Theoretical study of formation of pores in elastic solids: particulate composites, rubber toughened polymers, crazing

摘要

It is difficult to overestimate the mufti-functional role and practical meaning of the processes of the formation of pores in solids, especially in polymers and polymer based materials, which are capable to a noticeable plastic deformation. Various mechanisms are responsible for this phenomenon in different systems. Particularly, it is debonding in particulate filled composites, elastomeric inclusions failure in rubber toughened polymers, nucleation of microvoids at defects in glassy polymers. Two main effects of the formation of pores should be underlined. The first is a decrease in the material's stiffness, which is mostly emphasized for composites filled by rigid inclusions. The second is an improvement in the fracture toughness which is widely explored in practice. The nucleation of pores affects the fracture toughness, firstly, absorbing the energy for the new surface formation and, secondly, facilitating of a plastic flow of the basic material. The paper proposed is partly a review of previously obtained results and represents also the novel data and laws. It concerns two aspects of the problem. An analysis of the conditions advantageous for the appearance of a single pore and of the completeness of this event is the first. This part of the paper is mostly a review, but a novel comparable analysis of the regularities of a pore formation by the way of a debonding along the surfaces of rigid particles in particulate filled composites and caused by a failure of rubbery inclusions will be presented. The second aspect of the problem is a spatial cooperation in the nucleation of pores. Some results in this field also have been obtained previously. However, the corresponding part of the paper mostly represents new data as well as a new analysis. Three types of systems will be analyzed from the cooperation point of view: particulate filled composites, rubber toughened plastics and homogeneous polymers for which a formation of micropores in a diffuse or a cooperative manner is a well known phenomenon named as crazing. Certain corrections of the previous conclusions concerning the cooperation arising during the failure of rubbery particles have been performed. Furthermore, the angles of the disposition of porous zones will be estimated. In addition, it will be shown that the conditions advantageous for an individual cavitation as well as the laws of a diffuse or cooperative proceeding of the multiple crazing are qualitatively the same. However, the different features will also be stated. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 49]