"The goal of this research was to accurately predict the ultimate compressive load of impact damaged graphite/epoxy coupons using a Kohonen self-organizing map (SOM) neural network and multivariate statistical regression analysis (MSRA). An optimized use of these data treatment tools allowed the generation of a simple, physically understandable equation that predicts the ultimate failure load of an impacted damaged coupon based uniquely on the acoustic emissions it emits at low proof loads."--Leaf v.

"The purpose of this project was to investigate how accurately an artificial neural network could predict the ultimate compressive loads of impact damaged 24-ply graphite-epoxy coupons from ultrasonic C-scan images. The 24-ply graphite-epoxy coupons were manufactured with bidirectional preimpregnated tape and cut into 21 coupons, 4 inches by 6 inches each. The coupons were impacted at known impact energies of 10, 12, 14, 16, 18, and 20 Joules in order to create barely visible impact damage (BVID). The coupons were then scanned with an ultrasonic C-scan system to create an image of the damaged area. Each coupon was then compressed to failure to determine its ultimate compressive load."--Leaf iv.

Smart Composites: Mechanics and Design addresses the current progress in the mechanics and design of smart composites and multifunctional structures. Divided into three parts, it covers characterization of properties, analyses, and design of various advanced composite material systems with an emphasis on the coupled mechanical and non-mechanical behaviors. Part one includes analyses of smart materials related to electrically conductive, magnetostrictive nanocomposites and design of active fiber composites. These discussions include several techniques and challenges in manufacturing smart composites and characterizing coupled properties, as well as the analyses of composite structures at various length and time scales undergoing coupled mechanical and non-mechanical stimuli considering elastic, viscoelastic (and/or viscoplastic), fatigue, and damage behaviors. Part two is dedicated to a higher-scale analysis of smart structures with topics such as piezoelectrically actuated bistable composites, wing morphing design using macrofiber composites, and multifunctional layered composite beams. The analytical expressions for characterization of the smart structures are presented with an attention to practical application. Finally, part three presents recent advances regarding sensing and structural health monitoring with a focus on how the sensing abilities can be integrated within the material and provide continuous sensing, recognizing that multifunctional materials can be designed to both improve and enhance the health-monitoring capabilities and also enable effective nondestructive evaluation. Smart Composites: Mechanics and Design is an essential text for those interested in materials that not only possess the classical properties of stiffness and strength, but also act as actuators under a variety of external stimuli, provide passive and active response to enable structural health monitoring, facilitate advanced nondestructive testing strategies, and enable shape-changing and morphing structures.

The purpose of this investigation was to develop a method of testing the standard TELAC (Technology Laboratory for Advanced Composites) graphite/epoxy coupon directly in compression. Since thin coupons buckle under compressive loads, a compression jig was needed to support the coupon and prevent it from buckling. The most successful design for a compression jig was a set of 300 steel balls that are pressed onto both sides of the coupon. These 1/4 inch diameter steel balls are free to rotate insuring that no shear load is applied to the coupon. These steel balls are housed in two steel plates, one for each side of the coupon. An Aluminum cage bolted onto each plate holds the balls onto the plate. Preliminary tests indicate that this compression jig could provide valid test results.

The impact and post-impact response of graphite/epoxy and Kevlar/epoxy laminates was investigated over a wide range of parameters. The parameters considered were impactor kinetic energy, target boundary conditions, impactor mass, material type, and the influence of preload on the impact event. The study included analytical and experimental investigations for impact response and post-impact residual strength. After having inflicted impact damage with 12.7 mm spheres, the specimens were evaluated using dye-penetrant-enhanced X-ray and ultrasonic C-scan techniques. The specimens were loaded monotonically to failure to determine the post-impact residual strength. An analytical methodology using a global model to predict the impact event and a local model to predict the damage was developed and compared with the measured damage data. The global structural model is based on a Rayleigh-Ritz energy method to develop a set of coupled, ordinary differential equations in time. The local model is an analytic, theory of elasticity approach to the region near the impact. An equivalent membrane model for the damaged region with an average strain criterion was used to predict the post-impact residual strength given the damage state. The concepts of damage resistance and damage tolerance are, thus, considered independently. The results from the analytical impact models followed the same trends in predicting damage as the experimental data. The analytical residual strength predictions followed the same trends as the measured residual strength for in-plane dominated fracture. The results show that both the structural and material behavior must be considered in predicting damage. Residual strength was found to be a function only of the damage present for in-plane tensile fracture. A consistent analytical design philosophy for composite structures subjected to impact is proposed. This partitioning of the problem into global and local phenomena effectively separates structural and material effects. The method is illustrated via specific examples, demonstrating its usefulness in design.

Over the last few decades, uncertainty quantification in composite materials and structures has gained a lot of attention from the research community as a result of industrial requirements. This book presents computationally efficient uncertainty quantification schemes following meta-model-based approaches for stochasticity in material and geometric parameters of laminated composite structures. Several metamodels have been studied and comparative results have been presented for different static and dynamic responses. Results for sensitivity analyses are provided for a comprehensive coverage of the relative importance of different material and geometric parameters in the global structural responses.

An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.