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Initiation of parallel cracks from surface of elastic half-plane
354A
PERIPHERAL SUBJECTS:FRACTURE MECHANICS
Floorlift is a major problem in mining tunnels. Although the basic mechanics of the problem are simple to understand there is little quantified knowledge of the influence of floor rock strength or support pressure upon the problem. This note aims to study these two aspects using a viscoplastic finite element model developed for this type of application. A sequence of models investigating the influence of floor rock strength illustrates its importance in determining floor deformations. A second sequence of models investigating the influence of support pressure and distribution illustrates that control requires the use of inverts and high support pressures. (from Authors)
PERIPHERAL SUBJECTS Fracture mechanics 957375 Fracture analysis of base-edge-cracked reverse-tapered plates J. P. Dempsey, R. M. Adamson & S. J. Defranco, International Journal of Fracture, 69(4), 1995, pp 281-294. This paper presents a fracture mechanics analysis of the baseedge-cracked reverse-tapered (RT) fracture geometry. Motivation for this study was the use of this test geometry in Phase I of a recently completed joint-industry-agency project entitled 'Large-Scale Ice Fracture Experiments'. Underlying the choice of the RT fracture geometry for Phase 1 was the desirability of achieving crack propagation in a controlled and stable manner; such control would allow a number of observations to be made on one testpiece. Reverse tapering greatly improves not only crack growth stability but also crack path stability. The weight function method was used to provide accurate wide-ranging stress intensity factor (SIF), crack face displacement (COD) and crack opening area (COA) expressions for the RT subject to any loading. The required weight function was obtained through a finite element analysis of this geometry subject to a reference load case which determined the associated stress intensity factor and crack opening displacements. The Wu and Carlsson procedure was followed. (from Authors) 957376 Viscoplastic damage model applied to cracking of gravity dam Z. X. Li, Theoretical & Applied Fracture Mechanics, 22(2), 1995, pp 165-170.
Assuming that material damages with a viscoplastic behavior, a finite element formulation is developed to analyze the evolution of damage by cracking in a gravity dam. An effective damage matrix is constructed to predict the possible sites of cracking based on the maximum normal stress criterion. The parameter Z is introduced such that the closure of those cracks that were already initiated could he accounted for as new ones are being developed. Numerical results are obtained to illustrate the spreading of cracks as the load is increased. (Author) 957377 Embedded representation of fracture in concrete with mixed finite elements H. R. Lotfi & P. B. Shing, International Journal for Numerical Methods in Engineering, 38(8), 1995, pp 13071325. As an alternative to the smeared and discrete crack representations, an embedded representation of fracture for fimte element analysis of concrete structures is presented. The three-field Hu-Washizu variational statement is extended to bodies with internal discontinuities. The extended variational statement is then utilized for formulating elements with a discontinuous displacement field. The new elements are capable of modelling different deformation modes of an internal discontinuity at the element level. The satisfactory performance of the embedded crack representation is verified by several case studies on concrete fracture. (Authors) 957378 Initiation of parallel cracks from surface of elastic hnifplane Yuan N. Li, A. P. Hang & Z. P. Bazant, International Journal of Fracture, 69(4), 1995, pp 357-369. The paper deals with the problem of initiation of thermal or shrinkage cracks from the surface of a half plane. Linear elastic fracture behavior is assumed. The initial spacing and initial stable equilibrium length of parallel equidistant cracks emanating from the surface is determined fron~ three conditions formulated in a preceding study of penetration of sea ice plate: 1) The stress at the surface reaches a given strength limit. 2) After the initial ~'acks form, the energy release rate equals its given critical value. 3) The finite energy release due to the initial crack jump equals the energy needed to form the crack (according to the given fracture energy of the material or fracture roughness). The problem is reduced to a singular integral equation which is solved numerically by Erdogan's method. (from Authors)
PERIPHERAL SUBJECTS:FRACTURE MECHANICS
Floorlift is a major problem in mining tunnels. Although the basic mechanics of the problem are simple to understand there is little quantified knowledge of the influence of floor rock strength or support pressure upon the problem. This note aims to study these two aspects using a viscoplastic finite element model developed for this type of application. A sequence of models investigating the influence of floor rock strength illustrates its importance in determining floor deformations. A second sequence of models investigating the influence of support pressure and distribution illustrates that control requires the use of inverts and high support pressures. (from Authors)
PERIPHERAL SUBJECTS Fracture mechanics 957375 Fracture analysis of base-edge-cracked reverse-tapered plates J. P. Dempsey, R. M. Adamson & S. J. Defranco, International Journal of Fracture, 69(4), 1995, pp 281-294. This paper presents a fracture mechanics analysis of the baseedge-cracked reverse-tapered (RT) fracture geometry. Motivation for this study was the use of this test geometry in Phase I of a recently completed joint-industry-agency project entitled 'Large-Scale Ice Fracture Experiments'. Underlying the choice of the RT fracture geometry for Phase 1 was the desirability of achieving crack propagation in a controlled and stable manner; such control would allow a number of observations to be made on one testpiece. Reverse tapering greatly improves not only crack growth stability but also crack path stability. The weight function method was used to provide accurate wide-ranging stress intensity factor (SIF), crack face displacement (COD) and crack opening area (COA) expressions for the RT subject to any loading. The required weight function was obtained through a finite element analysis of this geometry subject to a reference load case which determined the associated stress intensity factor and crack opening displacements. The Wu and Carlsson procedure was followed. (from Authors) 957376 Viscoplastic damage model applied to cracking of gravity dam Z. X. Li, Theoretical & Applied Fracture Mechanics, 22(2), 1995, pp 165-170.
Assuming that material damages with a viscoplastic behavior, a finite element formulation is developed to analyze the evolution of damage by cracking in a gravity dam. An effective damage matrix is constructed to predict the possible sites of cracking based on the maximum normal stress criterion. The parameter Z is introduced such that the closure of those cracks that were already initiated could he accounted for as new ones are being developed. Numerical results are obtained to illustrate the spreading of cracks as the load is increased. (Author) 957377 Embedded representation of fracture in concrete with mixed finite elements H. R. Lotfi & P. B. Shing, International Journal for Numerical Methods in Engineering, 38(8), 1995, pp 13071325. As an alternative to the smeared and discrete crack representations, an embedded representation of fracture for fimte element analysis of concrete structures is presented. The three-field Hu-Washizu variational statement is extended to bodies with internal discontinuities. The extended variational statement is then utilized for formulating elements with a discontinuous displacement field. The new elements are capable of modelling different deformation modes of an internal discontinuity at the element level. The satisfactory performance of the embedded crack representation is verified by several case studies on concrete fracture. (Authors) 957378 Initiation of parallel cracks from surface of elastic hnifplane Yuan N. Li, A. P. Hang & Z. P. Bazant, International Journal of Fracture, 69(4), 1995, pp 357-369. The paper deals with the problem of initiation of thermal or shrinkage cracks from the surface of a half plane. Linear elastic fracture behavior is assumed. The initial spacing and initial stable equilibrium length of parallel equidistant cracks emanating from the surface is determined fron~ three conditions formulated in a preceding study of penetration of sea ice plate: 1) The stress at the surface reaches a given strength limit. 2) After the initial ~'acks form, the energy release rate equals its given critical value. 3) The finite energy release due to the initial crack jump equals the energy needed to form the crack (according to the given fracture energy of the material or fracture roughness). The problem is reduced to a singular integral equation which is solved numerically by Erdogan's method. (from Authors)