الفهرس 
ABSTRACT
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Abstract
Characterization of the mechanical behavior of biological materials under dynamic loading conditions is essential to study the response of the human body to high-rate of loading induced in events like automotive crashes, ballistic impact (e.g. behind armor blunt trauma), and violent sports. Computational and experimental models of the human anatomy have been constructed to predict the risk and severity of injury to the human body due to these events. It is critical that these models accurately simulate the response of human tissue to various loading conditions. Thus, the material behavior of biological tissues must be determined experimentally over a wider range of strain rates. High strain rates testing required usage of Split Hopkinson pressure bar (SHPB) arrangement which can be used in testing material at strain rate ranged from 100 s-1 to 4,000 s-1. Falling, dropping, car accident, and violent sports are considered the main source of skull fracture. These mechanically are transferred to the head as dynamic impact wave causing cracks and fractures. So, understanding the fracture failure mechanisms acts to the skull bone is important step for improving safety systems. Frontal skull bone is considered a flat bone consist of three layers cancellous between the two cortical outer layers, all have different mechanical properties resisting the impact dynamic wave. That could not be the only parameter dominate the failure mechanism, several parameters governed the fracture propagating failure mechanism, impact wave magnitude (force, velocity), bone density, bone thickness, and impact site. characterization of skull bone behavior under dynamic load is essential for improving the safety systems in cars and helmets, to simulate the impact traumas affects the head and mandible ramifications in vehicle accidents. In this work the three common types of Skull fractures have been studied experimentally using SHPB arrangement. Six stepped forces were applied on the frontal part of the head in vivo, the dynamic wave was propagated through the skull bone with its three layers, and thus cracks were propagated forming different types of fractures (depressed fracture, depressed fissure fracture, and multiple depressed with compound elevated skull fracture). Fracture propagation behavior depends on several parameters such as bone density, impact site, and impact force magnitude. In addition, the composition of the bone layers plays the main role of crack behavior versus impact dynamic load due to the mechanical properties of the combination of cancellous and cortical bone layers. The classical SHPB arrangement with steel bars must be modified to fit the tested specimen material (soft biological tissues). To get a good transmitted signal, the impedance of the bars and tested materials must be matched. So the recommended modification is to change the bars material from steel to viscoelastic material as Poly Methyl Meth Acrylate (PMMA). A free end test experimental work is applied to the bars to estimate its complex properties and propagation coefficient with its parameters the dispersion and attenuation coefficients.