Experimental Study on Mechanical Characteristics of PTFE Material

An innovative approach for predicting the reliability of a structure that is subject to a variable‐amplitude dynamic load is presented. In this approach, a Gassner durability curve with its scatter is modelled using a 2‐parametric Weibull's probability density function (PDF). The trend of the Gassner durability curve is modelled with a general hyperbola equation in a log‐log scale. The hyperbola equation is applied to represent the durability curve for the 63.2% probability of fatigue failure that describes the dependency of the Weibull's scale parameter on the loading spectrum's maximum stress. Equations are derived to link the parameters of the hyperbola curve to the material's S‐N curve and the loading spectrum. The Weibull's shape parameter is estimated from the scatter of the material's S‐N curve. The proposed Gassner‐curve model is applied to calculate the fatigue reliability from the PDF of the loading spectrum's maximum stress and the PDF of the durability‐curve's amplitude stress for the selected number of loading‐cycles‐to‐failure.

The fracture behavior of Si-Ti-C-O fiber-bonded ceramic composite produced by hot-pressing oxidized 8 harness-satin-woven Si-Ti-C-O fibers was investigated by using unnotched and double edge notched tensile test specimens with different width (8 and 40 mm). The main results are summarized as follows. (i) The tensile strength of unnotched specimens for 8 mm width was higher than that for 40 mm width. Such a width-dependence of the unnotched strength could be described fairly well from the viewpoint of effective volume by application of the experimentally estimated Weibull's shape parameter. (ii) The applicability of the fracture toughness criterion (fracture arises when the stress intensity factor reaches the critical value) and net section stress criterion (fracture arises when the strength of the ligament reaches the unnotched strength) to the present composite was examined. The fracture strength of a notched specimen for 8 mm width was described by the net stress criterion. On the other hand, the strength for 40 mm width obeyed the net stress criterion for a small notch length but it shifted toward the fracture toughness criterion for large one. The shift of the fracture criterion from net strength- to fracture toughness-criterion arose around at the relative notch length 0.2 (notch length 8 mm), corresponding to periodical spacing of fiber strands (8 harness). (iii) The fiber pull-out length (0.4 mm on an average) was nearly the same as the half length of the fiber strand whose deformation is not constricted by the other strands in the satin-weave. (iv) The present fiber-bonded ceramic composite is insensitive to notch under the condition where the width of specimen is narrow and the notch length is smaller than 8 mm. This composite could be therefore applicable to industrial objects safely when the objects are designed as to satisfy the notch-insensitive condition.

Introduction and objectives Cough frequency is known to correlate well with perceived cough severity and is commonly used as an endpoint to evaluate the efficacy of new anti-tussive agents. However, little is known about the distribution of cough and its impact on cough severity. The Weibull distribution is a probability distribution model often used to predict time between events, as applied in COPD exacerbations. The shape parameter describes if coughs are more or less likely to occur over time. We investigated if cough temporal distribution is modulated by an effective anti-tussive agent (morphine) and how this distribution influences perceived cough severity. Methods Cough recordings, made using the VITALOJAK™ cough monitoring system were analysed from 22 chronic cough patients (18 female, mean age 61.7 years, mean cough duration 14 years) who had participated in a previously reported randomised controlled trial of low dose morphine sulphate. Coughs were identified and the cough intervals recorded and fit to an exponential (random) and Weibull distribution. The goodness of fit was checked with the Akaike information criterion (AIC). The shape parameter was calculated and using generalised estimating equations compared for morphine versus placebo. Relationships between cough severity visual analogue scale (VAS), cough frequency and the shape parameter were also explored. Results The AIC indicated that cough distribution better fitted the Weibull equation than the exponential in 38/41 (93%) recordings. The Weibull shape parameter was significantly reduced by morphine compared with placebo (geometric mean 0.418 versus 0.548, p=0.04), suggesting more coughs occurred early, with a fall in the rate of subsequent coughs over time with morphine. Furthermore, cough severity VAS was significantly predicted by a combination of cough frequency (p Conclusions In chronic cough patients, low dose morphine, in addition to reducing cough frequency may also reduce the temporal clustering of cough events. This may be important as temporal clustering appears to be a component of perceived cough severity, independent of cough frequency.

Article history: Received 1 January 2010 Received in revised form 8 June 2010 Accepted 9 June 2010 Available online 9 June 2010 This paper conducts a simulation study of the effects of violating the ANOVA normality assumption in the presence of Weibull data. Twelve specific Weibull distributions, characterizing the life data of a variety of real-world products and systems, are investigated. Confidence intervals on test significance and power are generated and compared against intervals from normally distributed data. The ANOVA procedure is found to be robust in the majority of cases. Furthermore, a designed experiment is conducted to isolate the effects of the Weibull shape and scale parameters within the preceding study. The shape parameter is found to have a significant effect on significance and power, whereas the scale parameter does not have a significant effect at the target α = 0.05 test significance level. © 2010 Growing Science Ltd. All rights reserved.

