Papers by Keyword: Weibull Distribution

Abstract: Recently, there has been a growing interest in replacing synthetic fibres with natural fibres in polymer composites due to environmental concerns. This study examined the fibres from the Newbouldia laevis plant for their potential use in lightweight polymer composites, particularly in applications sensitive to strength and temperature. The fibres were extracted from the plant's stem, and various properties such as density, moisture content, moisture regain, and diameter were measured. Chemical analysis revealed the percentages of cellulose, hemicellulose, lignin, extractives, and ash present in the fibres. Furthermore, Fourier transform infrared analysis confirmed the presence of these essential components. Scanning electron microscopy images showed the rough surfaces of the fibres, which enhance the adhesion between the fibre and matrix during the production of polymer composites. Energy dispersive X-ray analysis identified carbon and oxygen as the main elements in the fibres. Thermal analysis provided insights into the thermal stability and maximum degradation temperatures of the fibres. Lastly, a single fibre tensile test was performed to evaluate the tensile strength, elastic modulus, and elongation at break of the fibres using Weibull distribution statistical analysis. The results of this study indicate that Newbouldia laevis fibres could be a promising reinforcement for lightweight polymer composites in strength and temperature-sensitive applications.

Abstract: The installed capacity of wind power plants at Indonesia can only generate up to 1.96 MW from 970 MW potential wind energy. The wind energy prospect in Tasikmalaya, which is part of southern java’s beach is assessed using Weibull distribution for a year. The data is compiled from monthly measurement and take frequency of maximum wind speed to define the potential of Tasikmalaya’s wind energy. The data consist of wind speed and wind direction at a 15m hub height for 12 months. Methods Of Moments (MOM) is used since it is the better parameter estimation compare to Graphical Method (GM) and Empirical Method (EM) and produce the smallest relative error. The Weibull parameter (k and c) from each month varies from 1.17 to 2.61, the scale factor ranges between 2.01 m/s to 4.27 m/s. The result of this research is represented on Weibull Probability Density Function (PDF) graph and real frequency of wind speed from observation. we can conclude that the most frequent wind speed that occur in Tasikmalaya’s area is 2 m/s, even though there are some months that has more frequent wind speed of 3 m/s like May and June. And judging from the Weibull distribution graph, February, March, May, August dan September were the most prospective windy months for this area.

Abstract: A study of Weibull distribution of 4H-SiC MOS capacitors has shown the effect of temperature as well as electric-field stress on the analysis of time-dependent breakdown. Time-Dependent Dielectric Breakdown (TDDB) is strongly electric-field dependent and temperature-dependent. In the paper, the test was at the stress level of 9.5, 10, and 10.5 MV/cm under 373K, through the TDDB model, the lifetime of the SiO₂ can reach more than 30 years when the field pressure is not more than 6.6 MV /cm. The acceleration factor for TDDB (using E-Model) under different temperature stress, it expected that the capacitors would last for 2.28×10⁷ years under 3MV/cm or 54 years under 6MV/cm at 373K.

Abstract: The research on the nanofluid as an alternative transformer oil has been widely attracted the concern of many researchers as the effectiveness as insulation and cooling agent of the existing transformer oil is not achieved satisfactory to accommodate the rising demand of high voltage rate. In this study, nanofluid with a nanomaterial, Carbon Nanotube (CNT), with and without Polyvinylpyrrolidone (PVP) has been formulated, and their AC breakdown voltage of the mineral oil (MO) according to IEC 60156 standard has been characterized. The concentration of CNT study is 0.005, 0.01, 0.015 and 0.02 g/L. It is found that the optimum concentration in nanofluids without PVP is 0.005g/L of nanofluids concentration with the highest breakdown voltage 53.52. In comparison, the highest breakdown voltage for nanofluids with PVP is 33.4kV at 0.01g/L. The existence of PVP in the nanofluids seems not significantly affect the dielectric performance of the degradation of the nanofluid from 5% to 43%. Hence, nanofluids with CNT addition are proofed as a good additive in insulation oil for future transformer applications.

Abstract: This work is based on an investigation study to develop bio-composite materials that are renewable, biodegradable, and environmentally safe. The fibers used in this work are extracted from the plant Ampelodesma Mauritanica, It is a wild plant that is produced in abundance in the Mediterranean regions. Through this work, an overview of Diss fibers was provided, developing bio-composite using different starch matrices reinforced by Diss fibers, and evaluate their mechanical behavior using Charpy-tests to determine standard test specimens to estimate Weibull parameters suitable for the composite using statistical methods based on Weibull distribution. The obtained results, it was found that the bio-composite starch/Diss 40% Glycerol and 5% fiber reinforcement (SG40/RF5) had better results compared to the rest of the bio-composite, The Charpy impact energy modulus was about 31.25 (KJ/m²), which is 2.1 times higher than that achieved Measured from SG40 matrix (40% glycerol), and 1.3 times higher than those fortified with 10% fiber SG40/RF10 (40% glycerol reinforcement 10% fiber), and the statistical study confirmed the distribution of the results obtained, especially Weibull, which has three parameters.

