Scholarly Works, Materials Science and Engineering (MSE)

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https://hdl.handle.net/10919/24370
Research articles, presentations, and other scholarship

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Browsing Scholarly Works, Materials Science and Engineering (MSE) by Department "Biomedical Engineering and Mechanics"

Now showing 1 - 5 of 5
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    Adaptive process control for achieving consistent particles' states in atmospheric plasma spray process
    Guduri, B.; Cybulsky, Michael; Pickrell, Gary R.; Batra, Romesh C. (2021-02-08)
    The coatings produced by an atmospheric plasma spray process (APSP) must be of uniform quality. However, the complexity of the process and the random introduction of noise variables such as fluctuations in the powder injection rate and the arc voltage make it difficult to control the coating quality that has been shown to depend upon mean values of powder particles' temperature and speed, collectively called mean particles' states (MPSs), just before they impact the substrate. Here, we use a science-based methodology to develop a stable and adaptive controller for achieving consistent MPSs and thereby decrease the manufacturing cost. We first identify inputs into the APSP that significantly affect the MPSs and then formulate a relationship between these two quantities. When the MPSs deviate from their desired values, the adaptive controller is shown to successfully adjust the input parameters to correct them. The performance of the controller is tested via numerical experiments using the software, LAVA-P, that has been shown to well simulate the APSP.
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    Nanoindentation of thin films: Simulations and experiments
    Nair, A. K.; Cordill, M. J.; Farkas, Diana; Gerberich, W. W. (Cambridge University Press, 2009-03-01)
    Atomistic Simulations of nanoindentation of a 20-nm-thick Ni thin film oriented in the [111] direction were carried out to study the effects of indenter velocity and radii, interatomic potentials, and the boundary conditions used to represent the substrate. The simulation results were compared directly with experimental results of Ni thin film of the same thickness and orientation. It was found that the high indenter velocity does not affect the hardness value significantly. Different radii used for indentation also have negligible effects on the hardness value. Two different interatomic potentials were tested, giving significantly different hardness values but both within 20% of the experimental result. Different boundary conditions used to represent the substrate have a significant effect for relatively deep indentation simulations.
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    Seasonal changes in morphology govern wettability of Katsura leaves
    Kang, Hosung; Graybill, Philip M.; Fleetwood, Sara; Boreyko, Jonathan B.; Jung, Sunghwan (PLOS, 2018-09-27)
    Deciduous broad-leaf trees survive and prepare for winter by shedding their leaves in fall. During the fall season, a change in a leaf's wettability and its impact on the leaf-fall are not well understood. In this study, we measure the surface morphology and wettability of Katsura leaves from the summer to winter, and reveal how leaf structural changes lead to wettability changes. The averaged contact angle of leaves decreases from 147 degrees to 124 degrees while the contact-angle hysteresis significantly increases by about 35 degrees, which are attributed to dehydration and erosion of nano-wax. Due to such wettability changes, fall brown leaves support approximately 17 times greater water volume than summer leaves.
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    Time-dependent damage evolution and failure in materials. I. Theory
    Curtin, William A. Jr.; Scher, H. (American Physical Society, 1997-05-01)
    Damage evolution and time-to-failure are investigated for a model material in which damage formation is a stochastic event. Specifically, the probability of failure at any site at time t is proportional to sigma(i)(t)(eta), where sigma(i)(t) is the local stress at site i at time t and differs from the applied stress because of the stress redistribution from prior damage. An analytic model of the damage process predicts two regimes of failure: percolationlike failure for eta less than or equal to 2 and ''avalanche'' failure for eta > 2. In the percolationlike regime, failure occurs by gradual global accumulation of damage culminating in a connected cluster which spans the system. In the avalanche regime, failure occurs by rapid growth of a single crack after a transient period during which the critical crack developed. The scalings of the transient period, the subsequent crack dynamics, and the time-dependent probability distribution for failure are determined analytically as functions of the system size and the exponent eta. Specific predictions are that failure is more abrupt with increasing eta, failure times scale inversely with a power of the logarithm of system size, and the distribution of failure times is a double exponential and broadens with increasing eta, so that the failure becomes less predictable as it is becoming more abrupt. The conditions for the transition to the rapid growth regime are identified, offering the possibility of early detection of impending failure. In a companion paper, numerical simulations of this failure process in two-dimensional lattices are compared in detail to the analytical predictions.
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    Toughening in disordered brittle materials
    Curtin, William A. Jr. (American Physical Society, 1997-05-01)
    The growth of a planar crack through a heterogeneous brittle material is investigated using a discrete cubic lattice of springs with distributed spring toughnesses and lattice Green's functions to determine crack propagation. The toughness, or stress required to grow an initial crack, is found to be a stochastic quantity and depends on the width of the distribution. For narrow distributions, the toughness is less than the thermodynamic value and is controlled by the nucleation of kinks at low toughness regions (weakest links), which then grow laterally in an unstable manner. For brood distributions, the average toughness approaches the thermodynamic value, with some specific configuration having greater values, and is controlled by high toughness regions pinning a rough crack front. The rough crack front exhibits nontrivial scaling with crack width and a ''strongest-link'' behavior that differs from the usual weak-link behavior found in weakly disordered materials. Materials with broad distributions are also less sensitive to small preexisting defects. The difference in toughness between narrow and broad distributions is only about 10%; that is much smaller than suggested by similar studies on 2d materials and demonstrates the very important role played by geometry-dimensionality in this problem. One implication of these results is that toughness in complex or heterogeneous materials does not stem from simple disorder in toughnesses; more complex and microstructure-specific mechanisms such as microcracking and grain bridging must occur.