The Analysis Of Multiaxial Fatigue Life Considering The Stress-factor And Temperature

Metal fatigue phenomenon widely existed in the service process of mechanical and engineering components,the fatigue analysis and design are very important to the safety of the equipment.In most cases,components and parts are suffer from multiaxial loadings.Multiaxial fatigue life prediction is always a difficult problem because of multiaxial loadings’ complexity and variability,many uncertain factors such as material defects,machining damage also make this question more complicated.For some high temperature alloys,the material performance is often influenced by the temperature,fatigue-creep process is unpredictable under this condition.In the views of these reasons,taking research on the fatigue theories under multiaxial loadings and carrying out corresponding life prediction studies must have a great significance to the practical engineering problems.Based on above views,some attempts are made for the fatigue life prediction under multiaxial loadings,the influence of temperature on multiaxial fatigue life is also considered.Relevant work is as follows:(1)Considering the different contributions to the fatigue damage of normal and shear stress,a stress factor which can reflect the multiaxiality and additional cyclic hardening is submitted.The factor taken both normal and shear stress into account,can well present the relationship between loading nonproportionality and fatigue life.The feasibility and accuracy of this method is verified by the experimental fatigue data of AISI304 referring to the corresponding literature.(2)Based on critical plane approach,a new fatigue life estimation model considering stress factor is proposed.The model used the stress factor to revise the multiaxial damage parameter,and introduced the stress and strain on critical plane into the building of the life equation.New model can reflect the additional cyclic hardening and the degree of nonproportionality of the applied loading at the same time,is suitable for multiaxial fatigue life prediction especially non-proportional cases.Five kinds of materials’ testing data are used to verify the effectiveness of the model.(3)Completed the 316 L stainless steel multiaxial fatigue test under five kinds of loading paths in room and high temperature.According to the hysteretic curve and cyclic curve obtained by the fatigue test,we further analysis and contrast the multiaxial fatigue behavior of the material under different temperature.Combined with experimental results: under the same equivalent strain,the tension and torsion test result show a big differences.Otherwise,the additional cyclic hardening phenomenon obviously decrease under high temperature,however,the fatigue life is still shorter than room temperature because of the outstanding contribution of creep.