Stages of fatigue fracture in nickel alloyed powder metallurgy steel

Abstract

Fatigue fracture of smooth rectangular specimens was investigated by testing at constant amplitude and zero mean stress, at a frequency of 30 Hz. Two nickel alloyed powder metallurgy steels with different contents of pores and MnS were examined. Fatigue fracture started with crack nucleation at pore interfaces by the formation of small steps. Growth of these nuclei was accomplished by stepwise crack tip blunting, which led to the formation of macrocracks. A dominant fatigue crack origin built up at the region of the largest number of macrocracks. Fatigue crack growth stages I, II, and III were found in this region.MST/4690

Methodology for Probabilistic Life Prediction of Multiple-Anomaly Materials

“…(7) and Eqs. (13) and (17), where it can be observed that the component risk results are nearly identical when the mean zone anomaly occurrence rate is less than 10 −3 . Because the zone anomaly occurrence rate for titanium ranges from 10 −7 to 10 −5 , both of these approaches are valid for this anomaly type.…”

“…11 However, in other materials, the crack formation life may be nonnegligible and must be considered in the risk computation. 7,17 A crack formation random variable can, therefore, be introduced to address the variability associated with the number of cycles required for an anomaly to form a growing crack.…”

“…Therefore, component risk is computed using Eqs. (13) and (17) for a finite number of anomalies or Eq. (19) for an infinite number of anomalies.…”

“…Normalized risk values for multiple-anomaly materials based on the use of Eqs. (13) and (17) are shown in Fig. 8 for a number of anomaly occurrence rate values.…”

Microstructural Characterization and Mechanical Properties of Free-Machining Sintered Steel Parts Containing up to 1 Wt Pct MnS

“…[38] Hence, increasing the volume fraction of MnS inclusions in the base powder particles decreased the mean free path between inclusions, which is favorable to the propagation of microcracks. Also, as seen in Figure 12, the microcrack propagates by decohesion of the metal/inclusion interface.…”