Large Circular Hole Research Articles

The crack detection and evaluation by elastic wave propagation in open hole structures for aerospace application

The rectangular plate made of aluminum alloy with a relatively large circular hole in the geometrical center of the structure is subjected to uniform tension. This loading causes that in the vicinity of a hole a process of crack formation is triggered. The crack is detected and evaluated with the use of elastic wave propagation method. The piezoelectric activator is located directly on the edge of the hole and the rest of sensors are placed at an equal distance from the activator. The crack is detected by comparison of the reference, obtained for the intact plate, and the actual signal (pitch-catch measurement). The appropriate damage magnitude measurement is proposed. Moreover, the system, which works without knowledge of an intact structure, is also discussed. In order to estimate and visualize the length of a crack, the advanced diagnostic imaging is introduced. The applied method is based on a visualization of sensing paths with an assigned value of correlation coefficients, computed for reference and actual signals. The effectiveness of the described system is verified with the use of numerical simulation and experimental test. The theoretical analysis is carried out with the use of the finite element method. The computations are performed for several assumed lengths of cracks. The obtained theoretical results, as well as the experimental analysis, confirm the fact that the crack can be detected at an early stage of formation. Moreover, a relatively good agreement between the real crack lengths and the ones obtained with the use of the proposed method is observed in the numerical analysis as well as in the experiment.

Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

During the loading process, buried gas pipes can experience severe stresses due to soil- structure interaction, the presence of traffic load, the soil’s column weight, daily and/or seasonal temperature changes and uniform internal pressure. In this research, the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene (MDPE) pipes which have been subjected to damage at the pipe crown. The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios, a/b, to simulate circular to crack-shaped defects. The computer simulation and stress analyses were performed using the ANSYS software finite element package. The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions. Then, the maximum values of Von Mises stresses in the damaged buried PE pipes, which were evaluated by finite element solution, were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years. Based on the results, the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35 °C. The previously mentioned stress values increase with the following factors: temperature increase, increase in circular hole diameter and decrease in elliptic hole diameter ratio (a/b). The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight, internal pressure, vehicle wheel load and pipe temperature increase. Additionally, the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.

A high-drop hole-type photonic crystal add-drop filter

Based on the effect of total internal reflection (TIR) and photonic band gap, a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring. The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide. Two-dimensional (2D) finite-difference time-domain (FDTD) method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency. It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes. The results show that the proposed structure can offer higher spectral selectivity than the traditional one. Two channel wavelengths of 1.425 μm and 1.45 μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90% and quality factor of 900 in the proposed configuration when the width of bus waveguide, the side length of inner ring and the coupling strength are 0.8 √3a, 4a and 0, respectively, where a is the lattice constant.

A model for release of fission products from a breached fuel plate under wet storage

MTR fuel elements burned-up inside the core of nuclear research reactors are stored worldwide mainly under the water of storage pools. When cladding breach is present in one or more fuel plates of such elements, radioactive fission products are released into the storage pool water. This work proposes a model to describe the release mechanism considering the diffusion of nuclides of a radioactive fission product either through a postulated small cylindrical breach or directly from a large circular hole in the cladding. In each case, an analytical expression is obtained for the activity released into the water as a function of the total storage time of a breached fuel plate. Regarding sipping tests already performed at the IEA-R1 research reactor on breached MTR fuel elements, the proposed model correlates successfully the specific activity of 137Cs, measured as a function of time, with the evaluated size of the cladding breach.

Supramolecular Aggregation of Hexameric Water Clusters into a 2D Water Polymer Containing (H2O)18 Holes

We report herein a novel infinite two-dimensional water morphology, found in a metallo-organic host, made up of discrete cyclic water hexamers and which contains large circular holes defined by 18 molecules of water.

Simple formulae for the stress concentration factor for two- and three-dimensional holes in finite domains

First, based on an approximate analysis, simple closed-form expressions of the stress concentration factor (SCF) for two- or three-dimensional models with a circular hole or a spherical cavity in a finite domain are derived. Then, an asymptotic method is adopted to improve the accuracy of the derived solutions for an extremely large circular hole or spherical cavity, when the remaining ligament approaches zero. Exact limit SCF values for these two kinds of models were given by Koiter; these values are used for the adjustment of the coefficients in the SCF expressions. Finally, simple SCF formulae for these finite domain problems are obtained, their accuracy is demonstrated to be very good by comparison with the available data from the literature, and the asymptotic validity is guaranteed.

EIGENSOLUTIONS OF ANNULAR-LIKE ELASTIC DISKS WITH INTENTIONALLY REMOVED OR ADDED MATERIAL

Many examples of elastic, isotropic, stationary annular-like disks are studied analytically and experimentally for free-free and clamped-free boundary conditions. Natural frequencies and deformation shapes of the first few flexural modes including repeated roots are examined and tabulated. Disks with large circular holes or annular holes or annular slots within the disk body with a volume or mass ratio Γ of 5 to 15% are studied with particular emphasis on mode shapes as they deviate from the regular annular plate modes. Material removal cases via incisions or minor cuts at the disk rim, hub or within the body are not considered in this investigation. Material addition cases are simulated by thickening the outer rim or inner hub regions, for Γvalues up to 60%. The final example considers a gear from a helicopter tail rotor gearbox; it has 8 holes and thick rim and hub. A bi-orthogonal polynomial-trigonometrical shape function series is proposed in the Ritz minimization scheme that employs both classical thin and Mindlin's thick plate theories. The effect of number of terms is evaluated by examining an expansion of the linearly independent basis function and by calculating an overall root mean square (rms) error associated with the prediction of a mode shape. The clamped inner edge is described by 4 alternate models and the impedance boundary condition described was found to be the most satisfactory. Predictions of the semi-analytical Ritz method closely match with measured eigensolutions and results yielded by finite element models. The Ritz method is especially attractive because of significant computational savings in addition to the ease with which it can be integrated within a component mode synthesis or multi-body dynamics framework for forced response or system design studies.

