Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear... more
Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear potential for it to be used to shape and form the topology of micro-scale surface features, such as those found on the micro-applications of additively manufactured (AM) parts, transmission electron microscopy (TEM) samples, micro-electromechanical systems (MEMs), biomedical stents, and artificial implants. This review focuses on the fundamental principles of electrochemical polishing, the associated process parameters (voltage, current density, electrolytes, electrode gap, and time), and the increasing demand for using environmentally sustainable electrolytes and micro-scale applications. A summary of other micro-fabrication processes, including micro-milling, micro-electric discharge machining (EDM), laser polishing/ablation, lithography (LIGA), electroc...
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Provided by the author(s) and University College Dublin Library in accordance with publisher policies. Please cite the published version when available. Downloaded 2016-05-18T08:52:45Z Some rights reserved. For more information, please... more
Provided by the author(s) and University College Dublin Library in accordance with publisher policies. Please cite the published version when available. Downloaded 2016-05-18T08:52:45Z Some rights reserved. For more information, please see the item record link above. Title Temperature effects on brain tissue in compression
Ice hockey is one of many contact sports which have a high incidence of brain injury. The current methods of evaluating protective devices use peak resultant linear acceleration as their pass/fail criteria which are not fully... more
Ice hockey is one of many contact sports which have a high incidence of brain injury. The current methods of evaluating protective devices use peak resultant linear acceleration as their pass/fail criteria which are not fully representative of brain injuries as a whole. The purpose of this study is to examine how the linear and angular acceleration loading curves from a helmeted impact influence currently used brain deformation injury metrics. A helmeted and instrumented Hybrid III headform was impacted in 5 centric and noncentric impact sites to elicit linear and angular acceleration responses. These responses were examined through use of a brain model. The results indicated that when the helmet is examined using peak resultant linear acceleration alone they are similar and protective, but when a 3 dimensional brain deformation response is used to examine the helmets there are risks of brain injury with lower linear accelerations which would pass standard certifications for safety.
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Extensive research has been carried out for at least 50 years to understand the mechanical properties of brain tissue in order to understand the mechanisms of traumatic brain injury (TBI). The observed large variability in experimental... more
Extensive research has been carried out for at least 50 years to understand the mechanical properties of brain tissue in order to understand the mechanisms of traumatic brain injury (TBI). The observed large variability in experimental results may be due to the inhomogeneous nature of brain tissue and to the broad range of test conditions. However, test temperature is also considered as one of the factors influencing the properties of brain tissue. In this research, the mechanical properties of porcine brain have been investigated at 22C (room temperature) and at 37C (body temperature) while maintaining a constant preservation temperature of approximately 4-5C. Unconfined compression tests were performed at dynamic strain rates of 30 and 50/s using a custom made test apparatus. There was no significant difference (p = 0.8559 - 0.9290) between the average engineering stresses of the brain tissue at the two different temperature conditions. The results of this study should help to und...
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Mechanical characterization of brain tissue has been investigated extensively by various research groups over the past fifty years. These properties are particularly important for modelling Traumatic Brain Injury (TBI). In this research,... more
Mechanical characterization of brain tissue has been investigated extensively by various research groups over the past fifty years. These properties are particularly important for modelling Traumatic Brain Injury (TBI). In this research, we present the design and calibration of a High Rate Tension Device (HRTD) capable of performing tests up to a maximum strain rate of 90/s. We use experimental and numerical methods to investigate the effects of inhomogeneous deformation of porcine brain tissue during tension at different specimen thicknesses (4.0-14.0 mm), by performing tension tests at a strain rate of 30/s. One-term Ogden material parameters (mu = 4395.0 Pa, alpha = -2.8) were derived by performing an inverse finite element analysis to model all experimental data. A similar procedure was adopted to determine Young's modulus (E= 11200 Pa) of the linear elastic regime. Based on this analysis, brain specimens of aspect ratio (diameter/thickness) S < 1.0 are required to minimi...
