Comparing stress gradient and other concepts for fatigue analysis of notched components
2022-01-0288
03/29/2022
- Event
- Content
- Nowadays simulation of the fatigue life is an essential part of the development of components in the automotive and machinery industry. Weak points can be identified fast and reliable with respect to stiffness, strength and lightweight. A pure virtual optimization of the design can be performed without the need of prototypes. Only for the production release a final test is necessary. A lot of parameters influence the fatigue life as the local stress, material, surface roughness, size of the component, temperature etc. Notches have the strongest impact on fatigue life, depending on radius and shape. Stresses at the notch base are increased because the load flow is forced through a reduced cross section, or changes its direction around an inwardly curved edge. But notches cause not only an increase of the local stress. Also, the local fatigue strength is increased because of a support effect from the neighboring areas, where the stress is already reduced. To account for this effect, several methods exist, each with their specific advantages and disadvantages. In this contribution an overview is given with brief descriptions for some common methods like the stress gradient concept, volume concept, the concept of the critical distance and the concept of effective stresses. The methods are compared both from a theoretical and practical point of view. The theoretical background is presented for the calculation of a local notch support number to characterize the increase of the local fatigue limit (according to Eichlseder, the German FKM-guideline and others). Test results from specimens with different notch radii and different materials are compared with simulation results. Next the focus is set to the stress gradient concept. A new calculation method is presented to reduce the influence of automatically generated, irregular Finite Element meshes to increase the accuracy. The applicability of the new method is demonstrated on a complex shaped automotive component. Finally, a summary is given with an outlook of further methodical improvements as e.g., the differentiation between alternating and rotating bending.
- Citation
- Spindelberger, G., Gaier, C., and Huebsch, W., "Comparing stress gradient and other concepts for fatigue analysis of notched components," SAE Technical Paper 2022-01-0288, 2022, .