Effects of Defects: Part A - Development of a Protocol for Defect Risk Management &amp; Improved Reliability of Composite Structures

32nd ASME Wind Energy Symposium

Riddle

2014

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Application of different damage modeling approaches for use with composite materials and composite material structures has grown with increasing computational ability. However, assumptions are often made for "worst case" scenarios with these modeling techniques In order to develop a tool that will allow for accurate analysis of a complete structure, modeling approaches must be optimized by including defects of different parameters. It was the optimization of these approaches that was investigated herein with specific application toward establishing a protocol to understand and quantify the effects of defects in composite wind turbine blades. A systematic, three-round study of increasing complexity was performed to understand the effects of three typical blade manufacturing defects while investigating continuum, discrete, and combined damage modeling. Through the three rounds of the benchmark material testing, significant coupon level testing was performed to generalize the effects of these defects. In addition, material properties and responses were analyzed and then utilized as material inputs and correlation criteria for each analytical technique. A standard defect case was initially used for each modeling technique and correlation was compared both qualitatively and quantitatively. While each modeling type offered certain attributes, a combined approach yielded the most accurate analytical/experimental correlation. Thus, a unique comparison of several different analytical approaches to composites with respect to manufacturing for consistency, accuracy, and predictive capability allowing for improved blade reliability and composite structural assessment. NomenclatureBRC = Blade Reliability Collaborative MSUCG = Montana State University Composites Group BMT = Benchmark Material Testing OP = Out-of-plane wave IP = In-plane wave CDM = Continuum Damage Model DDM = Discrete Damage Model UMAT = User Material Subroutine σ = Stress ε = Strain u = Displacement

Section: Table 3 Progressive Damage Outline and Degradation Approachmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Defects: Part B—A Comparison of Progressive Damage Modeling of Fiberglass/Epoxy Composite Structures with Manufacturing Induced Flaws

32nd ASME Wind Energy Symposium

Riddle

2014

Self Cite

“…Previous research has shown the utility of quantifying the influence of defects in composite laminates (Riddle et al, 2013;Dowling, 2012;Samborsky et al, 2012;Nijssen, 2011;Lin and Styart, 2007). Furthermore, a probabilistic design approach may be implemented, but has not been adopted as the common approach for wind turbine certification (FAA AC 25.571-1D, 2011).…”

Section: Model Overviewmentioning

confidence: 99%

Effects of defects in composite wind turbine blades – Part 3: A framework for treating defects as uncertainty variables for blade analysis

Riddle¹,

2018

Wind Energ. Sci.

Abstract. Given that wind turbine blades are large structures, the use of low-cost composite manufacturing processes and materials has been necessary for the industry to be cost competitive. Since these manufacturing methods can lead to the inclusion of unwanted defects, potentially reducing blade life, the Blade Reliability Collaborative tasked the Montana State University Composites Group with assessing the effects of these defects. Utilizing the results of characterization and mechanical testing studies, probabilistic models were developed to assess the reliability of a wind blade with known defects. As such, defects were found to be best assessed as design parameters in a parametric probabilistic analysis allowing for establishment of a consistent framework to validate categorization and analysis. Monte Carlo simulations were found to adequately describe the probability of failure of composite blades with included defects. By treating defects as random variables, the approaches utilized indicate the level of conservation used in blade design may be reduced when considering fatigue. In turn, safety factors may be reduced as some of the uncertainty surrounding blade failure is reduced when analyzed with application specific data. Overall, the results indicate that characterization of defects and reduction of design uncertainty is possible for wind turbine blades.

“…As such, the MSUCG has divided this effort into two distinct tasks: Part A-Flaw Characterization, and Part B-Effects of Defects. [5][6][7][8] The function of the Flaw Characterization effort has been to provide quantitative analysis for two major directives: (1) acquisition and generation of quantitative flaw data for use in the Effects of Defects numerical modeling program; and, (2) development of a flaw severity designation system and probabilistic risk management protocol for as-built flawed structures. The Effects of Defects portion is focused on the development of modeling capabilities to predict the damage progression and structural implications of common flaws found in composite wind turbine blades.…”

Section: Introductionmentioning

confidence: 99%

“…6 These results were then utilized to build simple analytical models with the purpose of performing laminate analysis with included defects in a coordinated effort with the Flaw Characterization task. 5,7 An understanding of the changes in the material properties associated with characterized flaws was achieved on a coupon level with physical testing being performed with several configurations of each of the different flaw types. This testing clearly indicated that fiber misalignment and porosity resulted in degraded material properties and decreased material performance.…”

Section: Introductionmentioning

confidence: 99%

Effects of Defects: Part B—Progressive Damage Modeling of Fiberglass/Epoxy Composite Structures with Manufacturing Induced Flaws Utilizing Cohesive Zone Elements

Woo

54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

et al. 2013

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The Effects of Defects is important for the reliability of modern composite wind turbine blades. The DOE has sponsored a comprehensive study to characterize common manufacturing defects and establish damage growth and validation tools to contribute to a wind turbine blade reliability infrastructure. To support this development of a reliability infrastructure, progressive damage modeling of blade representative coupons has been performed. A model has been developed that is combined of both continuum and discrete modeling approaches. A user-defined material subroutine has been created and used with material properties established from experimental testing for the former, while cohesive zone elements were placed between each fiber tow to capture the fracture that occurs in these areas for the latter. Two-dimensional (2D), four-layer coupon level models were generated based on the geometry of the as-tested specimens. Results from this model were compared to the visual damage progression and stress-strain data from in-plane wave tests in tension and compression. While the uniformity of the models resulted in more dramatic changes at failure points, the progression was found to match in these cases, thereby verifying the combined continuum and discrete modeling approach. NomenclatureBRC = Blade Reliability Collaborative MSUCG = Montana State University Composites Group OP = out-of-plane wave IP = in-plane wave CDM = Continuum Damage Model DDM = Discrete Damage Model σ = Stress ε = Strain u = displacement