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SUMMARY:Testing with Bars: From Dynamic to Quasistatic - Dr G Gary\, Labor
 atoire de Mcanique des Solides (LMS) de lEcole Polytechnique\, Palaiseau\,
  France
DTSTART:20060223T160000Z
DTEND:20060223T170000Z
UID:TALK4716@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:The results that will be presented in this seminar are a mixtu
 re of old and new. Most of them are related to the techniques developed at
  the LMS during the last 15 years in the field of dynamic testing.\nThe fu
 ndamentals of force and displacement measurements based on the knowledge o
 f wave propagation in a bar will be presented. An evaluation of the variou
 s assumptions made and their quality will be proposed in order to optimise
  the accuracy of the measurements\, in particular when considering the cla
 ssical Split Hopkinson Pressure Bar (SHPB). Various aspects of measurement
  problems will be emphasised such as force matching\, optimising specimen 
 dimensions\, precise shifting of the waves (including damping and dispersi
 on when viscoelastic bars are used). Specific problems found when extendin
 g the technique to tension or shear testing will also be addressed. A rece
 nt method for the measurement of dispersion relations in bars will also be
  described. \n A multi-point measurement technique will also be discussed.
  This may lead to the possibility of using bars for making measurements of
  unlimited time duration. The technique is based on a wave separation meth
 od making use of the maximum likelihood method. This method\, applied in t
 he processing of the strain and velocity measurements recorded at various 
 points on a bar\, takes wave dispersion into account. It permits the calcu
 lation of stress\, strain\, displacement and velocity at any point on the 
 bar. Since there is no intrinsic limit to the measurement time in an SHPB\
 , the maximum strain in a given specimen calculated using this technique n
 o longer decreases with strain rate\, as is the case for the classical pro
 cessing method. The technique will be illustrated by test results obtained
  on various materials for a wide range of strain-rates.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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