Pre-impregnated carbon fibre: the material of choice for advanced engineering applications

What is pre-impregnated carbon fibre?

Put simply, prepreg is a ‘semi-finished product’ of carbon fibre. It is composed of carbon fibre tows bonded to a resin matrix. To put it figuratively: the carbon fibre acts as ‘reinforcing bars’, providing strength and rigidity; the resin acts as ‘cement’, bonding the fibres together, transferring loads and providing protection. Although the resin accounts for only around 30 per cent of the material’s weight, it directly determines the finished product’s toughness, temperature resistance and flame-retardant rating.

This ‘fabric’ is typically only 0.1 millimetres thick, equivalent to a sheet of A4 paper. Yet it is precisely this ultra-thin prepreg, laid in layer upon layer (sometimes numbering over 300), that ultimately forms the ‘armour’ for critical structural components such as aircraft wings and fuselages.

Lightweight: lighter than aluminium alloy, yet stronger than steel

The most notable advantage of carbon fibre prepregs is their extremely high specific strength and specific modulus. Research data shows that their density is only one-fifth that of steel and half that of aluminium alloys, whilst their tensile strength is approximately 990 MPa and their tensile modulus is approximately 87 GPa; their specific strength can be more than 2.2 times that of steel.

This means that, whilst maintaining the same level of strength, the weight of the structure can be significantly reduced. In the aerospace sector, the use of carbon fibre prepregs to manufacture components such as fuselages and wings can achieve weight savings of over 30 per cent. For amphibious aircraft such as the AG600 ‘Kunlong’, the weight reduction from composite components alone is equivalent to that of five to six people, significantly enhancing manoeuvrability and fuel efficiency. In the new energy vehicle sector, the use of T800-grade carbon fibre prepregs to manufacture battery enclosures can similarly achieve weight reductions of 30 per cent to 50 per cent.

High Strength and High Toughness: Solving the Puzzle of ‘Combining Rigidity and Flexibility’

Simply reducing weight is not enough to conquer high-end sectors such as aerospace. The core challenge that prepreg technology has truly overcome is the simultaneous enhancement of a material’s tensile strength and impact toughness.

Traditional carbon fibre composites often face the bottleneck of ‘mismatched tensile and compressive properties’. Through technological breakthroughs, domestic enterprises have developed an entirely new, design-driven technical approach which increases the compressive-to-tensile strength ratio by more than 10 per cent without compromising tensile strength, thereby effectively overcoming the shortcomings in the mechanical properties of T800-grade carbon fibre composites. This technology has been successfully applied in the manufacture of key components for China’s domestically produced large aircraft, such as cabin doors and the rear fuselage section.

In terms of toughening, through the use of thermoplastic toughening agents and precise control of the interlaminar distribution of thermoplastic particles, the post-impact compressive strength (CAI) of prepreg laminates can reach over 280 MPa, significantly enhancing the safety margin of the structure following an impact.

Process Adaptability: The Key to Moving from the Laboratory to Mass Production

The reason why prepregs have become the material of choice for engineering applications lies in their mature manufacturing processes and ever-expanding range of moulding options.

Traditional autoclave moulding processes ensure exceptionally high internal quality—with porosity as low as 0.06 per cent. Today, however, an increasing number of out-of-autoclave (OoA) prepreg technologies are maturing, with post-moulding porosity controllable to within 0.11 per cent (well below the critical threshold at which mechanical properties begin to deteriorate), whilst delivering mechanical properties virtually indistinguishable from those achieved by traditional autoclave processes. This significantly reduces manufacturing costs and moulding constraints, making it possible to manufacture large, load-bearing structural components for unmanned aerial vehicles.

At the same time, rapid-curing prepreg systems have emerged to meet the demands of mass production. For example, Toray’s 3960-FC system can reduce curing time by up to 45 per cent whilst maintaining the original high toughness and high strength properties. It is compatible with a variety of automated processes, including automated fibre placement (AFP), automated tape laying (ATL) and compression moulding, thereby meeting the high-throughput production requirements of next-generation commercial aircraft and advanced air transport platforms.

Outlook for Future Applications

At present, the application of carbon fibre prepregs is rapidly expanding beyond traditional sectors such as aerospace and defence into markets including the low-altitude economy, new energy vehicles, wind turbine blades and consumer electronics. As domestic prepreg technology continues to advance and costs are continually optimised, this advanced ‘lightweight, high-strength’ material will become the preferred and indispensable solution in an increasing number of engineering applications.