Semi-elliptical Shape Research Articles

Influence of the Geometry of Corrosion-Fatigue Cracks on the Residual Service Life of Objects Intended for Long-Term Operation

We establish conditions for the prediction of the development of cracklike defects of semielliptic shape in a pipe wall according to the results obtained by using the experimental-numerical procedure. The relationship between the ultimate sizes of a semielliptic crack and the rate of its propagation in “metal–medium” systems is revealed. We propose a criterial dependence of the initial and ultimate crack sizes that can be used for the evaluation of hazard of the recorded defects and interpret the results of technical diagnostics of pipelines after long-term operation.

Surface crack growth prediction under fatigue load using the S-version Finite Element Model (S-FEM)

Prediction of fatigue crack growth is one of the vital issues to prevent catastrophic failure from damage tolerance perspective. The surface of crack shape usually in semi-elliptical that maintained during the whole propagation. The investigation of this paper is to illustrate the surface crack growth that subjected to fatigue loading. The four-point bending and three-point bending have been simulated by using the S-version Finite Element Model (S-FEM). The simulation is conducted for aluminium alloys A7075-T6 and A2017-T3 with all of the parameters based on the previous experiment. The semi-elliptical crack shape is applied during the simulation process to represent with the reality of crack growth phenomena. Paris’ Law model approach is presented in fatigue crack growth simulation. The S-FEM produced the surface crack growth and fatigue life prediction. The results of the S-FEM prediction then compared with the previous experiments. The results presented in a graph for comparison between S-FEM prediction with the experimental results. The S-FEM results obtained is good agreement with the experiment results.

Branching and softening of loading path during onset of crack at elastic-brittle interface

The load response during onset and reformation of an interface crack is investigated experimentally and theoretically using linear-elastic analysis. A number of double cantilever beam experiments is carried out under the prescribed displacement and the prescribed displacement rate loading conditions. During the onset of the interface crack with the initially straight front, the crack grows from the centre of the specimen before adopting a semi-elliptic shape. The shape of the crack front eventually becomes self-similar (sizes of the crack front process zone and the ratio between the crack front depth and its width become invariant) when reaching the free edges of the specimen. As a consequence, during the crack reformation the incremental crack area cannot be attributed to the growth along a single direction. Finite element calculations are implemented in which the recorded crack front morphologies are imposed as the crack front boundary conditions. It is concluded that the load response curve can become non-linear upon the geometrical reconfiguration of the crack front and quantitatively is associated with gradual transition from the plane strain to the plane stress conditions experienced by the adherend during the crack front reformation.

Stress intensity factor for a semi-elliptical rail head crack under traction

The complex loading conditions in rails induce stress and deformations in the material which keep on accumulating and evolve to rolling contact fatigue (RCF) cracks as soon as ductility exhaust. The cracks can occur at the surface or at the sub-surface level. Generally occurring surface crack is of semi-elliptical shape. Here, we consider a semi-elliptical crack located in such a way that its major axis is perpendicular to the rail axis and minor axis is in the depth direction. Stress intensity factor (SIF) of the crack is evaluated for friction and traction force by varying the speed of the train. A three-dimensional finite element analysis is carried out using ANSYS 14.0. UIC 60 rail profile cross-section is used for the simulation purpose. Results are evaluated by taking two values of coefficient of friction (0.1 and 0.35) at the wheel-rail interface. From the outcomes it is seen that the stress intensity factor value is maximum at the deepest point of the crack front. SIF estimation method of Tada, Paris and Irwin also gives analogous values.

Isolation and characterization of starch from pitomba endocarp.

