Emily E Ward

Johns Hopkins University, Baltimore, MD, United States

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Publications (13)17.89 Total impact

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    ABSTRACT: Strains and pressures in the brain are known to be influenced by rotation of the head in response to loading. This brain rotation is governed by the motion of the head, as permitted by the neck, due to loading conditions. In order to better understand the effect neck characteristics have on pressures and strains in the brain, a human head finite element model (HHFEM) was attached to two neck FEMs: a standard, well characterized Hybrid III Anthropometric Test Device neck FEM; and a high fidelity parametric probabilistic human FEM neck that has been hierarchically validated. The Hybrid III neck is well-established in automotive injury prevention studies, but is known to be much stiffer than in vivo human necks. The parametric FEM is based on CT scans and anatomic data, and the components of the model are validated against biomechanical tests at the component and system level. Both integrated head-neck models were loaded using pressure histories based on shock tube exposures. The shock tube loading applied to these head models were obtained using a computational fluid dynamics (CFD) model of the HHFEM surface in front of a 6 inch diameter shock tube. The calculated pressure-time histories were then applied to the head-neck models. The global head rotations, pressures, brain displacements, and brain strains of both head-neck models were compared for shock tube driver pressures from 517 to 862 kPa. The intracranial pressure response occurred in the first 1 to 5 msec, after blast impact, prior to a significant kinematic response, and was very similar between the two models. The global head rotations and the strains in the brain occurred at 20 to 100 msec after blast impact, and both were approximately two times higher in the model using the head parametric probabilistic neck FEM (H2PN), as compared to the model using the head Hybrid III neck FEM (H3N). It was also discovered that the H2PN exhibited an initial backward and small downward motion in the first 10 ms not seen in the H3N. The increased displacements and strains were the primary difference between the two combined models, indicating that neck constraints are a significant factor in the strains induced by blast loading to the head. Therefore neck constraints should be carefully controlled in studies of brain strain due to blast, but neck constraints are less important if pressure response is the only response parameter of primary interest.
    ASME 2013 International Mechanical Engineering Congress and Exposition; 11/2013
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    ABSTRACT: The skull-brain complex is typically modeled as an integrated structure, similar to a fluid-filled shell. Under dynamic loads, the interaction of the skull and the underlying brain, cerebrospinal fluid, and other tissue produces the pressure and strain histories that are the basis for many theories meant to describe the genesis of traumatic brain injury. In addition, local bone strains are of interest for predicting skull fracture in blunt trauma. However, the role of skull flexure in the intracranial pressure response to blunt trauma is complex. Since the relative time scales for pressure and flexural wave transmission across the skull are not easily separated, it is difficult to separate out the relative roles of the mechanical components in this system. This study uses a finite element model of the head, which is validated for pressure transmission to the brain, to assess the influence of skull table flexural stiffness on pressure in the brain and on strain within the skull. In a Human Head Finite Element Model, the skull component was modified by attaching shell elements to the inner and outer surfaces of the existing solid elements that modeled the skull. The shell elements were given the properties of bone, and the existing solid elements were decreased so that the overall stiffness along the surface of the skull was unchanged, but the skull table bending stiffness increased by a factor of 2.4. Blunt impact loads were applied to the frontal bone centrally, using LS-Dyna. The intracranial pressure predictions and the strain predictions in the skull were compared for models with and without surface shell elements, showing that the pressures in the mid-anterior and mid-posterior of the brain were very similar, but the strains in the skull under the loads and adjacent to the loads were decreased 15% with stiffer flexural properties. Pressure equilibration to nearly hydrostatic distributions occurred, indicating that the important frequency components for typical impact loading are lower than frequencies based on pressure wave propagation across the skull. This indicates that skull flexure has a local effect on intracranial pressures but that the integrated effect of a dome-like structure under load is a significant part of load transfer in the skull in blunt trauma.
    Biomedical sciences instrumentation 04/2013; 49:187-194.
