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Effect of PCBN tool grade on joint strength and tool life in friction stir spot welded DP 980 steel
Hartman, T.,Miles, M.P.,Hong, S.-T.,Steel, R.,Kelly, S. Elsevier 2015 Wear: An international journal on the science and Vol.328 No.-
<P><B>Abstract</B></P> <P>Friction stir spot welding of advanced high strength steel, like dual phase (DP) 980, is a very demanding application in terms of tool wear. The best candidate material currently being tested is polycrystalline cubic boron nitride (PCBN). The purpose of the current work is to study the effect of PCBN material grade, as specified primarily by CBN grain size, on weld quality and tool life, for the spot welding of DP 980 steel. With a nominal composition of 90% CBN, three tool grades were tested. Grade A had CBN grain sizes of 3–6μm, grade B had grain sizes of 12–15μm, and grade C had a multimodal distribution, with grain sizes ranging from 4 to 40μm. The best performance in terms of joint strength and tool life was achieved with grade A. The effect of fine CBN grain size was less adhesion of DP 980 on the tool surface over time, less abrasive wear, and higher lap shear failure loads of the welds that were produced, compared to the other grades. A-type tools were the most consistent in both the number of welds per tool, and the number of welds that reached acceptable lap shear failure loads. B-type tools, performed slightly better than C-type tools in terms of wear, but neither of them was able to achieve consistent, acceptable lap shear failure load values after the first 200 welds. In fact only one out of five C-type tools was able to produce acceptable lap shear failure loads after the first 100 welds. Based on the experimental evidence, tool wear was likely dominated by grain pullout. This is consistent with the correlation showing that larger CBN grain size was related to shorter tool life.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We monitored wear resistance of PCBN tools over thousands of friction stir spot welds in DP 980 steel. </LI> <LI> CBN grain size was found to have a significant impact on tool life and on joint strength. </LI> <LI> Grain pullout was postulated to be the primary wear mechanism based on the evidence. </LI> </UL> </P>
Slow-rate devolatilization of municipal sewage sludge and texture of residual solids
Miloslav Hartman,Bohumír Čech,Michael Pohořelý,Karel Svoboda,Michal Šyc 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.10
Ash-rich sludge samples originating in four large plants were analyzed and employed to explore primarily the kinetics and the chemistry of devolatilization. A gravimetric, slowly increasing-temperature method was used in the range 298-1,123 K in a milieu of nitrogen. As an intricate combination of numerous (bio)organic and inorganic compounds, the dry sludge commences devolatilizing at approximately 418 K. The bulk of organic matter is released up to 823 K, at the rate becoming very slow thereafter. Basic constituents of the product gas are CO2, CO, H2, and CH4 with undesired nitrogenous, sulfurous, and chloro compounds. The residual solids contain significant amounts of organic matter/carbon and, on account of their favorable textural characteristics, they can be viewed as promising sorbents or catalysts. Kinetic triad was inferred from the experimental data: the model is well-capable of simulating the process of devolatilization and can be used for design considerations. An explicit equation, based upon a tractable approximation to the temperature integral (for [E/(RT)]0.1), has been verified and proposed for predicting the maximum reaction rate temperature. Remarkable differences in thermal behavior were explored in detail between the sludge and the alkali bicarbonates.
Emma Hartman,Daniel M. Balkin,Alfred Pokmeng See 대한신경외과학회 2024 Journal of Korean neurosurgical society Vol.67 No.3
Vascular malformations are structural abnormalities that are thought to result from errors in vasculogenesis and angiogenesis during embryogenesis. Vascular malformations of the scalp present unique management challenges due to aesthetic and functional implications. This review examines the pathophysiology, clinical presentation, and management techniques for six common types of vascular malformations of the face and scalp : infantile hemangioma, capillary malformations, venous malformations, lymphatic malformations, arteriovenous malformations, and arteriovenous fistulas. These lesions range from common to rare, and have very different natural histories and management paradigms. There has been increasing understanding of the molecular pathways that are altered in association with these vascular lesions and these molecular targets may represent novel strategies of treating lesions that have historically been approached from a structural perspective only.
Integrating Storytelling and Visual Arts Therapy: Case Reflections with Young Adults with autism
Ashley L. Hartman,Paige E. Owings,Taylor Guttesman 대한무용/동작심리치료학회 2020 신체심리연구 Vol.6 No.1
This paper explores the integration of narrative therapy and art therapy practice in work with young adults on the autism spectrum. Group and individual cases will demonstrate how the narratives of these clients have the potential to be expressed in unique ways through the use of visual art media in connection with storytelling. It will outline group responses to diverse visual arts media, including collage, clay, and photography. This paper may inform future practices that integrate visual arts, narrative processes, storytelling, and other expressive therapies in work with this population.