Mode I crack tip field with strain gradient effects

A plane strain mode I crack tip field with strain gradient effects is investigated. A new strain gradient theory is used. An elastic-power law hardening strain gradient material is considered and two hardening laws, i.e. a separation law and an integration Law are used respectively. As for the material with the separation law hardening, the angular distributions of stresses are consistent with the HRR field, which differs from the stress results([19]); the angular distributions of couple stresses are the same as the couple stress results([19]). For the material with the integration law hardening, the stress field and the couple stress field can not exist simultaneously, which is the same as the conclusion([19]), but for the stress dominated field, the angular distributions of stresses are consistent with the HRR field; for the couple stress dominated field, the angular distributions of couple stresses are consistent with those in Ref. [19]. However, the increase in stresses is not observed in strain gradient plasticity because the present theory is based on the rotation gradient of the deformation only, while the crack tip field of mode I is dominated by the tension gradient, which will be shown in another paper.

Influence of Indenter Tip Roundness on Hardness Behavior in Nanoindentation

In this paper. the effect of indenter tip roundness on hardness behavior for two typical elastic perfectly plastic materials is studied by means of finite element simulation. A rigid conical indenter of semi apex angle 70.3 degrees fitted smoothly with a spherical tip is employed. It is shown that as the indentation depth increases hardness first rises from zero, reaches a maximum and then decreases slowly approaching asymptotically the limiting value equal to that due to a conical indenter of ideally sharp tip. The range within which hardness varies appreciably is comparable to the radius of the indenter tip. The difference between the maximum value and the limiting value depends on the yield stress over the Young's modulus ratio. The smaller this ratio the greater the difference is. Numerical simulation also provides an opportunity for checking the accuracy and limitations of the widely used Oliver-Pharr method.

Asymptotic analysis based on K-S constitutive law for a rubber wedge compressed by a line load at its tip

In the present paper, a rubber wedge compressed by a line load at its tip is asymptotically analyzed using a special constitutive law proposed by Knowles and Sternberg (K-S elastic law) [J. Elasticity 3 (1973) 67]. The method of dividing sectors proposed by Gao [Theoret. Appl. Fract, Mech. 14 (1990) 219] is used. Domain near the wedge tip can be divided into one expanding sector and two narrowing sectors. Asymptotic equations of the strain-stress field near the wedge tip are derived and solved numerically. The deformation pattern near a wedge tip is completely revealed. A special case. i.e. a half space compressed by a line load is solved while the wedge angle is pi.

Letras, 2002-2003, nº 46-47 (número completo)

Contenido: Resúmenes – Ángel J. Battistessa, 1902-2002 – Un abordaje lingüístico del texto. La sintaxis de la oralidad en “Cae la noche tropical” de Manuel Puig / Norma Carricaburo – Una lectura de los “Cuatro Cuartetos” de T. S. Eliot / Inés de Cassagne – El mundo de la palabra en la comunicación oral: percepción, reconocimiento y acceso al léxico / María Amalia García Jurado – La pluralidad discursiva en la narrativa argentina de las últimas décadas / Luis Martínez Cuitiño – Una perspectiva humanista para el estudio de las letras: los aportes de la fenomenología y la hermenéutica / Graciela Maturo – La acrecibilidad como rasgo genérico y la edición de una crónica medieval en dos versiones / José Luis Moure – Del Siglo de Oro al cine argentino / Saura, Norma – La locución conjuntiva tanto que y la correlación anafórica tanto… que en la subordinación temporal y consecutiva del “Amadís de Gaula” de Garci Rodríguez de Montalvo / Aquilino Suárez Pallasá – Notas – Reseñas bibliográficas

Prudentia Iuris, 1998, n° 47-48 (número completo)

Contenido: Editorial – Perspectivas del Derecho del Trabajo / Jorge Rodríguez Mancini – Conciliación laboral / Santiago A. Zarza – Modificaciones introducidas al régimen remuneratorio por la ley 24.700 / Liliana Hebe Litterio – Pago de la remuneración mediante depósito bancario / Liliana Hebe Litterio – Régimen de asignaciones familiares / José B. Gómez Paz – Trabajo humano y retribución justa / Mario F. Vivino – La reforma laboral según la Ley 25.013 / Juan Manuel Arias – Reflexiones contemporáneas: Presentación – La filosofía de la guerra y la paz más allá de las tres “tradiciones” / Hernando V. Cañardo – Democracia, modernidad y cristianismo / Philippe Benetón – Derechas e izquierdas en el pensamiento político contemporáneo / Dalmacio Negro Pavón – El mercado común del cono sur - Mercosur / Fernando P. Brebbia – Integración sudamericana y derecho / Francisco Arias Pellerano – Discurso televisivo y discurso judicial / Luis María Bandieri – Recensiones – Anexo legislativo

