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Since their development in the early 1930’s, strain gauges have become an integral part of our lives. The amount of strain measured using strain gauges are the basis for calculating the corresponding: car engine torque, train rail forces, detection of traffic flow and vehicle type, and monitoring bridge safety. As the design of structural parts become more complex in geometry, the need for highly sensitive strain sensors are becoming more essential to ensure the vitality of structural parts. This is especially true when it comes to additive manufactured (AM) parts made from metals, polymers and composites. If sensors can be miniaturized, or even in some cases, be incorporated as part of the host structure, this will provide a non-intrusive monitoring method during the manufacturing process and subsequent service life of the part. However prior to the actual use of embedded sensors, more information is needed regarding the sensitivity of the geometry to the fidelity of the signal. The objective of this research was to explore the feasibility of signal outputs from carbon nanotube (CNT)/epoxy strain sensors and their ability to sense strains on structural components. This research evaluated (1) how percolation within the sensors was affected based on sensor array geometry, (2) various weight percent (w/w%) loading of CNTs required for signal output, (3) how the various w/w% loading affected the mechanical and electrical resistance and conductivity of the sensors and (4) the ability of the sensors to give the same signal output under repeatable cyclic loading.

Quasi static and intermediate strain rate (5 s-1 and 500 s-1) tests are conducted on various aluminum and steel ASTM E8 subsize tensile specimens to validate a newly developed testing method which combines a previously developed serpentine bar for load monitoring and a newly described high-speed actuator. This new actuator is controlled by a semi-passive piezoelectrically actuated brake system mounted to a standard actuator, which allows for the actuator to produce high loads and quick response times (≈100 µs). Limitations of this experimental method are that tests must be monotonic (tension or compression but not cyclic loading) and strain rate rise times limit this method to the intermediate strain rate regime (below 500 s-1).

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Osteoblastic cells respond to mechanical stimuli with alterations in proliferation and/or phenotypic expression. In some cases, these responses occur within only a few applications of stimuli (i.e. 'cycle-dependent trigger response') rather than in a dose-dependent manner. To explore potential mechanisms of the cycle dependent trigger response, we raised the following questions: (1) Does strain of bone cells alter gene expression; if so, how quickly does it occur and how long does it last? (2) Are alterations in message level strain magnitude dependent? (3) Are alterations in steady-state message levels cycle dependent? Cultures were evaluated for osteocalcin mRNA one week following a daily stretch application at four stretch magnitudes and four cycle numbers and compared to nonstretched controls. Steady state mRNA message was ascertained prior to and at 10, 20, 30, 60, 120, 180, and 240 min following initiation of stretch. Following mRNA isolation, first strand cDNA synthesis was performed and fluorometrically quantitated. A reverse transcriptase based PCR (RT-PCR) approach allowed assessment of osteocalcin mRNA levels from microcultures (50,000 cells per 10 μl culture or 5000 cells mm2) of rat calvarial osteoblasts. Optimized PCR was performed using primers to the bone specific protein, osteocalcin (OC) and two 'housekeeping' genes, β-actin and GAP-DH. PCR products were separated on 4% agarose gels and band intensities digitized with relative quantitation based on internal standards in each gel. The lowest magnitude of stretch (-1 KPa) at 1800 cycles per day reproducibly depressed message for osteocalcin, but not β-actin when assayed immediately following the cessation of strain application. By three hours following the initiation of stretch, message levels returned to control values. At the time of stretch cessation, the 1800 cycle stretch regimen diminished (p < 0.0001) steady-state osteocalcin message independently of the four stretch magnitudes. Stretch for 300 cycles failed to depress (p = 0.05) osteocalcin message cultures at any time, but 600 cycles depressed message by 30 min. By one and two hours, cultures stretched 600, 900, and 1800 cycles showed similar levels of message depression. Four hours following the initiation of stretch, message levels returning to nonstrained levels in all groups. We conclude that alterations in cell response to strain are in part mediated by gene expression, that alterations last 3-4 h in this system, and that the message mechanism itself exhibits a triggerresponse dependency to cycle number.

