Life Distribution Model Research Articles

Performance degradation and reliability analysis of a MEMS flow sensor with accelerated degradation testing

In this article, we research the performance degradation of a MEMS flow sensor with accelerated degradation testing (ADT). The degradation of temperature stress (Ts) on sensor is studied. Based on the performance in the aging test, resistance degradation ∆R is selected as a more suitable degradation characteristic parameter. Furthermore, the degradation process of the characteristic parameter results from resistivity decreases, in which Ts leads to stress relief within the bulk of the resistor. By implementing the Constant-stress accelerated degradation test (CSADT), we estimate the lifetime of this MEMS flow sensor based on the Arrhenius model. The calculated lifetime is 6.833 years for the 120°C group, 3.942 years for the150°C group, and 2.492 years for the180°C group. In addition, using statistics analysis, the Weibull distribution (WD) is proved to be the better mode for the MEMS flow sensor acceleration life with the Anderson-Darling (AD) being 235.910. The scale and shape of WD was evaluation. On the other hand, to verify the rationality of the distribution, the Standard residual error method and the Cox-Snell residual error method have been used separately, to perform the Goodness-of-fit tests. The AD value of Standard residual error and Cox-Snell residual error is 3.476. It proves that the selected life distribution model of this MEMS flow sensor is befitting. Finally, in this research the CSADT results are original and novelty. The lifetime distribution results reveal that considering the Goodness-of-fit tests can significantly improve the accuracy of reliability analysis of this MEMS flow sensor. Based on those results, a reliability method for this MEMS flow sensor is established.

Research on life distribution model of electrical protection cover for energy meter in charging pile based on accelerated test technology

The electric protection cover for the energy meter in the charging pile is an important part to protect the power line terminal and signal line terminal from being damaged by pollution. However, due to the complex and diverse environment in which the charging pile is located, it is easy to cause damage such as damage to electrical protection cover in high temperatures, high humidity, and other harsh environments, resulting in pollution and corrosion of electrical terminals, affecting normal electricity metering. To solve this problem, this paper studies the important factors that affect the life distribution of the electric protective cover used for energy meters in charging piles in the process of use. The accelerated stress model and method are constructed by the comprehensive application of the accelerated test theory, and the accelerated life test is completed. Through experiments, the failure time distribution of typical electrical protection covers for energy meters in a natural service environment is found, the model is hypothesized, tested, and estimated, and the key parameters of life distribution are determined. This paper also provides a good technical idea for the research of aging failure data analysis of electric plastic materials.

P‐7.7: Static Fatigue Fragment Life Analysis and Application of Curved Display Panel

In order to ensure the service life of the curved display panel, it is necessary to test and analyze the fatigue fragment life distribution of the curved display panel to predict the fragment rate of the product, and design the proof test scheme and life reliability test scheme. First of all, this paper has carried out Weibull test by 300pcs OC (open cell) samples of 27‐inch R1000 curved product. The Weibull life distribution parameters of the samples were obtained by fitting the test data (shape parameter k=0.337, size parameter λ= 1.86×108). Then, according to the requirement of customer (8000ppm fragment rate in 3 years), the proof test stress (σp=81.2 MPa) was calculated, and the life distribution model after proof test and zero failure reliability algorithm were derived. Finally, based on 90% confidence level (1‐α), life reliability test time (TL) and the number of samples (N), calculated the life reli ability test stress (σL=62.7 MPa) by reliability algorithm and life acceleration formula, determined the test scheme {TL, N, σL} and successfully passed the test verification. The static fatigue fragment life analysis method in this paper can accurately evaluate the fragments of curved display panel, guide the design and development of curved products, and effectively improve the reliability of curved display.

An aging‐intensity‐function‐based parameter estimation method on heavily censored data

AbstractBuilding life distribution models of key components of a product is a basic reliability problem. When the data for modeling are heavily censored, the conventional estimation methods such as maximum likelihood method and least square method are no longer applicable. Several approaches have addressed this issue and innovative methods are still needed. This paper presents such a method. It is based on aging intensity function (AIF) of a distribution. The proposed method consists of two main steps. In the first step, a semi‐parametric method is used to estimate the empirical AIF, which is further transformed into the shape parameter values. These values are then fitted to a distribution, from which the point and interval estimates of the shape parameter are obtained. In the second step, the point estimate of the shape parameter is fixed and a single parameter maximum likelihood method is used to estimate the scale parameter. Two examples that involve six datasets are included to illustrate the performance of the proposed method. The results show that the proposed method has an excellent performance in terms of simplicity, generality, accuracy, and unbiasedness.

