Mazdak Ghajari

Mazdak Ghajari
Imperial College London | Imperial · Dyson School of Design Engineering

PhD, MSc, BSc

About

61
Publications
19,032
Reads
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1,190
Citations
Introduction
Biomechanics of Traumatic Brain Injury: computational modelling of TBI and new TBI prevention strategies Injury detection and prevention
Additional affiliations
October 2013 - October 2015
Imperial College London
Position
  • Researcher
Description
  • • Impact and blast biomechanics of traumatic brain injury. • Development of mitigation strategies.
February 2011 - September 2013
Imperial College London
Position
  • Research Associate
Description
  • • The peridynamic nonlocal and meshless method for fracture analysis of ceramics, bone and rocks. • Development of SHM methods

Publications

Publications (61)
Article
Full-text available
New oblique impact methods for evaluating head injury mitigation effects of helmets are emerging, which mandate measuring both translational and rotational kinematics of the headform. These methods need headforms with biofidelic mass, moments of inertia (MoIs), and coefficient of friction (CoF). To fulfill this need, working group 11 of the Europea...
Article
Full-text available
Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics ar...
Article
Full-text available
Cerebrospinal fluid (CSF) cavitation is a likely physical mechanism for producing traumatic brain injury (TBI) under mechanical loading. In this study, we investigated CSF cavitation under blasts and helmeted impacts which represented loadings in battlefield and road traffic/sports collisions. We first predicted the human head response under the bl...
Article
Cellular structures such as honeycombs are used to manage impact loads in many engineering applications, where often the impact load is oblique (non-axial). Although these structures have been extensively studied under axial impacts, a key question remains largely unaddressed: How may their axial and shear responses be independently tailored for ob...
Article
Motorcyclists are at high risk of head injuries, including skull fractures, focal brain injuries, intracranial bleeding and diffuse brain injuries. New helmet technologies have been developed to mitigate head injuries in motorcycle collisions, but there is limited information on their performance under commonly occurring oblique impacts. We used an...
Article
Full-text available
Finite Element (FE) models of brain mechanics have improved our understanding of the brain response to rapid mechanical loads that produce traumatic brain injuries. However, these models have rarely incorporated vasculature, which limits their ability to predict the response of vessels to head impacts. To address this shortcoming, here we used high...
Article
Full-text available
The current combat helmets are primarily designed to mitigate blunt impacts and ballistic loadings. Their protection against primary blast wave is not well studied. In this paper, we comprehensively assessed the protective capabilities of the advanced combat helmet and goggles against blast waves with different intensity and directions. Using a hig...
Article
E-scooters are the fastest growing mode of micro-mobility with important environmental benefits. However, there are serious concerns about injuries caused by e-scooter accidents. Falls due to poor road surface conditions are a common cause of injury in e-scooter riders, and head injuries are one of the most common and concerning injuries in e-scoot...
Article
Full-text available
Road traffic collisions are a major cause of traumatic brain injury. However, the relationship between road traffic collision dynamics and traumatic brain injury risk for different road users is unknown. We investigated 2,065 collisions from Great Britain’s Road Accident In-depth Studies collision database involving 5,374 subjects (2013-20). 595 su...
Article
Full-text available
Blast induced traumatic brain injury (bTBI) has been a prevalent injury in recent conflicts. Post-mortem studies have shown damage in the brain tissue close to the cerebrospinal fluid (CSF) in bTBI cases compared to non-blast TBI cases. CSF cavitation is a potential mechanism for this brain/CSF interface injury. In this study, our aim was to explor...
Data
Simulation of brain vasculatre in controlled cortical impact (CCI).
Article
Full-text available
Neurovascular injury is often observed in traumatic brain injury (TBI). However, the relationship between mechanical forces and vascular injury is still unclear. A key question is whether the complex anatomy of vasculature plays a role in increasing forces in cerebral vessels and producing damage. We developed a high-fidelity multiscale finite elem...
Article
Full-text available
New helmet technologies have been developed to improve the mitigation of traumatic brain injury (TBI) in bicycle accidents. However, their effectiveness under oblique impacts, which produce more strains in the brain in comparison with vertical impacts adopted by helmet standards, is still unclear. Here we used a new method to assess the brain injur...
