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PREFACE:
Mechanical engineering is an engineering discipline that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems.
This book covers leading-edge research in a cross-section of fields centering on mechanical engineering including current research data on the fracture mechanics of wood and wood-like reinforced polymers; thulium-doped fiber amplifiers; the role of microalloying elements on the microstructure of hot rolled steels; and high-strength titanium base alloys.
Chapter 1 - This chapter discusses the theory of fracture mechanics based on the flat elliptical crack; the derivation of the mixed "mode I - II" - interaction equation, with the relations between the mode I and mode II stress intensities and energy release rates, based on an orthotropic-isotropic transformation of the Airy stress function; the derivation of the softening curve with the explanation of the measurements; the derivation of the power law; the energy method of notched beams and of joints loaded perpendicular to the grain; and the necessary rejection of the applied crack growth models and fictitious crack models.
Chapter 2 - Magnetic resonance imaging (MRI) has developed into one of the most versatile techniques in clinical imaging and biomedical research by providing non-invasively high resolution, three-dimensional anatomical and contrast-enhanced images of living tissue.
The two most common groups of contrast-enhancing agents are gadolinium-based complexes and magnetic nanoparticles. Both types of contrast agents shorten locally the relaxation time of bulk water protons via rapid exchange of water molecules employing inner- or outersphere magnetic interactions to provide T 1-, T 2-, or T 2*-based contrast enhancement.
The quest for disease-specific and individualized approaches to imaging requires contrast agents with a relatively high sensitivity and has propelled the development of novel functional or target-specific agents. With this aim, the shift properties of paramagnetic complexes other than gadolinium have been exploited for designing new types of contrast agents with highly specific reporter functionalities. The particularly beneficial chemical shift properties of thulium(III) and their thermal sensitivity, therefore, have stimulated the development of novel thulium(III)-based contrast agents for MR imaging.
An important group of such agents is formed by those that generate contrast based on the transfer of saturated magnetization from the contrast agent or from water molecules interacting with a lanthanide shift reagent to the bulk water (chemical exchange saturation transfer (CEST) agents).
Magnetization saturation is created using either exchangeable protons of the paramagnetic thulium(III) chelate complex (paraCEST agents), or using water molecules that interact with a thulium shift reagent encapsulated in a liposomal carrier (lipoCEST agents). Various strategies have already been devised to modulate the CEST effect in response to a physiologically meaningful parameter,such as pH, metabolite concentration, or enzyme activity.
MR thermometry is another important target in the development of novel thulium(III)-based contrast agents. Such temperature mapping is based on the strong temperature dependence of the hyperfine chemical shifts of thulium(III) complexes, which can be measured in-vivo with different MR techniques. Upcoming applications of thulium-based contrast agents include disease-specific targeted contrast agents and theranostic agents suitable for image-guided drug delivery.
Chapter 3 - Due to the tremendous increase in communication traffic in recent years, more and more efforts in research have been directed towards developing highly efficient broad-band fiber amplifiers that will fully exploit the low-loss band of silica fibers in order to increase the transmission capacity of wavelength-division multiplexing (WDM) networks.
These broad-band amplifiers must be able to amplify the new short wavelength band (S-band) in addition to the existing C- and L-bands. Thulium-doped fiber amplifiers (TDFAs) are a promising candidate for the S-band amplification because the amplification bandwidth of the TDFA is centered at 1470 nm, which falls within the S-band. This chapter reviews the structure and amplification mechanism of various TDFAs. The mathematical model of single pass and double pass TDFAs is also described in detail. A development of hybrid S-band optical amplifier using a TDFA and a fiber Raman amplifier is also presented at the end of this chapter. The wide-band hybrid amplifier is suitable for application in S-band optical telecommunication systems. Chapter 4 - Some micro elements are very sensitive to long time creep rupture properties.
It is well known that harmful impurities such as S, O, Bi, Sb and Pb diffuse to local areas such as grain boundaries, interface between inclusion and matrix and surface of grain boundary cavity during creep exposure, and accelerate nucleation and growth of grain boundary cavity and crack, which lead to premature and low ductility grain boundary fracture. On the contrary, beneficial trace and microalloying elements such as B, Zr, Ca, Ti, V, Nb and Ta counteract the injurious elements by the grain boundary, the interface and the surface refinements, which improve properties of local areas, and prevent premature and low ductility fracture.
In this paper actual effects of these microalloying and trace elements on long time creep rupture properties of heat resistant steels are reported. In addition new microalloying methods preventing grain boundary fracture are introduced.
At National Institute for Materials Science Japan long time creep rupture data including longer than 100,000h have been obtained on several heats of principal heat resistant materials. The long time creep rupture life and ductility show a considerable amount of scattering among several heats of a same kind of steels, and it was thought that the scattering might include new effects of microelements on long time creep rupture properties, since the scattering is difficult to explain by using well-known effects.
Experimental results showed that main cause of the scattering is difference in microelements. It was indicated that very small amount of Mo and N in solid solution causes the scattering for carbon steels, and also trace of Al content in austenitic stainless steels causes long time creep rupture strength drop. Mo and soluble N atoms in the steels diffuse to dislocations, and the segregated pairs of the elements immobilizes dislocations. The Al in 12Cr and austenitic stainless steels precipitates as AlN at grain boundaries and accelerates nucleation and growth of creep cavities.
It is found that very small amount of B and N in austenitic stainless steels diffuse to creep cavity surface and cover creep cavity surface by segregationof B or precipitation of BN when S is removed almost completely. The segregated B and precipitated BN decrease surface diffusion rate of creep cavity and also creep cavity growth rateremarkably. The B segregates
