on FCG rate in hydrogen of the age-hardened 6061 aluminum alloy was also investigated. The FCG rate increases as the testing frequency decreases, though the FCG rate in hydrogen shows the tendency to saturate.

Loading Frequency Effects on the Fatigue Crack Growth Rate and Fracture Surface Morphology of Low Carbon Steel in Case of Long-Term Use in Hydrogen Gas

In order to investigate the effects of testing frequency on the fatigue crack growth rate of 6061-T6 aluminum alloy in hydrogen gas environment, fatigue crack growth tests were carried out on specimens with small artificial holes in 0.18 MPa hydrogen gas or in 0.18 MPa nitrogen gas. It takes long time to test at low testing frequency, so in this study an accelerated test method was proposed and fatigue tests were carried out using this method. The fatigue crack growth rate in hydrogen gas environment accelerates compared with in nitrogen gas environment. The crack growth rate at lower testing frequency tends to higher.

A13 水素ガス中における低炭素鋼S10Cの疲労き裂伝ぱ挙動に及ぼす繰返し速度の影響(A1 材料力学(水素I))

In order to investigate the hydrogen gas effect on non-propagation phenomena of a type 304 austenitic stainless steel, fatigue tests with in-situ observation using a Scanning Laser Microscope were performed in air, in 0.18MPa hydrogen gas and in 0.18MPa nitrogen gas. A nonpropagating crack was observed during the fatigue test in air. At almost the same stress level of non-propagating in air, non-propagating cracks were also observed in fatigue tests in hydrogen and in nitrogen. Stress level of the non-propagation is not sufficiently different in the three environments. However, the process up to non-propagation differs from each other, for example, the crack path and debris.

Effects of gaseous hydrogen on fatigue crack growth behavior of low carbon steel

In recent years, increasing attention has been paid to the effect of a hydrogen environment on the fatigue limit of hydrogen-power systems and infrastructure. In carbon steel, strain aging is one of the important factors influencing non-propagating crack behavior, which is related to the fatigue limit. In the present study, to investigate the effects of hydrogen on the strain aging of low-carbon steel (0.13 % carbon steel), Vickers hardness tests were carried out on the carbon steel. A couple of 0.13 % carbon steel specimens with a large-scale plastic zone were aging heat-treated; one was a hydrogen-charged specimen, whereas the other was an uncharged specimen. The Vickers hardness of the hydrogen-charged specimen was found to be lower than that of the uncharged specimen. This observation implies that hydrogen inhibits strain-aging hardening of low-carbon steel. The observation also suggests that hydrogen could affect the non-propagating crack behavior through the inhibition of strain aging.