Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session U6: SMGPB: Biomaterials |
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Chair: David Williamson, University of Cambridge Room: Broadway III/IV |
Thursday, June 20, 2019 3:15PM - 3:45PM |
U6.00001: Stress wave propagation and cavitation in gelatin due to ballistic impact Invited Speaker: Sikhanda Satapathy Gelatin is commonly used as a surrogate for characterizing soft tissues response including injury mechanisms in humans. However, characterization of high rate response of such soft material using conventional techniques is difficult due to large difference in shear and pressure wave speeds and inertia effects. Limited high pressure data exists for this material. We carried out plane-strain and ballistic experiments on ballistic gel and a synthetic gel made from thermoplastic elastomers as surrogate system to investigate stress wave propagation and cavitation as a potential injury mechanism for behind helmet blunt trauma. The stress wave generated from ballistic impact was recorded with piezoelectric pressure gages. In addition to monolithic gel blocks, experiments were also conducted with gel blocks where air bubbles was preplaced to investigate negative pressure regime that may lead to cavitation. High speed camera recorded the wave motion and bubble dynamics utilizing the transparency contrast and densification of the gel. The bubble dynamics was correlated with measured pressure. The cavitation threshold correlated well with theoretical estimates of cavitation threshold of these materials. We utilized both numerical simulations to obtain insight into the nature of stress wave propagation. The experimental measurements and simulations provide significant insight into potential injury mechanism arising out of stress wave and consequent large deformation of the soft material. [Preview Abstract] |
Thursday, June 20, 2019 3:45PM - 4:00PM |
U6.00002: Modeling dynamic finite deformation and stress wave mechanics in the lung John Clayton, Rohan Banton, Alan Freed A new constitutive model for lung parenchyma, including soft tissue and internal fluid, is developed for dynamic loading protocols and injury assessment. The material is approximated as a homogeneous isotropic, nonlinear viscoelastic solid. Internal energy depends on finite strain, entropy, and internal variables. The equilibrium response in the hyperelastic limit follows from a strain energy functional depending on strain attributes resulting from an upper triangular decomposition of the deformation gradient [1]. Viscosity is addressed via an internal variable formalism that corresponds, in certain cases, to a further multiplicative decomposition of distortion [2]. Stiffness degradation and injury mechanisms (e.g., contusion, edema, atelectasis) are tracked by internal variable(s). The response of a column to high rate compressive loading is calculated. Depending on rate of loading, internal and external pressures, and fluid interactions with the external environment, compressibility of air inside strongly influences the response. Solutions for ramp loading and planar shocks are compared with experiment. [1] A.D. Freed et al., J. Mech. Mater. Struct., vol. 12, pp. 219-247, 2017. [2] J.D. Clayton, Differential Geometry and Kinematics of Continua, World Scientific, 2014. [Preview Abstract] |
Thursday, June 20, 2019 4:00PM - 4:15PM |
U6.00003: CTH Simulation of a Shockwave Interaction with the Human Thorax Douglas Coldwell With the rise of non-state actors in terrorist actions, the use of high explosives in improvised devices (IED) has significantly increased over the past ten years. Contrary to public perception, the major cause of death is due to the interaction with the thorax, not traumatic brain injury. The thorax has a much lower limit of overpressure it can tolerate before damage occurs. The primary causes of death due to shock are: pulmonary damage (``blast lung''), stroke, heart attack, burns. These were successfully simulated using the Sandia National Laboratory's CTH Shock Simulation Program. A 2cm thick bar of highly pressured air was placed immediately in front of the chest and allowed to proceed through the thorax. Each organic component of the chest was individually represented with their characteristic mechanical properties. The model predicted and was consistent with both animal experiments and autopsy results demonstrating the injury to the lungs and burn damage suffered. The stroke and heart attack were also demonstrated by the appearance of cavitation in the cardiac chambers and the aorta leading to the formation of bubbles that act as emboli to both the carotid arteries and the coronary arteries resulting in death. [Preview Abstract] |
Thursday, June 20, 2019 4:15PM - 4:30PM |
U6.00004: Investigation of dynamic failure properties of biological materials to model human soft tissues in primary blast injury James Lee, Danyal Magnus, David Sory, Mansoor Khan, William Proud Understanding the dynamic failure properties of soft tissues under high strain-rate is fundamental to the characterization of human organs under blast loading that leads to primary blast injuries. As organs, such as the gastrointestinal tract, are composed of soft tissues of varying properties and composition, it is necessary to identify the suitable proxy that sufficiently models these characteristics and test their behaviour under blast loading. This study aims to investigate the dynamic failure properties of natural and synthetic soft biological materials using the Shock Tube and the Split-Hopkinson Pressure Bar (SHPB) with the aims to establish a sufficient background for the development of a model that will replicate \textit{in vivo} conditions. An overview of methods of blast loading on samples will be presented, including the two-gauge measurement method on the SHPB, to address the longer loading duration requirement for the soft materials to reach stress equilibrium. The outcome of the study will illustrate the effectiveness of the data analysis using the proposed measurement methods. A comparative overview of the behaviour of different specimen will be outlined and the suitability of these materials as a proxy for the real organs will be discussed. [Preview Abstract] |
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