ENGINEERING TRANSACTIONS
ROZPRAWY IN¯YNIERSKIE
A QUARTERLY JOURNAL
Review Paper
- P. Perzyna:
The thermodynamical theory of elasto-viscoplasticity
Original Contribution
- A. Be³zowski:
Evaluation of damage level in glass-fabric reinforced composite
- 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
- 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
- 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
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