• The materials selected for aeronautical applications must scrupulously meet many safety criteria, according to our partner The Conversation.

  • If an aircraft engine catches fire, it is designed so that the pilot can have 15 minutes to land.

  • The analysis of this research was carried out by Benoît Vieille, professor of mechanics of aeronautical materials at the National Institute of Applied Sciences (INSA) Rouen Normandie.

In the beginning was fire. About 1 million years ago, man domesticated the one who would permanently change the course of humanity. And we must remember that it was for the progress of civilization that Prometheus stole fire from the Gods. This fire which arouses many contradictory feelings: safety, danger, fear, comfort, pain, hope. Sometimes this everyday friend gets out of our control. From forest fires to home fires, everyone dreads these catastrophic scenarios. Even more when you take the plane or a fire breaks out in flight. Who has never trembled in front of a disaster film in which a burning plane crashes to the background of dramatic music?

But don't panic! Engineers and researchers work to choose materials and design planes that meet some of the most demanding safety standards. Thus, the materials selected for aeronautical applications must scrupulously meet many criteria: toxicity, fire resistance, smoke production, combustion, etc.

In the aeronautical field, composite materials are the most widely used (50% of the weight of the aircraft) because they offer a very good compromise between mechanical properties (rigidity, resistance) and lightness. These so-called “composite” materials generally combine fibrous reinforcements (mainly carbon fibers, as in tennis rackets or the bikes of Tour de France runners) and a polymer (also known as the binder or glue between the fibers) matrix. under the name of plastic). The reinforcement gives the material good mechanical properties while the matrix makes it possible to bond the fibers together.

An airplane is made up of different parts assembled together.

The choice of material for these different parts depends mainly on the area where they are located.

The engine area and adjoining rooms are among the most critical of the aircraft.

Especially when the engine catches fire.

In this case, planes are designed so that the pilot has 15 minutes to land his aircraft.

During these 15 minutes, the flame (resulting 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 thermo-mechanical coupling © B. Vieille (via The Conversation)

To prevent these critical conditions and avoid potential dramatic consequences, it is necessary to study the influence of heat and mechanical loading (the forces exerted on the various parts of the aircraft) to fully understand their effects. interactions. Imagine what happens when you put a glass on a chocolate bar (figure above) and it starts to melt ... Concretely, when you expose a composite part to a flame, the plastic will soften, melt (turn into liquid) then pyrolyze (turn into gas). These gases will then feed the flame and facilitate the spread of the fire. Obviously, the capacity of the part to support a force (the weight of the motor for example) will be greatly reduced. And it is these interactions that must be understood.

The characteristic dimensions of aeronautical composite parts vary from a few tens of cm to structures of the order of a meter. The difficulty then consists in reproducing as well as possible on the laboratory scale (therefore on a small scale) the real conditions of a thermal attack combined with a mechanical loading. The aeronautical certification (authorization) rules define a flame temperature of 1150 ° C and a thermal flux (the heat released per unit area) of approximately 120 kW / m2.

It is therefore necessary to develop specific technical means making it possible to measure all the physical quantities (temperature, force, deformation) involved in the physical phenomena involved in an engine fire.

In these extreme conditions, there is still good news.

Mankind has acquired for millennia knowledge and tools that enlighten engineers and researchers on how to design composite parts in aeronautics.

Test bench reproducing the simultaneous effect of a flame and a mechanical loading © B. Vieille (via The Conversation)

It is with this in mind that our research laboratories GPM (Group of Materials Physics -) and CORIA (Interprofessional Research Complex in Aero-thermo-chemistry -) have pooled their skills and combined their efforts to develop a bench of 'original tests (a prototype machine dedicated to the study of certain phenomena - see above) within the framework of a project, called Aeroflamme, funded by the Normandy region and Europe.

This bench combines a kerosene burner (imposing a flame) and a hydraulic cylinder (imposing a force).

It also integrates various measurement tools: infrared camera (temperature measurement), displacement sensor (measurement of deformation) and force.

With this test bench, it is then 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 properties / mechanical behavior.

Under these conditions, the composite part holds up well for fifteen minutes… but it could resist more.

Science is on board, have a good flight!

Our "AIR ACCIDENTS" file

The use of innovative composite materials in aeronautical applications is today confronted with ever more demanding safety standards to which it is imperative to provide reliable and relevant answers.

Also, enabling aeronautics manufacturers to understand / predict the fire resistance of their materials and, ultimately, of their parts and assemblies is essential.

Our research work on aeronautical materials is therefore part of the logic of certifying new materials for applications in a high temperature environment or even during a critical fire event.

These materials are supplied by aeronautics manufacturers.

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This analysis was written by Benoît Vieille, professor of mechanics of aeronautical materials at the National Institute of Applied Sciences (INSA) Rouen Normandie.


The original article was published on The Conversation website.

Declaration of interests

Benoît Vieille does not work, does not advise, does not own shares, does not receive funds from an organization that could benefit from this article, and has not declared any affiliation other than his research organization.

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