Measurement And Application Of Thermal Diffusivity Of Materials Based On Infrared Thermography

As an important thermophysical parameter,thermal diffusivity plays an important role in the measurement of thermophysical properties of materials.For the measurement problem of directional thermal diffusivity of the material,the pulsed line excitation is used in this paper to measure the in-plane thermal diffusivity of the conductive material by inductive pulsed eddy current thermography.The research on rapidly non-destructive testing of thermal diffusivity of materials is great significance for the quantitative analysis of thermal conductivity of new anisotropic materials and their components manufactured by Additive manufacturing.Firstly,the three-dimensional heat conduction equation is analyzed based on the basic heat conduction law by integral transformation method when an anisotropic material is applied on line pulsed excitation.For the inductive pulsed line excitation,the theoretical analysis of the single-turn coil induction heating approximate Gaussian line heat source is done based on the micro-element model,which lays a theoretical foundation for the measurement of thermal diffusivity of materials by pulsed eddy current thermography.Secondly,the experimental system of thermal diffusivity of materials is designed by pulsed eddy current thermography.The typical materials of AISI304,pure iron and pure nickel with different thermal diffusivity are measured.The variation of the temperature under the the in-plane Gaussian heat excitation is consistent with the Gaussian distribution and the selection of Gaussian fitting method is studied.The influence of interference on the measurement can be effectively reduced by adding the constant into the fitting function.The "training set" and "verification set" is introduced to judge the Gaussian over-fitting or under-fitting to provide a basis for the selection of Gaussian fitting order which guarantees the measurement accuracy.Accuracy analysis and uncertainty assessment are studied with the deviation from the literature value less than 5.0% and the extended uncertainty less than 4.0%.Then the effects of different experimental conditions on the measurement are studied and experimented parameters are optimized.The influence of material properties on the measurement is theoretically analyzed and it is concluded that the temperature distribution is related to the relative magnetic permeability and electrical conductivity of the material.The error analysis of the curve fitting is carried out,which provides a basis for the determination of the best fitting start frame and the time length.Lastly,the distribution of thermal diffusivity in different directions of anisotropic carbon fiber reinforced composites is measured,which further proved the effectiveness of this method.The corresponding outlook of the non-destructive testing of weld quality is made by measuring the distribution of thermal diffusivity of welded plates.Finally,the design of material thermal diffusivity measurement system is completed by combining software and hardware.It mainly includes three functional modules: infrared imagedisplay and basic operation,excitation control and acquisition parameter setting,data processing and analysis.