Development of a computer controlled engine-fluid power drive system for replacing mechanical tractor power take-off (PTO) shafts

Thomas, Roderick Scott The Pennsylvania State University 2001 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Nearly all tractor PTO arrangements used today consist of a rotating mechanical shaft with two or more universal joints. This arrangement has proven to be a hazard to farm workers. Commonly, PTO accidents involve the snagging of clothes resulting in the victim being rapidly and violently drawn into (and around) the rotating shaft. By driving the PTO load with fluid power, this entanglement hazard could be eliminated. This project included the design, development, and testing of an experimental tractor based on a John Deere 4040. To support direct laboratory and in-field comparison of hydraulic and mechanical scenarios, the research tractor was equipped with a computer controlled engine-fluid power PTO and ground drive system while leaving the original transmissions intact and fully functional. Since lack of efficiency is one of the principle drawbacks to the application of fluid power, evaluating the power efficiency of the hydraulic system in comparison with current designs is key to proving feasibility. Results show that at low power demand, the hydraulic system is more efficient than the mechanical equivalent, however the mechanical version remains more efficient over most of the load range and is capable of higher power output. The use of computer control helps to minimize fuel consumption in this engine-fluid power drive system by matching engine speed to loading conditions while maintaining operating speeds. Testing indicates that a hydraulic PTO system for the JD 4040, has the potential to increase fuel efficiency compared to its mechanical counterpart, up to about 44% of the maximum mechanical PTO output. Maximum power output in the hydraulic mode has the potential to be 80% of that achieved by the mechanical equivalent. For the wheel drive system, testing indicates that the hydraulic mode has the potential to increase fuel efficiency compared to its mechanical counterpart, up to about 40% of the maximum mechanical output. Maximum output in the hydraulic mode has the potential to be 70% of that achieved by the mechanical drive. A 30% more powerful engine is required if the hydraulically driven tractor is to perform all of the same tasks as it's mechanical counterpart.

