# Some Thoughts about Infrared Radiation Response Characteristics during Loading of Sandstone Samples
## 1 Introduction  
Mining hazards such as mine water inrush and rockbursts have always threatened mine safety [1, 2]. To forecast dangerous areas or disasters in underground constructions, many methods such as microseismic monitoring, acoustic emission measurements, and wave speed monitoring have been widely used in engineering practice. However, the application of these methods is often limited due to the complicated geological and operating conditions in underground mines. Therefore, non-contact monitoring and forecasting techniques such as the infrared radiation method have become promising [3, 4]. This technique can realize non-destructive and remote monitoring. It has become a potential and effective way to detect the damage evolution of rocks including coal, and can even give early warning and prediction of mine gas outbursts, water inrush, and rockbursts [5, 6, 7].  
Many researchers have carried out infrared radiation experiments [8, 9, 10] on various geotechnical materials. These studies have explored the relationships between the temporal-spatial distribution characteristics of infrared radiation and the fracturing process of coal/rocks [11, 12, 13]. For example, [PERSON] et al. found that the average infrared radiation temperature (AIRT) can be used as a quantitative indicator to characterize the stress distribution of coal and rock during compression [14]. They identified an abnormal AIRT during plastic yielding as rock failure precursors. On this basis, [PERSON] et al. proposed the 'Infrared Temperature Sudden Change' as the indicator and discovered the characteristics of the instantaneous change of infrared temperature at the moment of rock failure [15].  
[PERSON] et al. suggested the use of the variance of successive minus infrared image temperature (VSMIT) as an index and discovered the dominant effect of the stress distribution on infrared radiation [16].  
Although some predictive indicators have been defined in previous studies, they are still far from being applied in practice. One of the most important reasons is the heterogeneous nature of natural rocks. Mineral composition, grain size distribution, and the internal microstructure (e.g., void and inclusions) of rock samples can have a significant impact on deformation, cracking, and yielding. The failure behavior of rocks is closely related to the infrared radiation information on its surface. The difference in cracking behavior can cause infrared radiation scattering on the sample surface. Therefore, the understanding of the relationship between damage evolution and infrared radiation response characteristics considering different failure modes of rock samples is essential.  
This paper documents experiments monitoring the infrared radiation in combination with the strain measurements of sandstone samples under uniaxial loading. The surface AIRT and infrared thermal characteristics of specimens at different damage stages during uniaxial loading were investigated. The mechanisms of infrared radiation in the process of rock damage evolution are discussed. The results provide theoretical and technical hints for the monitoring and early warning of mine water inrush and rock dynamic disasters by infrared radiation remote sensing technique.