Accelerated Life Testing Research Articles

Statistical analysis for progressive stress accelerated life test with transmutation Weibull distribution

The Transmutation Weibull distribution is derived from the quadratic rank transmutation map of the Weibull distribution. This distribution integrates the high adaptability of the Weibull distribution in engineering and materials fields, and has great potential utility for modeling lifetime data. Therefore, the article explores the progressive stress accelerated life test model for components under the Transmutation Weibull distribution, conducts statistical analysis using the maximum likelihood estimation (MLE), Lindley’s approximation, and Markov Chain Monte Carlo (MCMC) algorithm to provide approximate estimates for the model. Finally, by comparing the results of numerical simulations, it is confirmed that the Bayesian estimation is more accurate and effective.

Accelerated Life Testing of Biodegradable Starch Films with Nanoclay Using the Elongation Level as a Stressor.

An attempt was made to evaluate the elongation level as a stressor on biodegradable starch films reinforced with nanoclay using a simple linear model. A total of 120 film units were subjected to increasing elongation levels and the exact break time of the failed units was monitored. Nine different attempts were made to fit the data distribution and the lognormal distribution was chosen as the most suitable because it resulted in the lowest values of the regression fit indices -2LL, AICc and BIC. Following the selection of the best fit, it was, generally, observed that an increase in the elongation level resulted in the decreasing exact break time of the films. Among several models, the best fit was provided by the simple linear model. Based on this model, the acceleration factor was estimated, and it was shown that it increased exponentially while increasing the elongation level. Finally, the probability of failure and the hazard rate of the film units as a function of the elongation level were estimated, demonstrating the applicability of this method as a tool for food packaging film failure prediction.

A Review of Common Acceleration Models in Accelerated Life Testing

The core of accelerated life testing (ALT) is the development of acceleration models. These models can be classified into three types based on their underlying methodologies: physics-based, empirical inductive, and statistical inference models. This paper primarily examines the acceleration models that are commonly applied in engineering practice and presents the relevant computational formulas to highlight the fundamental research methodologies of ALT. Additionally, the paper underscores that ALT is increasingly recognized as a vital and emerging trend, driven by its role in shortening design cycles, enhancing product reliability, and managing costs.

Remaining useful life prediction of nuclear reactor control rod drive mechanism based on dynamic temporal convolutional network

The control rod drive mechanism (CRDM) is a critical equipment of the nuclear reactor, and the prediction of its remaining useful life (RUL) is important for the efficient maintenance and ensuring the safe, reliable operation of nuclear power plants. In this paper, a novel framework for the RUL prediction of CRDM is proposed, which is a dynamic temporal convolution network (DTCN) based on dynamic activation function and attention mechanism. Firstly, the temporal convolution network (TCN) is used as the backbone of the prediction model, to extract the temporal dependence of the input data. Next, the dynamic activation function DReLU is integrated into the TCN, which can dynamically activate features and capture variable degradation information. Then, introducing the attention mechanism improves the influence of important high-level features extracted by the network on RUL prediction, thereby improving the efficiency of feature extraction in the network. Finally, the DTCN outputs the predicted RUL by performing non-linear mapping on the extracted features. The CRDM accelerated life test platform is established and a series of experiments are conducted using the collected CRDM full-life vibration dataset. The results demonstrated the performance and advantages of the proposed method.

Modeling Chronic Disease Mortality by Methods From Accelerated Life Testing.

We propose a parametric model for describing chronic disease mortality from cohort data and illustrate its use for Type 2 diabetes. The model uses ideas from accelerated life testing in reliability theory and conceptualizes the occurrence of a chronic disease as putting the observational unit to an enhanced stress level, which is supposed to shorten its lifetime. It further addresses the issue of semi-competing risk, that is, the asymmetry of death and diagnosis of disease, where the disease can be diagnosed before death, but not after. With respect to the cohort structure of the data, late entry into the cohort is taken into account and prevalent as well as incident cases inform the analysis. We finally give an extension of the model that allows age at disease diagnosis to be observed not exactly, but only partially within an interval. Model parameters can be straightforwardly estimated by Maximum Likelihood, using the assumption of a Gompertz distribution we show in a small simulation study that this works well. Data of the Cardiovascular Disease, Living and Ageing in Halle (CARLA) study, a population-based cohort in the city of Halle (Saale) in the eastern part of Germany, are used for illustration.

