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Bearing is one of the critical components in rotating equipment. Therefore, accurate estimation of the remaining useful life (RUL) of bearings plays a vital role in reducing the costly unplanned maintenance and increasing the reliability of machines. This paper proposes a method for bearing prognostics that uses iteratively updated degradation regression models to capture the degradation trend in bearing’s health indicator (HI), and the models are utilized to predict the degradation trajectory of HI and to estimate the RUL of bearings. The importance of determining the time to start prediction by elbow point is explained, which is often overlooked in prognostics. To improve the prognostic performance, an adaptive approach for elbow point detection is designed based on the gradient change of HIs, and a new smooth approach is applied to reduce spurious fluctuations in degradation trajectory. The effectiveness of the proposed method is validated on two publicly available data sets, i.e., IMS and FEMTO bearing prognostics data set, and its prognostic performance is compared with that of three state-of-the-art methods. The obtained results demonstrate that the proposed method can effectively detect elbow point and determine the time to start prediction, and can calibrate the degradation regression model dynamically according to the evolving degradation trend in the HI, which validates its superior prognostic performance.

Welding is prone to several defects. To test the fatigue properties of the welded defective joints of high-speed rail bogies, SMA490BW steel cruciform welded joints were employed with artificial defects treatment. Consequently, fatigue tests were conducted on the specimens. Fatigue fracture morphology was studied via scanning electron microscopy. The ABAQUS (version 2022) finite element software was used to calculate the stress distribution and concentration factor of cruciform welded joints with defects. The results show that the fatigue limits of 1 and 2.4 mm defect specimens were approximately 57.2 and 53.75 Mpa, respectively. Furthermore, the stress concentration factor of no, 1 mm, and 2.4 mm defects were 2.246, 4.441, and 6.684, respectively, indicating that the stress concentration factor of 1 and 2.4 mm defects increased by 98 and 198%, respectively, with respect to the no-defect case.

In this paper, the precrack propagation behavior of an SMA490BW welded joint in the core zone and heat-affected zone was analyzed through experiments based on the FRANC 3D and ABAQUS cosimulation method, and life prediction of these cracks was also investigated. The results show that the experimental crack propagation path and crack propagation rate in the weld core zone and heat-affected zone agree well with the simulation results, with a small relative error. The life span of the prefabricated crack in the heat-affected zone was higher than that in the core zone. Furthermore, regarding the life prediction results for the two samples, the relative error obtained using FRANC 3D was about 5%, which was verified using the method of joint simulation of crack propagation behavior in the zone simulation and their life prediction with accurate feasibility.

The three-parameter Weibull distribution is one of the most widely used probabilistic models for the characterization of fatigue failure data. The linear regression estimation (LRE), the minimum discrepancy estimation (MDE), errors-in-variables estimation (EIV) as well as the least squares estimation (LSE) are generally applied in the estimation of Weibull parameters for their simplicity, in which probability estimators play an important role. In this paper, compared with five commonly used estimators, an optimal probability estimator with the four methods for different sample sizes is obtained by Monte Carlo simulations. The optimal probability estimator shows more robustness and higher accuracy. In conclusion, an optimal probability estimator of the midpoint rank is recommended for LRE, MDE and EIV especially with small samples in practical applications.

MYB98 is a key regulator of the genetic network behind pollen tube attraction toward the female gametophyte. MYB98 is specifically expressed in the synergid cells (SCs), a female gametophyte component cells specialized for pollen tube attraction. However, it had not been clear how exactly MYB98 achieves this specific expression pattern. In the current study, we have determined that a normal SC-specific expression of MYB98 is dependent on a 16-bp-long cis-regulatory element, CATTTACACATTAAAA, freshly named as the “Synergid-specificActivationElement ofMYB98” (SaeM). An 84 bp fragment harboring SaeM in the middle was sufficient to drive exclusively SC-specific expression. The element was present in a significantly large proportion of SC-specific gene promoters and in the promoter of MYB98 homologous genes in the Brassicaceae (pMYB98s). Significance of such family-wide SaeM-like element conservation in exclusive SC-specific expression was confirmed by the Arabidopsis-like activation feature of Brassica oleracea–derived pMYB98 and absence of such feature of pMYB98 derived from a non-Brassicaceae member Prunus persica. Additionally, the yeast-one-hybrid assay showed that the SaeM can be recognized by ANTHOCYANINLESS2 (ANL2) and DAP-seq data further suggested for additional three ANL2 homologs targeting the similar cis-element. Overall, our study has concluded that SaeM plays a crucial role in driving exclusively SC-specific expression of MYB98 and strongly suggests for the involvement of ANL2 and its homologs in its dynamic regulation in planta. Future study on the transcription factors is expected to shed more light on the mechanism behind the process.

