Defect Orientation Research Articles

결함을 가진 증기발생기 U-튜브의 진동특성

This paper investigates the vibration characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio. Also, addressed is the effect of the internal pressure on the vibration characteristics of the tube.

On modelling the growth and the orientation changes of ellipsoidal voids in a rigid plastic matrix

A phenomenological ductile damage model is developed to take into account the growth and the changes of orientation of defects in a undamaged material matrix under large plastic straining. This constitutive model is based on a skew-symmetric tensor-valued function, originally presented by Wang C C (1970 New theorem for isotropic function part 1 and part 2 Arch. Rational Mech. Anal. 36 166–223) and modified for anisotropic functions by Boehler J P (1978 Lois de comportement anisotrope des milieux continus J. Mécanique 17 153–90). A finite element model of a three-dimensional unit cell containing a tilted ellipsoidal void is used to identify the constitutive parameters of the proposed model. Then, this law of orientation change is compared with the two-dimensional model of Bilby B A and Kolbuszewski M L (1977 The finite deformation of an inhomogeneity in two-dimensionnal slow viscous incompressible flow Proc. R. Soc. A 355 335–53) deduced from the original work of Eshelby J D (1957 The determination of the elastic field of an ellipsoidal innclusion and related problem Proc. R. Soc. A 241 376–96). In the proposed ductile damage model, the radius changes of the void are based on the modified version of the Rice and Tracey void growth law presented by Thomason and adapted for the transformation of an ellipsoidal void of any orientation in the sound matrix. The new proposals are checked with different non-linear finite element analyses.

Genetics of human laterality disorders: insights from vertebrate model systems.

Many internal organs in the vertebrate body are asymmetrically oriented along the left-right (L-R) body axis. Organ asymmetry and some components of the molecular signaling pathways that direct L-R development are highly conserved among vertebrate species. Although individuals with full reversal of organ L-R asymmetry (situs inversus totalis) are healthy, significant morbidity and mortality is associated with perturbations in laterality that result in discordant orientation of organ systems and complex congenital heart defects. In humans and other vertebrates, genetic alterations of L-R signaling pathways can result in a wide spectrum of laterality defects. In this review we categorize laterality defects in humans, mice, and zebrafish into specific classes based on altered patterns of asymmetric gene expression, organ situs defects, and midline phenotypes. We suggest that this classification system provides a conceptual framework to help consolidate the disparate laterality phenotypes reported in humans and vertebrate model organisms, thereby refining our understanding of the genetics of L-R development. This approach helps suggest candidate genes and genetic pathways that might be perturbed in human laterality disorders and improves diagnostic criteria.

Radiography of thin-section welds, Part 2: Modelling

This paper describes the validation and refinement of a simple model of radiography, first published by Pollitt in 1962, which treats defects as smooth, parallel-sided slots. It builds on similar work, which was presentedat NDT'99, on thick-section welds (thickness range 50-114 mm). The latest experimental data were collected from 12 realistic planar defects in welds of thicknesses 10-50 mm. They were radiographed under various exposure conditions, giving 278 defect/radiograph combinations (supplementing the 308 defect/radiograph combinations already available from TWI's earlier work on thick-section welds). Each radiograph was evaluated 'blind' by two radiographers. The specimens were then sectioned to determine defect size, orientation and gape. Part 1 of this paper describes the practical aspects of this work. The experimental data show variations in detectability that are strongly correlated with theoretical predictions. We have refined Pollitt's original theory, improving the observed correlation with the experimental data. In all cases, the refined theory is either accurate or pessimistic. The broader range of the available experimental data has also enabled us to improve the accuracy of our previously published statistical models for the reliability of radiography. TWI is already using such models to support the continued operation of its clients' plant.

Sh− Defects in Potassium Chloride Crystals

The Hartree-Fock-Rutane method in a semi-empirical version of the average neglect of differential overlapping has been used for calculation of the electronic structure and the spectroscopic properties of the SH− ion in potassium chloride. The orientation of impurity defect, shifts of surrounding ions, energies of optical absorption, ratios of harmonic frequencies and the first derivatives of dipole moment function of ions in free state and in a crystal were determined. The obtained values are in a good agreement with experimentally measured data.

