Home About us Contact
|
Home About us Contact | ||
|
|
||
Growth Behaviour (growth + behaviour)
Kinds of Growth Behaviour Selected AbstractsEffects of spectrum modification on fatigue crack growthFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2010D. KUJAWSKI ABSTRACT The purpose of this study was to investigate experimentally the effects associated with modification of a loading spectrum recorded from P-3 a maritime aircraft on fatigue crack growth behaviour. The material is 2324-T39 Al alloy widely used in the aircraft industry. Experiments were conducted using the full spectrum and modified versions of it such as only ,positive' (no negative loads) or with reduced (clipped) high peaks. The results show that the compressive loads decrease fatigue life of the specimen by ,300%. Furthermore, by running tests with clipped peaks it was found that the fatigue life was shorten significantly due to reduction of crack growth retardation caused by highest tensile peaks. Multiple tests were conducted in order to establish a scatter in the experimental data under spectrum loads. [source] Fatigue life prediction of cracked padded platesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3-4 2008K. GUO ABSTRACT The fatigue crack propagation analyses of padded plates are conducted to predict the crack growth behaviour under various loading conditions. The fatigue life of a padded plate with a single edge crack originating from the weld toe is calculated using the weight function approach. The fatigue strength of padded plates with different pad thickness under remote loading conditions was investigated and compared to the T-plate joint. The improvement of the fatigue strength of the pad design is verified. The thickness effect of the padded plate was investigated using the fracture mechanics approach. The geometrically similar model pairs with different initial crack sizes were investigated under remote loading conditions. It was shown that the thickness effect depends on both stress concentration and initial crack size. [source] Nanoscopic fatigue and stress corrosion crack growth behaviour in a high-strength stainless steel visualized in situ by atomic force microscopyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2005K. MINOSHIMA ABSTRACT In situ atomic force microscope (AFM) imaging of the fatigue and stress corrosion (SC) crack in a high-strength stainless steel was performed, under both static and dynamic loading. The AFM systems used were (1) a newly developed AFM-based system for analysing the nanoscopic topographies of environmentally induced damage under dynamic loads in a controlled environment and (2) an AFM system having a large sample stage together with a static in-plane loading device. By using these systems, in situ serial clear AFM images of an environmentally induced crack under loading could be obtained in a controlled environment, such as in dry air for the fatigue and in an aqueous solution for the stress corrosion cracking (SCC). The intergranular static SC crack at the free corrosion had a sharp crack tip when it grew straight along a grain boundary. The in situ AFM observations showed that the fatigue crack grew in a steady manner on the order of sub-micrometre. The same result was obtained for the static SC crack under the free corrosion, growing straight along a grain boundary. In these cases, the crack tip opening displacement (CTOD) remained constant. However, as the static SC crack was approaching a triple grain junction, the growth rate became smaller, the CTOD value increased and the hollow ahead of the crack tip became larger. After the crack passed through the triple grain junction, it grew faster with a lower CTOD value; the changes in the CTOD value agreed with those of the crack growth rate. At the cathodic potential, the static SC crack grew in a zigzag path and in an unsteady manner, showing crack growth acceleration and retardation. This unsteady crack growth was considered to be due to the changes in the local hydrogen content near the crack tip. The changes in the CTOD value also agreed with those of the crack growth rate. The CTOD value in the corrosive environment was influenced by the microstructure of the material and the local hydrogen content, showing a larger scatter band, whereas the CTOD value of the fatigue crack in dry air was determined by the applied stress intensity factor, with a smaller scatter band. In addition, the CTOD value in the corrosive environment under both static and dynamic loading was smaller than that of the fatigue crack; the environmentally induced crack had a sharper crack tip than the fatigue crack in dry air. [source] Laser shock peening on fatigue crack growth behaviour of aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2004Y. TAN