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Unconfined compression tests are more convenient to perform on cylindrical samples of brain tissue than tensile tests in order to estimate mechanical properties of the brain tissue because they allow for homogeneous deformations. The... more
Unconfined compression tests are more convenient to perform on cylindrical samples of brain tissue than tensile tests in order to estimate mechanical properties of the brain tissue because they allow for homogeneous deformations. The reliability of these tests depends significantly on the amount of friction generated at the specimen/platen interface. Thus, there is a crucial need to find an approximate value of the friction coefficient in order to predict a possible overestimation of stresses during unconfined compression tests. In this study, a combined experimental-computational approach was adopted to estimate the dynamic friction coefficient mu of porcine brain matter against metal platens in compressive tests. Cylindrical samples of porcine brain tissue were tested up to 30% strain at variable strain rates, both under bonded and lubricated conditions in the same controlled environment. It was established that mu was equal to 0.09 +/- 0.03, 0.18 +/- 0.04, 0.18 +/- 0.04 and 0.20 ...
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Traumatic brain injury (TBI) occurs when local mechanical load exceeds certain tolerance levels for brain tissue. Extensive research has been done previously for brain matter experiencing compression at quasistatic loading; however,... more
Traumatic brain injury (TBI) occurs when local mechanical load exceeds certain tolerance levels for brain tissue. Extensive research has been done previously for brain matter experiencing compression at quasistatic loading; however, limited data is available to model TBI under dynamic impact conditions. In this research, an experimental setup was developed to perform unconfined compression tests and stress relaxation tests at strain rates < 90/s. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate. Specifically, the compressive nominal stress at 30% strain was 8.83 +/- 1.94, 12.8 +/- 3.10 and 16.0 +/- 1.41 kPa (mean +/- SD) at strain rates of 30, 60 and 90/s, respectively. Relaxation tests were also conducted at 10%-50% strain with the average rise time of 10 ms, which can be used to derive time dependent parameters. Numerical simulations were performed using one-term Ogden model with initial shear modulus mu_...
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The mechanical characterization of brain tissue at high loading velocities is vital for understanding and modeling Traumatic Brain Injury (TBI). The most severe form of TBI is diffuse axonal injury (DAI) which involves damage to... more
The mechanical characterization of brain tissue at high loading velocities is vital for understanding and modeling Traumatic Brain Injury (TBI). The most severe form of TBI is diffuse axonal injury (DAI) which involves damage to individual nerve cells (neurons). DAI in animals and humans occurs at strains > 10% and strain rates > 10/s. The mechanical properties of brain tissues at these strains and strain rates are of particular significance, as they can be used in finite element human head models to accurately predict brain injuries under different impact conditions. Existing conventional tensile testing machines can only achieve maximum loading velocities of 500 mm/min, whereas the Kolsky bar apparatus is more suitable for strain rates > 100/s. In this study, a custom-designed high rate tension device is developed and calibrated to estimate the mechanical properties of brain tissue in tension at strain rates < 90/s, while maintaining a uniform velocity. The range of st...
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During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Moreover, diffuse axonal injury (DAI) occurs in animals and humans when both the... more
During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Moreover, diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue in shear at these strains and strain rates is thus of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. In this research, an experimental setup was developed to perform simple shear tests on porcine brain tissue at strain rates < 120/s. The maximum measured shear stress at strain rates of 30, 60, 90 and 120/s was 1.15 +/- 0.25 kPa, 1.34 +/- 0.19 kPa, 2.19 +/- 0.225 kPa and 2.52 +/- 0.27 kPa, (mean +/- SD), respectively, at the maximum amount of shear, K = 1. Good agreement of experimental, theoretical (Ogden and MooneyRivlin models) and n...
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The magnitude of force used in a stabbing incident can be difficult to quantify, although the estimate given by forensic pathologists is often seen as `critical' evidence in medico-legal situations. The main objective of this study is... more
The magnitude of force used in a stabbing incident can be difficult to quantify, although the estimate given by forensic pathologists is often seen as `critical' evidence in medico-legal situations. The main objective of this study is to develop a quantitative measure of the force associated with a knife stabbing biological tissue, using a combined experimental and numerical technique. A series of stab-penetration tests were performed to quantify the force required for a blade to penetrate skin at various speeds and using different `sharp' instruments. A computational model of blade penetration was developed using ABAQUS/EXPLICIT, a non-linear finite element analysis (FEA) commercial package. This model, which incorporated element deletion along with a suitable failure criterion, is capable of systematically quantifying the effect of the many variables affecting a stab event. This quantitative data could, in time, lead to the development of a predictive model that could help...
