46 results found
Du Y, Tavana S, Rahman T, et al., 2021, Sensitivity of intervertebral disc finite element models to internal geometric and non-geometric parameters, Frontiers in Bioengineering and Biotechnology, Vol: 9, ISSN: 2296-4185
Finite element models are useful for investigating internal intervertebral disc (IVD) behaviours without using disruptive experimental techniques. Simplified geometries are commonly used to reduce computational time or because internal geometries cannot be acquired from CT scans. This study aimed to 1) investigate the effect of altered geometries both at endplates and the nucleus-anulus boundary on model response, and 2) to investigate model sensitivity to material and geometric inputs, and different modelling approaches (graduated or consistent fibre bundle angles and glued or cohesive interlamellar contact). Six models were developed from 9.4T MRIs of bovine IVDs. Models had two variations of endplate geometry (a simple curved profile from the centre of the disc to the periphery, and precise geometry segmented from MRIs), and three variations of NP-AF boundary (linear, curved, and segmented). Models were subjected to axial compressive loading (to 0.86mm at a strain rate of 0.1/sec) and the effect on stiffness and strain distributions, and the sensitivity to modelling approaches was investigated. The model with the most complex geometry (segmented endplates, curved NP-AF boundary) was 3.1 times stiffer than the model with the simplest geometry (curved endplates, linear NP-AF boundary). Peak strains were close to the endplates at locations of high curvature in the segmented endplate models which were not captured in the curved endplate models. Differences were also seen in sensitivity to material properties, graduated fibre angles, cohesive rather than glued interlamellar contact, and NP:AF ratios. These results show that FE modellers must take care to ensure geometries are realistic so that load is distributed and passes through IVDs accurately.
Sanz-Pena I, Arachchi S, Halwala-Vithanage D, et al., 2021, Characterising the mould rectification process for designing scoliosis braces: towards automated digital design of 3D-printed braces, Applied Sciences, Vol: 11, Pages: 1-13, ISSN: 2076-3417
The plaster-casting method to create a scoliosis brace consists of mould generation and rectification to obtain the desired orthosis geometry. Alternative methods entail the use of 3D scanning and CAD/CAM. However, both manual and digital design entirely rely on the orthotist expertise. Characterisation of the rectification process is needed to ensure that digital designs are as efficient as plaster-cast designs. Three-dimensional scans of five patients, pre-, and post-rectification plaster moulds were obtained using a Structure Mark II scanner. Anatomical landmark positions, transverse section centroids, and 3D surface deviation analyses were performed to characterise the rectification process. The rectification process was characterised using two parameters. First, trends in the external contours of the rectified moulds were found, resulting in lateral tilt angles of 81 ± 3.8° and 83.3 ± 2.6° on the convex and concave side, respectively. Second, a rectification ratio at the iliac crest (0.23 ± 0.04 and 0.11 ± 0.02 on the convex and concave side, respectively) was devised, based on the pelvis width to estimate the volume to be removed. This study demonstrates that steps of the manual rectification process can be characterised. Results from this study can be fed into software to perform automatic digital rectification.
Draper D, Newell N, Masouros S, et al., 2021, Multiscale Validation of Multiple Human Body Model Functional Spinal Units, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 143, ISSN: 0148-0731
Tavana S, Masouros S, Baxan N, et al., 2021, The Effect of Degeneration on Internal Strains and the Mechanism of Failure in Human Intervertebral Discs Analyzed Using Digital Volume Correlation (DVC) and Ultra-High Field MRI, Frontiers in Bioengineering and Biotechnology, Vol: 8, ISSN: 2296-4185
The intervertebral disc (IVD) plays a main role in absorbing and transmitting loads within the spinal column. Degeneration alters the structural integrity of the IVDs and causes pain, especially in the lumbar region. The objective of this study was to investigate non-invasively the effect of degeneration on human 3D lumbar IVD strains (n = 8) and the mechanism of spinal failure (n = 10) under pure axial compression using digital volume correlation (DVC) and 9.4 Tesla magnetic resonance imaging (MRI). Degenerate IVDs had higher (p < 0.05) axial strains (58% higher), maximum 3D compressive strains (43% higher), and maximum 3D shear strains (41% higher), in comparison to the non-degenerate IVDs, particularly in the lateral and posterior annulus. In both degenerate and non-degenerate IVDs, peak tensile and shear strains were observed close to the endplates. Inward bulging of the inner annulus was observed in all degenerate IVDs causing an increase in the AF compressive, tensile, and shear strains at the site of inward bulge, which may predispose it to circumferential tears (delamination). The endplate is the spine's “weak link” in pure axial compression, and the mechanism of human vertebral fracture is associated with disc degeneration. In non-degenerate IVDs the locations of failure were close to the endplate centroid, whereas in degenerate IVDs they were in peripheral regions. These findings advance the state of knowledge on mechanical changes during degeneration of the IVD, which help reduce the risk of injury, optimize treatments, and improve spinal implant designs. Additionally, these new data can be used to validate computational models.
