Advanced composite materials have a long history of use in military and government aerospace applications, but as costs of production decline, they will eventually become more integrated into mainstream markets.
Advanced composite materials (ACM), also known as advanced polymer matrix composites, are composite materials that utilize particularly high strength fibers. The fibers have a high stiffness and modulus of elasticity and are bound together by weaker matrices than conventional composite materials. It is also important to note that these high strength fibers are often low density and occupy a large fraction of the material’s total volume.
Current Use of ACMs
Because of their high cost of manufacture, ACMs are often used in the high-value aerospace and sports equipment industries. ACMs also have enjoyed a decades long history of use in military and government aerospace applications. However, as the manufacturing process becomes more automated, ACMs costs will decline and they will eventually become more integrated into more mainstream markets.
Guidelines for Designing Composites
When designing composites, it is always important to keep in mind a few good guidelines. For maximum material strength, align fibers with the load direction and try to avoid shear loading. Additionally, avoid high operating temperatures when possible. Always think about manufacturing considerations early in a material’s design. Finally, use a light core material covered with a strong composite layer.
Categories of Matrix Resins
In general, there are two basic categories of ACM matrix resins: thermosets and thermoplastics. Thermosets are the predominant type in use today and are distinct in that a curing agent and impregnation onto the reinforcing material are required for them to be formed into their final shape. The impregnation is then followed by a curing step, after which the shape of the material cannot be changed save minor finishing changes. The selection of a curing agent is important for the manufacturing process because they are catalysts which determine the reaction rate, and therefore determine the performance of the finished material.
In contrast, thermoplastics make up a much smaller portion of the ACM manufacturing industry. Their raw materials take the form of a nonreactive solid which only require heat and pressure to form into the shape of the finished part. Beneficially, thermoplastic composites can also be reheated and reformed into another shape after cooling in most cases.
Limitations of ACMs
As prolific as their benefits are, ACMs do have a few limitations. For example, composites are notoriously difficult to inspect for flaws and can absorb moisture, which leads to material corrosion and eventual failure in many cases. Additionally, ACMs are prohibitively expensive because their manufacture is labor-intensive and often requires expensive machinery. Finally, metals like aluminum have a relatively high fracture toughness that allows the material to experience a lot of plastic deformation before failing. In contrast, composites have a much lower damage tolerance and experience less plastic deformation before failure. Therefore, composite are much more likely to fail suddenly and catastrophically when compared to metals which yield considerably before failure.
While ACMs have played a large role in the development of the aerospace industry, they have the potential to play a much larger role in the mainstream economy with the advent of cheaper manufacturing techniques. Perhaps someday, ACMs will be able to outperform conventional composites at a similar price point.