The most applied principles for parameter estimation are maximum likelihood and least square error. This paper presents a new principle with regard to the parameter estimation of the three-parameter Weibull distribution. By transforming the cumulative distribution function, constructed is a mapping from the value of the random variable and its corresponding cumulative distribution probability to the scale parameter. The scale parameter estimated by such a mapping is the random variable value and the corresponding cumulative distribution probability dependent when the shape parameter and/ or location parameter applied in the mapping is subject to error. Given a set of random variable values or a set of sample values, a larger error in the shape/location parameter brings about larger differences between the scale parameter values obtained with the individual random variable values or sample values, respectively. Based on such a causal relationship between the discrepancy and the shape/ location parameter value applied in the mapping relation, a new parameter estimation method is proposed. For the Weibull distribution parameter estimation according to a set of sample values, the right shape parameter and location parameter are those minimizing the discrepancy between the scale parameter values obtained with the individual sample values, respectively. Case studies demonstrate that the proposed method outperforms the maximum likelihood method and the Weibull plot-based least squares method.

Industrial robots are widely used in various industrial fields, such as handling and welding, due to their good repeat positioning accuracy. The motion error determines the absolute accuracy. For robot design, dimensional parameter errors and drive parameter errors, a mathematical model of a kinematic exponential product with error screws was proposed. The influence of different rod lengths and transmission errors on the accuracy of the end motion was analysed. A composite analysis method based on screw theory and vector method is proposed for the spatial deflection error of robot rotating joints with clearance. By using screw theory, a mathematical error model of the axial movement and spatial deflection of the joint gap was established. A mathematical model of joint space radial movement was established by using the three-dimensional vector method. Through numerical simulation, the position distribution law of the random error of the robot terminal in the workspace and the distribution of the plane projection density were obtained. By solving the attitude matrix, the distribution of each Euler angle error was obtained. A simulation test was carried out to verify the model's correctness. The calculation showed that the method is simple and correct, and the obtained error distribution characteristics are of great significance to improving robotic kinematic calibration accuracy and optimising the spatial position error distribution.

Shot peening technology is used to improve the fatigue strength of materials and parts, and is one of the most effective surface engineering techniques to prolong fatigue life. In this paper, according to the finite element simulation analysis of shot peening, a randomly distributed multiple-shot finite element model was established. The superimposed effects of multiple projectile impact craters in shot peening are fully considered. The effects of shot velocity, shot peening angle and shot coverage on the residual stress field and surface roughness were studied. The alloy steel 20MnTiB, widely used in the automotive industry, was used as the raw material to process the specimens. The shot peening tests of different process parameters were carried out. The test results verified the correctness and accuracy of the random distribution model of multiple-shot. The shot-peening simulation model proposed in this paper allows a more accurate analysis of the effect of shot-peening parameters on the surface residual stress field and helps to quickly set the correct shot-peening process parameters. This paper further investigates the effect of shot peening parameters on fatigue life, providing a basis for the rational development of shot peening solutions.

High-speed trains have a large amount of ancillary equipment, which is suspended from the underside of the train by means of a suspension structure. Due to the large mass of the ancillary equipment, the suspension structure is subjected to various loads during train operation and there is a risk of fatigue failure. In this paper, the stress distribution at the suspension point and the lo-cation of the maximum stress point under load are investigated in detail based on actual test loads at the suspension point and finite element simulation analysis. In order to further investigate the fracture failure of the suspension points, experimental studies were carried out. Firstly, static strength tests were carried out to obtain the load–displacement curves of the structural members and to determine the fracture strength of the structure based on the displacement sensors, and secondly, fatigue tests at different stress levels were carried out to obtain the load–life curves of the structural members and to investigate the probabilistic load–life curves at different reliability levels. The test results show that the structural component has a high fracture strength of 65kN, while the conditional fatigue strength is relatively low, corresponding to a load level of 12.5kN at a median life of 106 cycles. The above research work provides the necessary basis for the design, optimization and reliability assessment of the suspension structures of high-speed trains.