특성화 고등학교 기계전문교과에 나타난 삼각함수 관련 단원 분석을 통한 수업 개선방안연구

김준수 인천대학교 교육대학원 2023 국내석사

4차 산업시대를 맞이하여 사회의 많은 분야가 새롭게 변화하고 탄생하고 있으며, 특성화 고등학교도 시대의 흐름에 맞추어 다양한 교육과정을 운영해오고 있다. 사회수요에 따른 인력배출 유형을 조절하고 새로운 학과를 신설하는 등의 노력을 하고 있다. 지역별 특성을 반영하여 특색 있는 특성화 고등학교를 만들고 있다. 세심한 현장 조사와 교사의 노력에도 불구하고 지역 간 학습 내용 편차가 심화되고 있다. 일부지역에서는 특성화 고등학교를 취업의 수단으로만 간주하여 교육 내용의 다양화를 하지 못하고 있다. 더욱이 교육과 현장에서 사용하는 용어의 괴리도 심각하다. 사용 도구의 명칭이 지역과 학교, 현장에서 모두 다르게 사용하다보니 학생이 느끼는 혼란함은 교육의 혼란함으로 이어지고 있다. 산업체가 학생에게 요구하는 기초 능력은 점점 심화되고 있다. 교육부도 상황을 인지하여 2016년부터 국가 주도의 전문 교과 교육과정을 배포·운영하고 있다. 학교의 교육과정을 개선해 나가고 있지만 학생별 개별화 맞춤 수업까지는 이어지지 못하고 있는 실정이다. 학생이 의지할 수 있는 교과서에는 학습의 계속성이 부족한 경우도 여럿 존재한다. 계열성도 뒤바뀐 경우가 여럿 존재한다. 계속성이 부족하면 학습의 흐름이 단절되어 학습 내용이 장기기억으로 저장되지 않는다. 계열성이 제대로 잡혀 있는 않은 상태에서 난이도가 너무 높은 학습을 만나게 되면 학습을 되레 포기하게 되는 현상이 발생하게 된다. 2015개정 교육과정에서 요구하는 학습중도포기자를 줄이는 방안을 실현시키기 위해서는 학생이 현장에서 배우는 교과의 분석을 보다 면밀하게 진행할 필요가 있다. 이에 본 연구는 특성화고등학교 기초과목인 기계공작법과 기계설계 과목에서 삼각함수와 관련된 단원 연구를 진행하고자 한다. 삼각함수는 실제적 문제를 해결해야 하는 기계 공학에 반드시 필요한 분야이다. 하지만 내용의 어려움 때문에 특성화 고등학교 학생이 기계 교과 학습을 포기하게 되는 주요 원인 중 하나이다. 연구를 통해 교과에 나타난 문제점을 파악하고 향후 교과의 발전 방향을 도모하고자 한다. 이를 위해 다음과 같은 연구 문제를 제시하였다. 1) 기계 교과에 나타난 삼각함수 관련 단원은 특성화고 학생이 학습하기 적절한가? 선정한 연구 문제를 해결하기 위해 수학교과에 나타난 삼각함수 내용을 분석하여 제시하였다. 해당 삼각 함수 단원이 사용되는 기계교과 내용을 언급하고 내용 전개 방법에 대한 수준을 언급하였다. 다음 기계 교과에서 삼각함수 내용이 포함된 단원을 분석하여 제시 하였다. 기계 전문 교과의 단원에서 사용되는 삼각함수를 언급하고 수학교과에서 배운 내용과 비교하였고 학생이 받아들이기 적절한지에 대해 제시하였다. 다음 국가직무능력표준의 평가 준거를 기준으로 기계 전문교과의 내용이 적절한지 판단하였고 부족하다면 추가해야 될 내용을 제시하였다. 본 연구를 통해 얻어진 결과는 다음과 같다. 이전 개정 교과에 비해 난이도가 많이 낮아지고 삭제된 단원도 많이 보인다. 하지만 계속성, 계열성이 벗어난 단원과 수학교과에서 학습하지 않은 내용이 기계교과에 등장하는 단원이 존재한다. 현재 현장 교사의 추가 학습을 통해 학습자의 혼란을 막고 있지만 교육부 차원에서 개선과 개정이 필요하다. Due to the Fourth Industrial Revolution, many aspects of society are newly forming and developing. Specialized high schools have been managing various curriculums in order to keep up with societal trends. Efforts are being made to adjust the type of future workforce based on social demand and to create new majors. Distinct specialized high schools are being established with regional characteristics in mind. Despite efforts by teachers and field surveys, differences in curriculum between regions are intensifying. Since certain regions view specialized high schools as a means of employment, the curriculum has not been expanding. Moreover, the gap between academic terminology and practical terminology is also significant. Students are confused because tool names differ by school, region, and work, leading to educational chaos. Basic skills required by industry are becoming more sophisticated. Being aware of the situation, the Ministry of Education has been distributing and operating a national professional curriculum since 2016. Although the school curriculum has been improving, individualized custom classes have not been possible. There are several cases of textbooks, which students rely on, lacking educational continuity. Cases also exist where learning sequencing is disordered. When educational continuity is lacking, the flow of material is interrupted, and course content does not get stored as long-term memory. If learning sequencing is not properly established while engaging in advanced courses, then there are many instances of giving up. In order to carry out the plan to reduce the dropout rate in the 2015 revised educational curriculum, it is necessary to conduct a thorough examination of the teaching that students receive in class. Therefore, this research aims to conduct a study on units containing trigonometric functions, which is part of the manufacturing process and machine design, core subjects of specialized high schools. Trigonometric functions are necessary to solve practical problems in mechanical engineering. However, due to its difficulty, it is one of the main reasons why high school students give up on mechanical engineering. The purpose of the research is to identify problems in the curriculum and to promote a better educational direction. The following question was considered for research. 1) Is the trigonometric functions unit in mechanical engineering appropriate for specialized high school students? To answer the research question, the contents of trigonometric functions in the mathematical curriculum were analyzed and presented. The mechanical engineering unit containing trigonometric functions was mentioned as well as the difficulty of the content development method. Next, the unit containing trigonometric functions in mechanical engineering was analyzed and presented. The trigonometric functions unit in the mechanical engineering curriculum was compared to that in the mathematical curriculum and questioned whether it was an appropriate difficulty for students. Then, based on the evaluation criteria of the NCS(National Competency Standard), it was determined whether the mechanical engineering curriculum was appropriate, and if insufficient, what contents were needed. The results of the research are as follows. Compared to previously revised curriculums, the difficulty is much lower, and many units have been omitted. However, there are mechanical engineering units lacking educational continuity and sequencing, as well as containing material not taught in the mathematical curriculum. Currently, teachers are providing extra lectures to prevent students’ confusion in learning, but improvements and revisions are necessary by the Ministry of Education.

