Mehdi Salimi Jazi

A computational study of influence of helmet padding materials on the human brain under ballistic impacts

The results of a computational study of a helmeted human head are presented in this paper. The focus of the work is to study the effects of helmet pad materials on the level of acceleration, inflicted pressure and shear stress in a human brain model subjected to a ballistic impact. Four different closed cell foam materials, made of expanded polystyrene and expanded polypropylene, are examined for the padding material. It is assumed that bullets cannot penetrate the helmet shell. Finite element modelling of the helmet, padding system, head and head components is used for this dynamic nonlinear analysis. Appropriate contacts and conditions are applied between the different components of the head, as well as between the head and the pads, and the pads and the helmet. Based on the results of simulations in this work, it is concluded that the stiffness of the foam has a prominent role in reducing the level of the transferred load to the brain. A pad that is less stiff is more efficient in absorbing the impact energy and reducing the sudden acceleration of the head and consequently lowers the brain injury level. Using the pad with the least stiffness, the influence of the angle of impacts as well as the locations of the ballistic strike is studied.

Examination of the protective roles of helmet/faceshield and directionality for human head under blast waves

A parametric study was conducted to delineate the efficacy of personal protective equipment (PPE), such as ballistic faceshields and advanced combat helmets, in the case of a blast. The propagations of blast waves and their interactions with an unprotected head, a helmeted one, and a fully protected finite element head model (FEHM) were modeled. The biomechanical parameters of the brain were recorded when the FEHM was exposed to shockwaves from the front, back, top, and bottom. The directional dependent tissue response of the brain and the variable efficiency of PPE with respect to the blast orientation were two major results of this study.

Biomechanical parameters of the brain under blast loads with and without helmets

Computational results on biomechanics of brain for a human head model with and without a helmet under the blast loading are presented. The blast propagation is simulated using the hybrid method combining the multi-material arbitrary Lagrangian-Eulerian finite element formulation and empirical blast load equations. A three dimensional model of a combat helmet is integrated with a validated 50th percentile human head-neck model. The blast-head model interactions are modelled using a penalty-based fluid-structure interaction algorithm. Biomechanical data parameters of the head/brain such as intracranial pressures and maximum shear stress are recorded and compared both with and without a helmet. The results are studied the severity of the blast under different values for the high explosive explosions and the efficiency of the wearing ballistic impact under the blast situation.

Computational biomechanics of human brain with and without the inclusion of the body under different blast orientation

Abstract Three different human head models in a free space are exposed to blast waves coming from four different directions. The four head–neck–body models composed of model a, with the neck free in space; model b, with neck fixed at the bottom; and model c, with the neck attached to the body. The results show that the effect of the body can be ignored for the first milliseconds of the head–blast wave interactions. Also one can see that although most biomechanical responses of the brain have similar patterns in all models, the shear stresses are heavily increased after a few milliseconds in model b in which the head motion is obstructed by the fixed-neck boundary conditions. The free-floating head model results are closer to the attached-body model.

Confined blasts, and the impact of shock wave reflections on a human head and the related traumatic brain injury

We examine the effects of blast waves in a confined space on a human head model. A finite element human model (FEHM) is exposed to blast waves from explosions, as well as, to the reflected waves from the confinement walls. The intensity of the travelling blast shock waves is measured computationally and compared with experimental results. We monitor the mechanical response of the brain of the FEHM at different stand-off positions, either close to, or away from the surrounding walls in interaction with the travelling blast waves. The skull pressure, brain intracranial pressure (ICP), acceleration, shear stress, and principal stresses and strains are measured as the biomechanical parameters for injury diagnosis and compared for all the situations and stand-off positions considered. The results illustrate that the additional reflected shock waves due to the surrounding walls can dramatically change the brain biomechanical parameters.

Effect of volume fraction of reinforcement phase on mechanical behavior of ultra-high-temperature composite consisting of iron matrix and TiB 2 particulates

Recently, ultra-high-temperature ceramics have received abundance attention due to growing demand of new materials for extreme service conditions. In this study, titanium diboride particles as an ultra-high-temperature ceramic material have been used to reinforce iron matrix to fabricate a metal matrix composite. Iron–titanium diboride composite samples with different volume fractions of titanium diboride fabricated using powder metallurgy route. Physical, microstructural and mechanical properties of metal matrix composite were studied. The results indicated that addition of titanium diboride only up to 20 vol% increased mechanical properties of the processed composite. Microstructure-based finite element analysis could verify the experimental results.

Investigation on Fracture Toughness of Coating/Substrate Interface - Case Study: Thermally Sprayed Nickel Based Superalloy on Variety of Substrates

Nickel based superalloy materials have being extensively used in aerospace and other high tech industries. In the present work, the effect of different substrates on the mechanical properties of the coating-substrate interface has been studied. To this end, alloy 718, commercially known as Inconel 718, was deposited on alloy 718 and low carbon steel substrates using High Velocity Oxygen Fuel (HVOF) technique at the same condition. The bonding strength of the interfaces evaluated using Vickers indentation test on the coating-substrate interface. Hardness results were subjected to a valid empirical method to estimate the fracture toughness. Results illustrated that using the same material as coating and the substrate led to stronger interface bonding strength due to higher hardness, fracture toughness, and less crack propagation.

Innovative insulations for spacecraft on-surface monitoring system in harsh environments

In this paper, innovative multilayer insulation coatings are investigated to eliminate the environmental effects of spacecraft on-surface monitoring system in harsh environments and ultimately adjust the sensitivity the sensors towards the parameters needed to be sensed. The design of the composite insulation is guided through theoretical and numerical modeling analysis of heat transfer and thermal stress progressing. Detail theoretic, numerical, and experimental analysis proved the feasibility of the proposed multilayer structure of the insulation to work up to 700°C without inducing significant deformation on the top of sensor surface from heat.

The Effects of Retesting on the Mechanical Properties of the Brain Tissue

This research is intended to examine the amount of changes that can happen in material characteristics after retesting. Stress relaxation test is conducted on the same samples of the swine brain tissue for several times in small and large deformations. The mechanical properties of the substance are calculated before and after retest and the constants of the tissue, as mechanical characteristics, are determined and compared. Short- and long-term moduli, relaxation times and relaxation functions are of those data that are calculated and compared to understand how much they decay after repeating the experiments. The results show that applying different tests on one sample slightly changes the mechanical properties of the tissue and, as a result, it is partly possible to perform more than one test on the same sample resulting in less sample preparation, time and effort.Copyright

Study the Effects of Padding Materials on the Level of the Load in the Brain

Experiencing a speedy strain or acceleration causes Traumatic Brain Injury (TBI) that can be classified into mild, moderate and severe, based on the level of the injury. Motor vehicles crashes; violence related injuries; collisions in sports; and falls are most common causes of TBI. Moreover in the military service TBI can be happened when soldiers are exposed to shock waves due to blasts or because of ballistic impact.Copyright