The reliability of planetary equipment determines the economic affordability and service safety, to a large extent, for a helicopter transmission system. However, with the continuous improvement of the progressiveness and large-scale degree of new aviation planetary equipment, the contradiction between reliability design indexes and R&D economy is also gradually highlighted. This paper takes the large aviation planetary system as a research object, aims to accurately evaluate the system reliability level formed in design processes, and deeply excavates the inherent characteristics of the planetary system in functional realization and builds a system fatigue reliability evaluation model accordingly. An advanced hierarchical finite element technology is used to calculate dangerous tooth load histories under the influence of system global elastic behavior, and the tooth probability fatigue strength is obtained through the gear low-cycle fatigue test and life distribution transformation method, so as to provide economic load and strength input variables, respectively, for the reliability model. This prediction method can provide targeted structural optimization guidance in the development and design of the large aviation planetary system and significantly reduce the cost of reliability index realization for this kind of large-scale, high-end equipment in design iteration processes.

Objectives: We aimed to examine how COVID-19 incidence is associated with depressive symptoms in China, whether the association is transient, and whether the association differs across groups.Methods: We used a longitudinal sample from 2018 to 2020 waves of the China Family Panel Study. We constructed COVID-19 incidence rates as the number of new cases per 100,000 population in respondents’ resident provinces in the past 7, 14, and 28 days when a respondent was surveyed. We performed linear or logistic regressions to examine the associations, and performed stratified analyses to explore the heterogeneity of the associations.Results: Our sample included 13,655 adults. The 7-day incidence rate was positively associated with the CES-D score (coef. = 2.551, 95% CI: 1.959–3.142), and likelihood of being more depressed (adjusted odds ratio = 6.916, 95% CI: 4.715–10.144). The associations were larger among those with less education, pre-existing depression, or chronic conditions. We did not find any significant association between the 14- or 28-day local incidence rates and depressive symptoms.Conclusion: The impact of COVID-19 incidence on mental health in China’s general population was statistically significant and moderate in magnitude and transient. Disadvantaged groups experienced higher increases in depressive symptoms.

Objective We examined whether contraceptive method type, satisfaction with use, and confidence in correct use were independently associated with switching intentions, a precursor of switching behaviors. Study Design Data were from a probability-based sample survey carried out in Delaware and Maryland in 2016 and 2017 among women ages 18 to 44. Women's current contraceptive methods were classified into 5 categories: coitally-dependent methods (barrier methods, withdrawal, and natural family planning); oral contraceptive pills, patches, and rings; injections; implants; and intrauterine contraception (IUC). Satisfaction, confidence, and switching intentions were dichotomized into being very versus less satisfied, being completely versus less confident, and having very low versus not very low switching intentions. We conducted binomial logistic regression to examine whether method type, satisfaction, and confidence were independently associated with having very low switching intentions, adjusting for a range of covariates including sociodemographics, perceived health, religious attendance frequency, sexual, contraceptive, and reproductive experiences, and state of residence (Maryland or Delaware). Results Among 1,077 women using reversible contraception, those using IUC relative to implants, pills, patches, or rings, and coitally-dependent methods were more likely to have very low switching intentions. Among all survey respondents, those who were very satisfied and those who were completely confident in correct use were also more likely to report very low switching intentions. Conclusions Using IUC, being very satisfied, and being very confident in correct use were independently associated with having very low switching intentions. Implications These results suggest that those using IUC have very low intentions to switch for reasons in addition to satisfaction-level with their method. Other aspects of using IUC such as ease of use, perceived barriers to switching, or having very low switching intentions before beginning IUC may be such reasons.