Mechanical stress engineering for the shape design of DNA origami structures

김영주 서울대학교 대학원 2020 국내박사

In this thesis, we describe two design strategies that engineer mechanical stress to program static or dynamic conformations of the DNA origami structure. DNA origami nanotechnology facilitated the self-assembly of DNA strands into any conceivable shape encoded by their rationally designed sequences. Mechanics-based design approaches have played an important role in improving the structural diversity of the DNA origami structures. Due to low twist controllability and limited reconfiguration mode, however, they have still limitations in achievable diversity or complexity in structural shapes and their reconfigurations and their applications. To this end, first, we developed a design strategy for fine control of twisted DNA origami structures by considering not only amount of geometrical perturbations but also their arrangements within the structures. With the configurational design of geometrical perturbations, we can program various distributions of the mechanical stress enabling a fine control over twist rate of DNA origami structures. Second, we developed a design strategy that transforms a two-dimensional structure into three-dimensional supercoiled one on demand. We employed the topological invariant property to convert a simple twist deformation into complex bending one leading to supercoiling of the DNA origami structure. We expect that our mechanical stress programming strategies can be utilized to design DNA origami structures with desired shapes or reconfiguration motions and enhance the performance of functional structures. 본 학위논문은 목표하는 정적 및 동적 형상을 지닌 DNA 오리가미 구조 제작을 위한 기계적 응력 조절 기술에 기반한 설계방법을 제시한다. DNA 오리가미 나노기술은 DNA 가닥들의 자가조립 과정을 통해 기존에 제작이 어려웠던 다양한 형상의 나노구조물을 손쉽게 만들 수 만들 수 있다. 이를 활용해 목표 형상의 나노구조물을 만들기 위해 다양한 설계 방법들이 제시되어 왔다. 이중 역학적 원리에 기반한 설계 방법은 구조 내부에 의도적으로 기계적 스트레스를 발생시켜 구조의 비틀림, 굽힘 등을 정량적으로 조절할 수 있게 만들어, 제작 가능한 형상의 범주를 넓히는데 크게 기여하였다. 하지만 기존 방법들은 세밀한 비틀림 형상 제어가 어렵다는 점 그리고 제한된 종류의 형상변화만이 가능하다는 문제점으로 인해 목표 형상을 지닌 정적 혹은 동적 구조의 제작 및 이러한 구조들의 활용에 어려움이 존재한다. 이에 해결책으로써 본 연구는 다음과 같은 기계적 응력 조절 기술들을 제시한다. 첫째, 구조 내 기하학적 섭동의 분포 설계 통해 DNA 오리가미 구조물의 세밀한 비틀림 형상 조절을 위한 설계 방법을 제시한다. 이를 이용한 구조 내 변형 에너지의 조절을 통해, 미세한 비틀림 형상 조절이 가능해진다. 둘째, 단순한 2차원 구조물을 복잡한 3차원 형상의 구조물로 변환시키는 형상 변환 메커니즘을 제안한다. 양끝이 이어진 닫힌 구조가 지닌 위상학적 불변성을 이용해, 국부적 비틀림을 전역적 굽힘 변형으로 변환시킴으로써, DNA 오리가미 구조의 슈퍼코일링 현상을 제시한다. 이러한 기계적 응력 조절 기술들은 원하는 형상 및 변화 움직임을 지닌 DNA 나노구조물의 설계에 활용되어 기능성 나노구조물들의 성능을 향상시키는데 기여할 것이라고 기대된다.

