## 2 Materials and Methods
### Shock Impulse Test  
The instruments were considered an essential part of this study; an in-house pneumatic exciter was the main equipment used for this section; this rig is originally aimed for shock calibration, as mentioned in the literature [54] (see Figure 2), according to BS-ISO 16063:2015 [34]. The pressure is effectively regulated by a closed-loop control system, which is accompanied by a fire command on the Human-Machine Interface (HMI) developed with LabVIEW(tm) version 2020. The machine fingers were used to mount both of the lattice specimens, and upon a specific force, the specimen was impacted with an anvil. The impact data were then measured using an Endevco(r) accelerometer (2270 M8) with a sensitivity of (S = 2.06 pC\(\cdot\)g\({}^{-1}\)) [43] with a charge amplifier system (2771 C) with Gain (G = 0.1 mV\(\cdot\)pC\({}^{-1}\)) then all the data were recorded at high-speed with a maximum speed rate of 1.25 MS\(\cdot\)s\({}^{-1}\) by DAQ National Instrument NI-PXIe-4480 card, but the record speed rate used in this experiment was 512 KS\(\cdot\)s\({}^{-1}\) in order to reduce a redundant data. After that, all of the data from the accelerometer were converted from the voltage (V\({}_{\mathrm{s}}\), V) into acceleration (a) based on (Equation (2)) [33].  
\[|\,\mathbf{a}\,|=\mathrm{G}\times\mathrm{V}_{\mathrm{s}}/\mathrm{S} \tag{2}\]The prevalent units of an accelerometer (**a**) utilised are (m/s\({}^{2}\)) or the force of gravity (g), estimated at roughly 9.81 m/s\({}^{2}\). This experiment was performed by mounting two specimens on the finger of the test rig, as shown in Figure 2. All of the shock impulse specimens are again referred with an input force (**F**, N). Reference impulse force is an impulse (**P**, N-s) obtained from testing without the mount samples on the finger of an acceleration test rig (see Equation (3)).  
\[\textbf{P}(\textbf{t})=\int\textbf{F}(\textbf{t})\;\text{dt}=\text{m}\int \textbf{a}(\textbf{t})\;\text{dt} \tag{3}\]  
The linear impulse in this study was generally based on the instability of an acceleration in (g) over an impulse time (\(\tau\), ms) being transformed into a force over impulse time. This linear impulse represents the area under the curve between force over time, while acceleration is necessary to be estimated, using the following BS-ISO 16063:2015. According to this standard, an impulse curve would tread with a half-sine pulse, and the impulse time could be estimated by offsetting 10 per cent of a peak signal from the reference baseline. Not only did the results improve with a baseline correction, but it was necessary to perform pass filtering by the order 4 of a Butterworth filter.  
In this case, the variation of an acceleration, (**a**, g) would be affected by the fluctuating forces. (**F**, N). Because the acceleration in a time domain was a half-sine, this could, over time, result in the response of the force also becoming a half-sine. Hence, the integration of the area under the curve, between F and t, could yield a linear impulse. The half-sine pulse may either plot in a function of sine as shown in (Equation (4)).  
\[\mid\textbf{a}\mid=\mid\textbf{a}_{\textbf{max}}\mid\sin\left(\pi\text{t}/ \tau\right) \tag{4}\]  
where as **a\({}_{\textbf{max}}\)** represents the maximum amplitude of the acceleration and \(\tau\) is impulse time in (milli second, ms). The half-sine pulse may apply under the assumption of critical damping, which was found only in the single pulse with a single impact. Figure 2. shows the picture of the experiment rig. This rig is generally designed for a shock calibration and can generate a shock acceleration that can be converted into a very accurate linear impulse. There are two specimen mouths on the finger of the rig. After the pressure is provided, the anvil will move upward and collide with the specimen.