301 research outputs found
The Benedictus, Lucan Narrative, and Poetic Discourse
No full textDegree awarded: Ph.D. Biblical Studies. The Catholic University of AmericaThis dissertation can be viewed by CUA users only.The Benedictus (Luke 1:68-79) is closer to Luke's literary project than previous studies have admitted. The Benedictus has been assessed as having more in common with Jewish discourse or the story about John the Baptist than Luke's authorial persona, based on its supposed divergence from Luke's stylistic range and introduction of themes (vv. 68-69, 71-75, and/or vv. 78-79) that are not seen to be particularly relevant to its literary context (especially, Luke 1:5-25, 57-66). This study argues the contrary, that the Benedictus is closely related to its literary context and exhibits features that are consistent with Luke's stylistic range. There are four claims made in this argument. First, the message of the Benedictus is best understood through an evaluation of the structure of the Benedictus (vv. 68a + 68b-71 + 72-75; 76a + 76b-78a + 78b-79), which is indicated by the syntax of its clauses, whose predicates have the sequence indicative + infinitive + articular infinitive in the genitive. Second, the argument of its two parts (vv. 68-75, 76-79) are interdependent in their use of an exodus typology, the first part predicting that a God-appointed savior figure (vv. 69) will accomplish a Red Sea-type deliverance (v. 71), and the second part instructing the child to precede the savior, as the angel preceded the Israelites in the wilderness (v. 76b), and give people hope of this deliverance. Each part has two sections whose cola correspond thematically. Third, the Benedictus is integral to Luke 1:5-25, 57-67, 80, resolving narrative tensions and complementing issues introduced through allusion. Fourth, the Benedictus displays phrasing, a structure of argument, and themes that reappear in Luke-Acts, indicating that Luke either was the author of the Benedictus or had a significant role in its shaping, integrating features of Jewish liturgy into a form of poetic discourse that may have been influenced by liturgy in synagogues and/or church communities.Made available in DSpace on 2012-09-11T17:08:26Z (GMT). No. of bitstreams: 1
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Analysis of Stochastic Matrix Crack Evolution in CFRP Cross-Ply Laminates under Fatigue Loading
No full textThe present work aims at understanding the stochastic matrix crack evolution in CFRP cross-ply laminates under tension–tension fatigue loading. An experimental campaign was carried out on twenty-three specimens at different stress levels, while two optical techniques were used for the in-situ monitoring of the accumulation of transverse matrix cracks. The results showed a significant scatter in crack evolution among specimens. This stochastic behaviour was further investigated using image analysis and numerical modelling. It was found that transverse matrix cracks can be classified into the independent and dependent cracks based on a critical crack spacing. Furthermore, the severity of interaction among cracks was quantified by introducing a dependent crack ratio. Finally, a strength-based probabilistic model was proposed to describe the scattering regime of the crack evolution. The agreement between model and test results indicates that local strength variations of 90 plies are the dominant scattering source governing the initial fatigue resistance to cracking and determining the accumulation of transverse matrix cracks among specimens. These results may provide a new insight into the stochastic nature of matrix cracking in composite laminates and aid in the design of fatigue resistance properties.</p
Damage accumulation analysis of cfrp cross-ply laminates under different tensile loading rates
No full textThis paper investigates the loading rate effect on both mechanical properties and damage accumulation process of [0°2/90°4]S carbon fiber-polymer laminates under tensile loading. In-situ edge observations, Acoustic Emission and Digital Image Correlation techniques were utilized simultaneously to monitor the state of damage in real time. Results showed that the axial modulus and strength were less sensitive to loading rates than failure strain, which increased with the decrease of the loading rate. In the viewpoint of damage accumulation process, high density and uniform distribution of transverse matrix cracks, and H-shape crack patterns, incorporating inter-laminar cracks, were more likely to occur at low loading rates while variable crack spacing occurred at higher rates. When loading rates were lower than a certain level, maximum transverse matrix crack density decreased slightly due to the restriction of relatively widely generated inter-laminar cracks. Furthermore, the cumulative acoustic emission energy of low-frequency signals was linearly correlated to transverse matrix crack density, providing a promising way to quantify crack accumulation in real time. Finally, spatial consistence was observed between transverse matrix cracks at edges and stress concentrations at the exterior 0° ply, and the peaks of axial strain at local concentration regions locate either near the newest cracks or at the place with minimum crack spacing.Structural Integrity & Composite
