Japan tried to replace the fasteners with a glue to connect the composite structure of the fighter

According to the US "Aviation Weekly and Space Technology" website reported on November 20, 2018] Japanese engineers are working to replace fasteners with glue, using composite materials like the skin as the bearing structure of the fighter.

A full-size mid-body segment is being tested for strength as part of the technical acquisition work for the Future Fighter Project in Japan. The test piece is made of modules in which the composite skin is glued to the composite frame and beam interconnected by the adhesive.

An official of the Japan Defense Agency's Equipment Department (ATLA), who is responsible for this work with Mitsubishi Heavy Industries (MHI), said the assessment has not been completed but no major problems have occurred so far. The test will be completed on March 31, 2019. The official said that due to the difficulty of technology, it may take more time.

According to an analysis by Japanese engineers, one of the key factors limiting the widespread use of composite load-bearing structures is that such materials are prone to high scrap rates due to drilling. But if glue is used instead of the rivet, this problem is almost non-existent and the need for drilling is very small.

This mid-airframe test piece was built according to a conceptual design prepared by ATLA for future fighters. The future fighter is a large combat aircraft that will enter service in the 1930s. The Japanese government is considering alternatives to independent design including joint international R&D, but with other countries, R&D aircraft can still use the technical knowledge accumulated by Japan as expected.

MHI built this mid-body in FY2017. The sample is 8.6 meters (28.2 feet) wide and 5.2 meters long. A smaller glued composite structure has been previously tested for evaluation. Thanks to the bonding technology, the current fuselage section is simpler than the fuselage section originally intended to be manufactured using the prior art, with fewer structural parts.

The official said at the ATLA technical seminar that the test sample has been tested for limited loads, which is the maximum that may occur during flight, but not the ultimate load, which is 50% larger than the limit load.

Engineers are looking for signs of damage to the adhesive and the material at the junction of adjacent materials. They have not found it so far. As previously described by ATLA, the parts of the sample are separately fabricated in an autoclave and then bonded together under pressure to complete the assembly.

In addition to creating opportunities for the wider use of composite materials, the biggest direct benefit of bonding technology is weight loss. The glue is lighter in weight than the fasteners and the components do not need to be reinforced around the holes.

ATLA estimates that the structural components being tested are 10% lighter than the same structure manufactured using fastener technology and are a step forward in the use of lightweight materials. The department will not disclose how much weight is reduced by the use of composite materials.

The fuselage still uses metal material on the belly to absorb complex loads from the landing gear, a task that composites cannot accomplish. The weapon bay, also located in the lower part of the middle fuselage, also needs to be made of metal.

Fatigue testing is also needed for this Japanese technology, but so far no funding has been provided. This type of work should be done on smaller scale samples to control the size and cost of the required cooling facilities. Article source: