# Crasworthiness Analysis and Multi-Objective Optimization for Concave I-Shaped Honeycomb Structure
## 3 Materials and Methods
### Experimental Validation  
To verify the accuracy of the finite element model, a test model was built. The test pieces were made by additive manufacturing technology, also known as 3D printing. The model designed in SolidWorks software was saved in stereolithography (STL), which is a format used to define the sample geometry of the 3D printer software. The printer nozzle temperature of 300 \({}^{\circ}\)C and the chamber temperature of 77 \({}^{\circ}\)C were maintained and used as default temperature settings for all the specimens that were printed. The material we chose is a traditional resin material with high dimensional accuracy, the capacity to achieve fine measurements, and good surface quality for prototypes. As a result, it is employed in many different industries, including the mechanical and automotive sectors. The photosensitive resin 9400e is a more popular 3D printing material since metallic aluminum produces poor results. It has a density \(\rho=1.18\times 10^{-9}\)t/mm\({}^{3}\), elastic modulus \(E=2.1\times 10^{3}\)MPa, and Poisson's ratio \(\
u=0.35\). The cellular structure was \(5\times 5\) with a single cell structure of \(S=8\) mm, \(h=2.5\) mm, \(b=2.25\) mm, and \(t=0.65\) mm. Its overall length was 54 mm, height was 50 mm, and width was 30 mm. The dimensions of the 3D printed specimen had some errors, but the overall size was similar to that of the test model. A Changchun Kexin WDW-300 microcomputer-controlled electronic universal testing machine, as shown in Figure 9, was used for this test; this machine is mainly used for tensile, compression, and bending tests of metal and non-metal materials. The specimen was placed on the fixed base plate at the bottom of the uniaxial hydraulic press, and the upper compression plate was adjusted to a position 1 mm away from the specimen in advance. The material properties of the specimen and the test program were inputted at the computer end, where the compression speed was 2 mm/min, and the compression displacement was set to 20 mm. Since the pore wall is the main energy-absorbing structure, it plays the main supporting role when subjected to compression. When the structure starts to compress,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Velocity** & \multicolumn{4}{c}{**Origami-Inspired Honeycomb**} \\ \cline{2-5}  & **(m/s)** & \(S\) **(mm)** & \(h\) **(mm)** & \(b\) **(mm)** & \(t\) **(mm)** \\ \hline A1 & 10 & 6 & 2.25 & 2.25 & 0.65 \\ A2 & 10 & 8 & 2.25 & 2.25 & 0.65 \\ A3 & 10 & 10 & 2.25 &  
the lateral sides of the cytosol below the impact end curl first, and both sides contract to the inside. With the continuous downward pressure of the impact plate, the shear zone of the impact end is continuously driven by the curling deformation of the surrounding cytosol, and the local shear deformation range is continuously extended in the direction of stiffness softening, and the structure will produce an obvious \"necking\" phenomenon. With the mutual yielding deformation of adjacent cell elements, the cell wall gradually collapses, the material is in full contact, and the structure enters the compact stage. When the cell wall of the structural cell element collapses, the material enters the failure form. A camera was used to record the test process, and a comparison of the simulated and observed compression images is shown in Figure 10.  
Figure 11a shows a comparison of the force-displacement curves for the test solutions and the simulation results. In the elastic stage, the force of the simulation solution and the experimental solution both grow properly, but the force does not considerably increase in the yield stage. The force and displacement both quickly rise during the strengthening phase. Figure 11b shows the stress-strain curves. The linear elastic stage, where the stress and strain largely vary linearly with the slope of the modulus of elasticity, is defined as strain 0-0.1. The stage of the plastic plateau is strain 0.1-0.25.