Duane S Cronin

University of Waterloo, Waterloo, Ontario, Canada

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Publications (31)25.34 Total impact

  • Philip A Lockhart, Duane S Cronin
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    ABSTRACT: Head injury resulting from blast loading, including mild traumatic brain injury, has been identified as an important blast-related injury in modern conflict zones. A study was undertaken to investigate potential protective ballistic helmet liner materials to mitigate primary blast injury using a detailed sagittal plane head finite element model, developed and validated against previous studies of head kinematics resulting from blast exposure. Five measures reflecting the potential for brain injury that were investigated included intracranial pressure, brain tissue strain, head acceleration (linear and rotational) and the head injury criterion. In simulations, these measures provided consistent predictions for typical blast loading scenarios. Considering mitigation, various characteristics of foam material response were investigated and a factor analysis was performed which showed that the four most significant were the interaction effects between modulus and hysteretic response, stress-strain response, damping factor and density. Candidate materials were then identified using the predicted optimal material values. Polymeric foam was found to meet the density and modulus requirements; however, for all significant parameters, higher strength foams, such as aluminum foam, were found to provide the highest reduction in the potential for injury when compared against the unprotected head.
    Computer Methods in Biomechanics and Biomedical Engineering 02/2014; · 1.39 Impact Factor
  • Luis F. Trimiño, Duane S. Cronin
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    ABSTRACT: The use of lightweight materials in vehicle structures requires appropriate joining techniques, among them adhesive bonding. Testing full-scale structures such as vehicle crush tubes can be prohibitive in terms of cost and appropriate facilities may not be available, so it is often desirable to test sub-size structures. To address this need, the suitability of scaling to accurately describe the behavior of bonded crush tube structures during axial impact scenarios was investigated. A numerical simulation was validated using literature sources and experimental testing, and then used to investigate scaling. The predictions for structures constructed out of a single material, in terms of stress distributions and deformations were in good agreement between the numerical simulations of the model (experiment modified in size by a scale factor) and the prototype tubes (actual size experiment). When considering bonded structures with the possibility for joint separation, the Non-Direct Similitude technique was applied to scale the structure and the results showed a small departure between the predictions of the model and the prototype. For bonded crush tubes, where the presence of a second material in the form of an adhesive layer was small, the scaling method provides acceptable results. The limitations of the scaling technique were discussed.
    International Journal of Impact Engineering 01/2014; 64:39–52. · 1.68 Impact Factor
  • Dilaver Singh, Duane S Cronin, Tyler N Haladuick
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    ABSTRACT: Mild traumatic brain injury caused by blast exposure from Improvised Explosive Devices has become increasingly prevalent in modern conflicts. To investigate head kinematics and brain tissue response in blast scenarios, two solid hexahedral blast-head models were developed in the sagittal and transverse planes. The models were coupled to an Arbitrary Lagrangian-Eulerian model of the surrounding air to model blast-head interaction, for three blast load cases (5 kg C4 at 3, 3.5 and 4 m). The models were validated using experimental kinematic data, where predicted accelerations were in good agreement with experimental tests, and intracranial pressure traces at four locations in the brain, where the models provided good predictions for frontal, temporal and parietal, but underpredicted pressures at the occipital location. Brain tissue response was investigated for the wide range of constitutive properties available. The models predicted relatively low peak principal brain tissue strains from 0.035 to 0.087; however, strain rates ranged from 225 to 571 s-1. Importantly, these models have allowed us to quantify expected strains and strain rates experienced in brain tissue, which can be used to guide future material characterization. These computationally efficient and predictive models can be used to evaluate protection and mitigation strategies in future analysis. Copyright © 2013 John Wiley & Sons, Ltd.
    International journal for numerical methods in biomedical engineering. 11/2013;
  • Nasim Paryab, Duane S Cronin, Pearl Lee-Sullivan
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    ABSTRACT: Helical polymeric stents have been proposed as a suitable geometry for biodegradable drug-eluting polymer-based stents. However, helical stents often experience nonuniform local expansion (dog boning), which can prohibit full stent expansion using conventional methods. The development of stents and deployment methods is challenging and can be supported by numerical analysis; however, this complex problem is often approached with simplified boundary conditions that may not be appropriate for helical stents. The finite element method (explicit and implicit) was used to investigate three common stent expansion approaches with a focus on helical stent geometry, which differs from traditional wire mesh stent expansion. Although each of the three methods considered provided some insight into the expansion characteristics, common displacement controlled, and uniform expansion methods were not able to demonstrate the characteristic local deformations observed in expansion. A coupled stent-balloon model, although computationally expensive, was able to demonstrate the expected nonuniform deformation. To address nonuniform expansion, a progressive expansion approach has been investigated and verified numerically. This method may also provide a suitable solution for nonuniform expansion in other stent designs by minimizing loading and potential damage to the artery that can occur during stent deployment. Copyright © 2013 John Wiley & Sons, Ltd.
