Wohler’s curve

For a given grade of HD PE, Figure 4.5 displays an example of an SN or Wohler s curve concerning flexural tests with maximum stress of cr and average stress of 0. 

For a given grade of 20% talc-filled polypropylene, Figure 4.13 displays two examples of SN or Wohler s curves concerning flexural tests ... 

For two given grades of PPS, one glass-fibre-reinforced and the other glass fibre/mineral-filled. Figure 4.103 displays examples of SN or Wohler s curves. 

Figure 4.111 displays examples of SN or Wohler s curves for three given grades of neat and glass (GF) or carbon fibre (CF) reinforced PEI. 

Fig. 5.31 Wohler s curves or 5-A diagram obtained on a 2024-T351 aluminum alloy for various R ratios (data from [33])...

Once the analytical expression of the hysteresis loop has been derived, the following step is to infer the equation of the entire e-N curve or Wohler s curve. To this purpose, it is necessary to separate the two component of deformation, the elastic and the plastic one, as already done in Eq. (6.1). As to the elastic component Eg, it has been said in Sect. 5.2.2 that in 1910 Basquin [7] found a power law relationship with the cycles to failure N, see Eq. (5.22), so that in a log-log scale the elastic component of the S-N curve is a line. Later in the 50, Manson and Coffin [8-11] independently found that also the plastic component of the cyclic strain was related to life cycles N through a power law function, known as the Manson-Coffin relationship... 

Fig. 7.1 Wohler s curves for a carbon steel fillet shaft subjected to rotating bending (modified from [2])...

Fig. 7.12 Schematic of Wohler s curve under stress controlled conditions for notched and unnotched specimens...

This time the variation is about 15 %. The question arises now as to the knowledge of the fatigue limit of the plate containing 20 mm hole with respect to that oy of plate without hole. The Wohler s curve of the material is that already assessed in sample problem 4 of Sect. 6.3. It can be seen how the transition point N, between low cycle fatigue and high cycle fatigue, i.e., between plastic and elastic behavior, is at about — 0.0015 so that we can assume that in our case the behavior is mainly elastic and neglect the plastic component and draw the... 

Figure 8.34 schematizes on the Wohler s curve of the material the reference unit block and the m repeated blocks (in the example of Fig. 8.34 m — 3). The Miner s rule would indicate... 

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