Image processing in eddy-current testing for extraction of orientations of defects

Image processing in eddy-current testing for extraction of orientations of defects

Synthetic aperture focusing for defect reconstruction in anisotropic media

Ultrasonic inspection plays an important role in numerous industrial fields. One of the prominent tasks with respect to quantitative nondestructive evaluation is the determination of location, shape, size and orientation of defects. In this respect, the synthetic aperture focusing technique (SAFT) has been successfully applied to isotropic materials over the years. In anisotropic media, however, its application suffers from several phenomena, which are the direction dependence of the ultrasonic velocities, the beam skewing effect and the modified transducer radiation characteristics. In this article, a SAFT imaging algorithm is presented which fully accounts for the nature of wave radiation and propagation within anisotropic materials. For three-dimensional defect reconstruction, the spatial dependence of the ultrasonic group velocities as well as the radiation characteristics of the transducer are exploited––respective algorithms have been implemented for orthotropic material symmetry. Tests have been performed on unidirectional composite material.

HRTEM image simulations for the study of ultrathin gate oxides.

We have performed high resolution transmission electron microscope (HRTEM) image simulations to qualitatively assess the visibility of various structural defects in ultrathin gate oxides of MOSFET devices, and to quantitatively examine the accuracy of HRTEM in performing gate oxide metrology. Structural models contained crystalline defects embedded in an amorphous 16-A-thick gate oxide. Simulated images were calculated for structures viewed in cross section. Defect visibility was assessed as a function of specimen thickness and defect morphology, composition, size, and orientation. Defect morphologies included asperities lying on the substrate surface, as well as "bridging" defects connecting the substrate to the gate electrode. Measurements of gate oxide thickness extracted from simulated images were compared to actual dimensions in the model structure to assess TEM accuracy for metrology. The effects of specimen tilt, specimen thickness, objective lens defocus, and coefficient of spherical aberration (Cs) on measurement accuracy were explored for nominal 10-A gate oxide thickness. Results from this work suggest that accurate metrology of ultrathin gate oxides (i.e., limited to several percent error) is feasible on a consistent basis only by using a Cs-corrected microscope. However, fundamental limitations remain for characterizing defects in gate oxides using HRTEM, even with the new generation of Cs-corrected microscopes.

Pressure-temperature limit curve for reactor vessel evaluated by ASME code

A comparative assessment study for a generation of the pressure-temperature (P-T) limit curve of a reactor vessel is performed in accordance with ASME code. Using cooling or heating rate and vessel material properties, stress distribution is obtained to calculate stress intensity factors, which are compared with the material fracture toughness to determine the relations between operating pressure and temperature during reactor cool-down and heat-up. P-T limit curves are analyzed with respect to defect orientation, clad thickness, toughness curve, cooling or heating rate and neutron fluence. The resulting P-T curves are compared each other.

Preparation of Zinc Oxide Thin Films by Pulsed Current Electrolysis

ZnO thin films were prepared on indium-tin oxide (ITO) substrates by pulsed current electrolysis. The preferred orientation of the ZnO thin films prepared by pulsed current electrolysis changed in order to (0002), and (1010) by the change in overvoltage. Green-yellow emission centered around 580 nm was observed for the ZnO films. The increase of intensity of the green-yellow emission may be ascribed to effects brought about during the pause of electrolysis. The transmittance at 600 nm for ZnO thin films prepared by pulsed current electrolysis was over 95%. It was demonstrated that pulsed current electrolysis is effective for control of preferred orientation and concentration of lattice defects and for improvement of the transmittance of ZnO thin films. © 2002 The Electrochemical Society. All rights reserved.

