[Show abstract][Hide abstract] ABSTRACT: The electron-beam moiré method uses a high frequency grating to measure microscopic deformation. Increasingly fine gratings are being developed to achieve increasingly high resolutions in microscopic stress analysis. In this study, we improve the electron grid fabricating technique by using a common scanning electron microscope (SEM). An error analysis for the multi-scanning grating was performed by a sampling moiré method. The grating manufacturing parameters strongly affect the superfine grating quality. A high accelerating voltage or a short working distance yield better results generally. A set of optimal parameters is suggested based on a minimum-error criterion. A cross-line grid with a frequency of 10,000 lines/mm and a parallel grating with a frequency of 13,000 lines/mm were successfully fabricated.
[Show abstract][Hide abstract] ABSTRACT: The effect of rare earth element Nd addition on the microstructure and martensitic transformation behavior of Ni50Ti50−xNdx (, 1, 3, 7, 20) shape memory alloy was investigated experimentally. The results showed that the microstructure of Ni-Ti-Nd ternary alloy consists of the NiNd phase and the NiTi matrix. One-step martensitic transformation was observed in all alloys. The martensitic transformation start temperature increased gradually with increasing Nd content for Ni-Ti-Nd alloys.
Advances in Materials Science and Engineering 01/2014; 2014(4):1-6. DOI:10.1155/2014/489701 · 0.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A combination of in-situ scanning electron microscopy (SEM) and
geometric phase analysis (GPA) was used to study the deformation fields
around a crack-tip in single-crystal silicon under uniaxial tensile
load. The sub-microscale silicon pillars grating was fabricated using
holographic lithography followed by inductively coupled plasma etching.
A series of SEM images of dynamic crack with the sub-microscale grating
were obtained during tensile testing. The strain fields around the
crack-tip were mapped by GPA. The strain fields were compared with the
linear elastic fracture mechanics solutions. It was determined that the
deformation is performed around the crack-tip area. The normal strain
εxx and shear strain εxy are nearly
zero, and the strain fields are dominated by the normal strain
εyy component. With the increase of displacement load,
the crack propagated mainly along the  crystal direction and the
strains around the crack-tip increased gradually. It is noted that the
theoretical prediction is lower than the experimental results from 0 to
2 μm ahead of the crack-tip. However, the agreement between
experimental results and theoretical prediction is very good far from
the crack-tip (>2 μm).
Optics and Lasers in Engineering 12/2012; 50(12):1694-1698. DOI:10.1016/j.optlaseng.2012.07.017 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The strain field of GP zone plays a very important role in strengthening of the precipitation-hardened aluminum alloys by prohibiting movement of dislocations; however, quantitative analysis about the strain field of the GP zone in the aluminum alloys has been seldom reported elsewhere. In this paper, the microstructure of GP zone in an Al–Zn–Mg–Cu alloy was explored by using high-resolution transmission electron microscopy (HRTEM), and the displacement field of lattice planes within the GP zone was experimentally measured by geometric phase analysis (GPA) technique; then, the quantitative results about strains of the distorted lattice planes within the GP zone were also obtained. It is found that the GP zone core is convergence region of the strains, and the maximum value of the compressive strains within the GP zone is about 7.6%.
[Show abstract][Hide abstract] ABSTRACT: This paper investigated the high temperature mechanical properties of the hybrid fiber reinforced high performance concrete (HFHPC) and normal concrete (NC).After being subjected to different elevated heating temperatures, two kinds of concretes have been tested for the compressive strength, splitting tensile strength and flexural strength of test specimen at room temperature and 200 degrees C,400 degrees C,600 degrees C,800 degrees C.Microstructure changes of concrete were also observed by using Scanning Electron Microscopy (SEM) after high temperature. The results show that the hybrid fiber can significantly increase mechanical properties of the concrete at room temperature and high temperature. SEM and XRD analysis shows that there is a permeable diffusion layer in the steel fiber surface because of solid state reaction in the Interfacial Transition Zone of steel fiber and concrete. This permeable diffusion layer is white, bright, serrated and mainly consist of FeSi2 and the complex hydrated calcium silicate. The compounds of this layer change the Interfacial Transition Zone structure, enhance bonding capacity of the steel fiber and matrix, and increase the high temperature mechanical properties of concrete.
