Accelerated Degradation Test Method Research Articles

Accelerated degradation test method and performance prediction with service mileage of the yaw damper in railway vehicles

The performance of the yaw damper for rail vehicles degrades significantly degradation after long-term operation, which directly affects the dynamic behaviour of the vehicle operation. To quickly achieve the performance degradation of the yaw damper and predict the operating mileage under actual service conditions, the operating displacement spectrum of the yaw damper under actual operating conditions is analysed and decomposed using the short-time Fourier transform. Based on the equivalent principle of energy loss during vibration attenuation, an accelerated test method is proposed for the performance degradation of yaw dampers. By conducting the accelerated degradation test of the yaw damper on the test bench, the continuous degradation relationship between the performance parameters of the damper and the loading times is obtained. By combining the operating displacement spectrum and the accelerated degradation test data, the performance degradation trajectory model of the yaw damper is established, taking into account the equivalent energy loss between the service mileage and the loading times. The mapping relationship among loading times, service mileage and performance degradation is constructed. Finally, parameter performance tests are conducted on yaw dampers under different service mileage to verify the accuracy of the performance degradation trajectory model. The results show that the proposed acceleration test method and degradation trajectory model can quickly realise the performance degradation of the damper and accurately predict the performance parameters for different service mileage under actual operating conditions.

An improved accelerated degradation model for LED reliability assessment with self-heating impacts

Light-emitting diodes (LEDs) are a solid-state light source being used in numerous applications, including display, communications, medical services, etc. However, the reliability assessment of LED components is still challenging due to the growing up of the LED complexity and/or the miniaturization of assembly technologies. To face this challenge, this paper proposes a novel accelerated degradation testing (ADT) model considering the self-heating impact in the degradation process of a LED component. So, the self-heating impact is first analyzed and modeled. In fact, the junction temperature of a LED component depends not only on the heat generation (e.g., drive current, dispersing heat) but also on the current state (degradation level) of the component. Then, a modified stochastic difference equation is developed for modelling the degradation process by considering the self-heating impact. The LED reliability formulation is finally derived. In addition, an estimation method based on the maximum likelihood is developed to estimate the proposed model's parameters from experimental data. To validate our models, a case study for LED light sources is implemented. The obtained results show that, compared to the TM-21 standard and the conventional ADT methods, our proposed approach achieves better results in the LED reliability assessment.

Accelerated Degradation Testing With Long-Term Memory Effects

The accelerated degradation testing (ADT) has been widely applied as an efficient strategy to obtain the reliability (life) information of the assets in a shorter-than-normal period of time by exposing the assets to higher-than-normal stresses. Recently, with advances in the sensor technology, it has been revealed that the degradation of some assets demonstrates a long-term memory effect, which implies that the future degradation process not only depends on the current degradation state but also strongly correlates with the past degradation history across a long period of time, and the degradation increments are correlated for nonoverlapping time intervals. The existing ADT methods do not consider the long-term memories, which could lead to biased life testing results. In this article, we propose a novel ADT model by integrating the long-term degradation memory effect based on a utilization of the fractional Brownian motion. A maximum likelihood approach is developed to estimate the model parameters. A likelihood-ratio hypothesis test is designed to test the existence of long-term memories. Simulation studies are implemented to illustrate the developed methods. Physical experiments on accelerated testing of a atalyst are designed and conducted to demonstrate the proposed model and its advantage over benchmark approaches. The results show that the traditional ADT paradigm, which ignores the long-term memories, significantly underestimates asset lifetime uncertainties.

