Akihiro Misawa

Shear fracture of C/C composites with variable stacking sequence

Abstract Cross-ply laminated carbon–carbon composites with changing ply ratio of 0° and 90° were fractured under shear using several test methods. In these tests, special attention was placed on the understanding of the damage mechanisms. The ±45° off-axis shear test yielded the most precise shear stress–strain relation and was recommended to measure the shear modulus G 12 . On the other hand, for shear strength measurement, the Iosipescu test was superior. The non-linearity in the shear stress–strain curve was found to be solely due to matrix cracking, while the peak shear stress was determined by fibre failure. In order to measure the shear strength by the Iosipescu test, two fracture planes normal and parallel to the loading axes have to be considered. The shear strength increased linearly with fibre volume fraction normal to the corresponding plane. The overall highest shear strength was obtained for the (0/90) n laminate.

Effect of Saturation Pressure on Equivalency of Decompression Time and Foaming Temperature on Cell Density of Foamed Polystyrene

In this paper, the effect of saturation pressure on the time-temperature equivalent law of the decompression rate (decompression time) and foaming temperature of the cell density, the number of cells per unit volume remaining in foamed plastic was discussed. The foaming was carried out in the method described be by using batch foaming process. The blowing agent was soaked into the resin as a solid state at various high saturation pressures under temperatures higher than the glass transition temperature of the resin. After foaming agent reached its saturation state, cell nucleation and cell growth were accelerated by decompression. Finally, cell growth was halted by cooling. The polystyrene (PS) specimens were foamed under the various saturation pressures, foaming temperatures and decompression rates. The following results were obtained. (1) Cell density of foamed PS shows time and temperature dependence as follows. The cell density increases when the decompression rate is quick, i.e. the decompression time is shortened at the condition of low foaming temperature, and cell density decreases when the decompression rate is slow, i.e. decompression time is lengthened at the condition of high foaming temperature under various saturation pressures. (2) The time-temperature equivalent law is maintained between the time dependence and temperature dependence of the cell density of foamed PS, and it can expressed with the same time-temperature shift factor if the decompression rate is the same even if saturation pressure changes.

The Foaming Process and the Damping Capacity and Sound Insulation of Bell Structures

The forming process and the characteristics of bell structures produced using batch-type foaming with a supercritical-fluid blowing agent were examined. Various forming methods were tried for the production of bell structures. Impact and acoustic tests of the structures were conducted, followed by an evaluation of shock absorption and sound insulation. Bell structures, including various kinds of ball, were successfully produced by means of batch foaming. It was verified that these bell structures exhibit the required shock absorption and sound insulation performance.

An Approach to Peculiar Vibration Observed in a Rotating Viscoelastic Disk under Contact Load.

Wavy patterns of stress and temperature distribution are occasionally observed along the circumference of a rotating viscoelastic disk under a contact load. This phenomenon is caused by a combination of physical and mechanical features such as dynamic behavior, heat generation due to loss energy, heat conduction and various modes of vibrations in the viscoelastic disk including the loading system. This study attempts to give a rational explanation of the phenomenon, through experimental and theoretical approaches, by means of dynamic modeling of the entire vibrating system. The study by means of dynamic analysis revealed that the wavy stress pattern results from the resonant vibration of the loading mechanism which corresponded to its natural frequency. It is emphasized that the peculiar vibration is strongly influenced by temperature-dependent dynamic properties of the viscoelastic disk.

EVALUATION OF CRACK GROWTH RESISTANCE AND FRACTURE SURFACE CHARACTERISTICS IN SEVERAL EPOXY RESINS

ABSTRACT Not only mechanical properties but crack growth behavior in polymers such as epoxy resin are remarkably dependent on time and temperature. This paper discusses the evaluation of crack growth resistance J′Ic for linearly viscoelastic materials, which could be independent on time and temperature thus be a material constant, standing upon the extended J-integral for elastic one. In order to investigate the physical meaning of J′Ic, the fracture surface were carefully observed through the quantitative measurement of their roughness in the vicinity of initial crack tip.