Tavana S, Clark J, Newell N, et al., 2020, In vivo deformation and strain measurements in human bone using digital volume correlation (DVC) and 3T clinical MRI, Materials, Vol: 13, ISSN: 1996-1944
Strains within bone play an important role in the remodelling process and the mechanisms of fracture. The ability to assess these strains in vivo can provide clinically relevant information regarding bone health, injury risk, and can also be used to optimise treatments. In vivo bone strains have been investigated using multiple experimental techniques, but none have quantified 3D strains using non-invasive techniques. Digital volume correlation based on clinical MRI (DVC-MRI) is a non-invasive technique that has the potential to achieve this. However, before it can be implemented, uncertainties associated with the measurements must be quantified. Here, DVC-MRI was evaluated to assess its potential to measure in vivo strains in the talus. A zero-strain test (two repeated unloaded scans) was conducted using three MRI sequences, and three DVC approaches to quantify errors and to establish optimal settings. With optimal settings, strains could be measured with a precision of 200 με and accuracy of 480 με for a spatial resolution of 7.5 mm, and a precision of 133 με and accuracy of 251 με for a spatial resolution of 10 mm. These results demonstrate that this technique has the potential to measure relevant levels of in vivo bone strain and to be used for a range of clinical applications.
Newell N, Rivera Tapia D, Rahman T, et al., 2020, Influence of testing environment and loading rate on intervertebral disc compressive mechanics: An assessment of repeatability at three different laboratories, JOR SPINE, Vol: 3, ISSN: 2572-1143
Tavana S, Clark JN, Prior J, et al., 2020, Quantifying deformations and strains in human intervertebral discs using Digital Volume Correlation combined with MRI (DVC-MRI), Journal of Biomechanics, Vol: 102, Pages: 1-7, ISSN: 0021-9290
Physical disruptions to intervertebral discs (IVDs) can cause mechanical changes that lead to degeneration and to low back pain which affects 75% of us in our lifetimes. Quantifying the effects of these changes on internal IVD strains may lead to better preventative strategies and treatments. Digital Volume Correlation (DVC) is a non-invasive technique that divides volumetric images into subsets, and measures strains by tracking the internal patterns within them under load. Applying DVC to MRIs may allow non-invasive strain measurements. However, DVC-MRI for strain measurements in IVDs has not been used previously. The purpose of this study was to quantify the strain and deformation errors associated with DVC-MRI for measurements in human IVDs.Eight human lumbar IVDs were MRI scanned (9.4T) for a ‘zero-strain study’ (multiple unloaded scans to quantify noise within the system), and a loaded study (2mm axial compression). Three DVC methodologies: Fast-Fourier transform (FFT), direct correlation (DC), and a combination of both FFT and DC approaches were compared with subset sizes ranging from 8 to 88 voxels to establish the optimal DVC methodology and settings which were then used in the loaded study.FFT+DC was the optimal method and a subset size of 56 voxels (2520 micrometers) was found to be a good compromise between errors and spatial resolution. Displacement and strain errors did not exceed 28 µm and 3000 microstrain, respectively.These findings demonstrate that DVC-MRI can quantify internal strains within IVDs non-invasively and accurately. The method has unique potential for assessing IVD strains within patients.
