The Experts below are selected from a list of 1074 Experts worldwide ranked by ideXlab platform
Bernardo Disma Monelli - One of the best experts on this subject based on the ideXlab platform.
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fatigue cracks emanating from sharp notches in high strength aluminium alloys the effect of loading direction Kinking notch geometry and microstructure
International Journal of Fatigue, 2009Co-Authors: M Benedetti, Marco Beghini, V Fontanari, Bernardo Disma MonelliAbstract:Abstract The effect of notch geometry on the propagation of fatigue cracks emanating from sharp V-shaped notches was investigated. To this purpose, an experimental campaign has been conducted on Al-7075–T651 specimens carrying notches with aperture Angles of 45°, 90°, and 135°. In order to investigate the role of microstructure texture, specimens were extracted from the plates with the main axis either in the longitudinal rolling direction (L-samples) or in the transversal direction (T-samples), or 45° inclined with respect to both directions (LT-samples). The effect of stress amplitude was investigated by performing tests at two load levels. Three loading directions θ = 0°, 45° and 90° were considered. Some specimens experienced pure Mode I loading condition, whereas the remaining ones were subjected to combined Mode I and Mode II loading condition. The crack deflection induced by the variation in loading direction was determined by measuring the Kinking Angle. A linear elastic fracture mechanics approach was adopted for the analysis of experimental results. Stress intensity factors (SIF) of straight cracks were calculated using an appropriate weight function set up for studying inclined edge cracks emanating from sharp V-notches. On the contrary, a finite element model has been built up to derive the SIFs at the tip of the kinked cracks. The influence of K II on the crack propagation was discussed on the basis of theoretical and semi-empirical models. It has been found that (i) the crack initiation at the notch root occurred in mixed mode conditions, (ii) a decreasing Mode II component with growing crack length was observed under initial loading direction θ 0 = 45° and θ 0 = 90°, (iii) a crack deflection was observed after 45° rotation of the initial loading direction; a good prediction of the Kinking Angle was obtained using the maximum tangential stress criterion, and (iv) a fairly good rationalization of all the collected crack growth rate data is obtained if the driving force for crack propagation is expressed in terms of K I .
Andrea Spagnoli - One of the best experts on this subject based on the ideXlab platform.
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Fatigue Fractal Crack Propagating in a Self-Balanced Microstress Field
2016Co-Authors: Andrea Carpinteri, Lorenzo Montanari, Andrea SpagnoliAbstract:ABSTRACT. A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length
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Fractal Modelling of Kinked Cracks and its Implications for their Fatigue Propagation in Concrete
2013Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Sabrina Vantadori, Danilo ViappianiAbstract:Threshold condition and rate of fatigue crack growth appear to besignificantly affected by the degree of deflection of cracks. In this paper, the reduction ofthe fatigue crack growth rate for a so-called ‘periodically-kinked crack’ as compared tothat for a straight counterpart is quantified via the Paris-Erdogan law modifiedaccording to some simple theoretical arguments. It is shown that such a reductionincreases as the value of the Kinking Angle increases. Then, a so-called ‘continuouslykinkedcrack’ (the kink length tends to zero) is considered and modelled as a self-similarinvasive fractal curve. Using the Richardson’s expression, the fractal dimension of thecrack is expressed as a function of the Kinking Angle. It is shown that the fatigue crackgrowth rate in the Paris range depends not only on the above fractal dimension and inturn on the Kinking Angle, but also on the crack length. Some experimental results relatedto concrete and showing a crack size effect on the fatigue crack growth rate are analysed.
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006 Fatigue Fractal Crack Propagating in a Self-Balanced Microstress Field
2013Co-Authors: Andrea Carpinteri, Lorenzo Montanari, Andrea SpagnoliAbstract:A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length.
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Fatigue fractal cracks propagating in self-balanced microstress fields
2012Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Lorenzo MontanariAbstract:A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length
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Correlating the fractal dimension of a continuously-kinked fatigue crack with some material microstructural features
., 2011Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Sabrina VantadoriAbstract:An attempt to correlate the degree of crack Kinking to some material microstructural features is illustrated. In particular, the Kinking Angle is correlated to a periodic self-balanced multiaxial microstress field having self-similar characteristics. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. It is shown that threshold condition of fatigue crack growth is affected by the crack Kinking Angle, which in turn is a function of the ratio between crack length and microstructure characteristic length. The well-known Kitagawa diagram can be interpreted within the framework of the proposed model
Andrea Carpinteri - One of the best experts on this subject based on the ideXlab platform.