Objective Assess the impact of the Be Your Own Baby (BYOB) public awareness campaign including population-level exposure, the effectiveness of ad platforms, and the effect of the campaign on family planning clinic attendance, the campaign's primary goal. Data sources The study relied on administrative data on traffic and engagement from the campaign's website, population survey data measuring campaign exposure, and clinic attendance volumes from state-by-year restricted-use versions of the Office of Population Affairs' Family Planning Annual Reports (2006-2018). Study design Bivariate analyses were used to assess website traffic and engagement and population-level exposure across key subgroups. We then used the synthetic control method to examine the impact of the BYOB campaign on per capita Title X clinic attendance among the target demographic, women 18-29 years of age. Data collection/extraction methods Not applicable. We relied on secondary sources. Principal findings Primary media platforms used by the campaign included social media, digital display, streaming audio, YouTube, and search. Website traffic was driven primarily by digital display ads, but engagement was highest for search. Our results suggest nearly 12% of Delaware women 18-29 years of age were exposed to the campaign. However, exposure was measured at the end of the campaign and was likely much larger during its peak. Our results indicated that the campaign was associated with between 13 and 23 additional Title X clinic visits per 1000 women compared with 110 users per 1000 at baseline in 2014. Conclusions Our findings suggest the BYOB campaign was successful at increasing clinic attendance among the target demographic. These results have important implications for other programs seeking to use public awareness messaging to increase participation in the health care system and are especially important for Title X administrators who have faced declining patient volumes for over 10 years.

ObjectiveAs elderly parents today will share a longer life with their children than ever before, the spillover effects of children’s human capital on parents’ well-being become increasingly important. This study investigated whether children’s schooling leads parents to give up smoking and whether the effects were moderated by their education or child–parent contact frequency.MethodsUsing data from the China Health and Retirement Longitudinal Study, we conducted an instrumental variable (IV) analysis using China’s compulsory schooling reform in the 1980s as a natural experiment.ResultsThe IV estimates suggest that elderly parents of more highly educated children are more likely to quit smoking. Moreover, the effects are more significant among parents who had not finished primary school and also slightly stronger among parents who live close to their children or meet their children frequently.DiscussionOur findings add to current evidence regarding spillover effects of education on smoking cessation. A child’s education may exert an impact through the spillover of health knowledge.

As a core strategic technology industry, the wind power plays an important role in protecting national energy reserves. The large gear component is one of the core foundation parts in wind turbines, and its quality indexes greatly affect the service performance of the wind turbine drive chain and even the wind turbine as a whole. This paper calculates the fatigue load history of the wind power large gear system under the coupling mechanism of elastic behavior based on a multidimensional finite element method, and obtains the probabilistic fatigue strength of gear teeth through the gear low circumference fatigue test and life distribution transformation method, and deeply explores the inherent characteristics of the wind power gear system in functional implementation and then establishes a system fatigue reliability evaluation model. Finally, a mapping path from the global structural elements of the wind power gearbox to the reliability indexes of the gear system is constructed with significant simulation and test cost advantages. It can provide structural optimization guidance in the development and design of large wind power gear systems, and significantly reduce the cost of achieving reliability indexes in the design iterations of such large high-end equipment. At the same time, it can provide cost-effective training data for intelligent optimization algorithms such as the deep reinforcement learning, which will eventually achieve multi-objective optimal stiffness matching for wind power gearboxes under reliability index constraints.

Objectives We aimed to estimate the association of sleep, sedentary activity and physical activity with cognitive function among older adults, with consideration of the competing nature between variables of activity status. Design Cross-sectional study. Methods A total of 3086 older adults (60 years or older) in the 2011–2014 National Health and Nutrition Examination Survey were included. The Global Physical Activity Questionnaire was used to measure self-reported time for sedentary activity, walking/bicycling and moderate-to-vigorous physical activity (MVPA). Cognitive function was examined using the CERAD Word Learning subtest (memory), Digit Symbol Substitution Test (executive function/processing speed), and Animal Fluency Test (language). Sleep duration was obtained via interview. Isotemporal substitution models using multivariable linear regression were applied to examine the associations of replacing sleep, sedentary activity, walking/bicycling, MVPA with each other and cognitive function, stratified by sleep duration per night (≤7 h, >7 h). Results Among participants with sleep duration ≤7 h/night, replacing 30 min/day of sedentary activity with 30 min/day of MVPA or 30 min/day was associated with better cognition. Among participants with sleep duration >7 h/night, replacing 30 min/day of sleep with 30 min/day of sedentary activity, walking/bicycling, or MVPA was associated with better cognition. Conclusions Replacing sedentary activities with MVPA was associated with favorable cognitive function among older adults sleeping no longer than 7 h/night, and replacing excessive sleep with sedentary or physical activities was associated with favorable cognition. Future research is expected to examine the associations of replacing different activity status on long-term cognitive outcomes in longitudinal studies.

