Axial Compression Experiments

The lateral specimen deformations were measured by a Sony XCL-UIOOO digital camera through the observation window of the chamber. The load and the axial displacements were recorded by the Instron system. 

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When a force is applied to the posterosuperior quadrant of the head or when a crown impact is administered while the head is in flexion, the neck is subjected to a combined load of axial compression and forward bending. Anterior wedge frartures of vertebral bodies are commonly seen, but with increased load, burst fractures and fracture-dislocations of the facets can result. The latter two conditions are unstable and tend to disrupt or injure the spinal cord, and the extent of the injury depends on the penetration of the vertebral body or its fragments into the spinal canal. Recent experiments by Pin tar et al. [1989, 1990] indicate that burst fractures of lower cervical vertebrae can be reproduced in cadaveric specimens by a crown impact to a flexed cervical spine. A study by Nightingale et al. [1993] showed that fracture-dislocations of the cervical spine occur very early in the impact event (within the first 10 ms) and that the subsequent motion of the head or bending of the cervical spine cannot be used as a reliable indicator of the mechanism of injury. 

The trends in cell parameters under pressure agree well with experimental data which is limited to the pressure range from 5.3 to 7.9 GPa[51]. At 8 GPa, the calculation correctly reproduces the observed trend of axial compressibilities, c/c > a/a > b/b. The magnitude of changes in monoclinic angle with pressure, d/ /dF is also correctly described (-0.09 0.02 compared with -0.11 0.01 degrees/GPa in the experiments). 

The target temperatures were the same as in the shear and tensile experiments. Three specimens were tested at each temperature (designated Cxx, with xx being the temperature). After the target temperature was reached, the axial compressive force was applied with a displacement rate of 1 mm min until specimen failure. 

Figure 5.14 Load-axial displacement curves for different temperatures from compressive experiments [19]. (With permission from SAGE.)...

A compression experiment on a cylindrical rock salt specimen of same dimensions and with the same measurement techniques as described in Subsection 11.6.3 was carried out in such a way that a constant axial strain... 

High pressure experiments on pristine Cgo have shown that the Tse-fee value increases with pressure [91], being strongly affected by the reduction in lattice parameters. Figure 6.19 displays the relationship between ao and Tgc-fcc, derived by combining the axial compressibility, = —dlnao/dp = 1.83 x 10" ... 

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