PSI - Issue 52

D. Kujawski et al. / Procedia Structural Integrity 52 (2024) 293–308 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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be exposed at the crack tip resulting in the production of aquo-metal ions that eventually cause the growth of the passive film outer layer, but it is concluded that the inner, or barrier layer, will be too thin to contribute to OICC. The above discussion is supported by an interesting experiment on fatigue threshold with an ASTM A542 Class-3 steel in distilled water Suresh and Ritchie (1982). Dry oxide thickness and  K th was measured at three R-ratios, Fig. 7.

Fig. 8 Dry oxide thicknesses and  K th variation with R in A542 steel in distilled water.

The dry oxide thickness was constant at ≈ 0.8 mm with increasing R, from R = 0.1-0.75. This experiment suggests that oxide formation and its thickness is influenced more by chemistry than cyclic loading, but  K th decreased monotonically with R. Their results were interpreted by the authors as a complex combination of both OICC and environmental effects on  K th . In contrast, we now can interpret the same data as being due mostly to the crack tip environmental access with increasing R to result in damage, with little contribution from OICC.

Fig. 9 Effects of silicone oil viscosity on fatigue crack growth rate in (a) 2.25Cr-1Mo steel (50 Hz) and (b) 316 stainless steel (4 Hz). Results compared with dry He and air in (a) and (b), respectively.

Figure 9a shows the results of Tzou et al. (1985) have studied the effect of viscous fluids (silicon oils) of