Study on Ultrasonic Response to Mechanical Structure of Coal under Loading and Unloading Condition

Figure 6

Experimental results for coal samples under cyclic loading.

(a) Cyclic loading and unloading pattern

(b) Dominant frequency response

(c) Ultrasonic testing results of coal before loading

(d) Ultrasonic testing results under the force of 1.5 kN

(e) Ultrasonic testing results under the force of 4.5 kN

(f) Ultrasonic testing results under the force of 7.5 kN

(g) Ultrasonic testing results under the force of 9 kN

(h) Ultrasonic testing results under the force of 11 kN