Steady-state crack growth and fracture work based on the theory of mechanism-based strain gradient plasticity

Mode I steady-state crack growth is analyzed under plane strain conditions in small scale yielding. The elastic-plastic solid is characterized by the mechanism-based strain gradient (MSG) plasticity theory [J. Mech. Phys. Solids 47 (1999) 1239, J. Mech. Phys. Solids 48 (2000) 99]. The distributions of the normal separation stress and the effective stress along the plane ahead of the crack tip are computed using a special finite element method based on the steady-state fundamental relations and the MSG flow theory. The results show that during the steady-state crack growth, the normal separation stress on the plane ahead of the crack tip can achieve considerably high value within the MSG strain gradient sensitive zone. The results also show that the crack tip fields are insensitive to the cell size parameter in the MSG theory. Moreover, in the present research, the steady-state fracture toughness is computed by adopting the embedded process zone (EPZ) model. The results display that the steady-state fracture toughness strongly depends on the separation strength parameter of the EPZ model and the length scale parameter in the MSG theory. Furthermore, in order for the results of steady crack growth to be comparable, an approximate relation between the length scale parameters in the MSG theory and in the Fleck-Hutchinson strain gradient plasticity theory is obtained.

Md Simulation Of Dislocation Mobility During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are simulated. Two partial edge dislocations are introduced into workpiece Si, it is found that the motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocations is far below the yield strength of Si. (c) 2008 Elsevier Ltd. All rights reserved.

An Improved Energy Method For Determining Young'S Modulus By Instrumented Indentation Using A Berkovich Tip

We previously proposed a method for estimating Young's modulus from instrumented nanoindentation data based on a model assuming that the indenter had a spherical-capped Berkovich geometry to take account of the bluntness effect. The method is now further improved by releasing the constraint on the tip shape, allowing it to have a much broader arbitrariness to range from a conical-tipped shape to a flat-ended shape, whereas the spherical-capped shape is just a special case in between. This method requires two parameters to specify a tip geometry, namely, a volume bluntness ratio V-r and a height bluntness ratio h(r). A set of functional relationships correlating nominal hardness/reduced elastic modulus ratio (H-n/E-r) and elastic work/total work ratio (W-e/W) were established based on dimensional analysis and finite element simulations, with each relationship specified by a set of V-r and h(r). Young's modulus of an indented material can be estimated from these relationships. The method was shown to be valid when applied to S45C carbon steel and 6061 aluminum alloy.

Molecular Dynamics Study Of Mechanical Behaviour Of Screw Dislocation During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are calculated. A screw dislocation is introduced into workpiece Si. It is found that motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocation is far below the yield strength of Si.

Sapientia, 1958, Vol. XIII, nº 47 (número completo)

Contenido: Ascética y filosofía / La Dirección – Ontología de la historia / Octavio N. Derisi – La filosofía moral en el cinismo / Benito R. Raffo Magnasco -- Despotismo universal y Katéchon Paulino en Donoso Cortés (I) / Alberto Caturelli – Notas y comentarios – Bibliografía

Multi-scale analysis of AFM tip and surface interactions

Thoroughly understanding AFM tip-surface interactions is crucial for many experimental studies and applications. It is important to realize that despite its simple appearance, the system of tip and sample surface involves multiscale interactions. In fact, the system is governed by a combination of molecular force (like the van der Waals force), its macroscopic representations (such as surface force) and gravitational force (a macroscopic force). Hence, in the system, various length scales are operative, from sub-nanoscale (at the molecular level) to the macroscopic scale. By integrating molecular forces into continuum equations, we performed a multiscale analysis and revealed the nonlocality effect between a tip and a rough solid surface and the mechanism governing liquid surface deformation and jumping. The results have several significant implications for practical applications. For instance, nonlocality may affect the measurement accuracy of surface morphology. At the critical state of liquid surface jump, the ratio of the gap between a tip and a liquid dome (delta) over the dome height (y(o)) is approximately (n-4) (for a large tip), which depends on the power law exponent n of the molecular interaction energy. These findings demonstrate that the multiscale analysis is not only useful but also necessary in the understanding of practical phenomena involving molecular forces. (c) 2007 Elsevier Ltd. All rights reserved.