Nano-mechanics of Optical Structures for High Laser-Damage Threshold Applications

Mehrotra, Karan University of Rochester 2016 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation focuses on the use of scanning electron microscopy (SEM), nano-indentation and finite-element analysis (FEA) to observe, measure and validate the nano-mechanical properties (elastic modulus, hardness, yield stress, deformation, fracture) of nm-level features in important optical micro- and nano-structures. The optical micro- and nano-structures include single layer oxide films, multilayers comprised of oxide layers, and optical diffraction gratings. In addition to the nano-mechanical properties, we also study the deformation in brittle (amorphous) silica walls that comprise the diffraction grating by suppressing fracture as well as on the nano-mechanics of defects in optical structures. We use this understanding of nano-mechanics in diffraction gratings to show that it naturally complements optical testing (laser-induced damage threshold tests), and mechanical fields (for example, deformation fracture strain) expose the same regions of the grating structure in a manner analogous to optical fields (for example, electric fields). In Chapter 2 we use nano-indentation to perform mechanical characterization of optical oxide single-layer and multi-layer thin films, and the results are interpreted based on the deposition conditions used. These oxide films are generally deposited to have a porous microstructure that is optimized to maximize the laser induced damage thresholds, but changes in deposition conditions lead to varying degrees of porosity, density, and possibly the microstructure of the thin film. Of the four single-layer thin films tested, alumina was observed to demonstrate the highest values of nano-indentation hardness and elastic modulus. We also demonstrate how single-layer thin film data may be used in the analysis of multilayer thin films and present an experimental study of indentation size effects (ISE) on multilayer thin films (silica-hafnia system). These multilayer coatings show a decrease in hardness for an increase in indentation loads when using a Cube-corner tip. The data are interpreted using the Nix & Gao model of gradient plasticity, and predicts an excellent correlation between for the depth dependence of hardness in our silica-hafnia multilayer thin films. In Chapter 3 we characterize "blisters", defects observed in multilayer dielectric (MLD) coatings after exposure to acid cleaning procedures. Nano-indentation is used to make site-specific indentations across blisters to measure the mechanical response, especially their elastic compliance under different conditions of loading. Two regions of statistically different mechanical response are identified within a blister defect and compared to the undisturbed regions of the MLD coating. We conclude that different blisters follow the general trend that maximum compliance is always seen in the "extended region" of the blister, furthest from the blister's initiating nodule/scratch and the coating age might have an effect on the indentation response for larger depths of penetration into the thin film. Additionally, our numerical model is used to estimate the extent of "blistering" in a coating, a result verified through cross-sectional SEM images of the "blister" defect. In Chapter 4 we measure the mechanical response of optical multilayer dielectric (MLD) diffraction gratings, geometries which are constrained in only one transverse direction but free in the other, using nano-indentation. Primarily, 2 types of indentation response were observed: indents almost perfectly centered on a particular grating "wall", without extending to a sidewall or the edge and without disturbing any adjacent walls; and indents made off-center on a "wall" which were catastrophic even at the same low load. The indentation record of load versus displacement uniquely distinguishes these two regimes, and is also correlated to the properties of bulk surfaces. The centered indents allow us to invoke a state of entirely ductile deformation and measure the yield stress of silica at the nm-scale (∼4.1--4.6 GPa). The direct measurement of yield stress if silica at the nm-level is an exciting result. Off-centered indents at the same loads fracture the grating walls and this is used to hypothesize a fracture mechanism and measure an estimate of fracture stress (∼1.1--3.3 GPa). Non-linear, 3-D FEA using ABAQUSRTM validates our experimental results as well as the deformation mechanism. Finally, in Chapter 5 we use the "slightly" off-centered indents on the gratings walls to study a combined response of ductility and fracture. Load-displacement curves in conjunction with observations from SEM images provide estimates of fracture strain. Mechanical field thresholds, represented by fracture strain, are used to correlate nano-mechanical damage in gratings to their optical performance (measured through laser-induced damage thresholds). FEA reveals that nano-indentation tests expose the same regions on the grating structure as an optical test. Here we draw attention to the important effects of inhomogeneities and non-uniformities (geometrical and material) in concentrating mechanical fields. Therefore, nano-mechanical testing complements and could even precede optical testing to gauge the performance of diffraction gratings. (Abstract shortened by UMI.).

