Chapter 4: Testing Materials Flashcards
What type of a material is flint?
ceramic
What type of a material is collagen?
polymer
What type of a material is calcium phosphate?
ceramic
What type of a material is bronze?
metal
What type of a material is glass?
ceramic
What type of a material is rubber?
polymer
Give another example of a ceramic
china porcelain
Give another example of a metal
iron
Give another example of a polymer
polythene
Give an example of a natural composite and a synthetic composite.
Natural - bone is made from the brittle ceramic calcium phosphate and the strong polymer collagen.
Man-made - carbon-fibre reinforced plastic is strong and lightweight.
Would you expect a shelf loaded with books to be in tension or compression?
The upper surface will be in compression and the lower surface will be in tension.
Name two brittle materials
glass, perspex, dried wood, china
Name two tough materials
steel, fibreglass
What is the equation for stress?
Stress = force/area
What are the units of stress?
Pa or N/m^2
What is the equation for strain?
Strain = extension/original length
What is the elastic limit or yield point of a material?
The point at which a material begins to deform plastically.
What is the breaking stress of a material?
The stress at which a material will break/fail.
What is toughness?
How much energy is required to create new surface area in a material or how much energy a cubic meter of the material can absorb without cracks propagating.
What is a brittle material?
The opposite of a tough material.
What is yield stress
The stress at which a material begins to deform plastically.
What is elastic deformation?
The temporary change in the shape of an object as a result of stress. Once the stress is removed, the object returns to its original shape.
What is plastic deformation?
The permanent change in the shape of an object as a result of stress. Once the stress is removed, the object does not return to its original shape.
Give an example of a ceramic with a very high yield stress
diamond
What is the Young’s Modulus?
A measure of how stiff a material is; namely the stress required for a particular strain.
What is the equation for Young’s Modulus?
E = σ/ε = FL/Ax
What is brittle fracture?
When a material breaks/fractures after a certain stress is applied
Which class of materials in generally the strongest?
ceramics
Which are stronger, pure metals or alloys?
alloys
How many times stronger is diamond than ice?
1000 times
How much stronger is reinforced concrete than cement which has not been reinforced?
10 times
A concrete block of cross-sectional area 0.01 square meters is crushed when a force of 1MN is applied to it. What is the breaking stress in MN/m^2? How many kg can the piece of concrete support?
breaking stress = 1/0.01=100MN/m^2
maximum mass which can be withstood = 100000 kg.
Are amorphous or crystalline materials more likely to be transparent?
amorphous materials.
What metal ions make glass greenish in colour?
copper(ii)
How do you calculate the refractive index of a material?
n=c/v=sin(i)/sin(r)
Define the critical angle
The angle of incidence at which all of the ray is totally internally reflected.
Pyrex has a refractive index of 1.47. For window glass, n = 1.51. In which does light travel faster?
Pyrex
The refractive index of water is 1.33 (4/3). What is the speed of light in water (c=3x10^8 m/s)
v=c/n=2.25x10^8 m/s
When does a refracted ray of light bend away from the normal?
When it enters a less optically dense material (with a lower refractive index)
Equation for resistivity
ρ = RA/l
Equation for conductivity
σ = Gl/A
