Comparison of strain and temperature fields between Micro-NPR and PR anchor rods under uniaxial tension

The deformation characteristics and thermal response of anchor rods are crucial for ensuring the stability and safety of surrounding rock support structures. However, existing research has predominantly concentrated on the mechanical performance of anchor rods, with limited attention to the coupled evolution of strain and temperature fields during tensile deformation. This knowledge gap hinders a comprehensive understanding of the synergistic mechanical-thermal response mechanisms in anchor rods under loading conditions. To address this limitation, the present study systematically investigated the evolution of strain and temperature fields, along with their correlation, during the test of micro-negative Poisson's ratio (NPR) and ordinary Poisson's ratio (PR) anchor rods. Digital image correlation (DIC) and infrared thermography (IRT) techniques were employed for this exploration. The uniaxial tensile tests were conducted at two different rates, and the ordinary PR anchor rod (Q235 anchor rod) was established as a control group for comparative analysis. The findings reveal that the micro-NPR anchor rod exhibit strain localization at multiple locations during the tensile process, whereas Q235 anchors show local strain concentration in only one region. The standard deviation evolution curves for both the strain and temperature field exhibit two distinct phases in the two anchor rods. The evolution patterns between these two types of curves are basically consistent. The two standard deviation curves for the micro-NPR anchor rod display a wavy increase in the second phase, while for the Q235 anchor rod, they increase steadily until the specimen is damaged. The correlation analysis reveals that the standard deviations of strain and temperature differences for both types of anchor rods are significantly correlated. These findings demonstrate the synergistic evolution mechanism of deformation and thermal response, providing a potential foundation for utilizing thermal monitoring to assess the stability of rock support structures.