Three-parameter Weibull distribution is one of the preferable distribution models to describe product life. However, it is difficult to estimate its location parameter in the situation of a small size of sample. This paper presents a stochastic simulation method to estimate the Weibull location parameters according to a small size of sample of product life observations and a large amount of statistically simulated life date. Big data technique is applied to find the relationship between the minimal observation in a product life sample of size n (n ≥ 3) and the Weibull location parameter. An example is presented to demonstrate the applicability and the value of the big data based stochastic simulation method. Comparing with other methods, the stochastic simulation method can be applied to very small size of sample such as the sample size of three, and it is easy to apply.

The initial angular misalignment due to mounting error is unavoidable and uncertain during the application of rolling element bearings. The effects of the uncertainty of the initial angular misalignment on fatigue life of angular contact ball bearings and spindle system are investigated. To achieve this, the contact forces of ball bearings in spindle system are analyzed based on the system model considering initial angular misalignment and spindle speed. Two initial angular misalignment cases are taken into account, and the angular misalignment sample is extracted for each case by Monte carlo sampling method. The fatigue life results for each ball bearing are obtained. The results show that the uncertain initial angular misalignment can lead to the rating life dispersion of ball bearings and the degree of rating life dispersion is related to the angular misalignment case and spindle speed. Based on the reliability theory of series system, the spindle system rating life is obtained, the probability density distribution and cumulative distribution are both presented. The results show that two angular misalignment cases produce significantly different effects to the rating life and fatigue life distribution of spindle system.

As the power source of an aircraft, aero-engine tends to meet many rigorous requirements for high thrust-weight ratio and reliability with the continuous improvement of aero-engine performance. In this paper, based on the order statistics and stochastic process theory, an improved dynamic load-strength interference (LSI) model was proposed for the reliability analysis of aero-engine rotor blade system, with strength degradation and catastrophic failure involved. In presented model, the “unconventional active” characteristic of rotor blade system, changeable functioning relationships and system-component configurations, was fully considered, which is necessary for both theoretical analysis and engineering application. In addition, to reduce the computation cost, a simplified form of the improved LSI model was also built for convenience of engineering application. To verify the effectiveness of the improved model, reliability of turbojet 7 engine rotor blade system was calculated by the improved LSI model based on the results of static finite element analysis. Compared with the traditional LSI model, the result showed that there were significant differences between the calculation results of the two models, in which the improved model was more appropriate to the practical condition.

The three-parameter Weibull distribution is popular in reliability analysis. However, in the context of a small sample size, the issue of parameter estimation of the three-parameter Weibull distribution is difficult to address. If only a small sample size is available, a reasonable method is to empirically determine the shape parameter, and the emphasis is placed on location parameter estimation. This paper presents a theoretical model to establish the relationship between the location parameter, the minimal sample value, and the sample size. Moreover, an iterative method is proposed to estimate the Weibull location parameter and scale parameter with an empirical value for the shape parameter. Compared with the maximum likelihood method (MLE), the Weibull plot with the sample correlation coefficient and TL-moment, the proposed method can more effectively estimate the parameters of the three-parameter Weibull distribution.

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Objectives. To measure changes in the contraceptive methods used by Title X clients after implementation of Delaware Contraceptive Access Now, a public–private initiative that aims to increase access to contraceptives, particularly long-acting reversible contraceptives (LARCs). Methods. Using administrative data from the 2008–2017 Family Planning Annual Reports and a difference-in-differences design, we compared changes in contraceptive method use among adult female Title X family planning clients in Delaware with changes in a set of comparison states. We considered permanent methods, LARCs, moderately effective methods, less effective methods, and no method use. Results. Results suggest a 3.2-percentage-point increase in LARC use relative to changes in other states (a 40% increase from baseline). We were unable to make definitive conclusions about other contraceptive method types. Conclusions. Delaware Contraceptive Access Now increased LARC use among Title X clients. Our results have implications for states considering comprehensive family planning initiatives.

