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Abstract Details

Activity Number: 18
Type: Topic Contributed
Date/Time: Sunday, July 29, 2012 : 2:00 PM to 3:50 PM
Sponsor: Quality and Productivity Section
Abstract - #304695
Title: Photodegradation Path Modeling and Analysis with Nonlinear Mixed Models
Author(s): Yili Hong*+ and William Q. Meeker
Companies: Virginia Tech and Iowa State University
Address: 213 Hutcheson Hall, Blacksburg, VA, 24060,
Keywords: Coatings ; Photodegradation ; Random effects ; Reliability ; UV exposure ; Prediction

Photodegradation caused by ultraviolet (UV) radiation is a primary cause of failure for coatings, as well as many other products made from organic materials exposed to sunlight. Other environmental factors including temperature and humidity also have effect on the degradation process. Identifying a physically motivated model that can adequately describe the degradation path is an important step in service life prediction. The model should also incorporate the effects of covariates such as, the UV spectrum/intensity, temperature and humidity. We use a nonlinear mixed model to describe the data because the degradation path is nonlinear function of time. Random effects are also used to account for unit-to-unit variability. The parameters in the model are estimated by maximum likelihood approach. The effects of the explanatory are extensively studied. The developed method is applied to accelerated laboratory test data for a specific coating, in which spectral UV wavelength and intensity, temperature, and relative humidity are controlled over time. We also extend our model to allow for time-varying covariates and apply the method to outdoor test data where covariates are uncontrolled.

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