# Behavior and Damage Characterization of Impulsively Loaded Cross-Laminated Timber Panels
## 3 Results
### Damage Characterization
#### 3.3.3 Influence of Boundary Condition Rotational Rigidity on CLT Damage  
Figures 29 and 30 plot the maximum inbound displacements as a function of impact energy for the three-laminae and five-laminae specimens, respectively. Linear regressions of the data show a coefficient of determination of \(R^{2}=0.85\) and \(R^{2}=0.90\) for maximum inbound displacement as a function of impact energy for the three- and five-laminae specimens, respectively. The high degree of linearity is logical as they state that the maximum displacements in the CLT panels increase with increasing impact energy. The linear relationship between maximum inbound displacement and impact energy may be described by Equations (5) and (6) for the three- and five-laminae CLT specimens, respectively. \[\Delta=6.354\times 10^{-4}E_{k}-0.001508\ \text{[in,J]} \tag{5}\]  
\[\Delta=9.971\times 10^{-4}E_{k}-0.6186\ \text{[in,J]} \tag{6}\]  
Figure 28: CLT5\(-\)10 during impulsive loading at t = 32.51 ms. Counterclockwise From Top Left: Photograph of CLT5-10, strain gradients for \(\varepsilon_{xy}\), \(\varepsilon_{xx}\), and \(\varepsilon_{yy}\) calculated using DIC. Figure 31 and 32 plot the maximum inbound and residual displacements for the three- and five-laminae CLT panel tests, respectively. A torque of 65 in-lbs was used as the baseline torque parameter for comparison with higher levels of torque. At this level torque, the restraining moment at the boundary conditions is relatively low, and specimens tested at this level of torque behave mostly as simple beams. Resistance functions for a beam with ideal simple boundary conditions and the test fixture's boundary conditions were observed  
Figure 30: Maximum inbound displacements for five-laminae specimens. Figure 29: Maximum inbound displacements for three-laminae specimens. to be similar, thus demonstrating that the specimens behaved mostly as simple beams at the baseline torque. Figure 31: Residual and maximum inbound displacements for three-laminae specimens. Figure 32: Residual and maximum inbound displacements for five-laminae specimens. At impact energies of 3.5 kJ and greater, three-laminae specimens experienced complete failure, while five-laminae specimens experienced failure at impact energies of 6.1 kJ and greater. Some variability in the impact energies that caused complete failure was noted, as contrasted to the three-laminae tests, which showed greater consistency. At the higher levels of rotational rigidity, three-laminae CLT specimens exhibited lesser maximum inbound displacements as compared to specimens with the baseline level of rotational rigidity and tested at similar impact energies. Tests on five-laminae CLT where torque was varied were conducted at two impact energy ranges: 1.0 kJ to 2.0 kJ and 6.0 kJ to 6.5 kJ. At lower impact energies, i.e., 1.0 kJ to 2.0 kJ, specimens tested with 200 in-lbs of torque exhibited 4.0% to 43.1% lower maximum inbound displacement than the baseline tests torqued to 65 in-lbs. While the residual displacements for the specimens tested with 200 in-lbs of torque were lower than those of the baseline tests (0% to 75%), they were fairly similar in magnitude and indicated that minimal damage occurred at lower impact velocities. At higher impact energies, i.e., 6.0 kJ to 6.5 kJ, lower maximum inbound displacements were observed in specimens tested with 130 in-lbs (12.24% to 28.68%) and 200 in-lbs (2.3% to 38.43%) of torque. Similarly, lower residual displacements were observed is specimens tested with 130 in-lbs (12.24% to 28.68%) and 200 in-lbs (2.3% to 38.43%) of torque. Additional tests at 130 in-lbs and 200 in-lbs of torque are required at the tested velocities and middle velocities not tested in order to establish whether the above observations hold at other velocities and if there is a function that describes the relationship between displacement and energy for the higher torques tested.