Abstract: Cube compressive strength of raw-soil based mater is an important index of mechanical property. Because the test results vary by different curing modes and trial curing time, compressive strength test on 160 cubic raw-soil test-pieces which were made by 4 curing modes (natural curing, indoor curing, indoor+ preservative film curing, curing in standard curing chamber) and 4 Curing period (4d, 14d, 21d, 28d) was designed.In this study,the failure mechanism, failure mode, force mechanism of test were analyzed.Using Weibull distribution theory, the influence of different environmental factors on material strength is discussed.The research revealed that the different curing methods and curing time had remarkable effect on failure mode of material, but the load displacement curves had not affected. The compressive strength with 21d and 28d ‘s indoor curing and standard curing method were same in the test.The strength of raw soil increases with time, and the curing temperature had a significant effect on the early strength of raw soil materials, but had little effect on the later strength. The humidity had a great influence on the later growth of material strength. Constant temperature and humidity could effectively ensure the full response of internal water loss hardening of raw soil-based materials, and the strength of specimens increases obviously.The recommended curing mode and standard curing time for standard test of raw-soil test-pieces were temperature of 25-30oC, humidity of 50%-55%, and 28day, respectively.

Abstract: The quasi-static and dynamic compressive mechanical behaviors of two kinds of fiber reinforced SiC ceramic matrix composites including 2D-C/SiC and 2D-SiC/SiC were investigated. Their compressive behaviors of materials at room temperature and strain rate from 10^-4 to 10⁴ /s were studied. The fracture surfaces and damage morphology were observed by scanning electron microscopy (SEM). The results showed that the dynamic failure strengths of 2D-C/SiC and 2D-SiC/SiC obeyed the Weibull distribution. The Weibull modulus of the two materials were 13.70 (2D-C/SiC) and 5.66 (2D-SiC/SiC), respectively. It was found that the two kinds of fiber reinforced ceramic matrix composites presented a transition from brittle to tough with the decrease of strain rate. The 2D-SiC/SiC materials demonstrated a more significant strain rate sensitivity and smoother fracture surface compared to the 2D-C/SiC composites, implying that the former composites present brittle features. This was because the SiC/SiC composites possessed high density and the bonding strength in interface of fiber/matrix is very strong.

Abstract: A new surface treatment, wide peening cleaning (WPC), was developed to improve fatigue strength of steels using shot peening and sandblast technologies. The combination of induction heating (IH) and WPC is expected to introduce higher compressive stress on the steels than single IH or single WPC. We investigated effect of IH and WPC on rolling contact fatigue life of 13Cr-2Ni-2Mo stainless steel. Vickers hardness and residual stress measurements, and RCF life evaluation using the Weibull distribution were carried out. It was found that the residual stress was introduced by WPC near the surface to improve life fatigue

Abstract: The first failure mode in tensile quasi-static and in tension-tension fatigue (cyclic) loading of composite laminates is intralaminar cracking in layers with off-axis fiber orientation. These tunnel-building cracks are result of combined action of in-plane transverse and shear stresses. We assume that due to non-uniform fiber distribution (clustering) which leads to local stress concentrations, different positions in the layer have different resistance to crack initiation (initiation strength). If so, the weakest position in quasi-static loading is also the weakest in fatigue and some of the distribution parameters for fatigue behavior can be obtained in quasi-static tests, thus significantly reducing the number of required fatigue tests. Methodology is suggested and validated for cases when the cracking is initiation governed-initiated crack almost instantly propagates along fibers. Distribution parameters are identified using data in low crack density region where stress perturbations from cracks do not interact. Monte-Carlo simulations are performed for cracking in layers under quasi-static and cyclic loading using novel approach for computationally efficient stress state calculation between existing cracks.

Abstract: One important method to improve the material properties is refinement of the prior austenite grain size. Repeated quenching is used as a grain refinement method. In the present work, samples of SUJ2 steel were furnace quenched once and thrice in order to investigate the effect of repeated quenching on rolling contact fatigue (RCF) strength. After the RCF tests, maicrostructure observations, Vickers hardness and retained austenite measurements, RCF life evaluation using the Weibull distribution were carried out. It was found that the dispersion of the life population was reduced by repeatedly quenching.