Tensile fatigue behaviour and life distribution model of the pultruded fibre reinforced composites

Pultruded fibre reinforced composite (PFRC) can be used in oil drilling because of the corrosion resistance and energy conservation. The studies of fatigue behaviour and life distribution model are essential to the design and application of PFRC. In this paper, the tensile fatigue behaviour of PFRC was studied by the experiment combining with the acoustic emission technology, and the fatigue life distribution model is established to explore the distribution characteristics of fatigue life. The results show that, the fatigue load level has little effect on the failure modes of PFRC, and the matrix damage occurred firstly followed by the appearance of the delamination and the fibre damage. The proposed fatigue life distribution model can accurately describe the three stages of the fatigue life curve, and can well predict the fatigue life under different survival rates.

Applying User Surveys and Accelerated Tests Data to Estimate Reliability of New Consumer Products Using a Discrete Life Distribution Model

Assessing the reliability of consumer products that are subject to random discrete damage is critical during their design. Previous studies have approximated a continuous life distribution for consumer products by treating the occurrence (cycles) of accumulating damage as a continuous random variable. However, when the lifetime of a product is only a few damage cycles (e.g., ten drop cycles of a laptop), using a discrete lifetime distribution is more accurate. Using a discrete lifetime distribution is challenging because it contains a summation term with an unknown upper bound, which makes calculating its likelihood function cumbersome. This paper proposes a method to address this issue. First, the upper bound of the summation term is approximated through a gradient descent algorithm and the Maximum Likelihood Estimation method. Then, the upper bound is fixed, and the other parameters of the reliability model are estimated using Bayesian analysis. The paper presents a hypothetical case study that shows that using the discrete model leads to a more accurate estimation of product life when dealing with a small number of cycles.

Accelerated life reliability evaluation of grating ruler for CNC machine tools based on competing risk model and incomplete data

Grating rulers are high-precision linear displacement sensors used in the servo control system of CNC machine tools. Due to the long lifetime of these rulers, evaluating their reliability level by using traditional methods takes huge amounts of time and resources. Meanwhile, some incomplete data are observed in the failure data, which will cause inaccurate evaluation results. In this study, an accelerated life reliability evaluation method of a grating ruler based on a competing risk model and incomplete data is proposed. Firstly, according to the characteristics of the grating ruler, the life distribution model based on competitive risk is established. The representation and conversion methods of failure data, considering incomplete data, are also proposed. Secondly, the accelerated life test (ALT) system is set up, and the 4500 h step stress ALT is conducted. Results indicate that the reliability level of the grating ruler is MTBFt = 8864.12 h, and that of each subsystem is MTBFt(MS) = 13,351.98 h, MTBFt(OS) = 14,283.48 h and MTBFt(ES) = 17,038.65 h. The advantages of the proposed method are that it is helpful in determining the subsystem with the highest failure rate in each stage and puts forward targeted suggestions for subsequent improvement designs.

Reliability Life Estimation Considered fault Correlation of Aerial Bearing

The purpose of this paper is to study the reliability life calculation model of aerial rolling bearing considered the correlation of failure model. By mean of collecting relevant experiment data of vibration signal and temperature signal in the life test of the aerial rolling bearings, and analyse time domain and frequency domain, we can analyse the main failure modes and mechanism (e.g. wear, fatigue). The characteristic parameters that characterize the healthy state of aerial rolling bearings obviously are extracted further. Considering that the bearings expose multiple failure modes in the working process in most case, bearing fault diagnosis method is based on fuzzy theory. It is used to clarify the failure mechanism of different failure modes and the degradation rule of performance characteristic parameters. It’s very essential that establish the clear relationships between performance degradation and symptomatic set. According to the fault diagnosis results, each of failure modes is established the performance degradation model respectively. Considering the correlation between multiple different failure modes, Copula theory is introduced to analyse the correlation between multiple failure modes. Base on Copula theory, it’s obtained the life distribution model of aerial bearing based on multiple failure modes. Life distribution model are verified by subsequent experiments, which show that life distribution model of aerial rolling bearing in this paper, is feasible and necessary.