    International journal for numerical methods in biomedical engineering. 10/2013;
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    ABSTRACT: Craniovertebral ligaments were tested to failure under tensile loading. Ligaments tested included: transverse ligament, anterior atlanto occipital membrane, posterior atlanto occipital membrane, capsular ligaments between Skull-C1 and C1-C2, anterior atlantoaxial membrane, posterior atlantoaxial membrane and the tectorial membrane/vertical cruciate/apical/alar ligament complex. The objective of this study was to obtain mechanical properties of craniovertebral ligaments of a younger population, at varying strain rates representative of automotive crash scenarios, and investigate rate and gender effects for use in numerical models of the cervical spine. There have been few studies conducted on the mechanical properties of human craniovertebral ligaments. Only one study has tested all of the ligaments, and previous studies use older age specimens (mean age 67, from most complete study). Further, tests were often not performed at elongation rates representative of car crash scenarios. Previous studies did not perform tests in an environment resembling in vivo conditions, which has been shown to have a significant effect on ligament tensile behaviour. Fifty-four craniovertebral ligaments were isolated from twenty-one spines, and tested to failure in tension under simulated in vivo temperature and hydration levels, at quasi-static (0.5s(-1)) and high strain rates (150s(-1)). Values for failure force, failure elongation, stiffness, and toe region elongation were obtained from force-displacement curves. Values were analyzed for strain rate and gender effects. Increased strain rate produced several significant effects including: higher failure forces for the transverse ligament and capsular ligament (Skull-C1), lower failure elongation for the tectorial membrane complex, higher stiffness for the tectorial membrane complex and capsular ligament (Skull-C1), and lower toe region elongation for capsular ligament (Skull-C1). Gender effects were limited. Ligament tests demonstrated expected rate effects. Younger specimens had a higher failure force and stiffness and failed at lower elongations than older specimens from previous studies. Gender effects suggest there may be a difference between male and female properties, but require further testing to establish greater significance.
    Journal of the mechanical behavior of biomedical materials. 04/2013; 23C:71-79.
  • Duane S Cronin
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    ABSTRACT: The rate of soft tissue sprain/strain injuries to the cervical spine and associated cost continue to be significant; however, the physiological nature of this injury makes experimental tests challenging while aspects such as occupant position and musculature may contribute to significant variability in the current epidemiological data. Several theories have been proposed to identify the source of pain associated with whiplash. The goal of this study was to investigate three proposed sources of pain generation using a detailed numerical model in rear impact scenarios: distraction of the capsular ligaments; transverse nerve root compression through decrease of the intervertebral foramen space; and potential for damage to the disc based on the extent of rotation and annulus fibre strain. There was significant variability associated with experimental measures, where the range of motion data overlapped ultimate failure data. Average data values were used to evaluate the model, which was justified by the use of average mechanical properties within the model and previous studies demonstrating predicted response and failure of the tissues was comparable to average response values. The model predicted changes in dimension of the intervertebral foramen were independent of loading conditions, and were within measured physiological ranges for the impact severities considered. Disc response, measured using relative rotation between intervertebral bodies, was below values associated with catastrophic failure or avulsion but exceeded the average range of motion values. Annulus fibre strains exceeded a proposed threshold value at three levels for 10g impacts. Capsular ligament strain increased with increasing impact severity and the model predicted the potential for injury at impact severities from 4g to 15.4g, when the range of proposed distraction corresponding to sub-catastrophic failure was exceeded, in agreement with the typically reported values of 9-15g. This study used an enhanced neck finite element model with active musculature to investigate three potential sources of neck pain resulting from rear impact scenarios and identified capsular ligament strain and deformation of the disc as potential sources of neck pain in rear impact scenarios.
