Experimental study on damage characteristics of granite under ultrasonic vibration load based on infrared thermography

Infrared temperature precursor anomalies are always accompanied by the propagation of cracks in rocks under external loads. Experiments were conducted to observe the infrared temperature change of granite surfaces to investigate the damage characteristics and failure mechanism of granite under ultrasonic vibration. Ultrasonic vibration load test of cylindrical granite samples with a 200 N force were carried out using a 30 kHz piezoelectric ceramic ultrasonic vibrator. During testing, an infrared thermal imager was used to observe and measure the infrared radiation temperature of the rock during the entire loading process. The experimental results show that sharp infrared temperature increase serving as a precursor to rock failure under ultrasonic vibration. The damage and failure process of the rock can be divided into the following three stages: Stage I, corresponding to elastic deformation (0–102.23 s, temperature range 26–150 °C), Stage II, which include micro-fracture and yield (102.3–118.5 s, temperature range 150–306.9 °C), and Stage III, in which macrocracks and failure are produced (118.5–191.833 s, temperature range 256.9–397.2 °C). The core of the rock may be divided into a fracture zone, plastic deformation zone, and elastic deformation zone according to the axial temperature variation of the sample. The effective fracture depth achieved in the rock is 10 mm. As a principal result we show that the fatigue damage caused by ultrasonic vibration and the thermal damage caused by rising temperature are the major factors for breaking granite. The research results in this paper will provide guidance for the application of ultrasonic technology in the drilling field.