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Domestic Aviation Composite Materials: Those Resins That Dare Not Rely On Imports

Oct 21, 2020

A recent report by an authoritative media reporter "What is stuck in the neck of China's carbon fiber: insufficient toughness of epoxy resin, lack of strength | core technology that needs to be overcome" is all the rage, occupying the headlines of the carbon fiber industry. All the epoxy resins used in domestically produced high-end carbon fibers are imported."

Maybe this reporter only knows that all domestic large aircraft use foreign prepregs. It is true that carbon fiber must have high-end resins that match it in order to be used. No high-end resin will really get stuck on the neck of Chinese carbon fiber, so he came to this conclusion.

As everyone knows, domestic military aircraft also use high-end carbon fiber and epoxy resin, not only epoxy resin, but also a large number of higher-end Bima resin and polyimide resin, but not a single gram of resin is purchased from abroad. The resin system for aviation structure has always been a prohibited material to China. Even civil aircrafts only sell you prepregs, and strictly monitor the product application objects. China's high technology is not as good as some people claim, but it is not as useless as the article said. As a member who has worked in the aviation field for decades, it is necessary to let everyone know the performance of aviation people.

In fact, for aviation people, they have never thought of importing resins for aviation composite materials. The raw materials used in aerospace structures so far are mainly prepregs, and there are different types of carbon fiber and resin composites (ie prepregs) for different purposes. For example, Boeing's early use of T300/5208, and currently the most used T800/ 3900-2, 52098 and 3900-2 are Toray's patents, resins that are impossible to buy on the market.

Whether it is domestic or foreign, whether it is military or civil aircraft, aviation composite resins have never been available on the market. They are all supplied in the form of prepregs with carbon fiber. The prepregs exclusively for Boeing or Airbus are not available. May supply other companies, let alone resin.

The application of my country's aviation composite materials in military aircraft structure dates back to the mid-1970s. The first carbon fiber composite component used in military aircraft was produced by the 320 Plant (now Hongdu Aviation Group) of the Third Aircraft Department (the predecessor of AVIC). The air inlet wall panels of the J-12 aircraft developed by the 625 Institute (the predecessor of AVIC Composite Materials) and the 623 Institute (now AVIC Institute of Strength) use Jihua’s high-strength No. 1 carbon fiber, and the resin used is usually used for FRP The 648 epoxy resin, which made its first flight successfully on December 28, 1977 (see Figure 1).


Figure 1 The outer side wall of the F-12 inlet

Starting in 1980, the Ministry of Machinery Industry and Technology organized the development of strong 5 and F 8-II carbon fiber composite vertical tails. At the beginning, Jihua’s high-strength No. 1 carbon fiber and 648 epoxy resin available on the market were still used. Since Toray T300 of high quality and low price can be purchased from abnormal channels, the material system used is T300/648 (later named 4211). Even though the 648 is just a resin with extremely general performance, significant weight reduction has been achieved through the designer's design, and it has been used for more than 15 years.

Aeronautics have been developing epoxy resins for aviation since the early 1980s. Indeed, epoxy resins for aviation composites are "analyzed from the formulation system and molecular structure. This is a very complex system work with high technological content. Research is difficult." Aviation people are not afraid of evil. Faced with foreign embargoes and blockades, after more than 30 years of unremitting efforts, AVIC has formed an aerospace resin R&D team represented by Sun Zhanhong. , There are also a group of high-end resin research teams in universities and research institutes. In particular, AVIC Composites has developed aerospace resins suitable for various purposes and applications for almost all military aircraft. At present, all the high-end resins used in the composite structure of domestic military aircraft are supplied domestically, and not a single gram comes from abroad.

It is true that the epoxy resin used in aircraft requires a relatively high CAI (compressive strength after impact) after being compounded with carbon fiber, and at the same time, it also needs to have a sufficiently high open-hole compressive strength under damp and heat conditions. This is a contradiction, but aviation people have already This contradiction is well resolved. At present, the CAI of high-temperature epoxy resin (180°C curing system) used in military aircraft can reach about 300MPA, which is basically equivalent to the performance of epoxy resin used in Airbus A350 and Boeing 787.

