Indications of fatigue cracking in the lower right wing spar cap of the Chalks Ocean Airways Grumman Mallard G73 that crashed during takeoff December 19, 2005. This is an example of using accumulated knowledge and experience with metallic structures to identify possible factors in an accident (NTSB, 2005).
• And third, our inspection and maintenance requirements will no longer be driven by fatigue and corrosion performance, as they are for metallic structures, because composites are not as susceptible to these failure mechanisms. Instead, accidental subsurface damage and subsequent failure progression will be more important
复合材料结构 及其力学 10
复合材料与结构研究所
复合材料及其结构的分析方法
多尺ቤተ መጻሕፍቲ ባይዱ 多物理场 不确定性
• With the increased use of composites in primary structures, accident investigators will likely encounter failed composite structures with increasing frequency in the coming decades
Tension failure in composites. Macroscopically, even simple tension can produce fractures with a wide variety of features. Microscopic analysis is
paramount (Ginty and Chamis, 1987).
• What evidence would be produced by a failed composite structure?
• The analysis of microstructural evidence becomes paramount
• Microstructural evidence refers to relatively local deformation and changes in the structure, such as fracture surfaces, that typically require close visual or microscopic analysis.
The ductility of metal structures provides macrostructurally visible information regarding an accident (Wanttaja, 1994)
• Typical aircraft composites are not ductile; they are brittle, which means they undergo relatively minor permanent deformation prior to final failure
• Why would these composite structures fail? • First, we are building composite structures on a
scale never before achieved.
• Second, we are building composite structures through relatively new, automated techniques rather than relying on traditional methods of constructing composites by hand
拉伸 压缩
弯曲
冲击分层
Fatigue
A300-600 composite vertical stabilizer that failed during American Airlines flight 587 in November 2001 (NTSB, 2004).
• the vertical stabilizer of the Airbus A300-600 is one of the largest composite principal structural elements in commercial aviation （before A 380 ）
• The vertical stabilizer of the A300-600 is attached to the fuselage by three pairs of composite lugs -- forward, middle, and aft
• Analysis of flight recorder data by the NTSB indicates that the aircraft was subjected to a violently changing oscillatory sideslip motion, causing loads in excess of the ultimate design loads of the stabilizer