ABSTRACT The effect of laser shock peening (LPS) in the fatigue crack growth behaviour of a 2024-T3 aluminium alloy with various notch geometries was investigated. LPS was performed under a ,confined ablation mode' using an Nd: glass laser at a laser power density of 5 GW cm,2. A black paint coating layer and water layer was used as a sacrificial and plasma confinement layer, respectively. The shock wave propagates into the material, causing the surface layer to deform plastically, and thereby, develop a residual compressive stress at the surface. The residual compressive stress as a function of depth was measured by X-ray diffraction technique. The fatigue crack initiation life and fatigue crack growth rates of an Al alloy with different preexisting notch configurations were characterized and compared with those of the unpeened material. The results clearly show that LSP is an effective surface treatment technique for suppressing the fatigue crack growth of Al alloys with various preexisting notch configurations. [source] Initiation and early growth of fatigue cracks in an aerospace aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2002S. A. Barter Abstract Material imperfections usually play a substantial role in the early stages of fatigue cracking. This article presents some observations concerning fatigue crack initiating flaws and early crack growth in 7050-T7451 aluminium alloy specimens and in full-scale fatigue test articles with a production surface finish. Equivalent initial flaw size (EIFS) approaches used to evaluate the fatigue implications of metallurgical, manufacturing and service-induced features were refined by using quantitative fractography to acquire detailed information on the early crack growth behaviour of individual cracks; the crack growth observations were employed in a simple crack growth model developed for use in analysing service crack growth. The use of observed crack growth behaviour reduces the variability which is inherent in EIFS approaches which rely on modelling the whole of fatigue life, and which can dominate EIFS methods. The observations of realistic initial flaws also highlighted some of the significant factors in the fatigue life-determining early fatigue growth phase, such as surface treatment processes. Although inclusions are often regarded as the single most common type of initiating flaw, processes which include etching can lead to etch pitting of grain boundaries with significant fatigue life implications. [source] Study of crack growth in solid propellantsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2001E. E. Gdoutos The stress and displacement fields in an edge-cracked sheet specimen made of a solid propellant and subjected to a uniform displacement along its upper and lower faces was studied. The solid propellant was simulated as a hyperelastic material with constitutive behaviour described by the Ogden strain energy potential. A non-linear finite deformation analysis was performed based on the finite element code ABAQUS. A detailed analysis of the stress field in the vicinity of the crack tip was undertaken. The deformed profiles of the crack faces near the crack tip were determined. The results of stress analysis were coupled with the strain energy density theory to predict the crack growth behaviour including crack initiation, stable crack growth and final termination for two specimens with different dimensions. Crack growth resistance curves representing the variation of crack growth increment versus applied displacement were drawn. [source] The effect of overload on the fatigue crack growth behaviour of 304 stainless steel in hydrogenFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2001M. H. Kelestemur Fatigue crack growth (FCG) behaviour and its characteristics following tensile overloads were investigated for AISI 304 stainless steel in three different atmospheres; namely dry argon, moist air and hydrogen. The FCG tests were performed by MTS 810 servohydraulic machine. CT specimens were used for the tests and crack closure measurements were made using an extensometer. FCG rates of 304 stainless steel at both dry argon and moist air atmospheres have shown almost the same behaviour. In other words, the effect of moisture on FCG of this material is very small. However, in a hydrogen atmosphere, the material showed considerably higher crack growth rate in all regimes. In general, for all environments, the initial effect of overloads was to accelerate the FCG rate for a short distance (less than a mm) after which retardation occurred for a considerable amount of time. The main causes for retardation were found as crack blunting and a long reinitiation period for the fatigue crack. Regarding the