Optimized Goodman Diagram for the analysis of Fiberglass Composites Used in Wind Turbine Blades

Mandell, et al have recently presented an updated Goodman diagram for a fiberglass composite that is a typical wind turbine blade material. Their formulation uses the MSU/DOE Fatigue Data Base to develop a Goodman diagram with detailed S-N information at thirteen R-values. This diagram is the most detailed to date, and it includes several loading conditions that have been poorly represented in earlier studies. Sutherland and Mandell have used this formulation to analyze typical loads data from operating wind farms and the failure of coupons subjected to spectral loading. The detailed Goodman diagram used in these analyses requires a significant investment in materials testing that is usually outside the bounds of typical design standards for wind turbine blades. Thus, the question has become: How many S-N curves are required for the construction of a Goodman diagram that is sufficient for an “accurate ” prediction of equivalent fatigue loads and service lifetimes? To answer this question, the loads data from two operating wind turbines and the failure of coupons tested using the WISPERX spectra are analyzed using both a linear and a non-linear damage model. For the analysis, the predicted service lifetimes that are based on the Goodman diagram constructed from 13 R-values are compared to the predictions for Goodman diagrams constructed with fewer R-values. The results illustrate the optimum number of R-values is 5 with them concentrated between R-values of –2 and 0.5, or –2 an