The relative ease of tuning the properties of two-dimensional materials compared to their three-dimensional counterparts offers great potential to achieve previously inaccessible multifunctional devices. In this Dissertation, we use strain engineering as a non-destructive way to control the properties of two-dimensional materials, employing density functional theory and chemical vapor deposition. In the first part of the Dissertation, density functional theory is used to investigate the effect of biaxial strain on the structural, electronic, and magnetic properties of pristine and Janus Cr-trihalide monolayers. We find that the broken inversion symmetry of the Janus monolayers X3-Cr2-Y3 (X, Y = Cl, Br, and I) enhances their functionality by making the magnetic anisotropy tunable by strain and inducing an out-of-plane electric polarization. A very negative magnetic anisotropy energy of ̶ 3.77 meV per formula unit is realized in the Cl3-Cr2-I3 monolayer under ̶ 5% strain. In the second part of the Dissertation, we perform a comprehensive investigation of thermally strained monolayer MoS2, both theoretically and experimentally, to tune the sulfur vacancy density. Due to a dominant role of the intralayer electrostatic interaction, compressive (tensile) biaxial strain decreases (increases) the sulfur vacancy formation energy and, thus, increases (decreases) the probability of creating sulfur vacancies. This fundamental relationship opens a new venue for defect engineering of transition metal dichalcogenides.

Thesis advisor: Sara Moorman / Studies show that family caregivers are at high risk for morbidity and mortality due to high strain and low efficacy. Dementia caregivers experience a particular type of strain because of the long term nature of the disease. Caregiver studies and intervention programs aim to lower strain and improve perceived efficacy, but they do not often look at these outcomes over time and how they may change throughout the prognosis. This thesis aims to analyze caregiver outcomes in relation to the duration of caregiving, individual characteristics, and type of diagnosis. By using linear regressions and hierarchical linear modeling, I find that caregiver outcomes do not change over time for the average caregiver but vary significantly among individuals. This emphasizes that caregiver strain and efficacy are not solely guided by caregiving tasks. Understanding relationships, perception of one's role, and the ability to adapt to changes are crucial to effective and sustained caregiving. / Thesis (BA) — Boston College, 2019. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Sociology.

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Every year, more than 2.4 million eye injuries occur in the United States, with over 30,000 of those injured left blind in at least one eye as a result. Computer modeling is one of the most versatile ways to study ocular trauma, however, existing models lack accurate stress and strain properties for ocular globe rupture. A pressure system was built to examine static and dynamic globe rupture pressures for healthy postmortem human and porcine (pig) eyes. Maximum rupture stress for the quasi-static tests was found to be 11.17MPa for human tissue and 12.08MPa for porcine tissue, whereas stress for the dynamic tests was found to be 30.18MPa for human tissue and 26.01MPa for porcine tissue. Maximum rupture stress results correlate well with static material properties used in published research (9.4MPa), and dynamic properties of 23MPa found in published research. Healthy postmortem human eyes were ruptured statically and dynamically to determine the relationship between stress and strain for the ocular globe under intraocular pressure loading. Stress-strain relationships were investigated and values for the elastic modulus were found to be slightly lower than that previously published. This research shows that it is important to differentiate between tissue type, and static versus dynamic failure properties before drawing conclusions from computer models and other published research. Now that rupture can be accurately determined, safety systems designed to protect eyesight in automotive, sports, and military applications can also be applied to protect the quality of life for humans in these applications. / Master of Science

This work is a stepping stone towards developing higher order shell element for simulating composite manufacturing procedure. In this study, a continuum approach suitable for combined material and geometrically nonlinear analysis for an eight node solid shell element SS8 is explained. The formulation of SS8 comprises two ingredients to alleviate undesirable locking effects: 1) Assumed Natural Strain concept, which has proven to alleviate the curvature thickness and transverse shear locking problems. 2) Enhanced Assumed Strain, which adds enhanced degrees of freedom to improve the in-plane response of the element and the curvature thickness locking problem. This formulation has been extended to represent geometric and material non-linearity using Total Lagrangian approach. Finally, finite strain formulation has been verified by numerical examples. Results when compared to continuum shell element in ABAQUS show a reasonable agreement with a relative error of less than 2%.