Tecnalia in Spain
The aim of ESR3 is to study the thermomechanical behaviour of three selected Titanium, Aluminium and Nickel based alloys. The ESR3 will have to provide a detailed experimental behaviour law and perform microstructural investigations in order to clearly establish interdependences between microstructure and strain. The main technological and scientific steps to overcome concern :
- the definition of thermomechanical tests able to reproduce the same solicitations than during machining (high deformation rate and medium range deformation), FSW (medium deformation rate, high deformation) and Additive Manufacturing ( high temperature),
- the identification the kinetic changes parameters
- the ability to relate these parameters to the microstructures and dynamic behaviours observed.
Design a new test bench
A new experimental dynamic torsion test device based on the principle of a fly wheel will be developed to reproduce locally the stress levels and strain rates encountered in processes such as machining or FSW. In a first step, this device must allow, by means of a torsional stress, to achieve very high deformations (of the order of ε = 2) at medium strain rate (of the order of 200 s-1). An evolution will then be made to perform temperature tests (up to 0.7 times the melting temperature for the three alloys studied). The novelty of this equipment lies in the dynamic tests in torsion and traction that can be carried out under extreme strain rates by controlling the speed of loading. Interrupted tests are also expected to be performed (i.e. where the test can be stopped at an imposed strain level), to allow the genesis of the microstructural transformation to be studied during loading. Strain and temperature in the sample will be measured during the tests.
Study the thermomechanical behaviour
Once the test bench has been developed, the ESR3 will have to set an accurate experimental behaviour law. For this purpose, she/he will rely on the design of experiment (DOE), in order to optimize and organize her/his tests campaign. This phenomenological constitutive law will generate baseline data to microstructural models.
Establish interdependences between microstructure and strain
The ESR3 will focus on the formation of adiabatic shear bands (occurring during dynamic processes like machining) and on dynamic recrystallization (DRX) that occurs especially in the FSW during hot and large deformation. The main effect of the DRX is the creation of an equiaxed, refined and homogenous microstructure. Several microstructural investigations will be performed in order to clearly identify the mechanisms governing the evolution for plastic response covering a wide range of temperature strain and strain rates. ESR3 will have to develop a DRX model and study the geneses of adiabatic shear bands for the 3 selected materials.