Vincent Delobelle

Heat Estimation from Infrared Measurement Compared to DSC for Austenite to R Phase Transformation in a NiTi Alloy

Heat source estimations from temperature field measurements deduced from infrared imaging are increasingly used to study thermo-mechanical coupling during materials’ deformation. These estimations are based on approximations of the derivative terms with respect to time and space which are involved in the heat diffusion equation. This paper proposes a first experimental validation of this method by applying it to an experimental uniform air cooling of a NiTi Shape Memory Alloy thin plate. In the studied cooling temperate range, heat sources are due to Austenite to R phase transformation. Transformation temperatures, heat sources, and energies are estimated from infrared temperature measurements and compared successfully to differential scanning calorimetry results.

Numerical study on the effect of the paint layer used for infrared thermography on heat source estimation

This paper investigates the effect of the paint layer used for infrared thermography on the heat source estimation for thin plates. The thermal behaviour of two plates is studied using finite element modelling. The first one is composed of the studied homogeneous material. The second one is a sandwich plate composed of a central material covered on each side with a high emissivity paint layer. For the two plates, two thermal loading cases are simulated. Case 1 corresponds to natural cooling from a initial uniform temperature to room temperature. Case 2 corresponds to a situation where the initial uniform temperature is equal to room temperature. In both cases, the central material is loaded with internal heat sources leading to temperature field variation. From the computed external surface temperature, heat sources and energy are then estimated using homogeneous plate and sandwich plate models derived from the heat diffusion equation. Then, the estimated heat sources are compared to the one input in the finite element model. It is shown that the paint layer significantly isolates the central material from the external environment. In case 1, it is shown that the error is reduced from 10% with the homogeneous plate model to 5%, with the sandwich plate model. In case 2, heat sources are estimated with an error of less than 8% with the homogeneous plate model while it is below 2% with the sandwich plate model. The sandwich plate model is thus significantly more accurate for heat source and energy estimations than the homogeneous plate model.

Heat source estimations to study the localized behaviour of superelastic NiTi shape memory alloys

Full field measurements (thermal and kinematics) are powerful techniques to study the thermomechanical behaviour of materials. This communication presents coupled full field measurements conducted on NiTi SMAs during tensile tests. Temperature fields are used to estimate the heat sources associated with the stress induced phase transformations. A spatio temporal synchronisation between the thermal and kinematics fields allows to express the thermal or heat source fields in the reference (undeformed) configuration. Finally, a temporal integration of the heat sources for each material point gives the evolution of the heat induced by the phase transformation. Examples of such measurements are given in this communication.