Research On Surface Crack Stress Field Characteristics Based On Friction Effect

In mechanical engineering,approximately 80%damage of components is caused by fatigue failure.Surface crack is one of sources of fatigue failure and its shape is generally semi elliptical.In recent years,with the development of tribo-fatigue,the interaction between friction/wear and fatigue failure makes it not comprehensive to evaluate the damage,life or limit state of mechanical system singly from tribology or fatigue.In this mechanical system,friction process is realized and alternative load is taken up and transmitted through simultaneously.Therefore,the study on damage mechanism under the compound action between friction/wear and fatigue failure is of great significance.In this paper,the sliding friction load system is studied,and finite element method is adopted to analyze the impact of sliding friction on the fatigue failure.The main work is as follows:Firstly,the modeling method of components with semi elliptical crack in ANSYS is explored,and the correctness of the modeling method is verified.The simulation of surface crack front singular stress field,parametric modeling of cracked components,and the macro of calculating stress intensity factor in post-processing are realized with the parametric language APDL supported by ANSYS.Secondly,a typical sliding friction/wear and fatigue finite element model is established,and the sliding friction process is simulated by the finite element method.The equivalent stress nephogram of crack front with time are obtained.The variation regulation of stress field and stress intensity factor under different normal load,different friction coefficient,different elliptical shape ratio and different ellipse parameters angle are analyzed.At the same time,the stress field characteristics under various factors are discussed.The greater load leads to greater strain and stress of crack front,and then the stress intensity factor will become larger.Compared with the results without considering the friction effect,the friction effect is contrary to the action of compressive stress field and stress intensity factor decreases when the sliding block gradually close to the crack.But when the sliding block is away from the crack,the situation is opposite.The results shows that the bigger friction coefficient makes friction effect stronger.The effect of elliptical shape ratio on the stress intensity factor is also influenced by friction effect and ellipse parameters angle.Whether the friction effect is considered or not,ellipse parameters angle is bigger,K? and K? are smaller,while K?is larger.Finally,based on the thermal analysis and finite element thermal-structural coupled analysis theory,the temperature contours and the influence of thermal effects on crack front stress field under sliding friction effect are obtained.Under the thermal effect,K? and K?increase.Only when the sliding block is near the crack,K? is bigger,but it is smaller on the other positions.In general,the friction heat effect accelerates the fatigue crack propagation.