Abstract The seed of pitomba (Talisia esculenta) represents half the total weight of this exotic Brazilian fruit, highly appreciated in the north and northeast regions. Extracting starch from this seed is an alternative for the utilization of non-conventional starches. Thus, the present study aimed to extract starch from pitomba seed and characterize it with respect to physical, chemical, technological, thermal and morphological characteristics. Extraction was performed by grinding the seeds in sodium metabisulfite solution (0.2%) followed by drying at 50 °C. Starch yield was equal to 44.0%, with low contents of protein and lipid, 77.78% purity and amylose content of 19.25%, indicating low level of retrogradation after gelatinization. Water and oil absorption capacities were 89.49 and 85.07, respectively. Gelatinization temperature was 66.92 °C, maximum temperature was 72.84 °C, transition enthalpy was 4.70 J/g, peak viscosity was 2531 cP, final viscosity was 1607 cP, retrogradation viscosity was 551 cP, in addition to smoothed-surface granules with predominance of semi-elliptical shape, showing the potential of this starch to be used in food industry

Numerical and physical modeling of the stability of the workings developing the slope

Enhancement of modern urban infrastructure, expansion of transport networks, creation of innovative engineering communications as well as plenty more factors stimulate the development of underground construction both in our country and throughout the world. Like any structure, an underground construction must be capable to perceive external loads without collapsing. For the successful operation of such structures throughout all term of their service, it is necessary to evaluate regularly the impact degree of all factors that one way or the other affect the construction durability. It was therefore decided to study by means of a model experiment, how the geometric parameters of the slope and underground workings’ system affect the stability of the latter. We’ll assume the cross-sectional shape of the workings and their position relative to the basis of a model from homogeneous ground massif as the geometric parameters. In this paper we examine the stability of the models of horizontal underground workings with round and semi-elliptical shape worked in an isotropic soil slope, at various distances from the point of transition of the sole into a slope. As a measure of long-term stability we chose the criterion (Bogomolov A.N., Bogomolova O.A., 2010) where a qualitative feature is the absence of zones of inelastic (plastic) deformations on the contours of the workings as well as zones manifesting the processes of loosening or breed fragmentation. The value of the reduced pressure of coherency σc is used as a quantitative indicator. The paper presents the results of numerical processing of model experiments studying the fracture processes both of the ground slope weakened by the workings and the workings themselves. In the course of the model experiments, we defined the distances L, measured from the base of the slope to the center of the workings with circular and semi-elliptical cross-sectional shape, under which the contour of the workings was stable. It is established that the stability of the round and semi-elliptical shaped workings can be provided practically at the same values of L on condition that the physical and mechanical properties of the equivalent material of the model, its geometric parameters and the transverse dimensions of the imitation workings are practically identical. The coincidence of the results of model experiments and calculations performed with the help of a computer program makes it possible to speak about their reliability.

The Effect of Indentation Load, Tilted Angle, and the Amount of Surface Removal to the Fracture Toughness of Silicon Nitride Measured by the Surface Crack in Flexure (SCF) Test Method

The surface crack in flexure (SCF) is a method for the evaluation of the fracture toughness of advanced ceramics. Conventionally is practiced by using a Knoop indenter to make a very small precrack. Removal on indent and the plastically deformed zone is required before the fracture test. The purpose of this removal is to eliminate residual stresses under the Knoop impression and to obtain a semi elliptical precrack shape. In this work the influence of the variation of several experimental parameters is investigated. Fracture toughness values by the SCF method are compared with those measured using the SEVNB (single edge V-notched beam) method. The material chosen for this purpose was gas pressured sintered silicon nitride (Si3N4) containing 3wt.%Al2O3 and 3 wt.%Y2O3 (SL200B, Ceram Tec, Plochingen, Germany). The varied parameters were indentation load, orientation of the indentation crack with respect to the bending axis and the amount of material removed from the surface. Additional investigations were performed to determine the crack geometry for various indentation loads. A procedure was developed to facilitate the location and measurement of the precrack size on the fracture surfaces. The effect of measurement accuracy of the results is evaluated. The fracture toughness of specimens with a surface removal in the range suggested from ASTM C 1421 were found to agree with the results obtained from SEVNB. A surface removal below the recommendation resulted in low values of fracture toughness. Increasing the amount of surface removal moderately was found to still fit with results obtained from SEVNB. Surface removal of much more from the recommended amount leads to failure from natural flaws. Observations from serial sectioning revealed that precracks obtained from HK20 and HK30 have an irregular precrack shape with large lateral cracks. It is suggested to use HK5 and HK10 to produce semi-elliptical surface cracks.