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    ABSTRACT: A human head finite element model (HHFEM) was developed to study the effects of a blast to the head. To study both the kinetic and kinematic effects of a blast wave, the HHFEM was attached to a finite element model of a Hybrid III ATD neck. A physical human head surrogate model (HSHM) was developed from solid model files of the HHFEM, which was then attached to a physical Hybrid III ATD neck and exposed to shock tube overpressures. This allowed direct comparison between the HSHM and HHFEM. To develop the temporal and spatial pressures on the HHFEM that would simulate loading to the HSHM, a computational fluid dynamics (CFD) model of the HHFEM in front of a shock tube was generated. CFD simulations were made using loads equivalent to those seen in experimental studies of the HSHM for shock tube driver pressures of 517, 690 and 862kPa. Using the selected brain material properties, the peak intracranial pressures, temporal and spatial histories of relative brain-skull displacements and the peak relative brain-skull displacements in the brain of the HHFEM compared favorably with results from the HSHM. The HSHM sensors measured the rotations of local areas of the brain as well as displacements, and the rotations of the sensors in the sagittal plane of the HSHM were, in general, correctly predicted from the HHFEM. Peak intracranial pressures were between 70 and 120kPa, while the peak relative brain-skull displacements were between 0.5 and 3.0mm.
    Journal of biomechanics 09/2012; · 2.66 Impact Factor
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    ABSTRACT: Although soft armor vests serve to prevent penetrating wounds and dissipate impact energy, the potential of nonpenetrating injury to the thorax, termed behind armor blunt trauma, does exist. Currently, the ballistic resistance of personal body armor is determined by impacting a soft armor vest over a clay backing and measuring the resulting clay deformation as specified in National Institute of Justice (NIJ) Standard-0101.04. This research effort evaluated the efficacy of a physical Human Surrogate Torso Model (HSTM) as a device for determining thoracic response when exposed to impact conditions specified in the NIJ Standard. The HSTM was subjected to a series of ballistic impacts over the sternum and stomach. The pressure waves propagating through the torso were measured with sensors installed in the organs. A previously developed Human Torso Finite Element Model (HTFEM) was used to analyze the amount of tissue displacement during impact and compared with the amount of clay deformation predicted by a validated finite element model. All experiments and simulations were conducted at NIJ Standard test conditions. When normalized by the response at the lowest threat level (Level I), the clay deformations for the higher levels are relatively constant and range from 2.3 to 2.7 times that of the base threat level. However, the pressures in the HSTM increase with each test level and range from three to seven times greater than Level I depending on the organ. The results demonstrate the abilities of the HSTM to discriminate between threat levels, impact conditions, and impact locations. The HTFEM and HSTM are capable of realizing pressure and displacement differences because of the level of protection, surrounding tissue, and proximity to the impact point. The results of this research provide insight into the transfer of energy and pressure wave propagation during ballistic impacts using a physical surrogate and computational model of the human torso.
    The Journal of trauma 07/2008; 64(6):1555-61. · 2.35 Impact Factor
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    ABSTRACT: To assess the possibility of injury as a result of behind armor blunt trauma (BABT), a study was undertaken to determine the conditions necessary to produce the 44-mm clay deformation as set forth in the National Institute of Justice (NIJ) Standard 0101.04. These energy levels were then applied to a three-dimensional Human Torso Finite Element Model (HTFEM) with soft armor vest. An examination will be made of tissue stresses to determine the effects of the increased kinetic energy levels on the probability of injury. A clay finite element model (CFEM) was created with a material model that required nonlinear properties for clay. To determine these properties empirically, the results from the CFEM were matched with experimental drop tests. A soft armor vest was modeled over the clay to create a vest over clay block finite element model (VCFEM) and empirical methods were again used to obtain material properties for the vest from experimental ballistic testing. Once the properties for the vest and clay had been obtained, the kinetic energy required to produce a 44-mm deformation in the VCFEM was determined through ballistic testing. The resulting kinetic energy was then used in the HTFEM to evaluate the probability of BABT. The VCFEM, with determined clay and vest material properties, was exercised with the equivalent of a 9-mm (8-gm) projectile at various impact velocities. The 44-mm clay deformation was produced with a velocity of 785 m/s. This impact condition (9-mm projectile at 785 m/s) was used in ballistic exercises of the HTFEM, which was modeled with high-strain rate human tissue properties for the organs. The impact zones were over the sternum anterior to T6 and over the liver. The principal stresses in both soft and hard tissue at both locations exceeded the tissue tensile strength. This study indicates that although NIJ standard 0101.04 may be a good guide to soft armor failure, it may not be as good a guide in BABT, especially at large projectile kinetic energies. Further studies, both numerical and experimental, are needed to assist in predicting injury using the NIJ standard.
