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Microstructure arrays are the basis for micro-optical systems. This paper presents a roll-to-plate (R2P) hot embossing method and process equipment that are developed for precision manufacturing of glass microstructures. The surface crack generation and deformation mechanism of glass in R2P hot embossing process are analyzed. A temperature control method and an elastic clamping fixture are developed to avoid warping and cracking of the glass workpiece. Surface microstructures are successfully replicated to glass through R2P hot embossing. Experimental results show high fidelity and good uniformity between the microstructure patterned plate mould and the workpiece. The forming ability increases with increasing embossing temperature and loading displacements, and decreasing mould feed rate. The results demonstrate that the R2P hot embossing process is effective for the precision manufacturing of large-area micro-structured surfaces on glass. [ABSTRACT FROM AUTHOR]

To understand the relationship between the damage mechanism of sapphire and the anisotropic characteristic of its crystal structure, in-situ scratch tests under the confocal laser scanning microscope (CLSM) were performed along different directions of C-plane sapphire wafer. The relation between in-situ images and normal/lateral forces was established. Craters in front of the contact region (CR) between the indenter and the material, and subsurface special cracks separated from CR were observed. As the scratch direction changed, these special cracks and craters initiated and propagated on the left front, front, and right front of the CR, respectively. The scratch phenomena in different scratch directions exhibited triple symmetric characteristic around the c-axis. The probability of slip/twinning activation and the theoretical stress field in front of the indenter were calculated to investigate the fracture mechanism of sapphire. Craters and those special cracks appeared in the region with the highest probability of rhombohedral twinning and basal twinning activation, respectively. According to the theoretical stress field, the material ahead of the indenter axis was separated into regions I and II. Craters in front of the CR and those special cracks separated from the CR appeared in these two regions, respectively.

In this paper, a brake cylinder coating comprising composite material of Fe3Al and Cr3C2 mixed powder was prepared by laser cladding onto carbon structural steel. The microstructure of the cladding materials was investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The influence mechanism of the Cr3C2 content and process parameters on crack generation of Fe3Al/Cr3C2 composites were studied. The crack is mainly caused by the mismatch between the plastic phase of Fe2AlCr, the brittle phase of Fe3Al, and Cr7C3 in the cladding layer. With the increase in Cr3C2 content, Fe2AlCr and Cr7C3 in the cladding layer increased, while Fe3Al decreased. When the content of Cr7C3 is low, the cladding layer mainly reflects the plastic increase brought by Fe2AlCr; when the content of Cr7C3 is too much, the property of the cladding layer is reflected as the brittleness of Cr7C3. The number of cracks reached the lowest value at 15 wt.%. The process parameters mainly affect the dilution rate of the cladding layer and thus affect the content of Fe2AlCr. [ABSTRACT FROM AUTHOR]

A molecular dynamics (MD) simulation study was performed to investigate the effects of helium (He) on the mechanical properties of nanocrystalline body-centered cubic iron (BCC Fe). Simulated X-ray diffraction (XRD) was used to explore the relationship between the generation of cracks and the change of the crystal structure in nanocrystalline BCC Fe during tensile deformation. It is observed that the peak stress and the elastic modulus decrease with increasing concentration of He atoms, which are introduced into the grain boundary (GB) region of nanocrystalline Fe. The generation and connection of intergranular cracks are enhanced by He atoms. Significant peak separation, which is associated with the generation of cracks, is found in the simulated XRD patterns of nanocrystalline Fe during the tensile process. The lower diffraction angle of the {211}′ peak suggests a more serious lattice distortion during loading. For all nanocrystalline Fe deformed to 6% strain, the degree and fraction of the lattice distortion increases with the increasing loading stress.