    Journal of the mechanical behavior of biomedical materials. 02/2013;
  • Philip A Lockhart, Duane S Cronin, Brock Watson
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    ABSTRACT: Objective: Vehicle impacts with fixed roadside structures, such as poles, constitute a significant portion of road fatalities in North America. The purpose of this study was to evaluate occupant response in pole crash scenarios and compare the current vehicle kinematic-based injury metrics to occupant-based metrics to determine whether the vehicle metrics are representative of the injury levels sustained by an occupant. Methods: To better understand vehicle and occupant response during impact with a pole, frontal crash scenarios with 3 common pole types (a rigid pole, a rigid pole with a frangible base, and a deforming or energy-absorbing pole) were investigated at various impact velocities. A numerical model of a Hybrid III human surrogate was integrated with a numerical model of a mid-size sedan, including improvements to the vehicle and seat models, and implementation of an air bag and restraint system. The vehicle model was validated using the National Highway Traffic Safety Administration's (NHTSA) frontal crash data for varying impact velocities into a rigid wall. A numerical model of a high-energy-absorbing pole was developed and validated, along with a rigid pole and a previously developed breakaway pole, to examine the effects of pole compliance on the vehicle and occupant response. Occupant response was investigated at varying impact velocities with the poles aligned with the vehicle centerline. Offset impacts were then investigated with the energy-absorbing pole aligned with the driver-side crush structure. Results: The vehicle kinematic response metrics currently used to evaluate poles were compared to the currently accepted occupant injury response metrics and it was found, in general, that the occupant-based injury criteria predicted lesser injury than the vehicle kinematic response metrics for the same impact scenario. Specifically, the occupant impact velocity provided trends that differed from all other metrics. This can be attributed in part to the improvement in vehicle safety systems not accounted for by the vehicle-based metrics. Conclusions: For the same impact scenario, the breakaway pole resulted in the lowest predicted injury metrics for the vehicle occupant but was noted to be a potential threat to pedestrians and other nearby road users. The rigid pole resulted in the highest occupant injury predictions, whereas the energy-absorbing steel pole resulted in injury metrics below the threshold values, controlled the vehicle deceleration, and detached from the base only at higher velocity impacts. Appropriate evaluation of energy-absorbing poles requires consideration of the occupant response in addition to the current kinematic criteria.
    Traffic injury prevention 01/2013; 14(5):509-519.
  • Jennifer A DeWit, Duane S Cronin
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    ABSTRACT: Many detailed cervical spine models have been developed and primarily used to investigate kinematic response of the neck in impact scenarios. However, the goal of detailed models is to predict both kinematic response and provide insights into injury mechanisms and thresholds through tissue-level response. The objective of this study was to verify and validate an enhanced cervical spine segment finite element model to predict tissue-level failure under four load conditions: tension, flexion, and extension using a C4-C5 segment, and compression using a C5-C6-C7 segment. Mechanical tissue test data in relevant modes of loading was used in the model, and this data was also used to model ultimate tissue failure. The predicted failure locations were representative of reported cervical spine injuries for the different modes of loading, and the predicted peak failure forces were within the reported experimental corridors. The displacement to failure of the tension simulation was lower than expected in some cases, attributed to limitations in the constitutive model. This study provided a validated approach to predict tissue-level failure for cervical spine segments, predicting the location and sequence of tissue failure, and can be applied to future full cervical spine models for the prediction of injurious loading in automotive crash scenarios.
    Journal of the mechanical behavior of biomedical materials. 06/2012; 10:138-50.
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    ABSTRACT: The cervical spine ligaments play an essential role in limiting the physiological ranges of motion in the neck; however, traumatic loading such as that experienced in automotive crash scenarios can lead to ligament damage and result in neck injury. The development of detailed neck models to evaluate the response and the potential for injury requires accurate ligament mechanical properties at relevant loading rates. The objective of this study was to measure the mechanical properties of the cervical spine ligaments, by performing tensile tests at elongation rates relevant to car crash scenarios, using younger specimens (≤50 years), in simulated in vivo conditions, and to provide a comprehensive investigation of gender and spinal level effects. The five ligaments investigated were the anterior longitudinal ligament, posterior longitudinal ligament, capsular ligament, ligamentum flavum, and interspinous ligament. Ligaments were tested in tension at quasi-static (0.5 s(-1)), medium (20 s(-1)) and high (150-250 s(-1)) strain rates. The high strain rates represented typical car crash scenarios as determined using an existing cervical spine finite element model. In total, 261 ligament tests were performed, with approximately even distribution within elongation rate, spinal level, and gender. The measured force-displacement data followed expected trends compared to previous studies. The younger ligaments investigated in this study demonstrated less scatter, and were both stiffer and stronger than comparable data from older specimens reported in previous studies. Strain rate effects were most significant, while spinal level effects were limited. Gender effects were not significant, but consistent trends were identified, with male ligaments having a higher stiffness and failure force than female ligaments.
