Abstract
According to the change characteristics in the toughness of the metal material during the fatigue damage process, the fatigue tests were carried out with the standard 18CrNiMo7-6 material. Scanning the fracture with an electron microscope explains the lack of linear cumulative damage in the mechanism. According to the obtained results, a nonlinear damage accumulation model which considered the loading sequence state under the toughness dissipation model was established. The recursive formula was devised under two-level. The fatigue test data verification of three metal materials showed that using this model to predict fatigue life is satisfactory and suitable for engineering applications.
Highlights
The failure of most engineering structures or mechanical parts is caused by the accumulation of fatigue damage caused by a series of cyclic loads
In order to verify the effectiveness of the proposed improved model, based on the fatigue test data of the material 18CrNiMo7-6 listed in Table 3, the life prediction results of this model, the linear damage accumulation model, and the ductile dissipation model, are compared
Based on the ductile dissipation theory, a nonlinear fatigue cumulative damage model considering the loading sequence is established, that is, an improved toughness dissipation model, which can consider the impact of loading sequence on damage with parameters which are simple and suitable for engineering applications; The fracture sections of the 18CrNiMo7-6 specimens, which were scanned by electron microscope, explain from the mechanism why Miner’s rule has different damages under two-level loading
Summary
The failure of most engineering structures or mechanical parts is caused by the accumulation of fatigue damage caused by a series of cyclic loads. The cumulative effect of fatigue damage directly determines the life and reliability of mechanical parts. The bilinear cumulative damage theory considers the effect of load sequence on crack growth to a certain extent, its theoretical model cannot accurately simulate the actual damage process because it is difficult to determine the inflection point of crack growth. For the strain control of austenitic stainless steel, Taheri [7] proposed a conservative model of fatigue damage accumulation under variable amplitude load. This model does not require the constitutive law but considers plasticity through the cyclic strain stress curve
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