Study on Dynamic Mechanical Properties and Fine-scale Characteristics of Concrete under Thermal Coupling Effect

To investigate the dynamic mechanical behavior, microscopic characteristics, and damage evolution of concrete subjected to combined temperature and impact air pressure, a series of experiments were conducted using a Φ75 mm large-diameter split Hopkinson pressure bar (SHPB), complemented by numerical simulations. C30 concrete specimens exposed to different temperature levels were tested under dynamic loading conditions, and corresponding numerical analyses were performed. On this basis, a damage-inclusive piecewise constitutive model was developed to describe the material response. The experimental and simulation results indicate that the temperature-related parameter K increases with rising temperature and reaches its peak at approximately 400°C, after which it decreases as temperature continues to increase. In contrast, the air-pressure-related parameter D exhibits a continuous growth with increasing impact air pressure. Elevated temperatures cause pronounced deterioration of the internal microstructure of concrete, while impact loading significantly accelerates crack propagation. Cracks initially penetrate along the axial direction from the specimen center and subsequently expand radially, reflecting a transition in the dominant failure mode. This research provides a theoretical basis for evaluating the mechanical performance of concrete structures and for guiding engineering design under high-temperature environments.