A Liquid Well Barrier Element for Temporary Plug and Abandonment Operations: A Breakthrough Approach

Plug and abandonment (P&A) operations demand valuable time and resources for operational procedures and materials to establish the well barrier element. This study aims to investigate the application of a water-based fluid as a liquid well barrier element for temporary abandonment, based on estimates of its lifespan and the survival probabilities of downhole temperatures acquired through accelerated life tests. To achieve this, the water-based formulation was tested and exposed to 95, 110, 140, and 150 °C temperatures for time intervals ranging from 1 to 10 days. After the temperature exposure, the fluid properties were verified, and failure was detected by accounting for any deterioration in rheological parameters and/or a substantial increase in filtrate volume. A statistical analysis of the failure data was performed in RStudio 4.1.3 software using the Weibull Model, and the fluid average lifespans and survival probabilities were estimated for the P&A temperatures. The results obtained demonstrate that the degradation of the fluid was only observed for 140 and 150 °C temperatures. According to the results, the fluid is a promising alternative for temporary abandonment until 80 °C, with no need for monitoring once its lifetime expectation exceeds three years at this temperature. For downhole temperatures above 80 °C, the fluid is a possible alternative, however, the operation’s maximum time and monitoring requirements should consider reliability metrics for each temperature.

Lifespan Evaluation for a Standard RV Reducer based on Fatigue Strength Theory

Rotate vector (RV) reducers are the two-stage deceleration device comprising involute and cycloid-pin gear transmission mechanisms. As the typical deceleration elements, they are widely applied in industrial robots, digitally controlled machine tools and automation fields due to their compact structure and high precision. However, a reducer may lose precision after a long-term operation. Moreover, pitting and metal peeling of internal components may also occur, leading to a fatigue failure. Therefore, it is necessary to conduct investigations on lifespan evaluation for RV reducers. In this study, the CRV-80E reducer is taken as the research object. Firstly, according to its transmission characteristics, the lifespan evaluation model for a standard RV reducer is established based on fatigue strength theory and Palmgren-Miner linear cumulative damage law, with the internal crankshaft bearing is considered as the key component. Then, the simulations are carried out on crankshaft bearing by the ANSYS Workbench and SKF SimPro. The contact stress, deformation on bearing rollers, and the rated lifespan of the reducer are simulated. Finally, the accelerated life test is conducted on an RV reducer by increasing the external load with the positioning precision as an output and criterion. After the test, the reducer is disassembled, and metal peeling failure is observed on the crankshaft bearing while other parts are relatively intact. The test results validate the feasibility and accuracy of the service life evaluation model and simulation analysis. This study provides a new research approach for researchers and manufacturers and a design reference for engineers to improve the lifespan of RV reducers by optimizing crankshaft bearings, which have a certain academic value.

The CRITIC-AHP performance degradation staged fusion evaluation of wet clutch friction components

The performance of wet clutches plays a crucial role in the efficiency and durability of mechanical transmission systems. As a vital component of the clutch, the degradation of friction components directly affects its stability and reliability. To investigate the performance degradation of friction components, we establish a multi-indicator evaluation system and conduct an accelerated life test, which is validated by an accelerated model. Next, we build a Random Forest model to classify the friction stage. Criteria Importance through Intercriteria Correlation (CRITIC) and the Analytic Hierarchy Process (AHP) is proposed to assign weights for each degradation indicator during different stages. A Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) scoring method combines indicator weights to construct a CRITIC-AHP staged fusion evaluation model of friction components. Notably, the average relative error of the evaluation results of the model is 9.35%.

Reliability inference for dual constant-stress accelerated life test with exponential distribution and progressively Type-II censoring

Accelerated life test provides a feasible and effective way to rapidly derive lifetime information by exposing products to higher-than-normal operating conditions. However, most of the previous research on accelerated life test has focused on the application of a single stress factor and a traditional censoring scheme. This article considers the reliability inference for a dual constant-stress accelerated life test model with exponential distribution and progressively Type-II censoring. Point estimates for model parameters are provided using maximum likelihood estimation and the weighted least squares method based on random variable transformation. In addition, we construct asymptotic confidence intervals, approximate confidence intervals, and bootstrap confidence intervals for the parameters of interest. Finally, extensive simulation studies and an illustrative example are presented to investigate the performance of the proposed methods.