Article
Full-text available
American football players are frequently exposed to head impacts, which can cause concussions and may lead to neurodegenerative diseases such as chronic traumatic encephalopathy (CTE). Player position appears to influence the risk of concussion but there is limited work on its effect on the risk of CTE. Computational modelling has shown that large...
Article
Full-text available
The Cerebrospinal Fluid (CSF) can undergo shear deformations under head motions. Finite Element (FE) models, which are commonly used to simulate biomechanics of the brain, including traumatic brain injury, employ solid elements to represent the CSF. However, the limited number of elements paired with shear deformations in CSF can decrease the accur...
Article
Full-text available
Bicycle helmets are shown to offer protection against head injuries. Rating methods and test standards are used to evaluate different helmet designs and safety performance. Both strain-based injury criteria obtained from finite element brain injury models and metrics derived from global kinematic responses can be used to evaluate helmet safety perf...
Article
Full-text available
The relationship between biomechanical forces and neuropathology is key to understanding traumatic brain injury. White matter tracts are damaged by high shear forces during impact, resulting in axonal injury, a key determinant of long-term clinical outcomes. However, the relationship between biomechanical forces and patterns of white matter injurie...
Article
Full-text available
Mechanisms of blast-induced Traumatic Brain Injury (BTBI), particularly those linked to the primary pressure wave, are still not fully understood. One possible BTBI mechanism is cavitation in the cerebrospinal fluid (CSF) caused by CSF tensile failure, which is likely to increase strain and strain rate in the brain tissue near the CSF. Blast loadin...
Article
Material jetting, particularly PolyJet technology, is an additive manufacturing (AM) process which has introduced novel flexible elastomers used in bio-inspired soft robots, compliant structures and dampers. Finite Element Analysis (FEA) is a key tool for the development of such applications, which requires comprehensive material characterisation u...
Article
This paper evaluates the effects of topology and relative density of helmet lattice liners on mitigating Traumatic Brain Injury (TBI). Finite Element (FE) models of new lattice liners with prismatic and tetrahedral topologies were developed. A typical frontal head impact in motorcycle accidents was simulated, and linear and rotational accelerations...
Article
Full-text available
Blast‐induced Traumatic Brain Injury (TBI) has been affecting combatants and civilians. The blast pressure wave is thought to have a significant contribution to blast related TBI. Due to the limitations and difficulties of conducting blast tests on surrogates, computational modelling has been used as a key method for exploring this field. However,...
Article
Standards for sports headgear were introduced as far back as the 1960s and many have remained substantially unchanged to present day. Since this time, headgear has virtually eliminated catastrophic head injuries such as skull fractures and changed the landscape of head injuries in sports. Mild traumatic brain injury (mTBI) is now a prevalent concer...
Article
Full-text available
Traumatic brain injury (TBI) affects millions of people worldwide with significant personal and social consequences. New materials and methods offer opportunities for improving designs of TBI prevention systems, such as helmets. We combined empirical impact tests and computational modelling to test the effectiveness of new viscoelastic add-on compo...
Article
Neck protective devices for motorcyclists have been introduced fairly recently but there is no standard method to evaluate their performance. The goal of this study is to compare the response of riders’ necks to direct impacts on the helmet with and without such a device. We investigate three common types of cervical injury mechanisms i.e. hyperfle...
Article
Tactile sensors are essential for robotic systems to interact safely and effectively with the external world, they also play a vital role in some smart healthcare systems. Despite advances in areas including materials/composites, electronics and fabrication techniques, it remains challenging to develop low cost, high performance, durable, robust, s...
Article
Full-text available
This paper investigates the design optimisation of a magnetic field based soft tactile sensor, comprised of a magnet and Hall effect module separated by an elastomer. The aim was to minimise sensitivity of the output force with respect to the input magnetic field; this was achieved by varying the geometry and material properties. Finite element sim...
