Tawfik B. Khalil

Dynamic response of the human head to impact by three-dimensional finite element analysis.

The impact response of the human head has been determined by three-dimensional finite element modeling. This model represents the essential features of a 50th percentile human head. It includes a layered shell closely representing the cranial bones with the interior contents occupied by an inviscid continuum to simulate the brain. A thin fluid layer was included to represent the cerebral-spinal fluid. To validate the model, its response was obtained by applying a sine-squared pulse of 6.8 kN in magnitude and 10 ms in duration. The load was applied to a freely supported head on the frontal bone in the midsagittal plane. The computed pressure-time histories at 5 locations within the brain material compared quite favorably with previously published experimental data from cadaver experiments and provided a reasonable level of confidence in the validation of the model. A parametric study was subsequently conducted to identify the model response when the impact site (frontal, side, occipital) and the material properties of the head were varied. Interestingly, the model predicted higher contre-coup pressure in the frontal lobe (from occipital impact) than that predicted in the occipital region from frontal impact. This finding supports clinical findings of contre-coup injury being more likely to result from occipital impact than from frontal impact.

A NEW MODEL COMPARING IMPACT RESPONSES OF THE HOMOGENEOUS AND INHOMOGENEOUS HUMAN BRAIN

We have developed a totally new three-dimensional human head model in which the gray matter, white matter, vehicles and parasagittal bridging veins were included. This study is a continuation of the modeling efforts of the two-dimensional porcine brain models by Zhou et al. (1994) and three-dimensional human head model by Ruan et al. (1994). The paper presents some preliminary simulation results of the new three-dimensional model for a direct frontal impact and an indirect sagittal plane rotational impact ro delineate differences between the homogeneous and inhomogeneous brain models, and to study the mechanism of the subdural hematoma. Language: en

Literature review of head injury biomechanics

Summary The high incidence of head injuries resulting from transportation system crashes, sports, military activities, falls, assaults, etc. contributes to a preponderance of head injury biomechanics research. A wealth of publications result, addressing phenomenological and mechanistic issues associated with head response to mechanical impact. This literature survey provides an assessment of hypothesized brain injury mechanisms, brain injury criteria, mathematical models of head injury and available techniques for measuring head kinematics and brain tissue deformations associated with exposure to dynamic loads.

Shear Stress Distribution in the Porcine Brain Due to Rotational Impact

In the study, developed were two-dimensional finite element models for three coronal sections of the porcine brain and the results were compared with injury data from animal experiments performed at the University of Pennsylvania. The models consisted of a three-layered skull, dura, CSF, white matter, gray matter and ventricles. The maximum shear stress distribution produced from the models was found to be in good agreement with experimental findings. Diffuse axonal injury as indicated by the experiments was found in areas of high shear stress which persisted for relatively longer periods during the impact.

Mechanical Properties of the Cadaveric and Hybrid III Lumbar Spines

This study identified the mechanical properties of 10 cadaveric and 2 Hybrid III lumbar spines. Eight tests were performed on each specimen: tension, compression, anterior shear, posterior shear, left lateral shear, flexion, extension, and left lateral bending. Each test was run at a displacement rate of 100 mm/sec. The maximum displacements were selected to approximate the loading range of a 50 km/h Hybrid III dummy sled test and to be non-destructive to the specimens. Load, linear displacement, and angular displacement data were collected. Bending moment was calculated from force data. Each mode of loading demonstrated consistent characteristics. Load-displacement curves of the Hybrid III lumbar spine demonstrated an initial region of high stiffness followed by a region of constant stiffness. The exception was the tension tests, as the steel cables in the spine seemed to dominate the mechanical response in tensile loading. Loading curves of cadaveric spines demonstrated an initial region of low stiffness followed by a region of increasing stiffness, typically a feature of soft tissue response. Notable findings included the observation that the whole cadaveric lumbar spine specimens are stiffer in posterior than in anterior shear. This finding is in contrast to motion segment studies, in which the opposite trend is observed.