Embedded Files
Students Learn About:
materials for braking systems
– steels
– cast irons
– composites
– manufacturing/forming processes of composites
testing of materials
– tensile and compression test
– hardness test
Students Learn To:
investigate the macrostructure and microstructure as well as the properties of appropriate materials used in braking systems
describe the manufacturing processes and application of composites to friction materials
describe and/or conduct relevant mechanical tests on materials
- materials for braking systems
Driving Question: Why are samurai swords consider the finest in the world
steels
steels
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Steels are allotrpic as is iron. As a mild steel cools from liquid, the iron forms a BCC structure, then changes to an FCC, then back to BCC at room temperature. each change has great effect on how steel behaves. The amount of carbon determines at what temperature these changes occur and weather they occur fully or partially. If the steel has more then 0.3% carbon, then it becomes FCC from liquid. In fact the liquid BCC to FCC change is often ignored as it is of little importance to the steel behaviour at room temperature.
Best case use (When would this be a highly desirable state of steel)
Best case of use is buildings that need to support large amount of weight and it is able to do this as it has a atom stcuture of BCC and therefore does not want more cells inside this atom structure. This makes the materila tougher comapred to others and are therefore heavily used in buildings or oher strcutures siuch as kitchen ultenzils. It is also a low-priced material with properties that are suitable for most general engineering applications
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
looking at the image, why does this proccess go from BCC to FCC and back to BCC?
Austenite
Austenite
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Ferrite
Ferrite
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Cementite
Cementite
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Pearlite
Pearlite
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Eutectoid Steel
Eutectoid Steel
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Hypo-Eutectoid Steel
Hypo-Eutectoid Steel
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Hyper-Eutectoid Steel
Hyper-Eutectoid Steel
Allotropy Of Steels
Allotropy Of Steels
Image or Video Link (consider use of time specifc link on youtube)
Description (With specifc details such as temp & cell structure - refer to BCC FCC in chapter 1)
Best case use (When would this be a highly desirable state of steel)
Concept Check (Create a short answer or multiple choice question that would check someones understanding of your Steel component)
Concept Check:
Concept Check:
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cast irons
cast irons
Cast irons have carbon content between 2 and 4% and steels have less than 2% carbon. They are so named because they are generally cast in a mould.
The important difference between steels and cast irons is that steel has carbon in the form of cementite (carbide or Fe₃C), whereas cast irons (except white cast iron) have carbon in the form of graphite which is very weak.
Silicon is a catalyst which facilitates the formation of graphite from Fe₃C.
Fe₃C + heat + Silicon→3Fe + C (graphite)
composites
composites
manufacturing/forming processes of composites
manufacturing/forming processes of composites
Concept Check:
Concept Check:
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- testing of materials
tensile and compression test
tensile and compression test
These tests are used to determine the tensile and compressive properties of a material. The tension test usually involves using some machine to stretch a test piece, whereas a compression test squeezes the test piece. A tensile testing machine usually consists of a set of grips to hold the test piece and either a screw thread or hydraulic system to place the object into tension. There will be either a revolving drum or a computer linked to the tester to record the load extension diagram.
The compression test is used to determine how well a material behaves under compressive forces. It is essentially a tensile test in reverse. Malleable materials will tend to deform while brittle materials will display characteristic breakage. Fig. 3.18 shows some of the possible fractures when testing concrete and cast iron.
Left
Left
an hourglass fracture. When compressed, concrete often does this.
Centre
Centre
a shear cone failure that also occurs in concrete.
Right
Right
a single shear plane; cast iron or concrete will fail this way.
hardness test
hardness test
Brinell
Brinell
A hardened steel ball is forced into an object under specified load conditions. The diameter of the ball is dependent on the test piece's thickness. The hardness number is determined by measuring the depth and surface area of the impression and using a formula, which also incorporate the applied load.
Vickers
Vickers
Here a small square pyramid is forced into a test piece under specified load conditions; the hardness number is derived from a formula that contains the load and area of the indentation. More useful for thin metals than the Brinell test as the loads are lower and the indentor smaller.
Rockwell
Rockwell
This is a simple test that dispenses with the use of a formula. A diamond cone (or sphere) is forced into a test piece under specified load conditions and a reading is displayed on the dial. There are different scales for different loads depending on the material tested. Rockwell hardness testers are the most common hardness testers in schools as they used to be provided to NSW high schools.
Shore Scleroscope
Shore Scleroscope
This test involves a small striker in a tube. The tube is placed over an item and the striker is dropped, the height the striker rebounds from the item is a measure of the hardness. Soft items will absorb more of the energy of the falling striker giving a lower rebound than hard materials
Impact test
Impact test
Izod & Charpy Tests
Izod & Charpy Tests
The Izod and Charpy Tests are essentially the same except the test piece is held differently. The test involves a large pendulum being raised to a specified height to give it potential energy (PE). Upon release, it loses PE and gains kinetic energy (KE). At the bottom of its swing it will strike the test piece, with some KE absorbed in breaking the test piece. After passing the test piece, the pendulum will swing up in height gaining PE and losing KE, until all energy of swing is used up. The height reached is recorded. The difference between the initial height and the final height is proportional to the energy absorbed when breaking the test piece.
Hounsfield balanced impact tester
Hounsfield balanced impact tester
The Hounsfield balanced impact tester is smaller, and used for schools and colleges or in industry, as a transportable machine. It uses two pendulums, with one solid one swinging through the other hollow pendulum. The result is double the impact that would be had with a single pendulum, thus allowing a smaller tester. The energy required to break the material, is merely read from a scale on the pendulum pivot.
The test piece used in all these testers is a small cylinder with a V notch placed in it to concentrate the stress and provide a place to promote crack propagation. In the Hounsfield test, the notched piece is held in the solid pendulum, so the outer pendulum hits both ends. In the Izod test, the notched bar is held vertically, with the upper end free, ready to be struck by the pendulum. The notch is placed so it faces the pendulum. In the Charpy test, the notched bar is held horizontally at both ends. The pendulum strikes it in the middle, with the notch facing away from the pendulum.
Concept Check:
Concept Check:
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