The Experts: Do Nord-Lock washers work with fibre composites?

Q: Can Nord-Lock washers be used on fiber composite materials?

A: Yes! However, since fiber composite materials crack and delaminate easily it is important to optimise load distribution and to calculate the correct preload and the corresponding tightening torque in order to avoid damage. Since sliding occurs between the fastener and upper washer during tightening and between the cam faces of the washers during untightening, the surface is not scratched.

Figure 1

Exceeding the compressive and delaminating strength of the composite material around the hole can be avoided, for example, by using adhesively bonded metallic inserts. A metallic insert (Figure 1) can act as a threaded hole or as a durable contact surface which also improves the behaviour of a bolted connection in composite material. An existing design without inserts can be protected by using a metal washer covering two holes or a pattern of holes (Figure 2).