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Aging of HTPB/Al/AP Rocket Propellant Formulations Investigated by DMA Measurements
No full textThree HTPB-based rocket propellant formulations containing ammonium perchlorate and aluminum particles, with different aluminum content and particle size, have been manufactured. The study has focused on the change of mechanical properties with aging time by using dynamic mechanical analysis (DMA). Therefore, propellant formulations underwent an accelerated aging program, in air (RH<10 %), between 60 °C and 90 °C with aging time adjusted to a thermal equivalent load of 15 to 20 years at 25 °C. DMA investigations revealed distinct changes in the shape of the loss factor curve. These curves were modeled with three exponentially modified Gaussian (EMG) functions in order to get the molecular interpretation of the involved aging phenomena by separating the binder fractions with different mobility. Aging of propellant formulations can be followed by considering only two parameters: the areas of the second and third loss factor transition peaks (A2, A3), and the corresponding maximum temperature values of the assigned Gauss peaks (Tc2, Tc3)
Ageing of HTPB/Al/AP Rocket Propellant Formulations Investigated by DMA Measurements, Sol-Gel and GPC Analysis
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Ageing Behaviour of Composite Rocket Propellant Formulations Investigated by DMA, SGA, and GPC
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Aging of ADN Rocket Propellant Formulations with Desmophen-Based Elastomer Binder
Get PDFDesmophen® binder-based rocket propellant formulations containing ammonium dinitramide (ADN) and different fuel filler types (Al, HMX) were manufactured and investigated. Desmophen® D2220 is a polyesterpolyol. Polyesters are seen as a binder possibility, because of the relatively low temperature of the glass transition region compared to polyether-based prepolymers such as GAP. The analogous formulations with AP instead of ADN were also included for comparison. The aging was followed by SEM, DSC, and DMA measurements. The accelerated aging program was developed on the principle of thermal equivalent load and the generalized van't Hoff rule with a scaling factor equal to F=2.9. The aging was performed in air (RH<10%) at temperature values between 65 and 85°C and aging times adjusted to a thermal equivalent load of 15 years at 25°C. DMA measurements of the aged ADN/Desmophen®- based propellants identified changes in the loss factor curve. In contrast to HTPB-Al-AP rocket propellant formulations, the loss factor curve of the ADN formulations with Desmophen®-based elastomer binder shows only one main apparent peak. The loss factor curves were modeled with exponentially modified Gaussian functions, which have revealed the presence of a second hidden peak. It was found that the aging could be characterized by the time-temperature dependence of the areas of the hidden peak. The area increased with aging, which is explained by scissioning of the polymer in the shell around the ADN particles. By this process the strength is reduced, which was recognized by the decrease in storage shear modulus
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
Characterization of ADN/GAP-Based and ADN/Desmophen-Based Propellant Formulations and Comparison with AP Analogues
Get PDFSeveral ADN-based rocket propellant formulations containing different pre-polymers (GAP diol/triol, Desmophen® 2200), curing agents (BPS, Desmodur® N100, Desmodur® N3400), plasticizers (BDNPA-F, TMETN), and filler types (Al, HMX) have been manufactured. Propellant formulations were characterized by tensile tests, SEM analyses and DMA measurements. The study has focused on characterizations of the propellants in terms of evaluation of the strength and strain capability, investigation of the presence/absence of dewetting phenomena, compatibility issues and evaluation of the glass transition temperature. Ammonium perchlorate-based propellant formulations have also been manufactured and analyzed in order to make comparisons. Aging was investigated using mass loss measurements
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