An in-depth study of the failure of granular materials, which is known as a mechanism to generate defects, can reveal the facts regarding the origin of the imperfections, such as cracks in the carbon anodes. The initiation and propagation of the cracks in the carbon anode, especially the horizontal cracks below the stub-holes, reduce the anode efficiency during the electrolysis process. The failure analysis of coke aggregates can be employed to determine the appropriate recipe and operating conditions in order to avoid the formation of cracks in the carbon anodes. In this paper, it will be shown that a particular failure mode can be responsible for the crack generation in the carbon anodes. The second-order work criterion is employed to analyze the failure of the coke aggregate specimens and the relationships between the second-order work, the kinetic energy, and the instability of the granular material are investigated. In addition, the coke aggregates are modeled by exploiting the discrete element method (DEM) to reveal the micro-mechanical behavior of the dry coke aggregates during the compaction process. The optimal number of particles required for the failure analysis in the DEM simulations is determined. The effects of the confining pressure and strain rate as two important compaction process parameters on the failure are studied. The results reveal that increasing the confining pressure enhances the probability of the diffusing mode of the failure in the specimen. On the other hand, the increase of strain rate augments the chance of the strain localization mode of the failure in the specimen.

Abstract Boron in low carbon steel can improve hardenability and hot ductility remarkably. However, defects including cracks, internal half way cracks, and even breakouts commonly appear during the continuous casting process, due to the segregation and remelting behaviors of boron-containing steel. In the present investigation, morphology characteristics around the crack were observed by optical microscope (OM). The segregation and distribution of boron around grain boundary were observed by secondary ion mass spectroscopy (SIMS), and the remelting phenomenon around the crack was observed by the high temperature confocal laser scanning microscope (CLSM). Results show that BN particles are detected in the crack region, Boron is concentrated at grain boundaries. Due to the boron segregation, liquid phase is observed at 1420–1400 °C and 1340–1330 °C in cooling process with boron content even of 0.0013 wt%. The low and high temperature brittle zones are revealed based on boron segregation and remelting behavior. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of Ti 2 AlC coating using hypersonic flame spraying, Ti 2 AlC powder was synthesized and deposited on low carbon steel. The tribological and mechanical properties of Ti 2 AlC coating at room temperature and 800 °C were investigated by frictional tests under different contact loads and sliding velocities. Stresses and crack generations of Ti 2 AlC coating were analyzed by finite element analysis. The phases at room temperature and 800 °C were shown, and the reasons of low frictional coefficients were explained. Results show that Ti 2 AlC can be used as an excellent self-lubrication material at a wide range of temperature due to the special mix of metallic/covalent bonds and phase change performance. Contact loads and sliding velocities have significant effects on the frictional properties of Ti 2 AlC coating. As the buffer action of Ti 2 AlC coating, stress of substrate is decreased by 41.3%. The deformation of substrate is circular in nature and the crack is not easily generated due to the coating protection. [ABSTRACT FROM AUTHOR]

The crack geometry and associated strain field around Berkovich and Vickers indents on silicon have been studied by X-ray diffraction imaging and micro-Raman spectroscopy scanning. The techniques are complementary; the Raman data come from within a few micrometres of the indentation, whereas the X-ray image probes the strain field at a distance of typically tens of micrometres. For example, Raman data provide an explanation for the central contrast feature in the X-ray images of an indent. Strain relaxation from breakout and high temperature annealing are examined and it is demonstrated that millimetre length cracks, similar to those produced by mechanical damage from misaligned handling tools, can be generated in a controlled fashion by indentation within 75 micrometres of the bevel edge of 200 mm diameter wafers. [ABSTRACT FROM AUTHOR]

The characteristics of cyclic bending deformation and fatigue fracture are studied on polycrystalline aluminum and Al-1.0mass%Mg alloy from the metallurgical point of view. It is found that the fatigue life mainly depends on grain size and the kind of materials. Cracks are preferentially formed at grain boundaries inclined 40 – 60°to the tension-compression direction, suggesting that shear stress affects the crack formation. EBSD measurements reveal the inhomogeneity of deformation. Intense development of sub-grain is seen in the grain interior close to a crack. It indicates that the work hardening close to grain boundaries triggers the crack formation. [ABSTRACT FROM AUTHOR]

