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Performant Alternative to Nickel-based alloys for Turbine of Helicopter Engine Replacement

Periodic Reporting for period 1 - PANTHER (Performant Alternative to Nickel-based alloys for Turbine of Helicopter Engine Replacement)

Reporting period: 2019-01-03 to 2020-07-02

Improvements in design of the gas turbine engines over the years have importantly been due to development of new materials. Indeed, those materials have always played a prime role in the turbine performance with the capability to withstand elevated temperature service and at the same time to contribute to weight reduction. Stress rupture, low cycle fatigue life, resistance to oxidation are among the usual important parameters, that are well known by the Aerospace industry. The potential hazard resulting from uncontained turbine engine rotor blade failure has also always been a longterm concern for engine manufacturer.

To fully contain the failed blades under operating conditions is one of the most important considerations to meet the rotor integrity requirements. There are many factors involving the engine containment capability which need to be reviewed during the engine design phases, such as case thickness, rotor support structure, blade weight and shape. For this specific purpose, the sizing of those parts is based on the Shock Physics, which is among one of the most challenging scientific discipline. The first method to demonstrate the engine containment capability has always been a blade-off test, which is still a key milestone for certification. Simulation tools have been later introduced but have still a greater role to play in certification program.

Thus, the world class turbines engines manufacturer needs the best technology capabilities in material innovation, shocks physics at a very high speed/very high temperature and advanced simulation tools. The CleanSky program supports the European industry to remain in a leading position and address this specific topic in the CfP07 calls. The purpose of the ENG-01-29 call is to evaluate the ability of the innovating TiAl material to replace Nickel-based super-alloys for low-pressure or free turbine application. The project will focus on the investigation of the resistance of TiAl turbine blades to impacts through original experiments as well as through simulation with the ambition to create a reliable transient dynamics material model for behaviour and failure.

THIOT is one of the sole private company being a pure player of the Shock Physics. For 30 years, THIOT has been delivering its own gas guns benches as well as engineering studies combining simulation and test. THIOT has a strong business relationship with the main actors in the fields of Aeronautics, Space and Defence.

Hereafter are the specific objectives of the project as described:
- Understand and characterize the dynamic behaviour of the TiAl material
- Develop and validate a numerical model of the TiAl dynamic material behaviour
- Improve the knowledge of the dynamic behaviour of materials at very high temperature
- Validate THIOT equipment for very high temperature dynamic testing conditions of blade-off
- Strengthen THIOT methodology for aeronautic material dynamic studies and develop its awareness in the community to contribute to the success of the Cleansky Roadmap situation
WP1 includes first a material health analysis aiming at identifying any deviation in terms of mechanical properties due to the manufacturing process. The second section of this WP consists in the evaluation of the mechanical properties of the material both under dynamic and high temperature loading on Split Hopkinson (SH) pressure bars. So far, the TM was only able to supply a few small samples of the rough material. A set of 5 (out of around 120) SH tests were carried out on compression loading to evaluate the plastic behaviour of the material under dynamic loading (see Figure 1). Some feasibility tests of Digital Image Correlation (DIC) were performed at the beginning of the project. At this time, THIOT is still waiting for the delivery of the rough material in order to continue the SH testing, especially in tension loading, allowing to evaluate the behaviour up to failure.

WP2 consists in a phenomenological analysis aiming at identifying the loading range the material will exhibit during a blade-off. The second step is the design of test specimen and conditions relative to the loading range previously identified. The last step is the material model calibration by simulating and correlating the SH tests (after tests). So far, the phenomenological analysis has started by building the blade-off model (with the
help of the TM who supplied us with a generic model). The numerical model runs and now requires firsts input from a first batch of dynamic tension tests. Tension results are indeed mandatory as failure drives the way a blade-off occurs. THIOT is therefore at this time waiting for the material to be tested in tension before being able to continue this first task, and start the following.
The application within the frame of this proposal is initially focusing of the use of TiAl for LP turbine blades for the WP3 demonstration platform, which is a high performance short range gas turbine for helicopter or Turbo-prop aircraft. Should the project be successful, and the model been validated, the PANTHER project might transfer its innovations to the following project/market:

- Use of TiAl turbines blades in other engines development
- Upgrade of current certified engine with TiAl turbines blades
- Implementation of the methodology for Nickel based super alloy turbine blade to reduce design safety margin, thanks to a greater accuracy of the model
- Use of TiAl for other parts in the Aeronautic engine
- Use of TiAl for other applications facing high speed and high temperature (re: Space, Automotive)
- Use of THIOT test bench and simulation tools for other cases of shock physics at very high temperature
- Development of further material models for LS-DYNA implementation based on the PANTHER project works

The direct beneficiaries of this work will be of course engine manufacturers such as Safran that are already interested on using more and more TiAl in their products. The methodology proposed in this project could also be applied to the dynamic characterization of other materials working at high temperature. THIOT thinks that the parts made of this material had not been optimized and there is still work to do in order to reduce their mass while conserving a sufficient resistance to impact (blade-off, etc.).

It could also be applied to state-of-the-art competition cars engines where performances the mass are critical. THIOT has already worked with a partner from the automotive industry in order to test the resistance of Nickel-based super-alloys at high temperature. The FIA (International Automobile Federation) indeed imposes the manufacturers to prove that in case of a turbocharger bursts the debris can be contained inside the casing. As these parts can be ejected at velocities up to 300 m/s and uses to work at temperature up to 1000°C then the threat is exactly the same as the one encounter by aircraft engine manufacturers.
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