Papers by Keyword: Weibull Modulus

Abstract: Reliability analysis of dense and porous sintered clay-based ceramic was compared using three-parameter Weibull model. The raw and the sintered clay at temperatures 900-1300°C were characterized using XRF and XRD. The raw clay (dense) and clay mixed with cassava starch (porous) were compacted and sintered at 1300°C. Flexural strength of the dense (24.11-46.56MPa) and the porous (13.58-23.26MPa) sintered clay were determined using three-point bending test. The results were analyzed by three-parameter Weibull probability distribution using Minitab 15 software at 95% confidence interval. Scale and threshold parameters of the dense sintered clay were higher than that of the porous sintered clay. However, the Weibull modulus of the porous ceramic was higher than the dense ceramic. The morphology of the porous sintered clay shows a relative distribution of porosity while the dense ceramic shows a random distribution of cracks. Three- parameter Weibull is a suitable tool to model the reliability of dense and porous sintered clays.

Abstract: Within the scope of the project ENERTHERM: Energy efficiency of thermal processes which is funded by the Bavarian Ministry of Economy (BMWi) components and systems for high-temperature are being developed. Monolithic oxide ceramics (mullite, Al₂O₃) and oxide-fiber reinforced ceramics (O-CMC) show a high potential for high temperature (HT) applications. Additionally, the demand for complex HT-components such as HT-fanwheels for kilns, supporting HT-lightweight structures or hot gas liners increases. In according to the required component design, joining techniques are needed in order to realize such complex geometries. The generated joints were made by using commercial glass solder from the type Al₂O₃-SiO₂-MgO. For realizing the joining process sintering-joining in HT-kilns was used because of the homogeneous temperature distribution. A CO₂ laser (wavelength of 10.6 microns and a power of 1.5 kW) was used for rapid joining process. The mechanical properties were determined in according to DIN EN 843-1 and DIN EN 658-3 (4-point bending strength) and evaluated according to Weibull distribution.

Abstract: This research analyzed the results of flexural strength of dense and porous mullite ceramic prepared from kaolin clay by using two-parameter Weibull probability distribution with different estimates. Chemical and physical characterizations of the clay were conducted using XRF, XRD and FESEM. The samples were tested using three point bending tests. The different estimates used in analyzing the results include mean rank, median rank, modified Kaplan Meier and Kaplan Meier. Among the estimates, Kaplan Meier was found to give the best fit with the highest correlation coefficient (R²) value. The porous ceramic had the higher value of Weibull modulus in comparison to the dense ceramic, while the characteristic strength (scale parameter) of the dense ceramic was higher than that of the porous ceramic. The micrograph of the porous ceramic showed a relatively balanced distribution of rounded pores, which is associated with the higher Weibull modulus in the porous ceramic.

Abstract: This paper mainly presents experimental investigation and stress analysis on static fatigue property of optical fiber. By analyzing the weibull distribution of experiment, the weibull modulus was obtained. From the weibull distribution, the modulus decreased continuously with the decrease of stress, and a conclusion that experiment distributes discretely can also be drawn. Simultaneously, based on the experiment, we also obtain the feature life of optical fiber in different stress and s-t curve of the static fatigue experiment, as well as the analytical expression of static fatigue .

Abstract: This paper reports the influence of sintering additives (RE2O3, Al2O3RE2O3, RE = Yb, Y and Gd, 13 vol%) and mixing effect of 30 nm SiC powder with 800 nm SiC powder on phases of grain boundaries, grain size of SiC, fracture toughness and strength of SiC hot-pressed at 1950°C under 39 MPa of applied pressure. Rare earth ions were uniformly adsorbed on negatively charged SiC particles with 150 nm Al2O3 particles in aqueous suspensions at pH 5. A rapid densification of SiC with one component RE2O3 occurred above 1700°C when a liquid of SiO2 (formed on SiC particles)RE2O3 system was formed. The Al2O3RE2O3 additives lowered a liquid formation temperature to 14001500°C and enhanced the densification rate of SiC. An increased solubility of 30 nm SiC in a liquid during dissolution-precipitation process provided an amorphous phase of SiCSiO2Al2O3RE2O3 system at grain boundaries and suppressed the grain growth of SiC. The fracture toughness of dense SiC was dominated by the grain boundary thickness controlled by grain size of SiC and amount of oxide additives. Mixing of 30 nm SiC with 800 nm SiC improved greatly the strength of SiC with two component oxides and the mean flexural strengths reached 740810 MPa.