    Journal of the mechanical behavior of biomedical materials. 06/2012; 10:216-26.
  • Jason B Fice, Duane S Cronin
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    ABSTRACT: Whiplash injuries continue to have significant societal cost; however, the mechanism and location of whiplash injury is still under investigation. Recently, the upper cervical spine ligaments, particularly the alar ligament, have been identified as a potential whiplash injury location. In this study, a detailed and validated explicit finite element model of a 50th percentile male cervical spine in a seated posture was used to investigate upper cervical spine response and the potential for whiplash injury resulting from vehicle crash scenarios. This model was previously validated at the segment and whole spine levels for both kinematics and soft tissue strains in frontal and rear impact scenarios. The model predicted increasing upper cervical spine ligament strain with increasing impact severity. Considering all upper cervical spine ligaments, the distractions in the apical and alar ligaments were the largest relative to their failure strains, in agreement with the clinical findings. The model predicted the potential for injury to the apical ligament for 15.2 g frontal or 11.7 g rear impacts, and to the alar ligament for a 20.7 g frontal or 14.4 g rear impact based on the ligament distractions. Future studies should consider the effect of initial occupant position on ligament distraction.
    Journal of biomechanics 01/2012; 45(6):1098-102. · 2.66 Impact Factor
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    ABSTRACT: Antipersonnel blast landmines pose a significant threat in affected areas, with injuries to the lower extremity and amputation being common. Addressing a need for injury prediction and protection evaluation, a 50th percentile physical surrogate lower leg was developed incorporating the load transmission paths in the lower leg. Biofidelic and frangible materials were evaluated and selected based on high deformation rate properties compared to those for human tissues. The predicted leg injuries from experimental blast testing were in agreement with injury data for unprotected and protected legs. Post-test examination was found to be the only consistent and reliable evaluation method for predicting injury outcome, and an evaluation based on tissue damage was shown to be sensitive to changes in loading conditions, not possible with existing approaches. This study identified the severity of calcaneal fracture as the primary determinant of serious injury, which should be the focus of future protection development.
    Military medicine 12/2011; 176(12):1408-16. · 0.77 Impact Factor
  • B. Watson, D. S. Cronin
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    ABSTRACT: Injuries in side impact collisions, particularly to the thorax, are one of the leading causes of fatalities and severe injury in automotive collisions. Current side impact crash testing standards stipulate an initial position of the anthropometric test device (ATD) before impact; however, there is limited data regarding the relationship between initial ATD position, response and predicted injury. In this study, a finite element model of a full-scale side impact test was developed integrating full-vehicle, barrier and ATD models. The individual models were verified and validated, followed by validation of the fully integrated model using vehicle-specific crash tests and a broader study of late model sedan crash tests. The model predicted that the velocity profile of the impacted door was dominated by occupant interaction during contact and by the vehicle structure before and after contact with the occupant. Generally, the predicted level of injury increased when the ATD model was positioned closer to the intruding door or moved further rearwards due to interaction with the B pillar. Additionally, the door interior geometry was found to have a significant effect on the results due to the timing and location of interaction with the thorax. The thorax deflection was found to be much less sensitive to changes in position than the viscous criterion, which incorporated a velocity term in addition to a deflection. This study demonstrates the importance of occupant position on response and the possibility to enhance safety through interior door design and standoff distance.
    International Journal of Crashworthiness 10/2011; 16(5):569-582.
  • Matthew B Panzer, Jason B Fice, Duane S Cronin
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    ABSTRACT: Predicting neck response and injury resulting from motor vehicle accidents is essential to improving occupant protection. A detailed human cervical spine finite element model has been developed, with material properties and geometry determined a priori of any validation, for the evaluation of global kinematics and tissue-level response. Model validation was based on flexion/extension response at the segment level, tension response of the whole ligamentous cervical spine, head kinematic response from volunteer frontal impacts, and soft tissue response from cadaveric whole cervical spine frontal impacts. The validation responses were rated as 0.79, assessed using advanced cross-correlation analysis, indicating the model exhibits good biofidelity. The model was then used to evaluate soft tissue response in frontal impact scenarios ranging from 8G to 22G in severity. Disc strains were highest in the C4-C5-C6 segments, and ligament strains were greatest in the ISL and LF ligaments. Both ligament and disc fiber strain levels exceeded the failure tolerances in the 22G case, in agreement with existing data. This study demonstrated that a cervical spine model can be developed at the tissue level and provide accurate biofidelic kinematic and local tissue response, leading to injury prediction in automotive crash scenarios.
