Alternative dynamic torsion test to evaluate the elastic modulus of polymers

Author(s)

Piedade, Lucas Pereira ^[1] ; Pintao, Carlos Alberto Fonzar ^[2] ; Foschini, Cesar Renato ^[1] ; Silva, Marcos Ribeiro da ^[2] ; Azevedo Neto, Nilton Francelosi ^[2]

Affiliation

^[1] Sao Paulo State Univ, Sch Engn FEB, Mech Engn Dept, BR-17033360 Bauru, SP - Brazil

^[2] Sao Paulo State Univ, Sch Sci FC, Dept Phys, BR-17033360 Bauru, SP - Brazil

• Document type: Journal article
• Source: MATERIALS RESEARCH EXPRESS; v. 7, n. 9 SEP 2020.
• Web of Science Citations: 0

Abstract

This work presents an alternative for the determination of the torsion modulus, G, of polymers. These materials may be subjected to shear stresses in some structural applications; thereby, the knowledge of G is of great interest. For this purpose, a mechanical system featuring a simplified torsion pendulum version and a rotational motion sensor (RMS) coupled to it was used to establish an angular position as a function of time. The applied technique is considered non-destructive and makes it possible to obtain G without the Poisson's ratio through an equation derived from mechanical spectroscopy and material strength. The main goal is to present and validate the employment of this method for polymers. Therefore, circular cross-sectional samples of extruded polytetrafluoroethylene (PTFE) were subjected to torsional stresses, in which a physical and quantitative explanation is given for the frequency and G curves as a function of the prefixed rotational inertia (I), length (L), and diameter (d). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were also made to ensure the reliability of data. It is possible to establish an L/d ratio, which explains why G converges to a single value when the sample dimensions are different from each other. It was found that G is approximately 350 MPa for an L/d ratio equivalent to 10.64. Such a value is within limits found in the literature, opening the possibility of assessing other polymers. (AU)

• FAPESP's process: 07/04094-9 - Measure of the moment of inertia of solids and liquids: moment of the inertia and internal friction
• Grantee: Carlos Alberto Fonzar Pintão
• Support Opportunities: Regular Research Grants
• FAPESP's process: 17/08820-8 - Synthesis and characterization of biopolymers from vegetable oils and glycerol following the principles of green chemistry
• Grantee: Gilbert Bannach
• Support Opportunities: Regular Research Grants