Pearce AP, Marsden M, Newell N, et al., 2020, Trends in admission timing and mechanism of injury can be used to improve general surgical trauma training, Annals of the Royal College of Surgeons of England, Vol: 102, Pages: 36-42, ISSN: 0035-8843
INTRODUCTION: The temporal patterns and unit-based distributions of trauma patients requiring surgical intervention are poorly described in the UK. We describe the distribution of trauma patients in the UK and assess whether changes in working patterns could provide greater exposure for operative trauma training. METHODS: We searched the Trauma Audit and Research Network database to identify all patients between 1 January 2014 to 31 December 2016. Operative cases were defined as all patients who underwent laparotomy, thoracotomy or open vascular intervention. We assessed time of arrival, correlations between mechanism of injury and surgery, and the effect of changing shift patterns on exposure to trauma patients by reference to a standard 10-hour shift assuming a dedicated trauma rotation or fellowship. RESULTS: There were 159,719 patients from 194 hospitals submitted to the Network between 2014 and 2016. The busiest 20 centres accounted for 57,568 (36.0%) of cases in total. Of these 2147/57,568 patients (3.7%) required a general surgical operation; 43% of penetrating admissions (925 cases) and 2.2% of blunt admissions (1222 cases). The number of operations correlated more closely with the number of penetrating rather than blunt admissions (r = 0.89 vs r = 0.51). A diurnal pattern in trauma admissions enabled significant increases in trauma exposure with later start times. CONCLUSIONS: Centres with high volume and high penetrating rates are likely to require more general surgical input and should be identified as locations for operative trauma training. It is possible to improve the number of trauma patients seen in a shift by optimising shift start time.
Newell N, Carpanen D, Grigoriadis G, et al., 2019, Material properties of human lumbar intervertebral discs across strain rates, Spine Journal, Vol: 19, Pages: 2013-2024, ISSN: 1529-9430
Background context:The use of finite-element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. Purpose:The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates.Study Design:A human cadaveric experimental study coupled with an inverse finite element study.Methods:To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39 ± 19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate.Results:Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the anulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young’s Modulus of AF fibers (YMAF - MPa) to strain rate (ε ̇ - /s) relationship of YMAF=31.5ln(ε ̇ )+435.5, and the C10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa.Conclusions:These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications.Clinical SignificanceFinite element models can be used for many applications including investigating low-back p
Soltani S, Nogaro MC, Rougelot C, et al., 2019, Spontaneous spinal epidural haematomas in children, EUROPEAN SPINE JOURNAL, Vol: 28, Pages: 2229-2236, ISSN: 0940-6719
Newell N, Carpanen D, Evans JH, et al., 2019, Mechanical function of the nucleus pulposus of the intervertebral disc under high rates of loading, Spine, Vol: 44, Pages: 1035-1041, ISSN: 0362-2436
Study Design. Bovine motion segments were used to investigate the high-rate compression response of intervertebral discs (IVD) before and after depressurising the nucleus pulposus (NP) by drilling a hole through the cranial endplate into it.Objective. To investigate the effect of depressurising the NP on the force-displacement response, and the energy absorption in IVDs when compressed at high strain rates.Summary of Background Data. The mechanical function of the gelatinous NP located in the centre of the IVDs of the spine is unclear. Removal of the NP has been shown to affect the direction of bulge of the inner anulus fibrosus (AF), but at low loading rates removal of the NP pressure does not affect the IVD's stiffness. During sports or injurious events, IVDs are commonly exposed to high loading rates, however, no studies have investigated the mechanical function of the NP at these rates.Methods. Eight bovine motion segments were used to quantify the change in pressure caused by a hole drilled through the cranial endplate into the NP, and eight segments were used to investigate the high-rate response before and after a hole was drilled into the NP.Results. The hole caused a 28.5% drop in the NP pressure. No statistically significant difference was seen in peak force, peak displacement, or energy-absorption of the intact and depressurised NP groups under impact loading. The IVDs absorbed 72% of the input energy, and there was no rate dependency in the percentage energy absorbed.Conclusions. These results demonstrate that the NP pressure does not affect the transfer of load through, or energy absorbed by, the IVD at high loading rates and the AF, rather than the NP, may play the most important role in transferring load, and absorbing energy at these rates. This should be considered when attempting surgically to restore IVD function.Level of Evidence: N/A
Injuries sustained due to attacks from explosive weapons are multiple in number, complex in nature, and not well characterised. Blast may cause damage to the human body by the direct effect of overpressure, penetration by highly energised fragments, and blunt trauma by violent displacements of the body. The ability to reproduce the injuries of such insults in a well-controlled fashion is essential in order to understand fully the unique mechanism by which they occur, and design better treatment and protection strategies to alleviate the resulting poor long-term outcomes. This paper reports a range of experimental platforms that have been developed for different blast injury models, their working mechanism, and main applications. These platforms include the shock tube, split-Hopkinson bars, the gas gun, drop towers and bespoke underbody blast simulators.
