The research on freezing performance in the cap-type stringers of composite fuselage

Abstract Composite materials are increasingly used in civil aircraft, where there is water accumulation in the lower panel for special reasons, some of which can enter the interior of the cap-type stringers. The accumulated water inside the stringer undergoes a change of liquid-solid–liquid on each flight, and the thermal expansion and cold contraction caused by ice can have a stripping effect on the co-bonded interface of the stringer to the skin, which potentially causes delamination of the co-bonded interface of the stringer to skin and affects the flight safety. In this paper, the cap-type stringer structure of a common composite fuselage is used as an example to study the reciprocating change process of water in the stringer from liquid to solid. When the total number of cycles exceeds one time the flight life of 34000 cycles, there is some problem with whether the co-bonded interface of the stringer to skin exists the phenomenon of debonding. Due to physical freezing, melting, and the longer test cycle, establishing a similar finite element model is considered after completing appropriate physical tests. The physical change process is usually translated into the mechanical loading test to accelerate the test schedule. The test results showed that the loads from the thermal expansion and cold contraction caused by ice were very small, which caused no delamination of the stringer and the skin and had no effect on flight safety.