Browsing by Subject "pressure"

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    Impact Force and Stress Distribution of Drop Impact
    (2021-08) Sun, Ting-Pi
    Drop impact is ubiquitous and relevant to many important natural phenomena and industrial applications. Although the kinematics of drop impact has been extensively studied through simulations and high-speed imaging, the understanding of drop impact is still far from fully understood. The studies of dynamics such as the impact force and the stress distribution of drop impact are still relatively scarce. The impact force and the stress distribution lead to the most important consequence throughout the industrial processes and are crucial factors to erosion on substrates or waterjet cutting. Here, we systematically investigate the impact force and the stress distribution of drop impact through experimental studies. To measure the impact force of drop impact, we synchronize the high-speed camera and the piezoelectric force sensor to obtain the temporal evolution of the impact force and the morphology of drop impact over several orders of magnitudes of Re. We verify the force-time scaling proposed by the self-similar theory at the high $Re$ regime. In the finite Re regime, we consider the effects from the viscosity of liquids and analyze the scaling by using a perturbation method, which matches our experimental results very well. The influence of viscoelasticity is also discussed. To obtain the temporal evolution of the stress distribution, which has not been measured experimentally, we develop a novel technique "high-speed stress microscopy." We confirm the propagation of the self-similar non-central maximum pressure and shear stress predicted by theories, and the shear force is also quantified. Moreover, we discover the impact-induced surface shock waves, which are crucial to the origin of erosion induced by drop impact. Furthermore, we measure the shear stress distribution of drop impact on micropatterned surfaces with high-speed stress microscopy. We investigate the influence of micropillars on substrates to the displacement distribution, the shear stress distribution, and the shear force. We hypothesize that the change of shear stress distribution may result from the formation of vortices. Finally, the results show that on the micropatterned surface, the maximum shear stress is suppressed, which is helpful for mitigating erosion to substrates. Our studies provide the experimental results for understanding the dynamics of drop impact. In addition to the pioneering works of measuring the stress distribution, high-speed stress microscopy can be applied to complicated conditions such as non-Newtonian drop impact and varying the ambient pressure. Besides, it opens the door for experimental exploration of the detailed information inside an impacting drop, including the patterns of the flow and the boundary layer.
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    Temperature and Pressure Effects on Tissue Sealing and Protein Denaturation
    (2016-05) Scheumann, Joel
    Tissue sealing is an attractive method for tissue sealing in laparoscopic (minimally in-vasive) surgeries as it does not leave any materials in a patient’s body. Most of the re-search for tissue sealing has been concerned on the end-goal results of burst pressure, and not as much time has been spent investigating the more fundamental properties of tissue sealing which include temperature, pressure, time, vessel composition, disease state, and sealing modality (i.e., thermal, radiofrequency, and ultrasonic). This work in-vestigates temperature and pressure by studying how these parameters affect collagen denaturation and burst pressure. Ethicon provided carotid arteries that were sealed under controlled temperature and pressure with a constructed Thermal Jig. Additionally, dena-turation of collagen was studied with the use of carotid arteries and rat tail tendons with the use of FTIR spectroscopy under temperature and pressure control from an ATR ac-cessory. From the research, it was determined that the burst pressure was highest with the temperature of 140ºC. Changing the weight from 20lb to 50lb did not yield any sig-nificant difference. The results for burst pressure from the treatments of 100ºC;80psi;30s, 100ºC;330psi;30s, 140ºC;80psi;30s, and 140ºC;330psi;30s were 188.4 ± 55.3mm Hg, 439.9 ± 232.6mm Hg, 647.3 ± 241.3mm Hg, and 678.1 ± 153.7mm Hg, respectively. Denaturation onset was observed to be delayed with the application of pressure. For rat tail tendon, denaturation onset was observed to be 58.0 ± 2.5ºC and 60.1 ± 4.9ºC for loads of 0N and 2N, respectively. For carotid artery, the denaturation onset was observed to be 59.8 ± 0.7ºC, 59.8 ± 1.9ºC, 79.1 ± 4.3ºC, indeterminable, and indeterminable for loads of 0N, 2N, 10N, 20N, and 50N, respectively. To form an effec-tive seal one must increase the temperature above 100ºC. Additionally, the denaturation was delayed significantly as the load was increased. This mechanical pressure correlates with results from osmotic pressure that also cause a delay in protein denaturation. Fu-ture work should investigate protein denaturation to higher temperature and tissue fu-sion by varying disease state of arteries, tissue composition (i.e., collagen and elastin content), and sealing time.