92
understand the high energy physics related to explosive and shock events. There are many advantages of using the PDV
system with the TTHB apparatus. Firstly, the technique is noninvasive and insensitive to impacts in the system, in contrast to
the traditional strain gauge technique, since the impact event can affect the strength of bonding between the strain gauge and
the bars, and/or break electrical connections (thus, abruptly terminating the measurement). Secondly, the data is recorded in
the frequency domain of the measured signals, which makes the PDV data insensitive to electrical noise, and more reliable
than the strain gauge technique. Moreover, it is an active diagnostic tool to monitor not only the experimental but also the
sample itself, e.g., measuring the time-dependent radial expansion of the specimen during the experiment. The PDV system
is calibrated using the tensile and shear strain gauges implemented on both input and output bars.
16.4 Validation
Bar-attached tests are conducted to validate the capability of the TTHB system to store sufficient combined tensile force and
torque and to achieve quick and clean release. Under different pre-loads applied, the tensile waves are derived from the strain
gauge on the output bar, as shown in Fig. 16.2. After a few optimizations of the clamp design, bar deflection and wave oscillations are considerably mitigated, resulting in smooth and clean square-like waves. The apparatus shows its capability of
generating the high-magnitude tensile wave. The time zone of the combined tensile and shear waves in Fig. 16.3 is shifted to
the connecter sandwiched between the input and the output bar. The difference of the arrival time between the tensile and the
shear waves at the bar connector is initially 45 μs but decreases dramatically along the wave rise. The difference of the arrival
time can be adjusted by the distance between the clamp and the bar connector, i.e., the specimen in a combined tensiontorsion test. The rise time of the tensile wave favorably varies from 50 to 100 μs, while the shear wave around 30 μs. The
length of the tensile wave approximates 800 μs, while the shear wave 1200 μs, corresponding to the length of the pre-stressed
section of the input bar and the bar material.
Fig. 16.2 Bar-attached
validation: tensile wave
obtained at different
pre-tension
Y. Xu et al.
understand the high energy physics related to explosive and shock events. There are many advantages of using the PDV
system with the TTHB apparatus. Firstly, the technique is noninvasive and insensitive to impacts in the system, in contrast to
the traditional strain gauge technique, since the impact event can affect the strength of bonding between the strain gauge and
the bars, and/or break electrical connections (thus, abruptly terminating the measurement). Secondly, the data is recorded in
the frequency domain of the measured signals, which makes the PDV data insensitive to electrical noise, and more reliable
than the strain gauge technique. Moreover, it is an active diagnostic tool to monitor not only the experimental but also the
sample itself, e.g., measuring the time-dependent radial expansion of the specimen during the experiment. The PDV system
is calibrated using the tensile and shear strain gauges implemented on both input and output bars.
16.4 Validation
Bar-attached tests are conducted to validate the capability of the TTHB system to store sufficient combined tensile force and
torque and to achieve quick and clean release. Under different pre-loads applied, the tensile waves are derived from the strain
gauge on the output bar, as shown in Fig. 16.2. After a few optimizations of the clamp design, bar deflection and wave oscillations are considerably mitigated, resulting in smooth and clean square-like waves. The apparatus shows its capability of
generating the high-magnitude tensile wave. The time zone of the combined tensile and shear waves in Fig. 16.3 is shifted to
the connecter sandwiched between the input and the output bar. The difference of the arrival time between the tensile and the
shear waves at the bar connector is initially 45 μs but decreases dramatically along the wave rise. The difference of the arrival
time can be adjusted by the distance between the clamp and the bar connector, i.e., the specimen in a combined tensiontorsion test. The rise time of the tensile wave favorably varies from 50 to 100 μs, while the shear wave around 30 μs. The
length of the tensile wave approximates 800 μs, while the shear wave 1200 μs, corresponding to the length of the pre-stressed
section of the input bar and the bar material.
Fig. 16.2 Bar-attached
validation: tensile wave
obtained at different
pre-tension
Y. Xu et al.