Novel methods and kits for creating defects in composite materials, as well as an engineered part or structure with one or more designed defects, are disclosed. The disclosed inventions advantageously permit the intentional introduction of one or multiple defects of any desired size and shape, either between the same two chosen laminae or on different layers within a multi-layer composite, having mechanical and thermal properties that are akin to those found for actual defects. One disclosed method involves creating a mask having a cut-out in the size and shape of a desired defect, placing the mask at a location on a first substrate where the defect is desired, applying a release agent, removing the mask, and adding a second substrate over the first substrate with release agent. The first substrate may be a cured lamina or an uncured lamina pre-impregnated with resin having a barricade in the size and shape of the outline of the desired defect.