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Mass production of small, high-precision, high-value-added plastic parts has been made possible by microinjection molding technology. The fabricated parts are typically micro components, weighing a few milligrams, or larger parts with... more
Mass production of small, high-precision, high-value-added plastic parts has been made possible by microinjection molding technology. The fabricated parts are typically micro components, weighing a few milligrams, or larger parts with micro/nanoscale surface features. These products have a characteristically high surface-to-volume ratio (103–106m 1) and a correspondingly faster cooling rate than larger components.1 However, due to the intrinsic low thermal conductivity of polymer materials, a large thermal gradient exists across the part thickness. To fill features at the micro/nanoscale, high temperatures and high injection speeds are required, leading to correspondingly high stresses and shear rates during molding. This variable thermomechanical environment influences the nucleation and growth rate of crystalline entities and therefore the mechanical properties of the resultant micropart. Recent efforts to understand the morphology of microparts have focused on comparing millimete...
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Cycle helmets have continued to increase in popularity since their introduction half a century ago. Many studies indicate that overall, head injury can be significantly reduced by wearing them. This study was conducted using two distinct... more
Cycle helmets have continued to increase in popularity since their introduction half a century ago. Many studies indicate that overall, head injury can be significantly reduced by wearing them. This study was conducted using two distinct sets of real-world cycling collision data from Ireland, namely cases involving police collision reports and cases involving admission to a hospital emergency department. The analyses sought to simulate and analyse the protective performance of cycle helmets in such collision scenarios, by comparing the Head Injury Criterion score and peak head accelerations, both linear and angular. Cycle collisions were simulated using the specialised commercial software MADYMO. From the simulation results, these key metrics were compared between the same-scenario helmeted and unhelmeted cyclist models. Results showed that the inclusion of bicycle helmets reduced linear accelerations very significantly, but also increased angular accelerations significantly compare...
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The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding... more
The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the moulding material. The influence of feature configuration, length, width, gap distance between features, location on substrate, and substrate thickness on the quality of replication was investigated. The experiments revealed that the replication of ridges, including feature edge, profile and filling distance, was sensitive to the flow direction; a critical feature length was found below which the filling of features was significantly reduced. Both the feature location and the substrate thickness had an influence on the filling of micro/nano features while the gap distance had a negligible effect on ...
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Linear and depressed skull fractures are frequent mechanisms of head injury and are often associated with traumatic brain injury. Accurate knowledge and understanding of the fracture of cranial bone can provide insight into the prevention... more
Linear and depressed skull fractures are frequent mechanisms of head injury and are often associated with traumatic brain injury. Accurate knowledge and understanding of the fracture of cranial bone can provide insight into the prevention of skull fracture injuries and associated lesions of soft neural tissue and help aid the design of energy absorbing head protection systems. Cranial bone is a complex material comprising of a three-layered structure: external layers consisting of compact, high-density cortical bone and a central layer consisting of a low-density, irregularly porous structure. In the current study, a significantly large set of cranial bone specimens (parietal and frontal bones) were extracted from 8 crania and, after μCT imaging, the specimens were tested in a three-point bend set-up at dynamic speeds. Important mechanical and morphological properties were calculated for each specimen. The mechanical properties were consistent with those previously reported in the l...
