Abstract.A new modeling method of wall thickness is put forward and the multi-axial fatigue life of bellows is acquired. The finite element mode is built considering the varied bellow's wall thickness. The test results show the mode is reasonable and the precise strain is got. Based on the result of the upwards, multi-axial fatigue mode is apply in to life calculation. The results show that the critical-plain model's results are consistent very well with test results. The available of modeling method is validated by the results and the multi-axial fatigue method is formed.

Abstract. Estimation of the fatigue life of pipelines under the random load was carried out. The power spectrum density of the stress on the dangerous location was calculated by the finite element method. The frequency method was implemented into the vibration fatigue life prediction. The applicability of the four models of the direct frequency method was analysis, which compare with the indirect frequency method. The results show that power spectrum density of the stress has the characteristic of two peaks. The probability density function of the stress amplitude calculated by different model have great differences. The application of the Dirlik model and ZB model get the reasonable value of the fatigue life. The fatigue life of the pipeline was optimized by changing the value of the fillet.