A Note on the Existence of the Location Parameter Estimate of the Three-Parameter Weibull Model Using the Weibull Plot

The Weibull model is one of the widely used distributions in reliability engineering. For the parameter estimation of the Weibull model, there are several existing methods. The method of the maximum likelihood estimation among others is preferred because of its attractive statistical properties. However, for the case of the three-parameter Weibull model, the method of the maximum likelihood estimation has several drawbacks. To avoid the drawbacks, the method using the sample correlation from the Weibull plot is recently suggested. In this paper, we provide the justification for using this new method by showing that the location estimate of the three-parameter Weibull model exists in a bounded interval.

Experimental and theoretical study on the strain rate dependence of the mechanical properties of Twaron fiber tows with different fiber fineness

In this study, the tensile impact property of Twaron fiber tows with different fiber fineness were characterized and compared. A self-designed split Hopkinson tension bar apparatus and MTS materials tester (MTS 810.23) were used to determine the tension behavior of Twaron fiber tows under different strain rates (quasi-static: 0.001 s–1, dynamic: 800–2400 s–1). The results showed that the mechanical properties of the Twaron fiber tows were sensitive to strain rate; the stiffness and failure stress of the fiber tows increased distinctly as the strain rate increased, whereas the failure strain decreased. The scanning electron microscope photographs showed that a fibrillated end of a Twaron single fiber failed at both quasi-static and high strain rates. The observations reaffirmed that the fiber fibrillation was more severe as the strain rate increases. In addition, the fiber of 220 dtex exhibited higher strength and stiffness than that of 1680 dtex. Combined with the aligned fiber bundle model and the statistical theory, a single Weibull distribution function is adapted to evaluate the strength distribution, and the Weibull plot for Twaron fiber tows under different strain rates provided a more accurate agreement with the experimental results.

The Influence of Surface Pit Shape on 4H-SiC MOSFETs Reliability under High Temperature Bias Tests

The influence of surface pit shape on 4H-SiC double implanted MOSFETs (DMOSFETs) reliability under a high temperature drain bias test has been investigated. Threading dislocations formed two types of pit shapes (deep pit and shallow pit) on an epitaxial layer surface. The cause of the failure was revealed to be an oxide breakdown above the pit generated at the threading mixed dislocation in both pit shapes. Weibull distributions between two types of pits were different. Although the DMOSFETs on the epitaxial layer with the deep pit show longer lifetime than those with the shallow pit, the epitaxial layer with the shallow pit is suitable to estimate the lifetime of the DMOSFETs because of a linearity of the Weibull plot. The lifetime of the DMOSFETs with the shallow pit was dominated by an oxide electric field. The maximum oxide electric field required to obtain the lifetime of more than 10 years was estimated to be 2.7 MV/cm.

Formation and Effect of Moisture Contents to Kraft Paper’s Life of In-Service Power Distribution Transformer

Examples of solid and liquid electrical insulations for power transformer are mineral oil and cellulose based paper. As transformers performed their function to step-up or step-down voltage level, its’ insulations will be degraded. Paper insulation is considered the most critical component in a transformer insulation system because it is not easily replaced if compared to oil where it is easily reconditioned in-order to remove water and contaminants. Studies show that temperature, moisture contents and oxygen contributed to paper insulation degradation. Moisture and furanic compound were produced from these deterioration processes. This paper is focused on the formation and effect of moisture to Kraft paper’s life. Levels of moisture contents were obtained from in-service power distribution transformers. These data then is used to assess the Kraft paper’s life by means of Weibull plot. This study shows that level of moisture contents can be used to assess the life of Kraft paper insulation.

The Reliability Life Test and Analysis of Wiper Motor for Automobiles

Reliability of automotive parts has been one of the most interesting fields in the automotive industry. Especially wiper motor for automobiles is important part because of improving visual comfort for the driver and the passengers. Therefore, we have dealt with the reliability test procedure of wiper motor. The failures such as wear-out of brush, bearing damage, motor coil burnout are caused by the electrical and mechanical operating for low and high actions of wiper motor. In this research, we have qualitatively selected the efficient test items through the analysis of the life and potential failures of wiper motor. So, wiper motor itself requires an estimation of life causing failure of brush wear out in order to operate the system safely. We have tested six wiper motors. The result is established by employing the weibull plot. We validated the life of wiper motor to the experimental result.

Labeled Weibull Plot of a C-Derived Si3N4-SiC Nanocomposite

Four-point bending strength and Weibull distribution of the strength values of a carbon derived Si3N4-SiC nanocomposite have been investigated. The fracture origins were identified and characterized and a “labeled Weibull plot” was constructed. The fracture origins are surface, subsurface and volume located technological defects with a dimension from 10 µm to 180 µm, mainly in the form of cluster of pores and large SiC grains.