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Search Results: 1 - 10 of 5612 matches for " fracture mechanics "
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Fracture and Damage Behaviors of Concrete in the Fractal Space  [PDF]
Heng Zhang, Demin Wei
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.11006
Abstract: The fracture toughness, the driving force and the fracture energy for an infinite plate with a fractal crack are investigated in the fractal space in this work. The perimeter-area relation is adopted to derive the transforma-tion rule between damage variables in the fractal space and Euclidean space. A plasticity yield criterion is introduced and a damage variable tensor is decomposed into tensile and compressive components to describe the distinct behaviors in tension and compression. A plastic damage constitutive model for concrete in the Euclidean space is developed and generalized to fractal case according to the transformation rule of damage variables. Numerical calculations of the present model with and without fractal are conducted and compared with experimental data to verify the efficiency of this model and show the necessity of considering the fractal effect in the constitutive model of concrete. The structural response and mesh sensitivity of a notched unre-inforced concrete beam under 3-point bending test are theoretical studied and show good agreement with the experimental data.
Roughness Research of Center Profile Curve on Rock Fracture Surface Based on Statistical Method  [PDF]
Xuezai Pan, Zhigang Feng, Guoxing Dai, Hongguang Liu
Geomaterials (GM) , 2013, DOI: 10.4236/gm.2013.32006

In order to research roughness of rock fracture surfaces whether to depend on scale effect, Brazil discs were fractured under tensile and compression stresses in Brazil split test with MTS (Mechanics Test Systems) and a laser profilometer was used to scan rock fracture surfaces and coordinates datum of central profile were acquired. A figure of the central profile was plotted through the coordinates datum. A certain line segment length is regarded as a step length, which is called scale and the scale length is taken to connect pairs of closer peak points on the profile curve. The directional distribution of every scales normal vector is analyzed by statistics and normal hypothesis test. Finally, some statistics of sample degrees datum are compared with other ones and reach a conclusion that roughness of center profile curve depends on scale effect. The distribution of degrees more and more approximates normal distribution along with increase of scale.

Fatigue Limit Prediction and Estimation for the Crack Size Rendered Harmless by Peening for Welded Joint Containing a Surface Crack  [PDF]
Ryutaro Fueki, Koji Takahashi, Keiji Houjou
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.66053
Abstract: In this study, the effects of portable pneumatic needle-peening (PPP) on the bending fatigue limit of a low-carbon steel SM490A welded joint containing a semi-circular slit on the weld toe were investigated. PPP was applied to the specimens with a semi-circular slit with depths of a = 0.4, 0.8, 1.2, and 1.6 mm. Then, three-point bending fatigue tests were carried out under R = 0.05. The fatigue limits of low-carbon steel welded specimens containing a semi-circular slit were increased for peened specimens compared with non-peened specimens. Peened specimens having a semicircular slit with a depth of a = 1.2 mm had high fatigue limits, almost equal to those of the non-slit peened specimens. It was concluded that a semi-circular slit with a depth of less than a = 1.2 mm can be rendered harmless by peening. Then, the fatigue improvement by peening was predicted. The fatigue limits before and after peening could be estimated accurately by using a modified Goodman diagram considering the effects of residual stress, stress concentration, and Vickers hardness. Moreover, the maximum depth of a semi-circular slit that can be rendered harmless by PPP was estimated based on fracture mechanics assuming that the semi-circular slit was equivalent to a semi-circular crack. The prediction results were almost consistent with the experimental results.
Predicción de vida remanente en ejes de masa superior de molino de ca?a
Rodríguez Pulecio,Sara; Coronado Marín,John Jairo; Arzola de la Pe?a,Nelson;
Ingeniería e Investigación , 2006,
Abstract: a fracture mechanics-based method is presented for determining critical crack size and residual life of upper sugar-mill shafts having semi-elliptical and circumferential cracks. due to the multiaxial stress field, an equivalent strain energy release rate stress intensity solution is used in paris? law to predict crack growth. ultrasonic inspection intervals for the shaft were established. the crack zone evaluated was located in the shoulder of the bearing nearest to the square box coupling where about 25% of service failures in these types of shaft are observed.
