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Title: ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC

Abstract

The testing and evaluation of candidate glasses for transparent armor served as a primary goal. Other armor ceramics were evaluated too, in support of the development of innovative test methods, whose use will ultimately help in the improvement of armor ceramics or help in better predicting their ballistic performance. The following summarizes this report and this year's work: (1) The elastic properties of a spherical indenter affect the forces necessary to initiate fracture in a target ceramics. The lower the elastic modulus of an indenter material, the easier (i.e., lower forces required) it is to initiate fracture. This implies the fracture initiation of an armor ceramic will depend on the elastic properties of a projectile material, and that this effect, represented by the Dundurs Parameter, can be managed to guide improvement of both armor and projectile materials. (2) The largest flaws in a population dictate both contact damage and fracture initiations. This implies the ballistic response of armor ceramics will improve if those large flaws are precluded from appearing in the materials during their processing. (3) Failure stress dependence on effective area for Hertzian indentation was developed. Such analysis is adaptable to predict ballistically produced fracture initiation as a functionmore » of projectile material and projectile size. (4) A simple, quick, and inexpensive test method was developed to measure the apparent yield stress of armor ceramics. This is significant because yield stress is used as input in ballistic models, and yield stress is traditionally measured using (complex, timeconsuming, and expensive) shock physics experiments. (5) Radial confinement increases the necessary indentation forces to initiate fracture and yield-like responses in ceramics. Ballistic improvement of an armor ceramic will occur if the ceramic can be compressively pre-stressed. (6) The median crack produced by a Hertzian indent is associated with a dramatic increase in target ceramic compliance. More so than any other produced damage mechanism. This suggests that a ballistically induced median crack in an armor ceramic may be associated with the dwell penetration event. (7) Glass exhibits tensile strength that is very much dependent on the amount of material, the side being tested (air versus tin if a float glass), and where it is being tensile stressed (in the middle or near an edge). The management of these effects will improve ballistic resistance of transparent armor (or any ceramic armor that is undergoing deflection as a consequence of a ballistic impact). (8) Plasma-arc heat treatment is a quick and relatively inexpensive method to improve the strength of glass. It is implementable into the production line for the mass production of glass. Increased strain-to-failure and bending deflections are concomitant with increased strength, and therefore, ballistic resistance is improvable using this method. (9) The Hertzian stress field at high contact stresses is very similar to the stress field from a ballistic impact. This is significant because the results from Hertzian indentation measurements have the prospect of being used as input in ballistic models to predict dwell conditions. (10) The understanding of glass densification and fragmentation behaviors are aided by piezo-Raman spectroscopy and quasi-static, high-energy fracture. Continued refinement of these test methods will improve the understanding of glass impact resistance. (11) In addition to glass, strength-size scaling was evident in SiC and B{sub 4}C. Previously proposed strength dependencies on rate from shock experiments may instead be explained by this strength-size scaling effect. (12) The quantification of strength-size scaling in armor ceramics clearly shows there is no single strength value that can be used to describe that ceramic. A ballistic modeler can therefore use more appropriate failure stress value(s) as input to predict deflection and expanding cavity responses in the ceramic target. These follow-on efforts are recommended based on the above statements: (1) Dynamic Hertzian indentation using a dynamic hardness tester; (2) Quantify flaw population size in strategic armor ceramics; (3) Refine and increase robustness of apparent yield stress measurement; (4) Quantify fracture and yield processed in armor ceramics as a function of confined stress; (5) Develop test method to accurately measure stress condition of median crack formation; (6) Measure strength-size scaling in glass ceramic candidates for transparent armor; (7) Refine plasma-arc heat treating to maximize strengthening of glasses and glass ceramics; (8) Refine ballistic modeling analysis to improve adaptability of Hertzian indentation results; (9) Refine densification and fragmentation test methods and interpretations; and (10) Predict ballistically-induced armor deflection and expanding cavity performance using strength-size scaling results.« less

Authors:
 [1];  [1];  [1];  [2]
  1. ORNL
  2. SWRI
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
Work for Others (WFO)
OSTI Identifier:
970913
Report Number(s):
ORNL/TM-2009/234
400403209; TRN: US201003%%647
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; MILITARY EQUIPMENT; VEHICLES; ARMOR; GLASS; CERAMICS; MATERIALS TESTING; ELASTICITY; FRACTURE PROPERTIES; TENSILE PROPERTIES; YIELD STRENGTH; glass; strength; strengthening; Hertzian indentation; Weibull analysis; plasma arc heat treatment

