1,721,182 research outputs found
Image-based methods for the identification of in-plane composite moduli at high strain rates
No full textThis thesis describes the development of new image-based methods to characterise in plane moduli for off-axis composites at high strain rates. It is difficult to accurately identify these properties with current experimental methods such as the split-Hopkinson bar, because the assumptions that the technique is based on can be violated at strain rates above a few hundred s−1. With this new approach, transverse and shear moduli of Carbon Fibre Reinforced Polymer (CFRP) composite samples have been identified at strain rates in the 500 to 2000 s−1 domain. The off-axis composite modulus identification methods were developed within the Image-Based Inertial Impact (IBII) test technique. Using the Virtual Fields Method (VFM), full-field measurements and rigid body virtual fields were included in the principle of virtual work to derive stress averages on a test sample. Transverse and shear moduli were then identified from linear fits to the averagestress-strain response. This thesis details the numerical implementation of the VFM theory used to derive these moduli for unidirectional (UD) and multi-directional (MD) composite samples with configurations of UD90◦, UD45◦ and MD45◦.An image deformation study was undertaken to verify the identification methods and to assess smoothing parameters for processing experimental images. Two full-field measurement techniques for calculating the displacement fields were evaluated in the image deformation simulations: the Grid Method and Digital Image Correlation (DIC). The first major goal of the study was to verify that DIC displacements could be used within the IBII test methodology. This was achieved by comparing the moduli identified from unsmoothed strain and acceleration fields with no simulated camera noise overlayed on the images. Here, the moduli identified with DIC were similar the Grid Method values. The second goal of the study was to obtain optimised smoothing parameters that gave the best trade-off between systematic and random errors on the identified moduli. This analysis showed that different optimised smoothing parameters were obtained for the UD45◦ samples, because of their more-complex kinematic fields compared to the UD90◦ samples. Optimised smoothing parameters that resulted in systematic and random errors of less than 1% were obtained for both grid and DIC images. IBII tests were performed at the University of Southampton’s high speed impact laboratory, where a 50 mm bore gas gun was used to launch aluminium projectiles at composite samples with impact speeds around 40 m.s−1. A Shimadzu HPV-X ultra-high speed video camera operating at 2 MHz recorded images of the impacted samples and moduli were obtained from the deformed image sets. Validation of the modulus identification methods was achieved by comparing the moduli from different sample configurations. The transverse modulus E22 obtained from the UD45◦ samples was within one standard deviation (SD) of the UD90◦ sample result. Shear strain waves were detected in the UD90◦sample strain maps, which were generated by a slight pitch-angle misalignment between the impacting components in the test. As a result, shear moduli were also obtained from the UD90◦ samples, with G12 values within on SD of the UD45◦results. Shear moduli obtained from MD45◦samples were around 6 % lower than the UD values, which was consistent with the reduced laminate density of the MD samples. Comparison of the high strain rate moduli obtained in this study suggests that values reported in literature could be over-estimated, including both a material and a testing system response. Comparison of the identified moduli from the two full-field measurement techniques showed that theE22 and G12 values were lower for DIC to the Grid Method. Voids were detected in thecomposite plates that the UD DIC samples were cut fro m, which provided an explanation for the lower DIC values. Shear moduli identified from MD45◦ samples using DIC and the Grid Method were within 1%, which was expected given that both samples were cut from the same plate. Results from this study suggest that both the Grid Method and DIC are suitable for high strain rate moduli identification within the IBII test methodology.<br/
A chemical warfare module for the Airland Advanced Research Model (ALARM).
Get PDFNANAhttp://archive.org/details/achemicalwarfare109452220
Dataset for 'The off-axis IBII test for composites' (JDBM-D-20-00043R1)
No full textThis dataset supports the publication: 'The off-axis IBII test for composites' in Journal of Dynamic Behavior of Materials.
IBII test raw images, kinematic fields, material property figures and processing codes for UD90, UD45 and MD45 CFRP specimens. Quasi-static data for the UD45 tensile test samples.
List of Acronyms
IBII = Image-Based Inertial Impact
UD = Uni-Directional
MD = Multi-Directional
CFRP = Carbon Fibre Reinforced Polymer</span
Dataset for IBII tests on Onera CFRP using DIC
No full textData to support University of Southampton Doctoral Thesis "Image-based methods for the identification of in-plane composite moduli at high strain rates". This dataset contains results from IBII tests performed on UD90, UD45 and MD45 ONERA CFRP samples. Folders are arranged in sample configuration and contain:
- Raw images
- Stress-strain curves
- Modulus vs. position plots
- Strain rate data
Static image sets and alignment images are also given. </span
The off-axis IBII test for composites
No full textComposite components regularly experience dynamic loads in service. Despite this, it is still difficult to obtain accurate mechanical properties of composite materials under high strain rate conditions. In this study, a new application of the Image-Based Inertial Impact (IBII) test methodology was developed, to generate an accurate in-plane transverse and shear moduli dataset from unidirectional (UD) off-axis composite specimens. The obtained dataset was consistent across different sample configurations, where results from the UD45^{\circ } off-axis specimens agreed well with the UD90^{\circ } values. Validation of the shear modulus identification was also undertaken by comparing the results from the UD90^{\circ } and UD45^{\circ } specimens with a multi-directional (MD) configuration. Here, it was found that MD±45^{\circ } specimen shear modulus values where marginally lower than that from the UD specimens, in accordance with the lower fibre volume fraction of the MD laminate. Low strain rate sensitivities in the 0.5-2\times10^{3} \hbox {s}^{-1} regime evidenced in this work suggest previously published data (often from split-Hopkinson bar tests) may include both a material and system i.e. testing apparatus response
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
