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The modeling of human body biomechanics resulting from blast exposure poses great challenges because of the complex geometry and the substantial material heterogeneity. We developed a detailed human body finite element model representing both the geometry and the materials realistically. The model includes the detailed head (face, skull, brain and spinal cord), the neck, the skeleton, air cavities (lungs) and the tissues. Hence, it can be used to properly model the stress wave propagation in the human body subjected to blast loading. The blast loading on the human was generated from a simulated C4 explosion. We used the highly scalable solvers in the multi-physics code CoBi for both the blast simulation and the human body biomechanics. The meshes generated for these simulations are of good quality so that relatively large time-step sizes can be used without resorting to artificial time scaling treatments. The coupled gas dynamics and biomechanics solutions were validated against the shock tube test data. The human body models were used to conduct parametric simulations to find the biomechanical response and the brain injury mechanism due to blasts impacting the human body. Under the same blast loading condition, we showed the importance of inclusion of the whole body.

In this chapter, a review of the current state-of-the-art in techniques, efforts and ideas in the area of modeling skeletal injuries in military scenarios is provided. The review includes detailed discussions of the head, neck, spine, upper and lower extremity body regions. Each section begins with a description of the injury taxonomy reported for military scenarios for a particular body region and then a review of the computational modeling follows. In addition, a brief classification of modeling methods, tools and codes typically employed is provided and the processes and strategies for validation of models are discussed. Finally, we conclude with a short list of recommendations and observations for future work in this area. In summary, much work has been completed, however, there remains much to do in this research area. With continued efforts, modeling and simulation will continue to provide insight and understanding into the progression and time course of skeletal injuries in military scenarios with a high degree of spatial and temporal resolution. However, more work is needed to improve mechanistic-based modeling of injury mechanisms, such as fracture, and increase the inclusion of bio-variability into simulation frameworks.

Skeletal trauma occurs in many blunt, ballistic and blast impact events. Even though the personal body armors and protective equipment were effective in stopping the penetration of bullets or fragments, the resulting impact loading could lead to the significant injuries and fractures to the thoracic skeleton and extremities. The finite element (FEM) method, with its capability to handle complex geometries and nonlinear materials, are commonly used to analyze the tissue biomechanical responses and correlate the simulation results with the injury outcomes. However, it is very difficult to construct the three-dimensional (3D) FEM model for the skeletal biomechanics analysis because of the complex geometry and different materials involved. Moreover the simulation of 3D FEM model is computationally expensive because both small element size and high speed of sound in materials lead to very small time step in an explicit transient analysis. The simulation process is often not robust enough when the model experiences the large deformation. To shorten modeling and simulation times, we have developed a fast running model based on a novel nonlinear beam element for the skeletal impact biomechanics analysis. In contrast to the conventional beam elements, the kinematics of the developed beam element is free of rotational degrees of freedom (DOFs). The current beam element offers the desired constant lumped mass matrix for the large deformable explicit transient analysis. The realistic treatment of junctions and surface intersections among beams becomes straightforward. Furthermore the model can account for the irregular shape and different materials at beam cross sections by using the numerical integration. The sophisticated material models such as elastoplasticity can also be incorporated directly in the integration points. Thus the fast running model is suitable for the analysis of complex nonlinear composite structures such as the loading-carrying thoracic skeleton and extremities. The stereolithograph (STL)-based anatomical geometry of skeletal structure is used to extract the one-dimensional (1D) curved beam model and the associated beam cross sections. The anatomical surface of skeleton is also utilized for the calculation of transferred loads to the underlined beams. The 3D responses such as displacements and stresses from the fast running model are subsequently reconstructed on the anatomical surface for the visualization and skeletal trauma analysis. We demonstrate the efficiency of such modeling technique by simulating the rib cage and the lower extremity under the impact loadings. As compared to the 3D FEM model, the developed model runs fast and robust, and achieves good results without the need of laborious 3D meshing process.Copyright © 2015 by ASME

