RANDOM GLASS MAT REINFORCED THERMOPLASTIC COMPOSITES .4. CHARACTERIZATION OF THE TENSILE-STRENGTH

Random glass mat thermoplastic composites, which can be thermostamped to form complex deep-drawn parts with ribs and bosses, are excellent materials for making low-cost stiff parts with relatively high impact strength. However, the mechanical properties of these materials, as determined by standard tensile tests, are known to exhibit large scatter. And the tensile modulus in these materials can vary by a factor of two over a 12.7-mm distance. In an earlier effort, measurements of the local tensile moduli of long, thin, 12.7-mm-wide strips along both thin edges (left and right) of the specimen and across the face were used to show that the local tensile modulus is well approximated by the arithmetic mean of the local left- and right-edge tensile moduli. To establish the tensile strength of these materials, the local tensile moduli of long dog-bone specimens are first characterized along the length, after which the specimens are pulled to failure. The tensile strength is shown to correlate well with the arithmetic mean of the local left- and right-edge tensile moduli.