关键词: 非线性拟合/
透射式脉冲红外检测/
碳/碳复合材料/
热扩散系数
English Abstract
Application of nonlinear data fitting method to thermal diffusivity of carbon-carbon composite measured by transmission pulsed thermography
Li Xiao-Li1,Sun Jian-Gang2,
Tao Ning3,
Zeng Zhi4,
Zhao Yue-Jin1,
Shen Jing-Ling3,
Zhang Cun-Lin3
1.Beijing Key Lab. for Precision Optoelectronic Measurement Instrument and Technology, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China;
2.Nuclear Engineering Division, Argonne National Laboratory, IL 60439, USA;
3.Beijing Advanced Innovation Center for Imaging Technology, Beijing Key Lab for Terahertz Spectroscopy and Imaging, [1 mm]Key Lab of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048, China;
4.Robot and Intelligent Equipment Engineering Research Center, College of Computer and Information Science, Chongqing Normal University, Chongqing 400047, China
Fund Project:Project supported by the Innovation Promoting Project to City-belonging University of Beijing Education Committee, China (Grant No. TJSHG201510028008) and the National Natural Science Foundation of China (Grant No. U1233120).Received Date:09 April 2017
Accepted Date:06 June 2017
Published Online:05 September 2017
Abstract:In order to measure diffusivity of carbon/carbon composite,a nonlinear fitting method for data processing of transmission pulsed infrared thermography is proposed.It is a kind of method of comparing the experimental data with the theoretical values under a fitting parameter and obtaining the optimal result by an iteration method.Traditional half rise time method calculates the diffusivity through searching the half maximum temperature rise time,which is very difficult when a long capture time is required or a big temperature rise is needed.Unlike the traditional half rise time method,the nonlinear data fitting method can effectively eliminate the capture time restriction and weaken the badsignal-to-noise ratio effects.Before applying this method to carbon/carbon composite examination,a common stainless steel 304 specimen that has reliable diffusivity indicated in the literature,is employed to evaluate the measurement accuracy and confirm the effect of fitting length on the fitting results.The examination results illustrate that the measurement accuracy of stainless steel 304 is as high as 0.3%,and the influence is very small if the fitting data length keeps no less than 1/5 that of half rise time method (t1/2).Specifically,the fitting result changes less than 1% when the fitting length varies from 1 to 4 times of t1/2.With this evaluation result,the nonlinear fitting method is further applied to testing 6 carbon/carbon composite specimens from both sides of each specimen.Furthermore,the diffusivity differences among the specimens and the uniformities of the materials are analyzed through the thermal diffusivity results gained from the examination.The results demonstrate that average diffusivity values of both sides are similar,but the diffusivities among the specimens are different greatly.Of the diffusivities of specimens,the diffusivity value 5.125 is the smallest,while the diffusivity value 6.915 is the biggest.The gap between them is nearly 30% of their mean value. Some nonuniformity areas are also examined from the diffusivity images of carbon/carbon composite samples.So we can obtain not only diffusivity values but also uniformity information of the carbon/carbon composite from this nonlinear fitting transmission thermography examination.
Keywords: nonlinear data fitting/
transmission pulsed thermography/
carbon/carbon composites/
diffusivity measurement