A Design of Coverage Area for Textured Surface of Sliding Journal Bearing Based on Genetic Algorithm

This paper aims to improve the tribological performance of journal bearings by optimizing the coverage area of circular microtextures in divergent region of the sleeve. A numerical model is proposed to calculate the friction coefficient and bearing load of textured journal bearings. The surface of the sleeve is divided into rectangular squares. Textures that located at the center of rectangular grids are assumed to be present or absent, marked as 1 and 0, respectively. Afterward, different texture coverage area arrangements are evolved and selected based on the genetic algorithm (GA). The area of semi-elliptical shape is obtained as the novel and preferable textured coverage area design for journal bearings. Influences of width and eccentricity ratio are discussed, which confirm the semimajor and semiminor axes of the semi-elliptical shape of texture coverage area equal to one-third of the circumferential length and half of the width of the journal bearing, respectively.

Circularly polarised filtering dielectric resonator antenna for X‐band applications

A circularly polarised filtering dielectric resonator antenna is proposed. Left hand circularly polarised electromagnetic field is generated by virtue of a rectangular ring slot present on the ground plane of the dielectric laminate, beneath the dielectric resonator antenna, which is fed by a 50 Ω microstrip line. Additionally, a semi-elliptical shape bandpass filter is incorporated in the feed line to produce high selectivity, flat gain and wide stopband. A detailed analysis of the filter and the antenna has been carried out. The design offers fractional bandwidth of 6.13% ranging from 7.9 to 8.4 GHz, gain around 5.3 dBic and 3 dB axial ratio bandwidth of 3.68%. The simulated radiation efficiency is >80% in the pass band. The proposed structure has been fabricated and the results are compared with the simulated values.

Diel hysteresis between soil respiration and soil temperature in a biological soil crust covered desert ecosystem.

Soil respiration induced by biological soil crusts (BSCs) is an important process in the carbon (C) cycle in arid and semi-arid ecosystems, where vascular plants are restricted by the harsh environment, particularly the limited soil moisture. However, the interaction between temperature and soil respiration remains uncertain because of the number of factors that control soil respiration, including temperature and soil moisture, especially in BSC-dominated areas. In this study, the soil respiration in moss-dominated crusts and lichen-dominated crusts was continuously measured using an automated soil respiration system over a one-year period from November 2015 to October 2016 in the Shapotou region of the Tengger Desert, northern China. The results indicated that over daily cycles, the half-hourly soil respiration rates in both types of BSC-covered areas were commonly related to the soil temperature. The observed diel hysteresis between the half-hourly soil respiration rates and soil temperature in the BSC-covered areas was limited by nonlinearity loops with semielliptical shapes, and soil temperature often peaked later than the half-hourly soil respiration rates in the BSC-covered areas. The average lag times between the half-hourly soil respiration rates and soil temperature for both types of BSC-covered areas were two hours over the diel cycles, and they were negatively and linearly related to the volumetric soil water content. Our results highlight the diel hysteresis phenomenon that occurs between soil respiration rates and soil temperatures in BSC-covered areas and the negative response of this phenomenon to soil moisture, which may influence total C budget evaluations. Therefore, the interactive effects of soil temperature and moisture on soil respiration in BSC-covered areas should be considered in global carbon cycle models of desert ecosystems.

