Testing and Analysis of Low Cost Composite Materials Under SpectrumLoading and High Cycle Fatigue Conditions

摘要

This paper provides an overview of the results of a twelve-year experimental study of lowcostcomposite materials for wind turbine blades. Wind turbines are subjected to 109 or more potentiallydamaging fatigue cycles over a typical service lifetime of 30 years. Stress conditions cover the range fromtension dominated to compression dominated, with associated differences in and potential interactionsbetween failure modes. Wind turbine design codes typically assume a Miner’s rule linear damage law topredict failure from constant amplitude test data, which appears to be significantly non-conservative. Thepaper summarizes results from three areas. First, an extensive constant amplitude database including over8800 test results with varying R-value (minimum stress / maximum stress) on over 150 materials,including variations in type of fiber and matrix, fiber content, reinforcement architecture, environment,flaws, and manufacturing method. Second, for a single E-glass/polyester material system, a study ofspectrum loading effects. The third area is a study of high cycle fatigue behavior, including somespecialized tests to 1010 cycles.New results are presented comparing typical wind turbine loads from a long term study, resolved byR-ratio, with a detailed data set for a typical structural laminate, tested at thirteen R-values. These resultsallow a direct comparison of turbine loads and material fatigue resistance at each R-ratio. The Goodmandiagram is the most detailed to date, including several loading conditions which have been poorlyrepresented in earlier studies. The new data should allow more accurate lifetime prediction underspectrum loading.