Recent advances in fiber/matrix interphase engineering for polymer composites

The effective mechanical behaviour of composite materials with imperfect contact between the constituents

The practical usefulness of the concept of the stress intensity factor at a crack tip in an elastic medium in the theory of fracture mechanics has led to a variety of theoretical, as well as experimental techniques for the evaluation of these factors Most of them concern the case of a crack inside an isotropic elastic medium under generalized plane stress or plane strain conditions, but several other cases have also extensively considered in the literature Among the first theoretical treatments of crack problems in plane isotropic elasticity we can mention those included in the well-known monograph by Muskhelishvili [1], as well as in the well-known paper by Westergaard [2] Today thousands of papers reporting elasticity solutions of crack problems and providing formulas and diagrams for the evaluation of stress intensity factors at crack tips can be found in the literature and are referenced in the recently appeared handbooks for the evaluation of stress intensity factors by Tada, Paris and Irwin [3] and Rooke and Cartwright [4] Furthermore, the most important theoretical techniques for the solution of plane elasticity crack problems and the evaluation of stress intensity factors were reviewed by Paris and Sih [5] and Sih [6] in the first volume of this series

Elastic stress intensity factors evaluated by caustics

The thermomechanical behaviour of a particle composite was evaluated under the assumption that a boundary interphase between the matrix and the filler particles develops, upon the thermomechanical properties of which the overall behaviour of the composite depends. This interphase exists in reality and it contains both areas of adsorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. Under the assumption that the interphase is homogeneous and isotropic exhibiting perfect adhesion with both main phases a theory was developed providing quantitative means of assessing the adhesion efficiency between the phases and its effect on the thermomechanical behaviour of the composite. Experimental results are in good agreement with theoretical predictions.

The concept of boundary interphase in composite mechanics

Experimental detection of a transcrystalline interphase in glass-fibre/polypropylene composites

Thermal expansion coefficients and glass transition temperatures for metal–epoxy composites were determined experimentally. Results were in fair agreement with existing theories when certain fundamental assumptions were fulfilled. The effects of filler content and particle size as well as of adhesion between matrix and filler particles were investigated. The latter, in particular, was found to be of cardinal importance for the properties examined in the present work.

Thermal properties of metal‐filled epoxies

State of stress around inhomogeneities by the method of caustics

The thermomechanical behaviour of polymeric matrices reinforced with long unidirectional fibres in their glass transition region was investigated. Based on rigorous theories for the mechanical moduli and the coefficients of thermal expansion for viscoelastic composites, it was proved analytically that the introduction of reinforcing fillers in polymeric matrices causes glass transition temperature to increase to an extent proportional to the reinforcing effect. This is confirmed by numerous experimental results available in the literature, except for highly-filled composites, where imperfect adhesion may counterbalance the reinforcing effect. Dilatometric as well as two different dynamic mechanical tests confirmed the latter. The variation of glass transition temperature as function of the various aspects of mechanical reinforcement was investigated.

Thermomechnical properties of unidirectional composites in their transition region

A class of plasticized epoxy polymers were subjected to indentation tests over a wide range of temperature and plasticizer percentage. Constant or continuously varying temperature tests were carried out under constant load, and the materials exhibited creep behavior according to the temperature and the amount of plasticizer. Thermal expansion properties were also studied, and glass transition temperature as well as thermal expansion coefficients a1 and a2 were determined for each individual material. Theoretical predictions were found valid under the present conditions.

S. A. Paipetis

Papers

The concept of boundary interphase in composite mechanics

Thermal properties of metal‐filled epoxies

State of stress around inhomogeneities by the method of caustics

Thermomechnical properties of unidirectional composites in their transition region

Indentation studies in plasticized epoxy polymers