Professor Janice M. Dulieu-Barton, Mechanical Engineering, University of Southampton, UK

Using thermomechanical behaviour to assess the material condition in the vicinity of welds in 316 L stainless steel
When Nov 12, 2018
from 02:00 PM to 03:00 PM
Where LR1, Thom Building
Contact Name
Contact Phone 01865-273030
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Mechanical deformation of a material is accompanied by a change in temperature caused by both thermoelastic and dissipative effects known as the ‘thermomechanical heat sources’.  The dissipative effect is caused by the thermodynamically irreversible processes occurring within the microstructure of the material causing an increase in the temperature of the material. The dissipative heat source can be obtained by using an infrared camera to measure the temperature rise during cyclic loading and application of the heat diffusion equation. Recent findings show that even under loading below macroscopic yield stress, the dissipative heat source response of 316 L stainless steel differs for different microstructures. As such, the possibility of characterising the inhomogeneous microstructural distribution in a welded joint is explored. The key challenge is that the temperature change resulting from the dissipation is very small and below the thermal resolution of the infrared camera, hence image processing routines must be devised to extract the dissipative source.  The presentation describes the experimental setup required to measure the small temperature increase and the design of the laser welded 316 L stainless steel specimen to demonstrate the feasibility of the measurement. The image processing procedure required to extract the heat source based on spatio-temporally resolved data is describe.  The findings are validated using optical micrographs of the weld as well as the full-field strain distribution during a monotonic tensile test obtained using Digital Image Correlation (DIC). It is shown that the approach has the potential to provide a new, rapid means of weld assessment.