Constant Stress-Partially Accelerated Life Tests of Vtub-Shaped Lifetime Distribution under Progressive Type II Censoring

In lifetime tests, the waiting time for items to fail may be long under usual use conditions, particularly when the products have high reliability. To reduce the cost of testing without sacrificing the quality of the data obtained, the products are exposed to higher stress levels than normal, which quickly causes early failures. Therefore, accelerated life testing is essential since it saves costs and time. This paper considers constant stress-partially accelerated life tests under progressive Type II censored samples. This is realized under the claim that the lifetime of products under usual use conditions follows Vtub-shaped lifetime distribution, which is also known as log-log distribution. The log–log distribution is highly significant and has several real-world applications since it has distinct shapes of its probability density function and hazard rate function. A graphical description of the log–log distribution is exhibited, including plots of the probability density function and hazard rate. The log–log density has different shapes, such as decreasing, unimodal, and approximately symmetric. Several mathematical properties, such as quantiles, probability weighted moments, incomplete moments, moments of residual life, and reversed residual life functions, and entropy of the log–log distribution, are discussed. In addition, the maximum likelihood and maximum product spacing methods are used to obtain the interval and point estimators of the acceleration factor, as well as the model parameters. A simulation study is employed to assess the implementation of the estimation approaches under censoring schemes and different sample sizes. Finally, to demonstrate the viability of the various approaches, two real data sets are investigated.

A novel random-effect Birnbaum-Saunders distribution for reliability assessment considering accelerated mechanism equivalence

ABSTRACT Birnbaum-Saunders (B-S) distribution has been widely used in reliability assessment of products. However, the basic B-S distribution fails in characterizing the variation of damage caused by different units. In this paper, a novel random-effect B-S distribution which considers the unit heterogeneity is proposed. First, the novel distribution incorporates the inverse gamma distribution into the shape parameter of B-S distribution, and statistical inferences of the novel distribution are thoroughly investigated. Then, an extension of the proposed B-S distribution is developed to handle accelerated life test (ALT) data. In order to ensure the validity of ALTs, a coefficient of variation hypothesis test method employing the necessary condition for mechanism equivalence of the proposed distribution is executed. To estimate the parameters of the novel B-S distribution with explanatory variables, a two-step algorithm combining analogue least square and expectation maximization (ALS-EM) is proposed based on the data with constant coefficients of variation. A simulation is conducted to verify the effectiveness of the proposed ALS-EM method. Finally, two actual engineering cases are utilized to show the advantages of the random-effect B-S distribution in terms of goodness-of-fit and reliability assessment precision.

Different estimation techniques and data analysis for constant-partially accelerated life tests for power half-logistic distribution

Partial accelerated life tests (PALTs) are employed when the results of accelerated life testing cannot be extended to usage circumstances. This work discusses the challenge of different estimating strategies in constant PALT with complete data. The lifetime distribution of the test item is assumed to follow the power half-logistic distribution. Several classical and Bayesian estimation techniques are presented to estimate the distribution parameters and the acceleration factor of the power half-logistic distribution. These techniques include Anderson–Darling, maximum likelihood, Cramér von-Mises, ordinary least squares, weighted least squares, maximum product of spacing and Bayesian. Additionally, the Bayesian credible intervals and approximate confidence intervals are constructed. A simulation study is provided to compare the outcomes of various estimation methods that have been provided based on mean squared error, absolute average bias, length of intervals, and coverage probabilities. This study shows that the maximum product of spacing estimation is the most effective strategy among the options in most circumstances when adopting the minimum values for MSE and average bias. In the majority of situations, Bayesian method outperforms other methods when taking into account both MSE and average bias values. When comparing approximation confidence intervals to Bayesian credible intervals, the latter have a higher coverage probability and smaller average length. Two authentic data sets are examined for illustrative purposes. Examining the two real data sets shows that the value methods are workable and applicable to certain engineering-related problems.

Effect of Staining, Glazing and Polishing on the Survival Probability of Monolithic Zirconia Crowns.