Article
Full-text available
The chin bar of motorcycle full-face helmets is the most likely region of the helmet to sustain impacts during accidents, with a large percentage of these impacts leading to basilar skull fracture. Currently, helmet chin bars are designed to mitigate the peak acceleration at the centre of gravity of isolated headforms, as required by standards, but...
Article
Traumatic brain injury can lead to the neurodegenerative disease chronic traumatic encephalopathy. This condition has a clear neuropathological definition but the relationship between the initial head impact and the pattern of progressive brain pathology is poorly understood. We test the hypothesis that mechanical strain and strain rate are greates...
Article
Full-text available
Tactile sensors are essential for robotic systems to safely interact with the external world and to precisely manipulate objects. Existing tactile sensors are typically either expensive or limited by poor performance, and most are not mechanically compliant. This work presents MagTrix, a soft tactile sensor array based on four 3D Hall sensors with...
Data
This is a demo Video for the MagOne senosr we developed. Please read our paper for more details: Design Methodology for Magnetic Field-Based Soft Tri-Axis Tactile Sensors http://www.mdpi.com/1424-8220/16/9/1356
Article
Full-text available
Tactile sensors are essential if robots are to safely interact with the external world and to dexterously manipulate objects. Current tactile sensors have limitations restricting their use, notably being too fragile or having limited performance. Magnetic field-based soft tactile sensors offer a potential improvement, being durable, low cost, accur...
Conference Paper
Sensors take measurements and provide feedback to the user via a calibrated system, in soft sensing the development of such systems is complicated by the presence of nonlinearities, e.g. contact, material properties and complex geometries. When designing soft-sensors it is desirable for them to be inexpensive and capable of providing high resolutio...
Conference Paper
Full-text available
Finite element simulations have been performed in order to study the effects of using neck brace as an item of Personal Protective Equipment (PPE) for motorcycle riders. The neck brace model was generated and coupled with the helmet and Hybrid III dummy using Hypermesh software and the simulations have been carried out using LS-Dyna. Hyperflexion a...
Chapter
This research investigates the post-impact behaviour of CFRP coupon specimens subjected to multisite impacts. Sequential low-velocity impacts at different locations were performed on coupons with different thicknesses. The impact load history was recorded, and the extent of damage was assessed by ultrasonic inspection. The residual strength in comp...
Chapter
This research investigates the post-impact behaviour of composite fuselage panels subjected to multi-site low-velocity impacts. Large curved stiffened panels (1.2 m × 0.8 m, with composite skins/stiffeners and aluminium frames) of two different skin thicknesses were subjected to sequential drop-weight impacts at locations previously determined to b...
Article
Full-text available
In this work, application of the electro-mechanical impedance (EMI) method in structural health monitoring as a damage detection technique has been investigated. A damage metric based on the real and imaginary parts of the impedance measures is introduced. Numerical and experimental tests are carried out to investigate the applicability of the meth...
Article
رشد سریع صنعت موتورسیکلت در سالهای اخیر در ایران و استقبال مردم از آن بدون رعایت نکات ایمنی در هنگام رانندگی با این وسیله نقلیه موجب شده است که موتورسیکلت سواران به عنوان دومین گروه از آسیب دیدگان تصادفات رانندگی در ایران شناخته شوند. آسیب وارد به سر در تصادفات رانندگی بسیار رایج م یباشد و علیرغم اینکه استفاده از کلاه ایمنی در کاهش صدمات وارد به سر...
Conference Paper
Full-text available
Statistical studies showed that the chin bar of full-face helmets is the region with the highest number of impacts. In an Australian research fifty percent of severe impacts took place to the front of helmet and forty percent of these resulted in Basilar Skull Fracture (BSF). There are two standards, which include some criteria for helmet’s chin ba...
Article
The determination of a reliable transfer function for force reconstruction of impacts on composite panels is addressed in the paper. The reconstruction of the impact force history requires the knowledge of the transfer function which relates the response to the contact force. In this paper, a new method to determine the transfer function of a compo...
Article
A new material model for the dynamic fracture analysis of anisotropic materials has been proposed within the framework of the bond-based peridynamic theory. This model enables predicting complex fracture phenomena such as spontaneous crack nucleation and crack branching, curving and arrest, a capability inherited from the bond-based peridynamic the...