Prediction of Hydraulic Automatic Transmission Reliability Using Failure Data Based on Exponential Decay Oscillation Distribution Model

Aiming at the problem that the traditional reliability models of mechanical products are used to predict the reliability of hydraulic automatic transmission and the expected result is relatively large, firstly, the empirical distribution model line is used to statistically analyze the failure distribution law of the hydraulic automatic transmission; then, the Fourier transform is used to perform frequency domain analysis on experience distribution; on this basis, comprehensively consider the characteristics of experience distribution and frequency domain characteristics of experience distribution, constructs the reliability model of exponential decay oscillation distribution and the corresponding reliability, failure efficiency and average life calculation model; meanwhile, studies the influence of attenuation coefficient, oscillation amplitude, oscillation angle frequency, and other parameters on the probability distribution characteristics. On this basis, the established probability distribution models are adopted to fit the failure time data of hydraulic automatic gearbox carried by a forklift, and the fitting results are compared with exponential distribution models, three‐parameter Weibull models, and “bathtub curve” models. The comparing results show that the established exponential decayed oscillation distribution model can better describe the probability distribution characteristics of the fault‐free working time of automatic transmission, and the use of this model can obtain a smaller root mean square error. Simultaneously, the research conclusions of this paper can provide meaningful guidance and reference for the analysis of the life distribution model of mechanical products with exponentially attenuated oscillation probability density change law.

A distribution model of ultra-high cycle fatigue property based on crack density for braided CFRP

The microscopic observation and statistical investigation of matrix cracks are carried out through the ultra-high cycle bending fatigue experiment of braided CFRP (Carbon Fiber Reinforced Plastic) in this paper, and the matrix crack development law of CFRP under ultra-high cycle fatigue load has been studied. It is found that there are two different forms of matrix cracks under the ultra-high cycle fatigue load, and a bimodal distribution model of matrix crack density is established based on the distribution law of matrix crack density. At the same time, the ultra-high cycle fatigue life distribution model of braided CFRP is established based on the matrix crack density distribution model. At last, the corresponding fatigue life of CDS (Characteristic damage state) is obtained through the crack density evolution curve, and the life distribution model is verified.

Reliability analysis of the cutting tool in plasma-assisted turning and prediction of machining characteristics

ABSTRACT Heat-assisted machining (HAM) is an alternative method for the successful machining of difficult-to-cut aerospace superalloys. However, the tool wear progression in HAM has been substantially affected by the workpiece external heating temperature along with the machining parameters. It is of great importance to precisely estimate the tool wear progression and reliability of the cutting tool operated in HAM to enhance the machining efficiency and economics. Hardened AISI4340 alloy steel was machined under plasma-arc heating conditions with WC cutting tools. The experimental results reviled that for 200°C of preheating temperature, the surface roughness noted as 2.03µm and tool life as 870s. While at 600°C, the surface roughness as 1.68µm, and tool life extended to 1885s to reach the set threshold value of 0.4mm flank wear. Notch wear as dominant tool wear mechanism at 200°C and 400°C, while it is diffusion wear at 600°C. On the establishment of stochastic tool life distribution and reliability models, tool lives measured at all heating conditions followed a Weibull distribution. Empirical models for tool wear, surface roughness, and material removal rate were postulated and validated statistically as-well-as experimentally. The derived reliability and empirical models can be used to predict the machining characteristics to enhance its performance.

An experimental investigation of static and fatigue behaviour of GFRP sandwich beams with a web reinforced wood core

Three-point static and fatigue bending experiments were performed on 51 composite sandwich beams with glass fibre reinforced polymer (GFRP) face sheets and paulownia wood cores. Specimens with no lattice, one lattice and two lattices were prepared, and the fatigue bending failure mode, fatigue life distribution and stiffness degradation model of the sandwich beams were obtained. The results show that the specimens with no lattice exhibit two brittle failure modes, i.e., interface debonding and core shearing. The failure modes of the specimens with one lattice are local buckling and crushing, while the specimens with two lattice webs only exhibit tensile failure of the bottom face sheet. Moreover, the specimens with webs exhibit ductile failure characteristics. Based on the Weibull model, the Weibull distribution equations of each specimen under different survival rates were established, and the engineering fatigue curve was drawn. Furthermore, the secant stiffness curve of the specimens with webs was established based on the fatigue cumulative damage theory, and the fatigue lives of three specimens were predicted.