The purpose of this in vitro study was to evaluate the effect of staining, glazing, and polishing on the survival probability of monolithic crowns manufactured with preshaded stabilized zirconia with 5 mol% of yttrium oxide (5Y-TZP). Monolithic crowns in the shape of an upper canine (1.5 mm of thickness) were manufactured by CAD/CAM, adhesively cemented on metallic foundation, and divided into 6 groups (n = 21): C (control), S (staining), G (glazing), P (polishing), SG (staining and glazing), and SP (staining and polishing). The survival probability was determined by step-stress accelerated life testing with a load applied to the palatine concavity of the crown. First, the specimens were subjected to a single-load to fracture test (SLF) and next to the fatigue test (5 Hz, thermocycling immersed in water varying 5-55°C), including the light (n = 9), moderate (n = 6), and aggressive (n = 3) loading profiles (load ranged between 20% and 60% of SLF). The survival probability was calculated considering the cycles for failure (CFF) and fatigue failure load (FFL) and illustrated using a Kaplan-Meier graph. The comparison among groups was performed using a Log-Rank test (α = 0.05). The mean value of SLF was 586.7 N. There was no difference among groups in survival probability, considering CFF and FFL. Staining, glazing, and polishing can be performed safely without damaging the mechanical behavior of 5Y-TZP monolithic crowns. Staining is used to characterize and improve the esthetic of zirconia monolithic crowns. It can be used to reproduce the color gradient in the cervical region of the crown and pigmented grooves. This study showed that staining, glazing, and polishing did not affect the survival probability and the use of finishing procedures (glazing or polishing) after staining did not improve the survival probability of zirconia monolithic crowns.

Investigation on the failure of the space HgCdTe detector with long-term storage tests

The HgCdTe detector is the core device of the infrared imaging system, its reliability directly restricts the performance of the whole imaging system. For some special applications, it maintains in a non-operating storage state for a long time, it is significant to study its storage reliability. Due to the long lifetime of detectors, most studies have been conducted with accelerated life tests, there is a lack of experimental information concerning the failure of these detectors after longtime storage. In this article, the performance degradation of Hg1-xCdxTe detector with the 127 months long-term storage test is studied. The failure mode and failure mechanism of detectors are investigated through the statistics analysis and optical photomicrography. The results indicate that there are three failure modes, such as low-temperature opening circuit, chip circuit opening, and signal reduction accompanied by increased noise. The main type of failure is in the mode of signal reduction accompanied by increased noise, which is a typical failure mode for long-term storage of HgCdTe detectors. In this typical failure mode, corrosion products are observed near the photosensitive surface in the failure detector, which prove to be a metal product of indium. The long-term storage results can provide data support for accelerating storage test and improve the HgCdTe detectors design.

Hypochlorous acid electrosynthesis and service life assessment of a Ti|Ti–Ru–Ir-oxides anode assembled in a flow electrolyzer: Understanding the influence of the concurrent O2 bubbling flow

This paper addresses the influence of bubbling flow and service life of the Ti|Ti–Ru–Ir-oxides anode during the electrosynthesis of HClO in a laboratory-scale filter-press-type electrolyzer. The electrolyzer was assembled in a flow plant in recirculation mode. Polarization curves in rotating disk electrode (RDE) revealed the coexistence of the oxygen evolution reaction (OER) during HClO electrosynthesis in diluted chloride solutions (containing 35 mM NaCl at pH 3). CFD simulations of the two-phase (O2–H2O) flow were obtained by solving simultaneously the Navier-Stokes and charge conservation equations using a finite element method code. The O2–H2O simulations show the efficient gas release in the electrolyzer provoked by the continuous phase (H2O) inertia and the well-engineered cell design. The moderated O2 dispersion caused a quasi-homogeneous current distribution along the anode. However, the current efficiency during HClO electrosynthesis gave values of ∼32% provoked by the OER on the anode. The HClO accumulations (from 3.02 to 6.64 mM) showed excellent agreement with CFD simulations. The accelerated life tests revealed that the Ti | Ti–Ru–Ir-oxides anode has a lifetime of at least 26 years during the HClO electrosynthesis in diluted chloride solutions.

Fabrication of Ti/Zr-SnO2/PbO2-Nd Electrode for Efficient Electrocatalytic Degradation of Alizarine Yellow R

Introduction: A novel attempt to degrade alizarine yellow R (AYR) by lead dioxide (PbO2)/ neodymium (Nd) coated Ti anode was investigated. Method: Ti/Zr-SnO2/PbO2-Nd electrode showed high oxygen evolution potential, high current density, and neutral conditions, which favored the degradation of AYR. The PbO2-Nd layer on Ti/Zr-SnO2 was further characterized by scanning electron microscopy, and X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The electrochemical properties of Ti/Zr- SnO2/PbO2-Nd electrode were evaluated by cyclic voltammetry, AC impedance spectroscopy, and accelerated life test. Result: The relatively higher oxygen evolution overpotential (~1.80 V) of the developed electrode can effectively suppress the occurrence of surface side reactions and oxygen evolution. A relatively lower charge transfer resistance (Rct, 18.0 Ω) of Ti/Zr-SnO2/PbO2-Nd electrode could be found. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited an accelerated lifetime of 110 min under a very high current density of 10,000 A/m2. The doping of Nd could produce loosely-stacked sheet-like structures, thus, the number of active sites on the electrode surface increases. Conclusion: Moreover, an outstanding conductivity of Ti/Zr-SnO2/PbO2-Nd electrode was obtained, which favored the electron transfer and catalytic activity of the modified electrode. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited improved electrochemical performances and higher oxygen evolution potential, and the highest oxygen evolution potential is 1.80 V. Under the current density of 30 mA/cm2, the electrocatalytic degradation of 92.3% could be achieved in 180 min. The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater. conclusion: The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater.

