Materials microstructures

The evolution of spall in a body subject to transient tensile stresses is complex. A state of homogeneous tensile stress is intrinsically unstable and small perturbations in the material microstructure (microcracks, inclusions, etc.) can lead to the opening of voids and initiation of the spall process. 

What is novel is the manner in which they are tied together. In IP, new nondestructive evaluation sensors are used to monitor the development of a materials microstructure as it evolves during production in real time. These sensors can indicate whether the microstructure is developing properly. Poor microstructure will lead to defects in materials. In essence, the sensors are inspecting the material on-line before the product is produced. 

S. Torquato, Random Heterogeneous Materials Microstructure and Macroscopic Properties,... 

Material microstructures were characterized using standard metallographic techniques. 

How does the local water content in fuel cell media depend on the materials microstructure and the operating conditions ... 

We hope to have demonstrated that computer simulation of transport and transformation processes on digitally reconstructed multi-phase media can be beneficial to practical chemical engineering applications. We believe that as chemical engineering becomes more product-oriented, the need to model phenomena that control material microstructure formation will gain in importance. We hope that this chapter will provide a useful starting point for those who wish to familiarize themselves with the relevant computational techniques. 

The changes undergone by US on interacting with a solid, and the information that can thus be obtained from the solid, have been measured mainly through the US velocity and attenuation under resonant conditions. The ultrasonic parameters to be used and their processing are dictated by the final information required. Thus, the resistance to deformation is obtained by calculating the elastic moduli, the number and nature of which are a function of the nature of the solid (e.g. isotropic, anisotropic). However, equations relating the acoustic measurement to sample density, dimensions, material microstructure and thickness can usually be derived from simple parameters such as US velocity... 

The Silicone Resin Network in Building Material Microstructure and Building Stone... 

Microstructured surfaces, as well as micromachined substrates and devices discussed in Sects. II, III, and iy are suitable for a number of applications. They include reflective and absorbing surfaces, wavelength-sensitive filters, multiaperture lens arrays and Fresnel microoptics, field emitter arrays, precision apertures, or molds for microstructured surfaces of other materials. Microstructured alumina ceramics can also be used for tuned broadband infrared emitters. In addition, due to the robustness at high temperatures and well-developed and controlled porosity, the freestanding, heat-treated micromachined anodic alumina substrates can be used for the fabrication of sensors that incorporate a high temperature microheater with low power consumption. 

A light microscope for examining material microstructure can use either transmitted or reflected light for illumination. Reflected light microscopes are the most commonly used for metallography, while transmitted light microscopes are typically used to examine transparent... 

Both small angle X-ray (SAXS) cind neutron scattering (SANS) are established techniques and their experimental application is similar. However, limitations on sample size, thickness and containment are much more restricted with X-rays because of absorption of radiation. One problem which can arise with neutrons is the subtraction of the flat incoherent contribution which can be quite large in the case of hydrogenous materials. This disadvantage can be partially offset by the possibility of using isotopic substitution. SANS is particularly powerful because the penetrating power of neutrons makes it possible to study material microstructure in the wet state. Instrumentally, both SAXS and SANS require a source of radiation, collimation system, sample containment and a detection system. 

Figure 13.4 PD peak profile for zero strain (no macrostrain and no microstrain) (a), (tensile) macrostrain (b), microstrain (c) and combined effect of micro strain and macrostrain (d). Strain (s) is plotted on the left as a function of the position within a material microstructure sketched in the middle drawing.

M. Leoni and P. Scardi, in Diffraction Analysis of Materials Microstructure, ed. E. J. Mittemeijer and P. Scardi, Springer Series in Materials Science, vol. 68, Springer-Verlag, Berlin, 2004, p. 413. 

We begin with a brief overview that attempts to make sense of the wide variety of microstructures that are found in materials (primarily metallic). This part of our task should be seen as taxonomical we aim to observe and classify with the hope that certain classes of microstructures will suggest broad classes of models. The observations of these structures will then be supplemented by an analysis of how by exploiting the twin strategies of heating and beating a material, microstructures can be tailored to a desired form. 

In the example given above, the formation of a material microstructure was seen to take place as a result of the deposition of atoms on a substrate. Another, equally important, route to solid microstructures is via the solidification process. During the solidification process, the baseline microstructure, which will have a significant impact on both the material s properties as well as its subsequent microstructural evolution, is created as the liquid is superseded by a solid. The nature of the microstructure in the resulting solid can be quite diverse, ranging from featureless equiaxed polycrystals, to microstructures riddled with dendrites. 

Figure 1-2 show the relationship between Young s modulus, Poisson s ratio and the thermal expansion coefficient of TiC-NiyAl composites and the volume fraction of NiyAl, respectively. For the discussion of the relationship between the properties and the material microstructures, figure 1-2 also give the numerical results of Young s modulus, Poisson s ratio and the thermal expansion coefficient of TiC-NiyAl composites calculated by a two-... 

Many high-performance structural metallic materials contain two or more phases. Most often these are created starting with a homogeneous melt or material, and phase transformations create the various phases that make the final material microstructure. Not all two-phase materials can, however, be produced in this way. Thermodynamics and kinetics place restrictions on the nature, shape and mechanical properties of phases that can be combined within a single material. Alternative processes have therefore been devised for the production of multiphase materials. The result is then generally a composite material, because its different phases originate, not from a common melt, but from initially distinct starting materials [1]. 

The superficial phenomena of physical-chemical interaction of the liquid and solid phases and formation of the composite material microstructures proceed most intensively during rubber binder preparation. Therefore, the conditions under which the binder is prepared exert essential influence on the properties of composites. Uniformity of the prepared binder is defined by the intensity of the agitation process and depends on the process s speed and duration. 

Harlow, D. G., and Wei, R. P., Probability Modeling and Material Microstructure Applied to Corrosion and Fatigue of Aluminum and Steel AUoys, Engineering Fracture Mechanics, 76, 5 (2009), 695-708. 

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