Measurement of flexural modulus of polymeric foam with improved accuracy using moiré method

• Published in: Polymer testing 2010-05, Vol.29 (3), p.358-368
• Main Authors: Yen, K.S., Ratnam, M.M., Akil, H.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Beams (structural); Bend tests; Cellular; Deflection; Exact sciences and technology; Flexural modulus; Foams; Forms of application and semi-finished materials; Modulus of rupture in bending; Moiré method; Plastic foam; Polymer industry, paints, wood; Polymeric foam; Properties and testing; Stress strain curves; Stress-strain relationships; Technology of polymers; Testing and control
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/j.polymertesting.2009.12.011

The flexural modulus of polymeric foams determined from three-point bending tests is usually inaccurate due to the local deformation undergone by the material during testing. The machine used in the test gives deflection values larger than the actual deflection of the foam specimen due to the deformation of the material at the loading point. This leads to errors in the computation of the modulus value. In this work, the deflection values of a beam made of polymeric foam in a three-point bending test were determined using the moiré method. The change in the moiré pattern at the neutral axis of the foam during loading was recorded and converted into deflection values. The deflection data were used to generate the stress–strain curve from which the flexural modulus of the foam material was determined. The proposed method was verified using aluminum beams, where a high correlation between the deflection data from the machine readings and the moiré method was obtained. The flexural modulus of the foam determined using the moiré method was found to be within 3% of the value published in the material data sheet.