Shigetoshi Araki

Micromechanical Analysis of Crack Closure Mechanism for Intelligent Material Containing TiNi Fibers

Micromechanical modeling of an intelligent material containing TiNi fibers is performed by taking into consideration the existence of crack-bridging fibers given a tensile transformation strain. The total amount of shape memory shrinkage of the fiber corresponds to the transformation strain and this shrinkage strain is replaced with the eigenstrain of the fiber. Moreover, the thermal expansion strain due to the mismatch between the thermal expansion coefficients of a fiber and a matrix is also considered in the model. By analyzing the model, stress and strain fields in the composite, the total potential energy of the system is derived. Moreover, from the resultant total potential energy, the stress intensity factor at the tip of a crack in the composite is derived and expressed successfully in terms of the shrinkage strain of fibers and the thermal expansion strain in the material.

Micromechanical Analysis of Vibration Damping Properties of A Polymer Based Composite Material

A tangent delta of a polymeric material, which influences the vibration damping capacity strongle, is high in value nearby the glass transition temperature of the material. Therefore, when the constituents of a polymer-based composite material are various in their glass transition temperatures, the magnitude of the macroscopic tangent delta of such a composite is expected to be high in wider range in temperature. In the present study, a shape memory polymer (SMP) particle/SMP matrix is used as a sample material and its macroscopic complex modulus and tangent delta are derived explicitly by using the equivalent inclusion method and the Mori-Tanakas theorem. For the case of a four mode type of distribution of the glass transition temperatures of particles, the value of the macroscopic tangent delta becomes higher than that of the monolithic SMP at any temperature and it becomes constant in the temperature range from 20°C to 60°C.

Effects of Matrix Resin and Fiber Content on Mechanical and Fracture Properties of Continuous-Fiber-Mat Reinforced CP-Resin Composites.

The purpose of the present work is to reveal the behavior of two kinds of different matrix resins in composite materials through the experimental results of mechanical and fracture properties and observation of macro and micro fracture surfaces. The composite specimens are made of ductile or brittle resin and continuous glass fiber mats with various fiber contents. The elastic modulus and the tensile strength of these two resins are nearly of the same values, while the elongation is different.The results obtained are as follows:(1) The tensile strength of the ductile matrix resin composites is higher by 20-30% than that of the brittle matrix resin composites. The values of both composites with fiber content 20wt%, however, are lower than those of the matrix resins. These results can be understood based on the observations of macro fracture processes and fracture surfaces.(2) The fracture toughness Kin at crack growth initiation increases with increasing fiber content for both composites. The values of Kin for the ductile matrix resin composites with fiber contents 0wt% and 20wt% are higher than those of the brittle ones. For the composites with fiber contents 40wt% and 60wt%, the values of Kin for both composites scatter randomly.