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SUMMARY:Hardness-induced elastic\, plastic\, cracking observations - Ron A
 rmstrong\, Center for Energetic Concepts Development\, University of Maryl
 and
DTSTART:20110331T150000Z
DTEND:20110331T160000Z
UID:TALK29856@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:A useful stress – strain method is illustrated for compariso
 n of the elastic\, plastic\, and cracking behaviors exhibited in hardness 
 tests done on a number of crystal\, polycrystal\, and composite materials 
 [1].  Hertzian-type elastic modulus values are able to be easily determine
 d from either loading or unloading curves obtained in continuous nano-inde
 ntation hardness tests as compared with macro-indentation test results [2]
 .  And for nano-indentation testing\, there is the issue of determining th
 e highest Hertzian pressure that a material can support before plastic flo
 w is initiated.  For indentation-induced plastic deformation behavior\, th
 ere is the opportunity stemming from early micro-hardness test results obt
 ained on MgO (001) crystal surfaces to probe dislocation pile-up stress co
 ncentrations and crack-forming reactions [3]. Such crack size dependence o
 n hardness load connects with specification of indentation fracture mechan
 ics parameters and\, based on comparison with conventional fracture mechan
 ics test results\, prediction of material failure conditions [4].\n\nRefer
 ences \n\n1. R.W. Armstrong and W.L. Elban\, “Macro-to-nano-indentation 
 hardness stress-strain aspects of crystal elastic\, plastic\, and cracking
  behaviors”\, Exp. Mech.\, 50 (2010) 545-552.\n2. L. Ferranti\, Jr.\, R.
 W. Armstrong\, and N.N. Thadhani\, “Elastic/plastic deformation behavior
  in a continuous ball indentation test”\, Mater. Sci. Eng. A\, 371 (2004
 ) 251-255.\n3. R.W. Armstrong and C. Cm. Wu\, “Lattice misorientation an
 d displaced volume for microhardness indentations in MgO crystals”\, J. 
 Amer. Ceram. Soc.\, 61 (1978) 102-106.\n4. R.W. Armstrong and O. Cazacu\, 
 “Indentation fracture mechanics toughness dependence on grain size and c
 rack size: Application to alumina and WC-Co”\, Intern. J. Refract. Met. 
 & Hard Mater.\, 24 (2006) 129-134.            \n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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