Experimental study of cutting-parameter and tool life reliability optimization in inconel 625 machining based on wear map approach

As a result of its excellent properties, nickel-base superalloy has been widely used in the manufacture of shaft-disc-type components for aeroengines. However, tool wear and short tool life are prominent problems related to the machining process, because of the poor thermal conductivity, high hardness, and strong cohesiveness of nickel-base superalloy. Therefore, optimization of both the processing parameters and tool life reliability is attracting increasing research attention. In this study, coated carbide tools are used in turning tests of Inconel 625 superalloy. The wear morphologies and mechanisms of these tools under different parameters are analyzed, and a two-dimensional tool wear map is constructed. The influence of the cutting parameters on the workpiece surface roughness and flank wear is analyzed with consideration of the wear map, so as to determine the optimal cutting parameters. On this basis, a complete tool life experiment is performed, and a tool life distribution model and tool life reliability model are established to facilitate tool life reliability evaluation under the optimal parameters. These findings provide theoretical support for process optimization in Inconel 625 machining.

A novel MTTF estimator and associated parameter estimation method on heavily censoring data

AbstractMany reliability and maintenance decision problems need to estimate mean‐time‐to‐failure (MTTF) of a particular product component and/or build its life distribution model as early as possible based on field failure data. The field failure data are often heavily censored. In this case, the exponential‐assumption–based method can considerably overestimate the MTTF, and the classical parameter estimation methods such as the maximum likelihood method (MLM) cannot provide robust estimates. This paper aims to address this issue through proposing a novel method to estimate the MTTF and life distribution parameters. The proposed method first derives a nonparametric estimator of MTTF based on the decomposition of the integral expression of the theoretical MTTF and sample statistical characteristics. The estimated MTTF is then combined with a two‐step single‐parameter MLM to estimate the distribution parameters. A numerical experiment is carried out, and a real‐world dataset is analyzed. The results show that the proposed method can provide accurate and robust estimates for the MTTF and distribution parameters. The method is applicable for any life distribution and offers practitioners an efficient tool for reliability analysis.

Accelerated Life Testing of Thermoplastic Polyurethane Encapsulants Used in Underwater Acoustic Sensor

The lifetime of thermoplastic polyurethane (TPU) encapsulants used in underwater acoustic sensor (UAS) was predicted using accelerated life testing (ALT). The TPU specimens for tensile and tear strength tests were aged at six different temperatures, and the strengths of the aged specimens were then measured. The measured tensile and tear strengths as a function of aging temperature were used as ALT data for the analysis of the TPU encapsulant lifetime using ReliaSoft’s ALTA software. For the analysis of ALT data, the acceleration models and the life distribution models in the ALTA software were combined. The maximum likelihood estimation (MLE) method was used to find the most reliable acceleration-life distribution model when interpreting ALT data for tensile and tear strengths. It reveals that the Arrhenius-Weibull distribution model best fits the ALT data of the TPU encapsulant. The lifetime of the TPU encapsulant for tensile and tear strength was estimated using the Arrhenius-Weibull distribution model. The estimated results exhibited that the lifetime for tear stress was much shorter than that for tensile stress at 25 °C. Tensile and tear stresses are applied simultaneously to the TPU encapsulant during UAS operation. Thus, its replacement time should be determined by its tear strength lifetime.

A novel parameter estimation method for the Weibull distribution on heavily censored data

It is desired to build the life distribution models of critical components (which are assumed to be non-repairable) of a repairable system as early as possible based on field failure data in order to optimize the operation and maintenance decisions of the components. When the number of the systems under observation is large and the observation duration is relatively short, the samples obtained for modeling are large and heavily censored. For such samples, the classical parameter estimation methods (e.g. maximum likelihood method and least square method) do not provide robust estimates. To address this issue, this article develops a hybrid censoring index to quantitatively describe censoring characteristics of a data set, proposes a novel parameter estimation method based on information extracted from censored observations, and evaluates the accuracy and robustness of the proposed method through a numerical experiment. Its applicable range in terms of the hybrid censoring index is determined through an accuracy analysis. The experiment results show that the proposed approach provides much accurate estimates than the classical methods for heavily censored data. A real-world example is also included.