Grigoriadis G, Carpanen D, Webster CE, et al., 2019, Lower limb posture affects the mechanism of injury in under-body blast, Annals of Biomedical Engineering, Vol: 47, Pages: 306-316, ISSN: 0090-6964
Over 80% of wounded Service Members sustain at least one extremity injury. The 'deck-slap' foot, a product of the vehicle's floor rising rapidly when attacked by a mine to injure the limb, has been a signature injury in recent conflicts. Given the frequency and severity of these combat-related extremity injuries, they require the greatest utilisation of resources for treatment, and have caused the greatest number of disabled soldiers during recent conflicts. Most research efforts focus on occupants seated with both tibia-to-femur and tibia-to-foot angles set at 90°; it is unknown whether results obtained from these tests are applicable when alternative seated postures are adopted. To investigate this, lower limbs from anthropometric testing devices (ATDs) and post mortem human subjects (PMHSs) were loaded in three different seated postures using an under-body blast injury simulator. Using metrics that are commonly used for assessing injury, such as the axial force and the revised tibia index, the lower limb of ATDs were found to be insensitive to posture variations while the injuries sustained by the PMHS lower limbs differed in type and severity between postures. This suggests that the mechanism of injury depends on the posture and that this cannot be captured by the current injury criteria. Therefore, great care should be taken when interpreting and extrapolating results, especially in vehicle qualification tests, when postures other than the 90°-90° are of interest.
Grigoriadis G, Carpanen D, Webster C, et al., 2018, The posture of the lower limb alters the mechanism of injury in under-body blast, International Research Council on the Biomechanics of Injury, IRCOBI, Pages: 758-759, ISSN: 2235-3151
Draper D, Newell N, Wernicke P, et al., 2018, A comparison of the compressive behaviour of lumbar intervertebral discs in five human body finite element models, International Research Council on the Biomechanics of Injury, IRCOBI, Pages: 242-244, ISSN: 2235-3151
Newell N, Pearce AP, Spurrier E, et al., 2018, Analysis of isolated transverse process fractures sustained during blast related events, Journal of Trauma and Acute Care Surgery, Vol: 85, Pages: S129-S133, ISSN: 2163-0763
BACKGROUND: A range of devastating blast injuries have been sustained by personnel during recent conflicts. Previous studies have focused on severe injuries, including to the spine, however, no study has specifically focused on the most common spinal injury; transverse process (TP) fractures. Although their treatment usually requires limited intervention, analysis of TP fractures may help determine injury mechanisms. METHODS: Data was collected from victims with spinal fractures injured in Improvised Explosive Device (IED) attacks, from the UK's Joint Theatre Trauma Registry. The level and side of each TP fracture was recorded, as well as associated injuries, whether they were mounted or dismounted, and outcome (survivor or fatality). RESULTS: The majority of TP fractures were lumbar (80%). More bilateral (both left and right fractures at the same level), and L5 TP fractures, were seen in fatalities than survivors. In the mounted group, lumbar TP fractures were statistically significantly associated with fatality, head injury, non-compressible torso haemorrhage, pelvic injury, and other spinal injuries. In the dismounted group, thoracic TP fractures were associated with head, chest wall, and other spinal injuries, and lumbar TP fractures were associated with pelvic, and other spinal injuries. CONCLUSIONS: Different injury mechanisms of the TP in the mounted and dismounted groups are likely. Inertial forces acting within the torso due to rapid loading being transferred through the seat, or high intra-abdominal pressures causing the tensile forces acting through the lumbar fascia to avulse the TPs are likely mechanisms in the mounted group. Blunt trauma, violent lateral flexion-extension forces, or rapid flail of the lower extremities causing tension of the psoas muscle, avulsing the TP are likely causes in the dismounted group. Isolated lumbar TP fractures can be used as markers for more severe injuries, and fatality, in mounted blast casualties. LEVEL OF EVIDENCE: P
Grigoriadis G, Carpanen D, Webster C, et al., 2017, The effect of the posture of the lower limb in anti-vehicular explosions, 2017 IRCOBI Conference, Pages: 709-710, ISSN: 2235-3151
Christou A, Grigoriadis G, Carpanen D, et al., 2017, Biomechanics of a lumbar functional unit using the finite element method, 2017 IRCOBI Conference, Pages: 668-669, ISSN: 2235-3151
Newell N, Carpanen D, Christou A, et al., 2017, Strain rate dependence of internal pressure and external bulge in human intervertebral discs during axial compression, 2017 IRCOBI Conference, Pages: 670-671, ISSN: 2235-3151
Newell N, Grant CA, Keenan BE, et al., 2017, A comparison of four techniques to measure anterior and posterior vertebral body heights and sagittal plane wedge angles in adolescent idiopathic scoliosis., Med Biol Eng Comput, Vol: 55, Pages: 561-572
Adolescent idiopathic scoliosis (AIS) is a three-dimensional (3D) spinal deformity of unknown aetiology. Increased growth of the anterior part of the vertebrae known as anterior overgrowth has been proposed as a potential driver for AIS initiation and progression. To date, there has been no objective evaluation of the 3D measurement techniques used to identify this phenomenon and the majority of previous studies use 2D planar assessments which contain inherent projection errors due to the vertebral rotation which is part of the AIS deformity. In this study, vertebral body (VB) heights and wedge angles were measured in a test group of AIS patients and healthy controls using four different image analysis and measurement techniques. Significant differences were seen between the techniques in terms of VB heights and VB wedge angles. The low variability, and the fact that the rotation and tilt of the deformed VBs are taken into account, suggests that the proposed technique using the full 3D orientation of the vertebrae is the most reliable method to measure anterior and posterior VB heights and sagittal plane wedge angles in 3D image data sets. These results have relevance for future investigations that aim to quantify anterior overgrowth in AIS patients for comparison with healthy controls.
