Volume 9, Issue 2 (June 1986)
Characteristic Threshold and Infrared Vibrothermography of Sand
Rheological properties of granular soils under vibratory, cyclic, and transient loading can be interpreted at the grain level where the solid particles interact with one another. Macroscopic deformations result mainly from the principal following mechanisms: (1) compaction mechanism that forces the solid particles closer together and leads to a denser packing; (2) distortion mechanism governed by irreversible grain slidings generating heat; and (3) attrition mechanism caused by breakage of asperities and crushing of grains under high pressures.
The infrared vibrothermography used in our laboratory is a nondestructive test that allows records and observations in real time of heat patterns produced by the dissipation of energy caused by friction between grains. Such dissipative heat occurs when granular soil is subjected to vibratory loading exceeding the characteristic threshold, and it shows with evidence the distortion mechanism.
The infrared thermographic technique described, which couples mechanical and thermal energy, offers the potential of directly monitoring the stress state of particle rearrangement or characteristic threshold and predicting the macroscopic mechanical response of granular materials.