Papers by Keyword: Weibull Analysis

Abstract: Cast aluminum alloy 354 is widely used in the automobile industry due to its attractive set of mechanical properties and excellent castability. The compressor wheel in turbochargers, for example, is used for the production of this alloy. Apart from mechanical properties like fracture toughness and tensile strength, the fatigue life of the component is also a critical issue while considering the performance. This study makes an attempt to improve the fatigue life of a component made out of this alloy by subjecting it to interrupted aging cycles similar to T6I4 and T6I6 (discussed in the published literature) instead of the normally used T61 standard aging treatment. Results show that subjecting the material to these interrupted aging treatments gives lower fatigue life than that obtained after subjecting it to standard T61 conditions.Also, T6I4 treatment yields better fatigue life as compared to T6I6.

Abstract: Cast aluminium alloy 354 finds extensive applications in the automobile and aerospace industry due to its attractive combination of mechanical properties and excellent castability. A high fatigue strength value is desirable for these applications. The present study explores the possibility of improving the fatigue life of cast aluminium alloy by subjecting it to Hot Isostatic Pressing (commonly known as Hipping). A three parameter Weibull analysis of the fatigue test results was carried out for both Hipped and Non-Hipped samples. The Hipped samples showed an improved fatigue life compared to the Non-Hipped samples.

Abstract: Cast aluminium alloy 354 has extensive applications in the automobile industry. Due to its attractive combination of mechanical properties and excellent castability, it is being used in production of automobile components like the compressor wheel for turbochargers. Performance of this component under fatigue loading conditions is a critical issue. The present study explores the possibility of improving the fatigue life of the component by bringing in process changes (i) adopting a two-step aging treatment in place of the normally used single step aging treatment (ii) adopting a lower artificial aging temperature (171°C) instead of the temperature normally used for artificial aging (188°C) while performing T61 treatment. In all cases Weibull analysis of fatigue test results was carried out. Weibull analysis of Ultimate Tensile Strength (UTS) values obtained after artificial aging at 171°C and 188°C was also carried out. Among the four variants of two-step aging treatment carried out, the one consisting of 100°C for 5 hours followed by 170°C for 5 hours was found to have the best characteristic fatigue life for the components. The modified T61 treatment where aging was carried out at 171°C instead of the normally used 188°C yielded better characteristic fatigue life as well as better Ultimate Tensile Strength (UTS).

Abstract: High Pressure Die Casting is an economical means of manufacturing complex thin walled parts in high volumes. However, the process is prone to high levels of surface turbulence and fluid break-up, which results in the entrainment of bifilm defects. A study was carried out on a commercial casting to identify how changes in melt velocity and mould geometry affected the distribution of damaging bifilm defects, and the distribution of fracture stress. The statistical analysis of tensile test data indicated that two distinct defect populations existed; one of which caused relatively few failures, but often accounted for a large reduction in fracture stress when present. Where this defect population was not significant, Weibull moduli of 20 to 30 were achieved, comparable to sand castings with well-designed running systems. SEM fractography was also performed on a selection of samples to determine the probable cause of failure. A comparison of the SEM analysis to the statistical results indicated that bi-film defects initiated the fracture of those samples that failed at significantly lower stresses. Additionally, it was demonstrated that the geometric distribution of these cases was strongly correlated to changes in fluid flow conditions, suggesting that targeted modifications to mould geometry could increase the in-service reliability of High Pressure Die Castings.

Abstract: The failure data of crank rod system was analyzed by using weibull parallel model on the base of the simple weibull method. The distribution parameters of the weibull parallel model were estimated by using drawing method. The solving process of WPP drawing method was given in detial. Results show that the fitting degree of the failure data in the weibull parallel model is higher than that of the simple weibull distribution model, and it can more accurately described the failure distribution curve of the system in life cycle, which can provide necessary information for engine reliability indexes computation.