This Chapter provides clinical, physical and mechanical details of a set of ten real world accidental falls which resulted in non-fatal head impact injury in the form of various traumatic brain lesions. These are described in depth and as... more
This Chapter provides clinical, physical and mechanical details of a set of ten real world accidental falls which resulted in non-fatal head impact injury in the form of various traumatic brain lesions. These are described in depth and as such constitute a database of documented head injury cases that may be of use to the wider research community. Accompanying time profiles of linear and angular velocities, which were predicted using multibody dynamics modeling simulations, are freely available to those researchers who would wish to use this set of data upon direct request to the authors. Correspondence/Reprint request: Prof. Michael D. Gilchrist, School of Electrical, Electronic & Mechanical Engineering, University College Dublin, Belfield, Dublin 4, Ireland. E-mail: michael.gilchrist@ucd.ie Gilchrist & Doorly 2
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Abstract Compared to adults, it has been documented that children are at elevated risk for concussion, repeated concussions, and experience longer recovery times. What is unknown, is whether the developing brain may be injured at... more
Abstract Compared to adults, it has been documented that children are at elevated risk for concussion, repeated concussions, and experience longer recovery times. What is unknown, is whether the developing brain may be injured at differing strain levels. This study examined peak and cumulative brain strain from 20 cases of concussion in both young children and adults using physical reconstructions and finite element modelling of the brain response to impacts. The child group showed lower impact kinematics as well as strain metrics. Results suggest children may suffer concussive injuries with lower brain strains compared to adults.
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Accidental falls occur to people of all ages, with some resulting in concussive injury. At present, it is unknown whether children and adolescents are at a comparable risk of sustaining a concussion compared to adults. This study... more
Accidental falls occur to people of all ages, with some resulting in concussive injury. At present, it is unknown whether children and adolescents are at a comparable risk of sustaining a concussion compared to adults. This study reconstructed the impact kinematics of concussive falls for children, adolescents, and adults and simulated the associated brain tissue deformations. Patients included in this study were diagnosed with a concussion as defined by the Zurich Consensus guidelines. Eleven child, 10 adolescent, and 11 adult falls were simulated using MADYMO, with three ellipsoid pedestrian models sized to each age group. Laboratory impact reconstruction were conducted using Hybrid III head forms, with finite element model simulations of the brain tissue response using recorded impact kinematics from the reconstructions. The results of the child group showed lower responses than the adolescent group for impact variables of impact velocity, peak linear acceleration, and peak rotat...
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Abstract This study examined the effects and interaction of four primary impact parameters (impact velocity, angle of impact relative to the ground, ground compliance and helmet impact location) on head kinematics and brain tissue... more
Abstract This study examined the effects and interaction of four primary impact parameters (impact velocity, angle of impact relative to the ground, ground compliance and helmet impact location) on head kinematics and brain tissue response for falls that are most commonly associated with equestrian sports. A helmeted headform was subject to parametric tests using a rail guided launcher at three impact velocities (6, 9 and 12 m/s), four angles of incidence (15°, 30°, 45° and 60°), three ground compliance levels (High, Medium and Low) and three helmet locations (front, front-boss and rear-boss). Head kinematics were obtained from the headform and a finite element model was used to estimate brain tissue response. Velocity and angle had the largest effects on the risk of concussion, as measured by head kinematics and brain tissue response, while compliance and location were less influential. Interactions such as angle and compliance were found to greatly influence the risk of concussion. These findings suggest that an increased ground compliance can decrease linear acceleration and Head Injury Criterion (HIC) but not necessarily decrease rotational kinematics and brain tissue response. Consequently, the use of technological designs to attenuate rotational acceleration and decouple the helmet from that of the head may provide better safety than simply the addition of extra protective layers to the ground or a helmet liners.
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OBJECTIVES Equestrian helmets are designed to pass certification standards based on linear drop tests onto rigid steel surfaces. However, concussions in equestrian sports occur most commonly when a rider is thrown off a horse and... more
OBJECTIVES Equestrian helmets are designed to pass certification standards based on linear drop tests onto rigid steel surfaces. However, concussions in equestrian sports occur most commonly when a rider is thrown off a horse and obliquely impacts a compliant surface such as turf or sand. This paper seeks to elucidate the mechanics of such impacts and thereby propose corresponding thresholds for the occurrence of concussion that can improve equestrian helmet standards and designs. DESIGN The present study examined the biomechanics of real-world equestrian accidents and developed thresholds for the occurrence of concussive injury. METHODS Twenty-five concussive and 25 non-concussive falls in equestrian sports were reconstructed using a combination of video analysis, computational and physical reconstruction methods. These represented male and female accidents from horse racing and the cross-country phase of eventing. RESULTS The resulting thresholds for concussion [59g, 2700rad/s2, 28rad/s, 0.24 (MPS), 6.6kPa and 0.27 (CSMD10) for 50% risk] were consistent with those reported in the literature and represent a unique combination of head kinematic thresholds compared to other sports. Current equestrian helmet standards commonly use a threshold of 250g and a linear drop to a steel anvil resulting in less than 15ms impacts. This investigation found that concussive equestrian accidents occurred from oblique impacts to turf or sand with lower magnitude and longer duration impacts (<130g and >20ms). This suggests that current equestrian helmet standards may not adequately represent real-world concussive impact conditions and, consequently, there is an urgent need to assess the protective capacity of equestrian helmets under real-world conditions.
