This book is intended for engineer analyst end users with basic knowledge of composite material and finite element analysis requesting more information on how to design, build, and test a durable and damage-tolerant composite wind turbine blade. The wind blade industry utilizing composite materials is being periodically challenged with the manufacturing process, service load, nondestructive evaluation (NDE) and establishing material properties. In this chapter, discussions will be centered around: (1) composite material modeling and effect of defects using nanoassisted micromechanics algorithms; (2) structural design considerations of durability and reliability and scale-up; (3) blade manufacturing techniques; (4) virtual testing and building block validation strategy considering the effect of defects for in-service performance utilizing multiscale modeling; and (5) certification by analysis supported by minimum tests. There are multiple sections in this chapter and the highlights of these sections are the following: 1. Problems and challenges in the design of blade manufacturing, and material type, and structural concepts of as-built parts. Building block strategy to minimize tests, considering the effect of defects, scatter, uncertainty, and the environment in the material and the structure. 2. Detailed material property generation process of both unnotched and notched coupons of a typical toughened epoxy material system. In this section, the generated material properties are calibrated, validated, and predicted based on available test data. Further, the entire set of generated material properties is used as inputs to finite element analysis. 3. Detailed material allowable generation material scatter and uncertainty and CMH-17 authority definition and requirements, and available public data. 4. Discusses the in-service loading structural performance under static and fatigue cyclic loading. Emerging multiscale dehomogenized material models, and damage evolution process.
A capability consisting of software development and experimental techniques has been developed and is described. The capability is integrated into GENOA-PFA to model polymer matrix composite (PMC) structures. The capability considers the physics and mechanics of composite materials and structure by integration of a hierarchical multilevel macro-scale (lamina, laminate, and structure) and micro scale (fiber, matrix, and interface) simulation analyses. The modeling involves (1) ply layering methodology utilizing FEM elements with through-the-thickness representation, (2) simulation of effects of material defects and conditions (e.g., voids, fiber waviness, and residual stress) on global static and cyclic fatigue strengths, (3) including material nonlinearities (by updating properties periodically) and geometrical nonlinearities (by Lagrangian updating), (4) simulating crack initiation. and growth to failure under static, cyclic, creep, and impact loads. (5) progressive fracture analysis to determine durability and damage tolerance. (6) identifying the percent contribution of various possible composite failure modes involved in critical damage events. and (7) determining sensitivities of failure modes to design parameters (e.g., fiber volume fraction, ply thickness, fiber orientation. and adhesive-bond thickness). GENOA-PFA progressive failure analysis is now ready for use to investigate the effects on structural responses to PMC material degradation from damage induced by static, cyclic (fatigue). creep, and impact loading in 2D/3D PMC structures subjected to hygrothermal environments. Its use will significantly facilitate targeting design parameter changes that will be most effective in reducing the probability of a given failure mode occurring.
This report describes methods and corresponding computer codes that are used to evaluate progressive damage and fracture and to perform probabilistic assessment in built-up composite structures. Structural response is assessed probabilistically, during progressive fracture. The effects of design variable uncertainties on structural fracture progression are quantified. The fast probability integrator (FPI) is used to assess the response scatter in the composite structure at damage initiation. The sensitivity of the damage response to design variables is computed. The methods are general purpose and are applicable to stitched and unstitched composites in all types of structures and fracture processes starting from damage initiation to unstable propagation and to global structure collapse. The methods are demonstrated for a polymer matrix composite stiffened panel subjected to pressure. The results indicated that composite constituent properties, fabrication parameters, and respective uncertainties have a significant effect on structural durability and reliability. Design implications with regard to damage progression, damage tolerance, and reliability of composite structures are examined.
