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Nonlinear response of plain concrete shear walls with elastic-damaging behavior

Description: This report summarizes the theoretical and computational efforts on the modeling of small scale shear walls. Small scale shear walls are used extensively in the study of shear wall behavior because the construction and testing of full size walls are rather expensive. A finite element code is developed which incorporates nonlinear constitutive relations of damage mechanics. The program is used to obtain nonlinear load-deformation curves and to address the initial loss of stiffness due to shrinkage cracking. The program can also be used to monitor the continuous degradation of the fundamental frequency due to progressive damage.
Date: February 1, 1997
Creator: Yazdani, S. & Schreyer, H.L.
Partner: UNT Libraries Government Documents Department

Formulation and computational aspects of plasticity and damage models with application to quasi-brittle materials

Description: The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.
Date: September 1, 1995
Creator: Chen, Z. & Schreyer, H.L.
Partner: UNT Libraries Government Documents Department

Single chain stochastic polymer modeling at high strain rates.

Description: Our goal is to develop constitutive relations for the behavior of a solid polymer during high-strain-rate deformations. In contrast to the classic thermodynamic techniques for deriving stress-strain response in static (equilibrium) circumstances, we employ a statistical-mechanics approach, in which we evolve a probability distribution function (PDF) for the velocity fluctuations of the repeating units of the chain. We use a Langevin description for the dynamics of a single repeating unit and a Lioville equation to describe the variations of the PDF. Moments of the PDF give the conservation equations for a single polymer chain embedded in other similar chains. To extract single-chain analytical constitutive relations these equations have been solved for representative loading paths. By this process we discover that a measure of nonuniform chain link displacement serves this purpose very well. We then derive an evolution equation for the descriptor function, with the result being a history-dependent constitutive relation.
Date: January 1, 2001
Creator: Harstad, E. N. (Eric N.); Harlow, Francis Harvey, & Schreyer, H. L.
Partner: UNT Libraries Government Documents Department

Accurate Numerical Solutions for Elastic-Plastic Models

Description: The accuracy of two integration algorithms is studied for the common engineering condition of a von Mises, isotropic hardening model under plane stress. Errors in stress predictions for given total strain increments are expressed with contour plots of two parameters: an angle in the pi plane and the difference between the exact and computed yield-surface radii.
Date: March 1980
Creator: Schreyer, H. L.; Kulak, R. F. & Kramer, J. M.
Partner: UNT Libraries Government Documents Department

Analysis of strain wave propagation in polymeric materials

Description: Polymeric materials used as binders in energetic materials exhibit interesting and unique material behavior. These include full geometrical recovery after deformation and a rate dependent stress strain relationship which can be categorized as viscoelastic. Taylor Cylinder Impact Tests have been conducted for adiprene-100 polyurethane. These produce time resolved cylinder profiles from which deformation wave speed can be extracted as a function of strain and strain-rate. Using this information and a set of conservation `Jump` relationships applied across the deformation wave front, stress points as a function of strain and strain rate can be extracted. This discretized information then can be used in the development of a constitutive relationship suitable for use in a three dimensional computer code calculation.
Date: July 1, 1996
Creator: Harstad, E.N.; Foster, J.C., Jr; Wilson, L.L.: Maudlin, P.J. & Schreyer, H.L.
Partner: UNT Libraries Government Documents Department