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Fluid percussion injury (FPI) is a widely used experimental model for studying traumatic brain injury (TBI). However, little is known about how the brain mechanically responds to fluid impacts and how the mechanical pressures/strains of... more
Fluid percussion injury (FPI) is a widely used experimental model for studying traumatic brain injury (TBI). However, little is known about how the brain mechanically responds to fluid impacts and how the mechanical pressures/strains of the brain correlate to subsequent brain damage for rodents during FPI. Hence, we developed a numerical approach to simulate FPI experiments on rats and characterize rat brain pressure/strain responses at a high resolution. A previous rat brain model was improved with a new hexahedral elements-based skull model and a new cerebrospinal fluid (CSF) layer. We validated the numerical model against experimentally measured pressures from FPI. Our results indicated that brain tissues under FPI experienced high pressures, which were slightly lower (10-20%) than input saline pressure. Interestingly, FPI was a mixed focus- and diffuse-type injury model with highest strains (12%) being concentrated in the ipsilateral cortex under the fluid-impact site and diffuse strains (5-10%) being spread to the entire brain, which was different from controlled cortical impact in which high strains decreased gradually away from the impact site.
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Abstract Sporting helmets with linear attenuating strategies are proficient at reducing the risk of traumatic brain injury. However, the continued high incidence of concussion in American football, has led researchers to investigate novel... more
Abstract Sporting helmets with linear attenuating strategies are proficient at reducing the risk of traumatic brain injury. However, the continued high incidence of concussion in American football, has led researchers to investigate novel helmet liner strategies. These strategies typically supplement existing technologies by adding or integrating head-helmet decoupling mechanisms. Decoupling strategies aim to redirect or redistribute impact force around the head, reducing impact energy transferred to the brain. This results in decreased brain tissue strain, which is beneficial in injury risk reduction due to the link between tissue strain and concussive injury. The purpose of this study was to mathematically demonstrate the effect of ten cases, representing theoretical redirection and redistribution helmet liner strategies, on brain tissue strain resulting from impacts to the head. The kinematic response data from twenty head impacts collected in the laboratory was mathematically modified to represent the altered response of the ten different cases and used as input parameters to determine the effect on maximum principal strain (MPS) values, calculated using finite element modeling. The results showed that a reduced dominant coordinate component (contributes the greatest to resultant) of rotational acceleration decreased maximum principal strain in American football helmets. The study theoretically demonstrates that liner strategies, if applied correctly, can influence brain motion, reduce brain tissue strain, and could decrease injury risk in an American football helmet.
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ABSTRACT Current equestrian standards employ a drop test to a rigid steel anvil. However, falls in equestrian sports often result in impacts with soft ground. The purpose of this study was to compare head kinematics and brain tissue... more
ABSTRACT Current equestrian standards employ a drop test to a rigid steel anvil. However, falls in equestrian sports often result in impacts with soft ground. The purpose of this study was to compare head kinematics and brain tissue response associated with surfaces impacted during equestrian accidents and corresponding helmet certification tests. A helmeted Hybrid III headform was dropped freely onto three different anvils (steel, turf and sand) at three impact locations. Peak linear acceleration, rotational acceleration and impact duration of the headform were measured. Resulting accelerations served as input into a three-dimensional finite element head model, which calculated Maximum principal strain (MPS) and von Mises stress (VMS) in the cerebrum. The results indicated that impacts to a steel anvil produced peak head kinematics and brain tissue responses that were two to three times greater than impacts against both turf and sand. Steel impacts were less than half the duration of turf and sand impacts. The observed response magnitudes obtained in this study suggest that equestrian helmet design should be improved, not only for impacts to rigid surfaces but also to compliant surfaces as response magnitudes for impacts to soft surfaces were still within the reported range for concussion in the literature.