We present in this paper an efficient and accurate low-order solid-shell element formulation for analyses of large deformable multilayer shell structures with non-linear materials. The element has only displacement degrees of freedom (dofs), and an optimal number of enhancing assumed strain (EAS) parameters to pass the patch tests (both membrane and out-of-plane bending) and to remedy volumetric locking. Based on the mixed Fraeijs de Veubeke-Hu-Washizu (FHW) variational principle, the in-plane and out-of-plane bending behaviours are improved and the locking associated with (nearly) incompressible materials is avoided via a new efficient enhancement of strain tensor. Shear locking and curvature thickness locking are resolved effectively by using the assumed natural strain (ANS) method. Two non-linear 3-D constitutive models (Mooney–Rivlin material and hyperelastoplastic material at finite strain) are applied directly without requiring the enforcement of the plane-stress assumption. In particular, we give a simple derivation for the hyperelastoplastic model using spectral representations. In addition, the present element has a well-defined lumped mass matrix, and provides double-side contact surfaces for shell contact problems. With the dynamics referred to a fixed inertial frame, the present element can be used to analyse multilayer shell structures undergoing large overall motion. Numerical examples involving static analyses and implicit/explicit dynamic analyses of multilayer shell structures with both material and geometric non-linearities are presented, and compared with existing results obtained from other shell elements and from a meshless method. It is shown that elements that did not pass the out-of-plane bending patch test could not provide accurate results, as compared to the present element formulation, which passed the out-of-plane bending patch test. The present element proves to be versatile and efficient in the modelling and analyses of general non-linear composite multilayer shell structures. Copyright © 2005 John Wiley & Sons, Ltd.

In this paper, we present an optimal low-order accurate piezoelectric solid-shell element formulation to model active composite shell structures that can undergo large deformation and large overall motion. This element has only displacement and electric degrees of freedom (dofs), with no rotational dofs, and an optimal number of enhancing assumed strain (EAS) parameters to pass the patch tests (both membrane and out-of-plane bending). The combination of the present optimal piezoelectric solid-shell element and the optimal solid-shell element previously developed allows for efficient and accurate analyses of large deformable composite multilayer shell structures with piezoelectric layers. To make the 3-D analysis of active composite shells containing discrete piezoelectric sensors and actuators even more efficient, the composite solid-shell element is further developed here. Based on the mixed Fraeijs de Veubeke–Hu–Washizu (FHW) variational principle, the in-plane and out-of-plane bending behaviours are improved via a new and efficient enhancement of the strain tensor. Shear-locking and curvature thickness locking are resolved effectively by using the assumed natural strain (ANS) method. We also present an optimal-control design for vibration suppression of a large deformable structure based on the general finite element approach. The linear-quadratic regulator control scheme with output feedback is used as a control law on the basis of the state space model of the system. Numerical examples involving static analyses and dynamic analyses of active shell structures having a large range of element aspect ratios are presented. Active vibration control of a composite multilayer shell with distributed piezoelectric sensors and actuators is performed to test the present element and the control design procedure. Copyright © 2005 John Wiley & Sons, Ltd.

An “underbody blast” (UBB) is the detonation of a mine or improvised explosive device (IED) underneath a vehicle. In recent military conflicts, the incidence of UBBs has led to severe injuries, specifically in the lower extremities The foot and ankle complex, particularly the calcaneus bone, may sustain significant damage. Despite the prevalence of calcaneal injuries, this bone’s unique properties and the progression of fracture and failure have not been adequately studied under high strain rate loading. This research discusses early efforts at creating a high-resolution computational model of the human calcaneus, with primary focus on modeling the fracture network through the complex microstructure of the bone and creating micromechanically-based constitutive models that can be used within full human body models. The ultimate goal of this ongoing research effort is to develop a micromechanics-based simulation of calcaneus fracture and fragmentation due to impact loading. With the goal of determining the basic mechanisms of stress propagation through the internal structure of the calcaneus, a two-dimensional model was employed for preliminary simulations with a plane-strain approximation. In this effort, a cadaveric calcaneus was scanned to a resolution of 55 μm using an industrial micro-computed tomography (microCT) scanner. A mid-sagittal plane slice of the scan was selected and post-processed to generate a 2D finite element mesh of the calcaneus that included marrow, trabecular bone, and cortical bone elements. The calcaneus was modeled using two-dimensional quadratic plane strain elements. A fixed boundary condition was applied to the portion of the calcaneus that, in situ, would be restrained by the talus. A displacement of 1.25 mm was applied to the heel of the calcaneus over 5 ms. In a typical result, following impact, the strain and stress are propagated throughout the cortical shell and then began to radiate into the bone into the bone along the trabeculae. Local stress concentrations can be observed in the trabecular structure in the posterior region of the bone following impact. Upon impact, cortical and trabecular bone show different stresses of 13MPa and 1 MPa, respectively, and exhibit complex high frequency responses. Observed results may offer insight into the wave interactions between the different materials comprising the calcaneus, such as impedance mismatch and refraction. Pore pressure in the marrow may be another important factor to consider in understanding stress propagation in the calcaneus.

