If you snap a wooden pencil, it makes a noise: this is an example of acoustic emission. The fact that the pencil is made of wood means that the fracture process is complicated: wood is a fine example of an anisotropic material. Wood prefers to fracture along the grain. Wood is often used to make layered materials, such as plywood and veneers. Delamination, defined here as “a debonding of two adjoining layers in the laminated woodbased composite,” is a common (and potentially dangerous) form of damage. Its detection by nondestructive means is a major topic of this book.
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