The p-v-T device which we previously developed was used to investigate a polymethylmethacrylate (PMMA), a polycarbonate (PC) in the liquid and glassy states, a standard high density polyethylene (PE), a nylon-6 (PA 6) and a polyphenylene sulfide composites containing 40wt% glass fibers (PPS), ranging from the room temperature to 250°C and from the atmospheric pressure to the pressure of 187MPa. This purpose is to measure the p-v-T properties of these polymers in the three measurement techniques of isobaric, isothermal and isochoric. The results show that the straight line T_m′ which consists of each melting point T_m of PE in the isobaric technique is 15∼25°C higher than that in the isothermal technique. The gradient θ_b (in the isobaric) and the gradient θ_t (in the isothermal) of each v-T diagram at temperature beyond the T_m′ lines are θ_b<θ_t in the each pressure. The p-T diagrams of PMMA, PC, PA 6 and PPS obtained by the isochoric technique are presented in the two different straight lines. The intersection of these lines correspond to either the melting temperature T_m or the glass transition temperature T_q in the polymers, but those temperatures are 50∼80°C higher than the real temperature, because the loaded pressure of the polymer in a closed barrel was relaxed.

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The technique of introducing an initial crack in specimens for Kc and Gc tests has a significant effect on their values. This study is concerned with the technique of sliding a razor blade a method which is recommended in the ASTM Standard protocol. A new equipment for machining a saw slit and subsequently sliding a razor blade at the bottom of the slit has been made and the machining and sliding conditions which introduce a residual stress-free crack have been investigated. The polarized observations revealed that the most stress-fee crack tip could be obtained by machining using a U-shaped blade at low rotational speeds while moving the specimen at high speeds. The slow sliding of a razor blade is also preferable to reduce the residual stress at the crack tip.

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