Study on dynamic properties and dynamic temperature of concreteunder 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 using a self-built high-speed infrared temperature measurement system. The time resolution of the high-speed infrared temperature measurement system is in the order of microsecond. The concrete temperature curve was fitted by static calibration test as a reference. 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 and substantial influences of the steel fiber content on both dynamic performance and temperature. Specifically, as the steel fiber content increases, the compressive strength of the concrete improves, reaching optimal mechanical performance at 1.5% steel fiber content. However, at 2.0% 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 the 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 the evaluation of crack propagation behavior.