environmental effect, the overload retardation was lowest in a hydrogen atmosphere. This low degree of retardation was explained by a hydrogen embrittlement mechanism. In a general sense, hydrogen may cause a different crack closure mechanism and hydrogen induced crack closure has come in to the picture. Scanning electron microscope and light microscope examinations agreed well with the above results. [source] Fatigue strength of Inconel 718 at elevated temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000Kawagoishi The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long-life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix (, phase) and the surface oxidation at elevated temperatures. [source] Void growth and damage models for predicting ductile fracture in weldsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2000Wilsius This study reports on a numerical and experimental investigation of ductile tearing using a local approach to fracture. Two models have been analysed: (i) the Rice,Tracey (RT) void growth model; and (ii) the Rousselier continuum damage theory. The effects of the model parameters, including the mesh size, on the crack growth behaviour have been analysed, and a significant influence on both the J -values and the slopes dJ/da has been noted. The crack propagation in an overmatched welded joint has also been investigated. For the RT model, crack propagation has been simulated using the release node technique. Because this method requires one to previously assign the crack propagation path, using such a model is somewhat restrictive. This problem vanishes when dealing with Rousselier's model (and more generally with coupled models) because the elements which are damaged automatically give the crack path. [source] The global trend in plant twining directionGLOBAL ECOLOGY, Issue 6 2007Will Edwards ABSTRACT Aim, To examine, at a global scale, patterns in the direction in which climbing plants twine. We tested three hypotheses: (1) that twining direction is determined randomly; (2) that twining direction is determined by apices following the apparent movement of the sun across the sky; and (3) that twining direction is determined by the Coriolis effect. Location, Seventeen sites spanning nine countries, both hemispheres and 65° of latitude. Methods, Twining direction was recorded for the first c. 100 stems encountered along transects through natural vegetation at each site. Results, Ninety-two per cent of the 1485 twining stems we recorded grew in right-handed helices, i.e. they twined in an anticlockwise direction. This is significantly (P < 0.001) different from random. The proportion of stems twining right-handedly (anticlockwise) was independent of both latitude (P= 0.33) and hemisphere (P= 0.63). These data are inconsistent with the idea that twining direction is determined by either the relative passage of the sun through the celestial sphere or by the Coriolis effect. Thus, we reject all three of our hypotheses. Main conclusions, The predominance of right-handed helical growth in climbing plants cannot be explained by hypotheses attempting to link plant growth behaviour and global location. One alternative hypothesis for our findings is that the widespread phenomenon of anticlockwise twining arises as a function of microtubule orientation operating at a subcellular level. [source] ZnO Hierarchical Micro/Nanoarchitectures: Solvothermal Synthesis and Structurally Enhanced Photocatalytic Performance,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008Fang Lu Abstract A novel ZnO hierarchical micro/nanoarchitecture is fabricated by a facile solvothermal approach in an aqueous solution of ethylenediamine (EDA). This complex architecture is of a core/shell structure, composed of dense nanosheet-built networks that stand on a hexagonal-pyramid-like microcrystal (core part). The ZnO hexagonal micropyramid has external surfaces that consist of a basal plane (000) and lateral planes {011}. The nanosheets are a uniform thickness of about 10,nm and have a single-crystal structure with sheet-planar surfaces as {20} planes. These nanosheets interlace and overlap each other with an angle of 60° or 120°, and assemble into a discernible net- or grid-like morphology (about 100,nm in grid-size) on the micropyramid, which shows a high specific surface area (185.6,m2,g,1). Such a ZnO micro/nanoarchitecture is new in the family of ZnO nanostructures. Its formation depends on the concentration of the EDA solution as well as on the type of zinc source. A two-step sequential growth model is proposed based on observations from a time-dependent morphology evolution process. Importantly, such structured ZnO has shown a strong structure-induced enhancement of photocatalytic performance and has exhibited a much better photocatalytic property and durability for the photodegradation of methyl orange than that of other nanostructured ZnO, such as the powders of nanoparticles, nanosheets, and nanoneedles. This is mainly attributed to its higher surface-to-volume ratio and stability against aggregation. This work not only gives insight into understanding the hierarchical growth behaviour of complex ZnO micro/nanoarchitectures in a solution-phase synthetic system, but also provides an efficient route to enhance the photocatalytic performance of ZnO, which could also be extended to other catalysts, such as the inherently excellent TiO2, if they are of the same hierarchical micro/nanoarchitecture with an open and porous nanostructured surface layer. [source] Effects of climate on the growth of exotic and indigenous trees in central ZambiaJOURNAL OF BIOGEOGRAPHY, Issue 1 2005E. N. Chidumayo Abstract Aim, Climate change has far-reaching effects on species and ecosystems. The aims of this study were to determine how climate factors affect the growth pattern of indigenous and exotic trees in Zambia and to predict tree growth responses to a warmer climate with the use of mathematical models. Location, Two savanna sites in central Zambia. Methods, Diameter at breast height (1.3 m above ground, d.b.h.) of 91 permanently marked trees belonging to three indigenous and four exotic species was measured fortnightly for periods of 1,2 years from 1998 to 2003. Correlation and regression analysis was used to determine the effect of climate factors (minimum, maximum and average temperature and rainfall) on monthly daily d.b.h. increment of each species. Regression models were used to predict the growth behaviour of trees under a 0.5 °C warmer climate. Results, Interactions between temperature and rainfall explained 60,98% of the variation in d.b.h. increment in all the tree species, except the exotic Eucalyptus grandis. For deciduous species, stem expansion was delayed by 2,12 weeks following leaf-flush and d.b.h. increment peaked during the rainy season. Evergreen and deciduous species could not be separated on the basis of annual d.b.h. increment because the higher growth rates of deciduous species compensated for the shorter growing period. Mathematical models predicted slight changes in d.b.h. growth pattern under a 0.5 °C warmer climate in five of the seven species. Significant changes in d.b.h. growth patterns were predicted in the indigenous Bridelia micrantha and exotic Gmelina arborea under a warmer climate. However, models failed to adequately represent potential soil water stress that might result from changes in tree growth patterns and a warmer climate. Main conclusions, Climate factors explained a large proportion of the variation in diameter growth of both indigenous and exotic trees, rendering it possible to model tree growth patterns from climate data. Tree growth models suggest that a rise in temperature of 0.5 °C is unlikely to induce significant changes in the growth behaviour of the majority of the studied species. However, because the growth behaviour of some species may be substantially affected by climate change, it is recommended that strategies for the future production of such climate-sensitive trees should incorporate aspects of climate change. [source] Verfahren zur vollständigen Ermittlung der R-Abhängigkeit des Rissausbreitungsverhaltens mit nur einer Probe,MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 9 2007A. Tesch Dr. fatigue crack growth; Kmax -tests; threshold; Al 2524-T351 Abstract Ein neues Prüfungskonzept für Ermüdungsrisswachstumsversuche ermöglicht es mit nur einer Probe für den gesamten Bereich des Spannungsverhältnisses von R = 0,9 bis R = -1 Ermüdungsrisswachstumskurven (da/dN-,K-Kurven) für jedes beliebige R-Verhältnis zu erstellen. Zusätzlich erhält man auch die Schwellenwerte der Spannungsintensitätsschwingbreite ,Kth als Funktion von R und Kmax. In Kombination mit einer Methode zur kontinuierlichen Risslängenbestimmung, wie der Gleichstrompotenzialmethode, erfordert dieses Verfahren sehr geringen Personal- und Zeitaufwand. Das Prüfungskonzept besteht aus einer Aneinanderreihung von Kmax -konstant-Versuchen. Da die Kmax -Werte stufenweise ansteigen, sollte es bei diesem Verfahren keine Lastfolgeeffekte geben. Die ermittelten Daten stimmen sehr gut mit Ergebnissen aus da/dN-,K-Versuchen, die nach der ASTM Norm E 647 mit mehreren Proben durchgeführten wurden, überein. Die Versuche erfüllen alle Bedingungen der ASTM E 647. Procedure for the determination of the complete R-dependency of the crack growth behaviour with only one specimen A new concept for fatigue crack propagation tests has been developed. Using a single specimen, it is possible