Showing papers by "Zdenek P. Bazant published in 1990"

Determination of fracture energy, process zone longth and brittleness number from size effect, with application to rock and conerete

Abstract: The dependence of the fracture energy and the effective process zone length on the specimen size as well as the craek extension from the notch is analyzed on the basis of Ba

Random particle model for fracture of aggregate or fiber composites

Abstract: A particle model for brittle aggregate composite materials such as concretes, rocks, or ceramics is presented. The model is also applicable to the behavior of unidirectionally reinforced fiber composites in the transverse plane. A method of random computer generation of the particle system meeting the prescribed particle size distribution is developed. The particles are assumed to be elastic and have only axial interactions, as in a truss. The interparticle contact layers of the matrix are described by a softening stress‐strain relation corresponding to a prescribed microscopic interparticle fracture energy. Both two‐ and three‐dimensional versions of the model are easy to program, but the latter poses, at present, forbidding demands for computer time. The model is shown to simulate realistically the spread of cracking and its localization. Furthermore, the model exhibits a size effect on: (1) The nominal strength, agreeing with the previously proposed size effect law; and (2) the slope of the post‐peak l...

Nonlocal microplane model for fracture, damage, and size effect in structures

Abstract: A generalized microplane model, which was previously developed to describe tensile cracking and nonlinear triaxial response of brittleplastic materials in compression and shear, is implemented in a

Size Effect in Fracture of Ceramics and Its Use To Determine Fracture Energy and Effective Process Zone Length

Abstract: The paper shows that a previously proposed size effect law can be used to identify nonlinear fracture properties solely from measured maximum loads of geometrically similar ce­ ramic fracture specimens of sufficiently different sizes. This law represents a first-order global approximation of the de­ viations from linear elastic fracture mechanics, independent of the type of the toughening mechanism in the fracture process zone. It provides a simple and unambiguous way to determine the size- and shape-independent values of the fracture energy, the effective length of the process zone, and the effective crack-tip opening displacement. It also yields the R curve, which is geometry (shape) dependent. The prox­ imity of response to linear elastic fracture mechanics is characterized by a brittleness number, which is shape in­ dependent. [Key words: mechanical properties, fracture, R curve, energy, modeling.]

Cracking and Damage

Abstract: Proceedings of the France-US Workshop on Strain Localization and Size Effect due to Cracking and Damage, Laboratorie de Mecanique et Technologie, Cachan, France, 6-9 September 1988.

Antiplane Shear Fracture Tests (Mode III)

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France‐U.S. Workshop on Strain Localization and Size Effect Due to Cracking and Damage

Abstract: The workshop of the above title took place in Paris, France where 36 invitees made presentations followed by extensive discussions. The themes covered at the workshop are discussed and are as as follows: observation and measurement of damage and localization; micromechanics of fracture and micro-macro relaionships; stability, bifurcation, and localization; nonlocal models, and localization limiters and size effect. Although it would not be possible formulate to conclusions acceptable to all, certain views appeared to reflect a broad consensus. In static, time-independent modeling of the tensile fracture of concrete and geomaterials, the structural size effect is widely regarded as the key macroscopic consequence of fracture, and the most important yardstick for the evaluation of various theories. It is noted that the knowledge of the effect of the loading rate due to viscoplastic behavior, and especially the general effect of load and deformation history is rather limited. These and other observations are discussed.

Fracture properties and brittlenesss of high-strength concrete

Abstract: The size effect method for determining material fracture characteristics, as previously proposed by Bazant is applied to typical high-strength concrete. Geometrically similar 3-point bending specimens are tested and the measured peak load values are used to obtain the fracture energy, the fracture toughness, the effective length of the fracture process zone, and the effective critical crack tip opening displacement. The brittleness of the material is shown to be objectively quantified through the size-effect method. Comparing the material fracture properties obtained with those of normal strength concrete shows that an increase of 16 % in compressive srength causes: (1) increase of fracture toughness; (2) decrease of effective fracture process zone length; (3) more than doubling of the brittleness number. The brittleness number, however, is still not high enough to permit the use of linear elastic fracture mechanics. The R-curves are demonstrated to derive according to the size effect law exclusively from the maximum loads of specimens of various sizes and yield remarkably good predictions of the load-deflection curves.

Equilibrium Path Bifurcation Due to Strain-Softening Localization in Ellipsoidal Region

Abstract: The bifurcation occurs when the tangential moduli matrix becomes singular, which coincides with Hill's classical bifurcation condition for localization into an infinite layer. The bifurcation is normally of Shanley type, occurring in absence of neutral equilibrium while the controlled displacements at infinity increase