BS ISO 6721-8:2019 pdf free

BS ISO 6721-8:2019 pdf free.Plastics一Determination of dynamic mechanical properties
Figure 1 shows, schematically, suitable apparatus for measuring velocity by an immersion method. Two ultrasonic transducers are mounted coaxially in a bath containing a liquid, one acts as a transmitterT of longitudinal ultrasonic wave pulses and the other as a receiver R. The transmitter is driven by a series of high-voltage, short-duration electrical pulses from the transducer drive unit. A pulse repetition interval of about 1 ms is satisfactory. Acoustic pulses launched by the transmitter travel through the liquid and the specimen and are detected by the receiving transducer. The specimen is mounted on a turntable,located between the transducers T and R, such that the angle of incidence of the acoustic beam can be varied and measured to±0,5°. The specimen can be removed from the beam. The receiving transducer is connected to electronic equipment that will enable measurement of the difference in the arrival times of pulses received with and without the specimen in the beam. An oscilloscope, whose time base is accurately calibrated and triggered by the transducer drive unit, is suitable for this purpose.
The receiving transducer may be replaced by a reflecting surface, such as a metal block, positioned normal to the axis of the transmitter as shown in Figure 2. The transmitting transducer is now used to detect the beam of pulses reflected back through the liquid and the specimen and is connected to the transit-time measuring equipment.
This test arrangement may be more appropriate if the specimen is only available as a thin sheet since the transit time in the specimen is twice that obtained using the transmitter and receiver arrangement.Figure 3 shows a method for measuring wave velocity by direct contact between the transmitting and receiving transducers and the surfaces of the specimen. For the determination of the longitudinal wave velocity, transducer pairs that launch and receive longitudinal acoustic waves are used while, for the determination of the transverse wave velocity, shear (transverse) wave transducers are employed. The transducer separation can be varied to accommodate specimens of different thickness including direct contact between the two transducers. A coupling fluid is necessary to maximize the pulse amplitude transmitted to the specimen and to the receiver.BS ISO 6721-8 pdf free download.