Molding and torsional testing of tubular specimens of glass fiber‐reinforced polypropylene

Abstract This paper describes a torsion pendulum based on the free vibration method and designed for studies on tubular samples. The design and fabrication of the injection mold used for molding the tubular specimens is also described. Tubular specimens were injection molded form polypropylene and glass fiber‐reinforced polypropylene having different glass fiber contents. The sample, which is enclosed in an insulated chamber, can be cooled with the help of liquid nitrogen and heated electrically. The damped oscillations were recorded on a moving chart paper using a lamp and a photodyne between −40 to 100°C. The results indicate that both storage modulus and the logarithmic decrement are affected by the glass fiber and its content. The reinforcing effect of glass fiber and the suppression of viscoelastic effects are briefly discussed.