Fatigue Damage Calculated by the Ratio-Method to Materials and Its Machine Part

Several new calculating equations on the damage-evolving rate are suggested for describing the elastic-plastic behavior of some materials under un-symmetric cyclic loading. And the estimating formulas are given of the life relative to varied damage value D oi at each loading history. The method is to adopt the ratio of plastic strain range to elastic strain range as the stress-strain parameter, using the staple material constants as the material parameters in damage calculating expression. And it gives out a new concept of the compositive material constant, that has a functional relation with the staple material constants, average stress,average strain and critical loading time. In addition, it calculates fatigue damage as example for a part of car, its calculating results are accordant with the Landgraf’s equation, and calculating precision is more rigorous, so could avoid unnecessary fatigue tests and will be of practical significance to stint times, manpower and capitals, and to provide convenience for engineering applications.

CALCULATIONS TO ITS FATIGUE DAMAGE FRACTURE AND TOTAL LIFE UNDER MANY－STAGE LOADING FOR A CRANK SHAFT

Suggests some calculating formulas and methods with respect to the damage evolvingrate da / dN|i and the fatigue life and in varied history from uncrack to microcrackinitiation until fracture for a crankshaft, which are suitable to stress concentration positionsabout its journal fillets and oil holes on a crankshaft, that it is undergone to bending, twistingand shearing loading and subjected to unsymmetric cyclic many-stage loading. Last the total lifein whole process is estimated by

Space-time evolution rules study on acoustic emission location in rock under cyclic loading

An acoustic emission(AE)location experiment was performed on sandstone using an advanced AE test system.The space-time evolution rule regarding damage was analyzed under cyclic loading as well as AE.The results show that AE on static loading process is consistent with the damage evolution rule of compression and the elastic-plastic deformation phase;at the beginning of cyclic loading with low duration time and energy,AE events came from a small crack.The location result showed that most events occurred in the core zone forming at the static loading process,and the location points changed slowly.AE energy changed little during the metaphase of cyclic process.There was a modest increase of location points in every cycle.The tendency of steady development could be predicted from the AE location events.At the end of each cyclic loading,the quantity of AE events and energy increased quite rapidly,reaching a maximum at the last cycle.AE events had high energy and duration time.Location events changed quite rapidly and assembled and linked continuously in the core zone.At the same time,they expanded to the top of specimen.A macroscopic crack finally formed.In the postfailure process,some AE events still existed due to fracturing of gliding friction.Owing to the inner stress balance of rock even after loading stopped,minor AE events still occurred.