The Research Of Measurement Of Thermal Stresses With Digital Speckle Correlation Method

The intensity and rigidity questions which are caused by thermal stresses, affect the safety and stability of components of equipments during working in the fields including aviation, astronautics, the nuclear power reactor engineering and MEMS/NEMS etc. Therefore calculating material thermal stresses which come into being working is necessary. Because thermoelectric cooler has many advantages like miniaturization, noise-resistant, non-vibration etc, it is applied in a lot of applications such as national defence, industry, scientific research and so on. The thermal stresses emerge when thermoelectric cooler works possess representativeness to a great extent. It has contained external constraint, mutual deformation constraint and internal constraint, as a result studying about it is a highly significant job.The thermal stresses calculation is dependent on the physical parameters of material, of which the thermal expansion coefficient is the most important. The requirement of experiment condition of digital speckle correlation method is lower, so it can be applied to measure tiny deformation and large deformation. The semiconductor module of single stage thermoelectric cooler is a tiny part which thermal deformation is suitable to observe by the microscope. Digital speckle correlation method is chosen to measure the thermal expansion coefficient of semiconductor module in this paper. The comparison has been made among four different kinds of reconnaissance algorithms. Through carrying out an experiment by using aluminium of which thermal expansion coefficient is known to us, the pictures are taken by Olympus microscope before and after the temperature of aluminium accessory goes up. New-Raphson method, Ameliorative Steepest Decent method, Ameliorative New-Raphson method and Ameliorative Variable Metric method are picked to calculate two digital pictures of original and deformed object surface respectively. The results indicate that the Ameliorative Variable Metric method is suitable for this experiment.Based on the results we obtain above, with Ameliorative Variable Metric method we calculate thermal expansion coefficient of x and y directions of p and n type components of single stage thermoelectric cooler respectively. Finite- element method is adopted to simulate the distribution of the thermal stresses in different working states. The results show that the maximum stresses and strains appear at the joint bottom of semiconductor and solder, which is consistent with the observation in engineering activities.In order to realize in-situ elevated temperature scanning, this paper developed a variable-temperature sample stage on the basis of BenYuan CSPM-930 scanning probe microscope, which can heat the sample to 100℃by single stage thermoelectric cooler, that enables us to see the changes of image of microcosmic material surface with the fluctuation of temperature, so as to study the property of this material further.