Masuo Shimodaira

Gigacycle fatigue data sheets for advanced engineering materials

Abstract Gigacycle fatigue data sheets have been published since 1997 by the National Institute for Materials Science. They cover several areas such as high-cycle-number fatigue for high-strength steels and titanium alloys, the fatigue of welded joints, and high-temperature fatigue for advanced ferritic heat-resistant steels. Some unique testing machines are used to run the tests up to an extremely high number of cycles such as 1010 cycles. A characteristic of gigacycle fatigue failure is that it is initiated inside smooth specimens; the fatigue strength decreases with increasing cycle number and the fatigue limit disappears, although ordinary fatigue failure initiates from the surface of a smooth specimen and a fatigue limit appears. For welded joints, fatigue failure initiates from the notch root of the weld, because a large amount of stress is concentrated at the weld toe. The fatigue strength of welded joints has been obtained for up to 108 cycles, which is an extremely high number of cycles for large welded joints. The project of producing gigacycle fatigue data sheets is still continuing and will take a few more years to complete. r 2007 Published by Elsevier Ltd.

Fatigue threshold and low-rate crack propagation properties for structural steels in 3 Pct sodium chloride aqueous solution

The fatigue threshold and low-rate crack propagation properties for a carbon steel, two high-strength steels, and two stainless steels were investigated in a 3 pct sodium chloride aqueous solution at frequencies between 0.03 and 30 Hz. Tests were conducted in a manner designed to avoid crack closure. Under freely corroding conditions, the effective values of the threshold stress intensity factor range, ΔKth,eff, were lower than in air for all of the steels. In particular, the ΔKth,eff values for the carbon and high-strength steels were almost equal to the theoretical ΔKth value of about 1 MPa m1/2 calculated on the basis of the dislocation emission from the crack tip. At a given ΔK level higher than the threshold, the fatigue crack propagation rates accelerated with decreasing frequency for all of the steels. Under cathodic protection, the threshold and fatigue crack propagation properties were coincident with those in air regardless of material and frequency. The observed fatigue crack propagation behavior in a 3 pct NaCl solution was closely related to the corrosion reaction of the bare surface formed at the crack tip during each loading cycle.

Strength of Materials at Elevated Temperatures. Fatigue Properties of TiAl Intermetallic Compounds and Dependences of the Microstructure.

Axial strain-controlled fatigue tests were carried out at room temperature and 800°C for several kinds of TiAl intermetallic compounds with a duplex microstructure consisting of γ and lamellar phases. The results obtained in this study are as follows:(1) Fatigue lives of relatively ductile TiAl were predicted by Manson-Coffin equation using tensile ductility and slope of 0.5.(2) The fatigue strength at 103 cycles was correlated with the cyclic 0.2% proof stress.(3) The fatigue strength at 103 cycles was dependent on volume fraction of the γ phases.

Effect of Frequency on Corrosion Fatigue Life Prediction for High Strength Steel (HT 80) in Synthetic Sea Water

Corrosion fatigue crack growth behavior of HT80 steel was studied in synthetic sea water under various frequencies and potentials for the purpose of corrosion fatigue life prediction. In general, the slower the load frequency was, the faster the crack growth rate was. When 4K<5MPam1/2 or 4K>20MPam1/2, crack growth curves under various frequencies were parallel to each other, but when 5 MPam1/2<4K<20MPam1/2, the acceleration of the crack growth rate cased by intergranular cracking was observed on the parent metal but not on the weld metal. The crack growth rate at 0.3Hz was minimum at potential of -0.7V (Ag/AgCl) in all tested AK regions. There was a good correlation between the acceleration rate of the crack growth and the transition rate from the bare metal to the steady-state metal. The corrosion fatigue life was estimated by using the crack growth curves and the theoretical curve well fitted to the experimental data. From this, it is proved that the corrosion fatigue life can be predicted if the crack growth properties at low AK regions is understood properly.