Duane S Cronin

University of Waterloo, Ватерлоо, Ontario, Canada

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Publications (66)60.07 Total impact

  • Hamed Shateri · Duane S Cronin ·
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    ABSTRACT: Objective: Whiplash injuries can occur in automotive crashes and may cause long-term health issues such as neck pain, headache, and visual and auditory disturbance. Evidence suggests that nonneutral head posture can significantly increase the potential for injury in a given impact scenario, but epidemiological and experimental data are limited and do not provide a quantitative assessment of the increased potential for injury. Although there have been some attempts to evaluate this important issue using finite element models, none to date have successfully addressed this complex problem. Methods: An existing detailed finite element neck model was evaluated in nonneutral positions and limitations were identified, including musculature implementation and attachment, upper cervical spine kinematics in axial rotation, prediction of ligament failure, and the need for repositioning the model while incorporating initial tissue strains. The model was enhanced to address these issues and an iterative procedure was used to determine the upper cervical spine ligament laxities. The neck model was revalidated using neutral position impacts and compared to an out-of-position cadaver experiment in the literature. The effects of nonneutral position (axial head rotation) coupled with muscle activation were studied at varying impact levels. Results: The laxities for the ligaments of the upper cervical spine were determined using 4 load cases and resulted in improved response and predicted failure loads relative to experimental data. The predicted head response from the model was similar to an experimental head-turned bench-top rear impact experiment. The parametric study identified specific ligaments with increased distractions due to an initial head-turned posture and the effect of active musculature leading to reduced ligament distractions. Conclusions: The incorporation of ligament laxity in the upper cervical spine was essential to predict range of motion and traumatic response, particularly for repositioning of the neck model prior to impact. The results of this study identify a higher potential for injury in out-of-position rear collisions and identified at-risk locations based on ligament distractions. The model predicted higher potential for injury by as much as 50% based on ligament distraction for the out-of-position posture and reduced potential for injury with muscle activation. Importantly, this study demonstrated that the location of injury or pain depends on the initial occupant posture, so that both the location of injury and kinematic threshold may vary when considering common head positions while driving.
    Traffic Injury Prevention 02/2015; 16(7). DOI:10.1080/15389588.2014.1003551 · 1.41 Impact Factor
  • Stephen F E Mattucci · Duane S Cronin ·
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    ABSTRACT: Experimental testing on cervical spine ligaments provides important data for advanced numerical modeling and injury prediction; however, accurate characterization of individual ligament response and determination of average mechanical properties for specific ligaments has not been adequately addressed in the literature. Existing methods are limited by a number of arbitrary choices made during the curve fits that often misrepresent the characteristic shape response of the ligaments, which is important for incorporation into numerical models to produce a biofidelic response. A method was developed to represent the mechanical properties of individual ligaments using a piece-wise curve fit with first derivative continuity between adjacent regions. The method was applied to published data for cervical spine ligaments and preserved the shape response (toe, linear, and traumatic regions) up to failure, for strain rates of 0.5s(-1), 20s(-1), and 150-250s(-1), to determine the average force-displacement curves. Individual ligament coefficients of determination were 0.989 to 1.000 demonstrating excellent fit. This study produced a novel method in which a set of experimental ligament material property data exhibiting scatter was fit using a characteristic curve approach with a toe, linear, and traumatic region, as often observed in ligaments and tendons, and could be applied to other biological material data with a similar characteristic shape. The resultant average cervical spine ligament curves provide an accurate representation of the raw test data and the expected material property effects corresponding to varying deformation rates. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Journal of the Mechanical Behavior of Biomedical Materials 01/2015; 41:251-60. DOI:10.1016/j.jmbbm.2014.09.023 · 3.42 Impact Factor
  • Donata Gierczycka · Brock Watson · Duane Cronin ·
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    ABSTRACT: Side impact continues to be a significant source of vehicle occupant injuries and fatalities requiring an improved understanding of response sensitivity to occupant position and the potential for injury. The primary interaction between the occupant and vehicle in near-side impact is the intruding door and vehicle structure where contact with the intruding structures is observed to be the most frequent cause of injuries. Restraints and protective systems are tested for a specific driving position with a prescribed set of anthropometric test devices; however, studies have shown that the initial position and posture of the occupant within the vehicle may have an influence on occupant response. In this study, a finite-element human body model with a detailed representation of the thorax and an ES-2re anthropomorphic test device (ATD) model were integrated with a mid-sized sedan vehicle model to investigate occupant response from a moving deformable barrier side impact. All models were verified using established tests (pendulum, side sled) and physical test data available in the literature. A parametric study was undertaken to evaluate the effect of arm position and car door material properties on thoracic response, assessed using thoracic deflection and the viscous criterion. In the standard driving position, the human and ATD model responses were similar. The human body model demonstrated significant sensitivity, relative to the ATD, to different arm positions with a lesser sensitivity to the door interior properties. It was found that in side impact which has the characteristics of high energy and limited displacement, the arm aligned with the body can act as a significant source of load transmission to the thorax, increasing the potential for injury. This study demonstrates that the choice of occupant model, injury metric and occupant arm position plays an important role in evaluating side impact safety.