    The Journal of trauma 06/2007; 62(5):1127-33. · 2.96 Impact Factor
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    ABSTRACT: Both computational finite element and experimental models of the human torso have been developed for ballistic impact testing. The human torso finite element model (HTFEM), including the thoracic skeletal structure and organs, was created in the finite element code LS-DYNA. The skeletal structure was assumed to be linear-elastic while all internal organs were modeled as viscoelastic. A physical human surrogate torso model (HSTM) was developed using biosimulant materials and the same anthropometry as the HTFEM. The HSTM response to impact was recorded with piezoresistive pressure sensors molded into the heart, liver and stomach and an accelerometer attached to the sternum. For experimentation, the HSTM was outfitted with National Institute of Justice (NIJ) Level I, IIa, II and IIIa soft armor vests. Twenty-six ballistic tests targeting the HSTM heart and liver were conducted with 22 caliber ammunition at a velocity of 329 m/s and 9 mm ammunition at velocities of 332, 358 and 430 m/s. The HSTM pressure response repeatability was found to vary by less than 10% for similar impact conditions. A comparison of the HSTM and HTFEM response showed similar pressure profiles and less than 35% peak pressure difference for organs near the ballistic impact point. Furthermore, the peak sternum accelerations of the HSTM and HTFEM varied by less than 10% for impacts over the sternum. These models provide comparative tools for determining the thoracic response to ballistic impact and could be used to evaluate soft body armor design and efficacy, determine thoracic injury mechanisms and assist with injury prevention.
    Journal of Biomechanics 02/2007; 40(1):125-36. · 2.50 Impact Factor
  • Journal of Biomechanics 01/2007; 40. · 2.50 Impact Factor
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    ABSTRACT: According to the National Institute of Justice (NIJ) Standard 0101.04, the maximum deformation a soft armor vest can undergo without penetration is 44 mm. However, this does not take into account the effect of the pressure wave or energy transferred to the organs within the torso due to behind armor blunt trauma (BABT). Therefore, a study was undertaken to develop a finite element model (FEM) to study these effects. A finite element model (FEM) of the human thorax; complete with musculoskeletal structure and internal organs (heart, liver, lungs and stomach), intercostal muscle and skin, has been developed in LS-DYNA. A Kevlar vest was modeled on the chest to simulate non-penetrating ballistic impact. Using a projectile modeled with a size and mass equivalent to a 9 mm (124 grain) bullet at 360 and 425 m/s, four impacts were simulated against NIJ Level II and Level IIIa Kevlar vests at the midsternum and right thorax. At the same velocity, the pressures decreased by a factor of 3 and the energy absorbed by the organs decreased by a factor of 6 for the NIJ Level II and Level IIIa vests, respectively. As the projectile velocity increased, the peak pressures increased by a factor of 3 while the energy absorbed by the organs increased by a factor of 4. The resulting pressure profiles and kinetic energy exhibited by the respective organs indicate this model may be useful in identifying mechanisms of injury as well as organs at an elevated injury risk as a result of BABT.
    The Journal of trauma 07/2005; 58(6):1241-51. · 2.96 Impact Factor
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    ABSTRACT: Background: According to the National Institute of Justice (NIJ) Standard 0101.04, the maximum deformation a soft armor vest can undergo without penetration is 44 mm. However, this does not take into account the effect of the pressure wave or energy transferred to the organs within the torso due to behind-armor blunt trauma (BABT). Therefore, a study was undertaken to develop a finite element model to study these effects. Methods: A finite element model of the human thorax, complete with musculoskeletal structure and internal organs (heart, liver, lungs, and stomach), intercostal muscle, and skin, has been developed in LS-DYNA. A Kevlar® vest was modeled on the chest to simulate non-penetrating ballistic impact. Results: With use of a projectile modeled with a size and mass equivalent to a 9-mm (124-grain) bullet at 360 and 425 m/s, four impacts were simulated against NIJ level II and level IIIa Kevlar® vests at the midsternum and right thorax. At the same velocity, the pressures decreased by a factor of 3 and the energy absorbed by the organs decreased by a factor of 6 for the NIJ level II and level IIIa vests, respectively. As the projectile velocity increased, the peak pressures increased by a factor of 3 while the energy absorbed by the organs increased by a factor of 4. Conclusion: The resulting pressure profiles and kinetic energy exhibited by the respective organs indicate this model may be useful in identifying mechanisms of injury as well as organs at an elevated injury risk as a result of BABT.
