Research On Numerical Analysis Method And Application Of Crack Diagnosis For Mechanical Structure

In recent years,with social development and progress of science and technology, many mechanisms are in trend of heavy,high speed,the automation to meet the needs of the transport industry,industry and agriculture.The metal structure's load-bearing performance has affect on the safety in production more and more. Metal structure crack is considered as main hidden danger in production and has attracted various aspects personnel's attention.So it has an important theory significance and practical application value to study on method of crack diagnose for mechanical structure.This description take fracture mechanics theory as the basis and study on method of crack diagnose for mechanical structure through some technologies such as FEM and its secondary development,AE,meshless method.The dissertation consist of the following new results:(1) The stress intensity factor(SIF) is key parameter in fracture mechanics,the description calculate the crack specimen's SIF through FEM and EFGM.The results of both have little difference so the results calculated through two methods are valid. Because the meshless method calculates SIF based on node-displace,the description put forward a method that binary linear equation is used to the weitht function arguments to dispose of the crack's non-continuous interface to get the value of SIF. And this function can avoid the value overflow phenomenon which the node and a computation superposition occurs in the present processing method,has provided the new mentality and the method for the present meshless method in crack analysis.(2) In current,the diagnosis result is got in condition to the crack is thought as I-mode and expirial decided work-conditons,that lead to error.The description put forward the crack propagation remain life forecast method in moving load.In the description,a crack specimen as an example is analyzed,its crack propagation remain life change rule is studied in the load change process and the load change influence on crack propagation remain life is analyzed,the crack propagation remain life relation curve with load position is obtained to determinate the load position and load circle number relatively make crack growth most rapidly,that the method make the diagnosis more comprehensive and closer to the actual situation.And the crack specimens AE experiment are carried on in the different load position.Then the AE localization number of times rule is analyzed.The rule is compared with the calculated result through FEM that the qualitative confirmed proposed the forecast technique rationality.(3) In view of the shortcomings of the static modify method in the submodel analysis,such as time cost is so much in the model modifition,the extraction, analysis and delivery of the parameters,error-prone,low efficiency,the description put forward the method on crack growth for mechanics structure based on paramater submodel,namely automatically modifies coarse model,crack structure submodel and the model analysis data file based on the sub-model analysis enhanced in the entire crack growth building and the analysis efficiency.At latst a gantry crane crack, as the example is carry on according to the method.(4) In the view of the complexity and the randomness for the structure of the crack location,shape,according to the above-mentioned research results,the description construction crack analysis module using software's UIDL and the APDL technology,guide user input parameters and so on crack position,length to the procedure can produce automatically the crack finite element model and completes crack propagation remain life analysis.