Annex A1 is used to measure torsional yield strength, maximum torque and angle at break for metallic bone screws. A description of the ASTM F543-A1 test procedure is as follows:
- Clamp the specimen in a holding device so that five threads below the head of the screw are exposed. The clamping mechanism should prevent screw rotation. Refer to the ASTM specification if the screw is partially threaded or is too small.
- Drive the specimen at 1-5 rpm in the direction of insertion using an appropriate sized screwdriver bit by applying a torsional force until break. If an axial load is required to maintain the screwdriver bit in the screw head, its value should be recorded.
- Analysis: a) Torsional Offset Yield Strength is determined at 2 degrees offset using the torque versus angle of rotation curve. b) Maximum Torque is determined by the largest value on the torque versus angle of rotation curve. c) Breaking Angle is the point at which torque portion of the curve demonstrates its most rapid descent to total failure.
The embedded video demonstrates the use of an ADMET 81T Vertical Torsion Tester for determining offset yield torque, maximum torque and angle at break according to ASTM F543-A1. The torsion test apparatus is rated for 20Nm and is equipped with ADMET's MTESTQuattro® PC based Torsion Testing Software.
You can find more information on bone screw torque testing at ADMET's Biomedical page.