Estimation of crack growth behavior in welded space vehicles structural components
- Paper number
IAC-11,C2,7,15,x9988
- Author
Mr. Fengxiang Zhang, China Xichang Satellite Launch Center, China
- Year
2011
- Abstract
Safety is the essential topic in structural design and mechanical assessments of space vehicle structures, especially for the re-usable components. During the last years significant improvements have been achieved for enhancing the safety by using new design philosophy, of which damage tolerance is commonly used to manage the structural failure caused by crack extension from any initial manufacturing flaws, in service fatigue damage and environmental damage. Crack growth analysis is one of the key aspects for damage tolerance design. Although lots of achievements have been made, new problems in crack growth analysis arise continuously with the increasingly application of new materials and manufacturing techniques to achieve low-weight structures in aerospace industry. Advance weld techniques for high strength aluminum alloys and Al-Li alloys, e.g. VPPA, FSW, etc., are adopted in manufacturing tanks and frames of rockets, space shuttles and space station to reduce structural weight. The advanced weld techniques result in remarkable material property changes and complex residual stresses which affect the crack growth behavior significantly. Therefore, accurate crack growth assessment in such welded components is important to ensure the safety of the structures. The key issue of accurate assessment is the knowledge of the relationship between crack growth rates and residual stress fields. There are two aspects, one is crack growth life estimation when the weld induced residual stress field is given, and the other is residual stresses evaluation through the crack growth data. The first aspect is addressed in this paper. For the crack growth life estimation in residual stress field, methods are developed based on the superposition law and applied successfully to the mode I crack growth in plate specimens. These methods are extended in this paper to be applied to estimate the crack growth in space components with thin wall cylinder structural characteristics and under taken both internal pressure and bi-axial weld residual stresses. An example of VPPA welded 2XXX aluminum alloy thin wall internal pressure cylinder is illustrated. The initial crack is assumed to perpendicular to the weld line. The combined stress fields of internal pressure and residual stresses in crack tips in terms of stress intensity factors are calculated by finite element method firstly, and then the crack growth path and rate are estimated based on linear elastic fracture mechanics. The results of the calculation will be helpful to avoid the crack caused failure in such welded aerospace structural components.
- Abstract document
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