ASTM D638 (Standard Test Method for Tensile Properties of Plastics) vs. ASTM D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials). ASTM D3039 is recommended for highly oriented and/ or high tensile modulus fiber reinforced polymer composites. ASTM D638 is recommended for randomly oriented, discontinuous, moldable, or low reinforcement volume composites or composites with tensile modulus less than 3 MSI