This paper focuses on the development of fully-coupled 3D thermomechanical field measurement techniques applied for monitoring thermal fatigue tests. First, an original hybrid and multiview system composed of one infrared (IR) camera and two visible light cameras is introduced. The spatial registration of multimodal imaging devices is solved successfully using global Hybrid Multiview Correlation (HMC) based on the NURBS representation of the 3D calibration target and the surface of interest. The measurement uncertainties are estimated with an initial heating up phase prior to the fatigue test. Then, HMC is performed to measure the 3D surface displacement and temperature fields during laser shocks onto an austenitic stainless steel plate. Last, the HMC measurements are validated in comparison with finite element simulations of the test.
Thermal fatigue tests on AISI 316L(N) austenitic stainless steel samples are performed through pulsed laser on specimen that can be subjected to an additional static mechanical load. These tests are carried out in Helium environment with a dedicated and heavily instrumented setup , FLASH. The fatigued surface is monitored by a hybrid multiview system composed of two visible light and one infrared cameras that, through 3D-registration, provides in-situ access to the 3D surface displacement fields and 2D temperature fields. At a fatigue frequency of 1 Hz, the surface temperature range covered per cycle can be varied from 150°C to 250°C, conditions that allow surface damage to be reproduced. The multiview system reveals the time-resolved mechanisms of surface damage, from significant cyclic plasticity with persistent slip bands to micro-crack initiation and growth, leading to their quantitative characterization (micro-crack density, length of major crack, orientation) all along the test. These observations are confirmed at a few check points where the test is interrupted for optical microscopy inspection of the surface. Finally, the thermal fatigue data are compared to purely mechanical isothermal uniaxial fatigue data through the use of an equivalent strain, and an excellent (and conservative) agreement is obtained.
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