Ping Qian

Optimal design of multiple stress constant accelerated life test plan on non-rectangle test region

For optimal design of constant stress accelerated life test(CSALT) with two-stress, if the stresses could not reach the highest levels simultaneously, the test region becomes non-rectangular. For optimal CSALT design on non-rectangle test region, the present method is only focused on non-rectangle test region with simple boundary, and the optimization algorithm is based on experience which can not ensure to obtain the optimal plan. In this paper, considering the linear-extreme value model and the optimization goal to minimize the variance of lifetime estimate under normal stress, the optimal design method of two-stress type-I censored CSALT plan on general non-rectangular test region is proposed. First, two properties of optimal test plans are proved and the relationship of all the optimal test plans is determined analytically. Then, on the basis of the two properties, the optimal problem is simplified and the optimal design method of two-stress CSALT plan on general non-rectangular test region is proposed. Finally, a numerical example is used to illustrate the feasibility and effectiveness of the method. The result shows that the proposed method could obtain the optimal test plan on non-rectangular test regions with arbitrary boundaries. This research provides the theory and method for two-stress optimal CSALT planning on non-rectangular test regions.

Design criteria for planning multiple stresses accelerated life test

In general, there are three types of methods to arrange the stresses combinations in optimal design of multiple CSALT: Escobar-Meeker method, orthogonal design method and uniform design method. In this paper, these methods are compared through computer experiments, and the design criterion for multiple stress accelerated life test is proposed. Considering the linear-extreme value statistical model, the plans are obtained based on the above three methods under V-optimality. These plans are compared from the following three indicators: the estimation precise of the p-th quantile of life distribution under normal stress, the robustness of optimal test plans to misspecified model parameters and the estimation precise of model parameters. The results show that, the plans obtained from Escobar-Meeker method is the best, and followed by orthogonal design and uniform design; Escobar-Meeker plan with five test points is the best plan compromising the three aspects. The research in this paper provides theoretical support to select the best methods to arrange the stresses combinations in multiple stress accelerated life test planning.

Optimal Time-Censored Constant-Stress ALT Plan Based on Chord of Nonlinear Stress-Life Relationship

This paper proposes a method for designing an optimal plan for the type-I censoring constant-stress accelerated life test (ALT) with a nonlinear stress-life relationship. This method derives the optimal plan based on the line segment (the chord) that connects the highest and lowest points of the curve or surface that corresponds to the nonlinear stress-life relationship, and consequently, it transforms the problem of designing the optimal plan of an ALT with a univariate or multivariate nonlinear stress-life relationship to the problem of designing the optimal plan of an ALT with a univariate linear stress-life relationship. The theoretical analysis and examples show that compared with the methods that find the optimal plan based on the nonlinear stress-life relationship itself, the proposed method can simplify the design problem and obtain better plans.

Optimal Design of Multiple Stresses Accelerated Life Test Plan Based on Transforming the Multiple Stresses to Single Stress

For planning optimum multiple stresses accelerated life test plans, a commonly followed guiding principle is that all parameters of the life-stress relationship should be estimated, and the number of the stress level combinations must be no less than the number of parameters of the life-stress relationship. However, the general objective of an accelerated life test(ALT) is to assess the p-th quantile of the product life distribution under normal stress. For this objective, estimating all model parameters is not necessary, and this will increase the cost of test. Based on the theoretical conclusion that the stress level combinations of the optimum multiple stresses ALT plan locate on a straight line through the origin of coordinate, it is proposed that a design idea of planning the optimum multiple stresses ALT plan through transforming the problem of designing an optimum multiple stresses ALT plan to designing an optimum single stress ALT plan. Moreover, a method of planning the optimum multiple stresses ALT plan which can avoid estimating all model parameters is established. An example shows that, the proposed plan which only has two stress level combinations could achieve an accuracy no less than the traditional plan, and save the test time and cost on one stress level combination at least; when the actual product life is less than the design value, even the deviation of the model initial parameters value is up to 20%, the variance of the estimation of the p-th quantile of the proposed plan is still smaller than the traditional plans approximately 25%. A design method is provided for planning the optimum multiple stresses ALT which uses the statistical optimum degenerate test plan as the optimum multiple stresses accelerated life test plan.

Accelerated Aging Test and Study of Storage Life Prediction of NBR O-Ring

Nitrile Butadiene Rubber (NBR) is a kind of common sealing materials for the electric hydraulic servo mechanism, there exists the aging failure problem in its storage environment, which is the key factor determining the storage life of the electric hydraulic servo mechanism. Through the analysis of aging failure mechanism of the NBR o-ring, the degradation path that varies with the changes of aging time based on compression set was established. And the Arrhenius equation, which is the acceleration equation of the aging reaction velocity varies with the changes of temperature, was established as well. In order to obtain the related parameters of the model, the accelerated aging test was conducted and its data were processed by applying the approximation standards and least square method. Also through the test the prediction of storage life of NBR o-ring under special storage conditions was made, and its predicted results were basically identical with the actual storage life.

Statistical Analysis on Accelerated Degradation Test Data Based on Multiple Performance Parameters

In view of the multiple performance parameters accelerated degradation and need to consider its dependence, we should know how to statistical analysis on the data of testing, establish multiple performance parameters degradation path model and its distribution model and the accelerated model of degradation rate. The multiple performance parameters degradation data’s statistics has two different situations which are independent and dependent. So, A method is proposed which is multiple performance parameters of reliability comprehensive evaluation method based on least squares parameters estimation. This method can achieve rapid and effective assessment of their reliability by using an efficient Monte-Carlo simulation method to get the performance parameters degradation data.

Motion Performance Analysis and Experiment Research of the Hooke’s Joint-Gear Mechanism of Differential Velocity Vane Pump

Based on the analysis of its motion performance about Hooke’s joint-gear mechanism, the Hooke’s joint-gear mechanism of differential velocity vane pump is brought forward. By analyzing its motion rule on the driving system of the differential velocity vane pump, the design parameters of the Hooke’s joint-gear mechanism of differential velocity vane pump are shown. The overall structure and its principle prototype are designed. Based on the principle prototype of the differential velocity vane pump, the experimental platform is established to testify the draining and trapping fluid. The results are shown that Hooke’s joint-gear mechanism of differential velocity vane pump can achieve the function of draining and aspirating fluid, and the design on the driving system and the pump structure are correct.

Deploying Impact Dynamics Simulation on Deployable Mechanism of Folding Wing with Clearance

Based on the non-linear equivalent spring-damper model in the two-state model, Impact model with hinge clearance for deployable mechanism of folding wing is set up and deploying dynamics on deployable mechanism of folding wing is simulated including impact force variation caused by the size of clearance and the clearance friction by using ADAMS software. The results show that the random continuous impact force is produced by the influence of clearance; as dimensions of the clearance increase, impact times decrease and amplitudes of impact forces are increased; System energy consumption is speeded up and to some extent times of impacts with clearance and disturbance effects of deployable mechanism is suppressed by friction in the whole deployable process.