Shelterbelts/Windbreaks: How to Assess Partial Damage

This publication provides information on assessing monetary damage to trees and shrubs in windbreaks. It explains the types of damage: physical, fire, and chemical, as well as a method for calculating damage percentages

Some remarks on the damage unilateral effect modelling for microcracked materials

This study deals with the macroscopic modelling of the mechanical behaviour of microcracked materials and particularly with the unilateral aspect of such damage which leads, at the closure of microcracks, to a partial damage deactivation. By means of a micromechanical analysis, the aim of this article is first to point out the influence of the opening-closure of microdefects on the effective elastic properties of a microcracked medium. According to these considerations, a new elastic moduli recovery condition at damage deactivation is proposed. The introduction of this condition within the anisotropic damage model proposed by Halm and Dragon, 1996 allows to extend its micromechanical background while preserving its main advantages, in particular the continuity of the stress-strain response and the symmetry of the stiffness tensor

A degenerating PDE system for phase transitions and damage

In this paper, we analyze a PDE system arising in the modeling of phase transition and damage phenomena in thermoviscoelastic materials. The resulting evolution equations in the unknowns \theta (absolute temperature), u (displacement), and \chi (phase/damage parameter) are strongly nonlinearly coupled. Moreover, the momentum equation for u contains \chi-dependent elliptic operators, which degenerate at the pure phases (corresponding to the values \chi=0 and \chi=1), making the whole system degenerate. That is why, we have to resort to a suitable weak solvability notion for the analysis of the problem: it consists of the weak formulations of the heat and momentum equation, and, for the phase/damage parameter \chi, of a generalization of the principle of virtual powers, partially mutuated from the theory of rate-independent damage processes. To prove an existence result for this weak formulation, an approximating problem is introduced, where the elliptic degeneracy of the displacement equation is ruled out: in the framework of damage models, this corresponds to allowing for partial damage only. For such an approximate system, global-in-time existence and well-posedness results are established in various cases. Then, the passage to the limit to the degenerate system is performed via suitable variational techniques

Changes in the Cell Squad of Iliac Lymph Nodes of White Rats in Case of Longterm Influence of Nalbufin

The article presents data on the change in the cellular composition of the lymph nodes of the white rats, males of reproductive age, who received intramuscular opioid analgesics - nalbuphine every day for six weeks. The weekly dose of nalbuphine was gradually increased, creating a model of physical opioid dependence according to the patent of Ukraine No. 76564 U. All experimental animals were divided into 8 groups.Morphometric method was used to determine the relative number of cells of the lymphoid series - small, medium and large lymphocytes, blasts and plasmocytes in the cloak zone and the embryonic center of the secondary lymphoid nodes and brain strands of the lymph nodes. Morphometric studies were performed using a system of visual analysis of histological preparations.It was established that nalbuphine in the lymph nodes causes reactive and destructive changes: the number of large lymphocytes increases in all structural components of the lymph node with a maximum after 4 weeks, respectively, the relative number of small lymphocytes decreases in the nucleus centers and brain tracts, the relative number of plasmocytes in the brain strains increases sharply . In all structural components of the lymph nodes hemocapillaries and venules are dilated and full-blooded, around vascular edema and partial damage to the walls of the microvessels.One week after the discontinuation of nalbuphine, the relative number of lymphoid cells in the structural components of the lymph nodes does not return to the indicators of intact animals, no reversible changes are noted

Thermomechanical Description of Moving Discontinuities, Application to Fracture and Wear

The propagation of moving surface inside a body is analysed within the framework of thermomechanical couplings, when the moving surface is associated with an irreversible change of mechanical properties. The moving surface is a surface of heat sources and of entropy production, intensities of which are related to particular energy release rates defined in terms of Hamiltonian gradients. As emamples, we analyse the evolution of partial damage in a composite sphere and a model for study the contact wear phenomena between two bodies

A cohesive-zone crack healing model for self-healing materials

A cohesive zone-based constitutive model, originally developed to model fracture, is extended to include a healing variable to simulate crack healing processes and thus recovery of mechanical properties. The proposed cohesive relation is a composite-type material model that accounts for the properties of both the original and the healing material, which are typically different. The constitutive model is designed to capture multiple healing events, which is relevant for self-healing materials that are capable of generating repeated healing. The model can be implemented in a finite element framework through the use of cohesive elements or the extended finite element method (XFEM). The resulting numerical framework is capable of modeling both extrinsic and intrinsic self-healing materials. Salient features of the model are demonstrated through various homogeneous deformations and healing processes followed by applications of the model to a self-healing material system based on embedded healing particles under non-homogeneous deformations. It is shown that the model is suitable for analyzing and optimizing existing self-healing materials or for designing new self-healing materials with improved lifetime characteristics based on multiple healing events