Modeling and Analysis of Performance Degradation Data for Reliability Assessment: A Review

Reliability engineering plays an important role in the design, manufacture, maintenance, and replacement of industrial products. Over the last few decades, accelerated degradation testing (ADT) has been largely utilized to shorten test durations, reduce the samples needed, and provide sufficient degradation data to ensure the effective reliability assessment of the concerned products. Meanwhile, performance degradation modeling has been recognized as an essential approach to help researchers and producers understand the health conditions of the deteriorating systems. However, the diversity in reliability tests, degradation models, and statistical analysis techniques has increased the difficulty in selecting appropriate reliability assessment methods in specific scenarios. Besides, there are no systematic reviews focused on modeling and analysis of performance degradation data. Therefore, this paper aims to (1) present ADT fundamentals, including the basic theory, ADT methods, accelerated stress variables, type of acceleration models, as well as ADT optimization, (2) comprehensively review current states and future challenges in degradation modeling, (3) discuss the problem of model mis-specification and compare different approaches for parameter estimation, (4) highlight future opportunities and possible directions deserving further research.

Experimental study on the life prediction of servo motors through model-based system degradation assessment and accelerated degradation testing

The advent of smart factories has resulted in the frequent utilization of industrial robots within factories to increase production automation and efficiency. Due to the increase in the number of industrial robots, it has become more important to prevent any unexpected breakdowns of the factory. As a result, the lifespan prediction of machinery has become a crucial factor because such failures can be directly associated with factory productivity resulting in significant losses. Most of the failures occur within one of the core components of the robot arm, the servo motor, and thus we will focus on the analysis of the servo motor in this study. However, sensor attachment to such equipment is considered difficult due to the dynamic movement of the robot arm, meaning that internal instrumentation should be utilized during analysis. In addition, no definite measure to determine the degradation of the motor exists, and thus a new degradation index is proposed in this study. Therefore, in this study, the lifespan of the servo motor will be estimated through accelerated degradation testing methods based on a new system degradation assessment method, which estimates the fault of the system using observer-based residuals with encoder data obtained from internal instrumentation.

STATISTICAL ANALYSIS OF CONSTANT-STRESS ACCELERATED DEGRADATION TESTING WITH MULTIPLE PERFORMANCE PARAMETERS

For the long-life and highly-reliable product, accelerated degradation testing (ADT) method is an effective approach for evaluating life and reliability. However, most of previous researches have been focusing on the ADT method based on single performance parameter. The statistical analysis method of constant-stress ADT (CSADT) with multiple performance parameters based on Principal Component Analysis (PCA) and Support Vector Machine (SVM) is proposed in this paper. PCA is utilized to process the CSADT data in order to reduce the dimension of performance parameters. Then, SVM is applying in modelling the degradation process of the principal components. The engineering example proves that the method is feasible and efficient.

고분자 전해질 연료전지 스택에서 전해질막의 열화 가속시험

최근까지 고분자전해질 연료전지(PEMFC)의 열화연구는 대부분 단위전지에서 연구되었다. 그런데 실제 PEMFC의 구동과 열화는 PEMFC 스택에서 이루어진다. 그래서 본 연구에서는 스택에서 열화가속 시험을 진행하여 단위전지의 결과와 비교하였다. 여러 종류의 열화 가속 시험 중에서 전기화학적 열화와 기계적 열화를 반복해 고분자전해질 막을 열화시키는 방법을 사용했다. 312시간 동안 전해질막을 열화시킨 후 0.6V에서 전류밀도는 스택과 단위전지에서 각각 28.4%, 27.8% 감소했다. 수소 투과 전류밀도는 스택은 16.8% 단위전지는 15.2% 증가했다. 스택과 단위전지에서의 열화 가속 시험 결과가 비슷해 단위전지의 가속 시험 방법을 스택에 적용해도 됨을 확인하였다. Until a recent day, degradation of PEMFC (Proton Exchange Membrane Fuel Cells) has been mainly studied in unit cell. But operation and degradation of real PEMFC going along in stack instead of unit cell. Therefore in this work, ADT (Accelerated Degradation Test) of PEMFC was done in stack and the result from stack's test was compared with that of unit cell. The polymer electrolyte membrane was degraded by repeated electrochemical and mechanical degradation method among several ADT methods. Current densities of MEA at 0.6V decreased in stack and unit cell, 28.4% and 27.8% respectively after ADT for 312 hours. Hydrogen crossover current densities of membrane increased in stack and unit cell, 16.8% and 15.2% respectively after ADT for 312 hours. The result of ADT in stack was similar that of ADT in unit cell, which showed that ADT method of unit cell was available to the stack.

