Materials Definitions

Question 1

Elastic Deformation

Answer 1

returns to original length/shape when force is removed

Question 2

Plastic Deformation

Answer 2

does not return to original length/shape when force is removed

Question 3

Elastic Limit

Answer 3

force/stress/stain/extension beyond which plastic deformation occurs

Question 4

Hooke’s Law

Answer 4

up to the elastic limit extension is proportional to applied force

Question 5

the Spring Constant

or ‘force constant’

Answer 5

where Hooke’s law is obeyed;

the spring constant is force ÷ extension

Question 6

Stress

Answer 6

force ÷ cross-sectional area

Question 7

Strain

Answer 7

extension ÷ original length

Question 8

Yield stress

Answer 8

stress at which a material begins to deform plastically. (N.B. One measure of material strength.)

Question 9

Breaking stress /
Fracture stress /
Ultimate Tensile Strength

Answer 9

stress at which a material fractures

N.B. Another measure of material strength.

Question 10

Young modulus

Answer 10

tensile stress ÷ tensile strain; for small stresses

N.B. A measure of material stiffness. Can be found from initial gradient of a stress-strain graph.

Question 11

Brittle material

Answer 11

does not deform plastically, exhibits uniform elastic deformation before fracture
examples: glass/cast iron/porcelain

Question 12

Ductile material

Answer 12

exhibits considerable plastic deformation before fracture

examples: copper/polythene

Question 13

Polymeric material/ Elastomer

Answer 13

exhibits non-uniform elastic deformation

example: rubber