ENGINEERING TRANSACTIONS
ROZPRAWY INŻYNIERSKIE

A QUARTERLY JOURNAL

Abstracts of papers for

Previous issue vol. 50, no. 1-2 (2002)

vol. 50, no. 3 (2002)

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Contents of issue 3, vol. 50

1. P. Perzyna : Thermodynamical theory of inelastic single crystals
2. V.E. Rosca, V.F. Poterasu, N. Taranu and B.G. Rosca : Finite-element model for laminated beam-plates composite using layerwise displacement theory
3. Aimin Yu : Study on normal stresses in composite curved beams subjected to unsymmetrical bending
4. J.W. Wekezer, I. Kreja, M. Issa : Retrofit analysis of Florida Beam-and-Post reinforced concrete bridge barriers

P. Perzyna : Thermodynamical theory of inelastic single crystals

The paper aims at the development of the thermodynamic theory of elasto-viscoplasticity of single crystals which takes account of the evolution of the dislocation substructure. The next objective is the application of the theory developed for the investigation of the adiabatic shear-band formation in single crystals under dynamic loading processes. The description of the kinematics of finite elasto-viscoplastic deformations of single crystal is based on notions of the Riemannian space of manifolds and the tangent space. A multiplicative decomposition of the deformation gradient is adopted and the Lie derivative is used to define all objective rates for the introduced vectors and tensors. A general constitutive model is developed within the thermodynamic framework of the rate-type covariance constitutive structure with finite set of the internal state variables, and takes account of the effects as follows: (i) thermomechanical coupling; (ii) influence of covariance terms, lattice deformations and rotations and plastic spin; (iii) evolution of the dislocation substructure; (iv) deviation from the Schmid rule of a critical resolved shear stress for slip; (v) rate sensitivity (viscosity). A notion of covariance is understood in the sense of invariance under arbitrary spatial diffeomorphisms. The developed thermoviscoplasticity theory of single crystals is based on the axioms as follows: (i) existence of the free energy function; (ii) invariance with respect to any diffeomorphism (any superposed motion); (iii) assumption of the entropy production inequality; (iv) assumption of the evolution equations for the internal state variables in the particular rate-dependent form. To describe the evolution of the dislocation substructure, a finite set of the internal state variables is interpreted as follows: the density of mobile dislocations, the density of obstacle dislocations and the concentration of the point defects. Physical foundations and experimental motivations are given. Two fundamental constitutive equations of the rate-type for the Kirchhoff stress tensor and temperature are formulated. To show that the thermodynamic theory of viscoplasticity of single crystals takes account of all the mentioned effects, an analysis of the thermomechanical couplings and internal dissipation is presented. Particular attention is focused on synergetic effects, generated by cooperative phenomena of thermomechanical couplings and the influence of the evolution of the dislocation substructure. The initial boundary value problem (the evolution problem) for rate-dependent elasto-plastic single crystal has been proved to be well posed. Criteria for adiabatic shear-band localization of plastic deformation are obtained by assuming that some eigenvalue of the instantaneous adiabatic acoustic tensor for rate-independent response is equal to zero. The formation of the adiabatic shear-band is investigated. It has been found that the synergetic effects generated by cooperative phenomena of thermomechanical couplings and the influence of the evolution of the dislocation substructure play a fundamental role in the inception of localization. The results obtained are compared with available experimental observations.

Contents

V.E. Rosca, V.F. Poterasu, N. Taranu and B.G. Rosca : Finite-element model for laminated beam-plates composite using layerwise displacement theory

The paper uses the layerwise theory, i.e. the zigzag behaviour of the in-plane displacements through the thickness, and the Lagrange interpolation functions for finite element to compute the stresses and displacements in beams made by composite materials. The layerwise method can determine the interlaminar stresses and other localized effects with the same accuracy as 2D finite element method but less computer effort. We present as illustration two examples.

Contents

Aimin Yu : Study on normal stresses in composite curved beams subjected to unsymmetrical bending

Based on the formula for normal stresses in curved beams of one material, the formulae for normal stresses in composite curved beams with general cross-sectional shape under complicated loads can be derived. The novel formulae presented in this paper can be used in evaluating the normal stresses of connecting rod bush coated with bearing metal for internal combustion engine. These normal stress formulae, in special case, are reduced to those for composite curved beams subjected to symmetrical bending. A numerical example is given for verification at the end of this paper.

Contents

J.W. Wekezer, I. Kreja, M. Issa : Retrofit analysis of Florida Beam-and-Post reinforced concrete bridge barriers

The major objective of the study was to evaluate crashworthiness of the existing Florida Beam-and-Post reinforced concrete bridge barriers. These barriers were first installed thirty years ago, they are still popular, and represent a significant investment in transportation infrastructure of the State. The major emphasis of the paper is focused on utilization of computational mechanics to improve safety of the existing reinforced concrete bridge rails. It presents results of analytical efforts to simulate crash impacts between a pickup truck and the Florida Beam-and-Post barrier. Computer calculations were performed using LS-DYNA, explicit, dynamic, 3-D finite element code. Finite element models of a 2000P Chevrolet pickup truck and the model of the bridge barrier were used to simulate test 3-11 per NCHRP Report 350. Computer simulations revealed severe snagging problems and provided input for a better understanding of the barrier response. Specific recommendations for a retrofit of the existing Florida Beam-and-Post barriers were provided. These recommendations include guidelines for new, proposed, safe reinforced concrete bridge barriers for consideration by transportation engineers.

Contents

Abstracts for 50, 1-2, 2002 (previous issue)

Abstracts for 50, 4, 2002 (next issue)

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