Degradation Mechanisms of Mid-Power White-Light LEDs Under High-Temperature–Humidity Conditions

More and more mid-power white-light LED (MP LED) solutions have been used in outdoor illumination due to their good performance, cost attractiveness, and low energy consumption as compared with conventional lighting solutions. Hence, there is a need for MP LED manufacturers to develop more robust MP LEDs aimed at outdoor applications but still offer a significant cost benefit as compared with currently widely used high-power LEDs. This implies that MP LEDs would be operated in an environment with high humidity and high temperature. This may lead to serious degradation with different failure modes compared with an indoor operation. However, the combined effect of temperature and humidity on the MP LED reliability has not been extensively studied in literature. In this paper, MP LEDs were studied by the wet high-temperature operation life (WHTOL) test in order to understand their degradation mechanisms due to the combined effect of temperature and humidity. It is found that encapsulant discoloration (yellowing) is the major degradation mechanism in the WHTOL test, which will induce serious lumen degradation and color shift. Furthermore, it has been found that electrical degradation in terms of forward voltage increase will also affect the lumen maintenance. Finally, statistical analysis shows that lumen degradation mechanisms in the WHTOL test are similar to a failure in the LM-80-08 test, demonstrating that the WHTOL test is an efficient accelerated degradation test method, which dramatically reduces the test duration compared with the LM-80-08 test.

Statistical analysis of accelerated degradation testing for old products with initial working time

Statistical analysis of accelerated degradation testing has been of interest to researchers and developers for some time. Relevant study on accelerated degradation testing mainly assumes that samples subjected to accelerated degradation testing are new products, with samples that have not pre-degraded and possess reliability equal to 1 at the beginning of accelerated degradation testing. Old products, which have a pre-existing period of initial working time under use stress, are occasionally selected for accelerated degradation testing in practice. Old products are usually considered for economical reasons, occasionally when new products are no longer manufactured. For the purposes of this study, samples of old products have been degraded to a reliability less than 1 at the beginning of accelerated degradation testing, thus preventing the use of current accelerated degradation testing methods. Improved accurate life prediction for old products is proposed through our models of degradation path and lifetime distribution for constant stress accelerated degradation testing. Initial working time under use stress is evaluated, and actual circumstances are described. A suggested maximum likelihood estimation approach is then detailed accordingly, by combining accelerated degradation testing data and field data to obtain a more accurate estimation for model parameters. Simulation and case studies prove the proposed method’s validity, effectiveness, and ability to accurately obtain improved life prediction for old products with initial working time using accelerated degradation testing.

Failure Mode and Effect Analysis of Composite Cathode on Anode-Supported SOFCs under the Accelerated Durability Testing