Reliability calculation method based on the Copula function for mechanical systems with dependent failure

In order to accurately calculate the reliability of mechanical components and systems with multiple correlated failure modes and to reduce the computational complexity of these calculations, the Copula function is used to represent related structures among failure modes. Based on a correlation analysis of the failure modes of parts of a system, a life distribution model of components is constructed using the Copula function. The type of Copula model was initially selected using a binary frequency histogram of the life empirical distribution between the two components. The unknown parameters in the Copula model were estimated using the maximum likelihood estimation method and the most suitable Copula model was determined by calculating the square Euclidean distance. The reliability of series, parallel, and series–parallel systems was analyzed based on the Copula function, where life was used as a variable to measure the correlation between components. Thus, a reliability model of a system with life correlations was established. Reliability calculation of a particular diesel crank and connecting rod mechanism was taken as a practical example to illustrate the feasibility of the proposed method.

Fatigue Failure Analysis on Precracked 304 Stainless Steel Components Repaired by Laser with Addition of Nanocomposites

Abstract The service life of components can be extended by repairing fatigue crack with laser so as to improve resource utilization rate. However, the effect of laser repair may be influenced by the instability of laser treatment. To investigate the addition of nanocomposites on the laser repairing effect, fatigue test under uniaxial tension was carried out to evaluate the fatigue life of precracked 304 stainless steel components repaired by laser. According to the results obtained from fatigue tests, a probabilistic fatigue life distribution model considered the sampling size and discreteness of data was established based on the three-parameter Weibull distribution model and three-parameter stress-life equation. The results of probabilistic fatigue life distribution model show that the fatigue life of components repaired by laser with addition of WC nanocomposites can be enhanced significantly, especially the high cycle fatigue life. Moreover, the microstructure of repaired region show that the WC nanoparticles could refine the recrystallized grains and lead to the improvement of strength and toughness of material around crack tip, which are the main reason of improved fatigue life. Meanwhile, smooth surface of repaired region caused by WC nanoparticles can also prevent the initiation of microcracks.

Fatigue behavior of direct laser deposited Ti-6.5Al-2Zr-1Mo-1V titanium alloy and its life distribution model

The present work aims to investigate the fatigue behavior of Direct Laser Deposition (DLD) Ti-6.5Al-2Zr-1Mo-1V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5Al-2Zr-1Mo-1V titanium alloy standard cylinder specimens were tested under a stress level of 800 MPa with a stress ratio of 0.06. Fatigue fractography and fatigue life data were obtained. Through the fracture surface analysis, the specimens were divided into two categories in accordance with the location of crack initiation and defect types. Comparison of fatigue life and behavior between two specimen types was given, which was followed by a discussion about the impact of defect type, size and position on the fatigue life of the specimen. The fatigue test results also show a large variation of fatigue life. To illustrate the statistical characteristics of the fatigue life, probabilistic analysis was performed, and a novel bimodal lognormal model was established. The model has a good fit with the experimental data and can reduce the scatter of the fatigue life significantly.

Interval statistic based reliability analysis method on small sample hot test of satellite thruster

• Propose an interval statistic based reliability analysis method fulfilling the life information from the failure time to the censored time. • Improve the reliability assessment accuracy of satellite thrusters obviously. • Conducted the coating test under different thermal conditions. • Conducted reliability assessment and life prediction of the satellite thruster in both transfer and synchronous orbit phases. As one of the most important components of satellites, the thruster must maintain high reliability, but the assessment is difficult when lacking test failure data. When conducting hot test of the satellite thruster, we encountered the problem of reliability assessment on type-I censored data with only one failure, which is common for small sample tests. This paper proposes a novel interval statistic based reliability analysis method, which can fulfill the life information from the failure time to the censored time ignored by conventional methods, and improve the assessment accuracy. In this paper, a life distribution model is established by proper failure mechanism analysis and prior test information exploitation. As thrust chamber burning-through has been considered as the main failure mode, life test of the chamber coating was conducted under different thermal conditions to obtain the model parameter. Based on the interval statistic theory, a detailed derivation is illustrated. Then, reliability assessment and life prediction for the satellite thruster in both transfer orbit phase and synchronous orbit phase have been achieved, and the results show that our method performs very well, which provides an important way for dealing with test data with only one failure.