An Analytical Procedure for the Prediction of the Stress-Strain State in Notches under Multiaxial Fatigue

This work presents an analytical procedure for estimating elastic-plastic stresses and strains in notched shafts subjected to synchronous non-proportional torsional and tensile cyclic loading. The specification of the equivalent stress concentration factor is firstly accomplished. Neuber’s rule in conjunction with the assumed material law provides the relation between the applied loading and the equivalent stress and strain. Principal stresses and strains yield from the corresponding equivalent values incorporating Hencky’s equations. The transformation of the principal stresses and strains to the appropriate coordinate system yields the final result. For the assessment of the analytical procedure, notch stress-strain results from several finite element analyses of an axisymmetric cylindrical shaft with a circumferential groove subjected to multiaxial synchronous fatigue loading are presented. A satisfactory agreement between the analytical and numerical results is observed

Experimental and Theoretical Investigations on Mode I Crack Propagation in Notches under Cyclic Loading

Research works regarding crack opening stresses covering various types of Mode I cracks initiated and growing in notches under cyclic loading are shown. A large number of parameters influence the crack opening behavior, i.e. material, crack length, notch geometry, and load amplitude. The experimental results indicate uniform relationships cracks in notches and build the basis for developing improved formulae and algorithms to describe Mode I crack opening behavior. Theoretical calculations of crack opening stresses based on Newman’s equations have been found out to be in good agreement with corresponding experimental data determined from thin, notched specimens subjected to fatigue loading with constant amplitudes

Evaluation of the optical switching characteristics of erbium-doped fibres for the development of a fibre Bragg grating sensor interrogator

A polling topology that employs optical switching based on the properties of erbium-doped fibres (EDFs) is used to interrogate an array of FBGs. The properties of the EDF are investigated in its pumped and un-pumped states and the EDFs’ switching properties are evaluated by comparing them with a high performance electronically controlled MEM optical switch. Potential advantages of the proposed technique are discussed. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Experimental Investigation of Fatigue of Thin-Walled Welded Structures of Commercial Vehicle Frames

The fatigue behavior of bus frame components consisting of thin-walled tube beams joined together by fillet welding has been investigated. Numerical analysis by means of finite elements and experimental stress analysis by means of strain gages explored the failure-critical locations at the weld toe. In addition, a proposal for finite element modeling in particular of the welded area, and evaluation of hot spot stresses to be used for fatigue life calculations of such thin-walled structures has been developed. The calculation results have been verified based on experimentally determined fatigue lives of the components under constant amplitude loading. A satisfactory agreement between experimental and theoretical results has been observed

Light scattering from self-affine fractal silver surfaces with nanoscale cutoff: Far-field and near-field calculations

We study the light scattered from randomly rough, one-dimensional self-affine fractal silver surfaces with nanoscale lower cutoff, illuminated by s- or p-polarized Gaussian beams a few microns wide. By means of rigorous numerical calculations based on the Green theorem integral equation formulation, we obtain both the far- and near-field scattered intensities. The influence of diminishing the fractal lower scale cutoff (from below a hundred, down to a few nanometers) is analyzed in the case of both single realizations and ensemble average magnitudes. For s polarization, variations are small in the far field, being only significant in the higher spatial frequency components of evanescent character in the near field. In the case of p polarization, however, the nanoscale cutoff has remarkable effects stemming from the roughness-induced excitation of surface-plasmon polaritons. In the far field, the effect is noticed both in the speckle pattern variation and in the decrease of the total reflected energy upon ensemble averaging, due to increased absorption. In the near field, more efficient excitation of localized optical modes is achieved with smaller cutoff, which in turn leads to huge surface electric field enhancements.Comment: REVTeX 4, 10 page

Design of Microwave Pulse Compressors Using Small Form-Factor Waveguide Cavities

A microwave pulse compressor (MPC) consisting of an iris, a straight waveguide section, and a T-junction can be used in order to convert a long pulse with lower power to a shorter pulse with a higher power. A significant compression gain can be achieved, provided that the system is designed precisely. The duration of the compressed pulse is proportional to the cavity length, thus imposing a constraint on the development of mobile systems. In this work, we present the circuit/transmission-line-based design methodology that we follow in order to fold the cavity (while retaining the same electrical length) by using T-junction turns. For example, we design a 1.3-GHz folded compressor and compare its performance to the corresponding one of a straight-cavity compressor. The 3-D full-wave simulations with CST Studio Suite and experimental measurements with the developed compressor confirm the accuracy of the proposed design methodology

Transmission line method for the simulation of Fiber Bragg Gratings

A new method for the analysis and design of fiber Bragg gratings (FBGs) based on the theory of transmission lines has been developed and verified both theoretically and experimentally. The method is an extension of the coupled-mode theory and utilizes the equivalent transmission lines in order to simulate any type of grating, with an easy and direct implementation. The method provides the ability to analyze the optical devices without using full wave approaches, while also facilitating the incorporation of core materials with a complex or non-linear refractive index, non-uniform distributions of the grating&\#x2019;s refractive index, and tilted and phase-shifted gratings. The approach also allows the design of the grating for a given reflection spectra. Numerical results of the method&\#x2019;s application on a randomly varied inscription of the refractive index of a FBG have also been simulated and discussed. Using this method, the characteristics of an erbium-doped (ED)-FBG have been simulated and the predictions verified experimentally