4C2 Tripos 2014 Flashcards
What are the units of stress resultants?
N/m, Force per unit length (Pa*m)
What is the units of the stiffness matrix Q?
Pa (N m^-2)
What are the units of strain?
Unitless
What is the units of the compliance matrix S?
Pa^-1 (N^-1 m^2)
What are the units of the laminate stiffness matrix A?
N/m, Force per unit length (Pa*m)
What are the units of the coupling stiffness matrix B?
N (Force)
What are the units of the laminate bending stiffness matrix D?
Nm, Force times length (like a moment)
Give an example of a cause of low, medium and high energy impacts
Low- Tool drop
Medium- bird strike
High- Ballistic impact
Why are porosity and crack-like flaws of concern for composites?
They can act as starters for cracks which are particularly damaging given the low fracture toughness of the matrix.
What is a non-destructive testing method to find porosity and other flaws in composite’s?
Ultrasound
Describe the testing pyramid methodology widely used for aerospace composites applications.
The testing pyramid describes the process of testing a product in its full scale, through subcomponents, then generic test and then many coupon tests of the material properties. Ie you do lots of coupon tests, then fewer generic tests, then fewer subcomponent tests before finally testing the full scale product.
What are the main pros and cons of the testing pyramid method?
Pro- It is very thorough so gives confidence in design
Con- It is very expensive and limits the ability to modify/upgrade (a new material would have to go through the whole testing cycle)
How do you find the through thickness stress for an element in bending?
Perform a force balance on the element, with the through thickness equal to the component of the in average plane stresses in the radial direction (remembering that the angle at each edge is half that subtended at the middle)
