Threshold stress intensity, fatigue crack

Threshold Stress Intensity for Fatigue Crack Growth. 

The fatigue crack growth behavior of Mo, TZM, and W in the region near the threshold stress intensity, AX th, considered to correspond to fatigue crack growth rates of da/dN < 10 m/cycle, is shown in Fig. 3.1-178 [1.126]. The available crack growth and threshold data are included in Table 3.1-115. 

An effective threshold value for fatigue crack growth, AX th.eff, can be computed. Methods for the determination of this effective threshold stress intensity range are described in [1.197]. The available data on AX th.eff of Mo and TZM are listed in Table 3.1-115. 

Part (b) of the Figure 11.48 shows the superposition of the behaviors of mechanical fatigue and stress corrosion cracking. In general, the influence of the latter shows up mostly at low strain rates (d /dy = 10 - 10 s ). In the graph that represents Aa/AN as a function of log K, a step appears at the point where the stress intensity factor that corresponds to the maximum value of the applied cyclic stress, reaches the value iscc. the threshold stress intensity for stress corrosion cracking. 

This test method can be used to measure the relative susceptibility of materials by "Determining the Threshold Stress Intensity Factor for Environment-Assisted Cracking EAC of Metallic Materials. Constant load specimens, both the fatigue precracked single edge beam SE(B) and precracked compact specimens are tested in bending. The SE(B) was originally referred to as the Cantilever Beam Test. 

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