Research On Digital Speckle Correlation Method And Micro/Nano Thermomechanical Measurement

This paper puts forward a new digital speckle correlation method (DSCM) combined by circular window and moments character, which overcomes the shortcoming of general digital speckle correlation method that can't work under the condition that the tested object has a rotation angle above five degrees. The method can still perform calculation with high accuracy when the tested object has translation and rotation at the same time. The principle and search process, including the relationship between moments and deformation of image and the meaning of correlation peaks after calculating, are expressed in detail in this paper. The measurement accuracy of the DSCM software and the measurement error in the real condition are also analyzed through numerical simulation and experiment. Thus, we draw a conclusion that this method is feasible and advanced not only in the theory but also in the fact. Furthermore, this paper discusses factors of affecting accuracy and velocity of calculating as well.The new experimental method (DSCM) is utilized to investigate the thermal expansion coefficient of the far-infrared ceramic coated the semiconductor galvanothermy membrane. Compared with those conventional measurements, the new method is fitter for measuring in microscopic field. The thermal expansion coefficient curve with temperature can be obtained by DSCM. The results indicate that both the ceramic substrate and the galvanothermy membrane have anisotropy on thermal expansion. This paper also measures the thermal expansion coefficient of Sn-Ag intermetallic compound.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 110oC. Due to the usage of variable-temperature sample stage, utilizable range of temperature is widely extended, and thus topography images of materials changing with temperature can be observed so that thermal properties of materials can be studied further. Accordingly, theoretical basis of heat-transfer and the influence of temperature on tunneling current owing to temperature variation should be presented. In the view of microscale heat-transfer, this paper describes the problem that heat current transfers from surface of sample to tip of probe through layer of air by means of Boltzmann theory, which can be expressed by hyperbolic equation of heat conduction when the time is nearly equivalent to slack time and the scale is much larger than the characteristic scale of local thermodynamic equilibrium. The mode of hear-transfer on probe is also analyzed and the analytical solution is obtained in the paper. In addition, the influence of temperature increment of sample on tunneling current is discussed in detail and the change trend of tunneling current with temperature is also obtained in a limited temperature range. Due to such factors, which are possible to disturb topography images of sample, there is no doubt that many difficulties will be brought to developing new technology such as detecting displacement and strain of materials at microscale by using images of sample heated and unheated. To understand andcontrol such factors has important advantage for making progress in advanced scientific fields.Sn-Cu, Sn-Ag, and Sn-Au intermetallic compound in solder has important influence on the anti-fatigue character of metal used as electronic component. From mechanics and material science, respectively, this paper analyzes the fatigue fracture mechanism of Ag foil coated solder under the influence of Ag3Sn on the basis of the experiment on low-cyclic fatigue fracture of Ag foil coated Sn-Ag lead-free solder in -80oC～75oC alternating temperature environment. Ag3Sn is a kind of brittle material with high-strength. On the one hand, Ag3Sn on the interface between solder and Ag foil improves wetting property and joint intensity of solder and Ag foil, on the other hand, due to the reason that thermodynamic property of Ag3Sn can't match that of Sn and Ag, stress concentration appears on the interface and the interface is easy to generate fatigue cracks. That many fatigue cracks connect with micro holes in Ag3Sn results in rupture of Ag foil coated Sn with increasing of times of temperature cycle. This paper adopts elastic-plastic nonlinear finite element model to simulate the change course of Ag foil coated Sn under the condition that force and temperature cycle in-step, and obtains stress and strain distribution on the interface. In terms of these results calculated, this paper proves the above conclusion and obtains the change law of local stress concentration factor with times of external load cycle.