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Crack Growth Behaviour (crack + 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] 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] 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] | ||||||||||