Method and apparatus for determining the fundamental viscoelastic properties of a material

Abstract

Abstract An apparatus for determining the fundamental viscoelastic properties of a viscoelastic material includes means for imparting a torsional stress in a viscoelastic material; means for measuring the relaxation of the torsional stress over time and converting the relaxation stress to a representative waveform; and processing means for determining the frequency dependant fundamental viscoelastic properties of the material based on the shape of a portion of the waveform. Preferably, the processing means includes a first dedicated processor for producing a digital representation of the waveform and a second general processor, such as an IBM compatible microcomputer for determining the fundamental viscoelastic properties from a portion of the digital representation. To facilitate automating the determination of the fundamental viscoelastic properties of the test material, the first processor examines the waveform and aborts the determination if the digital waveform is atypical of an expected waveform for a viscoelastic material subjected to a torsional stress. A method of determining the fundamental viscoelastic properties of a viscoelastic material includes the steps of imparting a torsional stress in a viscoelastic material; measuring the relaxation of the torsional stress over time and converting the relaxation stress to a representative analog waveform; digitizing the representative analog waveform to produce a representative digital waveform; and, determining the frequency dependant fundamental viscoelastic properties of the material based on the shape of a portion of the representative digital waveform. To facilitate automating the method, the shape of the waveform may be analyzed to detect the start of a test, the end of the test, and whether the test is a valid test. Preferably, the fundamental viscoelastic properties of the test material are determined by converting the torque based amplitudes of the waveform to shear relaxation modulus values, such as by multiplying the torque amplitudes by the geometric form factor of the test material, and then by transforming the shear stress modulus values to frequency dependant fundamental viscoelastic properties through the known Yagii/Maekawa approximation. <IMAGE>

Inventors

• 👤 John P. Porter
• 👤 Ronald L. Dellangelo
• 👤 Emmitt R. Harrell, Jr.

Bibliographic Details