Fracture mechanics of polymer mortar made with recycled raw materials
Jurumenha, Marco Antonio Godoy;Reis, Jo?o Marciano Laredo dos;
Materials Research , 2010, DOI: 10.1590/S1516-14392010000400009
Abstract: the aim of this work is to show that industrial residues could be used in construction applications so that production costs as well as environmental protection can be improved. the fracture properties of polymer mortar manufactured with recycled materials are investigated to evaluate the materials behaviour to crack propagation. the residues used in this work were spent sand from foundry industry as aggregate, unsaturated polyester resin from polyethylene terephthalate (pet) as matrix and polyester textile fibres from garment industry, producing an unique composite material fully from recycled components with low cost. the substitution of fresh by used foundry sand and the insertions of textile fibres contribute to a less brittle behaviour of polymer mortar.
Análise da resistência ao choque térmico de refratários contendo carbono
Quintela, M. A.;Melo, T. M. F. de;Lage, I. J.;Pandolfelli, V. C.;Rodrigues, J. A.;
Ceramica , 2001, DOI: 10.1590/S0366-69132001000400002
Abstract: due to complexity, cost and time involved in evaluating the thermal shock resistance, carbon-containing refractories are usually selected based only on the thermal conductivity. it is therefore necessary to evaluate the physical properties that affect the thermal shock behavior of refractories and to generate suitable criteria for selection and development of microstructure aiming to increase the lining life. the present paper presents the methodology used at usiminas for the determination of the thermal shock damage resistance of carbon-containing refractories for casting ladles. the test method adopted involves measurements of the fracture energy using cmod (crack mouth opening displacement) and the determination of the thermal shock parameters (r'''' e rst).
Paulo Roberto Lopes Lima,Romildo Dias Toledo Filho,José Mário Feitosa Lima
Engevista , 2013,
Abstract: Although the use of vegetables fibers as reinforcement in cement based matrices goes back to the70s, few studies have been performed for analytical and experimental investigation of these composites indirect tensile. In this study, It was evaluated the tensile behavior of composite mortars reinforced with 1%,2% and 3% of short sisal fibers. The softening curve was represented by stress-strain diagram until first crackand, after this point, it was represented by stress-crack opening diagram. Compared with the matrix, whichshowed brittle fracture, the composites showed crack propagation to large displacements with maintenanceof residual stress. Analytical models based Fracture Mechanics were used to determine fracture energy andcharacteristic length of material and the results showed that presence of fibers increment the toughness ofcement based mortar under tensile.
Experimental Analysis of Fracture Processes in Concrete
Sousa, José Luiz Antunes de Oliveira e;Bittencourt, Túlio Nogueira;
Journal of the Brazilian Society of Mechanical Sciences , 2001, DOI: 10.1590/S0100-73862001000400015
Abstract: this paper draws on the basic problems related to the determination of parameters to characterize the structural behavior of concretes using fracture mechanics concepts. experimental procedures and results are discussed.
Experimental Analysis of Fracture Processes in Concrete
Sousa José Luiz Antunes de Oliveira e,Bittencourt Túlio Nogueira
Journal of the Brazilian Society of Mechanical Sciences , 2001,
Abstract: This paper draws on the basic problems related to the determination of parameters to characterize the structural behavior of concretes using Fracture Mechanics concepts. Experimental procedures and results are discussed.
Simulación numérica del proceso de fractura en concreto reforzado mediante la metodología de discontinuidades fuertes de continuo.Parte I: formulación
Linero Segrera,Dorian Luís; Oliver,Javier; Huespe,Alfredo E;
Ingeniería e Investigación , 2010,
Abstract: reinforced concrete structures generally refers to beams, columns and walls which are constituted by complex lattices of steel bars embedded in a concrete matrix, exhibiting multiple cracks due to high external loads. this paper presents the formulation of a numerical model aimed at describing the fracture process in reinforced concrete, from the volumetric ratio of concrete and steel. crack formation and propagation in a composite material is described in the model by an enhanced strain field, such as that established in the continuum strong discontinuity approach and mixture theory. the composite material is constituted by a concrete matrix and one or two steel bar orthogonal packages. the steel and concrete are represented by a one-dimensional plasticity model and a scalar damage model having different tension and compression strength, respectively. the dowel action and the bond-slip effects between the bars and the matrix are described with additional models relating component material stress and strain. it is concluded that the proposed model can easily be implemented in the finite element method, due to several conventional nonlinear numerical process characteristics which remain. the model would also allow the problem to be analysed at macroscopic scale, thereby avoiding a finite element mesh having to be constructed for each component material and its interaction effects and reducing computational costs.
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