FEA THEORY Flashcards
What are the METHODS FOR MECHANICALLY ANALYSING A SOLID STRUCTURE? (3)
1) Experimental
2) Analytical (Theoretical)
3) FEA
PROS AND CONS OF EXPERIMENTAL METHODS?
PROS
* Most reliable
CONS
* Time-consuming
* Expensive
* Only feasible on a small sclae
PROS AND CONS OF ANALYTICAL METHODS?
PROS
* Good for validation
CONS
* Only feasible on simple problems
* Some assumptions needed
PROS AND CONS OF FEA METHOD?
PROS
* Good for large, complicated models
* Can be very accurate
* Can record several properties simultaneously
CONS
* Requires time consuming setup to be accurate
What’s the DIFFERENCE BETWEEN ELEMENTS AND NODES?
ELEMENTS: The area of each section of the mesh
NODES: Shared points between elements (vertices)
What are the FOUR TYPES OF 2D ELEMENTS
1) Truss (2 nodes - 3 DOF)
2) Beams (3 nodes - 6 DOF)
3) Membrane (3/4 nodes)
4) Plate (3/4 nodes)
What are the TWO TYPES OF 3D ELEMENTS?
1) Tetrahedra (4/6 nodes)
2) Brick (8 nodes)
How can ELEMENTS HAVE INCREASED ACCURACY?
Add mid-side nodes (most FEA packages do it automatically)
What are the TEN TYPES OF MESHING? (5 pairs)
(Un)structured
(Non-)orthogonal
(Non-)uniform
(Non-)boundary fitted
Fine/Coarse
What are the FOUR TYPES OF LOADING?
1) TENSION (PULLING)
2) COMPRESSION (PUSHING)
3) TORSION (TWISTING)
4) SHEAR (SLIDING)
What is the difference between PLASTIC AND ELASTIC DEFORMATION?
PLASTIC: Once relaxed the original shape is lost (Permanent deformation)
Elastic: Once relaxed, it returns to its original shape and structure. (Temporary deformation)
What is STRESS?
Making these flashcards!
The result of a body attempting to absorb external forces by generating internal forces
Stress = Force/Area [N/m^2]
What are the FOUR TYPES OF STRESS?
- Normal (direct) stress
- Shear Stress
- Biaxial tension (pressurised tank)
- Hydrostatic compression (Scuba Diver)
What is STRAIN?
- The extent of deformation relative to original dimensions
Strain = Change in Length/Original Length
What are the TWO TYPES OF STRAIN?
- Normal strain (tensile or lateral)
- Shear strain
What does a LINEAR SECTION OF A STRESS STRAIN CURVE REPRESENT?
The ELASTIC deformation region
What does a CURVED SECTION OF A STRESS STRAIN CURVE REPRESENT?
The PLASTIC deformation region
What is the POISSON RATIO?
The ratio of lateral strain to axial strain
Possin Ratio = v = Lateral Strain/Axial Strain
(sometimes written as: Tranverse Strain/Longitudinal Strain)
What is a TRANSPOSED MATRIX?
The rows are the columns of the originals
What is an INVERSE MATRIX?
If ‘A’ is any SQUARE MATRIX and ‘B’ is another square matrix satisfying the conditions:
AB=BA=I
where,
I = 100
010
001
then,
A is INVERTIBLE and B is the INVERSE OF A or A^-1
What are the THREE PROPERTIES OF INVERSE MATRICIES?
1) (A^-1)^-1 = A
2) (kA)^-1=(1/k)(A^-1)
3) (AB)^-1 = A^-1B^-1
What is LINEAR STATIC ANALYSIS?
- The most common type of analysis
- Assumes linear material behaviour and neglects inertia forces
- The body returns to its original position when loads are removed
- It calculates displacements, strains, stresses, and reaction forces
- Material fails when the stress reaches a threshold (unique to the material)
- Used to test the failure of many materials
How does LINEAR STATIC ANALYSIS WORK?
- The solver finds the displacements in the X, Y and Z directions at each node.
- From the displacement the STRAINS in several directions
- Through the use of mathematical expressions the stresses can be calculated by the strains