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This article studied the demolding of an array of injection molded micro-structures based on a design of experiments (DOE) method. The demolding force (Fd) to eject an array of 4 × 5 micro-ridges from the cavity of a mold was calculated... more
This article studied the demolding of an array of injection molded micro-structures based on a design of experiments (DOE) method. The demolding force (Fd) to eject an array of 4 × 5 micro-ridges from the cavity of a mold was calculated indirectly. It was found that mold temperature had a significant effect on the demolding force: the demolding force decreased as mold temperature increased and as the part substrate thickness also increased. The demolding force is a combination of the adhesion force and friction force that exist between a molded feature and the microcavities of a mold. When the processing parameters were optimized to minimize the demolding force during the ejection process, it was found that the adhesion force had a bigger influence than the friction force. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers
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Abstract Two different polymer resins were used to create three different octet-truss lattice structures of different densities. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic... more
Abstract Two different polymer resins were used to create three different octet-truss lattice structures of different densities. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic compressive loading. The structures were printed using stereolithography (SLA) additive manufacturing. The basic building octet unit has a fixed strut length of L = 10 mm, with the designed strut radius varying from R = 0.7 mm to 1.3 mm to provide structures of different densities. It has been found that the mechanical behaviour of the printed octet structures depends on both the relative density and the intrinsic material properties. Higher density structures show larger effective yield and compressive strengths, while the basic printing material fundamentally determines its macroscopic properties: one material provides a brittle mechanical response under compression while the other provides a tough response. The former lattice structures behaved in a brittle manner at all relative densities, fracturing at small strains. For the latter resin lattice structures, on the other hand, under quasi-static compression, the stress-strain curves changed from a slightly stress oscillating mode at low relative density (i.e. ρ ¯ = 0.13) to a stable stress plateau mode at high relative density (i.e. ρ ¯ = 0.41). The Specific Energy Absorption (SEA) of both lattice structures had a monotonically increasing relationship with relative density, the SEA of the brittle resin specimen is higher than that of the tough resin specimen, while the tough resin specimen exhibits its excellent energy absorption under a wide displacement range. For the dynamic compressive tests, the tougher resin structures displayed strain-rate effects, while the more brittle ones did not. The numerically predicted response of both lattice structures agreed closely with the experimental results.
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Concussions are among the most common injuries sustained by goaltenders. Concussive injuries are characterized by impairment to neurological function which can affect many different brain regions. Understanding how different impact... more
Concussions are among the most common injuries sustained by goaltenders. Concussive injuries are characterized by impairment to neurological function which can affect many different brain regions. Understanding how different impact loading conditions (event type and impact site) affect the brain tissue response may help identify what kind of impacts create a high risk of injury to specific brain regions. The purpose of this study was to examine the influence of different impact conditions on the distribution of brain strain for ice hockey goaltender impacts. An instrumented headform was fitted with an ice hockey goaltender mask and impacted under a protocol which was developed using video analysis of real world ice hockey goaltender concussions for three different impact events (collision, puck, and fall). The resulting kinematic response served as input into the University College Dublin Brain Trauma Model, which calculated maximum principal strain in the cerebrum. Strain subsets w...
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Concussions are among the most common injuries sustained by ice hockey goaltenders and can result from collisions, falls and puck impacts. However, ice hockey goaltender helmet certification standards solely involve drop tests to a rigid... more
Concussions are among the most common injuries sustained by ice hockey goaltenders and can result from collisions, falls and puck impacts. However, ice hockey goaltender helmet certification standards solely involve drop tests to a rigid surface. This study examined how the design characteristics of different ice hockey goaltender helmets affect head kinematics and brain strain for the three most common impact events associated with concussion for goaltenders. A NOCSAE headform was impacted under conditions representing falls, puck impacts and shoulder collisions while wearing three different types of ice hockey goaltender helmet models. Resulting linear and rotational acceleration as well as maximum principal strain were measured for each impact condition. The results indicate that a thick liner and stiff shell material are desirable design characteristics for falls and puck impacts to reduce head kinematic and brain tissue responses. However for collisions, the shoulder being more...
