H.Y. Yeh

The Structural Characterization and Properties of SiO2-Epoxy Nanocomposites

SiO2-epoxy nanocomposites with different SiO2 nanoparticle contents are synthesized. Some micro/nanoscopic structural characterizations are studied, including the various degrees of nanoparticle dispersion, free-volume contents, and the interface between the nanoparticles and the polymer matrix. The thermomechanical properties of nanocomposites are also investigated. The influence of nanoparticle contents on the structural characterization is qualitatively and quantitatively analyzed. This study will be helpful for the structural design and property evaluation of nanocomposites.

Improvement of measurement error for modified coherent gradient sensing

Recently, a novel optical method, coherent gradient sensing (CGS), has been widely used in the study of deformation near crack tips under quasi-static and dynamic conditions, which can produce high contrast fringes and provide some degree of control on the sensitivity of measurement during experiment. It involves a simple optical set-up and is relatively insensitive to vibrations and rigid body motions. Like other interferometries, such as electronic speckle pattern interferometry, moire method, etc, the accuracy of the fringe order in the CGS interference image will deeply influence the precision of experimental study. But because of the different optical principle, the fringe order of CGS cannot be obtained through the phase-shift technology. In this paper, a modified CGS method is introduced and analysed, which can accurately obtain the fringe order of a random position in the CGS interference image. The modified CGS method needs two original CGS optical set-ups, and can be used in static and dynamic conditions, which requires no complicated image processing techniques. Static fracture experiments on mode-I crack in homogeneous materials show that this modified method can evidently improve the measurement precision of the CGS method.

Fracture visualization using hybrid optical technique combining coherent gradient sensing (CGS) with caustics

In this paper, a hybrid optical method combining coherent gradient sensing (CGS) with caustics is introduced. The application of hybrid technology to the fracture investigation of three-point bending specimens with the initial inclined edge-crack is performed. Both the shadow patterns of caustics and CGS fringe patterns are simultaneously recorded from the same specimen by different photographic frames. Based on the K-dominance condition, the stress intensity factors at the crack tip are extracted by means of the characteristic size of caustic spot and the fringe order of CGS, respectively. The influences of different crack combinations on fracture characterizations are analysed. These results will be useful in the reliable design and strength evaluation of engineering structures.