Quasistatic indentation studies and small-particle impact studies have been made of specimens of two specially developed silicon nitrides ST-2 and SN252. Indentation studies were made using diamond hemispheres of 2 and 4mm diameter, whereas the impact studies were made using samarium-cobalt spheres of 1 mm diameter with impact velocities of up to 500 m s−1. In the indentation studies, some preliminary experiments were conducted using tungsten carbide spheres of 1-4 mm diameter. They were, however, found to be inadequate as they deformed plastically and then fractured without causing any damage to the silicon nitrides. With the diamond indenters, true Hertzian cone cracks could not be obtained, as the specimens deformed plastically when the mean indentation pressure exceeded 12 GPa. As the mean indentation pressure was further increased, ring cracks sometimes formed at the edge of the plastic indentations; unlike the true Hertzian cone cracks, these ring cracks extended into the bulk almost normal to the indented surface. At still higher indentation pressures, median and lateral cracking occurred. It has been concluded from the observations that the two silicon nitrides are clearly stronger than those used by previous investigators. In the impact experiments, the projectiles themselves fractured for velocities greater than 10 m s−1. However, segmental ring cracks formed in ST-2 and in SN252 when the impact velocities were 410 and 460 m s−1 respectively. At the impact sites, plasticity was found to have occurred and it was consistent with calculated maximum impact pressure. A comparison of the response of single-piece specimens and split specimens for quasistatic indentation studies was also made and clear evidence has been provided showing that split specimens yield misleading results and that they should be avoided for such work.
In most solid state reactions the reaction velocity can be described as a product of two functionsK(T) andf(1−α) whereT is the temperature and α the degree of conversion of the solid reactant. The physical interpretation of these functions is discussed, and a systematic method is described by whichf(1−α) of a reaction is identified from its kinetic data.K(T) and the reaction mechanism are then determined. This method has been successfully applied to analyse the kinetics of the thermal decomposition of silver azide.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBoiling Points and Surface Tensions of Mixtures of Benzyl Acetate with Dioxane, Aniline, and meta-Cresol.P. K. Katti and M. M. ChaudhriCite this: J. Chem. Eng. Data 1964, 9, 1, 128–130Publication Date (Print):January 1, 1964Publication History Published online1 May 2002Published inissue 1 January 1964https://pubs.acs.org/doi/10.1021/je60020a042https://doi.org/10.1021/je60020a042research-articleACS PublicationsRequest reuse permissionsArticle Views74Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Colour high-speed photographic framing sequences of the normal impact of 2 mm diameter tungsten carbide spheres on a block of fused silica at 150 m s−1 were taken at 1 × 106 frames per second. The initiation and growth of the resulting two coaxial cone cracks, which formed within 0.1 µs of the initial projectile contact, were followed. The innermost cone crack of a semi included angle of 32° travelled at a velocity of (2270± 100) m s−1 which is close to the theoretical maximum crack velocity of 2180 m s−1 in fused silica. Importantly, the semi included angle of the cone crack was about a half of the angle of the cone crack produced by quasi-static loading. A suggested explanation, based on the localized decrease of the target's Poisson's ratio due to the high impact loading rate, has been proposed and examples are given which support this suggestion.
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