MT-1620 al.2002 Unit 2 Loads and Design Considerations Readings Rivello (Ch.1) Cutler book(at leisure G 7.1 Paul A Lagace, Ph. D Professor of aeronautics Astronautics and Engineering Systems Paul A Lagace @2001
MIT - 16.20 Fall, 2002 Unit 2 Loads and Design Considerations Readings: Rivello (Ch. 1) Cutler book (at leisure) G 7.1 Paul A. Lagace, Ph.D. Professor of Aeronautics & Astronautics and Engineering Systems Paul A. Lagace © 2001
MT-1620 Fall 2002 Sources of stresses and strains Depends on type of structure Aircraft Launch vehicles Space Structures General Other considerations Paul A Lagace @2001 nit -p 2
MIT - 16.20 Fall, 2002 Sources of Stresses and Strains Depends on type of structure Aircraft Launch Vehicles Space Structures General Other Considerations Paul A. Lagace © 2001 Unit 2 - p. 2
MT-1620 al.2002 Can generally divide these into Normal operational effects(regular use Environmental effects (internal stresses, material property degradation Isolated effects(lightning, impact) In a (large company) “ Design” group does general management Loads group determines operating conditions This is passed on to "stress" group that analyzes stresses and deformations Materials" group provides material ultimates, etc Need to understand each part NOTE New approach in companies: IPT (Integrated Product Teams) DBT (Design Build Teams)-people from each branch including manufacturing and marketing even more important to understand various factors Paul A Lagace @2001 Unit 2 -p. 3
MIT - 16.20 Fall, 2002 Can generally divide these into: • Normal operational effects (regular use) • Environmental effects (internal stresses, material property degradation) • Isolated effects (lightning, impact) In a (large company) • “Design” group does general management • “Loads” group determines operating conditions • This is passed on to “stress” group that analyzes stresses and deformations • “Materials” group provides material ultimates, etc. ⇒ Need to understand each part NOTE: New approach in companies: IPT (Integrated Product Teams) DBT (Design Build Teams) - people from each branch including manufacturing and marketing ⇒ even more important to understand various factors Paul A. Lagace © 2001 Unit 2 - p. 3
MT-1620 al.2002 Factors, Margins, etc. Two important definitions for static considerations Limit load/stress/Condition Maximum load/stress/condition where structure shows no permanent deformation Ultimate Load/stress/Condition Maximum load/stress/condition Where structure does not fail Definition is key; often defined as break(i.e, carry no more load Operationally, the limit load is the maximum load the structure is expected o see The ultimate load provides a factor of safety"for unknowns Ultimate Factor of Safety(U F.S. ) =Ultimate Load Limit load This is a design value Paul A Lagace @2001 Unit 2 -p 4
MIT - 16.20 Fall, 2002 Factors, Margins, etc. Two important definitions for static considerations Limit Load/Stress/Condition: Maximum load/stress/condition where structure shows no permanent deformation. Ultimate Load/Stress/Condition: Maximum load/stress/condition where structure does not “fail.” Definition is key; often defined as “break” (i.e., carry no more load) Operationally, the limit load is the maximum load the structure is expected to see The ultimate load provides a “factor of safety” for unknowns Ultimate Factor of Safety (U.F.S.) = Ultimate Load Limit Load This is a design value Paul A. Lagace © 2001 Unit 2 - p. 4
MT-1620 al.2002 F.O.S. is also a Factor of ignorance This accounts for probability statistics (also in material allowances) U FS =1.5 for aircraft 1.25 for Spacecraft(unmanned Design is usually conservative and an additional"Margin of Safety (M.O.S. )is used/results Limit mos tested limit x - limit x LimitⅩ Ultimate mos tested ultimate x-Ultimate X Ultimate X An MOS is an experimental reality. Paul A Lagace @2001 Unit 2 -p. 5
MIT - 16.20 Fall, 2002 F.O.S. is also a “Factor of Ignorance” This accounts for Æ probability & statistics (also in material allowances) U.F.S. = 1.5 for Aircraft 1.25 for Spacecraft (unmanned) Design is usually conservative and an additional “Margin of Safety” (M.O.S.) is used/results Limit MOS = Tested Limit X - Limit X Limit X Ultimate MOS = Tested Ultimate X - Ultimate X Ultimate X An MOS is an experimental reality. Paul A. Lagace © 2001 Unit 2 - p. 5