표제지
목차
Abstract 9
I. 서론 11
1. 연구 배경 11
2. 연구 목적 및 범위 14
3. 이론적 배경 19
3.1. 선형탄성파괴역학 (Linear elastic fracture mechanics) 21
3.2. 피로균열전파 (Fatigue crack propagation) 22
3.3. 피로균열 성장지연 효과 25
II. 실험 방법 30
1. 노후 항공기 이력 30
2. 알루미늄 시편 모재 32
3. 실험 장치 및 조건 35
III. 실험 결과 및 고찰 37
1. 노후 시편의 피로파괴 특성 37
2. 피로수명 비교 46
IV. 결론 52
참고 문헌 54
Table 1. Average Age USAF Active Fleet (As of Sept. 30, 2001) 16
Table 2. Average Age USAF Air National Guard Fleet (As of Sept. 30, 2001) 17
Table 3. Average Age USAF Reserve Fleet (As of Sept. 30, 2001) 17
Table 4. Aircraft history 30
Table 5. Materials of aircraft 33
Table 6. Chemical composition of A1 7075-T651 34
Table 7. Design mechanical and physical properties of A17075-T651X extrusion 34
Table 8. Tensile test of exposed specimen 39
Table 9. Specimens for fatigue test 40
Table 10. EIFS of specimens 50
Table 11. Predicted fatigue life by NASGROW 51
Figure 1. Preliminary design process to meet structural integrity requirements 13
Figure 2. Enhanced Significant Structural Item Process 18
Figure 3. Schematic illustrations for total fatigue life, Nf=Ni+Np(이미지참조) 28
Figure 4. Schematic illustration of fracture mechanics approaches to... 28
Figure 5. Schematic illustration of typical stress/crack geometries and... 29
Figure 6. Schematic plot of crack propagation rate, da/dNvs. stress... 29
Figure 7. Aerospace Maintenance And Regeneration Center 31
Figure 8. Materials of P-3 structure 33
Figure 9. Configuration of fatigue specimen 35
Figure 10. Dynamic testing machine (Instron 8872) 36
Figure 11. Stress-Strain curve of exposed specimen 39
Figure 12. S-N curve of exposed specimens 40
Figure 13(a). SEM fractograph for exposed specimen at 200 MPa 41
Figure 13(b). SEM fractographs for flaw near to crack initiation 41
Figure 14. SEM fractographs for exposed specimen... 42
Figure 15(a). SEM fractograph for exposed specimen at 500 MPa 43
Figure 15(b). SEM fractographs for defects of surface 44
Figure 16(a). SEM fractograph for exposed specimen at 310 MPa 45
Figure 16(b). SEM fractographs for defects of surface 45
Figure 17. Various measures of pit size for use as pit metrics 48
Figure 18. Definition of defect area suggested by Murakami et al 48
Figure 19. Equivalent initial flaw size at (a) 200 MPa, (b) 310 MPa, (c) 500 MPa 49
Figure 20. Configuration for NASGROW 50
Figure 21. Predicted fatigue life by NASGROW 51