Fracture Criterion for Surface Cracks in Plates under Remote Tension Loading

Surface-crack configurations are among the most important crack problems in the aerospace industry. The residual strength of a surface-cracked component is complicated by three-dimensional variation of the stress-intensity factor around the crack front and plastic deformations, which vary from plane stress at the free boundary, to nearly plane-strain behavior in the interior. In 1973, a two-parameter fracture criterion (TPFC) was developed to analyze fracture behavior of surface-crack configurations. Estimates were made around the crack front for fracture initiation—the critical parametric angle. Recently, NASA developed the Tool for Analysis of Surface Cracks (TASC) software that predicts critical location. This thesis is the application of the TPFC with the TASC critical angles using an equation developed from the TASC software. The TPFC was applied to three materials: a brittle titanium alloy, a ductile titanium alloy, and a ductile 301 stainless steel. The TPFC with the TASC critical angles correlated fracture behaviors well

Behaviour of compacted silt used to construct flood embankment

This paper investigates the unsaturated mechanical behaviour of a fill material sampled from flood embankments located along the Bengawan Solo River in Indonesia. In order to gain a better understanding of this fill material, in situ tests were carried out alongside an extensive laboratory programme. Two different phenomena related to changes in moisture content of the embankment fill material are experimentally studied herein: (a) volumetric collapse and (b) variation in shear strength with suction. At low densities, similar to those found in situ, the material exhibited significant volumetric collapse behaviour. Triaxial tests carried out under saturated, suction-controlled and constant water content conditions indicate that the shear strength of the material increased with suction; in particular the effective angle of friction increased from 24.9 degrees under saturated conditions to 35.8 degrees under air-dried conditions

Quantification of the performance of iterative and non-iterative computational methods of locating partial discharges using RF measurement techniques

Partial discharge (PD) is an electrical discharge phenomenon that occurs when the insulation materialof high voltage equipment is subjected to high electric field stress. Its occurrence can be an indication ofincipient failure within power equipment such as power transformers, underground transmission cableor switchgear. Radio frequency measurement methods can be used to detect and locate discharge sourcesby measuring the propagated electromagnetic wave arising as a result of ionic charge acceleration. Anarray of at least four receiving antennas may be employed to detect any radiated discharge signals, thenthe three dimensional position of the discharge source can be calculated using different algorithms. These algorithms fall into two categories; iterative or non-iterative. This paper evaluates, through simulation, the location performance of an iterative method (the standardleast squares method) and a non-iterative method (the Bancroft algorithm). Simulations were carried outusing (i) a "Y" shaped antenna array and (ii) a square shaped antenna array, each consisting of a four-antennas. The results show that PD location accuracy is influenced by the algorithm's error bound, thenumber of iterations and the initial values for the iterative algorithms, as well as the antenna arrangement for both the non-iterative and iterative algorithms. Furthermore, this research proposes a novel approachfor selecting adequate error bounds and number of iterations using results of the non-iterative method, thus solving some of the iterative method dependencies

Mesures (sud du Maroc)

Chez les Ichelhiyn (sud du Maroc), le système ancien des mesures traditionnelles recourt à certaines parties du corps comme l’avant-bras, le doigt, le pied, etc. L’idée même de « mesurer, mesure » est dérivée du nom de l’avant-bras : sɣel « mesurer » iɣil « avant-bras ». A partir du verbe sɣel, on a le nom asqqul [*asɣɣul] « mesure, mesurage ». On se servait autrefois de l’avant-bras iɣil pour mesurer les longueurs et les surfaces. Cette unité de mesure, qui correspond environ à 50 cm, iɣil,..

Maison, tigmmi en tachelhit (note linguistique)

Dans une bonne partie de l’aire géographique du tachelhit, « maison » est désignée par le terme tigmmi (fém. sing.). Le même mot est attesté aussi dans plusieurs parlers berbères avec des acceptions plus au moins proches qui se rapportent toutes du champ sémantique de l’habitation : « domaine, maison, tente », Ayt Hdiddou (Azdoud 1985 : 66) « vaste terrain de culture », kabyle (Dallet 1982 : 260) ; « douar, groupe de tentes dressées et disposées en cercles ; groupe de gens placés en rond ; pl..

Maison

wife is not suffering pain. I am faithfully yoursJohn MuirI start back to Adamana tomorrow. Had to come to the desolate home on business. Helen will probably have to remain in Arizona a year or more.[in margin: Muir]https://scholarlycommons.pacific.edu/jmcl/28427/thumbnail.jp

Use of bacterial ureolysis for improved gelation of silica sol in rock grouting

Low pH silica-based grouts suitable for penetrating fine aperture fractures are increasingly being developed for use in engineering applications. Silica sol has an initial low viscosity and mixing with an accelerator destabilises the suspension producing a gel. The influence of sodium, calcium and ammonium chloride accelerators on gel time, rate of gelation and shear strength of the resulting gel were investigated in this study. For the first time the potential use of bacterial ureolysis as an accelerator for the destabilisation of silica sol was also explored. This study demonstrates that bacterial ureolysis can be used to control the gelation of silica sol. The rate of ureolysis increases with increasing bacterial density, resulting in faster gel times and higher rates of gelation. In addition, for grouts with similar gel times, using bacterial ureolysis to induce destabilisation results in a higher rate of gelation, a higher final shear strength and a more uniform gel than direct addition of the corresponding chemical accelerator. These results suggest that bacterial ureolysis could potentially be used in rock grouting to achieve long gel times and hence greater penetration, while also maintaining sufficiently rapid gelation to minimise issues related to fingering and erosion of the fresh grout

A mechanism for bentonite buffer erosion in a fracture with a naturally varying aperture

In the deep geological disposal of nuclear waste in crystalline rock, erosion of the bentonite buffer may occur during periods of glaciation. Previous researchers have examined the mechanism and rates of extrusion and erosion for purified montmorillonite samples in smooth planar fractures. In this paper, we investigate the influence of using as delivered MX-80 material (i.e. including accessory minerals) and a naturally varying aperture on bentonite erosion. A bespoke fracture flow cell was constructed for this purpose and flow through conducted with deionised water. Throughout the experiment, gravimetric analysis was undertaken on the effluent and the swelling pressure of the bentonite monitored. Quantitative image analysis of the extrusion process was also undertaken. When the swelling pressure data was analysed, alongside both the oscillations in erosion rate and the area of the accessory mineral ring, a two-stage mechanism governing the erosion process became apparent. Once an accessory mineral ring had formed at the edge of the extruded material, further increases in swelling pressure resulted in a breach in the accessory mineral ring, triggering an erosive period. During which, the mineral ring was supplemented with additional minerals. The cycle repeated until the ring was sufficiently strong that it remained intact. This observed process results in erosion rates one order of magnitude less than those currently used in long-term safety case calculations