이종 영상을 활용한 탄소/페놀릭 복합재의 열분해 전후 밀도 산출 기법 연구 = Density Estimation of Carbon/Phenolic Composites Before and After Pyrolysis Using Micro-CT and FE-SEM

다국어 초록 (Multilingual Abstract)

Carbon/phenolic (C/P) composites are widely used as charring ablative thermal protection materials for atmospheric entry. Under severe aerothermal heating, the phenolic matrix pyrolyzes and carbonizes, accompanied by pore and microcrack formation. These microstructural changes lead to density changes and affect key thermophysical and mechanical properties. Although density evolution of neat phenolic resins has been studied in prior work, quantifying matrix density in the composite state remains challenging because fibers, matrix, and pores coexist and cannot be cleanly separated at the relevant length scales.
This study presents a multimodal imaging workflow integrating micro-computed tomography (micro-CT) and field-emission scanning electron microscopy (FE-SEM) for density estimation of tow-reinforced C/P composites before and after pyrolysis, including back-calculation of composite-state matrix density. Pyrolysis was performed in an inert atmosphere to a prescribed end temperature using thermogravimetric analysis. Consistently defined representative micro-CT volumes were segmented into solid and pore phases to compute bulk density, porosity, and true density. Tow domains were identified on representative micro-CT slices using structure-tensor analysis. Within each tow domain, fiber volume fractions were quantified from FE-SEM line profiles registered to the corresponding micro-CT slices. Assuming constant fiber density, matrix density was back-calculated from the true density and the measured fiber volume fractions using a two-phase rule of mixtures. Pyrolysis increased porosity from 0.0231 to 0.2199, decreasing bulk density from 1.3950 to 1.2110 g/cm³, while increasing true density from 1.4280 to 1.5530 g/cm³. The measured tow-scale fiber volume fractions (63.94% and 65.34%) yielded matrix-density estimates of 1.2974 g/cm³ (pre-pyrolysis) and 1.6991 g/cm³ (post-pyrolysis), indicating matrix densification concurrent with void growth.
Overall, the workflow enables imaging-based density quantification across pyrolysis by combining non-destructive micro-CT with correlative FE-SEM to recover tow-scale fiber-matrix partitioning beyond the micro-CT resolution limit. These composite-state, tow-resolved density/phase-fraction metrics support physically consistent TPS material-response modeling and post-test degradation assessment in ground-test environments.

목차 (Table of Contents)

• 목 차 ⅰ
• Abstract ⅲ
• List of Figures and Tables ⅴ
• 제 1 장 서 론 1
• 1.1 연구 배경 1
• 1.2 연구 동향 4
• 1.3 연구 목적 및 내용 6
• 제 2 장 열분해 실험 및 영상 획득 7
• 2.1 재료 및 시편 8
• 2.2 열분해 실험 10
• 2.3 Micro-CT 영상 획득 12
• 2.4 FE-SEM 영상 획득 17
• 2.5 이종영상 기반 분석 절차 21
• 제 3 장 CT 기반 고체/기공 분할 및 밀도·기공도 산출 22
• 3.1 Micro-CT 체적 기반 고체/기공 분할 23
• 3.1.1 3D 체적 정의 23
• 3.1.2 고체/기공 분할 27
• 3.2 열분해 전/후 벌크·고체 진밀도 및 기공도 산출 30
• 제 4 장 CT-SEM 기반 토우 분할 및 기지 밀도 산출 35
• 4.1 Micro-CT 단층 구조 텐서 기반 토우 분할 36
• 4.1.1 2D 단층 설정 36
• 4.1.2 구조 텐서 분석 이론 39
• 4.1.3 구조 텐서 분석 기반 토우 분할 42
• 4.2 FE-SEM line profile 기반 섬유 분율 산출 48
• 4.2.1 1D line 설정 48
• 4.2.2 섬유 분율 산출 51
• 4.3 열분해 전/후 기지 밀도 산출 57
• 제 5 장 결 론 60
• 참고 문헌 63