to determine fatigue crack growth curves (da/dN - ,K) for every stress ratio between R = 0.9 and R = -1. Additionally, the new concept also provides threshold values for fatigue crack growth for different values of R and Kmax. In combination with a continuous crack length measurement tool (such as the DC potential drop method) this testing procedure can be performed with minimal effort of personnel and time. The test procedure consists of a sequence of Kmax -constant tests with decreasing crack growth rates. As the applied Kmax is increasing stepwise there should be no load history effects. According to the procedures described in the ASTM Standard E 647, the results using this new testing procedure fit very well to the da/dN - ,K curves generated with different specimens. The tests also fulfil all the requirements of ASTM Standard E 647. [source] On Cauchy estimates and growth orders of entire solutions of iterated Dirac and generalized Cauchy,Riemann equationsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 14 2006D. Constales Abstract In this paper, we study the growth behaviour of entire Clifford algebra-valued solutions to iterated Dirac and generalized Cauchy,Riemann equations in higher-dimensional Euclidean space. Solutions to this type of systems of partial differential equations are often called k -monogenic functions or, more generically, polymonogenic functions. In the case dealing with the Dirac operator, the function classes of polyharmonic functions are included as particular subcases. These are important for a number of concrete problems in physics and engineering, such as, for example, in the case of the biharmonic equation for elasticity problems of surfaces and for the description of the stream function in the Stokes flow regime with high viscosity. Furthermore, these equations in turn are closely related to the polywave equation, the poly-heat equation and the poly-Klein,Gordon equation. In the first part we develop sharp Cauchy-type estimates for polymonogenic functions, for equations in the sense of Dirac as well as Cauchy,Riemann. Then we introduce generalizations of growth orders, of the maximum term and of the central index in this framework, which in turn then enable us to perform a quantitative asymptotic growth analysis of this function class. As concrete applications we develop some generalizations of some of Valiron's inequalities in this paper. Copyright © 2006 John Wiley & Sons, Ltd. [source] Further results on the asymptotic growth of entire solutions of iterated Dirac equations in ,nMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2006D. Constales Abstract In this paper, we establish some further results on the asymptotic growth behaviour of entire solutions to iterated Dirac equations in ,n. Solutions to this type of systems of partial differential equations are often called polymonogenic or k -monogenic. In the particular cases where k is even, one deals with polyharmonic functions. These are of central importance for a number of concrete problems arising in engineering and physics, such as for example in the case of the biharmonic equation for the description of the stream function in the Stokes flow regime with low Reynolds numbers and for elasticity problems in plates. The asymptotic study that we are going to perform within the context of these PDE departs from the Taylor series representation of their solutions. Generalizations of the maximum term and the central index serve as basic tools in our analysis. By applying these tools we then establish explicit asymptotic relations between the growth behaviour of polymonogenic functions, the growth behaviour of their iterated radial derivatives and that of functions obtained by applying iterations of the , operator to them. Copyright © 2005 John Wiley & Sons, Ltd. [source] Investigations on local Ga and In incorporation of GaInN quantum wells on facets of selectively grown GaN stripesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006B. Neubert Abstract Multiple GaInN quantum wells (QWs) were grown on side facets with reduced piezoelectric fields (PFs) of selectively grown GaN stripes oriented along the ,100, and ,110, directions by metalorganic vapor phase epitaxy (MOVPE). The different luminescence wavelengths observed for the QWs on these facets can be explained by the reduced PFs, additionally the QW thickness depends on the facet type. Although stripes running along ,100, and ,110, develop similar triangular or trapezoidal shape, their detailed growth behaviour, electrical and luminescence properties differ significantly pointing to different adsorption/desorption and inter-facet migration processes of In, Ga and the p-type dopant Mg. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||