Today, most electrical energy is generated by burning huge fossil fuels and special weather conditions such as acid rain and snow, climate change, urban smog, regional haze, several tornados, etc., have happened around the whole world. It is now clear that the installation of a number of wind turbine generators can effectively reduce environmental pollution, fossil fuel consumption, and the costs of overall electricity generation. Although wind is only an intermittent source of energy, it represents a reliable energy resource from a long-term energy policy viewpoint. Among various renewable energy resources, wind power energy is one of the most popular and promising energy resources in the whole world today. At a specific wind farm, the available electricity generated by a wind power generation system depends on mean wind speed (MWS), standard deviation of wind speed, and the location of installation. Since year-to-year variation on annual MWS is hard to predict, wind speed variations during a year can be well characterized in terms of a probability distribution function (pdf). This paper also addresses the relations among MWS, its standard deviation, and two important parameters of Weibull distribution. The wind resource varies with of the day and the season of the year and even some extent from year to year. Wind energy has inherent variances and hence it has been expressed by distribution functions. In this paper, we present some methods for estimating Weibull parameters, namely, shape parameter ( k ) and scale parameter ( c ). The Weibul distribution is an important distribution especially for reliability and maintainability analysis. The suitable values for both shape parameter and scale parameters of Weibull distribution are important for selecting locations of installing wind turbine generators. The scale parameter of Weibull distribution also important to determine whether a wind farm is good or not. The presented method is the analytical methods and computational experiments on the presented methods are reported.

Introduction Assessing objective measures of sleep fragmentation could yield important features reflecting impaired sleep quality in people with insomnia. Survival analysis allows the specific examination of the stability of NREM sleep, REM sleep and wake. The objective of this study was to assess the differences between survival dynamics of NREM sleep, REM sleep and wake between people with insomnia and healthy controls. Methods We analyzed polysomnography recordings from 88 people with insomnia and 92 healthy controls. For each participant, survival dynamics of REM sleep, NREM sleep and wake were represented using Weibull distributions. We used lasso penalized linear regression to analyze the difference between participant groups with respect to the Weibull scale and shape parameters, while correcting for age, sex, total sleep time and relevant interaction effects. Because comparisons were done for scale and shape parameters of REM sleep, NREM sleep and wake, a Bonferroni correction was applied, resulting in an alpha value of 0.05/6 = 0.0083. Results Significant effects of group were found for the NREM scale parameter (unstandardized model coefficient B=-0.79, t=-3.0, p=0.0035), and for the scale and shape parameters of wake (scale parameter B=7.6, t=2.8, p=0.0065; shape parameter B=0.20, t=2.9, p=0.0048). Results indicated that people with insomnia had less stable NREM sleep and more stable wake after sleep onset compared to healthy controls. Additionally, the altered distribution of wake segment lengths indicated an increased difficulty to fall asleep after longer awakenings in the insomnia group. However, these differences were mainly observed in younger participants. Significant effects of group for the survival parameters of REM sleep were not found. Conclusion As illustrated by our results, survival analysis can be very useful for disentangling different types of sleep fragmentation in people with insomnia. For instance, the current findings suggest that people with insomnia have an increased fragmentation of NREM sleep, but not necessarily of REM sleep. Additional research into the underlying mechanisms of NREM sleep fragmentation could possibly lead to a better understanding of impaired sleep quality in people with insomnia, and consequently to improved treatment. Support (if any):

Multimodal Daniels’ theory: An application to carbon nanotube twisted strands

Wind energy as a clean, source free and environmentally friendly alternative source of energy can be used for providing sustainable power supply to remedied an epileptic and unreliable power supply system. This paper carried out an analysis of wind data at Al-Najaf province using the WAsP model to estimate the wind potential in this location. Najaf site was chosen to be studied due to available real data from a metrological tower and planning to erect small wind turbine farm. Twenty-nine months real available data measured at 50m height were collected for statistical analysis and extrapolated to 65m height level for estimated the annual energy production of a suggested wind turbine and measured the Weibull parameters at this height. The mean wind speed was found to be 6.47 m/s, the Weibull scale parameter and shape parameter was found to be 7.3 and 2.38 respectively.