    The Journal of Trauma and Acute Care Surgery 05/2005; 58(6):1241-1251. · 1.97 Impact Factor
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    ABSTRACT: hen soldiers or law enforcement offi cers are shot in the chest or abdomen there may be internal injuries even though a soft armor vest prevents penetration of the pro-jectile. This nonpenetrating injury could remain undetected until the person succumbs, for instance, to hemorrhaging in the lungs or laceration of the liver. In addition, tools are needed to design more effective soft armor vests that are lightweight, are fl exible enough to fi t the body contour, and can defeat high-velocity rifl e rounds. To study internal organ injuries and design better vests under nonpenetrating ballistic impact, both a computa-tional (fi nite element) model (FEM) and a physical human surrogate torso model (HSTM) have been developed. These models consist of the heart, lungs, liver, and stomach sur-rounded by the skeleton. The HSTM was outfi tted with a soft armor vest, and ballis-tic tests were conducted using 9-mm ammunition at various velocities. While the peak accelerations and peak pressures from the FEM did not match those from testing, the trends and patterns were similar. These results represent a signifi cant step in developing an understanding of the deformations and energy transfer characteristics of ballistic impacts through personal body armor.
    01/2005; 1.
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    ABSTRACT: An anatomically detailed finite element model (FEM) of the male human torso has been generated using geometry obtained from a model of the human anatomy developed for the computer graphics industry. The model represents a 5th percentile male human based on anthropometric data from the US Army. The geometry was used as a starting point to create finite element models of all the anatomic components, including the skeletal structure (vertebral column, ribs, cartilage, and sternum), stomach, lungs, liver, heart (including the aorta), muscles, and skin. The model also includes personal body armor representing a Level II vest. LS-DYNA was used to analyze the 245,000 element model simulating air blast. Material properties for the various soft tissues were obtained from high strain rate experiments on human organ tissue samples at rates ranging from 200–3000 s−1 using a modified Kolsky (split-Hopkinson) bar. This model has been used to evaluate pressures and deformation in specific areas of the thorax in response to blast loading, and to compare the results to existing injury criteria.
    12/2004: pages 17-24;
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    ABSTRACT: A finite element model of a representative 50 th percentile male torso has been created by researchers at the Johns Hopkins University Applied Physics Laboratory. The components of this detailed Human Torso Finite Element Model (HTFEM) include the heart, lungs, liver, stomach, intestinal mass, kidneys as well as the thoracic skeletal structure system. The detailed components of the torso provide relevant internal geometries, material differences and boundary conditions to study the propagation of a blast pressure wave through the thoracic region. Injury due to blast has largely been predicted using the Bowen curves, which are based on experiments of various animal species exposed to air blast that provide a biological response to blast. LS-DYNA, a dynamic finite element modeling tool is used to simulate the complex system response of the HTFEM to an open air blast event. LS-DYNA's enhanced version of the CONWEP blast model will be used to load the HTFEM. Loading conditions representing the overpressure and positive phase duration as defined in existing injury curves adapted from Bowen's lethality model are applied to the HTFEM. These simulations will explore HTFEM response to peak overpressures in the range of 400-800 kPa and positive phase durations in the range of 2.0 to 4.5 ms. The temporal pressure plots show organ response for the various loading conditions. The HTFEM can be used as a tool used to examine the blast effects on the human torso and to aid in the design of personal protective equipment (PPE).
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    Emily Ward, Tim Harrigan
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    ABSTRACT: Blast-induced traumatic brain injury (bTBI) is a critical issue for warfighter protection. Since bTBI has many features in common with injuries due to impact loading, the Hybrid III crash test dummy can be used to study many aspects of this injury, and the head-neck assembly of the Hybrid III dummy can provide a relevant initial bench test for computational studies of traumatic brain injury. LS-DYNA ® has provided finite element models (FEM) of various Anthropomorphic Test Dummies (ATDs), and in this study the head-neck subassembly from the LSTC-NCAC 50th% Full FE H-III Dummy was used. To study the effects of blast on the head a shock tube experiment was simulated and the relevant loading conditions were applied to the head-neck assembly of the Hybrid III dummy FEM. The results were then compared to similar experimental test data. Since the initial tension in the neck cable of the Hybrid-III head-neck assembly is a key factor in the experimental response, simulating the initial tension in the neck cable is required in order to maintain a consistent boundary condition for the model. The neck cable definition in the Hybrid-III FEM was modified to include an initial stress, which was implemented using a dynamic relaxation step applied to initialize the model. The dynamic relaxation step is applied using explicit techniques and a sensitivity study is explored to understand impact of the initialization on the global response. The relative influence on the resulting global behavior response depends on the loading conditions.