항공기 압력차단벽 손상허용설계를 위한 피로균열성장거동 해석

Abstract

압력차단벽 구조는 보강박판 구조형태로 이루어져 있으며 초기 설계과정에서 균열성장평가를 위한 응력강도해석에 유한요소해석법을 널리 사용하고 있으나 반복되는 계산작업이 매우 번거롭고 많은 시간이 소요되게 된다. 특히 압력차단벽은 내압을 효과적으로 감당하기 위하여 보통곡면 보강구조 형태로 설계되며 이러한 구조적 특성상 보강평판과는 달리 내압에 의해 표피구조에 이축응력이 발생하고 균열면을 따라 부풀어오름(bulging)현상이 발생되기 때문에 설계과정에서 손상허용해석이 까다롭게 된다.

이에 본 연구는 보강평판 해석에 적용한 바 있는 중첩법을 활용하여 압력차단벽 구조의 응력강도해석을 수행하고 유한요소해석 결과와 비교함으로써 중첩법의 활용 가능성을 검토하였다. 또한 내압차단벽의 손상허용 범위를 중앙보강재가 건재한 경우와 파손된 경우로 나누어 표피균열 끝단의 응력강도 해석 및 균열성장해석을 수행함으로써 손상허용성 확장에 따른 균열성장수명을 비교하였다.

The fuselage pressure bulkhead is one of the important primary structures which should be designed satisfactorily damage tolerant. The calculation of fatigue crack growth in this study formed part of the preliminary analysis of damage tolerance design for the fuselage rear bulkhead of a medium civil transport. On the basis of superposition technique, stress intensity solution was derived for the cracked stiffened panel of the pressure bulkhead. The solution used is that of Poe for a built-up skin stiffener construction having a skin crack originating at a failed stiffener location. Both cases of intact and broken center stiffener were considered on the calculation of crack tip stress intensity factor. The only loading on the bulkhead is that of pressure, which is consisted of intermal cabin pressurization and external suction. The finite element analysis was also carried out for the stress intensity factor solution and its results were compared to that of closed form solution. The influence of center stiffener broken and biaxial stress state of skin, and also the effect of skin bulging due to internal pressure on crack growth behaviors, are also studied.

The fuselage pressure bulkhead is one of the important primary structures which should be designed satisfactorily damage tolerant. The calculation of fatigue crack growth in this study formed part of the preliminary analysis of damage tolerance design for the fuselage rear bulkhead of a medium civil transport. On the basis of superposition technique, stress intensity solution was derived for the cracked stiffened panel of the pressure bulkhead. The solution used is that of Poe for a built-up skin stiffener construction having a skin crack originating at a failed stiffener location. Both cases of intact and broken center stiffener were considered on the calculation of crack tip stress intensity factor. The only loading on the bulkhead is that of pressure, which is consisted of intermal cabin pressurization and external suction. The finite element analysis was also carried out for the stress intensity factor solution and its results were compared to that of closed form solution. The influence of center stiffener broken and biaxial stress state of skin, and also the effect of skin bulging due to internal pressure on crack growth behaviors, are also studied.