The Research On Improved Fatigue Damage Model And Fatigue Reliability Based-on P-S-N Curve

Fatigue Damage Model is the theoretical foundation of calculating fatigue life,and Miner maxim is the typical damage model used in the process of calculating.However, due to the fact that there exist hypothesis and empirical data, the resultswould more or less deviate from the engineering practice, which might result inpotential safety risks. On grounds of the present Miner fatigue damage maxim andconventional reliability design, this thesis is to put forward a computing model basedon virtual interval length equal portions and to forecast the fatigue life, which ofcourse has taken into account the influence of fatigue loading sequence on fatiguedamage crack. Also, the paper is expected to fit the experiment data from smallsamples with P-S-N curve in an attempt to analyze the fatigue reliability based onP-Sa-Sm-N surface.The innovative points of the research are embodied in these aspects:1) The advancing of a mathematical model, which can predict the fatigue damagelife, on the basis of virtual interval length equal portions. The study, according to thetraditional Miner maxim, is also to virtually and equally divide the loading stresssection of the virtual load spectrum and to build an improved fatigue damage model soas to prove theoretically the convergence of the fatigue life. The effectiveness of themodel can also be testified by applying it to predict the fatigue life of leaf springs.2) The formula fitting of P-S-N curve. By adopting the Linear regression method,the P-S-N curves of three frequently-used stress-life models, namely three parameters,Langer model and Basquin, are represented as the general form of logarithmic fatiguelife mean value and variance line. Also, the fitting results of these three models areanalyzed comparatively. The result of the symmetric cyclic loading experiment on45#steel sample has accounted for the validity of this method.3) Research on the accuracy of the calculating results of fatigue reliability andinfluencing factors based on P-S-N curve. In the light of Reliability-Stress-Life BasicTheory, this paper is to study the method of building P-Sa-Sm-N surfaces. Anothertask this paper is about to fulfill is that, in accordance with the fatigue reliability ofP-Sa-Sm-N surface and considering the uncertainty of the fatigue loading stress andintensity parameters, it should analyze in detail the impact of different values of themaximum stress, the minimum stress, the cyclic stress ratio, the strength variable coefficient, as well as the stress variation coefficient on fatigue reliability.The proposed model provides a new train of thought for the reasonabledevelopment of fatigue damage model, can reduce fatigue test cost and time. Fatiguereliability of the research results can be applied to product development and design,with engineering application prospects.