Complementary to animal testing and analysis of clinical data, a validated anatomy and physiology based mathematical models can provide capabilities for a better understanding of blast wave brain injury mechanisms, animal-human injury scaling, assessing and improving protective armor. We developed the 3D “virtual” animal models for multi-scale computational simulations of blast induced injury. A multi-scale modeling tool, CoBi, has been adopted for the analysis of blast wave primary TBI mechanisms and coupled biomechanics events. The shock wave over a rat in a shock tube was modeled by the CFD method. The primary biomechanics FEM study uses anatomic based animal geometry with a high resolution brain model. The virtual rat model has been validated against recently collected data from shock tube tests on rodents, including pressure time history in the free-stream and inside the rat brain. The model has been used to conduct parametric simulations to study the effect of animal placement location in the shock tube, and different loading orientations on the rat response. We also compared the rat brain biomechanical response between simulations of a free-to-move and a protected or constrained rat under the same shock tube loading to identify the role of body protection and head movement and on the rat TBI. The implications of these results suggest that virtual animal model could be used to predict the biomechanical response in the blast TBI event, and help design the protection against the blast TBI.Copyright © 2013 by ASME

Until today the modeling of human body biomechanics poses many great challenges because of the complex geometry and the substantial heterogeneity of human body. We developed a detailed human body finite element model in which the human body is represented realistically in both the geometry and the material properties. The model includes the detailed head (face, skull, brain, and spinal cord), the skeleton, and air cavities (including the lung). Hence it can be used to accurately acquire the stress wave propagation in the human body under various loading conditions. The blast loading on the human surface was generated from the simulated C4 blast explosions, via a novel combination of 1-D and 3-D numerical formulations. We used the explicit finite element solver in the multi-physics code CoBi for the human body biomechanics. This is capable of solving the resulting large system containing millions of unknowns in an extremely scalable fashion. The meshes generated for these simulations are of good quality. This enables us to employ relatively large time step sizes, without resorting to the artificial time scaling treatment. In order to study the human body dynamic response under the blast loading, we also developed an interface to apply the blast pressure loading on the external human body surface. These newly developed models were used to conduct parametric simulations to find out the brain biomechanical response when the blasts impact the human body. Under the same blast loading we also show the differences of brain response when having different material properties for the skeleton, the existence of other body parts such as torso.Copyright © 2012 by ASME

Previously we had developed an articulated human body model to simulate the kinematic response to the external loadings, using CFDRC’s CoBi implicit multi-body solver. The anatomy-based human body model can accurately account for the surface loadings and surface interactions with the environment. A study is conducted to calibrate the joint properties (for instance, the joint rotational damping) of the articulated human body by comparing its response with those obtained from the PMHS test under moderate loading conditions. Additional adjustments in the input parameters also include the contact spring constants for joint stops at different joint locations. By comparing the computational results with the real scenarios, we fine tune these input parameters and further improve the accuracy of the articulated human body model. In order to simulate the effect of a C4 explosion on a human body in the open field, we employ a CFD model with a good resolution and the appropriate boundary treatment to obtain the blast loading condition on the human body surface more accurately. The numerical results of the blast simulation are shown to be comparable to the test data. With the interface to apply the blast pressure loading from the CFD simulation on the articulated human body surface, the articulated human body dynamics due to the C4 explosions are modeled and the simulation results are shown to be physiological reasonable.

