# Non-Contact and Real-Time Measurement of Kolsky Bar with Temporal Speckle Interferometry
## 3 Experiment and Results
### Experimentnal Determination of the Dynamic Mechanical Properties of Materials  
The experimental setup for the determination of the dynamic mechanical properties of materials is shown in Figure 12. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Actual Value**} & \multirow{2}{*}{**Coordinate**} & \multicolumn{3}{c}{**Displacement (\(\mu\)m)**} & \multicolumn{3}{c}{**Velocity(um/s)**} \\ \cline{3-8}  & & **Value** & **Error** & **Relative Error** & **Value** & **Error** & **Relative Error** \\ \hline \multirow{8}{*}{**Displacement = 7.7 \(\mu\)m**} & A1(265,303) & 7.69 & 0.01 & 0.13\% & 1.538 & 0.002 & 0.13\% \\  & A2(333,296) & 7.74 & 0.04 & 0.52\% & 1.548 & 0.008 & 0.52\% \\  & A3(347,313) & 7.71 & 0.01 & 0.13\% & 1.542 & 0.002 & 0.13\% \\  & A4(419,311) & 7.71 & 0.01 & 0.13\% & 1.542 & 0.002 & 0.13\% \\  & A5(456,309) & 7.66 & 0.04 & 0.52\% & 1.532 & 0.008 & 0.52\% \\ \cline{1-1}  & B1(211,302) & 7.73 & 0.03 & 0.39\% & 1.546 & 0.006 & 0.39\% \\ \cline{1-1}  & B2(255,286) & 7.65 & 0.05 & 0.65\% & 1.530 & 0.010 & 0.65\% \\ \cline{1-1}  & B3(380,273) & 7.72 & 0.02 & 0.26\% & 1.544 & 0.004 & 0.26\% \\ \cline{1-1}  & B4(444,283) & 7.71 & 0.01 & 0.13\% & 1.542 & 0.002 & 0.13\% \\ \cline{1-1}  & B5(465,294) & 7.71 & 0.01 & 0.13\% & 1.542 & 0.002 & 0.13\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The comparison of two measurement results of multi-detection points. Figure 11: The in-plane displacement of the transmitter bar: (**a**) the intensity distribution over time; (**b**) the discontinuous phase map obtained by wavelet transformation; (**c**) the measured displacement over time; (**d**) average speed. The specimen described here is made of 304 L stainless steel, with diameter and thickness of 1.5 mm and 0.75 mm, respectively. The sample is held between the incident bar and the transmitter bar with butter. The pole longitudinal wave velocity \(C_{0}\) in the bar is 4934 m/s. In order to improve the detection of changes in light intensity, here, we use a high-speed photodetector as the detector device. The high-speed photodetector is Thorlabs' Biased Photo-detectors (DET36A/M, Thorlabs, NJ, USA), a Si biased detector covering the 350 nm to 1100 nm wavelength range and rise times as fast as 1 ns, as shown in Figure 13. A virtual oscilloscope (DSO3062 AL) produced by Hantek Company (Hantek, Qindao, China) was used to collect data. It needs to be emphasized that after the verification experiment was completed, we just removed the translation stage and the grating ruler, and the light path did not change. Therefore, the incident angle of the incident bar is still 70 degrees, and the incident angle of the transmitter bar is still 72.5 degrees. Figure 12: Dynamic mechanical properties of materials experimental setup: 1 and 18 are green lasers; 2 and 16 are beam lifters; 3 and 17 are spatial filters; 4 and 13 are beam splitters; 5 is a baffle; 6, 10, 11 and 15 are reflectors; 7 and 14 are point detectors; 8 is a virtual oscilloscope; 9 is the trigger device; 12 is an oscilloscope; 19 is the SHPB device. Figure 13: Photodetector. The typical original signal for the experiment is shown in Figure 14, where the green curve is the light intensity change on the incident bar and the blue curve is the light intensity change on the transmitter bar. It can be seen from the figure that the light intensities on the two bars have a similar trend. The dynamic mechanical properties of the specimen materials are shown in Figure 15.  
Figure 14: Original light intensity signal: (**a**) intensity of incident bar; (**b**) intensity of transmitter bar. Figure 15: Dynamic mechanical properties of the specimen: (**a**) stress curve; (**b**) strain curve; (**c**) strain rate curve; (**d**) stress–strain curve. Figure 15 shows that the maximum stress applied to the specimen during the experiment was 134.21 Mpa. As the stress increased from 0 to 134.21, the maximum strain of the specimen was 0.0166, indicating that the specimen is still in the elastic phase. The strain-rate increased from 0 to 7787(1/s).