    International Journal of Crashworthiness 01/2015; 20(3):1-28. DOI:10.1080/13588265.2014.998000 · 0.57 Impact Factor
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    Brett Campbell · Duane Cronin ·
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    ABSTRACT: The goal of this study was to evaluate side impact crash conditions using a detailed human body model and side impact crash model to provide an improved understanding of side impact injury and the primary contributing factors. This study builds on an advanced numerical human body model, including a detailed thorax, which has been validated using available PMHS test data for pendulum and side sled impact tests. Crash conditions were investigated through use of a coupled side impact model, used to reproduce full scale crash tests. The model accounts for several important factors that contribute to occupant response as noted in the literature: the relative velocities between the seat and door, the occupant to door distance, the door shape and compliance. The coupled side impact model was validated using FMVSS 214 and IIHS side impact test data, comparing the thoracic response predicted by the model to that of the ES-2 dummy used in the crash tests. Importantly, the door and seat models were developed based on experimental data in the literature. The side impact model was used to investigate the effects of door to occupant spacing, door velocity profile, restraint system, and seat foam properties. The current study was limited to the use of velocity profiles in the direction of impact and did not consider rotational effects or motion perpendicular to the impact direction. It was found that injury as predicted using the detailed human body model and the Viscous Criterion (VC) was controlled by the second velocity peak typically found in door velocity profiles.
    International Journal of Crashworthiness 12/2014; 19(4). DOI:10.1080/13588265.2014.909561 · 0.57 Impact Factor
  • Jeffrey B Barker · Duane S. Cronin · Naveen Chandrashekar ·
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    ABSTRACT: Numerical finite element models of the neck have been developed to simulate occupant response and predict injury during motor vehicle collisions. However, there is a paucity of data on the response of young cervical spine segments under dynamic loading in flexion and extension, which is essential for the development or validation of Detailed Finite Element (DFE) models. This limitation was identified during the development and validation of the DFE model used in this study. The purpose of this study was to measure the high rotation rate loading response of human cervical spine segments in flexion and extension, and to investigate a new DFE model of the cervical spine with the experimental data to address a limitation in available data. Four test samples at each segment level from C2-C3 through C7-T1 were dissected from eight donors and were tested to 10 degrees of rotation at 1 and 500 degrees per second in flexion and extension using a custom built test apparatus. There was strong evidence (p < 0.05) of increased stiffness at the higher rotation rate above six degrees of rotation for four segment level tests in extension, and one segment level in flexion. Below six degrees of rotation, there was no evidence of increased stiffness between the two rotation rates at any segment level. Cross-correlation software, CORA, was used to evaluate the fit between the experimental data and model predictions. CORA calculated an average score 0f 0.771, demonstrating good fit to the data.
    Journal of Biomechanical Engineering 07/2014; 136(12). DOI:10.1115/1.4028107 · 1.78 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.
    04/2014; 30(4). DOI:10.1002/cnm.2612
  • 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.
    03/2014; 30(3). DOI:10.1002/cnm.2605
  • 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; 18(6). DOI:10.1080/10255842.2013.829460 · 1.77 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 02/2014; 64:39–52. DOI:10.1016/j.ijimpeng.2013.10.001 · 2.20 Impact Factor
  • 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 07/2013; 14(5):509-519. DOI:10.1080/15389588.2012.732718 · 1.41 Impact Factor
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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.
    04/2013; 23C:71-79. DOI:10.1016/j.jmbbm.2013.04.005
  • A. Hosseini · D. Cronin · A. Plumtree ·
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    ABSTRACT: Cracks may occur coincident with corrosion representing a new hybrid defect in gas and oil pipelines known as crack in corrosion (CIC) that is not directly addressed in the current codes or assessment methods. Hence, there is a need to provide an assessment of CIC and evaluate the line integrity, as well as identify the requirements for defect repair or line hydrotest. An experimental investigation was undertaken to evaluate the collapse pressures of lines containing corrosion, cracks, or (CIC) defects in a typical line pipe (API 5L Grade X52, 508 mm diameter, 5.7 mm wall thickness). The mechanical properties of the pipe were measured using tensile, Charpy, and J-testing for use in applying evaluation criteria. Rupture tests were undertaken on end-capped sections containing uniform depth, finite length corrosion, cracks, or CIC defects. Failure occurred by plastic collapse and ductile tearing for the corrosion defects, cracks, and CIC geometries tested. For the corrosion defects, the corroded pipe strength (CPS) method provided the most accurate results (13% conservative on average). The API 579 (level 3 failure assessment diagram (FAD), method D) provided the least conservative collapse pressure predictions for the cracks with an average error of 20%. The CIC collapse pressures were bounded by those of a long corrosion groove (upper bound) and a long crack (lower bound), with collapse dominated by the crack when the crack depth was significant. Application of API 579 to the CIC provided collapse pressure predictions that were 18% conservative. Sixteen rupture tests were successfully completed investigating the failure behavior of longitudinally oriented corrosion, crack, and CIC. The pipe material was characterized and these properties were used to predict the collapse pressure of the defects using current methods. Existing methods for corrosion (CPS) and cracks (API 579, level 3, method D) gave conservative collapse pressure predictions. The collapse pressures for the CIC were bounded by those of a long corrosion groove and a long crack, with collapse dominated by the crack when the crack depth was significant. CIC failure behavior was determined by the crack to corrosion depth ratio, total defect depth and its profile. The results showed that the failure pressures for CIC were reduced when their equivalent depths were similar to those of corrosion and using crack evaluation techniques provided an approximate collapse pressure.
