| In-Situ Scanning Electron Microscopy Comparison of Microstructure and Deformation Between WE43-F and WE43-T5 Magnesium Alloys |
May 2012 |
10 pages |
| Authors:
Tomoko San; Jian Yu; Bruce Davis; Richard DeLorme; Kyu Cho; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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 | In-situ tensile testing in the scanning electron microscope was used to investigate the quasi-static deformation behavior and fracture mechanism of WE43 magnesium alloys. The in-situ tensile experiments were conducted at room temperature at a constant crosshead speed of 0.5 mm/min. One set of samples was a rolled and quenched F temper alloy and the other set was an artificially aged T5 temper alloy. The objective of this research was to ... |
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| Microstructural Characteristics of High Rate Plastic Deformation in Elektron (trademark) WE43 Magnesium Alloy |
Apr 2012 |
12 pages |
| Authors:
Joseph Hamilton; Sarah T Brennan; Yongho Sohn; Bruce Davis; Rick DeLorme; Kyu Cho; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| High strain rate deformation of WE43 magnesium alloy was carried out by high velocity impacts, and the characteristics and mechanisms of microstructural damage were examined. Six samples were subjected to a variety of high velocity impact loadings that resulted in both partial and full damage. Optical, scanning and transmission electron microscopy analyses were performed in order to identify regions of shear localization. These regions were used to map, both quantitatively ... |
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| Magnesium Technology and Manufacturing for Ultra Lightweight Armored Ground Vehicles |
Feb-2009 |
14 pages |
| Authors:
Kyu Cho; Tomoko Sano; Kevin Doherty; Chian Yen; George Gazonas; Jonathan Montgomery; Paul Moy; Bruce Davis; Rick DeLorme; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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| The current paper summarizes magnesium alloy metallurgy and wrought manufacturing with an initial emphasis on the Elektron WE43 alloy system for lightweight armored ground vehicle applications. Engineering design factors are reviewed and initial mechanical property data are presented along with ballistic results and findings from blast simulations. Finally the future role of magnesium alloys in ultra light metallic armor is discussed in terms of material development and application. |
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| A Materials Approach in the Development of Multi-Threat Warfighter Head Protection |
Dec 2008 |
9 pages |
| Authors:
Shawn M Walsh; Brian R Scott; Tyronne L Jones; Kyu Cho; James Wolbert; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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| The United States has historically capitalized on material and process advances to develop improved ballistic head protection for the warfighter. This also includes innovations in the design of various helmet elements based on careful consideration of the environment, patterns of use, interfacing with other equipment (e.g., weapons, body armor), and possible threat scenarios. As such the U.S. helmet bas evolved in both shape, composition, and manufacture, and this same trend ... |
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| Nanocrystalline and Ultra-Fine Grained Tungsten for Kinetic Energy Penetrator and Warhead Liner Applications |
JUN 2007 |
14 pages |
| Authors:
Kyu Cho; Laszlo Kecskes; Robert Dowding; Brian Schuster; Qiuming Wei; Ruslan Z. Valiev; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| For the first time, we have demonstrated adiabatic shear localization in pure, ultra-fine grain (UFG) and nanocrystalline (NC) tungsten (W). Fabricated by severe plastic deformation (SPD), microstructural and mechanical property analyses of the W samples show that the combination of fine grain size, stored strain energy, ultra-high strength, little or no work hardening capacity leads to a unique flow softening behavior. It is further hypothesized that, while maintaining material ductility, ... |
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| Status Report on SPS TiB2/TiB/Ti Functionally Graded Materials (FGMs) for Armor |
SEP 2006 |
26 pages |
| Authors:
James W. McCauley; G. D'Andrea; Kyu Cho; Matthew S. Burkins; Robert J. Dowding; Jr Gooch William A.; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD WEAPONS AND MATERIALS RESEARCH DIRECTORATE
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| The pioneering research by Wilkins and colleagues in the 1960s led many investigators to conclude that ceramic armor performance could be significantly enhanced with materials macrostructurally designed to grade from a pure ceramic to a stiff, more ductile material at the back surface. Several configurations of TiB2/TiB/Ti functionally graded materials were fabricated using a spark plasma sintering process. Detailed microstructural characterization of the as-processed material is presented as well as ... |
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| Crack Stability and Its Effect on Single-Edge-Precracked Beam (SEPB) Fracture Toughness of Hot-Pressed Silicon Nitride Beam Specimens |
JUN 1997 |
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| Authors:
ISA BAR-ON; Francis I. Baratta; Kyu Cho
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 | The effect of stable crack extension on fracture toughness test results was determined using single-edge-precracked-beam specimens. Crack growth stability was examined theoretically for bars loaded in three-point bending under displacement control. The calculations took into account the stiffness of both the specimen and the loading system. The results indicated that the stiffness of the testing system played a major role in crack growth stability. Accordingly, a test system and specimen ... |
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| Fracture Toughness Estimation From Ceramic Tensile Specimens by Fractographic Analysis |
JUN 1997 |
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| Authors:
R. NATHAN KATZ; Kyu Cho
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| Empirical criteria are presented for selection of uniaxial tensile failure origins that will yield valid fracture toughness estimations. Using these criteria, estimations of fracture toughness based on fractography of an AIN, two SiCs, an AIN-SiC solid solution and a particulate composite, and a TiB(2) were performed. Comparison of the fracture toughness values estimated from fractography with fracture toughness measured by the single-edge precracked beam (SEPB) method will be shown. Close ... |
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| Uniaxial Strength and Mode I Fracture Toughness of Hot Pressed Silicon Carbide (SiC) Materials |
JUN 1997 |
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| Authors:
Kyu Cho; R. NATHAN KATZ; ISA BAR-ON
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| Silicon carbide (SiC) ceramics are being used and considered for a number of room temperature wear and optical applications where strength and fracture toughness are critical design parameters. Thus, there is a requirement for high-quality tensile strength and Weibull data for this class of materials. This report will present room temperature uniaxial tensile strength data, single-edge precracked beam (SEPB) fracture toughness (K(IC)) data, and fractographic analysis for several hot-pressed (HP) ... |
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| MECHANICAL PROPERTIES OF HOT PRESSED TITANIUM DIBORIDE |
AUG 1996 |
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| Authors:
Kyu Cho; Robert N. Katz; ISA BAR-ON
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| ROOM TEMPERATURE UNIAXIAL AND FLEXURAL STRENGTH, WEIBULL PARAMETERS, AND FRACTURE TOUGHNESS OF HOT PRESSED TIB(2) ARE PRESENTED. FRACTURE TOUGHNESS ESTIMATED FROM FRACTOGRAPHIC ANALYSIS WAS COMPARED TO THE SINGLE EDGE PRECRACKED BEAM (SEPB) K(IC) MEASUREMENTS. DISCREPANCY BETWEEN THE ESTIMATED AND MEASURED VALUES WERE RATIONALIZED BY INVOKING THE POSSIBILITY OF R-CURVE BEHAVIOR. FRACTOGRAPHIC ANALYSIS AND THE LOAD DISPLACEMENT RECORDS OF VICKERS INDENTED SPECIMENS POINT TO THE EXISTENCE OF RISING R-CURVE BEHAVIOR. |
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Reports by Author
