Fabric reinforced polymer matrix composites are an integral structural material used in wind turbine blades. Wind turbines are expected to experience growth both in physical size and utilization as the focus of power generation shifts towards utilizing renewable sources more efficiently. Even current generation blades are experiencing reliability concerns. These factors are now driving improvements in design and manufacture of wind turbine blades. With this, progress in characterizing the mechanical behavior of materials is necessary. Composite materials possess unique damage mechanisms due to their constituent materials and these require further study. Composite materials were manufactured into four layups from four fabrics and an epoxy matrix. Acoustic emission sensors were applied in a linear locating arrangement to capture elastic waves from damage mechanisms during a tensile test. Data critical to this work that was extracted from the elastic waveforms include peak frequency and absolute energy. A static loading scenario was used to characterize the materials and their damage progression while an LUR loading scenario was used to correlate absolute energy to dissipated strain energy. Results of the material characterization found that a greater range of frequencies, thus damage mechanisms, were observed for increasingly complex fabric architectures. The observed frequency and energy data provided valuable information on the interaction of the various constituent materials. Attempts at obtaining an accurate and consistent correlation value were not successful with the LUR tests. However, total accumulated energy emerged as a consistent metric of equal value between static and LUR tests that shows promise of being an indicator of coupon damage state. Acoustic emission was found to provide a unique analysis that can identify and characterize damage and fabric composition in composite materials. The frequency content provides a consistent method of identifying damage mechanisms between varying materials. Correlating acoustic energy to strain energy dissipated appears to be more complex than is developed here but the concept does hold merit and requires further study. An applicable database of AE characteristics of the materials was created that will be of great use for future more complex sub-structure component testing.

In this book, two kinds of analysis based on acoustic emission recorded during mechanical tests are investigated. In the first, individual, analysis, acoustic signature of each damage mechanism is characterized. So with a clustering method, AE signals that have similar shapes or similar features can be group together into a cluster. Afterwards, each cluster can be linked with a main damage. The second analysis is based on a global AE analysis, on the investigation of liberated energy, with a view to identify a critical point. So beyond this characteristic point, the criticality can be modeled with a power-law in order to evaluate time to failure.

“...a comprehensive and well written book, which...will be useful reading for both researchers entering the field and experienced specialists looking for new ideas....a valuable and long-lasting contribution to experimental mechanics.” – Stepan Lomov, KU Leuven This expert volume, an enhanced Habilitation thesis by the head of the Materials Testing Research Group at the University of Augsburg, provides detailed coverage of a range of inspection methods for insitu characterization of fiber-reinforced composites. The failure behavior of fiber reinforced composites is a complex evolution of microscopic damage phenomena. Beyond the use of classical testing methods, the ability to monitor the progression of damage insitu offers new ways to interpret the materials failure modes. Methods covered include digital image correlation, acoustic emission, electromagnetic emission, computed tomography, thermography, shearography, and promising method combinations. For each method, the discussion includes operational principles and practical applications for quality control as well as thoughtful assessment of the method's strengths and weakness so that the reader is equipped to decide which method or methods are most appropriate in a given situation. The book includes extensive appendices covering common experimental parameters influencing comparability of acoustic emission measurements; materials properties for modeling; and an overview of terms and abbreviations.

This book provides a comprehensive overview of the current progress in fiber-reinforced plastics (FRP), covering manufacturing, mechanical behavior, and resistance performance. It includes the elastic and damage behavior of unidirectional FRP, and highlights the improvements achieved by adding multiwall carbon nanotubes. The material resistance is assessed through fatigue response, local behavior, local properties, and failure mechanisms, including crack density and microcrack propagation behavior. The book also explores the degradation of macroscopic mechanical properties such as elastic modulus and compressive strength versus plastic strains. Additionally, it focuses on the progress made in out-of-plane composite characterization and modeling response for simulations of critical mechanical parts currently used in different industries, thanks to advances in manufacturing techniques that allow for the production of increasingly complex and thicker geometries.

This book presents a detailed description of the most common nondestructive testing(NDT) techniques used for the testing and evaluation fiber-reinforced composite structures, during manufacturing and/or in service stages. In order to facilitate the understanding and the utility of the different NDT techniques presented, the book first provides some information regarding the defects and material degradation mechanisms observed in fiber-reinforced composite structures as well as their general description and most probable causes. It is written based on the extensive scientific research and engineering backgrounds of the authors in the NDT and structural health monitoring (SHM) of structural systems from various areas including electrical, mechanical, materials, civil and biomedical engineering. Pursuing a rigorous approach, the book establishes a fundamental framework for the NDT of fiber-reinforced composite structures, while emphasizing on the importance of technique’s spatial resolution, integrated systems analysis and the significance of the influence stemming from the applicability of the NDT and the physical parameters of the test structures in the selection and utilization of adequate NDT techniques. The book is intended for students who are interested in the NDT of fiber-reinforced composite structures, researchers investigating the applicability of different NDT techniques to the inspections of structural systems, and NDT researchers and engineers working on the optimization of NDT systems for specific applications involving the use of fiber-reinforced composite structures.