Fatigue of ceramics under stress was proved to be caused through the reaction of ceramics with chemical species supplied from the environment. Based on the conclusion, prediction of fatigue life of ceramics was studeied on the self-evident hypothesis on the crack propagation under stress as well as on the slow crack growth equation. The results were proved to explain the actual fatigue life well, and now are applied to acutual process for the quality control as well as the design of ceramic parts. The proof test of ceramics was also studied on the basis of the slow crack growth. Injection mould of ceramics parts for an automobile engine and CAE for the injection process were also studied. Furthermore modification of polymer including rubber by chemical reaction under shear stress, and synthesis of inorganic / organic hyblid material were studied.
Flexible and accurate simulation techniques are very important because they accomplish the efficient research and development in companies. On the other hand for the basic research, simulation methods that explain the mechanism of the many functional materials from molecule and/or atomistic levels are also very valuable. Considering these effects, simulation systems of viscoelastic properties of polydisperse polymer melt, interfacial tension between polymers melts and izod impact strength of polymers were developed. In the case of interaction strength between polymers, molecular theoretical methods, such as molecular mechanics and molecular dynamics, were also attempted. By using these methods, it can be clarified that the difference in fine chemical structure affects the interaction strength between polymers and the interfacial structure.
Rheo-optical studies on viscoelasticity of amorphous polymers in the vicinity of the glass-to-rubber transition zone are reviewed. One of important progresses is a finding of the modified stress-optical rule, MSOR. The rule says that the stress has two molecular origins. One (R component) is due to the chain orientation like rubbery materials and the other (G component) is due to deformation of packing state of repeating units. The G component has common features for glass forming materials. The MSOR successfully explains many characteristic features of the viscoelasticity around the glass transition zone such as breakdown of time-temperature superposition principle. Another significance is that the MSOR provides a new method to analyze the viscoelasticity around the glass transition zone. The separation into the two origins gives better prospects on the relationship between viscoelasticity and the molecular structure. The method can be applied to other important issues including nonlinear viscoelasticity around the glass transition zone and sub-relaxations in the glassy zone.
PVC has fine mechanical properties, but it also shows poor impact strength in low temperature region. We have succeeded in designing new PVC materials grafted to acrylic rubber particles aiming at strengthening surface bonding, dispersing particle homogeneously and achieving high speed elastic deformation of the particles on the basis of the Craze theory. The acrylic graft PVC gives high impact energy absorption. We have discovered the correlation among the surface of molding products and flow properties of melting resin, relaxation modulus, shear stress on the die wall, adhesion and slip-stick behavior, and consequently stabilized processing.
The good relationship was shown to exist between the glass transition temperature (Tg), cohesive energy, and free volume for linear polymers with large pendant groups. From this relationship, a reliable simulation method based on a group contribution method was developed for predicting the Tg of unknown polymers having the moiety similar to known polymers. This method was found to be very successful for polyolefines having branched side chains as well as maleimide polymers. Furthermore, the relationship was also applied for predicting the melting point.
We report on details of an apparatus constructed for the simultaneous small angle neutron scattering and rheological measurements under various sheared conditions. In addition to studies under steady (shear rate range; order of 10-3 - 103 sec -1) and oscillatory (frequency range; order of 10-3 -102 rad/sec) shear flows, other tests such as creep, stress relaxation, etc. can be performed for a wide variety of complex fluids. Moreover, because of its design, the apparatus itself has flexibility for further modification. It is now open to users as a permanent equipment of SANS-U spectrometer of Neutron Scattering Laboratory, ISSP, The University of Tokyo, at JAERI Tokai, Japan.
The dynamic viscoelastic properties of poly(L-lactic acid) (PLLA) were investigated in the molten state. The time-temperature superposition principle can be utilized and the master curves were obtained. The temperature dependence of the shift factor was expressed by the WLF equation. The fractional free volume at the glass transition temperature, the temperature coefficient of the fractional free volume, and the Vogel temperature were determined. These values are smaller than those of poly(methyl methacrylate) and polystyrene. Moreover the characteristic parameters; zero-shear viscosity, steady-state compliance, and elasticity coefficient were evaluated at 180 °C as a reference temperature.