A Rapid And Nondestructive Evaluation On The Thermal Diffusivity Of Thin Type Materials Based On Thermography

The thermal diffusivity is the important parameter of thermal physics,which is to characterize the unsteady heat conduction within the material.It is significant to comprehend the heat conduction properly by measuring it.The principle of the traditional measurement method,like flash method and periodic heating method,is to get the analytical solution for the partial differential equation of the heat conduction.This is accomplished by structuring the specific heat transfer model,including partial differential equations,boundary conditions and initial conditions.It always needs sophisticated experimental equipments and operation processes to control the experiment conditions,including thermal excitation,boundaries,the size of the materials,and make the model to approach the theory.By targeting the defects of traditional measurement methods,which have strict demands for the thermal excitation,boundary and the size of the materials,a hypothesis is proposed: estimating the differential terms from partial differential equation of heat conduction by curve fitting,so that the differential equation can be transformed into an algebraic equation to determine the thermal diffusivity.This article researches the measurement method from three aspects.First,a principle of measurement based on two dimension of an unsteady heat conduction model is proposed: collecting the changing temperature field data which was caused by the laser heating on a material surface through the imaging technology,and then estimating the differential terms from a partial differential equation of heat conduction by curve fitting.The differential equation can be transformed into algebraic equation to determine the thermal diffusivity.Second,designing the simulation experiment.Verifying the correctness of the measuring method and the rationality of the theoretical model thought COMSOL simulation software.Then set up an experimental platform,measuring the thermal diffusivity of H62 brass and 304 stainless steel in order to investigate the result of the actual measurement.Third,regarding the problem about the scope of application with thickness of materials,do some complementary researches to the measurement method.A characteristic condition which must be satisfied when this measurement method can be used is proposed.Analyzing the influence at different thickness of the model thought simulation experiment,and SNR(signal to noise ratio)problem.Comprehending the thickness of the material quantificationally by measuring the thermal diffusivity of 321 stainless steel.This article develop a novel measuring method which adapts to the thermal diffusivity of thin materials by theoretical modeling,simulation and experiment,and it achieve the rapid nondestructive testing.