# Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review
## 4 Dynamic Fracture Toughness and Failure Modes
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material Properties** & **Major Findings** & **Reference** \\ \hline Compressive Strength & At a temperature of 100–500 \({}^{\circ}\)C, linear changes were observed because ultimate rock strength was higher than the induced thermal strains. Above 500 \({}^{\circ}\)C, about 70\% reduction was recorded in the peak strength, which was a result of plastic deformation. & [82] \\ Compressive Strength & They tested the San Julian’s calcarente at a temperature of 100–600 \({}^{\circ}\)C to investigate the behavior of porous carbonate rocks. At 600 \({}^{\circ}\)C, they found a reduction in peak strength and elastic moduli by 35\% and 75\%, respectively. & [83] \\ Compressive Strength & They studied the mechanical behavior of thermally deteriorated carbonate rocks at a temperature window of 25–900 \({}^{\circ}\)C. They observed that, beyond the brittle–ductile transformation phase, the slippage-twining effect in crystal lattice governed the plastic deformation and significantly reduced the peak strength and elastic modulus & [84] \\ Compressive Strength & They found a significant reduction in elastic modulus at a temperature of 600 \({}^{\circ}\)C. Beyond this critical temperature (i.e., 600 \({}^{\circ}\)C), rock strength dropped to 81\%. The decomposition of carbonate at elevated temperature was considered the main reason for depreciation in mechanical characteristics. & [9] \\ Compressive & They investigated the thermal cycling effect on carbonate rocks at a temperature of 200 \({}^{\circ}\)C. They noticed a considerable decrement in compressive strength and tensile strength of dolostone by 27\% and 25\%, respectively. & [6] \\ Compressive & They noticed the dynamic response of rocks & [6] \\ \& Tensile Strength & [200 \({}^{\circ}\)C]. They noticed a considerable decrement in compressive strength and tensile strength of dolostone by 27\% and 25\%, respectively. & [6] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: A brief description of major findings regarding the variations in mechanical properties of the thermally damaged carbonate rocks. These issues are as follows: rate-dependent constitutive modeling, validation of numerical simulations, high-rate deformation measurements, etc. [86]. Under dynamic loading, microstructural variations in rocks are referred to as fracture properties, including fracture initiation, fracture propagation, fracture velocity, and energy absorption [96; 97; 98]. [PERSON] [86] performed a dynamic notched semi-circular bending (NSCB) test on carbonate rock at room temperature to study the fracture initiation toughness. Figure 7 shows a frame of four pictures captured by the high-speed camera at different stages of the test. The first frame at 0 \(\upmu\)s shows a zone of interest, the second frame displays the crack initiation phenomenon at 40 \(\upmu\)s, and the next frames demonstrate the crack propagation phenomenon up to the last frame, where the crack is visible at 64 \(\upmu\)s.  
To ascertain the dynamic behavior of thermally treated carbonate rocks, [PERSON] et al. [89] tested the limestone samples at the temperature window of 25 to 600 \({}^{\circ}\)C using the SHPB at an impact pressure range of 0.4 to 0.9 Mpa. Figure 8 shows that the dynamic stress-strain curves exhibited three stages, which include elastic phase, yielding phase, and failure point. At a constant temperature, the slope of the linear relationship between dynamic stress-strain increased with the increase in impact pressure. However, the increasing temperature gradually depreciated the elastic phase and enhanced the yielding phase up to the failure point under brittle-ductile transformation in which rock can withstand greater strain at minimum stress. The same results were also reported by [PERSON] et al. [91] while testing thermally treated limestones (25-900 \({}^{\circ}\)C) under quasi-vacuum and air-filled environments.