Compared to other-type of fuel cells, solid oxide fuel cells (SOFCs) have many advantages, such as higher efficiency and performance, environmental friendless, fuel flexibility and no use of precious metal catalysts [1]. For making the commercialization of SOFCs, however there is still forced to improve durability of components with high performance. In particular, researches for durability are only in the early stages, compared to the effort of developing materials to reduce operating temperature with enhanced performance.Recently, studies of SOFC durability have extended to understand main degradation mechanisms of components. The degradation phenomena of Ni cermets anode is often observed in low concentrations of hydrogen at high current density. Chen et al.[2] reported that the poor tolerance of Ni-ceria cermets may result in delamination of each layer of SOFC components by variation of anode volume. Other researchers examined that chemical reactions of LSM with YSZ during hot-temperature SOFC operations form insulating phases like SrZrO3 or La2ZrO7 [3, 4]. This phenomena lead to decrease SOFC performance with high polarization loss. The humidified air also occurs degradation of cathode materials because of variable hydration properties or formation of secondary phases [5, 6].In this study, degradation mechanisms of the neodymium doped ceria (NDC) based anode-supported SOFCs with cathodes related to perovskite structure are investigated by accelerated degradation testing methods. As the preparation of experiments, NiO-NDC cermets are used for anode substrates and NDC is synthesized by combustion process [7]. The NDC slurries are deposited on the substrate as an electrolyte. These green pellets are sintered at 1550 °C for 4 h with a 2 °C min-1 ramp rate in air. To compare influences of durability on the cathode materials, Ba0.5Sr0.5Co0.8Fe0.2O3- δ (BSCF) and Nd(Ba0.5Sr0.5)Co1.5Fe0.5O5+ δ (NBSCF) are prepared with NDC. The mixtures are screen-printed on anode-supported cells and sintered at 1150 °C for 2 h. A sintered cell is loaded on a reactor and sealed by glass rings.Durability of anode-supported SOFCs is investigated under various failure modes such as hydrogen and air depletion and highly humidified air. The experiments are carried out periodical turn- on/off of hydrogen (and air) in anode (and cathode) side under constant current density of 180 mA cm-2 at 650 °C. To find main degradation mechanism after failure tests, the impedance spectra and overpotential analysis are performed and the microstructure analysis is also carried out by SEM, TEM and XRD [8, 9]. Those experiments contribute to find design parameters for highly durable SOFC components.Lowering the Temperature of Solid Oxide Fuel Cells, E. D. Wachsman, and K. T. Lee, Science , 334, 935 (2011).Rapid degradation mechanism of Ni-CGO anode in low concentrations of H2 at a high current density, G. Chen, G. Guan, S. Abliz, Y. Kasai, A. Abudula, Int. J. Hydrogen energy,36, 8461 (2011).Microstructural studies on degradation of interface between LSM–YSZ cathode and YSZ electrolyte in SOFCs, Y. L. Liu, A. Hagen, R. Barfod, M. Chen, H. J. Wang, F. W. Poulsen, P.V. Hendriksen, Solid state ionics, 180, 1298 (2009).Effect of cathode gas humidification on performance and durability of solid oxide fuel cells, J. Nielsen, A. Hagen, Y. L. Liu, Solid state ionics, 181, 517 (2010).Fundamental mechanisms limiting solid oxide fuel cell durability, H. Yokokawa, H. Tu, B. Iwanschitz, A. Mai, J. Power sources, 182, 400 (2008).Hydration properties and rate determining steps of the oxygen reduction reaction of perovskite-related oxides as H+-SOFC cathodes, A. Grimauda, F. Mauvya, J. M. Bassata, S. Fourcadea, L. Rocherona, M. Marronyb, J. C. Grenier, J. the electrochemical society, 159, B683 (2012).Various synthesis methods of aliovalent-doped ceria and their electrical properties for intermediate temperature solid oxide electrolytes, G. Kim, N. Lee, K. -B. Kim, B. -K. Kim, H. Chang, S. J. Song, J. -Y. Park, Int. J. Hydrogen energy, 38, 1571 (2013).Polarization measurement of anode-supported solid oxide fuel cells studied by incorporation of a reference electrode, H. Xiao, T. L. Reitz, M. A. Rottmayer, J. Power sources, 183, 49 (2008).Reliability and accuracy of measured overpotential in a three-electrode fuel cell system, S. H. Chan, X. J. Chen, K. A. Khor, J. Applied electrochemistry, 31, 1163 (2001). * Corresponding authors: jyoung@sejong.ac.kr (J.-Y. Park).

