Technical Brief: Managing Defects and End of Life Prediction/Validation in Composite Wind Turbine Blades

Technical Brief:   Managing Defects and End of Life Prediction/Validation in Composite Wind Turbine Blades

Under a research grant from the US Department of Energy (DOE), and collaborating with Sandia National Laboratories, AlphaStar Corporation was able to solve Durability and Reliability challenges of composite wind turbine blades.

The Challenge: Determine Why, Where and How Wind Turbine Blades Fail

In the operational environment, the blades designed and built by Sandia Labs and TPI Composites (the blade manufacturer) were continually breaking (Fig. 1). The blade failures were costing Sandia and TPI valuable time, costs and resources to continually replace broken blades without understanding the root cause of the problem inherent to composite materials.

                              

Figure1: Progressive failure analysis and test validation of Sandia?s BSDS blade under static loading

The Solution: GENOA & MCQ-Advance Multi-Scale Progressive Failure Analysis

AlphaStar with its flagship products GENOA and MCQ provided an Advanced Simulation Methodology based on Multi-Scale Progressive Failure Analysis (MS-PFA) to answer why, where and how blades fail. Also, MS-PFA assessed the durability, damage tolerance and reliability of blade structures in the presence of uncertainties in composite material properties, such as manufacturing defects. 

Why Blades Fail

Composite blade design does not consider scatter in composite material properties, manufacturing processes and resulting defects ?As-Build Vs. As-Designed?, but it relies on empirical methods to establish design allowables for sizing of composite blades. 

Where and How Blades Fail

Ply drop off due to manufacturing processes causes (Fig. 2) high local stress concentration and results in unstable crack and delamination propagation from root to tip (as shown in Figure 1).  This means that due to resin rich voids matrix has been degraded. 

MS-PFA narrowed the blade failure to the region of ply-drop off very common in composite wind turbines for material thickness transitions for inherent weaknesses created by the design; the results are supported and verified by the test. 

Figure 2.  Ply Drop off of Thick Laminates Under Tension Loading

The unique advantages of the MS-PFA approach are as follows (details in references below):

·         Material Characterization and Qualification

·         Scale up from material to structure using a building block validation strategy

·         Accurately identifies the contribution failure mechanisms during the failure evolution process

·         Conditions that cause the delamination of first ply (on-start of failure), its location as well as track progressive damage evaluation/failure of the composite blade within the plies

·         Accurately considers inter laminar material and geometric discontinuities at the ply drop offs

·         MF-PFA simulation results are in good agreement with the Physical Test Data on actual wind turbine blades; composite blade material is calibrated against available ASTM standard test data

·         Simulation reproduced strength and fatigue life as observed in the test, thus ensuring reliance and confidence in simulation in guiding the design of blades for improved performance (Fig. 3)

·         Modified design changes of key composite material in the blade resulted in weight reduction of more than  10% 

Figure 3: Progressive failure analysis and test validation of Sandia?s BSDS blade under static loading

  References:

1.        Wind-Laminate-Ply Drop: Frank Abdi, Joshua Paquette, Glenn Crans, Levon Minnetyan, Pier Marzocca,  ?Durability of Tapered Composite Laminates under Static and Fatigue Loading ?, AIAA-SDM 2011 conference, Denver Colorado

2.        Wind-Blade-Robust-Design: Galib Abumeri, Joshua Paquette, Frank Abdi,  ?Durability and Reliability of Wind Turbine Composite Blades Using Robust Design Approach?, AIAA-SDM 2011 conference, Denver Colorado, AIAA_SDM_945357reliability. 

3.         33 Meter Wind Blade OPTIM: Galib Abumeri and Frank Abdi, Joshua Paquette ?DURABILITY AND RELIABILITY OF LARGE WIND TURBINE COMPOSITE BLADES?.  SAMPE Journal  Nov/Dec 2012, Vol 48, No 6 WWW.Sampe.org.