Study on Dynamic Properties and Dynamic Temperature of Concrete under High-speed Impact

In order to study the dynamic mechanical properties of concrete and the dynamic temperature at the crack under impact, steel-polypropylene fiber reinforced concrete ( SPFRC ) was taken as the research object, and a self-built high-speed infrared temperature measurement system was used. The response rate of the system reached the microsecond level, and the concrete temperature curve was fitted by static calibration test. Combined with the Hopkinson pressure bar test device, the dynamic properties of SPFRC specimens with different steel fiber contents and the dynamic temperature change at the crack were studied. The results indicate a significant coupling effect between the temperature evolution and mechanical properties of the concrete specimens, with the steel fiber content substantially influencing both dynamic performance and temperature. Specifically, as the steel fiber content increases, the compressive strength of the concrete improves, reaching optimal mechanical performance at a 1.5% steel fiber content. However, at a 2% steel fiber content, the mechanical performance slightly decreases due to an increase in internal voids within the concrete. During impact, the dynamic temperature effect at the crack location exhibits a "stepped" pattern, with temperature change occurring in two distinct stages: an initial slow rise during early crack formation, followed by a sharp increase as friction and shear effects intensify with crack propagation. The influence of varying steel fiber content on temperature change is limited, with peak temperature and peak stress showing similar trends. The primary temperature variations are driven by crack propagation and frictional effects. After impact, the overall temperature in SPFRC specimens continues to rise within the first 300 μs. Due to thermal lag, the temperature does not decrease immediately after unloading. The high-speed infrared temperature measurement system provides a new method for real-time monitoring of temperature changes at concrete crack locations, offering a basis for assessing temperature evolution at cracks and aiding in the evaluation of crack propagation behavior.