Design of Experiment for Thermal Diffusivity Measurements of Composite Material with Orthogonal Anisotropy

Abstract

This article deals with simultaneous measurements of three mutually orthogonal thermal diffusivities of a material with orthogonal anisotropy using the flash method. Unlike the conventional flash method, the modified measuring technique considers pulse heating over a rectangular area of the front face of a wall-shaped sample of an orthotropic composite material. The thermal diffusivities are calculated analyzing the temperature rise versus time evolutions when measured simultaneously at various positions on the sample surface. This article presents a data reduction method that enables estimates of the thermal diffusivities for the three principal axes. The theory takes into account heat losses from the front and rear faces. The results of an experimental design analysis are discussed.

Simultaneous and direct identification of thermophysical properties for orthotropic materials

“…In this method, the considered harmonics are equally weighted. The first term of equation 9, 2,3 (ϐ, ), corresponds to the temporal normalized harmonics, achieved by the Laplace inversion which is applied to the direct model output in equation (8), 2,3 ( ). This inversion is successfully realized using De Hoog algorithm [39] , that was found to be the most appropriate in the current problem.…”

“…The comparison of the evolution shows a very close agreement between the signals. The relative error between the experimental and the estimated signals are calculated separately for each harmonics following matrix (8).…”

“…T" = • 2,3 • ( ), that appears in equation (8) ,implies the knowledge of the excitation intensity , which is also identified in the present version of the method. Therefore, the parameters vector is ϐ = © " , $ , % , , ª.…”

“…having principle diffusivities directions aligned with the Cartesian coordinate system. The flash method is then used in cylindrical coordinates to separately estimate radial and axial diffusivities [8], [9]. Furthermore, the extension into 3D identification methods leads to some achievements, notably the compatibility between the model and the experimental conditions, which is usually a difficult task.…”

“…One should notice that some works are purely theoretical, others are based on experiments that rely on intrusive measurements (e.g. thermocouples) [8], and/or intrusive heating source [11]- [13], [27]. Also, the experimental protocol may be sophisticated, where some authors have developed methods based on two experiments (e.g.…”