Citation Formats

Wereszczak, Andrew A, Kirkland, Timothy Philip, Strong, Kevin T, and Holmquist, Timothy. ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC. United States: N. p., 2009. Web. doi:10.2172/970913.
Wereszczak, Andrew A, Kirkland, Timothy Philip, Strong, Kevin T, & Holmquist, Timothy. ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC. United States. doi:10.2172/970913.
Wereszczak, Andrew A, Kirkland, Timothy Philip, Strong, Kevin T, and Holmquist, Timothy. Tue . "ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC". United States. doi:10.2172/970913. https://www.osti.gov/servlets/purl/970913.
@article{osti_970913,
title = {ORNL Quasi-Static Mechanical Characterization and Analysis: FY09 Annual Report to TARDEC},
author = {Wereszczak, Andrew A and Kirkland, Timothy Philip and Strong, Kevin T and Holmquist, Timothy},
abstractNote = {The testing and evaluation of candidate glasses for transparent armor served as a primary goal. Other armor ceramics were evaluated too, in support of the development of innovative test methods, whose use will ultimately help in the improvement of armor ceramics or help in better predicting their ballistic performance. The following summarizes this report and this year's work: (1) The elastic properties of a spherical indenter affect the forces necessary to initiate fracture in a target ceramics. The lower the elastic modulus of an indenter material, the easier (i.e., lower forces required) it is to initiate fracture. This implies the fracture initiation of an armor ceramic will depend on the elastic properties of a projectile material, and that this effect, represented by the Dundurs Parameter, can be managed to guide improvement of both armor and projectile materials. (2) The largest flaws in a population dictate both contact damage and fracture initiations. This implies the ballistic response of armor ceramics will improve if those large flaws are precluded from appearing in the materials during their processing. (3) Failure stress dependence on effective area for Hertzian indentation was developed. Such analysis is adaptable to predict ballistically produced fracture initiation as a function of projectile material and projectile size. (4) A simple, quick, and inexpensive test method was developed to measure the apparent yield stress of armor ceramics. This is significant because yield stress is used as input in ballistic models, and yield stress is traditionally measured using (complex, timeconsuming, and expensive) shock physics experiments. (5) Radial confinement increases the necessary indentation forces to initiate fracture and yield-like responses in ceramics. Ballistic improvement of an armor ceramic will occur if the ceramic can be compressively pre-stressed. (6) The median crack produced by a Hertzian indent is associated with a dramatic increase in target ceramic compliance. More so than any other produced damage mechanism. This suggests that a ballistically induced median crack in an armor ceramic may be associated with the dwell penetration event. (7) Glass exhibits tensile strength that is very much dependent on the amount of material, the side being tested (air versus tin if a float glass), and where it is being tensile stressed (in the middle or near an edge). The management of these effects will improve ballistic resistance of transparent armor (or any ceramic armor that is undergoing deflection as a consequence of a ballistic impact). (8) Plasma-arc heat treatment is a quick and relatively inexpensive method to improve the strength of glass. It is implementable into the production line for the mass production of glass. Increased strain-to-failure and bending deflections are concomitant with increased strength, and therefore, ballistic resistance is improvable using this method. (9) The Hertzian stress field at high contact stresses is very similar to the stress field from a ballistic impact. This is significant because the results from Hertzian indentation measurements have the prospect of being used as input in ballistic models to predict dwell conditions. (10) The understanding of glass densification and fragmentation behaviors are aided by piezo-Raman spectroscopy and quasi-static, high-energy fracture. Continued refinement of these test methods will improve the understanding of glass impact resistance. (11) In addition to glass, strength-size scaling was evident in SiC and B{sub 4}C. Previously proposed strength dependencies on rate from shock experiments may instead be explained by this strength-size scaling effect. (12) The quantification of strength-size scaling in armor ceramics clearly shows there is no single strength value that can be used to describe that ceramic. A ballistic modeler can therefore use more appropriate failure stress value(s) as input to predict deflection and expanding cavity responses in the ceramic target. These follow-on efforts are recommended based on the above statements: (1) Dynamic Hertzian indentation using a dynamic hardness tester; (2) Quantify flaw population size in strategic armor ceramics; (3) Refine and increase robustness of apparent yield stress measurement; (4) Quantify fracture and yield processed in armor ceramics as a function of confined stress; (5) Develop test method to accurately measure stress condition of median crack formation; (6) Measure strength-size scaling in glass ceramic candidates for transparent armor; (7) Refine plasma-arc heat treating to maximize strengthening of glasses and glass ceramics; (8) Refine ballistic modeling analysis to improve adaptability of Hertzian indentation results; (9) Refine densification and fragmentation test methods and interpretations; and (10) Predict ballistically-induced armor deflection and expanding cavity performance using strength-size scaling results.},
doi = {10.2172/970913},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2009},
month = {12}
}

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