NDE Characterization of Metallic Interfaces

In recent years, the process of diffusion bonding has found considerable usage in the aerospace and nuclear power industries [1]. This process entails two surfaces being pressed together at elevated temperatures and high pressures. If ideal conditions are achieved, the bonded interface will have properties identical to those of the matrix metal and the microstructure will be continuous across the interface. There is a fine margin for error in attaining ideal conditions and the ability to characterize the bond nondestructively is highly desirable. The present project is aimed at the development of ultrasonic techniques for the characterization of interfaces between two joined parts. The techniques that are being used have applicability to components joined by diffusion bonding, pinch welding, and friction bonding, and may also be useful in nondestructive measurements of rubbing friction and for bond strength

Characterization of Microstructural Effects on Fatigue Crack Closure

The growth of a fatigue crack is modified by the development of contacts between the crack faces1,2creating shielding and thus canceling a portion of the applied load. These contacts develop through a number of mechanisms, including plastic deformation, sliding of the faces with respect to each other and the creation and collection of debris such as oxide particles3. Compressive stresses are created on either side of the partially contacting crack faces resulting in opening loads that must be overcome in order to apply a driving force to the crack tip for growth. In this way, the crack tip is shielded from a portion of the applied load, thus creating the need for modification1 of the applied stress intensity range from ΔK = KImax — KImin to ΔK = KImax — KIsh. Determination of the contact size and density in the region of closure from ultrasonic transmission and diffraction experiments4has allowed estimation of the magnitude of KIsh on a crack grown under constant ΔK conditions. The calculation has since5 been extended to fatigue cracks grown with a tensile overload block. The calculation was also successful in predicting the growth rate of the crack after reinitiation had occurred. This paper reports the results of attempts to define the amount of retardation remaining before reinitiation of crack growth in terms of the parameters used by the distributed spring model

Reflection of Ultrasonic Waves by an Imperfect Diffusion Bond

The analytical treatment of the reflection of ultrasonic wave motion by a planar distribution of cracks is of interest for the nondestructive evaluation of imperfect diffusion bonds. Preliminary results for an experimental approach have been given by Hosten et al.1, for two bonded stainless steel cylinders. In practice, new high strength steel tubing has complicated the pinch welding process and placed emphasis on the integrity of the resulting weld, see Rehbein et al2, Thomas et al3. Two ultrasonic nondestructive evaluation techniques to find defects in the pinch weld and to determine weld strength have been discussed by Thomas et al.4

Tensile Overload and Stress Intensity Shielding Investigations by Ultrasound

Growth of a fatigue crack is modified according to the development of contacts between the crack faces [1,2] creating shielding, thus canceling a portion of the crack driving force. These contacts develop through a number of mechanisms, including plastic deformation, sliding of the faces with respect to each other and the collection of debris such as oxide particles [3]. Compressive stresses are created on either side of the partially contacting crack faces resulting in opening loads that must be overcome in order to apply a driving force at the crack tip. In this way, the crack tip is shielded from a portion of the applied load, thus creating the need for modification [1] of the applied stress intensity range from ΔK = KImax − KImin to ΔKeff = KImax − KIsh. Determination of the contact size and density in the region of closure from ultrasonic transmission and diffraction experiments [4] has allowed estimation of the magnitude of Kish on a crack grown under constant ΔK conditions. The calculation has since [5] been extended to fatigue cracks grown with a tensile overload block. The calculation was also successful in predicting the growth rate of the crack after reinitiation had occurred. This paper reports the further extension to the effects of a variable ΔK on fatigue crack growth. In addition, this paper presents preliminary results on detection of the tightly closed crack extension present during the growth retardation period after application of a tensile overload as well as an observation of the crack surface during reinitiation of growth that presents some interesting questions

Crack Length Determination by Ultrasonic Methods

Accurate calculation of the stress intensity factor on a given component under load relies on an accurate size determination of the flaws present in the component. The challenge to the NDE community has been development of reliable techniques to provide that accurate size determination. Many research groups have investigated this problem using ultrasonic methods with summaries of their techniques and results provided by various authors [1–3]. In general, the techniques developed fall into three general categories; (1) determination of crack length from signal amplitude measurements, (2) determination of crack length from time-of-flight measurements, and (3) determination of crack length using diffracted waves. Sketches of representative techniques in each category are shown in Figure 1

The Elastic Compliance of Imperfect Interfaces: Review and Relationship to Ultrasonic Scattering

When a tensile load is applied to an elastic solid with an imperfect interface containing cracks or voids, the farfield displacement that would occur in the absence of the interface will be increased by localized deformations [1]. This extra extension can be modeled as the response of two half-spaces connected by a distributed spring. The spring stiffness per unit area, K, is a function of the topography of the partially contacting surfaces

S100P enhances the motility and invasion of human trophoblast cell lines

S100P has been shown to be a marker for carcinogenesis where its expression in solid tumours correlates with metastasis and a poor patient prognosis. This protein’s role in any physiological process is, however, unknown. Here we first show that S100P is expressed both in trophoblasts in vivo as well as in some corresponding cell lines in culture. We demonstrate that S100P is predominantly expressed during the early stage of placental formation with its highest expression levels occurring during the first trimester of gestation, particularly in the invading columns and anchoring villi. Using gain or loss of function studies through overexpression or knockdown of S100P expression respectively, our work shows that S100P stimulates both cell motility and cellular invasion in different trophoblastic and first trimester EVT cell lines. Interestingly, cell invasion was seen to be more dramatically affected than cell migration. Our results suggest that S100P may be acting as an important regulator of trophoblast invasion during placentation. This finding sheds new light on a hitherto uncharacterized molecular mechanism which may, in turn, lead to the identification of novel targets that may explain why significant numbers of confirmed human pregnancies suffer complications through poor placental implantation

Examining, discussing and suggesting the possible contribution and role of Buddhist economics for corporate social responsibility

Key principles of Buddhist economics are discussed in relation to the private sector's role in contributing to sustainable development. It is suggested that many aspects of a Buddhist approach are consistent with recent developments in the field of corporate social responsibility. But a more radical approach to that concept is required if we are to attain anything close to sustainable development. That approach is well informed by notions of Buddhist economics. Copyright © 2007 Inderscience Enterprises Ltd.link_to_subscribed_fulltex

The point placement problem on a line improved bounds for pairwise distance queries

This research is supported by the RGC grant HKU7119/05E.In this paper, we study the adaptive version of the point placement problem on a line, which is motivated by a DNA mapping problem. To identify the relative positions of n distinct points on a straight line, we are allowed to ask queries of pairwise distances of the points in rounds. The problem is to find the number of queries required to determine a unique solution for the positions of the points up to translation and reflection. We improved the bounds for several cases. We show that An/3 + O(√n) queries are sufficient for the case of two rounds while the best known result was 3n/2 queries. For unlimited number of rounds, the best result was 4n/3 queries. We obtain a much better result of using 5n/4 + O(√n) queries with three rounds only. We also improved the lower bound of 30n/29 to 17n/16 for the case of two rounds. © Springer-Verlag Berlin Heidelberg 2007.link_to_subscribed_fulltex