[Show abstract][Hide abstract] ABSTRACT: Misfit dislocations in a Ge/Si heterostructure were investigated experimentally in the present work. The misfit dislocations were demonstrated to be pure edge dislocations, with distances of about 10 nm between misfit dislocations. The strain fields around the misfit dislocation core were mapped using a combination of geometric phase analysis and high-resolution transmission electron microscopy. The strain measurement results were compared with the Peierls–Nabarro and Foreman models of dislocation networks. Based on the comparison results, the Foreman model can better describe the strain fields of the misfit dislocations in the Ge/Si heterostructure.
Optics and Lasers in Engineering 05/2012; 50(5):796–799. DOI:10.1016/j.optlaseng.2011.12.009 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The failure components made of silicon is an important issue in the electronic and nano-technological developments. A study on the near-crack-tip deformation of single-crystal silicon wafer under tensile load was presented. The strain formulas around the crack tip of mode I crack were deduced from linear elastic fracture mechanics. The strain fields around the crack tip were simulated and analyzed in detail.
[Show abstract][Hide abstract] ABSTRACT: A micro-crack in silicon was experimentally investigated by using a combination of transmission electron microscopy and geometric
phase analysis. The strain fields of the crack tip, with scales of a few tens of nanometers, were mapped. The crack tip dislocation
emission and stress relief by dislocation generation around a crack tip can be proved. And, the strain field of an edge dislocation
was compared with the Peierls–Nabarro dislocation model at the scale of a dislocation width. We show that the Peierls–Nabarro
model is the appropriate theoretical model to describe the deformation fields of the dislocation core.
Applied Physics A 10/2011; 105(1):207-210. DOI:10.1007/s00339-011-6488-8 · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The full strain field near the interface of steel fiber/concrete in a half-mold specimen was measured using a combined method
of pullout test and digital image correlation. The strain localization mechanism of the interfacial failure is discussed.
The strain distributions near the interface at a straight fiber under different loads show that the interfacial shear failure
has a distinct characteristic of intervals in time and space directly related to the strain localization, which makes the
interfacial failure initiate, develop and transfer successively. In particular, the local strain distributions around pores
near the straight fiber interface demonstrate that the strain changes its sign at the irregular parts of the pore where the
initial debonding took place and the deformation path is affected by the pore.
[Show abstract][Hide abstract] ABSTRACT: A micro-crack in a single-crystal silicon was investigated using a high-resolution transmission electron microscopy. In particular, geometric phase analysis and numerical moiré method were employed to analyze the deformation fields of this crack-tip. The strain field maps of the crack-tip indeed show that the deformation can only occur at the crack-tip area. The maxima of the strain components, namely, εxx, εyy, and εxy at the crack-tip area can reach 1.47%, 2.91%, and 2.47%, respectively. Linear strain–distance curves were obtained at a 10 nm scale from the crack-tip.
Optics and Lasers in Engineering 11/2010; 48(11):1104–1107. DOI:10.1016/j.optlaseng.2009.12.010 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report the quantitative strain characterization in semiconductor heterostructures of silicon–germaniums (Si0.76Ge0.24) grown on Si substrate by an ultra-high vacuum chemical vapor deposition system. The relaxed SiGe virtual substrate has been achieved by thermal annealing of the SiGe film with an inserted Ge layer. Strain analysis was performed using a combination of high-resolution transmission electron microscopy and geometric phase analysis.
[Show abstract][Hide abstract] ABSTRACT: Specially designed fibers are widely used in engineering practice because the specially-designed shape can help to improve
the bonding strength of the fiber and the interface. Studied in this paper is the interfacial shear stress transfer behavior
on both sides of the specially designed fiber when it is being pulled out; in which automatic analysis of three-dimensional
photoelasticity is employed and the finite element method is adopted. The results show that the stress transfer occurs mainly
in the region near the fiber’s embedded end where the stress reaches its critical point, leading to debonding of the interface.
