# A Review of Validation Methods for the Intracranial Response of FEHM to Blunt Impacts
## 2 Experimental Procedures Used in FEHM Validation
### Cadaver Experimentation
#### 2.1.2 Relative Brain Displacement Response
Instead of columns, NDTs were arranged in clusters of seven, creating an array of triads about a central NDT with an approximate radius of 10 mm. The placement of the clusters was dependent on the direction of impact. Four cadavers (tests C288, C241, C015 and C064) had clusters in the anterior and posterior regions of the right brain hemisphere and consequently experienced occipital and frontal impacts. Two more (cadavers C380 and C393) had clusters in the parietal-frontal region of each hemisphere and were subjected to lateral impacts. In this arrangement the central NDT of eachcluster was the key point. Pressure transducers were also inserted within the brain tissue of cadavers used in the later study [36] approximately at the expected coup and contrecoup locations. Impact characteristics are presented in similar ways across both of these studies [35; 36]. Tables summarise the impact location and speed (in [PERSON] et al. [35] only) and peak values for linear accelerations, rotational accelerations and rotational velocity. The cadaver motion is also described via plots of these kinematic parameters at the samples' centre of gravity, as exemplified for test C380-T2 [36]. The motion of the NDTs is recorded in two ways. The first, shown in Figure 3a, traces the co-ordinates of each NDT in a given plane, showing their path of motion from the impact. The second, shown in Figure 3b maps the displacement of key NDTs relative to that of the skull, along directions parallel to the anatomical axes. For cases in the later study [36], the pressure recorded throughout the impact is plotted, as are principal and shear strains calculated in each NDT cluster. Not all data was successfully captured for every impact scenario. Table 3 indicates which data are available and reported for each cadaver impact [35; 36]. The strain calculations provided by [PERSON] et al. [36] were made possible by the cluster arrangement used empirically. Strains were calculated from the relative displacements of the NDTs within each cluster. To achieve this, nodes were created in the LS-Dyna explicit simulation environment representing each NDT in their initial location. Each node was connected to its immediate neighbours to form a group of triangular elements representing the NDT cluster. The displacement histories of each NDT were applied to the relevant nodes, replicating their relative motion, allowing the strain between points, across the triangular elements to be calculated. However, a later re-examination of the data by [PERSON] et al. [45] found many cases had missing or low quality data affecting strain calculations. Once these were sifted out, data from 15 clusters across 14 impacts and five cadavers was deemed suitable for use. Furthermore, even within this group the strain measures required recalculation. NDTs were once again modelled as nodes in LS-Dyna, connected to their neighbours creating to form triangular elements and subjected to the relevant displacements. [PERSON] et al. [45] then considered the Green-Lagrangian strain in each element and registered the mean across the cluster as the indicative strain measure. These adjustments resulted in average principal strains increasing by up to 201% and shear strains decreasing by up to 247%, on average, across the 15 sifted clusters. Strain-rates were also affected by 40-49%. The predicted strains further increased when, instead of groups of planar triads, NDT clusters were considered as groups of tetrahedral elements in another re-examination by [PERSON] et al. [46]. NDTs were excited via their displacements as before to generate the strain response from experimental scenarios. The strains calculated by this were compared to the responses of five FEHM variations from [PERSON] et al. [25], [PERSON] et al. [44], [PERSON] [47]. Nodes within the volume occupied by NDT clusters were identified. The FEHM were subjected to impacts and their displacement fields recorded.