Fatigue of notched specimens

As explained in chapter 4, notches cause a stress concentration in a component. Thus, it should be expected that notches also affect the fatigue strength of a component. The stress concentration at the notch root is again described by the stress concentration factor Kt according to equation (4.1)  

If we assume that the maximum stress amplitude in the component must not exceed the fatigue limit of a smooth specimen, cte, we should expect that the maximum nominal stress amplitude for a notched specimen is 

Whether a growing crack can be stopped in this way depends on how rapidly the stress decreases at the notch root. To quantify this decrease, we define the relative stress gradient at the notch root 

As we will see below, this is not true an5rmore as soon as linear elastic fracture mechanics can be applied. In this case, the increase of the stress intensity factor due to the growing crack is larger than the decrease of the stress in the notch root, see figure 10.38. 

Here we want to stress the difference between the relative stress gradient X and the stress concentration factor Kt which both depend on geometry only. The stress concentration factor quantifies the concentration of the stress at 

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The influence of test frequency on fatigue crack propagation of notched specimens has been studied by several investigators, but mostly by Hertzberg, Manson and coworkers For PS, they observed a decrease in FCP rate as test frequency was increased from 1 Hz to 10 Hz to 100 No results were presented for HIPS... 

This section is of particular interest as a consequence of the fact that almost all ceramics have flaws, many in form of microcracks or even cracks on a larger scale. These are outcomes of the fabrication techniques however, reducing such pores or cracks to a viable, minimal level is very costly. Many such cracks end at surfaces, where they act as stress raisers. Notches may also be considered as cracks, though the difference between notches and cracks is only a matter of size, not kind. Thus, the study of notched specimens has practical significance, because, in engineering components, fatigue starts mostly at the surface, at those places where stress-... 

Many investigations of the mechanical properties of ABS and of the nature of rubber toughening in this material have been made and these findings are reviewed and discussed by Bucknall and by Mann and Williamson There have been fewer studies of fatigue performance, and most of these are concerned only with crack propagation in notched specimens Here we are concerned with the... 

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