Real-Time Measurement on Deformation Fields of Hole-Excavated Samples under Impact Tension

In this paper, the real-time deformation fields are observed in two different kinds of hole-excavated dog-bone samples loaded by an SHTB, including single hole sample and dual holes sample with the aperture size of 0.8mm. The testing system consists of a high-speed camera, a He-Ne laser, a frame grabber and a synchronization device with the controlling accuracy of I microsecond. Both the single hole expanding process and the interaction of the two holes are recorded with the time interval of 10 mu s. The observed images on the sample surface are analyzed by newly developed software based on digital correlation theory and a modified image processing method. The 2-D displacement fields in plane are obtained with a resolution of 50 mu m and an accuracy of 0.5 mu m. Experimental results obtained in this paper are proofed, by compared with FEM numerical simulations.

Experimental Study on Surface Deformation and Surface Wave of Fluid Convection with Free Surface

An optical diagnostic system consisting of Michelson interferometer with image processor has been developed for study of the kinetics of thermal capillary convection and buoyancy convection. This optical interferometer has been used to observe and measure surface deformation and surface wave of capillary convection and buoyancy convection in a rectangular cavity with different temperature’s sidewalls. Fourier transformation is used to image processing. The quantitative results of surface deformation and surface wave have been calculated from the interference fringe pattern. With the increasing of temperature gradient, the liquid surface slant gradually. It’s deformation has been calculated, which is related directly with temperature gradient. This is one of the characters introducing convection. Another interesting phenomenon is the inclining direction, which is different when the liquid layer is thin or thick. When the liquid layer is thin, convection is mainly controlled by thermocapillary effect. However, When the liquid layer is thick, convection is mainly controlled by buoyancy effect. Surface deformation in the present experiment are more and more declining in this process. The present experiment proved that surface deformation appears before the appearance of surface wave on fluid convection, it is related with temperature gradient, and the height of liquid layer, and lies on capillary convection and buoyancy convection. The present experiment also demonstrates that the amplitude of surface wave of thermocapillary-buoyancy convection is much smaller than surface deformation, the wave is covered by deformation.

The Geo-DSCM System and Its Application to the Deformation Measurement of Rock Materials

Digital Speckle Correlation Method (DSCM) is a useful tool for whole field deformation measurement, and has been applied to analyze the deformation field of rock materials in recent years. In this paper, a Geo-DSCM system is designed and used to analyse the more complicated problems of rock mechanics, such as damage evolution and failure procedure. A weighted correlation equation is proposed to improve the accuracy of displacement measurement on a heterogeneous deformation field. In addition, a data acquisition system is described that can synchronize with the test machine and can capture speckle image at various speeds during experiment. For verification of the Geo-DSCM system, the failure procedure of a borehole rock structure is inspected and the evolution of the deformation localization is analysed. It is shown that the deformation localization generally initializes at the vulnerable area of the rock structure but may develop in a very complicated way.

Deformation Twinning in Nanocrystalline NI

Deformation twinning is observed upon large plastic deformation in nanocrystalline (nc) Ni by transmission electron microscopy examinations. New and compelling evidence has been obtained for several twinning mechanisms that operate in nc grains, with the gain boundary emission of partial dislocations determined as the most proficient. Deformation twinning in nc Ni is discussed in comparison with molecular dynamics simulation results, based on generalized planar fault energy curves.

Dislocations and twins in nanocrystalline Ni after severe plastic deformation: the effects of grain size

Deformation microstructures have been investigated in nanocrystalline (nc) Ni with grain sizes in the 50-100 nm range. It was found that deformation twinning started to occur in grains of similar to 90 nm, and its propensity increased with decreasing grain size. In most of the nc grains dislocations were observed as well, in the form of individual dislocations and dipoles. It is concluded that dislocation-mediated plasticity dominates for grain sizes in the upper half, i.e. 50-100 nm, of the nanocrystalline regime. (C) 2007 Published by Elsevier B.V.