Composite materials can be the solutions to many design problems, but bonding them can prove difficult without expert advice. In this article we explore the essential information you need to have on bonding composites.
What is a Composite Material?
A composite is a material that is composed of a combination of components. By combining two or more elements together, composite materials benefit from increased strength, durability, efficiency or flexibility as compared to their constituent components individually. Composites are manufactured using various methods, such as through the addition of particles and fibers or by utilising different structuring techniques.
Bonding Composite Materials
Traditional bonding techniques such as welding or mechanical fastening often damage and weaken composite materials. As a result, adhesives have been the bonding agent revolutionising the use of composites in industries such as aerospace, automotive, wind and rail.
Bonding composites offers advantages such as even load distributions, shock absorption, high strength to weight ratio, reduced galvanic corrosion, improved aesthetics, and the bonding of dissimilar substrates. Provided you are taking the necessary precautions, using adhesives to bond composite materials can give you a strong, lightweight and aesthetically finished product.
To learn more about the advantages offered by adhesives, as compared to traditional fastening methods, read our article “What Are Structural Adhesives?“.
Adhesives for Bonding Composites
In order to choose the right adhesive for your needs, it’s useful to know 3 things about your chosen material. These are the modulus, the cohesive strength requirement, and the lap shear value. The compatibility of your composite material and chosen adhesive can then be determined by cross-checking these values with that of the adhesive; ensuring all are within the same range. It’s essential that the stresses present in the composite joints do not exceed the adhesive’s capabilities.
Generally speaking, however, different types of adhesives are suited to different composite applications. These types are explored below.
Epoxies
Epoxy adhesives such as Araldite are the most commonly used adhesives for bonding composites due to their excellent bond strength and durability. Different variations of epoxies are fit for different types of composite bonding.
Modified epoxies are flexible and shock-absorbing, ideal for use between composite pieces that have been bonded.
Two-component epoxies provide high strength bonding versatile to different manufacturing processes involving composites.
Heat-curing single component epoxies can also provide high strength bonds to composite materials; however, they require clamps and an oven for their curing process.
Structural Acrylics
Structural acrylic adhesives provide high strength bonds, with high peel strength, when used for composite bonding.
Surface activated structural acrylics provide fast-setting bonds between composite panels.
Methyl methacrylate structural acrylics provide are ideal for composite bonding of rough surfaces due to their gap filling properties.
Urethanes
Urethane adhesives, similar to epoxies, can be used for general composite bonding to provide durable bonds. Flexible urethanes are ideal for general applications requiring a flexible bond.
Polyurethanes
Two-component polyurethane adhesives are able to be used for bonding large composite panels together. One such example is the bonding of two composite panels making up a car bonnet.
Cyanoacrylates
Cyanoacrylate adhesives are capable of creating strong bonds very quickly. These are ideal in applications that don’t require a high peel or impact strength.
UV Curing Adhesives
UV curing adhesives can be used for bonding composite panels to plastic or glass.
Overall, various technologies provide differing benefits when it comes to bonding composites. To find the best product and technology, it is best to focus on the material and application at hand; along with specialist advice when required.
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