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In ice hockey, concussions can occur as a result of many different types of impact events, however hockey helmets are certified using a single injury scenario, involving drop tests to a rigid surface. The purpose of this study is to... more
In ice hockey, concussions can occur as a result of many different types of impact events, however hockey helmets are certified using a single injury scenario, involving drop tests to a rigid surface. The purpose of this study is to measure the protective capacity of ice hockey helmets for different impact events in ice hockey. A helmeted and unhelmeted Hybrid III headform were impacted simulating falls, elbow, shoulder and puck impacts in ice hockey. Linear and rotational acceleration and maximum principal strain (MPS) were measured. A comparison of helmeted and unhelmeted impacts found significant differences existed in most conditions (p < 0.05), however some shoulder and puck impacts showed no significant difference (p > 0.05). Impacts to the ice hockey helmet tested resulted in acceleration levels below reported ranges of concussion and TBI for falls up to 5 m/s, elbow collisions, and low velocity puck impacts but not for shoulder collisions or high velocity puck impacts ...
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Vacuum venting is a method proposed to improve feature replication in microparts that are fabricated using micro-injection molding (MIM). A qualitative and quantitative study has been carried out to investigate the effect of vacuum... more
Vacuum venting is a method proposed to improve feature replication in microparts that are fabricated using micro-injection molding (MIM). A qualitative and quantitative study has been carried out to investigate the effect of vacuum venting on the nano/microfeature replication in MIM. Anodized aluminum oxide (AAO) containing nanofeatures and a bulk metallic glass (BMG) tool mold containing microfeatures were used as mold inserts. The effect of vacuum pressure at constant vacuum time, and of vacuum time at constant vacuum pressure on the replication of these features is investigated. It is found that vacuum venting qualitatively enhances the nanoscale feature definition as well as increases the area of feature replication. In the quantitative study, higher aspect ratio (AR) features can be replicated more effectively using vacuum venting. Increasing both vacuum pressure and vacuum time are found to improve the depth of replication, with the vacuum pressure having more influence. Featu...
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different... more
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71-4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in v...
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Keywords: biological soft tissue; characterization; constitutive model; experiments; strain rate dependence
During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains... more
During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue in shear at these strains and strain rates is thus of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. However, very few studies in the literature provide this information. In this research, an experimental setup was developed to perform simple shear tests on porcine brain tissue at strain rates ≤120/s. The maximum measured shear stress at strain rates of 30, 60, 90 and 120/s was 1.15±0.25 kPa, 1.34±0.19 kPa, 2.19±0.225 kPa and 2.52±0.27 kPa, (mean±SD), respectively at the maximum amount of shear, K=1. Good agreement of experimental, theoretical (Ogden and Mooney–Rivlin models) and numerical shear stresses was achieved (p=0.7866–0.9935). Specimen thickness effects (2.0–10.0 mm thick specimens) were also analyzed numerically and we found that there is no significant difference (p=0.9954) in the shear stress magnitudes, indicating a homogeneous deformation of the specimens during simple shear tests. Stress relaxation tests in simple shear were also conducted at different strain magnitudes (10–60% strain) with the average rise time of 14 ms. This allowed us to estimate elastic and viscoelastic parameters (initial shear modulus, μ=4942.0 Pa, and Prony parameters: g1=0.520, g2=0.3057, τ1=0.0264 s, and τ2=0.011 s) that can be used in FE software to analyze the non-linear viscoelastic behavior of brain tissue. This study provides new insight into the behavior in finite shear of brain tissue under dynamic impact conditions, which will assist in developing effective brain injury criteria and adopting efficient countermeasures against traumatic brain injury.
Keywords
Diffuse axonal injury (DAI); Ogden; Mooney–Rivlin; Traumatic brain injury (TBI); Homogeneous; Viscoelastic; Relaxation
Keywords
Diffuse axonal injury (DAI); Ogden; Mooney–Rivlin; Traumatic brain injury (TBI); Homogeneous; Viscoelastic; Relaxation