Threshold stress intensity factor

POSTER TITLE Identification of the fatigue stress intensity factor threshold for different load ratios R From fretting fatigue to C(T) fatigue experiments... 

Yoshimura HN, Cesar PF, Soki FN, Gonzaga CC. Stress intensity factor threshold in dental porcelains. Journal of Materials Science Materials in Medicine 2008 19(5) 1945-1951. 

Crack Initiation and the Threshold Stress intensity Factor Range... 

A-2.8.1 Pressure and Temperature. An important general trend is that structural metals become more susceptible to hydrogen embrittlement as hydrogen gas pressure increases. An example of this trend is the measured threshold stress intensity factor, Km, as a function of gas pressure for low-alloy steels. Kjh decreases as gas pressure increases. Increasing hydrogen gas pressure enhances the concentration of dissolved hydrogen in materials, which promotes hydrogen embrittlement. 

Equation (18) is very similar to the result of Eqn. (17) which was derived for crack growth under elastic field control. From the result of Fig. 10.4, it is clear that Kmin represents the threshold stress-intensity factor for creep crack growth. Kmin is proportional to eceVFc so that an increase in ec and lc leads to an increase in the threshold stress-intensity factor. The creep crack growth rate, on the other hand, is decreased in the asymptotic limit by an increase in lc and ec, as would be expected. 

Standard Test Method for Determining Threshold Stress Intensity Factor for Environment-Assisted Cracking of Metallic Materials, Standard E 1681-03, ASTM International, West Conshohocken, PA, 2003. 

Effect of yield strength on the threshold stress intensity factor (Kjh) for crack propagation in hydrogen gas (a) low-alloy steels [5] and (b) austenitic steels [17]. 

Effect of gas pressure on threshold stress-intensity factor for crack propagation in hydrogen gas Kj ) or fracture toughness in hydrogen gas (XJh) 15, 30, 32]. The data are for low-alloy steels (open symbols), while the data are for carbon steel (filled symbols). 

This approach tends to be limited to high strength alloys since these often have mechanical properties that are closest to the ideal required and because of their engineering importance. The type of specimem employed takes into account the stress concentration arising from the presence of a crack in a specimen and employs a measured component K, the stress intensity factor, which is obtained from the applied stress a X c1/2, where c is the crack depth. It has units MN m 3/2. If such specimens are now tested as a function of time-to-failure, the results obtained are of the kind shown in Figure 2. Again, the question arises of a threshold which is such specimens is termed where the subscript I refers to the loading mode( 5). The whole term represents that value of K below... 

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