Experts and novices: Differences in their use of mental representation and metacognition in engineering design

Dixon, Raymond Anthony University of Illinois at Urbana-Champaign 2010 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Research shows that mental representation such as analogical reasoning is a fundamental cognitive tool for design problem solving (Daugherty & Mentzer, 2008; Hey, Lensey, Agogino, & Wood, 2008; Lewis, 2008). Not much is known, however, about the way students and professional engineers actively generate and change their mental representation when solving a engineering design problem. There are very few studies that show how different types of mental representations; such as metaphors, propositions, and analogies; interplay with higher order cognitive processes; such as planning, monitoring, and evaluation; as engineering designers navigate their problem and solution spaces. This empirical study investigated the mental representation and metacognitive regulation of student and professional engineers while they solve an engineering design problem. The intent is to gain a deeper insight in the differences that exists in the cognitive process of engineering students and professional engineers. The research questions guided this study were (a) How do the mental representations (propositions, metaphors, and analogies) of student and professional engineers differ in their problem and solution spaces in terms of their frequency, types, and attributes? (b) How does the metacognitive regulation (planning, monitoring, and evaluation) of student and professional engineers differ in their problem and solution spaces in terms of their frequency and characteristics? and (c) How do the mental representation and metacognitive regulation of students and professional engineers relate to their overall engineering design strategy? Concurrent and retrospective verbal protocols were collected from six mechanical engineering students and four professional mechanical engineers as they solved an engineering design problem. Their verbalizations were audio recorded, transcribed, and coded. The conclusions drawn from the data were: the use of mental representations such as propositions, analogies, and metaphors by experts and novice engineering designers in the different mental spaces are important in engineering design. Expert engineering designers use analogies differently in their solution space than do novice engineering designers. Expert engineering designers rely on within-domain analogies, between-domain analogies, heuristics, and formulas differently from novice engineering designers. In engineering design evaluation plays a larger role in the solution space of expert designers while novice designers tend to do more planning in the problem space. Finally, based on the findings recommendations are provided for engineering and technology education curriculum and instruction, engineering practice in industry, and for future research.

Modeling and simulation of microporous titanium: Effects of morphology with application to orthopaedic implants

Li, Huanlong Northwestern University 2006 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Effective and reliable material and structure as bone implant have been a continuing challenge for scientists from bioengineering, material science and mechanical engineering. Porous titanium has reduced stiffness comparable to bone and open pores to allow complete bone infiltration, thus making it attractive for bone-replacement implants in biomedical engineering. To facilitate the design and application of the material, it is necessary to develop an understanding of the relationship between the morphology of porous microstructure and the mechanical properties of the material. 2D finite element (FE) models based on simulate microstructures of different porosities are initially set up to investigate the effects of pore morphology and bone infiltration on the mechanical response of titanium foam in vivo. It is proved that several microstructural features and bone ingrowth have significant influence on the mechanical properties of porous titanium. Inspired by these results, a factorial design of experiment methodology (DOE) is therefore used to systematically compare the effect that these features have on the mechanical responses via 2D and 3D models based on simulate microstructures of titanium wire foam of 12% porosity. Five microstructural features, including pore shape, size, orientation, and arrangement, and bone infiltration, are varied to create test microstructures. The quantitative effects of the features are used to screen their relative importance for elastic moduli, yield stress and stress concentration factor. Finally, 2D FE models based on real microstructures at various porosities are compared with 2D and 3D FE models based on simulate microstructures at same or similar porosities. The results of these studies indicate that bone infiltration into the pores serves as the most dominant factor and is the key to improve mechanical performance of microporous titanium. Compared to other morphological factors, the orientation and arrangement of pores have relative more important effects on the mechanical response of titanium foam. 3D FE models based on simulate microstructures have been proved to predict more accurate results than 2D FE models based either on real or simulate microstructures. However, based on the DOE study, 2D and 3D FE models at low porosity (12%) have similar estimations on the effects of most factors on the macroscopic and microscopic responses. This implies the possible use of 2D models to observe the impact of microstructural features on mechanical responses.

