Methods for investigating and testing materials Flashcards
Why is material testing used?
To help select the most suitable material for a product/application
How do we make material tests fair?
- use same size material for each test
- make sure environmental conditions are the same
- use same technique and testing equipment
- use ome person to take all measurements
What are simple workshop tests?
They use basic tools and equipment
How can we tell is a material has more sensible strength?
Less deflection under load means more tensile strength
What is a toughness test?
Tough materials absorb impact, brittle materials bend or shatter
What is a hardness test?
Material is tested using a dot punch and the force from a Hammer
How can we tell the hardness of a material?
The smaller the indent from the dot punch, the harder the material
What is a malleability and ductility test?
When the test piece is bent to 90 degrees
What indicates a lack of ductility?
Cracks on the outside indicate a lack of ductility
What indicates a lack of malleability?
Cracks on the inside indicate a lack of malleability
What is Corrosion testing?
Place equally sized materials outside in an area exposed to effects of weather and leave for a period of time. Materials can be visually inspected for surface corrosion
What is an electrical conductivity test?
Collect samples of same dimensions and mark a set distance to place multimeter probes. Measure resistance on multimeter. The higher the resistance, the lower the conductivity
What is the thermal conductivity test?
- collect material samples of the same dimension
- measure a set distance from one end of material and place a thermometer there
- light a bunsen burner under the other end of the material
- record time it takes for the temperature to reach set point on material
- the shorter the time it takes, the higher the thermal conductivity of the material
What are industrial test?
They are usually carried out in a lab with specific testing machinery, using standardised test pieces of material
What is the machine used to measure tensile strength?
A tensometer machine tests for tensile strength
How do you perform a tensile strength test in industry?
- the standard test piece is held in a clamp at each end
- one clamp is fixed and other moves on a worm drive gear mechanism,putting the material under tension
- test piece is stretched, load and distance is plotted
What does the load and distance travelled give us information on? (Tensile strength)
- elastic limit
- yield point
- maximum load
- final breaking point after ‘necking’
What I’d the test for toughness in industry?
The izod impact test is used to test toughness
How do you perform a test for toughness in industry?
- a notched test piece is held virtually in the vice of the machine
- a pendulum is released from a set position and swings to strike the test piece
- the energy absorbed by the test piece is calculated from the height the pendulum swings to after it hits the test piece
- the material that absorbs the most impact is the toughest
- brittle materials absorb less energy less energy and the pendulum swings further
What is the test for hardness?
The rockwell, brunelleschi and vickers pyramid tests
What is the rockwell test?
Preload applied to material sample using a diamond indented which breaks through the surface of the material
- diamond will not deform under load
- preloaded is the datum or zero reference point
- an addition load is then applied to test material and held for a predetermined length of time
- load is released and distance between preloaded and applied load is measured
What is the brinell test?
- a hardened standard size steel ball is forced into the material’s surface using a pre-set load
- the diameter of the indent in the surface is measured
What is the vickers pyramid test?
- used for very hard materials
- uses a diamond square-based pyramid to indent the surface of the material
- a microscope is used to measure the size of the indent
What is NDT?
Non-destructive testing
What is NDT carried out on?
Carried out on products rather than materials
What is NDT used for?
Used to find defects in the material without breaking it
What are the two NDT method?
- ultrasonic
- x-ray
How to NDT test with ultrasonic?
Sound waves are pulsed into the material, different sounds indicate faults
How to NDT test with x-rays?
X-ray beam is passed through a material and image is projected onto a display which allows you to observe tiny details
How to test for malleability and ductility industrially?
Tested using a bend test
How do you carry out a bend test?
- test piece is placed into a bending machine and held
- a mandrel or plunger loss test piece and bends it to a predetermined angle untol piece fractures
- crack on outer bend indicate level of ductility
- cracks on inside of the bend indicate level of malleability
What is Corrosion testing in industry?
Similar to how it is testing for in a workshop except environmental effects are simulated in a lab.
What does a bend test test for?
Tests how well a material withstands cracking during one continuous bend
What is the test for electrical conductivity in industry?
It is the same as the test in a workshop except carried out on a larger scale
What is the test for thermal conductivity?
It is the same as in a workshop except everything is controlled using sensors and machinery
