TECHSiL’s Guide to Bonding Composite Materials; Composite Bonding FAQs

Composite materials are increasingly being used across industries becoming vital in modern manufacturing especially in automotive and aerospace applications. TECHSiL have put together a short guide to bonding composite materials, answering some frequently asked questions.

What are Composite?

Composite materials are engineered from two different materials, a matrix and a reinforcement with the goal of combining certain characteristics that neither material could achieve alone such as a high strength to weight ratio or corrosion resistance.

What are types of composite materials?

• Carbon fibre reinforced polymer (CRP or CFRP
• Fiberglass, GRP, or glass reinforced plastic
• Thermoplastic composites
• Metal matrix composites
• Reinforced concrete
• Composite honeycomb
• Fibre reinforced plastic (FRP)
• Ceramic matrix composites

Where are composites used?

Composite materials are key to weight reduction in vehicles, aircrafts, body armour, sports goods, drone structures and many more.

The automotive industry is the biggest utiliser of composite materials as they allow for lighter weighted vehicles which improves fuel efficiency in consumer vehicles, increased distance for EVs, speed for motorsports, and aesthetics for high end vehicles.

Other areas for composite use include:

• Aerospace – wings, structures, fuselages, interiors
• Defence – body armour, armoured vehicles, equipment housings
• Renewable Energy – wind turbine blades, infrastructure.
• Consumer goods – sporting goods, bicycle frames, kitchen counters
• Marine – boat hulls and decks, propellers, and pipework
• Speciality Vehicle – access panels, track beds, interior moulding and panelling

Why use adhesives to join composite materials?

Traditional joining methods like welding or mechanical fastenings aren’t suitable for composite materials. As they require drilling holes and/or adding heat they can damage the structure of the material, add weight and unsightly elements, and concentrate stress at specific points.

Instead, adhesives are used which mimic the properties of the composite material to reinforce them while also distributing load, absorbing shock and providing a clean, aesthetically pleasing bond line where required.

Adhesives also work well with dissimilar materials, LSE plastics, metals and more enabling more design flexibility.

Another key benefit of adhesive bonding is their ability to seal the area while providing a durable joint, they can protect against corrosion, moisture, chemicals, and other contaminants further improving the composite structure.

Do composites need surface treatment or preparation? 

For a higher strength, surface preparation is recommended to remove any containments. Depending on the material, the type of treatment and preparation required can vary.

Surfaces can be cleaned or degreased with isopropyl alcohol wipes, abraded to create a rough texture and remove unwanted layers, or primers can be used. For more information and advice contact our Technical Team.

What adhesive is suitable for bonding composites? 

Epoxies are the most popular choice, they tend to have the highest strength and performance, providing resistance to high temperatures, solvents and weathering.

Consider:

• Permabond ET5428 Black Thixotropic Adhesive – Excellent impact and vibration resistance as well as exceptional performance at elevated temperature, ideal for carbon fibre.
• Araldite 2015-1Toughened Epoxy Adhesive – Room temperature curing paste adhesive giving a resilient bond, ideal for bonding GRP and dissimilar materials.

Acrylics offer a faster cure speed and higher tolerance for oily or unabraded bonding surfaces than epoxies, but with a slightly lower strength and durability.

Consider:

• Permabond TA4208 Black Toughened Acrylic - Excellent shear strength on many substrates with little surface preparation.
• Plexus MA300 Fast High Strength Methacrylate - Designed for structural bonding of thermoplastic, metal and composite assemblies.

Urethane adhesives are relatively flexible when cured, they have excellent impact resistance and are a good choice for bonding materials with different coefficients of thermal expansion.

Consider:

• 3M DP6310NS Scotch-Weld Multi-Material Composite Urethane Adhesive- Excellent elongation and stress strain properties for durable bonding of composite parts.

For expert advice on which adhesive to bond your composite material application, contact our Technical Team.