A comparison of MiL‐Lx and Hybrid‐III responses in seated and standing postures with blast mats in simulated under‐vehicle explosions

Blast mats that can be retrofitted to the floor of military vehicles are considered to reduce the risk of injury from under‐vehicle explosions. Anthropometric test devices (ATDs) are validated for use only in the seated position. The aim of this study was to use a traumatic injury\ud simulator fitted with 3 different blast mats in order to assess the ability of 2 ATD designs to evaluate\ud the protective capacity of the mats in 2 occupant postures under 2 severities. \ud Tests were performed for each combination of mat design, ATD, severity and posture using an antivehicle under‐belly injury simulator. The differences between mitigation systems were larger under the H‐III compared to the MiL‐Lx. There was little difference in how the 2 ATDs and how posture ranked the mitigation systems. Results from this study suggest that conclusions obtained by testing\ud in the seated position can be extrapolated to the standing. However, the different percentage reductions observed in the 2 ATDs suggests different levels of protection. It is therefore unclear which ATD should be used to assess such mitigation systems. A correlation between cadavers and\ud ATDs on the protection offered by blast mats is required in order to elucidate this issue

Material properties of human lumbar intervertebral discs across strain rates

BACKGROUND CONTEXT: The use of finite element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. PURPOSE: The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates. STUDY DESIGN: A human cadaveric experimental study coupled with an inverse finite element study. METHODS: To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39±19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate. RESULTS: Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the annulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young modulus of AF fibers (—MPa) to strain rate (ε˙, /s) relationship of YMAF=31.5ln(ε˙)+435.5, and the C 10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa. CONCLUSIONS: These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications. CLINICAL SIGNIFICANCE: Finite element models can be used for many applications including investigating low back pain, spinal deformities, injury biomechanics, implant design, design of protective systems, and degenerative disc disease. The accurate material properties obtained in this study will improve the predictive ability, and therefore clinical significance of these models. </p

Material properties of bovine intervertebral discs across strain rates

AbstractThe intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10-3–1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (ε̇), the following relationship was derived:YM=35.5lnε̇+527.5. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates

Strain rate dependence of internal pressure and external bulge in human intervertebral discs during axial compression

Intervertebral discs (IVDs) lie between vertebrae of the spine. An understanding of their material behavior is of interest for research studies associated with injuries sustained during vehicle accidents, airplane ejections, sports injuries, and under-body blasts, and is particularly important for the development of biofidelic finite element (FE) models of these injurious events. The accuracy of such FE models depends on appropriate characterization of the material properties. The IVD consists of the anulus fibrosus (AF), which surrounds the nucleus pulposus (NP) and is encapsulated, above and below, by cartilage endplates (CEPs). The AF consists of 15–25 concentric layers, and each layer consists of collagen fiber bundles that have an orientation of approximately ±30 degrees to the transverse plane. The boundaries between the AF, the NP and the CEP are often unclear, which makes separating components of the IVD for mechanical testing a challenging task. The authors have previously used an inverse FE approach to obtain material properties of these components in bovine specimens; this approach involves obtaining subject-specific geometry of the whole IVD and optimizing individual components to ensure a close match between the experimental data and the numerical results. The aim of this study was to characterize experimentally the response of four human IVDs across strain rates. The results will be used to obtain material properties of the constituent components using an inverse FE approach

Material properties of bovine intervertebral discs across strain rates - dataset

<p>Raw experimental data from axial compression tests of each of the bovine intervertebral disc specimens and the .dat files from each of the subject specific FE models at each strain rate.</p

Mapping the Risk of Fracture of the Tibia From Penetrating Fragments.

Penetrating injuries are commonly inflicted in attacks with explosive devices. The extremities, and especially the leg, are the most commonly affected body areas, presenting high risk of infection, slow recovery, and threat of amputation. The aim of this study was to quantify the risk of fracture to the anteromedial, posterior, and lateral aspects of the tibia from a metal fragment-simulating projectile (FSP). A gas gun system and a 0.78-g cylindrical FSP were employed to perform tests on an ovine tibia model. The results from the animal study were subsequently scaled to obtain fracture-risk curves for the human tibia using the cortical thickness ratio. The thickness of the surrounding soft tissue was also taken into account when assessing fracture risk. The lateral cortex of the tibia was found to be most susceptible to fracture, whose impact velocity at 50% risk of EF1+, EF2+, EF3+, and EF4+ fracture types - according to the modified Winquist-Hansen classification - were 174, 190, 212, and 282 m/s, respectively. The findings of this study will be used to increase the fidelity of predictive models of projectile penetration