Newell N, Little JP, Chirstou A, et al., 2017, Biomechanics of the human intervertebral disc: a review of testing techniques and results, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 69, Pages: 420-434, ISSN: 1751-6161
Many experimental testing techniques have been adopted in order to provide an understanding of the biomechanics of the human intervertebral disc (IVD). The aim of this review article is to amalgamate results from these studies to provide readers with an overview of the studies conducted and their contribution to our current understanding of the biomechanics and function of the IVD. The overview is presented in a way that should prove useful to experimentalists and computational modellers. Mechanical properties of whole IVDs can be assessed conveniently by testing ‘motion segments’ comprising two vertebrae and the intervening IVD and ligaments. Neural arches should be removed if load-sharing between them and the disc is of no interest, and specimens containing more than two vertebrae are required to study ‘adjacent level’ effects. Mechanisms of injury (including endplate fracture and disc herniation) have been studied by applying complex loading at physiologically-relevant loading rates, whereas mechanical evaluations of surgical prostheses require slower application of standardised loading protocols. Results can be strongly influenced by the testing environment, preconditioning, loading rate, specimen age and degeneration, and spinal level. Component tissues of the disc (anulus fibrosus, nucleus pulposus, and cartilage endplates) have been studied to determine their material properties, but only the anulus has been thoroughly evaluated. Animal discs can be used as a model of human discs where uniform non-degenerate specimens are required, although differences in scale, age, and anatomy can lead to problems in interpretation.
Newell N, Grigoriadis G, Christou A, et al., 2017, Material properties of bovine intervertebral discs across strain rates, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 65, Pages: 824-830, ISSN: 1751-6161
The intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (View the MathML source), the following relationship was derived:View the MathML source. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates.
Grigoriadis G, Newell N, Carpanen D, et al., 2016, Material properties of the heel fat pad across strain rates, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 65, Pages: 398-407, ISSN: 1751-6161
The complex structural and material behaviour of the human heel fat pad determines the transmission of plantar loading to the lower limb across a wide range of loading scenarios; from locomotion to injurious incidents. The aim of this study was to quantify the hyper-viscoelastic material properties of the human heel fat pad across strains and strain rates. An inverse finite element (FE) optimisation algorithm was developed and used, in conjunction with quasi-static and dynamic tests performed to five cadaveric heel specimens, to derive specimen-specific and mean hyper-viscoelastic material models able to predict accurately the response of the tissue at compressive loading of strain rates up to 150 s−1. The mean behaviour was expressed by the quasi-linear viscoelastic (QLV) material formulation, combining the Yeoh material model (C10=0.1MPa, C30=7MPa, K=2GPa) and Prony׳s terms (A1=0.06, A2=0.77, A3=0.02 for τ1=1ms, τ2=10ms, τ3=10s). These new data help to understand better the functional anatomy and pathophysiology of the foot and ankle, develop biomimetic materials for tissue reconstruction, design of shoe, insole, and foot and ankle orthoses, and improve the predictive ability of computational models of the foot and ankle used to simulate daily activities or predict injuries at high rate injurious incidents such as road traffic accidents and underbody blast.