The crack geometry and associated strain field around Berkovich and Vickers indents on silicon have been studied by X-ray diffraction imaging and micro-Raman spectroscopy scanning. The techniques are complementary; the Raman data come from within a few micrometres of the indentation, whereas the X-ray image probes the strain field at a distance of typically tens of micrometres. For example, Raman data provide an explanation for the central contrast feature in the X-ray images of an indent. Strain relaxation from breakout and high temperature annealing are examined and it is demonstrated that millimetre length cracks, similar to those produced by mechanical damage from misaligned handling tools, can be generated in a controlled fashion by indentation within 75 micrometres of the bevel edge of 200 mm diameter wafers.

Abstract: When the particle simulation method is used to simulate large length-scale problems, such as crustal length-scale problems in the field of geology, it is necessary to include gravity effect into the particle model. To consider gravity effect appropriately, there is a minimum value requirement for the contact stiffness of a particle so that unexpected particle overlap can be avoided. This minimum value is called the critical contact stiffness of a particle due to gravity effect. Using the vertical force equilibrium condition of a particle at the bottom of a two-dimensional particle model, a theoretical formula has been successfully derived for determining the critical contact stiffness of the particle in this paper. For the two-dimensional particle model consisting of circular particles of unit thickness, there is a relationship between the critical contact stiffness of a particle and the critical elastic modulus of the particle material when a linear-elastic-contact model between any two particles is used. Since the elastic moduli of most crustal rocks are greater than the corresponding critical elastic modulus of the particle material, it has been theoretically demonstrated that the particle simulation method, which is based on the linear-elastic-contact model between any two particles, is suitable for simulating gravity effect within the particle model of a large length-scale. The related simulation results have demonstrated the usefulness of the particle simulation method for simulating spontaneous crack generation patterns within brittle crustal rocks. [Copyright &y& Elsevier]

An in-depth study of the failure of granular materials, which is known as a mechanism to generate defects, can reveal the facts regarding the origin of the imperfections, such as cracks in the carbon anodes. The initiation and propagation of the cracks in the carbon anode, especially the horizontal cracks below the stub-holes, reduce the anode efficiency during the electrolysis process. The failure analysis of coke aggregates can be employed to determine the appropriate recipe and operating conditions in order to avoid the formation of cracks in the carbon anodes. In this paper, it will be shown that a particular failure mode can be responsible for the crack generation in the carbon anodes. The second-order work criterion is employed to analyze the failure of the coke aggregate specimens and the relationships between the second-order work, the kinetic energy, and the instability of the granular material are investigated. In addition, the coke aggregates are modeled by exploiting the discrete element method (DEM) to reveal the micro-mechanical behavior of the dry coke aggregates during the compaction process. The optimal number of particles required for the failure analysis in the DEM simulations is determined. The effects of the confining pressure and strain rate as two important compaction process parameters on the failure are studied. The results reveal that increasing the confining pressure enhances the probability of the diffusing mode of the failure in the specimen. On the other hand, the increase of strain rate augments the chance of the strain localization mode of the failure in the specimen. [ABSTRACT FROM AUTHOR]

A molecular dynamics (MD) simulation study was performed to investigate the effects of helium (He) on the mechanical properties of nanocrystalline body-centered cubic iron (BCC Fe). Simulated X-ray diffraction (XRD) was used to explore the relationship between the generation of cracks and the change of the crystal structure in nanocrystalline BCC Fe during tensile deformation. It is observed that the peak stress and the elastic modulus decrease with increasing concentration of He atoms, which are introduced into the grain boundary (GB) region of nanocrystalline Fe. The generation and connection of intergranular cracks are enhanced by He atoms. Significant peak separation, which is associated with the generation of cracks, is found in the simulated XRD patterns of nanocrystalline Fe during the tensile process. The lower diffraction angle of the {211}′ peak suggests a more serious lattice distortion during loading. For all nanocrystalline Fe deformed to 6% strain, the degree and fraction of the lattice distortion increases with the increasing loading stress. [ABSTRACT FROM AUTHOR]