    Medical Engineering & Physics 06/2011; 33(9):1147-59. · 1.78 Impact Factor
  • D. S. Cronin
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    ABSTRACT: Ballistic gelatin is widely used as a soft tissue simulant for non-penetrating and penetrating, and the mechanical properties of gelatin are known to be highly sensitive to strain rate and temperature. Mechanical compression testing was undertaken across a range of strain rates at constant temperature to evaluate the material response. The material strength and stiffness increased with increasing strain rate, while the strain to failure was relatively constant across a wide range strain rates. The mechanical test data was implemented in two constitutive models: a quasi-linear viscoelastic model, commonly available in explicit finite element codes, and a tabulated hyperelasticity model. The implementations were verified using simulations of the experimental tests and it was found that the quasi-linear viscoelasticity model did not adequately capture the low and high strain rate response across the range of data. The tabulated hyperelasticity model was found to provide accurate representation of the material across the range of strain rates considered, and included a damage function to predict material failure.
    05/2011: pages 51-55;
  • Jason B Fice, Duane S Cronin, Matthew B Panzer
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    ABSTRACT: Predicting neck kinematics and tissue level response is essential to evaluate the potential for occupant injury in rear impact. A detailed 50th percentile male finite element model, previously validated for frontal impact, was validated for rear impact scenarios with material properties based on actual tissue properties from the literature. The model was validated for kinematic response using 4 g volunteer and 7 g cadaver rear impacts, and at the tissue level with 8 g isolated full spine rear impact data. The model was then used to predict capsular ligament (CL) strain for increasing rear impact severity, since CL strain has been implicated as a source of prolonged pain resulting from whiplash injury. The model predicted the onset of CL injury for a 14 g rear impact, in agreement with motor vehicle crash epidemiology. More extensive and severe injuries were predicted with increasing impact severity. The importance of muscle activation was demonstrated for a 7 g rear impact where the CL strain was reduced from 28 to 13% with active muscles. These aspects have not previously been demonstrated experimentally, since injurious load levels cannot be applied to live human subjects. This study bridges the gap between low intensity volunteer impacts and high intensity cadaver impacts, and predicts tissue level response to assess the potential for occupant injury.
    Annals of biomedical engineering 05/2011; 39(8):2152-62. · 2.41 Impact Factor
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    ABSTRACT: Head injury resulting from blast loading, specifically mild traumatic brain injury, has been identified as a possible and important blast-related injury for soldiers in modern conflict zones. A study was undertaken to evaluate head response to blast loading scenarios using an explicit finite element numerical model and to comment on the potential for head injury. The blast loading and simplified human body numerical models were validated using impulse, peak acceleration and the Head Injury Criterion from experimental blast test data. A study was then undertaken to evaluate head response at varying distances and orientations from the explosive. The accelerations and injury metrics for the head increased with decreasing distance to the explosive, as expected, but were also significant at intermediate distances from the explosive for larger charge sizes and intermediate heights of burst. Varying lateral position with constant standoff did not have a significant effect on the head kinematic response. The head injury criteria considered were exceeded in close proximity to the explosive (<35 charge radii) and depended on the height of burst for the range of charge sizes considered. The injury criteria were also exceeded at intermediate distances for larger charge sizes because of the influence of the mach stem. Although the injury criteria used in this study are typically applied to longer duration events, and may not be applicable for shorter duration blast loading, aggressive loading is predicted at small standoff distances and confirmed by the resulting head kinematics.