Explosive devices are the main weapon of terrorist attacks and a cause of major injuries to Soldiers and civilians. Recent military medical statistics show that a significant percentage of Soldiers injured in explosion events endures blast wave traumatic brain injury (BW-TBI). In the last few years, better understandings of BW-TBI mechanisms and of improved injury protection have become of paramount importance. Most studies have taken the conventional approach of animal testing, in vitro brain tissue study, and analysis of clinical data. These, while useful and necessary, are slow, expensive, and often non-conclusive. Physiology-based mathematical modeling tools of blast wave brain injury will provide a complementary capability to study both BW-TBI mechanisms and the effectiveness of protective armor.Copyright © 2009 by ASME

Bone conduction (BC) hearing is the process of transmitting sound energy through vibrations of the skull, cerebrospinal fluid (CSF) and brain, which results in an auditory sensation (Stenfelt and Goode 2005). BC communication is attractive for military operations because the transducers are lightweight, inconspicuous, and easily integrated into military headgear. Bone conduction (BC) headsets can present audio when ambient sounds must be either blocked by hearing protection or preserved to maintain situational awareness, and they can provide necessary radio communication in quiet and high noise environments, especially when combined with an appropriate hearing protection system (McBride et al. 2005, Henry and Letowski, 2007). The overall objective of this research is to develop, validate, and deliver anatomy and physics based modeling tools and experimental procedures for analysis and design of cranial bone conduction (BC) communication systems. The modeling tools will be used to optimize the design, attachment, and anatomical location of BC speakers and microphones for best communication clarity in various military environments.

A combat helmet is a helmet designed specifically for use during combat. The Advanced Combat Helmet (ACH) was developed to be the next generation of protective combat helmets for use by the United States Army. The ACH replaces the former Personnel Armor System for Ground Troops (PASGT) helmet. The ACH has improved design features such as lighter weight, chinstrap retention system, and pad suspension system, with more comfortable fit. It is also design to allow maximum sensory and situational awareness for the operator. The design process for combat helmets can be expensive due to prototype fabrications and physical testing, which can include user-acceptance, retention evaluation, quality assurance, and ballistic and blunt impact performance testing. The physical testing required for both ballistic and blunt impact testing destroys prototype and product line helmets. In order to speed up the design process and reduce the cost associated with prototype fabrications and physical testing, we developed a multi-physics helmeted-head computational model to simulate blunt impacts to a combat helmet. The blunt impact performance of a combat helmet was evaluated using computer model by simulating the structural dynamics of the helmet during and after the impacts. This helmeted-head model is a part of a more extensive computational model to analyze the biomechanics of head injury.Copyright © 2009 by ASME

Generally a helmet comprises two main components: the shell and the fitting system. Despite the variations in designs due to the different usage requirements, typically helmets are intended to protect the user’s head through an energy absorption mechanism. The weight and volume are important factors in helmet design since both may alter the injury risk to the head and neck. The helmet outer shell is usually made of hard material that will deform when it is hit by hard objects. This action disperses energy from the impact to lessen the force before it reaches the head. The fitting system frequently includes a dense layer that cushions and absorbs the energy as a result of relative motion between the helmet and the head. A balance needs to be achieved on how strong and how stiff a helmet should be to provide the best possible protection. If a helmet is too stiff it can be less able to prevent brain injury in the kinds of impacts that may occur. If it is too flexible or soft, it might not protect the user in a violent, high-energy crash. For military applications, the requirements for helmet performance may be even more demanding. Not only do helmets have to protect a Soldier’s head from blunt impacts, but helmets also are expected to provide mounting platforms for ancillary devices and to function in ballistic and blast events as well.

