A Study of Some Thermomechanical and Fractural Properties of Particle Reinforced Polymer Composites and SEM-Aided Microfailure Approach of CertainFracture Parameters

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.