Abstract: A set of ultrasonic probes for measurement of time of flight of ultrasonic pulses includes a housing (20), two transmitting ultrasonic probes (1, 2) and two identical receiving ultrasonic probes (9, 10) attached to the housing (20). The receiving ultrasonic probes (9, 10) are disposed between the transmitting ultrasonic probes (1, 2) and are disposed along one line with the transmitting ultrasonic probes (1, 2). Time t.sub.L of flight of wave pulse in the workpiece along the distance L between the receiving ultrasonic probes (9, 10) is calculated based on propagation time of a ultrasonic wave (7) transmitted by the transmitting ultrasonic probe (1) and received by the receiving ultrasonic probeheads (9, 10) and on propagation time of a ultrasonic wave (8) transmitted by the transmitting ultrasonic probehead (2) and received by the receiving ultrasonic probeheads (9, 10).

Abstract: The invention solves the problem of measurement of internal stresses in cylindrical objects, such as axles, shafts and tubes made of material with varying non-uniform homogeneous mechanical properties. The method consists in that a beam of ultrasonic waves is thrown onto the surface of a cylindrical object being tested, said beam being refracted at an angle of 90 degrees. Next the times of passage for every type of waves are measured. On the basis of the calculated differences of the times of passage with a standard the absolute values of components of stresses are calculated. The method is applicable for non-destructive testing of properties and structure of materials and products.