Stresses in a tensile strip with a large circular hole

This paper considers the determination of the stress concentration factor at the edge of a large circular hole in a flat strip under tension, as the diameter of the hole approaches the width of the strip. It is found that the stress concentration factor decreases as load increases, going from 1.94 to a limiting value of 1.00.

Studies on the Functional Characteristics and Digestibility of Starches from Phaseolus vulgaris Biotypes

AbstractThe functional properties of starches from black bean, kidney bean, navy bean, northern bean and pinto bean, all biotypes of Phaseolus vulgaris, were examined. Starch granule sizes ranged from 22 – 39 μm (length) to 19 – 28 μm (width) and shapes varied from elliptical to oval. Amylose content ranged from 30.2 – 37.3%. A highly ordered crystalline structure of granules (Ca) was suggested by restricted swelling power and solubility, resistance to α‐amylase attack, high gelatinization temperature and stable amylographic viscosities. Moreover, the existence of a crystalline structure of the highest and lowest order of stability among the Phaseolus starches was indicated for pinto bean and black bean, respectively, which were substantially different than those of kidney, northern and navy bean. The higher stability of pinto bean starch indicated a higher degree of associative bonding forces, namely, hydrogen and covalent, between oxygen and hydrogen atoms of closely packed parallel amylose chains. The wide range in amylographic viscosities was a reflection of crystalline stability, amylose exudation, granule swelling and pH of slurry. Gels exhibited a higher degree of retrogradation at +4 °C than at – 15 °C. Scanning electron microscopy showed that α‐amylase‐treated corn starch granules were degraded from the inside out by the formation of large circular holes, whereas those of kidney bean were less extensively degraded and showed only scaling and roughening of the surface as evidence of granule deterioration.

Studies on stress concentration in tensile strips with large circular holes

The stress concentration factor K in a tensile strip with large circular hole is accurately determined using a high precision, plane stress, triangular element. The values of a/ w where a is the diameter of the hole and w is the width of the strip, considered range from 0.99 to 0.999. The values of K obtained found to be very near to but greater than 2.0, when linear analysis is performed. Some discrepancies in the stress values at the outer free edge observed in the present linear analysis compared to the well documented experimental values prompted the authors to go for geometrically nonlinear analysis gave a K value which is a function of the load applied, less than 2.0 and for sufficiently large loads this value is very near but slightly greater than 1.0.

Stresses around large circular holes in uniform circular cylindrical shells

An experimental and finite element analysis of a uniform cylindrical shell with a large circular cut-out is presented. In this analysis three hole sizes are considered, namely μ = 2.037, 4.084, and 6.344 (where μ = {[12(1 - y2)]1/4/2} × [ a/( Rt)1/2]), for loadings of axial compression, torsion and three point bending. The experimental results are the only ones available for cylindrical shells with large values of μ (except for one graph by Savin (1)†), while for three point bending there is no previously published theoretical or analytical results. Good agreement is found between the calculated and experimental stresses around the holes.

Stress concentrations in tensile strips with large circular holes

A two-dimensional photoelastic study was made of the stress-concentration factor,k, in a statically loaded tensile strip of widthW, with a central circular hole of diameterD, to determine the value ofk asD/W→1. Here,\(k = \sigma _{\max } /\sigma _{nom}\) where\(\sigma _{\max }\) is the maximum stress at the hole and\(\sigma _{nom}\) is the nominal or average stress on the net cross-sectional area. Eight stress-concentration experiments were performed for 0.50≤D/W≤0.99, and it was found thatk→2 asD/W→1.

Stress concentrations in tensile strips with large circular holes

Stress concentrations in tensile strips with large circular holes

Stress concentrations in tensile strips with large circular holes

The purpose of this investigation was to determine more accurately the stress concentrations in tensile strips having large circular holes where the ratio of the hole diameter to strip width is greater than 0.5 Results of numerical elasticity analyses are presented for ratios of hole diameter to bar width ranging from 0.10 to 0.99, and photoelastic data are presented for the range from 0.40 to 0.94. Both numerical results and photoelastic data indicate that the stress-concentration factor based on net area approaches a value of one as the ratio of hole diameter to bar width approaches a value of one.

The Socketed Bronze Sickles of the British Isles; with special reference to an unpublished specimen from Norwich

In 1934 a schoolboy found ‘under a rubbish heap, but practically on the surface’ within the boundaries of the city of Norwich a socketed sickle (fig. 1, and pl. xxv, 14). The type is familiar to students of the Bronze Age since Wilde published an Irish example in his Catalogue of Antiquities in the National Museum at Dublin.The present handsome and perfect specimen, which I publish by courtesy of the Corporation of Norwich, and of the Curator of the Norwich Museum, Miss G. V. Barnard, measures 5.9 inches in greatest length, and 3.0 inches in height. The blade is double-edged: its bold curved outline is emphasized by raised beads defining a central rounded rib which expands towards the socket. On the socket, above a moulded necking from which the lower edge of the blade springs, is a decorative pattern in the form of an M, the upper angles of which extend to form outward-curving scrolls on which the headings of the blade are aligned more or less tangentially. The outer scroll, which is more complete than the inner, forms a moulded rim to a large circular hole. The hole was probably a loop for a thong; the sickle then may have dangled from the owner's waist.