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Test summary


The standard covers various dimensions for some different types of screws, and details tests to establish the mechanical strength of metallic medical screws. Measuring the torque developed while inserting the screw, and the pullout force are also prescribed



Test apparatus


A motorised torque testing system together with a force testing stand plus suitable loadcells



Preparation


Statistically significant quantities of the screws are tested by clamping in a torque testing system. Screws are also driven into reference material to simulate real bone, then subjected to an axial load to determine pullout forces



Test method


Refer to the standard and the required annexes for details of the test to be performed and apparatus involved. Several tests are given in the standards. Mecmesin can supply test equipment for:

Torsional yield strength

Medical screws are firmly held then subjected to rotational force. By monitoring the torsional load and angle, a torsional yield strength can calculated. (N.B. some manual calculation may be involved)


Maximum torque

The maximum torque is determined from the torque / angle curve.


Breaking angle

The clamped screws are tested to the point of failure, and the angle at which the screw breaks is recorded

Insertion and removal torque

Screws are driven into reference material to simulate real bone. The maximum torque is reported during the initial four revolutions on insertion, and the removal torque on the maximum encountered while reversing the direction.


Pullout strength

Screws are driven into reference material to a specified depth. An axial load is then applied until the screw fails or releases from the test block. The maximum load is reported.

 

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