Before debonding, as the pullout loading increases, the peak value of shear stress transfers along the fiber from the embedded
end to the interior of the matrix, and then stops at the hooked part of the fiber because of its impediment. When the interface
begins to debond as the load increases, the shear stress can be transferred to the hooked part.
KeywordsFiber-reinforced composites-Specially-shaped fiber-Interfacial stress transfer-Photo-elasticity-FEM
[Show abstract][Hide abstract] ABSTRACT: A micro-crack in silicon was experimentally investigated using high-resolution transmission electron microscopy (HRTEM). The crystal lattice structure of a micro-crack was carefully observed at a HRTEM image scale of approximately 18 nm. The crystal lattice structure of the crack tip region was observed to be regular with good periodicity. The HRTEM images of the micro-crack demonstrate that the micro-crack cleavage expands along two crystal planes, where the principal cleavage plane is the (1 1 1) crystal plane.
[Show abstract][Hide abstract] ABSTRACT: A nanoscale experimental study of micro-crack in silicon was presented by using a combination of high-resolution transmission electron microscopy and geometric phase analysis. The results show that there is an amorphous phase content in the crack body. The width of the amorphous narrow band which exists within the crack body is 2nm approximately. The geometric phase analysis technology was applied to calculate the strain fields of the crack tip. The trend of the experiment strain value ahead of the crack tip is the same with the trend of the isotropic elastic theory strain value.
Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839015 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The specially designed fiber is widely used in engineering because it can help to improve the bonding strength of the fiber and the interface. This study investigates the mechanical behavior near interface in fiber concrete when fiber is being pulled out using the photoelasticity. The results show that the shape of the specially designed fiber can increase its capacity against pullout but at the same time stress concentrations will take place at the specially shaped part, so it is important to design the shape optimally.
Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839302 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because of a significant mismatch between the thermal expansion
coefficients of the fiber and the matrix, the interfacial thermal
residual stress (TRS) in SiC/Ti-15-3 composites is induced during
cooling procedure when continuous SiC fiber reinforced titanium-based
composites are manufactured. The distance between fibers varies
randomly. The TRS in the region nearby one fiber will be affected by the
neighbor fibers. This paper aims to study the fibers interactional
influence of neighbor fibers interfacial thermal residual stress. After
pushing out neighbor fibers, TRS is measured using micro-moiré
interferometry. This process has also been numerically simulated using
the finite element software.
Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839300 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The strain field of an edge dislocation in silicon was experimentally investigated. High-resolution transmission electron microscopy and geometric phase analysis were used to map the strain fields of the edge dislocation. The strain measurement results were compared with the Peierls-Nabarro dislocation model. The comparison shows that the Peierls-Nabarro model is an appropriate theoretical model to describe the strain fields of edge dislocation in silicon.
Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839009 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ultrasonic shot peening treatment is used to treat structural surfaces, which can enhance the overall strength, stiffness and fatigue life of the treated material. This process induces a layer of nanocrystal grains in the surface of austenitic stainless steel. The microstructure and the composition of the surface layer are examined using X-ray diffraction and transmission electron microscopy. Experimental results show that the grains are mainly composed of oxide nanocrystal particles, NiFe2O4, and a few martensite particles. Phase transformations happen during the course of the ultrasonic shot peening. The chemical composition of the nano-layer is (8.03 Cr, 4.32 Ni, 3.86 Cu, 83.79 Fe) (mass %).
Proceedings of SPIE - The International Society for Optical Engineering 11/2008; DOI:10.1117/12.839240 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a displacement and strain analysis of edge dislocation core in gold. The displacement and strain field around the edge dislocation were mapped by geometric phase analysis of high-resolution transmission electron microscopy images. The displacement and strain measurement results were compared with the isotropic elastic theory dislocation model, the anisotropic elastic theory dislocation model, the Peierls–Nabarro dislocation model and the Foreman dislocation model (a=4). These comparisons show that the Peierls–Nabarro model is the most appropriate theoretical model to describe the deformation fields of the dislocation core.