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horng99
10-13-1999, 12:15 PM
--- 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
> To: BIOMCH-L@NIC.SURFNET.NL
>
> Date: 13 October 1999 05:32
> Subject: how important is the displacement?
>
>


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