This paper presents an effective methodology for characterizing the mechanical parameters of composites using digital image correlation combined with the virtual fields method.By using a three-point bending test configuration,this method can identify all mechanical parameters of the material with merely a single test.Successful results verified that this method is especially effective for characterizing composite materials.In this study,the method is applied to measure the orthotropic elastic parameters of fiber-reinforced polymer-matrix composites before and after the hygrothermal aging process.The results indicate that the hygrothermal aging environment significantly influences the mechanical property of a composite.The components of the parameters in the direction of the fiber bundle decreased significantly.From the accuracy analysis,we found that the actual measurement accuracy is sensitive to a shift of the horizontal edges and rotation of the vertical edges.
This paper explores the planar arrangement feature of the copper interconnects in a view field of several millimeters by the focused ion-beam(FIB) Moir'e inversion method quantitatively.The curved FIB Moir'e patterns indicate that the copper interconnects are a series of curves with continuous variations instead of beelines.The control equation set of the copper interconnects central lines is attained through the Moir'e inversion method.This work can be extended to inspect the structural defects and provide a reliable support for the interconnects structure fabrication.
Qinghua WangSatoshi KishimotoHuimin XieKewei XuJianfeng Wang
The mechanical properties of plasma-sprayed thermal barrier coating(TBC) play a vital role in governing their lifetime and performance. This work investigated the microstructural and mechanical properties of TBC with high temperature treatment at 1 400℃ by scanning electron microscopy and indentation.We calculated elastic modulus and hardness through the application of Weibull statistics analysis. The results indicate that the microstructure of ceramic coating will change continuously at high temperature, and accordingly the porosity decreases due to the grain growths and crack closes. In addition, the elastic modulus and hardness nonlinearly go up with the heat treatment time and go down with increasing porosity. This demonstrates that the microstructural evolution and porosity of TBC are caused by high temperature treatment, and as a result its mechanical properties are influenced.
In this paper the elastic constants of graphite at elevated temperature were experimentally investigated by using the virtual fields method(VFM). A new method was presented for the characterization of mechanical properties at elevated temperature. The three-point bending tests were performed on graphite materials by an universal testing machine equipped with heating furnace. Based on the heterogeneous deformation fields measured by the digital image correlation(DIC) technique, the elastic constants were then extracted by using VFM.The measurement results of the elastic constants at 500℃ were obtained. The effect on the experimental results was also analyzed. The successful results verify the feasibility of using the proposed method to measure the properties of graphite at high temperature, and the proposed method is believed to have a good potential for further applications.
Residual stress measurement is of critical significance to in-service security and the reliability of engineering components,and has been an active area of scientific interest.This paper ofers a review of several prominent mechanical release methods for residual stress measurement and recent developments,focusing on the hole-drilling method combined with advanced optical sensing.Some promising trends for mechanical release methods are also analyzed.
The fabrication technique of micro/nano-scale speckle patterns with focused ion beam (FIB) system is studied for digital image correlation (DIC) measurement under a scanning electron microscope (SEM).The speckle patterns are fabricated by directly etching the counterpart of the specimen to the black part of a template.Mean intensity gradient is used to evaluate the quality of these SEM images of speckle patterns fabricated based on different templates to select an optimum template.The pattern size depending on the displacement measurement sensitivity is adjusted by altering the magnification of FIB according to the relation curve of the etching size versus magnification.The influencing factors including etching time and ion beam current are discussed.Rigid body translation tests and rotation tests are carried out under SEM to verify the reliability of the fabricated speckle patterns.The calculated values are in good agreement with the imposed ones.
LI YanJieXIE HuiMinLUO QiangGU ChangZhiHU ZhenXingCHEN PengWanZHANG QingMing
This paper investigates the effect of the location of testing area in residual stress measurement by Moiréinterferometry combined with hole-drilling method.The selection of the location of the testing area is analyzed from theory and experiment.In the theoretical study,the factors which affect the surface released radial strainεr were analyzed on the basis of the formulae of the hole-drilling method,and the relations between those factors andεr were established.By combining Moiréinterferometry with the hole-drilling method,the residual stress of interference-fit specimen was measured to verify the theoretical analysis.According to the analysis results,the testing area for minimizing the error of strain measurement is determined.Moreover,if the orientation of the maximum principal stress is known,the value of strain will be measured with higher precision by the Moiréinterferometry method.
