Some Problems Research On Time-Dependent Reliability-Based Robust Optimization Design Of Mechanical Components

From understanding, research, development of reliability to its application, these are mostly based on static mechanical models, which belong to the fields of static reliability. Most of known and mature theoretical models concerned reliability design are deterministic as problems on dynamic reliability is more complicated than static reliability. In fact, the reliability of mechanical components is generally weakened due to their material properties, environment, using time, various loads, and other factors, and the reliability index would gradually weaken with the increasing time, which is a dynamic time-dependent process, thus the influence of time on the reliability, sensitivity and robust design of mechanical components should be considered, and this is also a dynamic time-dependent process. Therefore, establishing time-dependent reliability models more conform to practical conditions, and it has important theoretical and practical. significance to obtain accurate information of reliability engineering through the dynamic models.Taking National Key Technology R&D Program in the 11th Five year Plan of China in Ministry of Railways "Research of Key Techniques and Development of Key Equipments of High-Speed Train" and program "reliability sensitivity design of mechanical equipment" proposed by Northeastern University and as the background of this paper, theories such as reliability, reliability sensitivity and reliability-based robust optimization design are applied to design of mechanical components. Models of time-dependent reliability design of components are established, and time-dependent sensitivity design and reliability-based robust optimization design of components can be obtained with better numerical simulation results. This paper focuses some points as follows:(1) Mathematical models concerned state functions of time-dependent reliability of mechanical components under the action of random loads are established according to theories of order statistics and stochastic process, and reliability index and dynamic reliability can be obtained using methods of second moment and random perturbation. We have researched various rules of strength, loads, reliability and failure rate with time, the results show that reliability of components gradually decreases with the increase of using time, yet failure rate of components which obey the rule of bathtub curve in shape gradually increases with the increase of using time. Dynamic curves of reliability and failure rate with time are obtained by examples, which process certain guiding significance to determine test time and reliability lifetime of mechanical components.(2) Combined with the theory of reliability design and the method sensitivity analysis, computation method of time-dependent reliability sensitivity design of mechanical components is set based on models of time-dependent reliability, and various rules of reliability sensitivity are given, meanwhile, influence of the various design parameters on reliability are also researched, which supply theoretical data for reliability design of mechanical components.(3) Original sensitivity formula is practical under the condition that a state function is linear or not serious nonlinear. If the state function is serious nonlinear, precision of reliability sensitivity analysis is affected by the big or small change of parameters or design variable using difference or perturbation calculation as approximate substitution of differential, and even some completely wrong information can be obtained. Original sensitivity formula is modified according to this problem, and the proof of the formula is also given in this paper. Results show that the modified formula is more applicable for general state function, especially, serious nonlinear state function.(4) Reliability-based robust design that is on the basis of reliability design and reliability sensitivity design is related with time, thus robust design is also related with time, and it's in fact a process of time-dependent robust design. Combined with reliability models, time-dependent reliability sensitivity and reliability optimization design, engineering design method of time-dependent reliability-based robust optimization design of mechanical products is proposed. We can accurately obtain design information of reliability-based robust optimization design of mechanical components at any moment through the relation curves between robust design and time in this paper.(5) This paper proposes methods of time-dependent reliability design, time-dependent reliability sensitivity design and time-dependent reliability-based robust optimization design of mechanical components with arbitrary distribution parameters using random perturbation method, Edgeworth series method and corresponding empirical modification formula, and develops reliability design theory of mechanical components with arbitrary distribution parameters. Under the condition that the first four moments of basic random parameters are known, time-dependent reliability design, time-dependent reliability sensitivity design and time-dependent reliability-based robust optimization design of mechanical components with arbitrary distribution parameters can be realized through computer program, naturally, design information of time-dependent reliability-based robust of mechanical components with arbitrary distribution parameters can be given.(6) Time-dependent reliability-based robust optimization design of mechanical components whose state function is implicit or structures and conditions are more complicate are also researched. Take Multiple Units wheelset as an example in this paper, combined theories of time-dependent reliability, sensitivity and robust optimization design proposed and Miner linear cumulative damage theory; we have researched time-dependent fatigue reliability-based robust optimization design for Multiple Units wheelset by using some software such as MSC.Nastran, iSIGHT and MATLAB.