Early fatigue damage accumulation of CFRP Cross-Ply laminates considering size and stress level effects
No full textPly-block size and stress level effect on accumulation of transverse cracks and delamination are investigated during early fatigue life of CFRP laminates. Tension-tension fatigue tests under different stress levels were performed for two cross-ply configurations. Edge observation with digital cameras, digital image correlation and acoustic emission were employed for in-situ damage monitoring. Transverse cracks were dominant for [0/902]s laminates with almost non-existent delamination, while different interactive levels between both damage mechanisms occurred for [02/904]s laminates. Poisson's ratio identifies whether early fatigue damage is dominant by transverse cracks or involves delamination. Cumulative AE energy is a helpful indicator of crack density.Structural Integrity & Composite
Optical Coherence Tomography for Material Characterization
No full textOptical coherence tomography (OCT) is a non-invasive, contactless and high resolution imaging method, which allows the reconstruction of two or three dimensional depth-resolved images in turbid media. In the past 20 years, OCT has been extensively developed in the field of biomedical diagnostics, while OCT in the non-destructive testing (NDT) field is lagging far behind. The aim of this thesis is to use OCT as a novel NDT technique for material structure characterization and damage detection. Besides an overview of the OCT fundamentals and developments, the thesis is mainly driven by three tasks: instrument design, signal processing, and applications. An integrated OCT system working at a wavelength of 1550 nm has been built. It combines time domain (TD) and Fourier domain (FD) OCT to make the both types of measurement available in one instrument. TD-OCT has the advantage of a large A-scan range and high SNR, while FD-OCT system has tremendous superiority in fast imaging due to no movement of the reference mirror. These two kinds of measurement can be implemented based on the user request in the developed hybrid OCT system, e.g. improved imaging depth or speed. In TD-OCT, the envelope detector was selected as the ideal method for the demodulation of each axial signal. A bandpass filter and 2D median filter are applied before and after demodulation, respectively, to reduce OCT system and speckle noise. In FD-OCT, raw data was first processed to remove the influence from the optical source and dark noise of the CCD detectors. It was then linearly resampled to convert to evenly spaced intervals of wavenumber, instead of wavelength. With an inverse Fourier transform, one depth profile was recovered and a cross-sectional image was constructed by accumulating a series of depth profiles. The quality of cross-sectional images can be further improved by merging multiple images with different pathlength offsets. The application of the designed OCT system was mainly focused on glass fiber composites and the microstructure of the specimens was displayed by either cross-sectional or volumetric images. Special attention was given to delamination growth in a glass fiber composite for wind turbine blade applications. The glass fiber composite was tested by incremental loading. Volumetric images obtained by OCT were further processed to reconstruct 3D crack surface profiles, from which a full field view of the delamination crack was given, providing substantial information for the study of crack growth in the composites. Additionally, the study explored the use of optical coherence elastography (OCE) for the deformation measurement of glass fiber composites, for the first time to the best of our knowledge. The developed OCE system based on speckle tracking was first evaluated by a test of ridge body translation. Then experiments were implemented for a set of glass fiber composites under tensile testing and three point bending. The results show that OCE can measure the internal displacements of a glass fiber composite in the range from a few micrometers to hundreds of micrometers. Besides, other applications are also presented in the thesis. These include defects and thickness measurement of polymer coating and the microstructure characterization of a wooden-panel painting. The results show the designed OCT system also has high potential for these alternative applications. Recommendations for further improvement to the OCT design and the applications are presented at the end of the thesis.Aerospace Structures and MaterialsAerospace Engineerin
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