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Philippe Boutemy
04-24-1997, 05:54 PM
Hi!

Thank you for all your replies

My question was:
We would want to do a photoelasticimetric study on fresh bone,
and for that we thought to use a kind of spray to recover ours
bones. But after asking informations about that at Vishay
Micromesure, we learnt that it isnít so easy! The solution
is to use
a thermoformable plastic film what is hard to apply on the
fresh
bone. Then my question is: Do you know a easier solution for a
photoelasticimetric study on fresh bone? And have you ever
heard speaking about a ę spray Ľ?


Yours replies:
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[...] Pour plus d'informations regardez notre site WEB sur
http://www2.univ-poitiers.fr/spi/mds/index.html

COUSSI Olivier
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I have done some work using conventional thermoplastic photoelastic coating
(PL2 & PL8, Vishay). In that case, large errors must be expected due to the
reinforcing effect (L.Cristofolini, A.Cappello, A.Toni: "Experimental
errors in the application of photoelastic coatings on human femurs with
uncemented hip stems" Strain of August 1994: pp.95-104).

About the spray: yes, a technique exists, but as far as I know it is only a
prototype. I know the group of Eddie O'Brien (British Aerospace, Bristol,
UK) was working on it a couple of years ago.

Another problem you should consider: I am not sure what sort of bones you
want to test. If you are planning to test cadaveric specimens, you should
bear in mind that all the photoelastic materials are hygroscpic (they swell
in presence of humidity), and this may cause large additional apparent
strains due to the humidity contained in the specimen.
For this reason, I decided to use synthetic composite femur models
(Cristofolini L., Viceconti M., Cappello A., Toni A. 'Mechanical validation
of whole bone composite femur models', J. Biomechanics, 1996, 29(4),
525-535)

Luca Cristofolini
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We are just getting involved in a study using photoelastic methods to measure
strain in bone. I understand that sprays are available, but they allow only
a visualization of strain patterns. Because the sprays cannot be applied
such that a constant thickness results, strain measurements cannot be made.
Formable, partially polymerized sheets are cast that have a constant
thickness. These sheets are then formed to the bone and allowed to fully
cure, after which they are bonded to the bone using a reflective adhesive.
The process takes about three days to complete. I don't think an easier
method of obtaining strain readings by photoelastic methods is available.
The Vishay instructional bulletins provide a detailed step by step process.
The bone must be extremely clean of soft tissue. There are many references
available.

Brent Parks
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Sounds very difficult to me. I have never heard of a spray on
photoelasitc coating. How would you control the thickness of the
photoelastic layer? If I remember correctly the fringe order is also
a function of thickness. With the film one also must consider the
stiffening that the film itself will impart on the structure (bone).
Sorry to sound so discouraging.

Christof Hurschler
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Yours sincerely,

Philippe Boutemy
--
GEBOAS
(Groupe d'Etude en Biomecanique Osteo-Articulaire de Strasbourg)
http://www-ensais.u-strasbg.fr/geboas/source/geboas.htm