    Journal of Pressure Vessel Technology 04/2013; 135(2):021701. DOI:10.1115/1.4007644 · 0.36 Impact Factor
  • 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.
    02/2013; 33(1). DOI:10.1016/j.jmbbm.2013.01.006
  • B. Bedairi · D. Cronin · A. Hosseini · A. Plumtree ·
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    ABSTRACT: Cracks occurring coincidentally with corrosion (Crack-in-Corrosion or CIC), represent a new hybrid defect in pipelines that are not directly addressed in the current codes or assessment methods. To understand the failure response of these defects, the finite element method using an elastic–plastic fracture mechanics approach was applied to predict the failure pressures of comparable crack, corrosion and CIC defects in 508 mm diameter pipe with 5.7 mm wall thickness. Failure pressure predictions were made based on measured tensile, Charpy impact and J testing data, and validated using experimental rupture tests. Plastic collapse was predicted for corrosion and crack defects using the critical strength based on the material tensile strength, whereas fracture was predicted using the measured J0.2 value. The model predictions were found to be conservative for the CIC defects (17.4% on average), 12.4% conservative for crack-only defects, and 3.2% conservative for corrosion defects compared to the experimental tests, demonstrating the applicability of the material-based failure criteria. For the defects considered in this study, all were predicted to fail by plastic collapse. The finite element method provided less conservative predictions than existing corrosion or crack-based analytical methods.
    International Journal of Pressure Vessels and Piping 08/2012; 96-97:90-99. DOI:10.1016/j.ijpvp.2012.06.002 · 1.28 Impact Factor
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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.
    06/2012; 10:216-26. DOI:10.1016/j.jmbbm.2012.02.004
  • 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.
    06/2012; 10:138-50. DOI:10.1016/j.jmbbm.2012.02.015
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    ABSTRACT: Helical coil polymeric stents provide an alternative method of stenting compared to traditional metallic stents, but require additional investigation to understand deployment, expansion, and fixation. A bilayer helical coil stent consisting of PLLA and PLGA was investigated using the finite element model to evaluate performance by uniform expansion and subsequent recoiling. In vitro material characterization studies showed that a preinsertion water-soaking step to mimic body implantation conditions provided the required ductility level expansion. In this case, the mechanical contribution of the outer PLGA layer was negligible since it softened significantly under environmental conditions. The viscoelastic response was not considered in this study since the strain rate during expansion was relatively slow and the material response was primarily plastic. The numerical model was validated with available experimental expansion and recoiling data. A parametric study was then undertaken to investigate the effect of stent geometry and coefficient of friction at the stent-cylinder interface on the expansion and recoiling characteristics. The model showed that helical stents exhibit a uniform stress distribution after expansion, which is important for controlled degradation when using biodegradable materials. The results indicated that increasing stent width, pitch value, and coil thickness resulted in a larger diameter after recoiling, which would improve fixation in the artery. It was also noted that a helical stent should have more than five coils to be stable after recoiling. This work is part of a larger research study focused on the performance of a balloon-inflated polymeric helical stent for artery applications.
    Journal of Medical Devices 05/2012; 6(2):021012. DOI:10.1115/1.4005777 · 0.42 Impact Factor
  • 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. DOI:10.1016/j.jbiomech.2012.01.016 · 2.75 Impact Factor
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    Duane S Cronin · Kevin Williams · Christopher Salisbury ·
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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. DOI:10.7205/MILMED-D-11-00044 · 0.77 Impact Factor
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    ABSTRACT: Background: Traumatic brain injury caused by blast loading has been identified as an important injury for soldiers in modern times. A study was undertaken to refine and compare two previously developed finite element head models, in the sagittal and transverse planes, under various blast load conditions. Quasi-2D models were considered since 3D models at the necessary resolution are computationally prohibitive. Methods: The models were exposed to blast loads with three standoff distances, and compared in terms of head kinematics (acceleration, HIC) and brain tissue response (intracranial pressure, shear stress, and principle strain). Results: The brain tissue response of both models was generally in good agreement, although some key differences were observed. The predicted peak accelerations of both models were in good agreement with comparable physical tests; however the transverse model overpredicted HIC15 for closer standoffs. Conclusions: In general, the sagittal and transverse models predicted comparable results for head kinematics and brain tissue response. The tissue strains were lower and the strain rates were higher than those reported in automotive crash scenarios. The strains in the transverse plane were higher than those in the sagittal. Future research will focus on improved material properties evaluation in a wider range of blast scenarios.