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Fwd: responses on how important is the displacement?

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  • Fwd: responses on how important is the displacement?

    --- Andrew New wrote:
    > From: "Andrew New"
    > To: "Boon Kam"
    > Subject: Re: how important is the displacement?
    > Date: Wed, 13 Oct 1999 08:55:03 +0100
    > I assume you are pulling a bone screw from bone
    > using some kind of
    > mechanical testing device, and plotting force vs
    > displacement.
    > >When a pullout test is carried out, how important
    > is
    > >the displacement?
    > Probably not very important. The displacement you
    > are measuring (depending
    > on how and where it is actually being measured) is
    > likely to include, but
    > may not be limited to, the deflection of the bone
    > specimen about its
    > restraints, strain in the bone, strain in the screw
    > and deflection of your
    > testing apparatus. I imagine that the pull-out
    > occurs by failure of the bone
    > material around the threads of the screw and that
    > the quantity most likely
    > to be of interest to you is the maximum force
    > sustained by the screw.
    > >The peak falls tremendously to zero and below
    > >zero, after it hits the 300N before it even reaches
    > >the displacement of 6mm.
    > The fact that the load becomes less than zero after
    > failure is almost
    > certainly an artifact of your testing apparatus. If
    > it is a rapid ( spike to below zero, followed by a return to close
    > to zero, it is likely a
    > rebound effect due to the mass of the grips or
    > fixtures used to hold the
    > specimen and screw. If it remains below zero for
    > some time, then it is
    > likely to be a hysteresis effect in your load
    > transducer. Usually neither
    > are anything to worry about.
    > Hope this helps
    > Andrew New
    > Research Fellow in Bioengineering
    > Anglia Polytechnic University
    > T. 01245 493131 x 3316
    > F. 01245 252646
    > -----Original Message-----
    > From: Boon Kam
    > Newsgroups: bit.listserv.biomch-l
    > Date: 13 October 1999 05:32
    > Subject: how important is the displacement?


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