    The Journal of trauma 02/2011; 70(2):E29-36. · 2.35 Impact Factor
  • D. S. Cronin, C. Falzon
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    ABSTRACT: Ballistic gelatin is widely used as a soft tissue simulant in physical surrogates for the human body to evaluate penetrating impacts and, more recently to evaluate blunt impact and blast loading effects on soft tissues. It is known that the properties of gelatin are sensitive to temperature and aging time, but this has not previously been quantified. The mechanical properties of 10% ballistic gelatin were measured using a compression test apparatus with temperature controlled platens to maintain the sample temperature at a fixed level. Penetration testing was undertaken using a standard BB impact test to assess the effect of aging. The gelatin was found to be within calibration after 3days (72h of aging), based on the standard penetration test. The material properties were evaluated using the stress at failure, strain at failure and material stiffness as characterized by the Neo-Hookean constitutive model. The stress at failure and material stiffness increased with decreasing temperature and increasing strain rate, as expected, while the strain at failure remained relatively constant for the test conditions considered (1 to 23°C, strain rate from 0.01 to 1.0s−1). The study showed that the penetration resistance was consistent after 72h of aging, while the mechanical study demonstrated increasing failure stress and stiffness with decreasing failure strain at longer aging times, suggesting that these effects offset one another so that the penetration resistance remains relatively constant. The primary contribution of this study was to show the importance of temperature and aging time, through mechanical and penetration testing, to achieve appropriate and consistent response from ballistic gelatin. KeywordsMechanical properties–Ballistic gelatin–Strain rates–Mechanical testing–Tissue simulant
    Experimental Mechanics 01/2011; 51(7):1197-1206. · 1.55 Impact Factor
  • C. G. Thom, D. S. Cronin
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    ABSTRACT: It has been shown that, when exposed to air shock waves, soft materials such as fabrics can lead to amplification of the peak pressure measured on a reflecting surface behind the fabric. This occurs for a wide range of fabric configurations, including those used in soft-ballistic protection. The goal of this study was to validate a numerical model to develop an improved understanding of this phenomenon and investigate different fabric parameters, including density, permeability and standoff, and their influence on blast amplification. The investigation of fabric parameters was carried out using numerical simulations in an explicit finite element code with coupled fluid–structure interaction. The benefit of this method was the ability to isolate individual parameters. The model predicted similar trends to existing experimental data, though the numerically predicted peak pressures were consistently higher than the experimental values. The parametric study showed that low permeability fabrics result in the highest pressure amplifications. At areal densities on the order 100g/m2, typical of single layer fabrics, amplification also increased with areal density for low permeability materials.
    Shock Waves 03/2009; 19(1):39-48. · 0.60 Impact Factor
  • Matthew B Panzer, Duane S Cronin
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    ABSTRACT: Detailed cervical spine models are necessary to better understand cervical spine response to loading, improve our understanding of injury mechanisms, and specifically for predicting occupant response and injury in auto crash scenarios. The focus of this study was to develop a C4-C5 finite element model with accurate representations of each tissue within the segment. This model incorporates more than double the number of elements of existing models, required for accurate prediction of response. The most advanced material data available were then incorporated using appropriate nonlinear constitutive models to provide accurate predictions of response at physiological levels of loading. This tissue-scale segment model was validated against a wide variety of experimental data including different modes of loading (axial rotation, flexion, extension, lateral bending, and translation), and different load levels. In general, the predicted response of the model was within the single standard deviation response corridors for both low and high load levels. Importantly, this model demonstrates that appropriate refinement of the finite element mesh, representation at the tissue level, and sufficiently detailed material properties and constitutive models provide excellent response predictions without calibration of the model to experimental data. Load sharing between the disc, ligaments, and facet joints was investigated for various modes of loading, and the dominant load-bearing structure was found to correlate with typical anatomical injury sites for these modes of loading. The C4-C5 model forms the basis for the development of a full cervical spine model. Future studies will focus on tissue-level injury prediction and dynamic response.
    Journal of biomechanics 03/2009; 42(4):480-90. · 2.66 Impact Factor
  • C. P. Salisbury, D. S. Cronin
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    ABSTRACT: The characterization of soft or low impedance materials is of increasing importance since these materials are commonly used in impact and energy absorbing applications. The increasing role of numerical modeling in understanding impact events requires high-rate material properties, where the mode of loading is predominantly compressive and large deformations may occur at high rates of deformation. The primary challenge in measuring the mechanical properties of soft materials is balancing the competing effects of material impedance, specimen size, and rate of loading. The traditional Split Hopkinson Pressure Bar approach has been enhanced through the implementation of polymeric bars to allow for improved signal to noise ratios and a longer pulse onset to ensure uniform specimen deformation. The Polymeric Split Hopkinson Pressure Bar approach, including the required viscoelastic bar analysis, has been validated using independent measurement techniques including bar-end displacement measurement and high speed video. High deformation rate characterization of 10% and 20% ballistic gelatin, commonly used as a soft tissue simulant, has been undertaken at nominal strain rates ranging from 1,000 to 4,000/s. The mechanical properties of both formulations of gelatin exhibited significant strain rate dependency. The results for 20% gelatin are in good agreement with previously reported values at lower strain rates, and provide important mechanical properties required for this material.
    Experimental Mechanics 01/2009; 49(6):829-840. · 1.55 Impact Factor