4-Testing Materials Flashcards
What are the three main classes of materials?
Ceramics, polymers and metals
What are the main mechanical properties of ceramics?
-Hard, brittle and stiff
What are metals that can be shaped easily called?
Malleable
What property do pure metals tend to have?
Being soft
What are metals that can be drawn into wires called?
Ductile
What are synthetic materials examples of?
Polymers
What does hard mean?
Difficult to scratch
What does brittle mean?
The material will shatter into several pieces
What does stiff mean?
The material is difficult to stretch or bend
What does malleble mean?
The material can be shaped easily
What does ductile mean?
The metal can be drawn into wires
What does tough mean?
The material can undergo considerable deformation and can absorb more energy before breaking
When choosing a material, what are the 3 main factors you must consider?
- Mechanical properties of the material
- The cost
- The look of the finished product
What is Hooke’s law?
For small extensions
What is the equation for Hooke’s law?
F=kx
How do you calculate k in Hooke’s law equation?
Force/extension
If the force is 7N and the extension is 0.10m, what is the value of k?
70N/m
What does the spring constant value show you?
How stiff the specimen is
If you apply Hooke’s law to compression, what does that mean?
Squashing the springs rather than extending them
If you stretch a spring too far, what will occur?
It will not return to its original length when you let it go
What is elastic deformation?
When a wire returns to its original length after being stretched.
What is plastic deformation?
When extension exceeds the elastic limit
Is the plastic region of a graph linear or non-linear?
Non-linear
What does fracture mean?
Breaks
When do force extension graphs become non-linear?
At the elastic limit
What is the fracture point?
Where the wire fractures
What is the relationship between how hard you pull the string and the energy stored in it?
The harder you pull on it, the more energy is stored in it
What is the equation for energy stored in a spring?
Kx*2 / 2
What is the force required to stretch a spring by x?
kx if the force is proportional to the extension
When a body deforms elastically, what is the energy stored equal to?
The energy transferred stretching the spring
How can the energy transferred stretching a material be found?
The area under the line
What is stress?
Force per unit area
What is fracture stress?
The stress at which a material breaks
How is stress found?
Measuring the cross sectional area of the specimen, measuring the force on the specimen, and dividing the force by the area.
What is the yield stress of a material?
The stress at which the material begins to plastic ally deform and become permanently deformed.
What is the breaking stress?
The stress which breaks a material
What are the units of stress?
N/m*2 or Pa
What is the equation for stress?
Stress=Force/area
What is the force measured in?
N
What is the cross-sectional area measured in?
M*2
What is the strain?
The fractional increase in length
What is the equation for strain?
Extension / Original length
Why is there no units for strain?
Because the extension and original length are both measured in m.
What is 18% stress as a decimal?
0.18
Do tough materials have rounded edges on fracturing or sharp edges?
Rounded edges as they undergo considerable plastic deformation before fracture.
Do brittle materials have rounded edges on fracturing or sharp edges?
Sharp edges as they have little plastic deformation before fracture.
What is the Young Modulus a measure of?
The stiffness of a material.
What is the unit of Young Modulus?
E
Is the Young Modulus a measurement of the stiffness of the material or of a specimen?
The stiffness of the material as a whole
What is the equation of Young Modulus?
Stress / Strain
What is the second equation of Young Modulus?
(Force X length) / (Extension X area)
What are the 2 units of Young Modulus?
N/m*2 and Pa
What is strain proportional to?
Stress
How do you calculate percentage uncertainty?
(Uncertainty in measurement / measure value) x 100
What does the gradient of the stress-strain graph give you?
The Young Modulus
How do you measure the diameter of a wire?
By using a micrometer
What is the surgeon’s scalpel made from?
A steel that is strong, hard and non-corrosive.
What are clothes made from?
Natural or synthetic polymers which stretch to fit around your body.
When is a material in tension?
When a force is acting in a direction to stretch the material.
What is a compressive force?
A force which tends to compress or squash the material
What is the equation of density?
Mass / Volume
What do material selection charts allow to happen?
Quick comparisons to be made between different classes of materials.
Name 4 properties to consider when choosing a material?
- Density
- Toughness
- Cost
- Availibility
What do YM density graphs show about polymers?
Polymers have a wide range of stiffness values and a narrower range of densities
What do stength tougness graphs show about polymers?
They have a wide range of toughness.
What is 1Mpa?
1000000Pa
What is 1GPa?
1000000000Pa
