## 4 Conclusions  
In the present study, a new anti-buckling fixture developed for in-plane impact tests has been presented. To prevent catastrophic crushing due to the global bucking, flat specimens must be supported by a specific fixture. The newly designed fixture has to solve all the shortcomings that characterize the previously published solutions; in particular, it must have adjustable support length for specimens with various thickness, allow the frond formation, avoid the tearing failure at the impacted edge, and allow the removal of the debris from the crushing side. Numerical simulation was used to design and develop a fixture specifically devoted to lateral impact testing of laminate, aimed at material characterization. The designed fixture can be fully integrated with Instron drop tower testing machines and can be used to conduct crashworthiness tests up to 1850 J on composite flat-plate specimens measuring up to \(100\times 150\times 16\) mm. As a part of the numerical simulations, optimization was conducted on different design parameters. At first, the top plate was analyzed to set its thickness in order to avoid plastic deformation at high energy levels. A 30 mm thick steel plate only undergoes elastic deformation under the maximum impact energy. Further studies were conducted to determine the optimum diameter of and distance between anti-buckling columns. Column diameter of 10 mm and spacing of 65 mm allow progressive damage initiation from the bottom without significant local buckling. Moreover, the effect of different unsupported heights, as reported in previously published studies, was also discovered in numerical simulations and was confirmed through experiments conducted on GFRP plates. A 10 mm unsupported height avoids buckling of the specimen, whilst allowing fronds resulting from progressive crushing to propagate freely without interactions with fixture components, thereby providing results that are purely a function of material properties and specimen geometry. Experimental tests with CFRP and GFRP plates were conducted on this new fixture to assess the influence of unsupported height, impact mass, and velocity on the obtained force-displacement results. It was observed that with the same impact energy, changing the impact mass or velocity does not affect the mean force or specific energy absorption of the specimen. Only in the case of lower masses were more oscillations noted in the force-displacement curves. Experimental results showed that the newly designed fixture has the following features: \begin{table}
\begin{tabular}{c c c c} \hline
**Material** & **Impact Velocity (m/s)** & **SEA (k/kg)** & **Standard Deviation (k/kg)** \\ \hline NEMA FR4 glass fiber composite [32] & 3.96 & 51.316 & 0.79 \\  & 4.69 & 50.729 & 3.52 \\  & 5.34 & 49.679 & 2.80 \\  & 4.69 & 46.207 & 3.08 \\ GG630T-37 carbon fiber laminate [33] & 5.29 & 45.350 & 2.46 \\  & 5.83 & 45.002 & 1.83 \\ \hline \end{tabular}
\end{table} 
Table 6: Specific energy absorption calculated for tests at different impact velocities. Figure 16: Effect of impact velocity on carbon-fiber-reinforced epoxies: (a) force–displacement curves for tests with impact mass of 50 kg; (b) force–displacement curves for tests with impact mass of 70 kg. * It is able to initiate progressive crushing, allowing multiple failure modes without any influence of its components on the results or jamming due to froms or debris;
* It allows testing with various unsupported heights of up to 50 mm;
* It permits testing without the need for extensive calibration on standardized specimens of dimensions permitted according to CAI standard (ASTM D7137 and D7136);
* It is robust for energies up to 1850 J and fully integrable with the Instron drop tower testing apparatus that is widely used in academic and industrial institutions. This fixture exhibits these features all whilst producing reliable and repeatable results.