5.1.6 Joints with Plastic and Elastomeric Substrates

5.1.6 Joints with Plastic and Elastomeric Substrates

Compared to metals, plastic and elastomeric substrates are characterised by the following aspects:

• greater flexibility;
• lower modulus of elasticity;
• higher coefficient of thermal expansion; and
• anisotropy of physical/mechanical properties, meaning that the material may have different properties in different directions (i.e. directional grain structure).

These characteristics lead to a less even distribution of stresses in the adhesive layer, which is why flexible adhesives are generally recommended over rigid adhesives when bonding plastic and elastomeric substrates. However, the use of flexible adhesives is not always possible as they may limit the load capacity of the joint. The best compromise between load-bearing capacity and elasticity depends on the specific application and substrates.