The System To Predict The Auto Parts' Fatigue Life And Identify The Initial Point Of Macro Fatigue Cracks

Spurred by the rapid development of the automobile industry, China's auto parts industry has achieved a rapid progress and improved its position markedly in the global supply chain ; but compared with the same peer there are still many gaps; the domestic auto parts testing systems including equipment, standards , the methods and institutions are lack in the advanced technical level, high efficiency and sufficient accuracy; all of these make that the evaluations of product are not comprehensive enough. Most domestic testing equipments have purchased for a long time, in the past years there were no technical improvement and transformation for them . Now their detection accuracy and performance are not able to meet the performance parameters; also these equipments can only detect a single comparison and have a narrow usage. Therefore, extending the useful life of these equipments and improve their testing accuracy will be a very meaningful work.According to statistics, 50 percent to 90 percent of the mechanical Parts damaged is fatigue damage, the destruction process can be divided into three stages: (1) the germination of fatigue cracks (2) fatigue crack propagation; (3) transient fault. The definition of Fatigue Life is the number of load cycles when the fatigue damage happened,it also is defined as the elapsed time from the beginning of the test. The fatigue life is mainly made up of the crack initiation life and extended component life. Fatigue crack`s growth rate depends largely on the kind of material constants and load level for the same award specimen, its growth rate is basically equal. Therefore, we can acquire the information of the fatigue crack`s propagation from a macro aspect, further we can make a judgment of its extended life. The classical theories in the life of Fatigue Crack`s germination and extension are so scientific that they are beyond doubted, but their starting points are more concentrated in the micro-state and can not be directly applied to industrial fatigue life testing process.Combining the existing equipment in the test centre, starting with the relation of the expansion of the fatigue cracks in the specimen and the corresponding the macro parameters, after seriously studying the crack`s theory about its germination and expansion ,the paper research and develop a test system which are suitable to test fatigue life of the important parts in automobile chassis . By Using PL63N electro-hydraulic servo system as the experimental platform, basing on the Labview virtual instrument, employing the PCI6024E NI data acquisition card, this paper programmed a testing system for the Macroscopic Fatigue Cracks initial Point's Identification and Life Prediction of Automobile Parts. This software has solved the earlier gap of imported equipment, upgraded the ability in the test and analysis of these equipments.This system combines the computer technology,data acquisition and control technology and the international advanced LabVIEW virtual instrument technology; it can conveniently achieve docking with PL63N electro-hydraulic servo system; it offers amplitude calibration, signal filtering, extreme detecting, and other functions; the controling signals can be continuously exported, also the real-time data acquisition, real-time analysis and real-time preservation are all achieved; the experimental results can be fitted to conduct real-time analysis ,at the same time this system has full functions, clear Outline and a friendly user interface. After the test of practice, the system fully meet the requirements of practice and effectively solved the problem of the supporting software system for the PL63N electro-hydraulic servo, which make the implementation of its mandate to be a true automation.Through observing the process of the experiments and analysing its results ,we can obtain the following conclusions:1, The System to Predict the Auto Parts, Fatigue Life and Identify the Initial Point of Macro Fatigue Cracks has achieved to control the experimental process precisely, it meets the test`s requirements, has a good applicability and scalability ,so it exactly expands the testing function of the PL63N system detection.2, the error can reach 0.22 percent, fully competent fatigue test of the automatic control and determine the accuracy requirements.3, the fitting curve is also according with the actual experiment, and the interpretation of the results is very anastomosis. Therefore the curve equation is fitted with the practical significance.