The effect on curing deformation and strength of 90° plies in stringers for composite T-shaped stiffened panel were presented by numerical analysis and experimental measurement. In this work, the finite element model (FEM) for curing deformation based on cure kinetics formulation was utilized. The model for buckling and failure based on Tsai-Wu failure criteria and incremental/ Newton -Raphson mixed iteration equation was established. The curing, buckling and post-buckling analysis were performed on composite T-shaped stiffened panels to obtain the deformation, the critical load and mode of failure, with different 90° plies-ratios in stringers. Furthermore, the experimental investigation has been carried out for specimens with different plies-ratios of 90° plies in stringers. The good agreement between the numerical results obtained by finite element method and the experimental ones demonstrated that this kind of numerical analysis could estimate appropriately the behavior of the structure. In addition, it was found that the 90° plies in stringers play an important role in reducing the curing deformation, but it has little effect on the axial compression loading capacity for composite T-shaped stiffened panel, which is useful for application in civil aviation aircraft.

This paper develops an improved dynamic reliability model for compressor rotor system, defined as a “unconventional active system” here. First, regarding to the variety of system-component connections, system specific reliability modeling technique is presented, in which the stress and strength are both nonnegative stochastic processes. The new model fully considers the load characteristics of rotor blades, and inherently embodied the effect of the statistical dependence between the failures of the rotor blades. Then, calculated by the new model, the relationship between reliability and time, and that between the hazard rate and time, for a compressor rotor system are discussed, respectively. Comparing to the traditional series system reliability model, the new system reliability model developed in this paper has higher accuracy for compressor rotor system, since the traditional models neglect the difference between compressor rotor system and traditional active system. Moreover, in order to master the cruise characteristics of the aero-plane during reliability analysis of its compressor rotor blade set, a flight cruise is separated into several stages based on the value of Mach number and its change rate, and a subsection solution method is innovatively proposed accordingly. At the end of the paper, a certain cruise of fighter plane is analyzed to verify the accuracy of the new method. The results show that, as to a flight cruise with different stages, the new method is basically reasonable to most of the load histories, especially for the situation with impact loads existing.

Generalized reliability models and failure rate models of mechanical systems are developed in this paper according to the system working mechanism, which take the design parameters as input. The models consider strength degradation and imperfect maintenance. Besides, the models take into account the failure correlation caused by homologous load effect and the maintenance correlation owing to group maintenance. Unlike traditional reliability models, the models do not rely on empirical assumptions when considering failure correlation and maintenance correlation and have clear physical meaning. Moreover, the correctness and effectiveness of the models are verified by Monte Carlo simulations. Finally, the influences of failure correlation and maintenance correlation on generalized reliability, the influences of failure correlation on maintenance correlation, and the influences of maintenance correlation on failure correlation are analyzed via numerical examples. The results show that failure correlation and maintenance correlation have great influences on generalized reliability, and the interaction between the two correlation shows obvious time-varying characteristics.

An “index stress” (a constant amplitude cyclic stress) is introduced to characterize the scatter of the fatigue life under a variable amplitude load history. It is defined as a fatigue damage weighted average of the amplitudes of the individual stress cycles in a variable amplitude load history. The fatigue test results show that the scatter of fatigue life under variable amplitude load histories can be well characterized by such defined index stress. For probabilistic fatigue life prediction and failure probability estimation, a multiple-site damage structural part is taken as a series system, and the total probability theorem is applied to reflect the effect of load history uncertainty on failure probability.

It has been previously noted that the development of aerospace material technology and breakthroughs are inseparable when obtaining great achievements in the aerospace industry. Materials are the basis and precursor of modern high technology and industry. As one of the most powerful aluminium alloys, 7050 is widely used in the aerospace field. In this manuscript, the vibration fatigue behaviour of aircraft aluminium alloy 7050 is studied based on experiments. A vibration fatigue experiment and the traditional fatigue testing of aluminium alloy 7050 were performed. We found that there was an extreme difference between the vibration fatigue and the traditional fatigue curves. In addition, the experimental end criteria for the vibration fatigue experiment of aluminium alloy 7050 was obtained from the acceleration reduction and the frequency reduction value. For the acceleration experimental end criterion, 2% was the acceleration reduction value for the vibration fatigue experimental end criteria of aluminium alloy 7050. For the frequency experimental end criterion, 2% was the frequency reduction value for the vibration fatigue experimental end criteria of aluminium alloy 7050.