ECONOMIC STATISTICAL DESIGN OF X̄ CONTROL CHARTS FOR SYSTEMS WITH WEIBULL IN-CONTROL TIMES

ABSTRACTThe present article utilizes wind measurements from three buoys data collection stations in Ionian Sea to study the wind speed and power characteristics using the Weibull shape and scale parameters. Specifically, the site dependent, annual, and monthly mean patterns of mean wind speed, Weibull parameters, frequency distribution, most probable wind speed, maximum energy carrying wind speed, wind power density and wind energy density characteristics have been analyzed. The Weibull distribution was found to represent the wind speed distribution with more than 90% accuracy, in most of the cases. Moreover, the correlation between the percentages of times the wind speed was above cut-in-speed and the measured mean wind speed for the three selected sites, as the correlation between the aforementioned percentages and the scale parameter c were examined and were found linear. At all these sites, no definite increasing or decreasing trends in annual mean wind speed values could be detective over the data reporting period. The mean values of wind speed, scale parameter, most probable wind speed, maximum energy carrying wind speed, wind power and wind energy density values showed higher values during winter time and lower in summer time in Pylos and Zakynthos. Moreover, Pylos and Zakynthos were found to be the best sites from wind power harnessing point of view.

This study utilizes a 30-year (1980–2009) 10 m wind field dataset obtained from the European Center for Medium Range Weather Forecast to investigate the wind energy potential in the East China Sea (ECS) by using Weibull shape and scale parameters. The region generally showed good wind characteristics. The calculated annual mean of the wind power resource revealed the potential of the region for large-scale grid-connected wind turbine applications. Furthermore, the spatiotemporal variations showed strong trends in wind power in regions surrounding Taiwan Island. These regions were evaluated with high wind potential and were rated as excellent locations for installation of large wind turbines for electrical energy generation. Nonsignificant and negative trends dominated the ECS and the rest of the regions; therefore, these locations were found to be suitable for small wind applications. The wind power density exhibited an insignificant trend in the ECS throughout the study period. The trend was strongest during spring and weakest during autumn.

Basalt fibre reinforced polymer (BFRP) composites have been widely used for structural strengthening and reinforcement in civil engineering recently. Since fire risk is unavoidable for most civil structures, the degradation of BFRP at elevated temperatures needs to be known for the safe design of its strengthened or reinforced structures under fire risk. In this study, the mechanical properties of basalt fibre roving and pultruded basalt fibre reinforced epoxy plates were investigated at elevated temperatures. As the temperatures increasing from room temperature to 200 °C, the tensile strength and modulus of the fibre roving were reduced by 8.3% and 9.7%, respectively. Meanwhile, the Weibull shape parameter (m) of the fibre roving decreased by 20.5%. As regards the BFRP plates, however, the elevated temperatures show more adverse influence. The tensile strength and modulus of the BFRP plates is reduced by 37.5% and 31% as temperature rising to 200 °C. Compared to the tensile properties, the short beam shear strength (SBS) was reduced by around 90%, more susceptible to the elevated temperatures. The glass transition temperature (∼93 °C) plays a key role on the inflexion of the variation of the mechanical properties, especially for the tensile strength. In a wide temperature range, the relationship between the tensile strength and the SBS showed a good linearity, indicating the reduction of the tensile strength comes from the deterioration of the interlaminar shear strength at elevated temperatures.

The polytetrafluoroethylene (PTFE), which was implanted with Ni ion to different energy and doses, fabricated metallic structures by selective electroless copper plating. The characteristic and microstructure of the copper film were studied using SEM and X-ray diffraction. Friction performance of the interface between copper film and basal body of PTFE was tested with a CETR UMT-2 (CETR Co., Campbell, CA, USA) multifunction micromechanics instrument. The test loads were 10, 20 and 40 N, while the line velocity was 8 mm s−1, and the frequency of data acquisition was 1 Hz. The Ni ion implantation replaces the complicated electroless plating surface pretreatment, and it is an assisted technique of electroless plating of copper on the surface of PTFE and plate Cu directly on its surface. Continuous, prepressing and uniformity plating was obtained with proper technique parameters and the dosage of Ni+. The frictional performance comprehensive property of copper film was remarkably influenced by different plating methods, annealing treatment and testing loads under unlubricated condition. The friction coefficients and wear rates changed with the varied load. Annealing treatment improves the tightness and uniformity of the copper film, while it decreases its cavity. Friction performance of copper film was thus increased. The mechanisms of friction and wear of copper film under different test conditions are also discussed.

Influence of counter material on friction and wear performance of PTFE–metal binary coatings

Weibull renewal function has attracted a lot of attention because the Weibull distribution describes in a relatively simple analytical manner a wide range of realistic behavior and its shape and scale parameters can be readily determined with graphical or statistical procedure. On the other hand, there are no closed form analytical solutions for the Weibull renewal function except for the special case of exponential distribution. Bounds, approximations, and tables are usually used. In this article, some approximations based on Normal approximation of Weibull distribution are studied. Such a procedure, which is different from that in the existing literature, is shown to be good for Weibull renewal function when the shape parameter is of moderate or large size. Series truncation expression and approximation bounds can be obtained as well. Numerical examples and comparisons are shown to illustrate the procedure.