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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.