RANDOM GLASS MAT REINFORCED THERMOPLASTIC COMPOSITES .5. STATISTICAL CHARACTERIZATION OF THE TENSILE MODULUS

Random glass mat thermoplastic composites (GMT), which can be thermostamped to form complex deep-drawn parts with ribs and boxes. are complex material systems in which the local elastic modulus and local strength vary widely and randomly across the material (the tensile modulus can vary by a factor of two over a 12.7-min length scale). And the values of these local properties depend on the length scale of measurement. The random, large-scale point-to-point variations in their properties cannot be described by a single number. The broad distribution of elastic moduli in GMT has been modeled by a four-parameter probability density function. Moments of this distribution function provide numerical measures that can be used for comparing data sets representing properties of different material samples. This statistical characterization is used to establish the consistency and the random nature of previously obtained elastic moduli data sets. The framework is also used to predict the effect of the gage length used to measure the local elastic modulus on the shape of the modulus probability density function.