Abstract: Along with deterministic size effect theory statement, Weibull distributed size effect has been neglected generally. The author believes that, deterministic size effect is not established to the basic strength index of plain concrete without notches. Definite size effect has an application limitation on the large-size zone. The most recent development of size effect is the fracture size effect theory based on probability in modern times. As a result of stress concentration caused by the notches, failure mechanism is bond to be affected. Therefore, the existing fracture theory needs to be tested. Meanwhile, the weakest chain link theory of material unit is still used in the existing statistics energy size effect model, which still needs to fix Weibull parameter m. Through more than 1000 dates of 24 groups of various kinds of concrete cube compressive strength and splitting tensile strength statistical tests in the recent years by our project group, the article has analyzed the statistical characteristics of basic strength of concrete and its influencing factors. Regression statistical analysis on shape and scale parameters of Weibull distribution has been studied.

Abstract: The purpose of this study is to determine the bi-axial flexural strength, weibull modulus and fracture mode of bilayered alumina glass-infiltrated core and the veneering porcelain. Forty disk specimens were fabricated from alumina glass-infiltrated core (HSDC-A) and veneer porcelain (Vintage AL). The specimens were equally divided into four groups as: MV, monolithic specimens of veneer material; MC, monolithic specimens of core material; BV, bilayered specimens with the veneer in tension; BC, bilayered specimens with core material in tension. Mean flexure strength, standard deviation and associated Weibull modulus were determined using bi-axial flexure (ball-on-ring) for each group. Both optical and scanning electron microscopy were employed for identification of the fracture mode and origin. The surface loaded in tension influenced the bi-axial flexural strength and reliability of the composites. The frequency of specimen delamination, Hertzian cone formation and sub-critical radial cracking in the bilayered discs are also dependent on the surface loaded in tension.

Abstract: In this study hydroxyapatite (HA) was coated by sol-gel method on Ti6Al4V alloy substrates: on micropolished surface and after titania (titanium oxide) treatment. Former shows the cracks and poor bonding of HA whereas latter shows coating without cracks and higher bonding strength. The higher bonding strength of HA coating in titania treated sample could be attributed to the increased roughness by titanium oxide layer.

Abstract: This paper reports a study based on a novel concept of ‘self-healing’ coatings applied onto the brittle fibre surface to reduce the stress concentrations and thus to improve the reinforcing efficiency in a composite. The individual E-glass fibres as well as rovings were coated with a carbon nanotube (CNT) reinforced epoxy composite. The tensile strengths were measured for the individual and bundle fibres, which were treated statistically to determine the Weibull parameters and thus to evaluate the notch sensitivity of the fibres with and without coating. The results indicate that the tensile strength of the individual fibre increased by 10% after coating with neat epoxy. Coating with epoxy nanocomposite containing 0.3wt% MWNT further improved the tensile strength. However, increasing the nanotube content was not necessarily beneficial due to the formation of nanotube agglomerates within the matrix. The tensile tests on fibre roving also showed a clear trend of beneficial effect of nanocomposite impregnation on tensile strength. The rovings impregnated with nanocomposite exhibited a more uniform strength distribution and higher strengths than those impregnated with neat epoxy. Changes in prevailing failure mechanisms influenced by the epoxy and nanocomposite coatings are identified.