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RESEARCH PAPERS

# Optimized Constant-Life Diagram for the Analysis of Fiberglass Composites Used in Wind Turbine Blades

[+] Author and Article Information
Herbert J. Sutherland

Sandia National Laboratories, Albuquerque, NM 87185-0708hjsuthe@sandia.gov

John F. Mandell

Montana State University, Bozeman, MT 59717johnm@coe.montana.edu

For the residual strength model, the “damage” is the fractional loss of residual strength defined by the last term of Eq. 5.

J. Sol. Energy Eng 127(4), 563-569 (Jul 11, 2005) (7 pages) doi:10.1115/1.2047589 History: Received March 17, 2005; Revised July 11, 2005

## Abstract

Mandell have recently presented an updated constant-life diagram (CLD) for a fiberglass composite that is a typical wind turbine blade material. Their formulation uses the MSU/DOE fatigue data base to develop a CLD with detailed S-N information at 13 $R$-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 CLD 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 CLD that is sufficient for an “accurate” prediction of equivalent fatigue loads and service lifetimes? To answer this question, the load data from two operating wind turbines and the failure of coupons tested using the WISPERX spectra are analyzed using a nonlinear damage model. For the analysis, the predicted service lifetimes that are based on the CLD constructed from 13 $R$-values are compared to the predictions for CLDs 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 $−2$ and 0.7.

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## Figures

Figure 2

95∕95 CLDs for database material DD16, fit with Eqs. 2,3

Figure 1

Mean CLD for database material DD16, fit with Eq. 2

Figure 3

Comparison of mean and 95∕95 CLDs

Figure 4

Edgewise fatigue load spectrum for the 11–13m∕s wind speed bin for the Bushland turbine

Figure 6

Normalized WISPERX spectrum

Figure 8

Annual damage estimates for the Bushland turbine on the tension bending side of the blade

Figure 11

Damage estimates for the Bushland turbine on the tension bending side of the blade using the full mean CLD. (a) Damage in the edgewise bending direction. (b) Damage in the flapwise bending direction.

Figure 12

Damage estimates for the ART on the compression bending side of the blade using the full mean CLD. (a) Damage in the edgewise bending direction. (b) Damage in the flapwise bending direction.

Figure 13

Damage estimates for the ART on the tension bending side of the blade using the full mean CLD. (a) Damage in the edgewise bending direction. (b) Damage in the flapwise bending direction.

Figure 14

Comparison of experimental data to predicted failure using nonlinear Miner’s rule. (a) Failures predicted using the mean full CLD. (b) Failures predicted using the 95∕95 full CLD.

Figure 15

Damage estimates for the WISPERX spectrum using the full 95∕95 CLD

Figure 16

The mean CLD recommended for wind turbine spectra

Figure 5

Typical fatigue spectra for root bending moments, >17m∕s wind speed bin for the ART

Figure 7

Annual flapwise bending cycles for the Bushland turbine on the tension bending side of the blade

Figure 9

Annual damage estimates for the Bushland turbine on the tension bending side of the blade

Figure 10

Damage estimates for the Bushland turbine on the compression bending side of the blade using the full mean CLD. (a) Damage in the edgewise bending direction. (b) Damage in the flapwise bending direction.

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