Bhattacharyya Equivalent Method Of Low Loads In Fatigue Load Spectrum For Aluminum-alloy Notched Specimens

Although estimation methods like nominal stress approach, local stress-strain approach and stress field intensity approach etc. can be used to predict the fatigue life of the components, in a certain extent, there are still some deficiencies. In engineering application, fatigue tests are still needed to get the fatigue life of the components. So it is still a key problem at present to work out the load spectrum to take fatigue tests. The focus of compiling load spectrum is to simplify it reasonably. This paper is based on the two aspects, fatigue life and fatigue dispersion, the load sequence effect and local stress-strain dispersion are discussed, and the related experiments are carried out. New progress has been made in the field of load spectrum editing.The stress concentration of notched specimens resulting in order effects and interaction effects in random loading is noted, and there are also the spectrum order effects of spectral load. From the point of view of micro and macro, the influence on fatigue life is considered. The sequence effect of load effect is large, so the rainflow reconstruction spectrum method is chosen and the secondary injury spectrum which is similar to the actual situation to take the tests is programmed.In this paper, experimental study are based on the P-S-N curve of the test stress, but because the test methods to get the P-S-N curve cost a lot of time and money, The preconditioned finite element method is used. Notched specimens and smooth specimens together with the local stress-stain dispersion are related, then the prediction of the P-S-N curve are got, and the experimental study is also taken.In order to simplify and concentrate the load spectrum reasonably, the Bhattacharyya distance is selected as the parameter which measure the similarity of the original spectrum and the edited spectrum. The average life span and dispersion are considered comprehensively, and then a new method for spectrum editing is got. In the method, as many loads as possible is rejected which have little effect on fatigue damage as the Bhattacharyya distance is in a certain range when the low loads are omitted. And the solution to the corresponding equivalent spectrum are got as the Bhattacharyya distance is to the minimum when the conversion level in load equivalent conversion is known. Experimental results also show that this method can greatly reduce the test time, get the effective test spectrum, and further reduce the cost of fatigue test.