Lecture 3-4

Question 1

τ =

Answer 1

shear stress =

change in Ft / A

change in the tangential force / area

Question 2

Pulling effect is —– stress

Answer 2

tensile

Question 3

Pushing effect is —– stress

Answer 3

compressive

Question 4

Tangential effect is —– stress

Answer 4

shear

Question 5

When resolving the force equilibrium how do we intially set out the equation to prove that the stresses on both sides of the same body are equal?

Answer 5

(σ y X change in x X change in z) - (σ’ y X change in x X change in z)
+
(τ xy X change in y X change in z) - (τ’ xy X change in y X change in z)
+
(τ zy X change in x X change in y) - (τ’ zy X change in x X change in y)

= which simplifies to

(σ y - σ’ y) change in x X change in z
+
(τ xy - τ xy’) change in y X change in z
+
(τ zy - τ zy’) change in x X change in y

And as change in x/y/z tends to 0. Each σ/τ is equal to eachother

Question 6

γ =

Answer 6

shear strain =

π / 2 - (θ’)

90 degrees intial angle - (the 90 degree angle after deformation)

Question 7

F.S. =

Answer 7

factor of safety =

σ fail / σ allow

Question 8

Hooke’s Law relationship between stress and strain

Answer 8

Linear relationship, directly proportional relationship

Question 9

Poisson’s ratio states that elongation in one direction leads to….

Answer 9

a contraction in an orthogonal direction

Question 10

ν =

Answer 10

poissons ratio =

− εy / εx

• strain in y / strain in x

Question 11

Torsional deformation of a circular shaft is when…. (reference radial and longitudinal lines)

Answer 11

over time and wear the whole shaft twists and the longitudinal lines (lines parallel to the shaft) become twisted. Radial lines stay straight

Question 12

For torsional deflection what do we use instead of young’s modulus?

Answer 12

Shear modulus

Question 13

G =

Answer 13

shear modulus =

shear stress / shear strain

Question 14

Φ =

Answer 14

angle of twist =

T L / J G

torque force X length of bar / property of the area X shear modulus