Fardad Azarmi

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.

Steel bar corrosion monitoring with long-period fiber grating sensors coated with nano iron/silica particles and polyurethane

In this article, a recently proposed long-period fiber grating sensor coated with a thin layer of polyurethane and nano iron/silica particles is further developed and applied to monitor the corrosion process of deformed steel bars. Once calibrated, one coated long-period fiber grating sensor and one uncoated long-period fiber grating sensor for environmental compensation were attached to each of three steel bar samples that were tested in 3.5 wt% NaCl solution for 512 h. The resonant wavelength in long-period fiber grating spectra increased exponentially with immersion time due to corrosion of iron particles and thus reduction in coating thickness. The mass loss rate of steel bar #1 at the completion of corrosion tests (512 h of corrosion time) was correlated with that of sparse iron particles on long-period fiber grating sensor #1 after 130.5 h of immersion. The corrosion rates of long-period fiber grating sensors #2 and #3 were evaluated at 130.5 h and then used as a prediction of the corrosion rates of steel bars #2 and #3. The predicted corrosion rates by the long-period fiber grating sensors #2 and #3 were finally compared with those by potentiodynamic tests. The maximum mass loss prediction error by the long-period fiber grating sensors #2 and #3 is 26%. The coefficients of variation of three corrosion rate measurements are 0.049 by the long-period fiber grating sensors and 0.115 by the potentiodynamic tests, indicating more consistent and reliable measurements with the proposed technology.

Investigation on mechanical properties of cold sprayed Ni–Ni3Al composites

This study investigates the microstructural and mechanical characteristics of the Ni–Ni3Al composites fabricated by cold spraying. Investigations were conducted on pure Ni samples as well as composites consisting of 80 vol.-%Ni and 20 vol.-%Ni3Al. The results of a variety of hardness tests such as Vickers, Knoop, and nano-indentation are reported in this study. Furthermore, this study examines the application of analytical models to calculate the elastic modulus of coating materials from hardness test results. The validity of the obtained results was examined by performing impulse excitation (resonant frequency) test on all samples. A similar study was also performed on the same materials produced by the powder metallurgy (P/M) technique for the purpose of comparison. The reinforced samples exhibited better mechanical properties compared to the unreinforced ones regardless of the fabrication technique. The cold sprayed sample exhibited higher strength and density compared to the P/M processed ones.

Advanced Ultrasonic Testing Technologies with Applications to Evaluation of Steel Bridge Welding - An Overview

Non-destructive evaluation (NDE) methods are widely accepted for quality control of welding in steel bridges. Recent development of advanced ultrasonic testing technologies enriched the categories of NDE methods used for steel bridges and more importantly these enhanced techniques provided more effective flaw detection and characterization. No guidelines, however, is available in existing bridge welding code for their more widespread applications to bridges. In this study, we overview the state-of-the-art advanced ultrasonic testing technologies in welding inspection. Benefits of the enhanced ultrasonic testing technologies are summarized, aiming to pave the way for deciding methods need for various steel bridge welding inspections.

Integrated Fiber Optic Sensing System for Pipeline Corrosion Monitoring

Corrosion significantly impacts the reliability and safety of metallic pipelines, which is a leading cause of metallic pipeline failure. A real-time update for the pipeline corrosion status and a timely alert for corrosion induced pipeline damages would contribute to an appropriate plan for pipeline maintenance and repair and reduce the frequency of pipeline failures. To assess the pipeline corrosion, various technologies exist and the most common approach is to measure the pipe-to-soil voltage potential. However, to date, few techniques can yet achieve remote and real-time corrosion assessment for pipelines. Fiber optic sensors, with unique advantages of real-time sensing, compactness, immunity to electromagnetic interference and moisture, capability of quasi-distributed sensing, and long life cycle, is a potential candidate to meet this challenge. This study, therefore, an integrated fiber optic sensing system is developed to assess the corrosion of on-shore buried metallic transmission pipelines in a real time manner. The sensing principle, development of embedment technique, and laboratory accelerated corrosion tests will be discussed in detail. Upon validation, the embedded integrated fiber optic sensing system could potentially serve the purpose of corrosion monitoring on numerous metallic pipelines and would possibly reduce the pipeline corrosion induced failures.

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.

Innovative Fiber Optic Sensors for Pipeline Corrosion Monitoring

Corrosion, a leading cause of failure in metallic transmission pipelines, significantly affects the reliability and safety of metallic pipelines. To assess and monitor pipeline corrosion and provide substantial information to locate corrosion induced pipeline damage, this study proposes an optical fiber sensor based on long-period fiber gratings (LPFGs) for a corrosion-induced deterioration assessment of pipeline structures. A thin layer of nano iron/silica particles dispersed polyurethane is proposed to be coated on the outer surface of the LPFGs. With the thin metal dispersed layer over an LPFG, both its resonant wavelength and intensity of the resonant peak are altered. Accelerated laboratory corrosion tests are implemented to validate the feasibility of the proposed sensing system. Test results showed that within the detection limitation of the thin coated layer, the proposed sensor could monitor both the initial and stable corrosion rate consistently. With multiple LPFGs in a single fiber, it is possible to provide a cost-effective corrosion-monitoring technique for pipeline corrosion monitoring.

Microstructure characterization and modeling of splat formation during air plasma spraying for inconel 625 superalloy

There is a growing interest in use of the nickel-based alloy Inconel 625 coatings due to its ability to improve base materials high temperature properties. Thermal spraying methods such as Air Plasma Spraying (APS) can be considered as a convenient method to deposit this material. The present work deals with APS deposited Inconel 625 structures consisting of huge number of individual splats formed by impacting molten droplets on substrates during spraying process. It is clear that the splat formation mechanism which dominates its size, cohesion, and boundaries highly influences the microstructure of the coating. This paper presents a developed numerical technique performed to simulate splat formation using a three dimensional model. In this method flow field is solved by Finite Volume Method (FVM) and free surfaces are determined from Youngs’ Volume of Fraction method (VOF). Finally, the model prediction is correlated with the actual splat geometries.

Effects of Attached Body on Biomechanical Response of the Helmeted Human Head Under Blast

The results of a computational study on the effect of the body on biomechanical responses of a helmeted human head under various blast load orientations are presented in this work. The focus of the work is to study the effects of the human head model boundary conditions on mechanical responses of the head such as variations of intracranial pressure (ICP). In this work, finite element models of the helmet, padding system, and head components are used for a dynamic nonlinear analysis. Appropriate contacts and conditions are applied between different components of the head, pads and helmet. Blast is modeled in a free space. Two different blast wave orientations with respect to head position are set, so that, blast waves tackle the front and back of the head. Standard trinitrotoluene is selected as the high explosive (HE) material. The standoff distance in all cases is one meter from the explosion site and the mass of HE is 200 grams. To study the effect of the body, three different boundary conditions are considered; the head-neck model is free; the base of the neck is completely fixed; and the head-neck model is attached to the body. Comparing the results shows that the level of ICP and shear stress on the brain are similar during the first five milliseconds after the head is hit by the blast waves. It explains the fact that the rest of the body does not have any contribution to the response of the head during the first 5 milliseconds. However, the conclusion is just reasonable for the presented blast situations and different blast wave incidents as well as more directions must be considered.Copyright