Friction has a vital role in studying materials’ and systems’ behavior. The friction between two objects and the inner friction of materials under the condition of vibration usually can present different characteristics. These characteristics are different from the conventional conditions. It is shown in practice that vibration can reduce the friction coefficient and friction force between two objects. Vibration can lighten abrasion of objects and reduce energy consumption. All of these can give great efficiency, but, until now, the vibration friction-reducing mechanism has not been fully revealed. In this manuscript, the friction-reducing mechanism of materials under arbitrary vibration forces is investigated. The results show that the effective friction coefficient of materials under arbitrary vibration forces is always the minimum. The relationship between the effective friction coefficient and the negative gradient is investigated in this research. When the vibration force direction projects are in the first and the third quadrants, the negative gradient of the effective friction coefficient gets larger slowly, and then it becomes stable. When the vibration force direction projects are in the second and the fourth quadrants, the negative gradient of the effective friction coefficient decays to zero at the initial stage and then increases rapidly.

According to the motion characteristics of Axial-Symmetric Vectoring Exhaust Nozzle (AVEN), its motion process is divided into the convergence deflection of the adjusting piece of the A8 sub-mechanism and the expansion deflection of the adjusting piece of the A9 sub-mechanism. Taking the A9 sub-mechanism as an example, proposing a method based on Solidworks-Abaqus-Adams multi-software platform to establish a rigid-flexible coupled parametric model and run the motion simulation model to analyze the influence of different factors on the motion accuracy of the mechanism. Basing on the Monte Carlo sampling algorithm to design a program of automatic sampling solution that is separated from Adams platform. Under the condition of meeting certain accuracy requirements, the degree of automation in the sampling process is greatly improved. Finally, the probability distribution of the performance parameters of the A9 mechanism is obtained, and its reliability is calculated. The research results show that when considering various influencing factors, the motion accuracy of the mechanism will have corresponding deviations, which will have a certain impact on the reliability of the mechanism.

Aiming at the problem of motion accuracy caused by dispersive dispersion in the design of the aero-engine rear variable area bypass injector, a multi-body dynamics model mapping dimension tolerance, part flexibility, and collision contact is established based on multi-body dynamics theory and ADAMS. The simulation results are verified with the theoretical solution, which is calculated in MATLAB to ensure the correctness of the simulation’s results. The effect of key design variables on the motion accuracy of the mechanism is analyzed by the parametric module. The reliability calculation method is studied based on the improved Latin hypercube Monte Carlo method mapping the dimension dispersion. The method provides the relevant basis for the structural design of the RVABI.

The fatigue strength of a component is known to highly depend on its surface quality, and it is thus necessary to develop a reliable and appropriate mathematical model for fatigue strength assessment that consider the effect of surface roughness. In this paper, different underlying physical mechanisms of the roughness effect at different regions of specimens were studied by fatigue testing of 7N01 aluminum alloy. For a quantitative analysis of the surface roughness effect, a revised stress field intensity approach for a fatigue strength assessment of microsized notches was proposed as a theoretical support. In the new model, a new form of weight function was built to adapt the characteristics of microsized notches. In addition, the effect of the field radius was fundamentally weakened on solution of the stress field intensity and the difficulty of fatigue failure region definition in the traditional method was overcome correspondingly in the proposed model, which made the calculated field strength accurate and objective. Finally, to demonstrate the validity of the revised approach quantitatively, specimens with conventionally sized notches were subjected to stress field intensity calculations. The results showed that the revised approach has satisfactory accuracy compared with the other two traditional approaches from the perspective of quantitative analysis.

