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You searched for +publisher:"Temple University" +contributor:("Crandall, Jeff R."). Showing records 1 – 2 of 2 total matches.

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Temple University

1. Laksari, Kaveh. Nonlinear Viscoelastic Wave Propagation in Brain Tissue.

Degree: PhD, 2013, Temple University

Mechanical Engineering

A combination of theoretical, numerical, and experimental methods were utilized to determine that shock waves can form in brain tissue from smooth boundary conditions. The conditions that lead to the formation of shock waves were determined. The implication of this finding was that the high gradients of stress and strain that could occur at the shock wave front could contribute to mechanism of brain injury in blast loading conditions. The approach consisted of three major steps. In the first step, a viscoelastic constitutive model of bovine brain tissue under finite step-and-hold uniaxial compression with 10 1/s ramp rate and 20 s hold time has been developed. The assumption of quasi-linear viscoelasticity (QLV) was validated for strain levels of up to 35%. A generalized Rivlin model was used for the isochoric part of the deformation and it was shown that at least three terms (C_10, C_01 and C_11) are needed to accurately capture the material behavior. Furthermore, for the volumetric deformation, a linear bulk modulus model was used and the extent of material incompressibility was studied. The hyperelastic material parameters were determined through extracting and fitting to two isochronous curves (0.06 s and 14 s) approximating the instantaneous and steady-state elastic responses. Viscoelastic relaxation was characterized at five decay rates (100, 10, 1, 0.1, 0 1/s) and the results in compression and their extrapolation to tension were compared against previous models. In the next step, a framework for understanding the propagation of stress waves in brain tissue under blast loading was developed. It was shown that tissue nonlinearity and rate dependence are key parameters in predicting the mechanical behavior under such loadings, as they determine whether traveling waves could become steeper and eventually evolve into shock discontinuities. To investigate this phenomenon, the QLV material model developed based on finite compression results mentioned above was extended to blast loading rates, by utilizing the stress data published on finite torsion of brain tissue at high rates (up to 700 1/s). It was shown that development of shock waves is possible inside the head in response to compressive pressure waves from blast explosions. Furthermore, it was argued that injury to the nervous tissue at the microstructural level could be attributed to the high stress and strain gradients with high temporal rates generated at the shock front and this was proposed as a mechanism of injury in brain tissue. In the final step, the phenomenon of shock wave formation and propagation in brain tissue was further studied by developing a one-dimensional model of brain tissue using the Discontinuous Galerkin finite element method. This model is capable of capturing high-gradient waves with higher accuracy than commercial finite element software. The deformation of brain tissue was investigated under displacement input and pressure input boundary conditions relevant to blast over-pressure reported in the…

Advisors/Committee Members: Darvish, Kurosh;, Sadeghipour, Keya, Margulies, Susan, Seibold, Benjamin, Crandall, Jeff R.;.

Subjects/Keywords: Engineering; Mechanical engineering; Biomechanics;

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Laksari, K. (2013). Nonlinear Viscoelastic Wave Propagation in Brain Tissue. (Doctoral Dissertation). Temple University. Retrieved from http://digital.library.temple.edu/u?/p245801coll10,242293

Chicago Manual of Style (16th Edition):

Laksari, Kaveh. “Nonlinear Viscoelastic Wave Propagation in Brain Tissue.” 2013. Doctoral Dissertation, Temple University. Accessed October 31, 2020. http://digital.library.temple.edu/u?/p245801coll10,242293.

MLA Handbook (7th Edition):

Laksari, Kaveh. “Nonlinear Viscoelastic Wave Propagation in Brain Tissue.” 2013. Web. 31 Oct 2020.

Vancouver:

Laksari K. Nonlinear Viscoelastic Wave Propagation in Brain Tissue. [Internet] [Doctoral dissertation]. Temple University; 2013. [cited 2020 Oct 31]. Available from: http://digital.library.temple.edu/u?/p245801coll10,242293.

