A comparative analysis of techniques used to estimate the mean recoil compressive strength of high performance polymers

This study provides the first experimental analysis comparing multiple methods of interpreting recoil compressive failure data. A two-parameter Weibull model was used to provide an accurate mean recoil compressive strength for a batch of Kevlar-29 fibers. The Weibull model provides highly accurate results, but requires the testing of more than 1000 filaments. The results from the Weibull model were used as a basis to compare two simplified and less data-intensive models: The method of Allen and the moving average method. Each method was applied to 10 sets of 80 filaments each and the results of these tests were compared with the two-parameter Weibull model results from the same fiber batch. The results of these tests have shown that both the method of Allen and moving average method tend to slightly over-estimate the compressive strength calculated by the two-parameter Weibull model, yet both estimation methods fall in the range of published values (200-400 MPa) for the recoil compressive strength of Kevlar-29. This inaccuracy probably results from the assumption of a symmetric failure distribution that is made in both simplified models, but not in the Weibull model. A statistical analysis of the results was completed and shows with a 95% confidence level that there is no statistical significant difference between the two methods.