Importance measures, which are used to evaluate the relative significance of various components to system reliability, have been widely applied in system reliability designs and risk assessments. This article deals with the importance measure for the k-out-of- n system of which components are loaded by common stress. Based on system-level stress–strength interference model, a new computational method for the Birnbaum importance measure is proposed for the k-out-of- n system. Then, two numerical examples are presented to further illustrate the proposed method and some key contents are discussed particularly as follows: (1) the importance measures for the system with s-identical components and nonidentical components are developed, (2) component importance changes as its own strength distribution parameters change and (3) the new method corrects the errors caused by ignoring the failure dependency.

The gear transmission system is a typical time-domain series system, and its fatigue reliability evaluation under variable amplitude loading has long attracted the interests from scholars. The widely used Monte Carlo (MC) method to evaluate the reliability of a system with material and load uncertainties is time consuming, especially when used in combination with a fatigue analysis software. Concerning this problem, this paper proposes a “deterministic damage-random threshold (DDRT)” reliability model. The model converts the randomness from damage to the threshold, thus saving time because only the median damage and the damage for key reliability of each fatigue part are required in reliability evaluation. Based on this model, a reliability calculation flow of a gear transmission system is proposed considering the time-domain characteristic of gears. Finally, the model is verified by numerical examples and the fatigue test data of gears.

BACKGROUND. Title X supports access to family planning and preventive care services. Given its focus on low-income clients, Title X clinics may have been particularly affected by the Affordable Care Act’s Medicaid expansion. OBJECTIVES. To examine the impact of the Affordable Care Act’s Medicaid expansion on Title X client volumes, health insurance coverage, and contraceptive method mix. RESEARCH DESIGN. A difference-in-differences design compared changes in the outcomes of interest before and after expansion, for expansion versus non-expansion states. SUBJECTS. Administrative data from Family Planning Annual Reports that describe Title X clients who sought services. MEASURES. Female client volume was measured using a participation ratio defined as the number of female clients per 100 women age 15–44 with incomes less than 250% of the federal poverty line. We also examined the share of clients by insurance type and contraceptive method type. RESULTS. We did not find evidence that expansion was related to changes in client volume. We did find a significant 9.9 percentage point increase in the share of clients with Medicaid and a significant 10.0 percentage point decrease in the share of clients without coverage. We found suggestive evidence that expansion was associated with increased use of long-acting reversible contraceptives, but those esults were somewhat sensitive to model specification. CONCLUSIONS. Expansion was associated with meaningful increases in Medicaid coverage at Title X clinics and declines in uninsurance. Our results have important implications for the financial stability of Title X clinics in light of historical declines in Title X grant revenues.

A failure analysis was performed to determine the causes of a crack on a high-speed train bolster, which was observed after an accelerated corrosion-fatigue test. The nominal stress method was used to evaluate the crack initiation life. The crack is not the result of a deficient design or geometry defects, for the theoretical lifetime of the bolster is more than 1 × 107 load cycles. The fracture surface was observed by the scanning electron microscope, and the crack source was determined to be the micro-holes caused by welding defects. The fracture mechanics method was employed to examine the crack propagation life, and it only occupied about 0.55% of the whole test time. Thus, after operating for 10 years, this bolster could provide safe service for another 20 years. Meanwhile, advanced welding technology or more welding inspection is suggested to prevent and detect the similar cracks.

Conventional reliability models of belt drive systems in the failure mode of fatigue are mainly based on the static stress strength interference model and its extended models, which cannot consider dynamic factors in the operational duration and be used for further availability analysis. In this paper, time-dependent reliability models, failure rate models and availability models of belt drive systems are developed based on the system dynamic equations with the dynamic stress and the material property degradation taken into account. In the proposed models, dynamic failure dependence and imperfect maintenance are taken into consideration. Furthermore, the issue of time scale inconsistency between system failure rate and system availability is proposed and addressed in the proposed system availability models. Besides, Monte Carlo simulations are carried out to validate the established models. The results from the proposed models and those from the Monte Carlo simulations show a consistency. Furthermore, the case studies show that the failure dependence, imperfect maintenance and the time scale inconsistency have significant influences on system availability. The independence assumption about the belt drive systems results in underestimations of both reliability and availability. Moreover, the neglect of the time scale inconsistency causes the underestimate of the system availability. Meanwhile, these influences show obvious time-dependent characteristics.