V. Valeva

Aging and filler effects on the creep model parameters of thermoset composites

Abstract The effect of marble mineral filler on the creep response of polyester thermoset matrix before and after physical aging has been investigated. A number of composites with different filler content (0.29, 0.38, 0.45, 0.55) have been studied in order to understand the role of the filler for the creep response. A mathematical model has been chosen for interpreting the experimental results, its parameters having a definite physical sense and being related with the single components of deformation under creep conditions. This model represents the generalized equation of Maxwell for relaxing isotropic medium in the form presented by G.I. Gourevich (Maxwell–Gourevich equation). The influence of the filler and physical aging on the parameter values of the model has been discussed, respectively on the elastic and rubberlike elastic (inelastic) deformation. The possibilities of the proposed model to describe the creep response of the matrix and the composites before and after physical aging are shown.

Interfacial debonding of a piezoelastic bi-material structure applicable for wind rotor blades.

The main goal of the article is to model the straight line part of a wind blade by an analytical 1D shear lag model in order to analyze and detect possible interface delamination through the change of the voltage along the interface. A unit cell presented by a bi-material structure consisting of a first piezoelastic layer and an elastic second layer under static mechanical and electric load is considered. Numerical examples are provided and illustrated by figures and discussed. A criterion for detecting the interface elastic-brittle delamination and a safety zone for combined electrical and static loading is proposed.

Design sensitivity analysis for shape optimization by the BEM

Abstract In this paper the shape optimization problem for an inelastic case by the hybrid utilization of the BEM and design sensitivity analysis is examined. Gourevichs model for describing the inelastic behaviour of the solid is used. As a numerical example, the problem for determining the optimal shape of the free boundary of a hole in a rectangular elastic and inelastic metal plate unaxial tension is solved.

MODELLING THE SEPARATION OF PHYSICALLY NONLINEAR MATERIAL FROM THE INCLUSIONS BY BEM

A problem for the separation of a polymer matrix from one or three circular inclusions is considered. The principal task of the problem is to compute the extension of separation and the stress-strain state. The problem is solved numerically by BEM on the basis of Maxwell-GurevichRabinovich constitutive equations for a viscoelastic deformation of the material. The distribution of the plastic zones, the displacements and the stresses on the separation and contact zone, respectively, and the value of separation angle are obtained. INTRODUCTION The problems, which investigate the behaviour of inclusions in elastic or inelastic media are actual in relation with the intensive development and applications of the composite materials in practice. In the analysis of the mechanical behaviour of composite materials questions arise about the mechanism of their fracture as a result of forming separation of the matrix from the inclusions and to estimate the influence of such separations on the deformation characteristics of the material and on its stress-strain state. Of course, the stress analysis of inclusions has been extensively investigated in the past, but the separation has been given considerably less attention. The first investigation of the problems, involving the separation between a matrix and a circular inclusion in a field of unidirectional tension, when there is neither adhesion nor friction, was undertaken by Stippes et al. [1]. This problem has been taken up periodically by several investigators: Noble and Hussain [2], Keer et al. [3], Nicholson [4], Mizushima et al. [5,6]. In [6] the influence of friction is discussed using a method in which the general form of a stress function in polar coordinates is adopted and its coefficients are recurrently

Influence of Interface Gap on the Stress Behaviour of Smart Single Lap Joints Under Time Harmonic Load

Abstract Adhesive joints are frequently used in different composite structures due to their improved mechanical performance and better understanding of the failure mechanics. The application of such structures can be seen in aerospace and high technology components. The authors developed and applied modified shear lag analysis to investigate the hygrothermalpiezoelectric response of a smart single lap joint at environmental conditions (with/without an interface gap along the overlap zone) and under dynamic time harmonic mechanical and electric loads. The main key is the study of the appearance of possible delamination along the interface. As illustrative examples, the analytical closed form solution of the structure shear and the axial stresses response, as well as the interface debond length, including influence of mechanical, piezoelectric, thermal characteristics and frequencies is performed and discussed. All results are presented in figures. The comparison of the shear stress and electric fields for both cases of overlap zone (continuous or with a gap) is also shown in figures and discussed.