Durability of Alkali‐Activated Materials: Progress and Perspectives

In the last decade, there has been rapid growth in interest in alternative binders, as part of the toolkit of cement technologies needed to mitigate the carbon footprint associated with the construction industry. Alkali‐activated materials (AAMs), including geopolymer binders and other related systems, have been identified as a key component of this move to lower CO2 cements and concretes. These are clinker‐free cements which can exhibit comparable performance to conventional portland/blended cements, when they are adequately formulated and cured. However, AAMs have a somewhat limited record of durability in service, and this is one of the main limitations facing their commercial adoption at present. To provide the best possible answers to the question of long‐term durability within an experimentally accessible timeframe, standardized accelerated degradation testing methods have been widely adopted, in an attempt to simulate natural processes. It has been identified that the interactions between material and environment, which take place on microstructural and nanostructural levels, have a very significant influence on the outcomes of the durability tests. Here, we present an overview of the results obtained when AAMs are exposed to aggressive testing conditions such as elevated concentrations of CO2, sulfates or chlorides. The key outcome of this article is a broader synthesis of the available data regarding the interactions between these new materials and their surrounding environment, which is then available to be used in the design, development, and implementation of environmentally sustainable, high‐performance cements and concretes for the 21st century.

The Durability Dependence of Pt/CNT Electrocatalysts on the Nanostructures of Carbon Nanotubes: Hollow- and Bamboo-CNTs

The electrochemical durability of Pt/CNT with hollow- and bamboo-structured carbon nanotubes (H-CNT and B-CNT) as the support for PEM fuel cells was investigated. Both Pt/CNT electrocatalysts were degraded under cyclic voltammetry (CV, 0.6-1.1 V) accelerated degradation test method. Pt/CNT electrocatalysts were characterized with cyclic voltammograms, rotating disk electrodes, and TEM images. The changes in the electrochemical surface area of Pt and the activity toward oxygen reduction reaction (ORR) before and after the degradation indicate that Pt/B-CNT catalyst exhibited much higher durability than Pt/H-CNT. TEM images indicate that the sintering of Pt nanoparticles was much less for Pt/B-CNT. Pt/B-CNT also exhibited a little higher activity toward ORR than Pt/ H-CNT. These are attributed to the specific bamboo-like nanostructures which provide more "bamboo-knot" defects and edge plane-like defects. Pt-support interaction was therefore enhanced and the durability and activity were improved.

Development of carbon/epoxy structural components for a high performance vehicle

Development of the carbon/epoxy body panels and structural components of the Lamborghini Murcièlago is discussed, while use of aerospace grade technology and materials is justified for this particular application. The influence of fiber architecture on the strength of a composite panel for the same fiber/resin system is discussed, with a focus on the two failure modes usually considered the most critical in designing with polymer composites, delamination and flexural failure. Investigation covers four prepreg tapes and two fabrics, and the use of woven laminates over directional tape is motivated. Resin impregnated carbon fiber components can offer a great deal of weight saving with respect to their predecessors in high performance sport cars, high grade steel and aluminum, yet, while decades of research in metal science have produced manufacturing techniques that guarantee perfect surface finish, alloys that can withstand weathering agents during the vehicle lifetime, and very reliable joining methods, these relatively new materials require constant evaluation in automotive applications to ensure equal if not greater performance than their metallic counterpart. Engineering solutions for tooling operations in order to achieve class A surface certification are summarized. Design for environmental aging as well as accelerated degradation testing methods such as ASTM D2247 Cleveland and weatherometer ASTM G26 are described. Development and implementation of hybrid adhesive bonding as sole method of joining the composite body components to the tubular steel chassis is reviewed.

Accelerated degradation test method for a-Si PV modules

Abstract The first-year degradation rate of P max (degradation in 1 year) and the seasonal behaviour of amorphous silicon photovoltaic modules are very important for the design of PV systems using them and for R&D of a-Si PV modules with small degradation and high stabilized efficiency. It is profitable to estimate them in a short time. We obtained accurate degradation data from periodical measurements using a solar simulator at standard test condition (STC) and we have analyzed aoutdoor exposure test data at Setagaya site in Tokyo. Paying attention to two main stresses of light intensity and sample temperature for electrical parameters of a-Si PV modules, we tried to establish a constant-stress accelerated degradation test method for a-Si PV modules by using a light-temperature combined accelerated test chamber and studied an applicability of light soaking.