A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Geomaterials (i.e. rock, sand, soil and concrete) are increasingly being encountered and used in extreme environments, in terms of the pressure magnitude and the loading rate. Advancing the understanding of the mechanical response of materials to impact loading relies heavily on having suitable high-speed diagnostics. One such diagnostic is high-speed photography, which combined with a variety of digital optical measurement techniques can provide detailed insights into phenomena including fracture, impact, fragmentation and penetration in geological materials. This review begins with a brief history of high-speed imaging. Section 2 discusses of the current state of the art of high-speed cameras, which includes a comparison between charge-coupled device and complementary metal-oxide semiconductor sensors. The application of high-speed photography to geomechanical experiments is summarized in Sect. 3. Section 4 is concerned with digital optical measurement techniques including photoelastic coating, Moire, caustics, holographic interferometry, particle image velocimetry, digital image correlation and infrared thermography, in combination with high-speed photography to capture transient phenomena. The last section provides a brief summary and discussion of future directions in the field.

High-Speed Photography and Digital Optical Measurement Techniques for Geomaterials: Fundamentals and Applications

To quantitatively evaluate crack width of concrete structures surface, this paper presents a stereovision-based crack width detection method. Compared with the traditional visual inspection with single camera, this approach uses a pair of cameras to capture cracks images for recovering 3D coordinates of crack edge, and does not needs scale attached to concrete surface for converting measurement unit. A novel Canny-Zernike combination algorithm is utilized to obtain the image coordinates of crack edge in the left crack image, this combination algorithm can achieve 0.02 subpixel precision. The 3D coordinates of crack edge are acquired by projecting crack edge curve on concrete surface where cracks are located. The crack width is assessed by the minimum distance between two sides of crack edge. The detection tests are conducted on three concrete beams destroyed in static test, and the crack width of two inspection zones on each beam is acquired. Experimental results indicate that the stereovision-based crack width detection approach can accurately measure the crack width compared with the crack width gauge or the vernier calliper. This verifies the proposed method is applicable and useful for assessing the crack width of concrete surface.

A Stereovision-based Crack Width Detection Approach for Concrete Surface Assessment

http://photomech.ustc.edu.cn/File/2015%20olen%20cht.pdf

Investigation of Portevin-Le Chatelier effect in 5456 Al-based alloy using digital image correlation

With the rapid development of micro/nano manufacturing technology and nanomaterials, the accurate measurement of the mechanical properties and behaviors at the micro-nano scale represents a new field of mechanical experiments. Raman spectroscopy, which is based on lattice dynamics theory, is applicable to the detection of the statistical information of the lattice structure deformation within the measuring points. Due to its peculiarities, such as non-destructiveness, convenience and high-resolution, this technology allows the on-line in situ measurement of residual stress in microstructures caused by processing and can also achieve the real-time deformation of graphene, carbon nanotubes and other nanomaterials under force loading. In recent years, mechanical measurements based on Raman spectroscopy technology have developed rapidly. In this review, Raman-based stress measurement theories for several commonly used materials are briefly described. Applications related to the residual stress measurements of microstructure and experimental investigations of the mechanical properties of low-dimensional nanomaterials are then reviewed. Finally, the development trend of this method is proposed.

Xiaoping Wu

Papers

A brief review and prospect of experimental solid mechanics in China