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Material Testing of Ovine Tissues for Thorax Development

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title
Material Testing of Ovine Tissues for Thorax Development
author
Thomas, Patricia K
abstract
Behind armor blunt trauma (BABT) occurs from an impact to body armor without penetration, and typically impacts the thorax. The impact causes the armor to deform and impact the body at a high rate, resulting in injury to the wearer. The use of ovine animal models in the study of injury biomechanics and BABT is increasing, due to their favorable size and other physiological characteristics. Along with this increase, there has also been increased interest in the development of in-silico ovine models for computational finite element studies to compliment experimental studies. However, there remains a gap in the literature characterizing ovine tissue properties, particularly those of ovine ribs and adipose tissue. The objective of this thesis was to characterize ovine cortical rib and adipose material properties and demonstrate the stability of each of the selected material models in simplified high-rate loading environments simulating BABT injury.Material properties of ovine ribs (n=1) were quantified using micro-CT imaging, quasi-static bending, and dynamic tensile testing. From the micro-CT scans, the cortical bone thickness and cross-sectional area were measured, and the second moment of area was calculated. Based on a linear regression least squares statistical model, the cortical bone thickness significantly varied spatially (p<0.05), whereas the cross-sectional area remained consistent (p > 0.05) based on the region of the cross-section and the position along the length of the rib. Quasi-static three-point bend testing was completed on ovine rib samples (n=4) to obtain the stiffness, maximum load, displacement at maximum load, yield load, displacement at yield load, failure load, and displacement at failure. For the dynamic testing, samples were cut into coupons and tested in tension with an average strain rate of 18.9 strains/s to calculate the elastic modulus, failure stress, and failure strain. The resulting rib material parameters were then inputted into a piecewise linear plasticity material model and tested in a tensile set-up similar to experiment. Due to the stability and success of these simulations, the material model was then inputted into a simplified model of the thorax that simulated a BABT environment. As for the characterization of ovine adipose tissue, we first utilized spherical indentation to obtain compressive material properties. A total of four samples of adipose tissue from two animals were obtained for spherical indentation testing, and each was tested at each loading rate (0.2, 2, 20, and 200 mm/s). The resulting coefficients were then input into a general viscoelastic model in LS-Dyna to determine material stability. A viscoelastic material model was selected due to the loading rate dependencies of adipose tissue, and this accounted for stress-relaxation behaviors. The first set of simulations were the same as the experimental set-up, which showed model validity. The material properties were finally incorporated into the simplified thorax model that was also utilized for the ribs to simulate a BABT environment. The use of these new ovine-specific material and mechanical properties of cortical ribs and adipose tissue greatly improved the fidelity of high-rate BABT simulations and showed that a viscoelastic material model that incorporates the loading rate is more biofidelic than existing models.
subject
Adipose
BABT
Cortical Rib
Dynamic
Finite Element Modeling
Material Testing
contributor
Gayzik, F. Scott (advisor)
Brown, Philip J (committee member)
Rahbar, Elaheh (committee member)
date
2023-09-08T08:35:28Z (accessioned)
2023 (issued)
degree
Biomedical Engineering (discipline)
embargo
2028-09-05 (terms)
2028-09-05 (liftdate)
identifier
http://hdl.handle.net/10339/102624 (uri)
language
en (iso)
publisher
Wake Forest University
type
Thesis

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