Ranger TA, Newell N, Grant CA, et al., 2016, The role of the middle lumbar fascia on spinal mechanics: A human biomechanical assessment, Spine, ISSN: 1528-1159
Grant CA, Newell N, Izatt MT, et al., 2016, A comparison of vertebral venous networks in adolescent idiopathic scoliosis patients and healthy controls, Surgical and Radiologic Anatomy, Vol: 39, Pages: 281-291, ISSN: 0930-1038
Newell N, Grant CA, Keenan BE, et al., 2016, Quantifying Progressive Anterior Overgrowth in the Thoracic Vertebrae of Adolescent Idiopathic Scoliosis Patients A Sequential Magnetic Resonance Imaging Study, SPINE, Vol: 41, Pages: E382-E387, ISSN: 0362-2436
Newell N, Masouros SD, 2016, Testing and development of mitigation systems for tertiary blast, Blast Injury Science and Engineering A Guide for Clinicians and Researchers, Editors: Bull, Clasper, Mahoney, Publisher: Springer, Pages: 249-255, ISBN: 9783319218670
Biomechanics in blast is a key discipline in blast injury science and engineering that addresses the consequences of high forces, large deformations and extreme failure and thus relates closely to knowledge of materials science (Chap. 3) and ...
Newell N, Salzar R, Bull AMJ, et al., 2016, A validated numerical model of a lower limb surrogate to investigate injuries caused by under-vehicle explosions, Journal of Biomechanics, Vol: 49, Pages: 710-717, ISSN: 0021-9290
Under-vehicle explosions often result in injury of occupants׳ lower extremities. The majority of these injuries are associated with poor outcomes. The protective ability of vehicles against explosions is assessed with Anthropometric Test Devices (ATDs) such as the MIL-Lx, which is designed to behave in a similar way to the human lower extremity when subjected to axial loading. It incorporates tibia load cells, the response of which can provide an indication of the risk of injury to the lower extremity through the use of injury risk curves developed from cadaveric experiments. In this study an axisymmetric finite element model of the MIL-Lx with a combat boot was developed and validated. Model geometry was obtained from measurements taken using digital callipers and rulers from the MIL-Lx, and using CT images for the combat boot. Appropriate experimental methods were used to obtain material properties. These included dynamic, uniaxial compression tests, quasi-static stress-relaxation tests and 3 point bending tests. The model was validated by comparing force-time response measured at the tibia load cells and the amount of compliant element compression obtained experimentally and computationally using two blast-injury experimental rigs. Good correlations between the numerical and experimental results were obtained with both. This model can now be used as a virtual test-bed of mitigation designs and in surrogate device development.
Carpanen D, Masouros SD, Newell N, 2016, Surrogates of human injury, Blast injury science and engineering, Editors: Bull, Clasper, Mahoney, Publisher: Springer, Pages: 189-199
In this chapter we will explore surrogates that are being used to help in our understanding of the pathophysiology of human injury and of predicting injury risk when exposed to a set loading environment. We will mainly focus on anthropomorphic test devices (ATDs), usually known as dummies. Dummies are physical human surrogates that have been designed to evaluate occupant protection in response to collision. Even though ATDs are classified according to size, age, sex and impact direction, injury assessment in automotive and blast applications is mostly conducted using the adult midsize dummy.
Newell N, Neal W, Pandelani T, et al., 2016, The Dynamic Behaviour of the Floor of a Surrogate Vehicle Under Explosive Blast Loading, Journal of Materials Science Research, Vol: 5, Pages: 59-59, ISSN: 1927-0585
<jats:p><p class="1Body">Improvised Explosive Devices have been the signature weapon in the recent conflicts in Iraq and Afghanistan. High-rate axial forces exerted by the vehicle floor to the lower limbs of occupants have been the cause of severe injuries. In order to gain a greater understanding of the mechanisms of these injuries so that countermeasures can be developed, one is required to know how the vehicle floor behaves; therefore, the purpose of this study was to characterise the behaviour of a vehicle floor surrogate to a range of explosive loads. Explosive loads between 1 and 6 kg TNT were detonated beneath a vehicle floor surrogate resulting in peak floor velocities between 5.8 and 80.5 m/s reached in a time between 0.10 and 3.13 ms. The data can now be used to (a) test numerical models of blast and its interaction with structures for validity, and (b) ensure that the velocity profiles replicated in a laboratory environment to understand human tolerance to injury are relevant to the blast process. These will ensure that preventive measures are developed based on realistic physical and numerical models of injury.</p></jats:p>
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