Dynamic mechanical measurement, flexural test, and SEM observation for poly (vinyl chloride) (PVC) filled with pitch-based graphite short fibers (PGF) in the range of 0-0.469 in volume fraction (φ_f), and those treated with silane and titanate coupling agents by φ_f=0.261, were carried out. During the blending with a hot mixing roll, the PGF particles in the specimens were broken, but they were aligned parallel to the machine direction (MD). As the φ_f increase, the storage modulus (E') and flexural modulus (E_f) of the specimens became higher. The E' values of the specimens were larger than those estimated from rule of mixture and modified Halpin-Tsai's equation in the glassy region and that calculated from Mooney's equation in the pseudo-rubbery region. The flexural strength for MD was larger than that of PVC, but that for transverse to the MD (TD) was decreased as the φ_f increase. The increase of affinity between PVC and PGF particles treated with coupling agents was relatively small.

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The present paper reports the possibility of the acoustic emission (AE) application from the results of the testing performed at NASDA (National Space Development Agency of Japan) on H-I rocket motor nozzle holders (Graphite/Epoxy composites), such as materials tests, the burst test and the hydroproof test. Amplitude distribution during tests shows three types of the fracture mechanism, such as fiber breakage (over 70 dB), delamination (between 60 and 70 dB) and matrix cracking (under 60 dB). After the middle stage of the burst test, AE event rate is shown a saturated behavior, and a large scale delamination is observed in the fracture surface. The upper limit speed for data acquisition (40 events/s) of AE equipment (3000/3104: PAC) underestimated the number for middle amplitude events of the delamination. During the hydroproof test, both large amplitude events and large number of AE events are detected in spite of the higher threshold (+20 dB) than that of the burst test. The strain gages on the hydroproof sample indicate higher strain than that of the burst test. Both AE and strain results show that the hydroproof test sample would have bigger damage than the burst test sample.

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Acoustic Emission criterion of the fracture is developed for CFRP rocket motor case. This criterion can be applied to detect failure extension in FRP dynamically. Both the criterion of the fracture theories and the nondestructive evaluation methods for FRP are discussed. The developed AE criterion is based on the method of the statistics which includes the prior distribution, the data distribution and the posterior distribution. AE criterion shows the equivalent pressure which relates to the damage extension of the master sample. Three types of the equivalent pressure criterion, such as the fiber breakage criterion, the fiber breakage and delamination criterion and the all failure criterion are based on AE amplitude distribution. Weight functions used in this treatment based on the AE source characterization theory. The predicted burst pressure and the safety ratio are calculated by the equivalent pressure and the proof test pressure. Result of the evaluation indicates that the predicted burst pressure is 7.9MPa and the safety ratio is 1.6. These results are in good agreement with the strain measurement.

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