Article
Sequential multi-site low velocity impacts (LVI) were performed on CFRP composite plates with different thicknesses and the compression after impact (CAI) behaviour was then investigated. A modified CAI rig was designed and manufactured for testing thin composites. A Finite Element (FE) model of the laminate was developed using continuum shell elem...
Article
Full-text available
In this work, a new methodology is presented for reconstruction of the impact force history using artificial neural networks (ANNs) and spectral components of sensor data recorded by piezoceramic sensors. A large set of data, required for training the ANNs, was generated by using an efficient nonlinear finite element (FE) model of a sensorised comp...
Article
A number of small mass and large mass impacts on a sensorised aircraft stiffened panel were numerically simulated. Sensor signals and the contact force history were recorded during each impact. A significant difference was noticed between the small mass and large mass impacts with respect to the contact force. To distinguish between these two types...
Article
Full-text available
A SMART Platform is developed based on sensor readings for Structural Health Monitoring of a stiffened composite panel. The platforms main function is divided into three categories: Passive sensing, Active sensing and Optimal sensor positioning. The platform has self-diagnostic capabilities, i.e. prior to its application the health of the sensors a...
Article
Full-text available
In this work a methodology for impact identification on composite stiffened panels using piezoceramic sensors has been presented. A large number of impacts covering a wide range of energies (corresponding to small and large mass impacts) at various locations of a composite stiffened panel have been simulated using the finite element (FE) method. To...
Article
The oblique impact methods of motorcycle helmet standards prescribe using an isolated headform. However, in accidents the presence of the body may influence impact responses of the head and helmet. In this study, the effects of the presence of the body, in helmet oblique impacts, are investigated. Using the Finite Element method, oblique impacts of...
Article
Full-text available
Currently available motorcycle helmet standards employ headforms to assess the impact absorption capability of helmets. The mass and size of the headforms are similar to those of the human head. This fact implies that the standards rely on the assumption that the effect of the rest of the body on the performance of the helmet during impact is negli...
Article
In this work, a number of impacts on a composite stiffened panel fitted with piezoceramic sensors were simulated with the finite element (FE) method. During impacts, the contact force history and strains at the sensors were recorded. These data were used to train, validate and test two artificial neural networks (ANN) for the prediction of the impa...
Article
Full-text available
The most frequent type of injury that causes death or disability in motorcycle accidents is head injury. The only item of personal protective equipment that protects a motorcyclist's head in real-world accidents is the safety helmet. The protective capability of a helmet is assessed, according to international standards, through the impact of a hea...
Article
Full-text available
The purpose of this work was to investigate the influence of the presence of the body in helmet oblique impacts on the tissue level response of the human head. The kinematic field of the head obtained from full-body and detached-head oblique impacts were used to drive a validated Finite Element model of the human head and evaluate predictors of the...
Article
Full-text available
Motorcycle crash-related fatalities and injuries have a relatively increasing tendency compared to other vehicles. The new development of safety devices and technologies for prediction of their behaviour are therefore also increasingly important. Motorcycles have the least amount of protective devices amongst vehicles. A small disturbance in the mo...
Article
Motorcycle crash-related fatalities and injuries have a relatively increasing tendency compared to other vehicles. The new development of safety devices and technologies forprediction of their behaviour are therefore also increasingly important. Motorcycles have the least amount of protective devices amongst vehicles. A small disturbance in the mot...
Conference Paper
Full-text available
The Finite Element (FE) method was employed to develop and enhance numerical models that can be used for simulating accidents involving motorcyclists. They are the FE models of a commercial helmet, the human head and the Hybrid III dummy. The composite shell and foam liner of the helmet, which are the most important components in terms of energy ab...

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