Abstract: Plasma-sprayed HA coatings (HACs) on Ti-6Al-4V substrates with post-heat treatments were employed to improve the microstructural homogeneity, bonding strength and reliability of the HACs. A defect-healing effect can be recognized to diminish coating defects with the hydrothermal treatment, and 150°C hydrothermally-treated HACs shows a significant improved bonding strength than 600°C vacuum heating HACs because of its dense structure from the defect-healing effect. Low-temperature hydrothermal treatment demonstrates a more superior crystallization effect than vacuum heat treatment. Based on the statistical calculation by the Weibull distribution function, hydrothermally-treated HACs show a wear-out failure with a higher Weibull modulus than vacuum heating HACs. Hydrothermally-treated HACs possessed better reliability can be attributed to the suppression of defect content (about 2.6-3.2 volume %) and its smaller strength data fluctuation.

Abstract: Wiper blade is one of inexpensive automotive components, but the component is very important part considering car safety for securing automotive visual field. Therefore study for securing longer endurance of wiper blade was proceeding, that is about variables effecting on endurance. In this paper, it was proved that the effect to extend endurance could be acquired by securing proper friction coefficient. Be compared endurance in Weibull distribution that is reliability technique and seized effect about blade pressure distribution, contact pressure, blade rubber surface treatment etc. for securing proper friction coefficient. Relation between these variables was cleared through test. Also, designed and proposed tester for measuring friction coefficient of wiper blade.

Abstract: In order to evaluate strength reliability of micron size polycrystalline silicon (poly-Si) structure, bending tests of cantilever beam and Weibull analysis are performed. Recently, the importance of microelectromechanical systems (MEMS) in society is increasing, and the number of production is also increasing. The MEMS devices, which contain mechanical movement, have to maintain their reliability in face of external shock, thermal stress and residual stress from manufacturing processes. In greeting the mass production era of the MEMS, in case the material strength design of MEMS is performed, required strength data is not average value but the variation, especially minimum value of the material. Micron size poly-Si structure is widely employed in the MEMS such as microsensor, switching device and so on. Then, in order to evaluate strength reliability of micron size poly-Si structure, tests and analysis are performed. The specimen is made by chemical vapor deposition (CVD) process and thickness is 3.5, 6.4 and 8.3 micrometer and the specimen has notch. The test specimen used for the test changed characteristics of (1) film thickness (2) stress concentration, and investigation about the influence each effects of the variation in a bending strength are discussed.

Abstract: Fracture toughness data from the cleavage resistance test of structural steels often show a large scatter. Geometry dependency as well as the scatter makes it difficult to evaluate appropriate fracture integrity of cracked components. To address these restrictions, several stochastic models have been proposed by Beremin group, Mudry and other researchers while each of them employs specific estimation scheme and micro-mechanical parameters. The purpose of this paper is to investigate applicability of the Weibull stress model in transition temperature regime and to quantify constraint effect among different-sized CT and PCVN specimens. The constituting parameters m and σu are determined at three temperatures by maximum likelihood estimate (MLE) technique in use of FE analysis results and experimental data of PCVN specimens. Also, failure probabilities of PCVN and CT specimens are calculated from the Weibull parameters, which are used for derivation of a prototype of toughness scale diagram. The diagram provides a technical basis to resolve transferability issue in the same material under different temperatures and constraint conditions.

Abstract: The high performance of poly p-phenylene-2,6-benzobisoxazole (PBO) fibre in mechanical properties and environmental resistance provides great potential applications as reinforcement fibres for composites. However, poor adhesion between PBO fibre and matrix is found because of the chemically inactive and/or relatively smooth surface of the reinforcement fibre. Here, we report the surface modification of PBO fibres by O2 and NH3 plasma treatments. The surface energy and roughness are increased for both sized and extracted fibres after plasma treatments. The sized fibre shows marginal improvement in interfacial adhesion and no change in fibre tensile strength because of the barrier effect of the sizing layer. For the extracted fibre, the plasma treatments cause reduction in both interfacial adhesion and the tensile strength, which is sensitive to plasma treatment conditions as revealed by a bimodal Weibull statistical distribution analysis. The fibre surface roughness is increased and more surface flaws are induced, which could result in coarse interface structures when the treated fibre surface has no adequate wetting and functional groups.