Tensile stress and strain

Question 1

What is stress?

Answer 1

force / area

Nm^-2

Pa

symbol - σ

Question 2

What is tensile strain?

Answer 2

ε = ΔL / L

strain is a ratio and therefore has no unit

Question 3

What is Young modulus?

Answer 3

tensile stress / tensile strain

= T L / A ΔL

Question 4

What does from 0 to P show>

Answer 4

the limit of propotionallity

the tensile stress is propotional strain

the value of stress / strain is a constant, this is the Young modulus of a material

Question 6

What does E show?

Answer 6

the elastic limit

this is where the material is permanently stretched and suffers plastic deformation

Question 7

What is Y₁?

Answer 7

the yield point

where the wire weakens temporarily

Question 8

What happens beyond Y2?

Answer 8

a small increase in the tensile stress causes a large increase in tensile strain

this is because the material undergos plastic flow

Question 9

What is UTS?

Answer 9

the ultimate tensile stress - the maximum tensile stress

the wire loses its strength, extends and becomes narrower at its weakest point

increase of tensile stress occurs due to the reduced area of cross section at this point, until the wire breaks at point B

sometimes called the breaking stres

Question 10

How is the stiffness of a material compared?

Answer 10

compared using the gradient of the stress-strain line, which is equal to the Young modulus of a material

Question 11

What is the strength of a materail?

Answer 11

the UTS

Question 12

Which material is:

1. the strongest
2. the stiffest
3. the most brittle
4. the most ducticle

Answer 12

1. steel is strongest because it has the highest UTS
2. the stiffest is steel as its gradient is the largest
3. the most brittle is glass - breaks without any noticeable yield
4. the most ductile is copper - it can be drawn into a wire