
Simulation and experimental evaluation of the effects of small ammunition bullets entering a bulletproof vest
Billich, Richard ; Jelen, Karel (advisor) ; Otáhal, Jakub (referee) ; Chlup, Hynek (referee)
Title: Simulation and experimental evaluation of the effects of small ammunition bullets entering a bulletproof vest Objectives: The main objectives of the study were: parameterization of the wounding effects of bulletson artificial materials, quantification of bullet impacts using international and experimental gunshot wounding criteria, parameterization of the mechanical characteristics of polymer fibers used in bulletproof vests, objectification of the deformation effects of missiles on soft biological tissues and creating a simplified analysis of ballistic missile interaction. Methods: In this study, experiments were performed on two artificial materials: food gelatine and glycerine soap. Calculated values and individual parameters are reported for 9 mm weapon systems. The experiments were performed in a ballistic test laboratory under standardized conditions. Data processing and parameterization of shape changes were performed using computed tomography (CT), microCT,ultrasound elastography and 3D scanning. Other devices used were infrared vibration spectroscopy and highspeed camera. We used the collected datato create analytical relations describing the mechanical effects ofthe material under a bulletproof vest.. Results: The area of greatest impact for the ammunition was 1.48  1.6 times...


Water hammer experiment in artificial blood vessel
Hromádka, D. ; Horný, L. ; Žitný, R. ; Chlup, Hynek
This paper presents a water hammer experiment performed on an artificial blood vessel and the latex tube. Artificial blood vessel was manufactured from latex tubes and textile rubber bands. These bands were wound on outer surface of latex tube and they imitated reinforcing effect of collagen fibres. Mathematical model describes pulsation of pressure after instantaneous closing of valve at outlet of pipeline a part of which is a short elastic tested tube. It is shown that the observed pressure responses can be approximated by a simplified mathematical model assuming linear relationship between internal pressure and inflated volume.


Residual Strains of Arteries as Forensic Index
Adámek, T. ; Horný, L. ; Chlup, Hynek ; Žitný, R.
It has been known for long time that arteries are prestrained in situ. These residual strains play crucial role in arterial loadbearing capacity. However, to the best of authors’ knowledge they have never been considered from forensics point of view. This paper concerns a possibility of employing the longitudinal prestrain of human aortas as an indicator of human subject age. Lengths of abdominal aorta were measured within autopsies before and after segment resection. Longitudinal stretch ratio was calculated for 45 male and 12 female cadavers. It was found that both male and female data samples give approximately the same mean of the stretch ratio = 1.2. The correlation coefficients between the prestrain and age were R=0.7926, R=0.8684 in male and female samples, respectively. Linear regression equation with confidence intervals was employed. The correlation between prestrain and age seems to be suitable statistics to be used in forensic sciences.


Numerical Simulation and Experimental Modelling of Fluid  Structure Interaction in Veins
Štembera, V. ; Chlup, Hynek ; Maršík, František
The mixed formulation of the finite element method with the separately interpolated pressure is used for the numerical simulation of the fluid structure interaction. To describe a wider class of problems we consider in the simulation the three material models: the NeoHookean, the isotropic Gent model and the anisotropic Gent material model to include the influence of collagen structure of blood vessels. The fluid is modelled as Newtonian liquid. The strong coupling of both structure and fluid solvers allow us to simulate large deflection oscillations of the structure. The special experimental mock up line was designed for the investigation of unsteady fluid structure phenomena. Latex tubes with variable inner diameter and wall thickness are used as specimens. The qualitative and quantitative fluid structure phenomenon investigation are performed for both the continuous and pulsatile flow.


The Conditions of Vibrations and Collapse of Human Blood Vessels
Hemza, J. ; Chlup, Hynek ; Maršík, František
Biomechanical material properties of arteries and veins are investigated experimentally and theoretically. The main goal of the histological research and the developed theory is to formulate the biomechanical conditions (geometrical dimensions, viskoelastic properties of veins and blood fluid flow conditions) at which an unstable behavior or even the vein collapse can occur. One dimensional fluid structure approximation was starting point for the theoretical analysis of fluid flow through highly elastic collapsible tube. Provided that the neoHook’s material model was applied the analytical formula for the collapse conditions was found. It was proved that for the brain vein contraction about 5%, the vein collapse can occurs even under normal physiological condition into vessels – the angiosynizesis. The fluid structure interaction is studied experimentally on the special experimental line. Latex tubes with variable inner diameter and wall thickness are used as specimens.


Neinvazivní potické měření deformací elastických trubic
Macková, H. ; Chlup, Hynek ; Žitný, R.
Noninvasive optical measurement and evaluation of the pulse wave velocity of a selfoscillating elastic tube was done. A latex tube was loaded by selfexcited internal pulsatile flow as a simple model of human big arteries. The method is based on evaluation of high speed camera recordings and edges detection algorithm. Displacements of the tube edge were evaluated by a given scale factor from a standard gauge inserted to the recorded scene. Our goal is to recognize the pulse wave and measure its velocity along the tube.

 

Konstitutivní modelování tepenné stěny
Horný, L. ; Chlup, Hynek ; Adámek, T. ; Zitny, R. ; Macková, H.
Inflation tests and uni–axial extension tests of arterial tissue were performed. Experimental data were used in nonlinear regression analysis to identify material model. Arterial tissue was assumed to be incompressible hyperelastic material. 5–parameter strain energy density function based on combination of isotropic Neo–Hookean expression and Fung–type orthotropic expression was used. Computational model for material parameters identification was based on thick–wall tube with axial pre–strains. Residual strains were included. Internal structure of arterial wall was not considered. Fitted material models correspond to experimental data very well.


Optimalizace měření rychlosti pulzní vlny v tepnách
Macková, H. ; Chlup, Hynek ; Hulan, M. ; Žitný, R.
Measurements of the pulse wave velocity (PWV) in human arteries are important for two different reasons: an early diagnostics of atherosclerosis and identification of material properties of the vessel wall for numerical simulations. The PWV in blood vessels is not constant and classical methods of pressure wave shift between two points are not sufficient. We consider three methods: optical measurements of vessel wall displacement in several points by high speed camera, continual optical measurements of vessel wall displacement by correlator Q450 and measurements of flow rate and displacements by ultrasonic device. The first method can determine the PWV only between several points. The second method can show 3D reconstruction of displacements with very good resolution. The ultrasound measurements need combination of Doppler ultrasound velocimetry and Bscan imagining. However, the common devices used in medicine do not have any data output. It causes bad resolution.


Elastic tubes in the mode of selfexcited oscillation
Chlup, Hynek ; Maršík, František ; Konvičková, S.
Our paper studies experimentally the selfexcited oscillations of thinwalled elastic tubes with respect to the Korotkoff sounds. The selfexcited oscillation is a phenomenon, when an elastic tube looses stability of its shape and starts to oscillate, loaded only by continual flow, therefore without any external excitation. The mean flow rates, pressures at the ends of the tube, external pressures and photographs of the shape in two planes were recorded under various modes of oscillation. The effective crosssection and Young’s modulus of the tube wall were calculated by simplified formulas. The data analysis showed an increase of the oscillation frequency with a decrease of the tube wall compliance. It means the frequency of the oscillation is dependent on ratio of the wall thickness and the tube diameter. The mode of the oscillation is also influenced by the transmural pressure. The influence of the axial pretension of the tube is being studied now.
