ENGINEERING TRANSACTIONS
ROZPRAWY IN¯YNIERSKIE

A QUARTERLY JOURNAL


Abstracts of papers for
Previous issue Previous issue
vol. 53, no. 2 (2005)
vol. 53, no. 3 (2005)
Contents
Next issue Next issue
vol. 53, no. 4 (2005)

Contents of issue 3, vol. 53

    Review Paper
  1. P. Perzyna: The thermodynamical theory of elasto-viscoplasticity

  2. Original Contribution
  3. A. Be³zowski: Evaluation of damage level in glass-fabric reinforced composite
  4. A. Ossowski: Stability of an elastic column subjected to non-stationary compressive loads

Review Paper
P. Perzyna
: The thermodynamical theory of elasto-viscoplasticity
The main objective of this paper is to survey some recent developments in the constitutive modelling of inelastic polycrystalline solids, which may be used for the description of important problems in modern manufacturing processes, and particularly for mesomechanical issues. This description is needed for the investigation by using the numerical methods how to avoid unexpected plastic strain localization and fracture phenomena in manufacturing technology. Since modern manufacturing processes lead to very complex states of stress and deformation for a solid body under consideration, then in the description we have to take into account the influence of stress triaxiality and plastic spin effects. In this paper emphasis is laid on experimental and physical foundations as well as on mathematical constitutive modelling for the description of localization of plastic deformation and various modes of fracture phenomena in polycrystalline solids. The description of kinematics of finite deformations and the stress tensors is given. The development of a thermo-elasto-viscoplastic model within the thermodynamic framework of the rate-type covariance constitutive structure with finite set of the internal state variables is presented. Particular attention is focused on the determination of the evolution laws for the internal state variables. Fracture criterion based on the evolution of microdamage is formulated. By assuming that the mechanical relaxation time is equal to zero, the thermo-elasto-plastic (rate-independent) response of the damaged material can be accomplished. The thermodynamical theory of elasto-viscoplasticity of polycrystalline solids presented has important features as follows: (i) invariance with respect to diffeomorphism; (ii) finite plastic deformation and plastic spin effects; (iii) plastic non-normality; (iv) softening effects generated by microdamage mechanism; (v) plastic deformation-induced anisotropic effects; (vi) thermomechanical couplings (thermal plastic softening and thermal expansion); (vii) influence of stress triaxiality on the evolution of microdamage; (viii) rate sensitivity; (ix) length scale sensitivity; (x) regularization of the evolution problem; (xi) dissipation and dispersion effects; (xii) synergetic effects generated by cooperative phenomena. All these fundamental features have been carefully discussed. It should be noted that the very important part of constitutive modelling is the identification procedure for the material functions and constants involved in the constitutive equations proposed.

Contents Contents


Original Contribution
A. Be³zowski
: Evaluation of damage level in glass-fabric reinforced composite
A method is proposed for evaluating the extent of damage in fibre-reinforced polymer composites. The available methods for monitoring fatigue degradation in such materials are critically discussed. Reported are the results of actual tests on a glass-epoxy laminate under cyclic bending. The relative changes in the bending strength were several times higher than those of the dynamic stiffness, total elastic energy of a cycle and phase shift. A relationship is put forward for calculating the level of damage allowing for the mean value and the standard deviation of residual strength. The analysis is enhanced by presenting microscopic images of the material structure. The proposed model was shown to give reliable estimates of durability and can be especially useful to validate the damage parameter determined by other methods.

Contents Contents


A. Ossowski: Stability of an elastic column subjected to non-stationary compressive loads
The problem of dynamic stability of an elastic column with pinned ends subjected to non-stationary compressive axial loads is considered. The method of optimal Lyapunov functions for differential inclusions is applied to obtain sufficient conditions of stability of the column in the case of bounded loads. The obtained results, improving and generalising the classical solutions to the dynamic Euler problem, may be useful in designing civil engineering structures and mechanical systems consisting of compressed columns. The possibility of optimisation of the column characteristics with respect to its stability properties (e.g. stability margins in the space of parameters) is pointed out.

Contents Contents


Reprints of the full papers may be obtained from their authors. Contact Editorial Office in case you need the address of the respective author.


Abstracts for
Previous issue 53, 2, 2005
(previous issue)
Abstracts for
53, 4, 2005 Next issue
(next issue)
Engineering Transactions
Home Editors Scope Abstracts For authors Subscription