FEA THEORY

Question 1

What are the METHODS FOR MECHANICALLY ANALYSING A SOLID STRUCTURE? (3)

Answer 1

1) Experimental
2) Analytical (Theoretical)
3) FEA

Question 2

PROS AND CONS OF EXPERIMENTAL METHODS?

Answer 2

PROS
* Most reliable

CONS
* Time-consuming
* Expensive
* Only feasible on a small sclae

Question 3

PROS AND CONS OF ANALYTICAL METHODS?

Answer 3

PROS
* Good for validation

CONS
* Only feasible on simple problems
* Some assumptions needed

Question 4

PROS AND CONS OF FEA METHOD?

Answer 4

PROS
* Good for large, complicated models
* Can be very accurate
* Can record several properties simultaneously

CONS
* Requires time consuming setup to be accurate

Question 5

What’s the DIFFERENCE BETWEEN ELEMENTS AND NODES?

Answer 5

ELEMENTS: The area of each section of the mesh
NODES: Shared points between elements (vertices)

Question 6

What are the FOUR TYPES OF 2D ELEMENTS

Answer 6

1) Truss (2 nodes - 3 DOF)
2) Beams (3 nodes - 6 DOF)
3) Membrane (3/4 nodes)
4) Plate (3/4 nodes)

Question 7

What are the TWO TYPES OF 3D ELEMENTS?

Answer 7

1) Tetrahedra (4/6 nodes)
2) Brick (8 nodes)

Question 8

How can ELEMENTS HAVE INCREASED ACCURACY?

Answer 8

Add mid-side nodes (most FEA packages do it automatically)

Question 9

What are the TEN TYPES OF MESHING? (5 pairs)

Answer 9

(Un)structured
(Non-)orthogonal
(Non-)uniform
(Non-)boundary fitted
Fine/Coarse

Question 10

What are the FOUR TYPES OF LOADING?

Answer 10

1) TENSION (PULLING)
2) COMPRESSION (PUSHING)
3) TORSION (TWISTING)
4) SHEAR (SLIDING)

Question 11

What is the difference between PLASTIC AND ELASTIC DEFORMATION?

Answer 11

PLASTIC: Once relaxed the original shape is lost (Permanent deformation)

Elastic: Once relaxed, it returns to its original shape and structure. (Temporary deformation)

Question 12

What is STRESS?

Answer 12

Making these flashcards!

The result of a body attempting to absorb external forces by generating internal forces

Stress = Force/Area [N/m^2]

Question 13

What are the FOUR TYPES OF STRESS?

Answer 13

• Normal (direct) stress
• Shear Stress
• Biaxial tension (pressurised tank)
• Hydrostatic compression (Scuba Diver)

Question 14

What is STRAIN?

Answer 14

• The extent of deformation relative to original dimensions

Strain = Change in Length/Original Length

Question 15

What are the TWO TYPES OF STRAIN?

Answer 15

• Normal strain (tensile or lateral)
• Shear strain

Question 16

What does a LINEAR SECTION OF A STRESS STRAIN CURVE REPRESENT?

Answer 16

The ELASTIC deformation region

Question 17

What does a CURVED SECTION OF A STRESS STRAIN CURVE REPRESENT?

Answer 17

The PLASTIC deformation region

Question 18

What is the POISSON RATIO?

Answer 18

The ratio of lateral strain to axial strain

Possin Ratio = v = Lateral Strain/Axial Strain
(sometimes written as: Tranverse Strain/Longitudinal Strain)

Question 19

What is a TRANSPOSED MATRIX?

Answer 19

The rows are the columns of the originals

Question 20

What is an INVERSE MATRIX?

Answer 20

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

Question 21

What are the THREE PROPERTIES OF INVERSE MATRICIES?

Answer 21

1) (A^-1)^-1 = A
2) (kA)^-1=(1/k)(A^-1)
3) (AB)^-1 = A^-1B^-1

Question 22

What is LINEAR STATIC ANALYSIS?

Answer 22

• 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

Question 23

How does LINEAR STATIC ANALYSIS WORK?

Answer 23

• 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