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Fatigue Fractal Crack Propagating in a Self-Balanced Microstress Field
2016Co-Authors: Andrea Carpinteri, Lorenzo Montanari, Andrea SpagnoliAbstract:ABSTRACT. A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length
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Fractal Modelling of Kinked Cracks and its Implications for their Fatigue Propagation in Concrete
2013Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Sabrina Vantadori, Danilo ViappianiAbstract:Threshold condition and rate of fatigue crack growth appear to besignificantly affected by the degree of deflection of cracks. In this paper, the reduction ofthe fatigue crack growth rate for a so-called ‘periodically-kinked crack’ as compared tothat for a straight counterpart is quantified via the Paris-Erdogan law modifiedaccording to some simple theoretical arguments. It is shown that such a reductionincreases as the value of the Kinking Angle increases. Then, a so-called ‘continuouslykinkedcrack’ (the kink length tends to zero) is considered and modelled as a self-similarinvasive fractal curve. Using the Richardson’s expression, the fractal dimension of thecrack is expressed as a function of the Kinking Angle. It is shown that the fatigue crackgrowth rate in the Paris range depends not only on the above fractal dimension and inturn on the Kinking Angle, but also on the crack length. Some experimental results relatedto concrete and showing a crack size effect on the fatigue crack growth rate are analysed.
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006 Fatigue Fractal Crack Propagating in a Self-Balanced Microstress Field
2013Co-Authors: Andrea Carpinteri, Lorenzo Montanari, Andrea SpagnoliAbstract:A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length.
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Fatigue fractal cracks propagating in self-balanced microstress fields
2012Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Lorenzo MontanariAbstract:A kinked crack propagating in a periodic self-balanced multiaxial microstress field having self-similar characteristics is considered. The Kinking Angle of the crack is shown to depend on the properties of the microstress field. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. Crack size effect on the fatigue crack growth rate in the Paris regime can be interpreted by the present model. Further, the Kitagawa diagram can be interpreted by showing that the threshold condition of fatigue crack growth is affected by the crack Kinking Angle which, in turn, is a function of the ratio between crack length and microstructure characteristic length
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Correlating the fractal dimension of a continuously-kinked fatigue crack with some material microstructural features
., 2011Co-Authors: Andrea Carpinteri, Andrea Spagnoli, Sabrina VantadoriAbstract:An attempt to correlate the degree of crack Kinking to some material microstructural features is illustrated. In particular, the Kinking Angle is correlated to a periodic self-balanced multiaxial microstress field having self-similar characteristics. Using the Richardson’s expression for self-similar fractals, the fractal dimension of the crack is expressed as a function of the Kinking Angle. It is shown that threshold condition of fatigue crack growth is affected by the crack Kinking Angle, which in turn is a function of the ratio between crack length and microstructure characteristic length. The well-known Kitagawa diagram can be interpreted within the framework of the proposed model
M Benedetti - One of the best experts on this subject based on the ideXlab platform.
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fatigue cracks emanating from sharp notches in high strength aluminium alloys the effect of loading direction Kinking notch geometry and microstructure
International Journal of Fatigue, 2009Co-Authors: M Benedetti, Marco Beghini, V Fontanari, Bernardo Disma MonelliAbstract:Abstract The effect of notch geometry on the propagation of fatigue cracks emanating from sharp V-shaped notches was investigated. To this purpose, an experimental campaign has been conducted on Al-7075–T651 specimens carrying notches with aperture Angles of 45°, 90°, and 135°. In order to investigate the role of microstructure texture, specimens were extracted from the plates with the main axis either in the longitudinal rolling direction (L-samples) or in the transversal direction (T-samples), or 45° inclined with respect to both directions (LT-samples). The effect of stress amplitude was investigated by performing tests at two load levels. Three loading directions θ = 0°, 45° and 90° were considered. Some specimens experienced pure Mode I loading condition, whereas the remaining ones were subjected to combined Mode I and Mode II loading condition. The crack deflection induced by the variation in loading direction was determined by measuring the Kinking Angle. A linear elastic fracture mechanics approach was adopted for the analysis of experimental results. Stress intensity factors (SIF) of straight cracks were calculated using an appropriate weight function set up for studying inclined edge cracks emanating from sharp V-notches. On the contrary, a finite element model has been built up to derive the SIFs at the tip of the kinked cracks. The influence of K II on the crack propagation was discussed on the basis of theoretical and semi-empirical models. It has been found that (i) the crack initiation at the notch root occurred in mixed mode conditions, (ii) a decreasing Mode II component with growing crack length was observed under initial loading direction θ 0 = 45° and θ 0 = 90°, (iii) a crack deflection was observed after 45° rotation of the initial loading direction; a good prediction of the Kinking Angle was obtained using the maximum tangential stress criterion, and (iv) a fairly good rationalization of all the collected crack growth rate data is obtained if the driving force for crack propagation is expressed in terms of K I .
