The elastic constants of particulate composites are evaluated employing a theoretical cube-within-cube formation. Two new models of four and five components, respectively, formed by geometrical combination of three-component models existing in the literature, are used as Representative Volume Elements. Using the governing stress and strain equations of the proposed models, two new equations providing the static elastic and shear moduli of particulate composites are formulated. In order to obtain the dynamic elastic and shear moduli, the correspondence principle was applied successively to components connected in series and/or in parallel. The results estimated by the proposed models were compared with values evaluated from existing formulae in the literature, as well as with values obtained by tensile, dynamic, and ultrasonic experiments in epoxy/iron particulate composites. They were found to be close to values obtained by static and dynamic measurements and enough lower compared with values obtained from ultrasonic experiments. The latter is attributed to the high frequency of ultrasonics. Since measurements from ultrasonic's and from dynamic experiments depend on the frequency, the modulus of elasticity estimated by ultrasonic's is compared with that (storage modulus) estimated by dynamic experiments.

In the first part of this complex study the thermomechanical and fractural properties of particle reinforced polymer composites were experimentally obtained. The experimental values for modulus of elasticity, fracture stress, fracture strain and thermal expansion coefficient were compared with those derived from theoretical formulae existing in the literature and also from a theoretical model assuming the existence of an interphase between the two main phases the filler and the matrix. This model was used to obtain theoretical expressions for modulus of elasticity and thermal expansion coefficient. The mechanical properties of the material used in this investigation were determined from tensile experiments carried out with a composite material made of epoxy resin reinforced with iron particles the volume fraction of which varies from 0 to 25% and in some cases up to 40%. To obtain information concerning the thermal expansion coefficient and glass transition temperature of the same material thermomechanical analysis (TMA) measurements were performed. The effects of heating rate and filler content on the glass transition temperature were examined. In the second part of this study an attempt is made to explain on a more phenomenological basis the relative big discrepancies observed between theoretical models and experiments concerning certain strength parameters such as fracture stress and strain presented in the first part. This was possible by assuming a delayed kind of fracture behavior which was simulated by a subcritical crack growth based on the theory of elastic-small yielding fracture mechanics and by an arrest micromechanism. The above simulation in turn was achieved by a procedure of a semiquantitative gross estimation approach which has taken into consideration certain experimental fractographical and microstructural data such as interfacial decohesion features between grain and matrix, grain size and interinclusion spacing, parameters estimated by Scanning Electron Microscopic (SEM) measurements.

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In this complex study an attempt was made on the one hand to analyze and understand in a systematic way the exact nature of the formation of certain characteristic energy dissipationinduced fractographic features and patterns/markings revealed by scanning electron microscopy (SEM) in particulate epoxy systems under impact (dynamic) loading conditions, and on the other hand to correlate these patterns and features with relevant crack propagation effects. For this scope a combined approach consisting of a qualitative as well as a semiquantitative analysis was employed. In the qualitative analytical approach it was shown that depending on the actual velocity and direction of crack propagation the above observed fractographic entities can be correlated to certain highly localized energy dissipative processes at front-failures as well as to local inertial molecular mass effects.Depending on the changes in the velocity and direction of propagation, the associated effects may be controlled by two basic processes: the single crack front and the multiple crack front splitting. The first process seemed to be governed by a shear toughness-biased system, whereas the second one used a critical strain energy release rate subcracking mechanism. Under certain conditions both processes may be influenced by inertial molecular effects in promoting the formation of relative-smooth fracture surfaces.The increased presence of particles tends to restrict an increase in the surface roughness due to energy dissipation-induced crack retardation effects. The presence of the notch tends to lower the fracture surface roughness compared to notch-free specimens and also to suppress the occurrence of certain elastic as well as viscoelastic-plastic crack delay effects observed in notch-free specimens in function of particle volume fraction.Based on relevant kinematics-aided modeling and impact energy measurements it seems possible to explain, by a gross semi-quantitative approach, the above particles and notch effects. In this context it seems plausible that the existence of a defect-induced fracturing time spectrum of the propagating crack front, in combination with the 'notch-induced shift' behavior of this spectrum, can be valuable for some approximating explanations of the above notch effects and in general the 'kinematics' of the surface roughness formation.

The aim of this investigation is to determine the effect of low-filler volume fraction on the elastic modulus and the thermal expansion coefficient of particulate composites. In the theoretical part, theoretical model valid for low-filler volume fractions is used to evaluate these two magnitudes. In the experimental part, low-percentage filler contents of 3, 5, 7, and 10% are used. The density for these epoxy resin-iron particle composites is also determined. At the same time, an attempt to explain some of the disagreements observed between theoretical values and experimental data on a qualitative basis is also made. This attempt is in part assisted by scanning electron microscopy (SEM) observations concerning structural inhomogeneities and fractographical data. The comparison of the theoretical values derived from the present model with experimental results and with theoretical values derived from other workers appears satisfactory in many cases, but in some others the discrepancies among them are considerable.