Fatigue curves

McEvily A J (ed) 1990 Atlas of Stress-Corrosion and Corrosion Fatigue Curves (Materials Park, OH ASM)... 

Examples of fatigue curves for unreinforced (top) and reinforced (bottom) plastics are shown in Fig. 2-44. The values for stress amplitude and the number of load cycles to failure are plotted on a diagram with logarithmically divided abscissa and English or metrically divided ordinates. 

ASTM Special Technical Publication No. 91 discusses in detail the important ramifications to be considered in the various statistical aspects of fatigue testing. Most often, the fatigue curves as well as the tabulated values... 

Fig. 7-4 Example of long-term tensile fatigue curves.

Figure 1.13 Typical fatigue curve (S-N diagram for a material having an endurance limit, oe).

On the basis of empirical data and the fatigue curve, we arrive at the relation... 

ASM, 1990, Atlas of Stress-Corrosion Cracking and corrosion fatigue curves, AJ. McEvily (ed.), ASM International, Ohio, USA. 

Figure 9. (a) (above) Stress fatigue curve—limestone aggregate, (b) (below) Stress fatigue curve—volcanic aggregate. 

Figure 1. Endurance fatigue curve (S-N) for the AA2014 aluminum alloy in the in the Zr-modified and non modified conditions.

Fig. 7.11 7 Conventional S-N fatigue curves for 1 3% Cr steel (X 20 Cr 1 3) determined in indicated environments, (a) Smooth rotating bend specimen, (b) Notched rotating bend specimens. (a02 = 610-650 MN/m2 oUTS = 760-830 MN/m2 mean load = 0 frequency = 50 Hz temperature = 23 °C.) Source Ref 1 67...

Sa = allowable stress for any given number of cycles from design fatigue curves. 

Another model explicidy developed for life prediction under multiaxial loading is that by Fawaz and EUyin [76—78] the actual multiaxial loading conditions and load ratio are considered through modification of a reference fatigue curve. 

Table 7.1 Summary of the parameters of fatigue curves and fatigue notch factors for [0/90] woven glass/polyester tubes under pulsating tension—torsion loading [38]...

From the analysis of Figures 7.17 and 7.18 it can be concluded that the accuracy of the criterion is not very high and also depends on the type of data— slightly more conservative for global multiaxial data, frequently nonconservative for local multiaxial data. Moreover, as illustrated above, the choice of the reference fatigue curve can play an important role in increasing or decreasing this accuracy of the criterion. 

Table 7.4 Fatigue curves taken as reference for the calibration of Fa vaz and Ellyin s criterion [1]...

The accuracy of the model in the lifetime prediction was verified even in this case by comparison between model estimations and experimental fatigue lives. The parameters of the calibration fatigue curves together with the elastic properties of the laminates investigated are listed in Table 7.5. In some cases, elastic and static strength properties not available in the original sources were estimated from constituent properties or taken from literature. 

The criterion is, in general, rather easy to apply, since it requires only two fatigue curves for its calibration this is of great help in overcoming the difficulty in considering, explicitly, variations of the load ratio. A limitation, however, is that the model, in the present form, cannot be applied to life prediction of unidirectional laminates due to their anisotropic response resulting in different limits for the strain energy density in the fiber direction and normal to it. 

---