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Huge increases achieved in torsional resistance... thanks to Comeld

A radical surface treatment developed at TWI has enabled an Industrial Member, that manufactures drive shafts, to achieve far greater torque transfer in its transmission units.

The firm makes drive components for sports, rally and racing cars and uses composite drive shafts extensively.

The simple objective of the TWI work was to match the torsional performance criteria of a traditionally bonded joint to that of a Comeld joint. In fact the Comeld joint easily out performed the standard joint of the samediameter.

Comeld is joining of composite to metal using an innovative surface treatment called Surfi-Sculpt ® .

By applying Comeld technology, developed by TWI's composites team, far greater torsional loads have been successfully transmitted from metallic end fittings to their composite drive shafts.

The work formed part of both a product and process review, and a feasibility study under the National Composites Network.

By using a Comeld joint a smaller diameter, and consequently cheaper, tube is needed to transmit load to the metallic fitting. This in turn provides greater design freedom.

The joint's performance is largely dictated by orientation of the filament winding established during the composite's manufacture. This orientation affects both the loading resistance of the tube and its stiffness. It is importantto match the orientation of the composite with the orientation of the proggles on the metal fitting.

The eventual failure is one of interlaminar shear within the composite. This is a shearing force tending to produce a relative displacement between two laminae along the plane of their interface. So the fibres and laminate failwithin the composite rather than the composite breaking away from the metal fitting.

The conclusion of the feasibility study was that a Comeld joint is fit for purpose and it has the potential to be modified for greater performance.