Characteristics of Infrared Radiation of Coal Specimens Under Uniaxial Loading

An object in its natural state at temperatures greater than -273.15 C generates electromagnetic waves, including infrared radiation (Wu et al. 2000). Coal and rock under loading also produce detectable electromagnetic radiation anomalies including wavelengths in the infrared band (Brady and Rowell 1986; Luong 1987). Through studying the infrared radiation characteristics on the surface of coal and rock specimens under loading conditions, one can derive the relationship between infrared radiation and the mechanical parameters of the specimens under dynamic stress. This information can be used to predict dynamic phenomena including ground pressure, coal bursting, and rock bursting. In observational experiments of infrared radiation of solid materials (including coal, rock, and concrete)under loading, researchers have applied statistical parameters and analysis methods such as the average infrared radiation temperature (AIRT), maximum (or minimum) infrared radiation temperature, infrared thermal image sequences (Wu et al. 2006a, b), and infrared thermal image sequences of isotherms (Ji and An 2007). However, these results vary significantly and some results are often contradictory. Liu et al. (2004) argued that this was because of a difference among the instruments being used. They significantly improved the instrumentation and experimental procedures and proposed updated procedural standards (Liu et al. 2004). Nevertheless, owing to the heterogeneity, anisotropy, and discontinuity of the coal and rock, the performance improvement of the experimental system achieved by the improved measures did not completely solve the issues of inconsistent results. New statistical parameters and analysis methods should, thus, be proposed. This paper proposes a ‘‘two-image-sequence, four-indicator’’ method to study the infrared radiation characteristics of coal specimens under uniaxial loading.