Toughening Mechanisms in Quasi-Brittle Materials

1993 ◽  
Vol 115 (3) ◽  
pp. 300-307 ◽  
Author(s):  
S. P. Shah ◽  
C. Ouyang
Keyword(s):  
Fracture Process ◽  
Nonlinear Response ◽  
Large Scale ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Brittle Materials ◽  
Toughening Mechanisms ◽  
Theoretical Approaches ◽  
Cement Based Materials ◽  
Fracture Processes

Fracture processes in cement-based materials are characterized by a large-scale fracture process zone, localization of deformation, and strain softening. Many studies have been conducted to understand the toughening mechanisms of such quasi-brittle materials and to theoretically model their nonlinear response. This paper summarizes two innovative experimental techniques which are being developed at the ACBM Center to better define the fracture process zone in cement-based materials. A brief summary is also given of two types of theoretical approaches which attempt to simulate some of the observed nonlinear fracture response of these materials.

A Continuum Model with an Embedded Fracture Process Zone Modelled as a Cohesive Frictional Interface

2016 ◽  
Vol 846 ◽  
pp. 360-365 ◽  
Author(s):  
Arash Mir ◽  
Giang Dinh Nguyen ◽  
Abdul H. Sheikh
Keyword(s):  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Crack Opening ◽  
Brittle Materials ◽  
Peak Stress ◽  
Dissipated Energy ◽  
Internal Variables ◽  
Frame Work ◽  
Frictional Interface

Failure in quasi-brittle materials, such as concrete and rock, usually develops in a fracture process zone (FPZ), in which dissipative processes takes place. At the onset of bifurcation or upon formation of FPZ the homogeneity of kinematic fields is lost and the stress field is redistributed which gives rise to the so called deterministic size effect problem. The total strain energy stored within a specimen of quasi-brittle materials will scale with its size; however, the amount of dissipated energy does not depend on the specimen size but only on the width of the FPZ. This width is related to the microstructure of the material and is considered a characteristic of the material. In this paper, a cohesive frictional interface is used to model the dissipative behaviour of material inside FPZ. Fundamental micro-mechanisms of energy dissipation such as micro-crack opening in mode I and frictional sliding between micro-crack surfaces are formulated within the frame work of Thermodynamic with internal variables (TIV) to ensure the thermodynamics admissibility of the model. The link between the material behaviour inside and outside FPZ is given through the continuity of tractions along the boundaries of FPZ. It is shown that although the shape of the post-peak stress-strain varies, for specimens of different slenderness, the amount of dissipated energy remains the same in all cases.

Analysis of Energy Balance When Using Cohesive Zone Models to Simulate Fracture Processes

2002 ◽  
Vol 124 (4) ◽  
pp. 440-450 ◽  
Author(s):  
C. Shet ◽  
N. Chandra
Keyword(s):  
Cohesive Energy ◽  
Cohesive Zone ◽  
Strain Energy ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Elastic Strain Energy ◽  
Inelastic Strain ◽  
External Work ◽  
Cohesive Zone Models

Cohesive Zone Models (CZMs) are being increasingly used to simulate fracture and fragmentation processes in metallic, polymeric, and ceramic materials and their composites. Instead of an infinitely sharp crack envisaged in fracture mechanics, CZM presupposes the presence of a fracture process zone where the energy is transferred from external work both in the forward and the wake regions of the propagating crack. In this paper, we examine how the external work flows as recoverable elastic strain energy, inelastic strain energy, and cohesive energy, the latter encompassing the work of fracture and other energy consuming mechanisms within the fracture process zone. It is clearly shown that the plastic energy in the material surrounding the crack is not accounted in the cohesive energy. Thus cohesive zone energy encompasses all the inelastic energy e.g., energy required for grainbridging, cavitation, internal sliding, surface energy but excludes any form of inelastic strain energy in the bounding material.

Fiber Debonding Along a Crack Front in Paper

1998 ◽  
Vol 539 ◽  
Author(s):  
H. Kettunen ◽  
K. J. Niskanen
Keyword(s):  
Fracture Energy ◽  
Crack Front ◽  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Bond Properties ◽  
Crack Line ◽  
Pull Out ◽  
Microscopic Damage ◽  
Debonding Process

AbstractWe follow the accumulation of microscopic damage ahead the crack tip in paper. The fiber debonding process varies even within each specimen because of large variation in fiber and bond properties. In general, stiff and weakly bonded fibers tend to debond as a rigid body while ductile or well bonded fibers pull out gradually in a process that propagates from the crack line to the fiber ends. Particularly in the latter case the network ruptures coherently rather than through debonding of single fibers. Experimental analysis and simulations show that fracture energy correlates closely with the size of the fracture process zone (FPZ) irrespective the nature of the debonding process. Only the cases of low bonding and stiff fibers seem to make an exception in that FPZ can grow in size without a corresponding increase in fracture energy.

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