Microstructurally inhomogeneous

The mechanical properties of materials can be determined from wave propagation techniques. Thus the responses of composite polymers to mechanical perturbations as well as information on specific problems related to microstructural inhomogeneities can be obtained by using these techniques. 

Polymers showing a viscoelastic behaviour occupy the intermediate range. Out of all the existing hardness tests, the pyramid indenters are best suited for research on small specimens and microstructurally inhomogeneous samples (Tabor, 1951). Pyramid indenters provide, in addition, a contact pressure which is nearly independent of indent size and are less affected by elastic release than other indenters. 

Mesocopic flows are important to understand because they hold the key to the interaction between the macroscopic flow and the microstructural inhomogeneities. This is especially true in colloidal flows, which involve colloidal mixtures, thermal fluctuations and particle-particle interactions. Dynamic processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale, this... 

In addition cracking may be caused by local stress concentration due to microscopic processes on the scale of microstructural inhomogeneities. One of these processes is the formation of subcritical microcracks. 

Figure 4.12. Representative load-displacement traces observed during fracture toughness testing that show normal behavior and those that reflect severe microstructural inhomogeneity or environmental effect [1].

Although the onset of crack growth, on rising load, serves as the measurement point for fracture toughness, there are test records that exhibit behavior that reflects artifacts associated with microstructural inhomogeneity and severe environmental sensitivity, respectively. They serve as false (low) indicators of fracture toughness, and are deemed to be invalid. Typical examples are shown in Fig. 4.12. 

Processing of Powder Metallurgy Alloys. Powder metallurgy processed aluminum alloys suffer from three major microstructural problems that limit their full potential prior-particle boundaries with an aluminum oxide film, microstructural inhomogeneity, and remnant porosity. These microstructural features particularly hamper the ductility in very high-strength aluminum alloys. Berbon et al. (Ref 59, 134)... 

The mechanisms responsible for fracture in structural ceramics at elevated temperatures have been reviewed [154]. Sensitivity to flaws or microstructural inhomogeneities which nucleate microcracks are among the failure mechanisms. The flaws which control failure under creep conditions are different from those responsible for fast fracture at room temperature. A common feature is the development of cracks through gradual damage accumulation, depend on the microstructure. The role of cracks in the deformation and fracture behavior of polycrystalline structural ceramics have been reviewed [155]. 

The < 100 nm-scale phase separation on the gradient prepared in this approach is a unique feature that results from the two immersion steps, which involve a quenching of the adsorption of the first component followed by saturation with the second component. A mixed monolayer prepared in a similar way also revealed such phase separation, whereas a mixed monolayer prepared from coadsorption of two components from a mixed solution revealed homogeneously mixed monolayers on the same scale. These microstructural inhomogeneities will have an impact... 

After a region of a structural member or test material has been selected for examination, the samples are taken. Here it is important to consider microstructural differences between the longitudinal and transverse directions, as well as special conditions arising from the manufacture of ceramic workpieces. Sintered products may exhibit microstructural differences between the core and surface regions, for example. Examples of microstructural inhomogeneities may include the firing skin found on ceramics or the variations in porosity between different regions of a structural member, as caused by uneven compression. 

While in metals damage of practical importance is several orders of magnitude higher than potential microstructural inhomogeneities, this is not the case for most fiber reinforced plastics. 

As long as the interfacial microstructure inhomogeneity remains, which is frequently the case in conventional concrete reinforced with fibres, a complex mode of cracking and debonding may be induced, as outlined below. 

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