Previsione della durata a fatica su provino SAE utilizzando un approccio combinato di fatica oligociclica e meccanica della frattura

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Introduction 
 
 
The prediction of fatigue life in the high stress/strain field (relatively low number of 
cycles) is becoming more widespread. This is due to the increasing demand for improved 
performance in mechanical components. Design is becoming steadily oriented to more 
complicated shapes, which introduces more stress risers (usually reported as notches), and 
to lighter geometries, especially in fields such as the aircraft or automotive industries. In the 
early 1960s it was shown [1]1 that the low-cycle fatigue behaviour of metals is dominated 
by the strain, rather than by the stress as assumed previously. In fact, when a sharp notch 
occurs in a component, the effect on the stress field is so heavy that often the material yields 
locally. In such a case the quantity that must be used to describe the material behaviour is 
the local strain, so it is necessary to carry out a life prediction based on the strain-fatigue 
properties. From these considerations a method called the "Local Strain Approach" was 
proposed [2]. Its main points can be summarised as follows: 
 
(i) the actual strain at the notch root is evaluated. The most important method 
to solve this problem was proposed by Neuber [3] in 1961, and is still 
widely used; 
(ii) the prediction of the component life is made using strain based fatigue life 
law. This approach to low-cycle fatigue life was proposed by Manson and 
Coffin on several papers between 1954 and 1961. 
 
 
This methodology studies only the behaviour of the material at the notch root, so 
that the predicted life is referred to a small part of the resisting section, in the neighbourhood 
of the notch. The failure is assumed to occur when a relatively small crack appears at the 
notch root. 
                                                 
1
 Numbers in square brackets designate References at the end of paper.