View Full Version : Design of a torsion testing system for an existing materialstesting machine

John Costi
09-17-1996, 10:46 PM
Hi fellow Biomechanists!

We have an uniaxial Instron model 8511 servohydraulic dynamic materials
testing machine and I am currently designing a torsion testing system that
we can use with the existing setup. The Instron has a crosshead mounted
actuator (total stroke 100 mm) with a 20 kN load cell mounted on the base of
the machine frame.

We are looking to conduct sheep spinal torsion tests as well as other
torsion tests in the future.

There are certain criteria and constraints which I need to account for when
considering this design and they are :

1) Converting the linear actuator movement into torsion
2) Converting the torsion passed through the specimen back into a linear
force to be read by the load cell
3) Allowing for a pre-load to be placed onto the specimen prior to testing
4) Providing pure torsion only in the specimen during testing (ie no
additional compression or tension after pre-load had been applied)
5) Allowing the specimen to find its own centre of rotation during testing
(ie do not impose a fixed axis of rotation on the specimen)
6) Allowing for varying specimen heights

The major constraint that we have is that the load cell must be used in its
usual position on the base of the machine.

I have a design in mind which I think will work well, but I would be most
interested to hear of any suggestions you may have.

Thank you for your consideration of this design and I will post a summary of
responses received.

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John Costi
Biomechanical Engineer
Division of Surgery - Orthopaedic Department
Repatriation General Hospital
Daws Road, Daw Park
South Australia

Phone : +61 8 8275 1126
Fax : +61 8 8374 0712
VoiceMail : +61 8 8468 2317
Email : john.costi@flinders.edu.au
OR scostjj@rgh.sa.gov.au

Feel free to visit our Orthopaedic Home Page :
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