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

Abstract

Mandell et al. 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.

A failure-mode based anisomorphic constant life diagram for a unidirectional carbon/epoxy laminate under off-axis fatigue loading at room temperature

“…Mandell et al 21 and Sutherland and Mandell 22 presented modified Goodman diagrams that were built assuming linear interpolation of fatigue data at different stress ratios. Adam et al 23 proposed an asymmetric parabolic representation of CFL envelopes for different constant values of life.…”

Effect of Mean Stress on the Fatigue Life Prediction of Notched Fiber‐Reinforced 2060 Al‐Li Alloy Laminates under Spectrum Loading

“…After taking the logarithm on both sides of the formula, (21) is obtained, where the parameter a is the slope of the S-N curve and the parameter b is the intercept of the S-N curve. According to the theory of least squares regression, the test data can be fitted very well with the equation [24]. e values of σ p for constant amplitude loading at R � 0.06 and R � −1 depend on max ||σ p ||, ||σ v || , and the value of σ p for Mini-Twist spectrum loading will depend on the baseline stress of the load spectrum.…”

“…Without any assumptions, the piecewise linear (Pwlinear) interpolation was used between different S-N curves based on modified Goodman diagram concepts [23][24][25]. According to this idea, the analytical expressions for any desired S-N curve were proposed [26].…”

“…e piecewise linear CLD model is deduced by linear interpolation theory between different S-N curves on the (σ m -σ a ) plane [23][24][25][26]. is CLD model is constructed based on the compression static strength data and tension static strength data as well as a limited number of known S-N curves (generally at R � 10, R � −1, and R � 0.1).…”

Industrial experiences of bending fatigue strength in table liner for cement mill

“…According to X‐ray fractography and the Goodman diagram, repeated bending stress is the major cause of turbine blade fatigue failure. Mandell et al 4,8,9 proposed the Goodman diagram based on 13 stress ratios. This method formulated the S‐N behaviour considering the effect of mean stress.…”