Study of damage initiation and fracture in aluminum tailor welded blanks made via different welding techniques

The present paper addresses microstructural evaluation of failure in multi-gauge aluminum alloy tailor welded blanks (TWBs), welded using non-vacuum electron beam and neodymium:yttrium–aluminum–garnet laser techniques. The limiting dome height test is used to evaluate formability of the TWBs. Three gauge combinations utilizing AA5754 sheets are considered (2 to 1 mm, 1.6 to 1 mm and 2 to 1.6 mm). Different weld orientations have been considered: transverse and longitudinal. In general, TWBs show two different types of fracture: weld failure and failure of the thinner aluminum sheet. Interaction of several factors determines the type of failure occurring in a TWB specimen. These factors are weld orientation, morphology and distribution of weld defects as well as the degree of constraint imposed by the thicker sheet on the thin sheet. The last factor usually depends on the difference in thickness of the sheets and is represented here in terms of gauge ratio.

영향계수를 이용한 원자로 압력용기의 운전제한곡선 작성 : 냉각곡선

During heatup and cooldown of pressurized water reactor, thermal stress was generated in the reactor pressure vessel (RPV) because of the temperature gradient. To prevent potential failure of RPV, pressure was required to be maintained below the P-T limit curves. In this paper, several methods for constructing the P-T limit curves including the ASME Sec. XI, App. G method were explained and the results were compared. Then, the effects of the various parameters such as flaw size, flaw orientation, cooldown rate, existence of chad, and reference fracture toughness, were evaluated. It was found that the current ASME Sec. XI App. G method resulted in the most conservative P-T limit curve. As the more accurate fracture mechanics analysis results were used, some of the conservatism can be removed. Among the parameters analysed, reference flaw orientation and reference fracture toughness curve had the greatest effect on the resulting P-T limit curves.

Nondestructive characterization of defects using a novel hybrid ultrasonic array sensor

The concept of a novel hybrid array transducer is introduced in this article. Based on the principles of dynamic beam steering and ultrasonic shadowing, a transducer consisting of an assembly of a linear phased array and a static array is developed. Using a dynamic pitch-catch configuration, the transducer is capable of determining the location, size and orientation of a planar defect without scanning or relocating the transducer. A theoretical shadow analysis carried out in this work allows for developing a scheme to characterize a single defect. To demonstrate the feasibility of the technique, a rail specimen with real defect has been assessed. This scheme proves to be a viable approach for characterizing transverse defects (TD) with good accuracy.

Nondestructive Characterization of Planar Defects Using Laser-Generated Ultrasonic Shear Waves

This paper introduces a laser scanning technique to characterize internal planar defects in a specimen with parallel boundaries. Based on the principles of laser-based ultrasonic shear waves and shadowing, a procedure to determine flaw location, size, and orientation is described. The key feature of this scheme is the use of an optimum wave propagation angle where the maximum shear wave propagates. The feasibility of the approach is evidenced by testing specimens with various controlled and natural internal flaws. The experimental results are promising, in that the flaw characteristics can be determined with good accuracy. It is found that the scheme is especially useful for characterizing transverse-type flaws. The limitations of the technique are also addressed.

Nondestructive Characterization of Planar Defects Using Laser-Generated Ultrasonic Shear Waves

This paper introduces a laser scanning technique to characterize internal planar defects in a specimen with parallel boundaries. Based on the principles of laser-based ultrasonic shear waves and shadowing, a procedure to determine flaw location, size, and orientation is described. The key feature of this scheme is the use of an optimum wave propagation angle where the maximum shear wave propagates. The feasibility of the approach is evidenced by testing specimens with various controlled and natural internal flaws. The experimental results are promising, in that the flaw characteristics can be determined with good accuracy. It is found that the scheme is especially useful for characterizing transverse-type flaws. The limitations of the technique are also addressed.

A Micromechanical failure model for unidirectional fiber reinforced composites

Results from a newly developed model for failure in unidirectional fiber reinforced composites based on fracture mechanics are presented. The model is based on (i) analysis of branch crack initiation from the tip of an initial microcrack embedded in an anisotropic material, which serves as a model for the fiber reinforced composite and (ii) evaluation of anisotropy in homogenized elastic material properties and fracture toughness. Based on this model, failure envelope, dominant initial flaw orientation and failure mode for unidirectional fiber reinforced composites under a wide range of stress states are predicted. Parametric study provides quantitative evaluation of the effect of various mechanical and physical properties on the failure behavior, and their influence on strength is identified. Results from the current model are compared with those of existing phenomenological models, which show reasonable agreement.