Geomorphological records of diachronous quarrying activities along the ancient Appia route at the Aurunci Mountain pass (Central Italy)

The topic of this research consists in the description of landscape modifications occurring from the 4th century BCE to the 19th century CE as a consequence of quarrying activities on carbonate slopes along a tract of the ancient Appia route crossing the central Apennine belt at the Aurunci Mountain pass (Lazio region, central Italy).The main objectives were to discern different quarrying phases and techniques, quantify quarrying activities and understand the role of quarrying in create morphological features.Multidisciplinary studies were completed including aerial photogrammetry, geoarchaeological field surveys, morphometric characterization of quarry areas, structural analysis of rock outcrops aided by terrestrial photogrammetry, GPS measurements.The results of this study show how the local geomorpological and tectonic setting determined which kinds of extractable rock material, i.e., rock blocks or breccias, were used for different purposes. Moreover, different phases of extraction were evidenced. A main Roman quarrying phase, lasting between the 4th century BCE and the 1st century CE, was recognized as taking place over eight quarry areas. These are delimited by sharp edges and have regular shapes, revealing in some cases a staircase-like morphological profile, and are characterized by similar volumes of extracted rock material. A later quarrying phase —the Bourbon Age, 19th century CE—is assumed to be evidenced instead by five quarries with a peculiar semi-elliptical shape and different volumes of carved material. Seven quarries were found to be of uncertain age.The quarry system described in this paper, together with geomorphological records of slope cuts, terraced surfaces, and the remains of retaining walls, represents a unique and important example of anthropogenic landscape modification in the territory of the central Apennines caused by the construction and maintenance of a Roman road over the centuries. This could be relevant for further studies on the relations between natural environments and the development of civilisation. In addition, the multi-methodological analyses of geomorphological records originated by quarrying activities may be considered for the characterization of similar quarry landscapes.

ПРЕДОТВРАЩЕНИЕ ТРЕЩИНООБРАЗОВАНИЯ В ДЕТАЛЯХ ПРИ ОБЕСПЕЧЕНИИ НАДЕЖНОСТИ СОЕДИНЕНИЙ С НАТЯГОМ

When repairing agricultural machinery, the pressing of repair bushings for the restoration of worn parts is widely used. In the process of assembling a joint in the external part, cracks are often formed, which can be caused either by defects in its surface or by structural defects. Therefore, increasing the crack growth resistance of the press connection during assembly is an urgent task. The work analyzes the impact of the geometry of the external part on the resistance to fracture. Since it is possible to obtain complete information on defects by nondestructive testing methods only in individual cases, a technique for modeling the defects of the surface crack of a semielliptical shape was used. To evaluate the crack resistance, the force criterion of fracture mechanics is used - the stress intensity factor. As a result, it was found that the relationship between the thickness of the wall of the external part and its outer diameter makes a significant impact on the fracture toughness of the compression joint, which makes it possible to reduce the probability of nucleation and development of cracks by changing these parameters. Such a technique can be used in cases where the mechanical assembly is used for assembling the connection - by means of a press and a thermal one - with heating of the external part, methods of assembly. The greatest strength of the connection is achieved by cooling the internal part during assembly, but in this case the probability of formation and growth of cracks increases. This is due to a decrease in the critical stress intensity factor (fracture toughness), which is a mechanical characteristic of crack resistance when the temperature of the external part is lowered. The effect of this factor can be reduced by using a combined method of assembling the joint by cooling the internal and heating the external part. To evaluate the fracture resistance at low temperatures, it is optimal to carry out full-scale tests, where the cooling and heating temperatures of the press connection parts act as experimental factors.

An axial crack growth prediction procedure initiated at butt welded joint (Growth prediction for surface crack deeper than semi-circular and that retarded at weld fusion line)

