Week 1 Flashcards
What makes materials fail? - 5
Material issues, manufacturing, design, installation or in-service conditions
What is CES?
They demand things to be made of gold
What are examples of ways to make materials fail?
incorrect loading, degradation, misuse
What are material issues?
Considered as an issue with primary processing of the material from virgin or recycled stock
What are manufacturing issues?
Problems and defects that arise through the manufacturing process
What are design issues?
Issues with material selection, incorrect consideration of stresses in a component or stress raisers (sharp corners)
What are installation issues?
For example the wheel nut it will get to the correct torque and then cannot be tightened any further.
If too much torque is on this, the head can come off the nut (needs to be drilled out)
What do the in-service conditions inform?
- Material Selection
- Component design
- Correct manufacturing route to give you the correct microstructure and mechanical properties
- Correct installation processes
What are all of the ways of mechanical testing? - 7
Hardness testing
Tensile testing
Compression testing
Bend testing
Impact testing
Creep testing
Fatigue testing
What are the 4 main ways of hardness testing?
Brinell, Vickers, Knoop and Rockwell
What is Brinell Hardness Testing? and what is the indenter?
Macro harness due to
size of the indent Diameter of the indent measured.
Indenter: 10 mm Ball either
hardened steel or tungsten carbide
What is Vickers hardness testing? and what is the indenter?
Micro harness
Diameter of the indent
measured
Indenter: Diamond Pyramid
136°
What is Knoop hardness testing? and what is the indenter?
Similar to Vickers. Variesin the cross section of the diamond. Measure the long axis of the indent
Indenter: Diamond Pyramid
With an elongated
pyramid l/b
What is Rockwell hardness testing? and what is the indenter?
Tests are labelled A,B… etc. depending on the
indenter and load. Machine measures the depth of the indent.
Indenter: Diamond Cone 120°
Or Steel Ball
What is Tensile Testing?
A parallel sides specimen of uniform cross section is subjected to a gradually increasing tensile force. The extension of the specimen with increasing force is recorded.
The force and extension are directly proportional until breakage.
What is the double yield point?
Starting on a stress strain graph looking at the elastic and plastic stages. Once moving from the elastic phase, there is a upper yield point then interstitial locking then in the plastic region they can move again in the dislocations.
What is the safety factor?
difference between the upper yield point and the lower yield point on a stress strain graph.
What is interstitial locking?
Dislocations in the iron and carbon of steel, where the carbons sit on a dislocation in the structure and the dislocations are starting to move. also this is at the lower yield point
What is torsion testing?
measuring the torque, diameter and the length as well as the angle of twist and length of the sample.
How does tensile testing graph vary between metal and polymer?
1.They both have the initial linear region for elastic degradation
2. Then there is the yield point which is much clearer/evident for metals then polymers.
3. The plastic region is much more ductile for polymers (longer than for metals to deform before breaking) and metals shall not return to the original state when the strain is removed (causing strain hardening).
4. Metals under go necking sharply (brittle) after the ultimate tensile strength (where the plastic region peaks - broader in polymers). Polymers undergo strain softening (where material loses strength after reaching maximum stress level) and fracture instead of necking.
What is notch impact and fracture toughness testing?
Notch impact - measures impact resistance/ toughness through a specimen with a notch on it undergoing a pendulum hammer. Like the Izod or charpy test.
Fracture toughness testing - This is the materials resistance to crack propagation under tensile stress.
What is the ductile - brittle transition?
As the temperature decreases the transition zone exists where the material is both ductile and brittle. If the temperature at this point is too high in cold environments could be brittle.
At higher temperatures the energy absorbed is high = ductile
At lower temperatures, the absorbed energy decreases = brittle.
What is creep?
Elevated Temperature (T>0.4Tm)
and a static mechanical stress
Creep is time dependant
Prevalent in components that are
subjected to a constant load or
stress
What is fatigue?
Cyclic stresses
Axial (tension-compression)Flexural (Bending)
Torsional (Twisting)
