2018/4/27 Fail safety design 圆上活发大学 Fail Safe Design service experiences -fuselage 国上游大峰 Definition:fail safety is the ability to fly and land safely with significant structural damage Damage sources Fatigue cacking.,,manufacture defects, Alt ioad bes desian features Multiply redundant two-and three-plece primary bulkhesd Oout reinforcements Design for limit load capability with a two-bay crack Alternative/intermediate/adjacent members Crack arrest fea ures such as tear straps Timely inspection is key to prevent fatigue failure causing catastrophic rsiy -D Nenbin Song y -L. Fail Safe Design service experiences -wing 国上活大学 Fail Safety Design 国上活大学 But Fail safety design cannot by itself guarantee the continued safe onleratioegec2aeieteteabetorecatastophkresutshap -Which leads to damage tolerance design FWD Shanghar a Tong Uriversy-Dr.Wenbin Song chool of Aemnautics and As'ronautics Damage Tolerance Design 圈上承我大峰 Strength Requirements for Damage Tolerant Designs 国上游毛大堂 Definition:damage tolerance is the ability to sustain operating loads (up to ，esa9eaeeaSe96eatgUpea8gsnon uding non Da detected and to ultimate loa structures must be damage toleran capacity Developmentmethods: Large-scale component test Damage detection means Fracture mechsnics Proper inspection method and frequency Impact on design -Structural arrangements Materlals Working stress levels Damage detection thresh hold -Dt.Wentin Song 42018/4/27 4 © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Fail safety design • Definition: fail safety is the ability to fly and land safely with significant structural damage • Damage sources – Fatigue cracking, corrosion, accidental damage, manufacture defects, maintenance errors, discrete events. – All load bearing structures must be fail safe • Some fail safety design features – Stiffened wing and fuselage panels – Multiply redundant two- and three-piece primary bulkhead – Cutout reinforcements – Design for limit load capability with a two-bay crack – Alternative/intermediate/adjacent members – Crack arrest features such as tear straps – Boundaries of components such as major joints – Material toughness and slow crack growth characteristics – Low stress levels • Timely inspection is key to prevent fatigue failure causing catastrophic incidents 19 © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Fail Safe Design service experiences - fuselage © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Fail Safe Design service experiences - wing © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Fail Safety Design • But Fail safety design cannot by itself guarantee the continued safe operation because – Failures need to be detected before catastrophic results happen – Which leads to damage tolerance design © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Damage Tolerance Design • Definition: damage tolerance is the ability to sustain operating loads (up to limit load) in the presence of unknown fatigue, corrosion, or accidental damage until such damage is detected through inspections, including non￾destructive inspection (NDI), or safe malfunction, and then it is repaired. • Design requirements: – All primary flight-load structures must be damage tolerant – Sufficient damage growth properties and detection characteristics – Damage detectable in normal specified airline inspections • Development methods: – Inspection of older airplanes and fatigue test articles – Large-scale component test – Fracture mechanics – Proper inspection method and frequency • Impact on design – Structural arrangements – Materials – Working stress levels – Accessibility – Inspectability – reparability 23 © Shanghai Jiao Tong University – Dr. Wenbin Song School of Aeronautics and Astronautics Strength Requirements for Damage Tolerant Designs Damage detected and restored to ultimate load capacity Damage detection thresh hold Damage detection means