Planning Fatigue Tests for Polymer Composites

• Activity Number: 649
• Type: Contributed
• Date/Time: Thursday, August 7, 2014 : 10:30 AM to 12:20 PM
• Sponsor: Section on Physical and Engineering Sciences
• Author(s): Caleb King*+ and Yili Hong and Stephanie DeHart and Patrick DeFeo
• Companies: Virginia Tech and Virginia Tech and DuPont and DuPont
• Keywords: Cumulative damage model ; Large-sample approximate variance ; Lognormal ; Weibull ; Maximum likelihood ; Tolerance limits

Abstract

In this paper, we present optimal designs for cyclic fatigue testing with the goal of minimizing the asymptotic variance of a lifetime percentile at a design stress level. The designs are based on a model adapted from the fatigue literature that is derived from assumptions regarding damage accumulation in polymer composite materials. Specifically, this model is able to incorporate aspects of the testing procedure and is more suitable for modeling of cyclic fatigue in polymer composites than the model used in the current standards. We provide a comparison between our optimal designs and the traditional designs currently in use and propose a compromise design to combine the minimum variance with a suitable number of stress levels. The effects of the design and model parameters on the asymptotic variance are studied and suggestions for good designs are presented based on the results. A simulation study is used to compare the exact and asymptotic variances of the estimated lifetime percentile at the design stress level. Finally, we conclude with a summary of the results and provide some areas for future research.