Fatigue Property

Properties resulting from fatigue testing are given in references [173-185]. 

Room-temperature tests at 2500 cydes/min of longitudinal sped-mens from solution treated, air cooled and aged bar. 

Source Aerospace Structural Metals Handbook, Vol 4, Code 3711, Battelle Columbus Laboratories, 1969 

Mild-notch K =3) fatigue strength of forgings at 21 and 425 °C (70 and 800 °F) and a frequency of 1800 cydes/min. Spedmens were from mid-radius (forging A ) or web (forging location, radiai di- 

Axial load smooth and mild-notch fatigue properties for solution treated, air cooled, and aged bar. Longitudinal polish (5 pin., rms), frequency of 2500 cydes/min. 

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The magnitude and nature of the load are considered in formulating the design. The load may be essentially quasistatic, cycHc, or impact. Many stmctural failures, for example, have been caused by supposedly innocuous stmctural details welded in place without any consideration given to their effect on fatigue properties. The service temperatures are also important, since they affect the fracture resistance of a material. 

An important aspect of the mechanical properties of fibers concerns their response to time dependent deformations. Fibers are frequently subjected to conditions of loading and unloading at various frequencies and strains, and it is important to know their response to these dynamic conditions. In this connection the fatigue properties of textile fibers are of particular importance, and have been studied extensively in cycHc tension (23). The results have been interpreted in terms of molecular processes. The mechanical and other properties of fibers have been reviewed extensively (20,24—27). 

Figure 4 shows a typical hardness distribution (7). The case depth is considerably less than that for flame and induction hardening. The case has a high compressive residual stress, which improves the fatigue properties (8). 

The surface may gain a very high (eg, 1000 Vickers) hardness from this process. Surface deformation also produces a desired high compressive residual stress. Figure 9 illustrates the improvement in fatigue properties of a carburized surface that has been peened (18). 

Tire cords are characterized for their physical, adhesion, and fatigue properties for use in tires. These characterizations are conducted under normal and varying test conditions to predict their performance during tire operation. Various test methods used to characterize tire cords are described. 

Fatigue properties in bending are most appropriate for copper aHoys as these are often used as spring contact components in beUows and electrical switches and coimectors. These articles are usuaHy designed for acceptable service Hves at a moderate to high number of stress cycles. 

Because oxides are usually quite brittle at the temperatures encountered on a turbine blade surface, they can crack, especially when the temperature of the blade changes and differential thermal contraction and expansion stresses are set up between alloy and oxide. These can act as ideal nucleation centres for thermal fatigue cracks and, because oxide layers in nickel alloys are stuck well to the underlying alloy (they would be useless if they were not), the crack can spread into the alloy itself (Fig. 22.3). The properties of the oxide film are thus very important in affecting the fatigue properties of the whole component. 

The second failure mode to consider is fatigue. The drum will revolve about once every second, and each part of the shaft surface will go alternately into tension and compression. The maximum fatigue stress range (of 2 x 56 = 112 MPa) is, however, only a quarter of the fatigue limit for structural steel (Fig. 28.5) and the shaft should therefore last indefinitely. But what about the welds There are in fact a number of reasons for expecting them to have fatigue properties that are poorer than those of the parent steel (see Table 28.1). 

Figure 28.6 shows the fatigue properties of structural steel welds. The fatigue limit stress range of 120 MPa for the best class of weld is a good deal less than the limiting range of 440 MPa for the parent steel (Fig. 28.5). And the worst class of weld has a limiting range of only 32 MPa ...

Table 28.1. Weld characteristics giving adverse fatigue properties...

Fig. 28.6. Fatigue data for welded joints in clean air. The class given to a weld depends critically on the weld detail and the loading direction. Classes B and C must be free from cracks and must be ground flush with the surface to remove stress concentrations. These conditions ore rarely met in practice, and most welds used in general construction hove comparatively poor fatigue properties.

Medium strength, good fatigue properties streetlight standards... 

Hughes, A. N., Jordan, B. A. and Orman, S., The Corrosion Fatigue Properties of Surgical Implant Materials. Third Progress Report — May 1973 , Engineering in Medicine, 7, 135-141 (1978)... 

Gee, C. F., Fatigue properties of Zircaloy-2 in a PWR water environment , Proc. of 1st Int. Conf. on Environmental Degradation of Materials in Nuclear Power Systems- Water Reactors, Myrtle Beach, South Carolina, USA, 22-25 August 1983, NACE, pp. 687-98 (1984)... 

Fig. 2-45 Summary of high-performance fatigue properties of different materials based on their percent of ultimate static tensile strength.

As it has been shown lately, insertion of a small quantity (5—15% of the copolymer weight) of ISP monomeric units into the PAN macfomolecules results in an appreciable decrease of stiffness and in an increase of flexibility of the chain, which makes it possible to improve considerably the fatigue properties of usual PAN fibres30. In addition to that, by inserting a comparatively large amount (25—30%) of flexible ISP monomeric units into the copolymer one can decrease substantially the yield temperature of PAN, which makes it possible to spin fibres from thermoplastic state31. ... 

Since the early 1980s, the study of mechanical properties of materials on the nanometre scale has received much attention, as these properties are size dependent. The nanoindentation and nanoscratch are the important techniques for probing mechanical properties of materials in small volumes. Indentation load-displacement data contain a wealth of information. From the load-displacement data, many mechanical properties such as hardness and elastic modulus can be determined. The nanoindenter has also been used to measure the fracture toughness and fatigue properties of ul-... 

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