We develop a multi-scale high-fidelity biomechanical and physiologically based modeling tools for trauma (ballistic/impact and blast) injury to brain, lung and spinal cord for resuscitation, treatment planning and design of personnel protection. Several approaches have been used to study blast and ballistic/impact injuries. Dummy containing pressure sensors and synthetic phantoms of human organs have been used to study bomb blast and car crashes. Large animals like pigs also have been equipped with pressure sensors exposed to blast waves. But these methods do not provide anatomically and physiologically, full optimization of body protection design and require animal sacrifice. Anatomy and medical image-based high-fidelity computational modeling can be used to analyze injury mechanisms and to optimize the design of body protection. This paper presents novel approach of coupled computational fluid dynamics and computational structures dynamics to simulate fluid (air, cerebrospinal fluid)–solid (cranium, brain tissue) interaction during ballistic/blast impact. We propose a trauma injury simulation pipeline concept staring from anatomy and medical image-based high-fidelity 3D geometric modeling, extraction of tissue morphology, generation of computational grids, multi-scale biomechanical and physiological simulations, and data visualization.

We develop a multi-scale high fidelity biomechanical and physiologically-based modeling tools for trauma (ballistic/impact and blast) injury to brain, lung and spinal cord for resuscitation, treatment planning and design of personnel protection. Several approaches have been used to study blast and ballistic/impact injuries. Dummy containing pressure sensors and synthetic phantoms of human organs have been used to study bomb blast and car crashes. Large animals like pigs also have been equipped with pressure sensors exposed to blast waves. But these methods do not anatomically and physiologically biofidelic to humans, do not provide full optimization of body protection design and require animal sacrifice. Anatomy and medical image based high-fidelity computational modeling can be used to analyze injury mechanisms and to optimize the design of body protection. This paper presents novel approach of coupled computational fluid dynamics (CFD) and computational structures dynamics (CSD) to simulate fluid (air, cerebrospinal fluid) solid (cranium, brain tissue) interaction during ballistic/blast impact. We propose a trauma injury simulation pipeline concept staring from anatomy and medical image based high fidelity 3D geometric modeling, extraction of tissue morphology, generation of computational grids, multiscale biomechanical and physiological simulations, and data visualization.

Blast waves resulting from both industrial explosions and terrorist attacks cause devastating effects to exposed humans and structures. Blast related injuries are frequently reported in the international news and are of great interest to agencies involved in military and civilian protection. Mathematical models of explosion blast interaction with structures and humans can provide valuable input in the design of protective structures and practices, in injury diagnostics and forensics. Accurate simulation of blast wave interaction with a human body and the human body biodynamic response to the blast loading is very challenging and to the best of our knowledge has not been reported yet. A high-fidelity computational fluid dynamic (CFD) model is required to capture the reflections, diffractions, areas of stagnation, and other effects when the shock and blast waves respond to an object placed in the field. In this effort we simulated a representative free field blast event with a standing human exposed to the threat using the Second Order Hydrodynamic Automatic Mesh Refinement Code (SHAMRC). During the CFD analysis the pressure time history around the human body is calculated, along with the fragment loads. Subsequently these blast loads are applied to a fully articulated human body using the multi-physics code CoBi. In CoBi we developed a novel computational model for the articulated human body dynamics by utilizing the anatomical geometry of human body. The articulated human body dynamics are computed by an implicit multi-body solver which ensures the unconditional stability and guarantees the quadratic rate of convergence. The developed solver enforces the kinematic constraints well while imposing no limitation on the time step size. The main advantage of the model is the anatomical surface representation of a human body which can accurately account for both the surface loading and the surface interaction. The inertial properties are calculated using a finite element method. We also developed an efficient interface to apply the blast wave loading on the human body surface. The numerical results show that the developed model is capable of reasonably predicting the human body dynamics and can be used to study the primary injury mechanism. We also demonstrate that the human body response is affected by many factors such as human inertia properties, contact damping and the coefficient of friction between the human body and the environment. By comparing the computational results with the real scenario, we can calibrate these input parameters to improve the accuracy of articulated human body model.