In order to use composite materials in aeronautical turbo engines, their resistance to impact damage must be understood. In this work the subperforation flat-wise impact resistance of three kinds of high resistance material systems were evaluated under low and high velocity impact tests. Tested systems were AS4/PEEK (APC-2/AS4, ICI-Fiberite), AS4/PEEK + IL, which consists of APC-2 prepreg and PEEK film inserted between layers as an interleave, and toughened epoxy system T800/#3900 (Toray). To investigate the effects of stacking sequence on resistance, three lay-ups (0/ + 30/0/ -30)s, (0/ + 60/0/ -60)s, and (0/ + 45/90/ -45)s-were tested. A drop weight system was used for the low velocity tests, where the velocity ranged from 1.5 to 3.1 m/s. An air gun system was used for the high velocity tests, where the velocity range was between 50 and 100 m/s. Both velocity impact tests used the same specimens geometries, support structures, impactor head geometries, and incident energy range. The projected damage area was measured with an ultrasonic C-Scan. The relation between damage area (DA) and impact energy (IE) was linear, and the ratio of the DA/IE quantified the impact resistance of each specimen. The value of DA/IE for the high velocity tests was larger than the value for low velocity tests. To estimate the lay-up effect, a stacking parameter,B, which indicates the difference of the inplane stiffness between the adjacent laminae, was proposed. A proportional relation between the DA/IE and the f was obtained. The value of (DA/IE)/3, which was independent of stacking sequence, indicated the impact resistance of the tested material systems for both velocity levels. The ratio of (DA/IE)/3 for the high velocity to the value for the low velocity changed with material systems.

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The effects of particle size on the surface energy of the fracture surface and elastic moduli of nano-and micro-spherical silica-particle-filled epoxy composites were investigated experimentally. The Young's modulus and shear modulus of the composites agreed well with the results evaluated by Lewis and Nielsen's equation and were shown to be dependent on only the volume fraction of the particle. Surface energies of the fracture surface were evaluated from the critical energy release rates and the surface areas including the unevenness. The surface energies were shown to be constant regardless of the volume fraction of the particle.

We investigated the particle size effects on the fracture toughness of epoxy resin composites reinforced with spherical-silica particles. The silica particles had different mean particle diameters of between 1.56 and 0.24µm and were filled with bisphenol A-type epoxy resin under different mixture ratios of small and large particles and a constant volume fraction for all particles of 0.30. As the content with the added smaller particle increased, the viscosity of each composite before curing remarkably increased. We conducted the single edge notched bending test (SENB) to measure the mode I fracture toughness of each composite. The fracture surface with the small particle content exhibited more rough areas than the surface with larger particles. The fracture toughness increased below the small particle content of 0.8 and saturated above it. Therefore, near the small particle content of 0.8, the composite had a relatively low viscosity and a high fracture toughness.

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The mechanical effect on the oxygen ion mobility in zirconia stabilized with 8 mol% yttria was investigated in this study. A dynamic mechanical thermal analysis showed that the dynamic modulus decreased gradually with temperature while the mechanical loss had two peaks due to different relaxation mechanisms. From the comparison of activation energies between the ionic conductivity and the mechanical relaxation, the dominant factor for oxygen mobility was determined to be the migration of oxygen vacancies in the simple complexes. The result also illustrated the strong relationship between the modulus and the conductivity. An impedance analysis under mechanical tensile-loading conditions showed that the mechanical load improved the ionic conductivity by 6 % at maximum although the improvement was a temporary effect.

The impulsive responses of semi-finite and finite pipes filled with fluid are analyzed in order to clarify the validity of Joukowsky’s theory and the fluid-pipe coupling effect. In the analysis, Flu¨gge’s dynamic bending shell theory and the potential theory of compressible perfect fluid are used. The analytical solutions in Laplace transformed domain are obtained. The inversion of the solutions is performed numerically using the algorithm of FFT. When a pipe is fairly long, it is shown that the result of Joukowsky’s theory which has no pipe inertia effect approximately agrees with that of the coupled theory. When a pipe is short, Joukowsky’s theory shows rough approximation of the responses. The response of the uncoupled theory with the inertia of a pipe is different from that of the coupled theory for both long and short pipes.