Matching Items (4)

Structural Health Monitoring: Acoustic Emissions

Description

Non-Destructive Testing (NDT) is integral to preserving the structural health of materials. Techniques that fall under the NDT category are able to evaluate integrity and condition of a material without permanently altering any property of the material. Additionally,

Non-Destructive Testing (NDT) is integral to preserving the structural health of materials. Techniques that fall under the NDT category are able to evaluate integrity and condition of a material without permanently altering any property of the material. Additionally, they can typically be used while the material is in active use instead of needing downtime for inspection.
The two general categories of structural health monitoring (SHM) systems include passive and active monitoring. Active SHM systems utilize an input of energy to monitor the health of a structure (such as sound waves in ultrasonics), while passive systems do not. As such, passive SHM tends to be more desirable. A system could be permanently fixed to a critical location, passively accepting signals until it records a damage event, then localize and characterize the damage. This is the goal of acoustic emissions testing.
When certain types of damage occur, such as matrix cracking or delamination in composites, the corresponding release of energy creates sound waves, or acoustic emissions, that propagate through the material. Audio sensors fixed to the surface can pick up data from both the time and frequency domains of the wave. With proper data analysis, a time of arrival (TOA) can be calculated for each sensor allowing for localization of the damage event. The frequency data can be used to characterize the damage.
In traditional acoustic emissions testing, the TOA combined with wave velocity and information about signal attenuation in the material is used to localize events. However, in instances of complex geometries or anisotropic materials (such as carbon fibre composites), velocity and attenuation can vary wildly based on the direction of interest. In these cases, localization can be based off of the time of arrival distances for each sensor pair. This technique is called Delta T mapping, and is the main focus of this study.

Contributors

Created

Date Created
2019-05

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Optimal Modeling of Knots in Wood

Description

A model has been developed to modify Euler-Bernoulli beam theory for wooden beams, using visible properties of wood knot-defects. Treating knots in a beam as a system of two ellipses that change the local bending stiffness has been shown to

A model has been developed to modify Euler-Bernoulli beam theory for wooden beams, using visible properties of wood knot-defects. Treating knots in a beam as a system of two ellipses that change the local bending stiffness has been shown to improve the fit of a theoretical beam displacement function to edge-line deflection data extracted from digital imagery of experimentally loaded beams. In addition, an Ellipse Logistic Model (ELM) has been proposed, using L1-regularized logistic regression, to predict the impact of a knot on the displacement of a beam. By classifying a knot as severely positive or negative, vs. mildly positive or negative, ELM can classify knots that lead to large changes to beam deflection, while not over-emphasizing knots that may not be a problem. Using ELM with a regression-fit Young's Modulus on three-point bending of Douglass Fir, it is possible estimate the effects a knot will have on the shape of the resulting displacement curve.

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Created

Date Created
2015-05

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A Computational Investigation of Theoretical GeSn Alloys

Description

In materials science, developing GeSn alloys is major current research interest concerning the production of efficient Group-IV photonics. These alloys are particularly interesting because the development of next-generation semiconductors for ultrafast (terahertz) optoelectronic communication devices could be accomplished through integrating

In materials science, developing GeSn alloys is major current research interest concerning the production of efficient Group-IV photonics. These alloys are particularly interesting because the development of next-generation semiconductors for ultrafast (terahertz) optoelectronic communication devices could be accomplished through integrating these novel alloys with industry-standard silicon technology. Unfortunately, incorporating a maximal amount of Sn into a Ge lattice has been difficult to achieve experimentally. At ambient conditions, pure Ge and Sn adopt cubic (α) and tetragonal (β) structures, respectively, however, to date the relative stability and structure of α and β phase GeSn alloys versus percent composition Sn has not been thoroughly studied. In this research project, computational tools were used to perform state-of-the-art predictive quantum simulations to study the structural, bonding and energetic trends in GeSn alloys in detail over a range of experimentally accessible compositions. Since recent X-Ray and vibrational studies have raised some controversy about the nanostructure of GeSn alloys, the investigation was conducted with ordered, random and clustered alloy models.
By means of optimized geometry analysis, pure Ge and Sn were found to adopt the alpha and beta structures, respectively, as observed experimentally. For all theoretical alloys, the corresponding αphase structure was found to have the lowest energy, for Sn percent compositions up to 90%. However at 50% Sn, the correspondingβ alloy energies are predicted to be only ~70 meV higher. The formation energy of α-phase alloys was found to be positive for all compositions, whereas only two beta formation energies were negative. Bond length distributions were analyzed and dependence on Sn incorporation was found, perhaps surprisingly, not to be directly correlated with cell volume. It is anticipated that the data collected in this project may help to elucidate observed complex vibrational properties in these systems.

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Agent

Created

Date Created
2019-05

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"Jazz Happens Here": The Nash and the Formalization of Jazz in Phoenix, Arizona

Description

The Nash, a jazz venue in Phoenix, Arizona, is an example of a decades-long process of the formalization of jazz—being codified as an art music relying on academic and philanthropic support. Formalization developed as jazz began to be taken seriously

The Nash, a jazz venue in Phoenix, Arizona, is an example of a decades-long process of the formalization of jazz—being codified as an art music relying on academic and philanthropic support. Formalization developed as jazz began to be taken seriously as art music worth of critical evaluation from critics, academics, and the hallowed establishments of American high art. Jazz became increasingly dependent on an infrastructure of institutional support, and a neoclassical ideology sought to define what styles of jazz were ‘real’ and worthy of preservation. In Phoenix, the origins of The Nash were laid in 1977 when Jazz in Arizona was formed, a non-profit organization that aimed to support jazz through information dissemination, music scholarships, festival organizing, and attending jazz events throughout Arizona. The Nash was conceived as a way to more fully engage young people in the community. Herb Ely, a prominent Phoenix attorney and philanthropist, pitched the idea to Joel Goldenthal, then Executive Director of Jazz in Arizona. The venue was built under the auspices of Jazz in Arizona, and operates as the organization’s headquarters. In keeping with the broader trend of formalization, The Nash presents jazz as a performance of artistic expression. Continued philanthropic support allows The Nash a degree of independence from economic concerns. The Nash is also committed to providing support for jazz education, by partnering with local educational institutions and presenting educational programming. The focus on providing opportunities for young musicians, as well as its location in the hip neighborhood of Roosevelt Row have contributed to The Nash becoming relatively popular among young people. However, the formalized approach to jazz espoused by The Nash has created some conflicts within the Phoenix jazz community, as some professional musicians feel that The Nash is underpaying musicians for their labor. The American Federation of Musicians Local 586 argues that musicians are workers, and The Nash ought to be paying union scale.

Contributors

Created

Date Created
2016-12