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Design of a torsion testing system for an existing materialstesting machine

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  • Design of a torsion testing system for an existing materialstesting machine

    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.

    ================================================== ============
    John Costi
    Biomechanical Engineer
    Division of Surgery - Orthopaedic Department
    Repatriation General Hospital
    Daws Road, Daw Park
    South Australia
    AUSTRALIA, 5041

    Phone : +61 8 8275 1126
    Fax : +61 8 8374 0712
    VoiceMail : +61 8 8468 2317
    Email :

    Feel free to visit our Orthopaedic Home Page :
    ================================================== ============