Reliability Life Prediction Of Crack Initia-Tion And Propagation Based On Damage Mechanics

With the development of technology,all various types of mechanical products promote development of large scale and high accuracy.Because of the repeated fluctu-ating load on the equipment and components the fatigue crack has become the main reason of the equipment failure.The basic reason of fatigue fracture is fatigue crack and the production of different levels of crack will seriously affect the safety performance and operational performance of mechanical component.Currently the main method to deal fatigue crack divides it into crack initiation and crack expansion stages and use different methods to deal them.But it is hard for this method to determine the boundary of the two stages and it can't explain the whole damage process.At the same time,frac-ture mechanics cannot describe the damage stage of micro crack.Then it is necessary to establish a calculation that not only can describe micro-damage but also can unify the two stages.The work of this paper mainly includes the following several parts.Based on theo-ry of damage mechanics,the damage model of metal fatigue crack is constructed and combining the model with finite element method the whole life of crack initiation and crack propagation is predicted.The connection of damage factor and load cycles is been established by introducing damage evolution equation and use the established model to determine the computational procedure.The stiffness matrix is continuously calculated by introducing the calculation of additional load.The calculating program is designed in MATLAB and the calculation flow diagram has been showed in this paper.Then through the calculation of a single cell,the changing process of equivalent stress is showed with the cell from undamaged state to completely damaged state and the dam-age model of fatigue crack is given.It used the model to calculate the fatigue life of dif-ferent metal test specimen and compared calculation results and experimental results.The error is acceptable which verified the correctness of this method and it has im-portant reference significance for the study of the microscopic damage and fatigue life prediction of metal material.Then simulate the damage path and get the fatigue crack growth law by calculating different samples.Then it compares the calculated results and the results of cited examples to ensure the accuracy of the calculated results.Then the sensitivity analysis is carried out on the calculated to get the important influence ordinal of every parameters on the model and make sure most important parameter and the less important parameter which is significant to high efficient calculation.Finally it make reliability sensitivity analysis for the model to get the influence of every parameters on the specimen failure and it's meaningful to the prevention of specimen fail and safety production.The unified computation model of crack initiation and propagation established in this paper reduces the applied theory's scope and it is convenient for calculation and practical application.It has a important signification to fatigue life forecasting and sim-ulation if fatigue crack.