Fabrizio Nestola - One of the best experts on this subject based on the ideXlab platform.
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Thermal expansion and high-temperature P2_1/c–C2/c phase transition in clinopyroxene-type LiFeGe_2O_6 and comparison to NaFe(Si,Ge)_2O_6
Physics and Chemistry of Minerals, 2010Co-Authors: G.j. Redhammer, Fabrizio Nestola, F. Cámara, M. Alvaro, G. Tippelt, S. Prinz, J. Simons, G. Roth, G. AmthauerAbstract:A synthetic clinopyroxene with composition LiFe^3+Ge_2O_6, monoclinic s.g. P 2_1/ c , a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) Å^3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b -type reflections ( h + k = 2 n + 1, only present in the P -symmetry) with increasing temperature showed a displacive phase transition from space group P 2_1/ c to C 2/ c at a transition temperature T _tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b -type reflections, thus indicating a symmetry increase to space group C 2/ c . Below T _tr an expansion is observed for all the cell parameters, while the β Angle remained almost constant; at T > T _tr the thermal volume expansion is due to dilatation of the structure in the $$(\bar{1}\,0\,1) $$ plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β . From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P 2_1/ c expands more than the C 2/ c phase. The evolution of Q ^2 (calculated as the normalized intensity of b -type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe a jump of Q _0 ^2 = 0.538(2) at T _tr, with T _c of 481(7) K, b / a = −2,290 K, and c / a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe^3+Si_2O_6) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P 2_1/ c ↔ C 2/ c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron. The tetrahedra behave as rigid units with neither a significant change of volume at T > T _tr ( T _tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This deformation is related to a strong change by 51.4° at T _tr of the Kinking Angle (O3–O3–O3 Angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)° to 194.7(6)°]. The A-chain is S-rotated at T
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compressibility of protoamphibole a high pressure single crystal diffraction study of protomangano ferro anthophyllite
American Mineralogist, 2010Co-Authors: P F Zanazzi, Fabrizio Nestola, Daria PasqualAbstract:The high-pressure behavior of protoamphibole (space group Pnmn ) was studied by in situ single-crystal X-ray diffraction on a sample of protomangano-ferro-anthophyllite with formula (Mn 1.39 Fe 0.59 )(Fe 3.98 Mg 1.02 )Si 8 O 22 (OH) 2 , from Yokone-Yama, Awano Town, Tochigi Prefecture, Japan. Unit-cell parameters were collected at various pressures up to 9 GPa, and structural refinements were obtained from data collected at several pressures up to 7 GPa. Fitting the P-V data to a third-order Birch-Murnaghan equation of state (EoS) gives the following parameters: K T0 = 64(1) GPa, K ′ = 7.0(4), and V 0 = 926.4(4) A 3 . Axial moduli are: K 0 a = 30.7(8) GPa, K ′ a = 10.8(5), and a 0 = 9.430(2) A; K 0 b = 109(4) GPa, K ′ b = 2.7(8), and b 0 = 18.364(4) A; K 0 c = 94(5), GPa, K ′ c = 4(1), and c 0 = 5.354(2) A. The corresponding axial compressibilities (10 −3 GPa −1 ) are β a = 10.9(3), β b = 3.1(1), and β c = 3.5(2), and indicate that the HP behavior of protomangano-ferro-anthophyllite is highly anisotropic, the highest compressibility being along [100]. No discontinuous behavior or polymorphic transitions were observed in the pressure range studied. Structural refinements show that M1, M2, and M3 polyhedra have similar compressibilities, owing to their similar composition. M4 (72% Mn, 28% Fe) is a highly distorted site and is slightly softer than the other octahedra. The major movements in the tetrahedral ribbon concern Kinking of the double chain, bending along the [100] direction through the empty A site, and tetrahedral rotation, necessary to maintain coherence with the octahedral layer. The Kinking Angle of O5-O6-O5, which in air is 179.1(2)°, decreases to 174(2)° at 6.9 GPa. The T1-O7-T1 Angle changes from 143.8(3)° to 134(5)° at 6.9 GPa, and the tetrahedral rotation α increases from 0.2(2)° to 4(2)°.
