advances in mechanical engineering research volume 2 pdf

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 T1-, T2-, or T2*-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).

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.