Mechanical etiology of osteoarthritis after meniscectomy

Haemer, Joseph Michael Stanford University 2009 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The clinical association between meniscectomy and osteoarthritis has been well established; however the connection between the biomechanics and subsequent cartilage degeneration has not been thoroughly explained. The objective of this dissertation was to study how the biomechanics of meniscectomy leads to degenerative changes in articular cartilage with osteoarthritis. The sheep knee was used as a platform since meniscectomy-induced osteoarthritis in the sheep is an extensively studied in vivo model of osteoarthritis in humans. Changes in contact mechanics after meniscectomy were examined in cadaveric sheep knees. Decreased contact area and increased mean and peak contact pressures were determined. Patterns of contact pressure confirmed a loss of load peripherally and a concentration of load centrally. The biomechanical benefit of partial meniscectomy for limited, but not extensive, horizontal tears was demonstrated. The changes in contact mechanics compared well with other in vitro systems and provided a basis for validation of subsequent numerical models. Changes in cartilage mechanics after meniscectomy were evaluated through image-based FEA of a cyclically loaded sheep knee. The tissue-level cartilage mechanics underlying observed patterns of deformation were determined. A novel modeling methodology, using a contacting indenter, was developed to reproduce the transition from a reference to a deformed configuration known from image data. Central consolidation seen in MRI corresponded to increased fluid pressure, fluid exudation, loss of fluid load support, and increased tensile strains. Decreases in peripheral consolidation corresponded to reduced contact and fluid pressure. Articular cartilage mechanics were determined before and after meniscectomy with image-based FEA. Cartilage mechanics were correlated to patterns of biochemical and biomechanical results from a published in vivo model of meniscectomy-induced osteoarthritis. A high number of mechanical/biological correlations in intact knees indicated that articular cartilage structure and composition are finely tuned to the local mechanical environment. After meniscectomy, few correlations existed, indicating the cartilage could not remodel or adapt to a change in mechanical loading as dramatic as meniscectomy. Finally, the properties of the meniscus important for fluid flow distribution and fluid load support in the articular cartilage were examined. We hypothesized that the low permeability of the meniscus and labrum was important for maintaining fluid pressure and minimizing fluid efflux in the knee and hip, and that changes in fluid pressure and fluid flow after removal of the meniscus and labrum are related to observed patterns of osteoarthritis development. FE models were analyzed for an idealized knee and hip. The meniscus maintained fluid pressure and flow in knee articular cartilage, and similar effects were seen with the labrum in the hip. The low permeability of fibrocartilage was found important in limiting joint consolidation. The mechanical etiology of osteoarthritis was found in three pathways: (1) loss of cyclic fluid pressure in the joint periphery, initiating endochondral ossification, leading to cartilage thinning; (2) increased shear loading and fluid exudation centrally, leading to loss of proteoglycan content and collagen network integrity, potentially by altering chondrocyte metabolism; and (3) strains exceeding failure limits and reduced fluid load support at the location of joint contact, causing surface damage in the collagen fibril network, leading to fibrillation of the articular surface. Low permeability of the meniscus was required for cartilage load support and maintaining patterns of fluid pressurization and flow. This understanding will benefit the engineering of cartilage constructs, meniscal repair or replacement techniques, and rehabilitation strategies.

Coupled Mechanical and Electrochemical Phenomena in Lithium-Ion Batteries

Cannarella, John Princeton University 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Lithium-ion batteries are complee electro-chemo-mechanical systems owing to a number of coupled mechanical and electrochemical phenomena that occur during operation. In this thesis we explore these phenomena in the context of battery degradation, monitoring/diagnostics, and their application to novel energy systems. We begin by establishing the importance of bulk stress in lithium-ion batteries through the presentation of a two-year exploratory aging study which shows that bulk mechanical stress can significantly accelerate capacity fade. We then investigate the origins of this coupling between stress and performance by investigating the effects of stress in idealized systems. Mechanical stress is found to increase internal battery resistance through separator deformation, which we model by considering how deformation affects certain transport properties. When this deformation occurs in a spatially heterogeneous manner, local hot spots form, which accelerate aging and in some cases lead to local lithium plating. Because of the importance of separator deformation with respect to mechanically-coupled aging, we characterize the mechanical properties of battery separators in detail. We also demonstrate that the stress state of a lithium-ion battery cell can be used to measure the cell's state of health (SOH) and state of charge (SOC)--important operating parameters that are traditionally difficult to measure outside of a laboratory setting. The SOH is shown to be related to irreversible expansion that occurs with degradation and the SOC to the reversible strains characteristic of the cell's electrode materials. The expansion characteristics and mechanical properties of the constituent cell materials are characterized, and a phenomenological model for the relationship between stress and SOH/SOC is developed. This work forms the basis for the development of on-board monitoring of SOH/SOC based on mechanical measurements. Finally we study the coupling between mechanical stress and voltage in lithium-ion batteries. While the voltage changes at typical levels of stress are relatively insignificant from the standpoint of battery performance, we show that this piezoelectrochemical phenomenon is well-suited for certain mechanical energy harvesting applications. We demonstrate the working principle for mechanical energy harvesting and explore the potential of this technology.