Not only that, Bima resin and polyimide used at high temperatures are usually considered military materials and are definitely prohibited by foreign countries. Even prepregs are not allowed to be exported to China. However, aviation people have also developed performances comparable to those abroad. The resin can fully meet the needs of military aircraft research and development. This is the case for the aviation people. I am not afraid of your blockade and embargo. When a large number of foreign T300 carbon fibers are used, a resin with performance equivalent to foreign resin after being compounded with T300 is developed through independent research and development. At the beginning of this century, T300 has no market (equivalent to embargo) ), we also developed the domestic carbon fiber CCF300 and HF10A carbon fiber with similar performance to foreign countries. Aviation people and Hengshen people also developed corresponding aviation resins that are well compounded with domestic carbon fibers. The composite performance is basically the same as foreign Used quite. Of course, there is a gap in process performance between foreign resins and foreign resins, but after long-term use, they can be comparable. As for the prepregs used in civil aircrafts, all the prepregs involved in airworthiness are indeed purchased from abroad, but it is only a temporary phenomenon. In the face of the Sino-US trade war, composite prepregs will surely be fully localized, and domestic military aircraft applications have already This provides a foundation.

While talking about aviation resin, there is an aviation person worth remembering, that is, Zhao Qusen (1936~2003) of the former AVIC 625 Institute (Figure 2). Zhao Qusen was a public security officer who joined the army during the war to resist U.S. aggression and aid to Korea. He entered the aviation system after graduating from technical secondary school. He has long been engaged in the application of aviation materials. In the 1970s, he compiled and published the first domestic monograph called "Composite Materials". A must-read book for introductory materials in the domestic composites industry. In the 1980s, he learned that aerospace resins were being developed abroad. He could have ignored it. No one assigned him R&D tasks, and he did not set up a project in the planning of key national defense research projects. Sensitively aware that domestic military aircraft research and development will definitely need this material, take the initiative to take the country's needs as its own mission, and start research and development of dual horse resin for aviation. He has never researched and developed resins, not to mention double-horse resins for aviation, but he just doesn’t believe in evil. He used all kinds of opportunities to consult experts at home and abroad, and collected all the Chinese and foreign language materials he could find. Starting from scratch, he went through untold hardships. , Led a few young technicians, developed the first two-horse resin for aviation in China in the 1980s (the teacher who specializes in resin research and development at Western University of Technology also developed another double-horse resin almost at the same time). However, he was fortunate to have the strong support of the visionary leadership of his unit, and the support of the military aircraft model research and development related chief engineer. He used the dual horse resin he developed for the military aircraft model under development. Of course, it appeared in the application process. Various problems, sometimes almost unsolvable, may be difficult for ordinary people to know, but he unswervingly solves various problems and difficulties encountered in the application process, so that its performance is equivalent to similar foreign resins, and Successfully used in new machine composite material structure. Based on this, he led his team to develop a series of dual-horse resin systems for different occasions and needs. Now the dual-horse resin system created by him covers almost all high-speed military aircraft composite structures. Unfortunately, he died of illness in 2003. While he was still alive, he still missed the shortcomings of his two horses and the corresponding solutions.

The history of research and application of domestic aviation composite materials tells us that this is a struggle between blockade and anti-blockade. In the face of foreign blockades, aviation people like Zhao Qusen will stand up and develop our own performance comparable to foreign ones. Resins for aviation composite materials. In addition, history also tells us that even resins with slightly poor performance can still be applied to military aircraft structures through designer designs to achieve the goal of weight reduction.

This experience can also be used for domestic carbon fiber. Even if the performance is slightly poor, a high-performance carbon fiber composite structure can be developed through the designer's design, but the premise is whether the user is willing to use it. The application of resin for aviation composite materials is forced, even if the performance is slightly poor, users can still unswervingly support its improvement and improvement, and make it perfect. Does domestic carbon fiber have such an opportunity?