Subject:Generation of shock waves in the form of bursts in copper-based single-crystal shape memory alloys: study of mechanisms and optimisation of metallurgical and mechanical parameters

Materials subjected to stress contain elastic energy, which can be temporary, as is the case with elasticity, or permanent in the absence of external constraints, localized around dislocations, at grain or phase interfaces, or around inclusions or precipitates. If the stress or the temperature is modified, this energy can decrease quasi-continuously during restoration or annealing, or abruptly by releasing this energy in the form of a shock wave that transforms into an audible acoustic wave (tin cry for twinning and austenite to martensite transformation in steels during quenching).

In CuAlNi shape memory alloys (SMAs), the phenomenon occurs when a thermoelastic martensitic alloy has been compressed by reorientation beyond a certain value, which generates a second, non-thermoelastic martensite. When the temperature increases under zero stress, the inverse transformation from martensite to austenite is triggered in the form of a shock wave or Burst. The shape recovery can reach 9% with a stress of a few hundred MPa. If one face is resting against a mass large relative to that of the sample, its stored elastic energy is converted into kinetic energy, and the sample is projected at a speed of a few tens of meters per second. 

The results of this research would make it possible to improve certain currently qualified space actuators or even to imagine new types of actuators:

• Triggy: This actuator generates a significant shock when the tie rod breaks, and part of the shock comes from the SMA burst energy. The absence of a burst would make it possible to reduce the intensity of the shock generated.

• Gripper, Satlatch, others: Some actuators owe their performance to the gradual activation of the SMA component (Example: progressive preload loss before release on the Gripper). On these actuators, it is necessary to guarantee the absence of a burst in the SMA components.

• New Actuator Perspectives: Some actuators could consist of maximizing this burst energy and turning it into a projectile. Example: Cable cutter, separation mechanism, etc.

The goal is to determine the parameters that govern the transition from a continuous release of energy to an explosive form known as a Burst. An important metallurgical parameter is the composition (hypo- or hypereutectoid), which allows for the selection of a priority martensite or a mixture of the two martensites. The direction (tension or compression), the intensity of the stress, and the maximum deformation are also important. Grain size and crystallographic orientation are also noted. For simplification, the work will focus on single crystals with a constant orientation relative to the uniaxial compression stress. The influence of heat treatments—solution treatment temperature, quenching rate, tempering time and temperature for stabilization—must also be considered. The interaction between the two types of martensite is not documented and certainly plays an important role in triggering the Burst.

The volume shock wave can be the cause of cracking in certain samples, and the analysis of the morphology of the fracture surfaces of these samples could provide information on the mechanism of development of these cracks. Experiments without shocks relating to the interaction with the damper can be carried out to provide elements of response.

An exhaustive study of the influence of all parameters is necessary to control the presence or absence of bursts. In summary, the purpose of this study is to determine the parameters that make it possible to control the release rate of the elastic energy stored in a device using a single-crystal CuAlNi alloy.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - pascal laheurte@univ-lorraine.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!

The candidate's profile must match the description of the research project. The candidate must:
- Hold an engineering degree or a Master's degree in materials
- Have experience in mechanical domain and modelling
- Have skils in experimental mechanics, materials (SMA), space technologies
- Have ability to work as part of a team,
- Be able to commit fully to the project, with a strong motivation for the proposed subject and, more generally, for the field of space mechanisms
- Be intellectually curious, conscientious and diligent.
A good level of English is essential, as the candidate will be required to interact regularly with foreign researchers