Reliability assessment and accelerated life testing in a metalworking plant

Reliability assessments are useful for determining how well products, systems, and services maintain their quality over the course of time and through various conditions. In this paper, a reliability assessment of a metalworking plant was conducted, as well as accelerated life testing of the plant's spot-welded and riveted products. The overall layout of the plant was complex, requiring the use of equations to calculate the reliability of stations being connected in series and parallel in order to determine the overall reliability of the system. Furthermore, equations for mean life and failure rate were used in determining the estimate of mean life for the tested components, as well as the rate at which the components fail, respectively. The results indicated that the metalworking plant had a reliability of 0.81 or 81%. Moreover, the results indicated that the failure data of the spot-welded products follow the exponential model, with the failure rate of the products being constant throughout the period under investigation. The failure data of the riveted products follow the Weibull model, increasing throughout the period under investigation. This study presents a procedure for aiding production and maintenance managers in conducting reliability assessments of their production systems.

Reliability Assessment Method Based on Small Sample Accelerated Life Test Data

Aiming at the problems of small sample size, few test failure data and low reliability evaluation efficiency in accelerated life test of high-reliability and long-life products, an improved virtual augmentation Bootstrap-Bayes reliability evaluation method based on small sample accelerated life test data was proposed. Firstly, the test data under various stress conditions are augmented by virtual fusion. Secondly, the empirical distribution function and bootstrap sampling method are improved, and the kernel density estimation method is used to fit the density distribution of test data as prior information. Then, the parameter estimates of the test data are obtained by Gibbs sampling combined with Bayes formula. Finally, the reliability index under normal stress level is obtained by accelerating model extrapolation. The feasibility of the proposed method is verified by the accelerated life test data of a type of Ship communication equipment.

Quantitative evaluation of the degradation acceleration of insulation at local area in multilayer ceramic capacitors

The degradation acceleration based on dielectric thickness was evaluated by analyzing the local insulation degraded area in prototype Ni-BaTiO3 multilayer ceramic capacitors. Locally thinned dielectric layers, resulting from nickel internal electrode bulges, were associated with shorter lifetimes than the mean time to failure observed in highly accelerated life test. A strong correlation was observed between the minimum thickness of the dielectric layer at the degraded area and the lifetime. The electric field acceleration coefficient was derived from the correlation between the electric field strength, calculated from the dielectric thickness at the degraded area, and the lifetime. The impact of dielectric thinning on degradation acceleration was quantified by analyzing these local degraded areas. The factors influencing degradation acceleration were also discussed based on these findings.

Electrochemical degradation of m-nitrophenol using an innovative zeolite modified PbO2 anode: Electrode characterization, influence factors and degradation mechanism

In this study, a zeolite-doped PbO2 (Zeo-PbO2) anode was fabricated via electrodeposition technology for electrochemical oxidation of m-nitrophenol (m-NP). The results of characterization revealed that doping zeolite efficiently promoted the oxygen evolution potential and active sites of PbO2 anode, thereby higher performance to generate •OH radical and degrade the m-NP. The •OH radical was confirmed to be the primary contributor to the electrochemical oxidation of m-NP by scavenging tests. Thus, the effect mechanism of current density, supporting electrolyte, and initial pH on the removal of m-NP in the electrochemical oxidation process was explored by the generation of •OH radicals at different conditions. Based on the vulnerable sites of m-NP to the attack of •OH radical supposed by the theoretical calculation and degradation intermediates identified by GC-MS and IC, the degradation pathways of m-NP in the electrochemical oxidation process were speculated. Besides, the good recyclability and stability of Zeo-PbO2 anode were exhibited in consecutive m-NP degradation, •OH generation experiments, and accelerated life tests.