Problems of fatigue strength definition for shell structures

Stresses caused by oscillations of shell structures may vary significantly even for the same oscillation form. Therefore, during fatigue tests it is very important to solve the loading problem for these structures and further evaluate their fatigue strength statistical parameters. A new method for solution of these difficult problems is proposed in this paper. The basic idea is to take into account relative load values of fatigue tests instead of often used absolute load values. The fatigue loads are reproduced on a test bed by the same means by which the dynamic loads were determined. Levels of fatigue loads used in the tests are based on the individual dynamic loads for each of the structures investigated. The basic principles are described for axial fans used in railway transport. Axial fan blades are a characteristic example of shell structures.