Methods for Investigating and Testing Materials Flashcards
CH3
What is meant by simple workshop tests?
Tests carried out using basic tools and equipment
Simple test for tensile strenght
Put material under load, less deflection means that material has more tensile strength
Simple test for toughness
Tough materials absorb impact, brittle materials bend or shatter
Simple hardness test
The material is tested using a dot punch and force from a hammer. The smaller the indent, the harder the material
Simple test for malleability and ductility
When the test piece is bent to an angle of 90 degrees:
- cracks on the outside indicate lack of ductility
- cracks on the inside indicate lack of malleability
Simple test for corrosion
Leave material exposed to the weather for a set time. Visually inspect material for signs of surface corrosion
Simple test for electrical conductvity
Collect material samples of the same dimensions and mark a set distance to place the multimeter probes. Measure the resistance on the multimeter. The higher the resistance, the lower the conductivity
Simple thermal conductivity test
Collect material samples of the same dimensions, measure a set distance from one end of the material and place a thermometer there.
Light a Bunsen Burner under the other end of the material.
Record the time it takes for the temperature to reach the set point at the other end of the sample.
The shorter it takes, the higher the conductivity
What is meant by industrial tests of materials?
They are usually carried out in labs with specific testing machinery, using standardized test pieces of materials
Industrial test for tensile strength
- A tensometer machine is used
- The standard test piece is held in a clamp at each end
- One clamp is fixed and the other moves on a worm drive gear mechanism, putting the material under tension
- The test piece is stretched, the load and distance travelled is plotted, giving information on elastic limit, maximum load and final breaking point after “necking”
See diagram pg7
Industrial test for toughness
- The Izod impact test is used
- A notched test piece is held vertically 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 absorb the the most impact is the toughest one and gives the least pendulum swing
- Brittle material absorbs less energy and the pendulum swings further
See diagram pg8
Industrial test for hardness - What are the 3 tests for hardness?
Rockwell
Brinell
Vickers pyramid test
What do industrial hardeness tests involve?
The all involve a load being applied to a material with the resultant indentation determining the hardness of the material
Describe the Rockwell test for hardness
- Preload is applied to the material sample using a diamond indenter
- Diamond is used because it will not deform under the load
- Preload is the zero reference position
- An additional load is the applied to test the material and held for a predetermined set of time (dwell time)
- The load is released and the distance between the preload and the applied load is measured
Describe the Brinell test for hardness
- 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
Describe the Vickers pyramid test for hardness
- 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 Non-destructive testing (NDT)?
- What does it test?
- What is it used for?
- What are the two standard methods?
- NDT is carried out on products, not materials
- It is used to find defects in the material
- The two standard methods are:
1. ultrasonic where sound waves are pulsed into the material and different sounds indicate faults
2. x-ray: an e-ray beam passes through the material and an image is projected on to a display screen, allowing the observation of tiny details such as hairline cracks within the metal
Industrial test for malleability and ductility
- Bend test is used
- The aim is to test how well a material can withstand cracking during a continuous bend
- The test piece is placed into a bending machine and held, supported at the ends
- A mandrel or plunger loads the test piece at the centre and bends it to a predetermined angle or until the test piece fractures.
- Cracks on the outer bend indicate the level of ductility. A ductile material will have a lot plastic deformation prior to failure
- Cracks on the inside of the bend indicate the level of malleability
Industrial test for corrosion
- Similar to the test carried out in a workshop but the environmental effects are simulated in a lab.
- Material samples of equal size are placed in the simulated weather environment and left for a set amount of time
- then inspected for surface corrosion
Industrial test for electrical conductivity
- Collect material samples of the same dimension
- on top of the surface mark a set distance at each end
- place a multimeter probe on each mark
- measure resistance
Industrial test for thermal conductivity
- use a heat flow meter
- a square shaped material test sample is placed between two temperature controlled plates
- the temperature is increased at a controlled rate and the heath flow through the material is measured by sensors placed on the surface of the material.
- as the material is heated to a specific temperature, the sensors measure and record the rate of thermal conductivity
