Failing microstructure

Fushinobu, K., Phinney, L.M., Kurosaki, Y., and Tien, C.L. (1999) Optimization of Laser Parameters for Ultrashort-Pulse Laser Recovery of Stiction-Failed Microstructures, Numerical Heat Transfer, Part A, Vol. 36, pp. 345-357. 

Non-linear constitutive equations are developed for highly filled polymeric materials. These materials typically exhibit an irreversible stress softening called the "Mullins Effect." The development stems from attempting to mathematically model the failing microstructure of these composite materials in terms of a linear cumulative damage model. It is demonstrated that p order Lebesgue norms of the deformation history can be used to describe the state of damage in these materials and can also be used in the constitutive equations to characterize their time dependent response to strain distrubances. This method of analysis produces time dependent constitutive equations, yet they need not contain any internal viscosity contributions. This theory is applied to experimental data and shown to yield accurate stress predictions for a variety of strain inputs. Included in the development are analysis methods for proportional stress boundary valued problems for special cases of the non-linear constitutive equation. 

Owing to hydrogen embrittlement, the mechanical properties of metallic and nonmetal-lic materials of containment systems may degrade and fail resulting in leaks. Hydrogen embrittlement depends on many factors such as environmental temperature and pressure, purity of metal, concentration and exposure time to hydrogen, stress state, physical and mechanical properties, microstructure, surface conditions, and the nature of the crack front of material [23]. 

The microstructure of polyisoprene prepared in a variety of solvents and solvent mixtures (113) has been determined. Various ethers and sulphides vary in their ability to reduce the 1,4 content of the polymer. The most effective ether was tetrahydrofuran. The presence of only two molecules per active chain was reported to reduce the 1,4 content to that observed in the pure ether. More recent investigations have failed to confirm that the requirement is as low as this 74,126) but relatively small amounts of tetrahydrofuran do markedly decrease the cis-1,4 content and increase the 3,4 content. Similar results have been obtained for butadiene 60) with respect to 1,4 and 1,2 structures. 

The fabrication of microelectronic and photonic components involves long sequences of batch chemical processes. The manufacture of advanced microstructures can involve more than 200 process steps and take from 2 to 6 weeks for completion. The ultimate measure of success is the performance of the final circuits. The devices are highly sensitive to process variations and are difficult, if not impossible, to repair if a particular chemical process step should fail. Furthermore, because of intense competition and rapidly evolving technology, the development time from layout to final product must be short. Therefore, process control of electronic materials processing holds considerable interest [30, 31]. The process control issues involve three levels ... 

As in the case of corrosion failures, the sequence of steps involved in analyzing wear failures are initial examination of the failed component including service conditions to establish the mode or combination of modes of wear failure, metallographic examination to check if the microstructure of the worn part met the specification, both in the base material and in the hardened case or applied surface coatings, existence of localized phase transformations, shear or cold worked surfaces, macroscopic and microscopic hardness testing to determine the proper heat treatment, X-ray and electron diffraction analysis to determine the composition of abrasives, wear debris, surface elements and microstructural features such as retained austenite, chemical analysis of wear debris surface films and physical properties such as viscosity and infrared spectral determination of the integrity of lubricants and abrasive characteristics of soils or minerals in the cases of wear failures of tillage tools. 

The only characterization technique that can directly view heterogeneities of the order of 1 nm, i.e., the size of the ionic clusters is electron microscopy. There have been very few electron microscopy studies of ionomer microstructure and these have failed to provide a satisfactory picture of ionic clusters (106). With the advancements that have been made in recent years in the optics and theories of electron microscopy, microscopists are in a better position to reexamine these materials (See the chapter by Williams). 

In contrast to the nano-scale, where the periodic arrangement of atoms on crystal lattices is well established, and the macro-scale, where a continuous distribution of matter is assumed, adequate quantitative descriptions are notably lacking for structure at the micro- and mesoscales, where properties are described in terms of the behavior of dislocations, material in grains, particles of different phases and the boundaries among them. The traditional means of describing these microstructural attributes with descriptive terms that call to mind familiar shapes fails to provide an adequate quantitative basis for transferring this information to quantitative models. 

Fracture Stress and Strain. Yielding and plastic deformation in the schematic representation of tensile deformation were associated with microfibrillation at the interface and stretching of the microfibrils. Because this representation was assumed to apply to both the core-shell and interconnected-interface models of compatibilization, the constrained-yielding approach was used without specific reference to the microstructure of the interface. In extending the discussion to fracture, however, it is useful to consider the interfacial-deformation mechanisms. Tensile deformation culminated in catastrophic fracture when the microfibrillated interface failed. This was inferred from the quasi-brittle fracture behavior of the uncompatibilized blend with VPS of 0.5, which indicated that the reduced load-bearing cross section after interfacial debonding could not support plastic deformation. Accordingly, the ultimate properties of the compatibilized blend depended on interfacial char-... 

The description of failure modes with reliability functions and their respective parameters is, in the first place, suitable for individual microstructures which are the primary source of failures and which fail in total. The corresponding reliability features in a complete complex system, which consists of many subsystems, components, and structures, can be deduced in several steps by breaking the system down to its basic building blocks as diagrammed in Figure 5.9.10. 

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