## 4 Results and Discussion  
Figure 4 presents the velocity-time curves of impactor tested with four specimens of different thicknesses. In these figures, experimental results and numerical results conducted with the combined TCK-JH2 model and elastic model are given. The experimental results are presented with black solid lines. The numerical results conducted with the elastic model are presented with the red black dotted lines and the results conducted with TCK-JH2 model are presented with red dash lines. The elastic model conducted in this study can be described by the following equation:  
\[\sigma=E\varepsilon, \tag{24}\]  
Figure 3: Finite element model of the drop-weight test: (**a**) parts of the model, (**b**) 1/4 mesh model. where the \(\sigma\) is stress, \(\varepsilon\) is strain, and \(E\) is [PERSON]'s modulus. The impact process can be divided into two stages. In the initial stage, the glass layers are in elastic state. In this state, the results from the combined TCK-JH2 model and the elastic model are similar, which indicates that the combined model is able to simulate the elastic response of glass accurately. In the second stage, glass layers start cracking due to the accumulation of damage. After the cracking, the stiffness of the laminated glass pane significantly decreases. It can be observed that the slope of the velocity-time curve changes. From this we can conclude that the combined TCK-JH2 model can accurately simulate the accumulation of the damage of glass layers. Comparing the velocity-time curves of Figure 4a,b, when the impact velocity and the thickness of PVB interlayer are the same, it can be seen that the thicker glass layer has better deceleration effect. Comparing Figure 4c with Figure 4d, under the same impact velocity and glass thickness, it can be seen that the thicker PVB interlayer has better deceleration effect. Figure 5 depicts the force-time curves of impactor. Obvious vibration can be detected along the force-time curves, which mostly results from the reflection of stress wave. The vibration is serious in Figure 5a,b owing to the bigger impact velocity. Figure 4: Comparison of velocity-time curves between simulation results and experimental results of specimens: (**a**) LG-03114, (**b**) LG-06114, (**c**) LG-06076, and (**d**) LG-06038. Like velocity-time curve, the force-time curve can be divided into two stages. At the initial stage, the glass layer is in elastic state, and the force acting on the impactor gradually increases to a peak value. Along with the accumulation of damage, the glass begins to crack. At the same moment, the force dramatically reduces and remains at a lower value. The peak force at Figure 5a is 1.96 kN whereas 5.09 kN at Figure 5b, which shows that the laminated glass can be strengthened obviously by increasing the thickness of the glass. By comparing Figure 5c,d, it is found that increasing the thickness of PVB interlayer can also increase the strength of laminated glass. The numerical results simulating with the combined TCK-JH2 model are also presented in Figure 5. As comparison indicates, two stages of the impact process are correctly predicted. The peak force of the initial stage and the moment of cracking are close to the experimental results. Therefore, numerical simulation conducted with the combined TCK-JH2 material model for glass gives good predictions of reaction force in low-speed impact. To a minor extent, some mismatches of peak force time can be detected in the comparison between the numerical results and experimental results in Figure 5. The reasons for this phenomenon are various. For example, the flaws on the surfaces of the glass layers could result in the premature cracking of the glass, which may be the primary reason. After the cracking of the glass layer, the velocity curves keep decreasing in Figure 4 meanwhile the force curves still remain above zero in Figure 5. This phenomenon can be explained in that although the glass layers are damaged, the laminated glass panes still have the ability to carry loads.