Department of Aerospace Engineering and Mechanics

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Browsing Department of Aerospace Engineering and Mechanics by Subject "Biomechanics"

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    Biofidelic soft composites– experimental and computational modeling
    (University of Alabama Libraries, 2017) Chanda, Arnab; Unnikrishnan, Vinu U.; University of Alabama Tuscaloosa
    Biofidelic soft composites or tissues form the building blocks of the human body. Understanding the complex mechanics of these soft composites is the key to understanding the genesis and progression of disease. Biomechanically, soft composites exhibit anisotropic mechanical behavior and comprise of multiple fiber layers within a soft matrix. To date, there is a lack of understanding of the anisotropic mechanical behavior of soft composites, primarily due to unavailability of a robust characterization framework. In this dissertation, novel multiscale computational and experimental investigation models are developed to simulate and characterize anisotropic soft composite mechanical behavior. Soft composite surrogates were first developed to simulate various tissues in the human body namely the skin, brain, artery and vaginal tissues. Novel anisotropic soft composite models were also fabricated taking into consideration the tissue anisotropy and multifunctional properties. Hyperelastic anisotropic constitutive relationships were formulated to precisely characterize the mechanical behavior of soft composite considering varying fiber and matrix contributions, fiber-matrix interactions, fiber orientations and multiple fiber layers. Coupled with high fidelity experimental and computational models, microscopy, and Digital Image Correlation (DIC) studies, the damage and repair of soft composite surrogates are also discussed in this dissertation, with relevance to soft tissue wounds and suture. Computational modeling to understand the interaction between multiple soft composite systems and its effect on soft composite damage are also highlighted in this work. Some specific soft composite interaction systems modeled were the female pelvic system under abdominal loads, whole body impact due to blast, and ulceration in diabetic foot. This dissertation lays the foundation for micro and macro scale anisotropic soft composite modeling and characterization using high fidelity experimental and numerical techniques which will be indispensable for studying tissue mechanics and other soft composite applications in engineering and medicine.
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    Effect of increased intracranial pressure on blood flow through cerebral arteries and aneurysms -a fluid-structure interaction study
    (University of Alabama Libraries, 2016) Syed, Hasson Basha Quadri; Unnikrishnan, Vinu U.; University of Alabama Tuscaloosa
    The pathological changes due to many cerebral diseases lead to increase in intracranial pressure (ICP), which is a life threatening condition especially in severe head injuries such as traumatic brain injury, hydrocephalus, sub arachnoid hemorrhage etc. Elevated intracranial pressure (ICP) is a major contributor to morbidity and mortality in severe head injuries. Maintaining the ICP within acceptable range is important to contain the failure of auto regulation which maintains and regulates adequate cerebral blood flow inside the brain. These increased intracranial pressures are found to significantly affect the Wall Shear Stresses (WSS) distribution in the artery, which is an important hemodynamic parameter and may lead to the formation, progression and rupture of cerebral aneurysms (pathological dilatations in cerebral arteries) which go unnoticed until a stage when they are severe. Earlier research on cerebral arteries and aneurysms involves using constant mean ICP values. Recent advancements in ICP monitoring techniques have led to measurement of the ICP waveform and by incorporating time varying ICP waveform in the analysis of cerebral arteries helps in better understanding their effects on wall deformation and shear stresses. To date, such a robust computational study on the effect of increasing intracranial pressures on the cerebral arterial walls and aneurysms has not been attempted to the best of our knowledge. In this work, fully coupled fluid structural interaction (FSI) simulations are carried out to investigate the effect of variation of intracranial pressure (ICP) waveforms on the cerebral arterial walls and aneurysms. Three time varying ICP waveforms and three constant ICP profiles acting on the cerebral arterial wall are analyzed in this work. It has been found that the arterial and aneurysmal walls experiences significant deformation depending on the time varying ICP waveforms, while the WSS changes at peak systole for all the ICP profiles. Also, the maximum wall shear stresses decreased with increase in ICP inside the aneurysm dome and the minimum area of WSS distribution increased.
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    A multiscale analysis of blast impact mitigation on the human head
    (University of Alabama Libraries, 2014) Jenson, Daniel Bryan; Unnikrishnan, Vinu U.; University of Alabama Tuscaloosa
    The effectiveness of helmets in preventing shrapnel wounds and internal damage due to blast shock waves has been studied. Carbon nanotubes and similar nanostructures have also recently generated heightened interest due to their strength-to-weight ratio and other unique properties. Therefore, to understand and develop a helmet with improved protection, it is necessary to develop computational procedures that will enable the accurate modeling of traumatic head injuries as well as the precise measurement of the mechanical properties of nanostructures and how these characteristics behave when embedded as an advanced composite structure into a helmet. In this study, a multiscale simulation strategy is used to estimate the mechanical characteristics of advanced composite structures with embedded nanostructures. In most of the previous theoretical works, an analysis dedicated to improving the design of the helmet using composite structures was not included due to a lack of understanding of the interactions of the nanostructures with the matrix materials. In this work, the role of the helmet on the over pressurization and impulse experienced by the head during blast shock wave and blunt force trauma due to shrapnel impacts is studied. In addition, the properties of nano-composite structures are estimated using molecular dynamics (MD) simulations and then scaled to the macroscopic level using continuum mechanic formulations. This modeling is further developed using Finite Element (FE) analysis to demonstrate the effectiveness of various types of nanostructures in energy absorption. An analysis is carried out on a model of an unprotected head to compare the results to those obtained when protected by a helmet containing different nanostructures. The developed multiscale model is used to improve the composition of helmets and the general understanding of the effects of blast shock wave and shrapnel impacts thereby leading to the mitigation and prevention of traumatic head injuries.