This study investigates the use of ultrasonic through-transmission methods to determine rock crack damage stress thresholds. The research focuses on four rock types—marble, sandstone, granite, and basalt—under various stress levels. The study evaluates changes in ultrasonic signal characteristics, including velocity, amplitude, dominant frequency, and root-mean-square voltage (VRMS), to assess rock damage levels. Results show that the rate of signal variation can reliably estimate crack closure and crack initiation stress levels before failure. The study compares conventional stress-strain techniques with the new ultrasonic methods, highlighting the potential of ultrasonic monitoring for non-destructive rock damage assessment. The study finds that ultrasonic velocity and amplitude are sensitive to crack initiation and damage. The dominant frequency and VRMS also show variations that correlate with rock damage. The analysis of ultrasonic signals reveals that the maximum derivative of velocity aligns with the crack closure (CC) stress threshold, while the intersection of two linear regions on the derivative graph characterizes the crack initiation (CI) stress threshold. The ultrasonic methods consistently provide lower estimates for CI compared to conventional stress-strain methods, indicating their ability to detect microcracks earlier. The study concludes that ultrasonic through-transmission methods are effective in determining rock crack damage stress thresholds. These methods offer a reliable alternative to time-consuming and subjective stress-strain techniques, with potential applications in rock mechanics. Future research may focus on monitoring crack damage (CD) stress thresholds, improving automated procedures, and analyzing the effects of temperature, moisture, and different loading conditions. The findings support the use of ultrasonic methods for non-destructive rock damage characterization.This study investigates the use of ultrasonic through-transmission methods to determine rock crack damage stress thresholds. The research focuses on four rock types—marble, sandstone, granite, and basalt—under various stress levels. The study evaluates changes in ultrasonic signal characteristics, including velocity, amplitude, dominant frequency, and root-mean-square voltage (VRMS), to assess rock damage levels. Results show that the rate of signal variation can reliably estimate crack closure and crack initiation stress levels before failure. The study compares conventional stress-strain techniques with the new ultrasonic methods, highlighting the potential of ultrasonic monitoring for non-destructive rock damage assessment. The study finds that ultrasonic velocity and amplitude are sensitive to crack initiation and damage. The dominant frequency and VRMS also show variations that correlate with rock damage. The analysis of ultrasonic signals reveals that the maximum derivative of velocity aligns with the crack closure (CC) stress threshold, while the intersection of two linear regions on the derivative graph characterizes the crack initiation (CI) stress threshold. The ultrasonic methods consistently provide lower estimates for CI compared to conventional stress-strain methods, indicating their ability to detect microcracks earlier. The study concludes that ultrasonic through-transmission methods are effective in determining rock crack damage stress thresholds. These methods offer a reliable alternative to time-consuming and subjective stress-strain techniques, with potential applications in rock mechanics. Future research may focus on monitoring crack damage (CD) stress thresholds, improving automated procedures, and analyzing the effects of temperature, moisture, and different loading conditions. The findings support the use of ultrasonic methods for non-destructive rock damage characterization.