Yuki Kubota

Comparison of thermal deformations of carbon fiber-reinforced phenolic matrix ablators by arc-plasma wind tunnel heating and quasi-static heating

Thermal deformation mechanisms of ablators were elucidated using two types of different pore-size materials under quasi-static heating (QS) conditions. When the material has small pores (Material 1), large expansion in the thickness at temperatures higher than 500 °C occurred by buckling of fiber bundles caused by mismatch strain between the fiber and matrix when the matrix shrunk. In contrast, when large pores are included in the matrix (Material 2), the cracking in the matrix relaxed the mismatch strain and suppressed the buckling. Next, the deformation of Material 1 after arc-plasma wind tunnel heating (AP) tests was examined to identify the causes of thermal deformation. In this environment, expansion also occurred. However, in addition to the fiber bundle buckling, delamination leads to larger expansion than that in QS. The temperature generating expansion in AP tests was higher than that in QS tests. This behavior is caused by reaction rate slower than rapid heating rate.

Long-term thermal stability of addition-type polyimide resins derived from pyromellitic dianhydride, 2-phenyl-4,4′-diaminodiphenyl ether, and 4-phenylethynylphtalic anhydride:

The previously developed TriA-X polyimide resin, consisting of pyromellitic dianhydride/2-phenyl-4,4′-diaminodiphenyl ether; 9,9-bis(4-aminophenyl)fluorene/4-phenylethynylphthalic anhydride (PEPA), was exposed for 3000 h to air at 180, 240, and 270°C or a vacuum environment at 270°C, in order to study its long-term thermal stability. The weight loss and dimensional changes were measured. Elemental analysis was also conducted in order to estimate the TriA-X degradation process. The TriA-X exhibited excellent thermal stability at 180°C and a very small degree of degradation at 240°C, with the degradation becoming significant at 270°C. The latter was primarily dominated by the oxidation of a chain-extension moiety formed by the cure reaction of the end-cap PEPA.

Long-term thermal stability of carbon fibre-reinforced addition-type polyimide composite in terms of compressive strength

A previously developed carbon fibre-reinforced addition-type polyimide composite material was exposed to temperatures of 240, 270 and 300 °C in air for 3000 h to study its long-term stability in terms of its compressive strength. The in-plane shear modulus, compressive failure mode and transverse crack density were also evaluated to determine whether a degradation process induces a decrease in the compressive strength of a high-temperature polymer matrix composite having a laminated configuration of [90/0]4s. The carbon fibre-reinforced polyimide composite exhibited excellent thermal stability in terms of its compressive strength after being subjected to ageing at 240 °C for 3000 h and at 270 °C for 2000 h, with degradation becoming significant at 300 °C. The compressive strength decreased only when the surface degradation caused the 90° plies sandwiching the 0° plies to degrade severely.