Reliability assessment based on degradation measurements: How to compare some models?

An important issue in the validation of mechanical parts for vehicles is reliability assessment for high mileages, by means of tests. Since the tests should be as short as possible, and for parts subjected to degradation mechanism, such as wear or crack propagation, it would be appropriate using degradation measurements (such as mass loss or crack length) in order to estimate reliability. In this study, we present some statistical approaches responding to this concern and propose a method to compare theses models. Different types of data can be available; in this paper, we only consider the case in which one measure is available for each part. Only linear degradation is studied

Degradation test plan for Wiener degradation processes

This study describes an approach to design degradation validation test plan using the Wiener process. This approach allows to link accelerated test results and field reliability without acceleration laws but using a global severity factor when the component to test is not an innovation and an old version is in field. In this condition, field data is available. The field degradation level can be measured and compared to degradation obtained in test. The test severity is evaluated with field and test degradation measurements. We use the same test severity to design a test plan for the new version of component. This test plan is designed to demonstrate a field reliability target with confidence level. The final test plan is obtained using experimental feedback, tests results and numerical simulations. This study shows the necessity to strengthen the test acceptance criterion when the test duration is reduced. This method allows to quantify this

Measurements and Modeling of Wetting Efficiency in Trickle-Bed Reactors:Liquid Viscosity and Bed Packing Effects

An experimental parametric study on wetting efficiency is reported which evaluates the influence of liquid viscosity, as well as the effect of particle size(/shape) and bed porosity (εB), separately. A 10-fold increase of liquid viscosity improves slightly catalyst wetting (by about 10%), while an increase of either bed porosity or particle size has the opposite effect. Wetting efficiency is reduced by about 0.1 for an increase of εB from 0.38 and 0.40 due to a change of particle size from 1.8 to 7 × 10−3 m while the decrease is only 0.05 for a similar variation of εB (0.38−0.41) with the same particles. The effect of particle shape (cylindrical/trilobe extrudates or spheres) appears very small in the investigated conditions. A new correlation for wetting efficiency is proposed, using a bounded function and only three dimensionless groups (liquid Froude and Morton numbers and bed porosity). This correlation is able to predict wetting efficiency with a very good precision on a large database, provided wetting liquids are used. Adding fines in the fixed bed is also examined, and its positive effect can be correlated with the size ratio between catalyst particles and fines