Role of 3-D graphics in NDT data processing

Visualisation in 3-D can significantly improve the interpretation and understanding of imaged NDT data sets, The advantages of using 3-D graphics to assist in the interpretation of ultrasonic data are discussed in the context of an advanced software environment for the reconstruction, visualisation and analysis of 3-D images within a component CAD model. The software combines the analysis features of established 2-D packages with facilities for real-time data rotation, interactive orthogonal/oblique slicing and 'true' image reconstruction, where scanning-surface shape and reflection from component boundaries are accounted for through interaction with the full 3-D model of the component. A number of novel facilities exploit the graphics capability of the system. These include the overlay of 3-D images with individual control of image transparency; a floating tooltip window for interrogation of data point coordinates and amplitude; image annotation tools, including 3-D distance measurement; and automated defect sizing based on '6 dB drop' and 'maximum amplitude' methods. A graphical user interface has also been designed for a well established flaw response model, which allows the user to easily specify the flaw size, shape, orientation and location; probe parameters and scan pattern on the component. The output is presented as a simulated ultrasound image.

A New Approach for Restoration of Eddy Current Images

Eddy current images of defects are blurred due to convolution of point spread function of eddy current probe with defects. Disturbing variables such as lift-off, surface roughness, and material property variations influence the eddy current images. In order to restore the length, width, depth, and orientation of surface-breaking defects in the presence of disturbing variables, a new and comprehensive approach has been developed. This approach uses artificial neural network and image processing methods. Studies on austenitic steel plates confirm that through this approach it is possible to restore the spatial information of surface-breaking defects of uniform or slowly varying depth and also to form their accurate three-dimensional pictures. This approach is fast as well as amenable for automation.

Simulations of Realizable Photonic Bandgap Structures with High Refractive Contrast

AbstractThe transfer matrix method (TMM) software (Translight, A. Reynolds [1]) was used to evaluate the photonic band gap (PBG) properties of the periodic arrangement of high permittivity ferroelectric composite (40 wt% Ba0.45Sr0.55TiO3/60 wt% MgO composite, εR = 80, tanδ?= 0.0041 at 10 GHz) in air (or Styrofoam, εR ∼ 1) matrix compared to a lower permittivity material (Al2O3, εR = 11.54, tanδ?= 0.00003 at 10 GHz) in air. The periodic structures investigated included a one-dimensional (1D) stack and a three-dimensional (3D) face centered cubic (FCC) opal structure. The transmission spectrum was calculated for the normalized frequency for all incident angles for each structure. The results show that the bandgaps frequency increased and the bandgap width increased with increased permittivity. The effects of orientation of defects in the opal crystal were investigated. It was found by introducing defects propagation bands were introduced. It was concluded that a full PBG is possible with the high permittivity material.

Simulations of Realizable Photonic Bandgap Structures with High Refractive Contrast

AbstractThe transfer matrix method (TMM) software (Translight, A. Reynolds [1]) was used to evaluate the photonic band gap (PBG) properties of the periodic arrangement of high permittivity ferroelectric composite (40 wt% Ba0.45Sr0.55TiO3 /60 wt% MgO composite, εR= 80, tanδ = 0.0041 at 10 GHz) in air (or Styrofoam, εR~ 1) matrix compared to a lower permittivity material (Al2O3, εR= 11.54, tanδ = 0.00003 at 10 GHz) in air. The periodic structures investigated included a one-dimensional (1D) stack and a three-dimensional (3D) face centered cubic (FCC) opal structure. The transmission spectrum was calculated for the normalized frequency for all incident angles for each structure. The results show that the bandgaps frequency increased and the bandgap width increased with increased permittivity. The effects of orientation of defects in the opal crystal were investigated. It was found by introducing defects propagation bands were introduced. It was concluded that a full PBG is possible with the high permittivity material.