Lower Crack Propagation Rate Research Articles

Fatigue crack growth at 20 kHz-a new technique

A method is described for investigating fatigue crack propagation at very low crack propagation rates using resonant transverse 20 kHz oscillations of a three-point bend specimen. With this method the same fatigue crack propagation behaviour could be found as in conventional tests. At this high testing frequency fatigue crack propagation rates down to some 10-14 m/cycle could be measured in reasonable times.

Flight simulation fatigue crack propagation in 7010 and 7075 aluminium plate

The fatigue crack propagation resistances of 7010-T7651, 7010-T73651 and 7075-T7351 thick plate were compared for flight simulation (gust spectrum) loading conditions. The alloy 7075-T7351 was found to be slightly superior, and this superiority was not essentially due to its higher fracture toughness. The influence of specimen thickness on the crack propagation resistance was significant. Thinner specimens gave longer crack propagation lives and, generally, lower crack propagation rates and longer delays in crack growth following severe flights.

Fatigue crack closure at stress intensity threshold level

Recently, the application of fracture mechanics to metal fatigue has proven to be quite successful, that is, the fatigue crack propagation rate da/dn has been known to be expressed well by a power function of the range of stress intensity factor AK [I]. This expression, however, is not applicable to the case of very low crack propagation rate, and there is the stress intensity threshold level AK.. below which fatigue crack propagation becomes insignificant [2]. tn On the other hand, the stress ratio R(=o . /a =K . /K ) has been _. I mln _max mln max _ . found to influence the Xa~lgue crack propagation rate and the stress intensity threshold level [2-4]. Furthermore, observations of the tip of crack have revealed that the fatigue cracks are partially closed, even though loading is tension-tension. By considering the effective stress intensity range AK ~. which is calculated from the el crack opening stress, the effect of stress ratlo on the crack propagation rate has been explained [5]. The authors have suggested by a result of measurement on very low propagation rates for various stress ratios that the fatigue crack closure at the stress intensity threshold level shows a particular behavior [4]. To clarify this phenomenon further, the behavior of fatigue crack closure at AK _ was investigated for R of -i, -0.5, 0, 0.4, 0.6, and 0.8 in HTS0 stee~

Effect of heat treatment on time before failure of chromium steels in corrosive media

1. The increased resistance of steels to corrosion cracking is manifest in the longer induction period and lower crack propagation rate. 2. Susceptibility to corrosion cracking depends essentially on the heat treatment. The structure with the highest thermodynamic stability has the highest resistance.

主要構造部の検査間隔の設定に関する試考

The determination of inspection period of main structure has been accomplished based upon the operator's experience about their operating fleets. But the modern air transport is designed aiming at the increasing of fatigue resistance and the lower crack propagation rate, and they adopt completly the fail safe principle. To conform with above situation, the inspection period should be determined as theoretically as possible. The following analysis is a trial for this way and stands on the basis of the fail-safe test results, the load spectrum, the components fatigue tests, the critical incident rate and the statistical method.