On the Mechanics of Hydrogels for Tissue Engineering Applications

Lopez, Gabriel Ricardo University of California, Berkeley ProQuest Disser 2022 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The dissertation research focused on exploring relationships between composition, structure, and mechanical properties in hydrogels used for tissue engineering application. Specifically, these series of separate but related studies focused on agarose-based gels and co-gels, looking at how different concentrations of agarose, alginate, and collagen affected their ability to serve as a tissue-engineering scaffold with appropriate manufacturability, compressive mechanical properties, and extra-cellular matrix production of embedded cells. These relationships between composition and structure add to the growing literature of tissue-engineering scaffolds, and help researchers move closer towards functional repair of damaged tissues.The main results of this work identified agarose-alginate co-gels as a suitable candidate for bioprinting tissue engineering scaffolds. Later, it was observed that crosslinking agarose-alginate gels changes the short-term recovery behavior under unconfined compression, and increases elastic mechanical properties. This dissertation work also observed that methods used to quantify collagen content from commercial collagen type I gels vary by species source, and that combining these collagen gels in an agarose-based cell-embedded scaffolds produces a minimal, dose-dependent effect on matrix production and compressive mechanics.In short, the dissertation has expanded on the known literature of agarose co-gel mechanics under different loading scenarios. It is my hope that researchers will use the relationships between matrix production, initial gel content, and compressive and shear mechanics to continue improving the functionality of tissue engineered constructs.

Biofabrication of Collageneous Constructs via Electrochemical Compaction Process for Musculoskeletal Tissue Engineering

Younesi, Mousa Case Western Reserve University ProQuest Dissertat 2017 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

A variety of natural and synthetic polymers is commonly used in musculoskeletal tissue engineering. Collagen is a particularly promising material for musculoskeletal tissue engineering, especially for use in connective tissue regeneration. While most collagenous tissues have high mechanical robustness, the majority of the constructs made from collagen have much lower mechanical properties compared to those of native tissues. Commonly used methods for processing collagen are collagen sponges and gels, electrospinning, and wet spinning/extrusion. While each of these methods and products fabricated by these methods have their own advantages, in general, gels and sponges are mechanically very weak, electrospinning can only fabricate 1 or 2 dimensional constructs with a high chance of collagen denaturation and wet spinning/extrusion make collagen threads with partial alignment at best. We developed a method, electrochemical processing of collagen, which can process collagen solution to form mechanically robust 1, 2, and 3 dimensional constructs with enhanced the mechanical properties that match the level of native tissues without denaturation. Collagen threads and sheets fabricated by this method were used in several different skeletal tissue engineering studies, such as tendon, cartilage, and bone tissue engineering.Results of all of these studies demonstrated the electrochemical processing of collagen to be a powerful method for processing collagen solution into mechanically robust products for use in musculoskeletal tissue engineering applications. While this study showed some data on in-vivo performance of the products fabricated via electrochemical processing, further in-vivo studies need to be performed to attain more insight into in-vivo performance of the products in specific applications like cartilage, bone, and tendon tissue engineering. Moreover, the application of electrochemically processed products is not limited to musculoskeletal tissues. While collagen is one of the most biocompatible materials and one of the elements of the extracellular matrix in many tissues, electrochemically processed products can be designed and fabricated to be used in a wide variety of tissue engineering applications than musculoskeletal applications.