# Some Thoughts about Infrared Radiation Response Characteristics during Loading of Sandstone Samples
## 6 Conclusions  
The infrared radiation response characteristics and mechanisms of sandstone samples under uniaxial compression were investigated by using infrared thermal imaging and strain measurement techniques. The experimental results show that during loading, different processes (some of them reverse acting) contribute to heat production or consumption. Different fracture mechanisms (shear vs. tensile fracturing) determine the thermal behavior in a quite different way. Thermoelastic effects and the nearly adiabatic compression of the air in the pore space govern the temperature variations during crack closure and elastic deformation stage. However, the temperature changes are dominated by both the frictional sliding heat production and the cooling effect due to the expansion of gases in the pore spaces during the stable and unstable crack growth phase. Therefore, the infrared radiation response characteristics of the sandstone include the superposition of different mechanisms, leading to either temperature increase or decrease.  
Some thoughts for carrying out the infrared radiation rock mechanical tests are proposed: (1) Measurements have to be performed very accurately since the temperature deduced from infrared radiation changes are minimal. The use of reference samples and filtering techniques as well as temperature-stabilized measuring places are strictly recommended. (2) It seems questionable that AIRT alone will provide sufficient information (though it may be sufficient to obtain an overview of the overall heat balance), because most interesting information is coming from fracture propagation and this process is very local. Therefore, the local detection and analysis of hotspots may deliver more helpful information. (3) To obtain the complete picture, the surface should be monitored from all sides, otherwise, important features can be missed. (4) A minority of samples have shown decreasing temperature beginning with the onset of microcracking during the loading process. To date, no stringent explanation is available for this phenomenon, although processes such as adiabatic gas expansion in pores can partly help to explain this phenomenon. (5) Because infrared radiation monitoring is a non-destructive method to obtain information about the energy balance in rocks, it should be considered a valuable additional monitoring technique in rock mechanics.  
Figure 8: AIRT of sample A\({}_{1}\) before and after denoising processes. (**a**) Before denoising. (**b**) After denoising.  
**Author Contributions:** All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by H.S., H.Z., H.K. and F.W.; Data curation, M.H. The first draft of the manuscript was written by [PERSON] and all authors commented on previous versions of the manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Liaoning Provincial Department of Education Scientific Research Project under Grant L2020050, the Doctoral Research Fund of Liaoning Province under Grant 2021-BS-247, and the Talent Introduction Scientific Research Start-up Foundation of Liaoning Petrochemical University under Grant 2019 XJJL-025. The laboratory tests were conducted at the China University of Mining and Technology (CUMT) with the support of [PERSON]. Therefore, the first author greatly acknowledges the Ph.D. study on the infrared radiation characteristics of rocks at CUMT. All the colleagues from CUMT involved in the laboratory tests are also gratefully acknowledged.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.