Research On Methods Of Reliability Evaluation Through Combination Of Simulation And Test For Mechanical Products

There are a lot of new mechanical products in new military equipment.The reliability tests of these mechanical products play an important role for the equipment.Because of some defects in the test,such as the difficulty,high cost,long cycle,small sample and so on,the simulation is proposed to replace the test.However,the result errors of simulation are often difficult to control and the credibility is low,especially for the complicated machinery.Then the combination method of simulation and test is proposed to enhance the accuracy of result.On this basis,since the conventional reliability test cannot describe the product performance at the reliability boundary state.So,the method of reliability test for product at the reliability boundary state must be studied.In reliability tests,reliability assessment for product can be performed by hypothesis tests and parameter estimations based on a lot of reliability test data.It is an important work to get reasonable and accurate parameter estiamtion for the mechanical products.Therefore,this thesis studies the method of reliability simulation,test and assessment for mechanical products,including the following aspects:(1)The method of reliability test for mechanical products based on combination of simulation and test.Considering tests' high cost and simulation's low credibility,the thesis studies the reliability test methods based on combination of simulation and test,which includes a small amount of tests combined with a large number of simulation and a small amount of system-level test combined with a large number of component-level test.The gear-rack of a new aircraft slat is set as an example to illustrate the application of this method.The result shows this method can make full use of high accuracy for the test and low cost for simulation,which can make the reliability analysis of mechanical products be achieved well.(2)The method of reliability test and assessment based on reliability boundary.In order to make the comprehensive reliability test and evaluation,this thesis proposes and studies the test method of reliability boundary,including the concept of reliability boundary,the analysis method and the test method.The lock mechanism of aircraft cabin door is set as an example to discuss the application and performance of the proposed method.The result shows that this method could get the reliability boundary of influence factors for the product at the reliability boundary,and also analyze the performance of product at this state.This could contribute to the design,improvement and maintenance of the products.(3)Parameter estiamtion methods based on the Weibull family models.To make Weibull distribution has more flexible fitting capabilities,several new distribution models are proposed,such as Weibull-Pareto distribution(WPD),inverse Weibull distribution(IWD),generalized inverse Weibull distribution(GIWD)and new extended Weibull distribution(NEWD).This thesis studies the parameter estimations for above models using the maximum likelihood estimation and Bayes estimation.And several numerical examples are performed to illustrate the application and performance of these estimators.On this basis,the thesis continues to propose a new searching coordinates estimation(SCE)method and its application,with numerical examples also being performed.The result shows that this method could get the estimates more accurately and easily.(4)The research on reliability test and assessment for the lock system of aircraft landing gear door.Since the reliability of landing gear door lock system will seriously affect the aircraft safety when taking off or landing,the thesis studies the reliability test and assessment for the lock system of aircraft landing gear door,including the lock system of front landing gear door and main landing gear door.For the new lock mechanism of aircraft landing gear door,this thesis designed a reliability test device for the new lock mechanism of aircraft landing gear door under complex load conditions,solving the problem of complex and mutative variable loads(small load during locking process and large load during unlocking process)and get one invention patent.Based on the reliability test program of the lock system,this thesis finished the reliability test of 24 cycles for the lock system of front and main landing gear door respectively.The main purpose is to get the main failure mode,weaknesses and the methods of improving the function reliability.At the same time,the thesis make the reliability assessment for the lock system of landing gear door based on the reliability test data.This work could make contribution to the improvement of lock system and could be the theoretical and technical reference for the reliability test of other mechanical products.(5)The reliability simulation and test devices design for the key mechanical parts.In the engineering,many key mechanical parts,such as idler shaft,seals and threaded connections,whose failures will decrease the performance of mechanical products,even failure of products.This thesis studies the reliability problems for the idler shaft of a new tank,O-rings and premium connection based on simulation.Based on the above research,the thesis gets the function reliability,sensitivity and reliability boundary of above key mechanical parts under the actual working conditions.These reliability test cases could help the product design,analysis and improvement.For the rocket valve,it works under the complex loads,such as temperature,vibration and other complex bending torque.This thesis continues to design a test device for the rocket valve under complex loads,which achieved to perform the vibration,temperature and bending load simultaneously.