Council of Science Editors:

Laksari K. Nonlinear Viscoelastic Wave Propagation in Brain Tissue. [Doctoral Dissertation]. Temple University; 2013. Available from: http://digital.library.temple.edu/u?/p245801coll10,242293


Temple University

2. Shafieian, Mehdi. Toward a Universal Constitutive Model for Brain Tissue.

Degree: PhD, 2012, Temple University

Mechanical Engineering

Several efforts have been made in the past half century to characterize the behavior of brain tissue under different modes of loading and deformation rates; however each developed model has been associated with limitations. This dissertation aims at addressing the non-linear and rate dependent behavior of brain tissue specially in high strain rates (above 100 s-1) that represents the loading conditions occurring in blast induced neurotrauma (BINT) and development of a universal constitutive model for brain tissue that describes the tissue mechanical behavior from medium to high loading rates.. In order to evaluate the nature of nonlinearity of brain tissue, bovine brain samples (n=30) were tested under shear stress-relaxation loading with medium strain rate of 10 s-1 at strain levels ranging from 2% to 40% and the isochronous stress strain curves at 0,1 s and 10 s after the peak force formed. This approach enabled verification of the applicability of the quasilinear viscoelastic (QLV) theory to brain tissue and derivation of its elastic function based on the physics of the material rather than relying solely on curve fitting. The results confirmed that the QLV theory is an acceptable approximation for engineering shear strain levels below 40% that is beyond the level of axonal injury and the shape of the instantaneous elastic response was determined to be a 5th order odd polynomial with instantaneous linear shear modulus of 3.48±0.18 kPa. To investigate the rate dependent behavior of brain tissue at high strain rates, a novel experimental setup was developed and bovine brain samples (n=25) were tested at strain rates of 90, 120, 500, 600 and 800 s-1 and the resulting deformation and shear force were recorded. The stress-strain relationships showed significant rate dependency at high rates and was characterized using a QLV model with a 739 s-1 decay rate and validated with finite element analysis. The results showed the brain instantaneous elastic response can be modeled with a 3rd order odd polynomial and the instantaneous linear shear modulus was 19.2±1.1 kPa. A universal constitutive model was developed by combining the models developed for medium and high rate deformations and based on the QLV theory, in which the relaxation function has 5 time constants for 5 orders of magnitude in time (from 1 ms to 10 s) and therefore, is capable of predicting the brain tissue behavior in a wide range of deformation rates. Although the universal model presented in this study was developed based on only shear tests and the material parameters could not be found uniquely, by comparing the results of this study with previously available data in the literature under tension unique material parameters were determined for a 5 parameter generalized Rivlin elastic function (C10=3.208±0.602 kPa, C01=4.191±1.074 kPa, C11=79.898±18.974 kPa, C20=-37.093±7.273 kPa, C02=-37.712±5.678 kPa). The universal constitutive model for brain tissue presented in this dissertation is capable of characterizing the brain tissue…

Advisors/Committee Members: Darvish, Kurosh, Meaney, David F., Arbogast, Kristy B., Kiani, Mohammad F., Cohen, Richard, Crandall, Jeff R..

Subjects/Keywords: Biomechanics; Blast Neurotrauma; Brain Biomechanics; Finite Element Modeling; Quasilinear Viscoelasticity; Traumatic Brain Injury

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Shafieian, M. (2012). Toward a Universal Constitutive Model for Brain Tissue. (Doctoral Dissertation). Temple University. Retrieved from http://digital.library.temple.edu/u?/p245801coll10,204511

Chicago Manual of Style (16th Edition):

Shafieian, Mehdi. “Toward a Universal Constitutive Model for Brain Tissue.” 2012. Doctoral Dissertation, Temple University. Accessed October 31, 2020. http://digital.library.temple.edu/u?/p245801coll10,204511.

MLA Handbook (7th Edition):

Shafieian, Mehdi. “Toward a Universal Constitutive Model for Brain Tissue.” 2012. Web. 31 Oct 2020.

Vancouver:

Shafieian M. Toward a Universal Constitutive Model for Brain Tissue. [Internet] [Doctoral dissertation]. Temple University; 2012. [cited 2020 Oct 31]. Available from: http://digital.library.temple.edu/u?/p245801coll10,204511.

Council of Science Editors:

Shafieian M. Toward a Universal Constitutive Model for Brain Tissue. [Doctoral Dissertation]. Temple University; 2012. Available from: http://digital.library.temple.edu/u?/p245801coll10,204511

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