Structural integrity of cracked pipes is assessed by predicting crack growth. In the fitness-for-service code of the Japan Society of Mechanical Engineers (JSME), the crack growth is predicted using stress intensity factor at the deepest and surface points. A semi-elliptical crack is assumed not to become deeper than a semi-circular crack. However, in reality, the stress corrosion cracking initiated at nickel alloy welds stops growing at the fusion line and becomes deeper than a semi-circular crack. Furthermore, crack shape is close to a rectangular shape rather than a semi-elliptical shape. In this study, validity of the JSME code procedure was discussed for predicting the growth of stress corrosion cracking at nickel alloy welds. Crack growth was simulated by finite element analysis together with an auto meshing technique. Various residual stress distributions and retardation of the crack growth at the fusion line were considered in the simulation. It was demonstrated that the growth prediction procedure prescribed in the JSME code brought about a conservative prediction even if the crack became deeper than the depth of a semi-circular shape crack. It was revealed that, when the growth to the surface direction was retarded at the fusion line, the change in crack size in the depth direction could be predicted conservatively by the current JSME procedure. It was suggested that, when the retardation at the fusion line is assumed in the growth prediction, the crack shape should be modelled by a rectangular shape.

Fluid flow and heat transfer characteristics within a rectangular microchannel array of different manifold shapes - modelisation and optimisation using CFD and response surface methodology

Different manifold shapes of microchannel device are investigated for the pressure drop characteristics under the effect of varying microchannel depth, width and spacing. The response surface methodology is applied to optimise the operating conditions of different microchannel systems. Four operating parameters, the channel width, depth, spacing and the inlet Reynolds number are considered in this study. The individual effects of these operating parameters and the combined effects of multiple operating conditions on pressure drop characteristics are examined using CFD. The semi-elliptical manifold shapes results the high level of fluid flow uniformity within microchannels and lower pressure drop. The maximum percentage reduction in the pressure drop across the microchannel device is 70%, obtained for semi-elliptical manifold shape as compared to other. The heat transfer analysis is also carried out in the extent of the study.

Jet impingement cooling and optimization study for a partly curved isothermal surface with CuO-water nanofluid

Numerical and optimization study of jet impingement cooling of a partly curved surface with CuO-water nanofluid was performed with Galerkin weighted residual finite element method and COBYLA (constrained optimization by linear approximation) optimization algorithm. Target surface was partly curved which has a semi-elliptic shape and kept at constant hot temperature. Simulations were performed for various values of Reynolds number and solid particle volume fraction. It was observed that effects of curved wall on the distribution of fluid flow and heat transfer characteristics are more pronounced for higher values of Reynolds number as compared to a flat wall configuration. Highest heat transfer is obtained with curved wall and significant differences are observed between the peak values of Nusselt number between a flat wall and curved wall case. The average Nusselt number is a linear increasing function of nanoparticle volume fraction and the trends in local and average heat transfer are similar for curved wall and flat wall configurations when nanoparticles are added. Average Nusselt number enhances by about 20% at the highest particle volume fraction as compared to water. A polynomial type correlation for the average Nusselt number was derived which depends on the Reynolds number and solid particle volume fraction for both configurations.

Experimental and calculation challenges of crack propagation in notches – From initiation to end of lifetime

Notches reduce significantly the lifetime of cyclically loaded components due to their stress concentration and early crack initiation. In this work the initiation and crack growth behaviour of cracks in notches has been studied with the direct current potential drop technique. Due to the notch geometry and semi-elliptical shape of the starting crack, significant differences between the crack length determination by the Johnson equation and the real crack length have been observed. By means of numerical simulations for single and multiple crack initiation sites, a calibration function for determining the crack length from the potential drop has been developed. The calibration function results in a good agreement between the estimated and measured changes of the potential drop and permits a quite accurate estimation of the crack initiation life time.

Experimental/numerical investigation of mechanical behaviour of internally pressurized cylindrical shells with external longitudinal and circumferential semi-elliptical defects

This paper presents an experimental-numerical investigation on the mechanical behaviour of pressurized cylindrical shells with external longitudinal and circumferential cracks of semi-elliptical shape. The research is motivated by the need to develop advanced design methodologies for shell structures. For that purpose, strain gauges are utilized to monitor strain concentrations near the cracks, and finite element simulations are carried out to predict the corresponding stress intensity factor distributions. A good agreement between numerical simulations and experimental data is found. This confirms that virtual simulations/calculations provide a reliable approach to evaluating mechanical behaviour of pressurized cylindrical shells with crack defects.

