At first it was fire. they exist About a million years agoThe man has domesticated the one who will permanently change the course of humanity. It must be remembered that for the progress of civilization it
Prometheus stole fire from the gods. This fire awakens many contradictory feelings: security, danger, fear, solace, pain, hope. Sometimes that mutual friend gets out of our control. From wildfires to house fires, everyone fears these catastrophic scenarios. Even more so when on an airplane or when a fire breaks out during the flight. Who among us has not flinched from a disastrous movie where a burning plane crashes with dramatic music?

But do not spread panic! Engineers and researchers select materials and design aircraft with respect Safety Standards Among the most demanding. Thus, materials selected for aviation applications must strictly meet several criteria: toxicity, fire resistance, smoke production, combustion, etc.

In aviation, composite materials are the most widely used (50% of the mass of the aircraft) because it offers a good middle ground between mechanical properties (hardness and resistance) and lightness. These so-called “composites” materials generally combine a fibrous reinforcement (mainly carbon fibres, as in tennis rackets or Tour de France running bikes) and a polymer matrix (also known as an adhesive or glue between the fibers). under the name of plastic). Reinforcement gives good mechanical properties of the material, while the matrix allows the fibers to be connected to each other.

The aircraft consists of various assembled parts. The choice of material for these various pieces mainly depends on the area in which they are located. The engine area and adjacent rooms are among the most important areas on the plane. Especially when the engine catches fire. In this case, the aircraft are designed to be owned by the pilot 15 minutes small to drop your device. During these 15 minutes, the flame (from the combustion of fuel – kerosene – and plastic) must not pass through the composite parts and the part must maintain sufficient mechanical strength.

Illustration of thermomechanical coupling © B. Vieille (via The Conversation)

To prevent these critical conditions and avoid potentially severe consequences, it is necessary to study the effect of heat and mechanical loading (the forces exerted on different parts of the aircraft) to fully understand their effects. Imagine what happens when you place a cup on a chocolate bar (pictured above) and it starts to melt… Specifically, when a piece of compound is exposed to a flame, the plastic softens and melts (turns to liquid), and then pyrolysis (turns to gas). These gases will fuel the flames and facilitate the spread of the fire. It is clear that the ability of the part to withstand force (the weight of the engine, for example) will be significantly reduced. It is these interactions that must be understood.

The characteristic dimensions of composite flight parts vary from a few tens of centimeters to structures on the order of one meter. The difficulty lies in reproducing, at best, on a laboratory scale (and therefore, on a small scale), the true conditions of a thermal attack combined with a mechanical load. or Certificate Rules (Clearance) Air Force defines a flame temperature of 1,150°C and a heat flux (heat emitted per unit area) of approximately 120 kW/m2.

Therefore, it is necessary to develop specific technical means to measure all the physical quantities (temperature, force, deformation) that go into the physical phenomena involved in engine fire. Under these harsh conditions, there is still good news. For thousands of years, mankind has acquired knowledge and tools that enlighten engineers and researchers on how to design composite parts in aeronautics.

A test bench that reproduces the simultaneous effect of flame and mechanical load © B. Vieille (via The Conversation)

It is in this spirit that our research laboratories GPM (Material Physics Group -) and
Korea (The Aero-Thermo-Chemical Professional Research Complex -) joined forces with their skills and combined their efforts to develop an original test bench (a prototype machine dedicated to studying specific phenomena – see above) as part of a project, called Aeroflamme, funded by the Normandy region and Europe.

This bench combines a kerosene stove (which forces a flame) and a hydraulic cylinder (which forces a force). It also integrates several measurement tools: infrared camera (temperature measurement), displacement sensor (distortion measurement) and force. With this test bench, it is possible to better understand the fire behavior of composite materials and more specifically the coupling (interactions) between the effect of flame/heat on the evolution of mechanical properties/behaviour.

Under these conditions, the synthesized part stays well for fifteen minutes…but it can last much longer. Flag on board, good trip!

The use of innovative composite materials in aerospace applications is now facing increasingly demanding safety standards, for which it is necessary to provide reliable and relevant answers. Furthermore, it is essential to allow aviation manufacturers to understand/expect the fire resistance of their materials and, ultimately, their parts and assemblies. Therefore, our research work in aviation materials is part of the rationale for adopting new materials for applications in high temperature environments or even in the event of a serious fire. This material is provided by aviation manufacturers.

This analysis was written by Benoît Vieille, Professor of Aeronautical Materials Mechanics at the National Institute of Applied Sciences (INSA) Roanne Normandy.
The original article was published on the website of Conversation.