Anatomy and dimensions of fluvial crevasse-splay deposits: Examples from the Cretaceous Castlegate Sandstone and Neslen Formation, Utah, U.S.A.

Crevasse-splay deposits form a volumetrically significant component of many fluvial overbank successions (up to 90% in some successions).Yet the relationships between the morphological form of accumulated splay bodies and their internal facies composition remains poorly documented from ancient successions. This work quantifies lithofacies distributions and dimensions of exhumed crevasse-splay architectural elements in the Campanian Castlegate Sandstone and Neslen Formation, Mesaverde Group, Utah, USA, to develop a depositional model. Fluvial crevasse-splay bodies thin from 2.1m (average) to 0.8m (average) and fine from a coarsest recorded grain size of lower-fine sand to fine silt away from major trunk channel bodies. Internally, the preserved deposits of splays comprise laterally and vertically variable sandstone and siltstone facies associations: proximal parts are dominated by sharp and erosional-based sandstone-prone units, which may be structureless or may comprise primary current lineation on beds and erosional gutter casts; medial parts comprise sets of climbing-ripple strata and small scale deformed beds; distal parts comprise sets of lower-stage plane beds and complex styles of lateral grading into fine-grained floodbasin siltstones and coals. Lithofacies arrangements are used to establish the following: (i) recognition criteria for crevasse-splay elements; (ii) criteria for the differentiation between distal parts of crevasse-splay bodies and floodplain fines; and (iii) empirical relationships with which to establish the extent (ca. 500m long by 1000m wide) and overall semi-elliptical planform shape of crevasse-splay bodies. These relationships have been established by high-resolution stratigraphic correlation and palaeocurrent analysis to identify outcrop orientation with respect to splay orientation. This permits lateral changes in crevasse-splay facies architecture to be resolved. Facies models describing the sedimentology and architecture of crevasse-splay deposits preserved in floodplain successions serve as tools for determining both distance from and direction to major trunk channel sandbodies.

Stress intensity factors and interaction of two parallel surface cracks on cylinder under tension

This paper presents three-dimensional (3D) finite element solution on multiple surface cracks. The cracks on solid cylinder are similar in sizes, parallel each other, assumed to grow in semi-elliptical shape and subjected to remotely tension loading (mode I). A wide range of parametric study involving crack depth ratios ( 0.1<a/D<0.4), crack aspect ratios (0.2<a/b<1.2), normalized coordinates on crack front (0.0<x/h<0.93) and inter-crack distance ratios (0.005<c/l<0.32) are considered for numerical estimation of stress intensity factors (SIFs) along crack front. For multiple surface cracks under axial loading, the stress intensity factors along crack front decreased when c/l decreased. When multiple cracks approach one another, the stress intensity changes due to interaction of the stress field. The results show that it produces a stress shielding effects.

Eunotogramma litorale sp. nov., a marine epipsammic diatom from Southern California, USA

Eunotogramma litorale sp. nov. is described from marine littoral epipsammic assemblages collected from San Diego County, Southern California, USA. The valves of this common species are semi-elliptical in outline with a curved dorsal margin and a more or less straight ventral margin. Each valve has 1–6 transapical costae. Areolae are absent on the valve face; a small rimoportula is usually present on the valve face or uppermost mantle near each pole. One or more rimoportulae are usually found in a row along the dorsal mantle between the costae. Small areolae, visible only with SEM, are typically found between costae on the ventral mantle and along the ventral portion of the pars exterior of the valvocopulae. E. litorale can be distinguished from three other Eunotogramma species with hyaline valve faces by the semi-elliptical shape of its valve outline. The similarity of the internal openings of the rimoportuale of E. litorale and some Aulacodiscus species suggests that E. litorale may be allied with Aulacodiscus, a marine genus associated with inshore beaches.