Reference no: EM133046520
Task Description
Brittle Fracture
Analyse and understand the cause of materials failures
Introduction.
Fracture is a common cause of failure in metals. Whilst it will occur when a metal is stressed beyond its tensile strength under certain conditions it will also occur at stresses below the elastic limit.
Some metals may creep over long periods of time (particularly at high temperatures) until fracture occurs, whilst fracture which is the result of repeated cyclic stress is termed fatigue failure. Furthermore, some metals may fail by a form of brittle fracture (which is influenced by low temperatures) and other will fail due to ductile failure.
Object:
To investigate notched bar impact tests on metals over a range of temperatures to determine their susceptibility to brittle fracture.
Impact testing can be used to the investigate fracture characteristics of metals. Typically samples will tested through a range of temperatures and the energy absorbed during testing used to determine the fracture toughness of the material. Using a Hounsfield balanced impact tester the following data was gathered.
|
Temperature of sample during testing ( C )
|
Impact value (J)
Aluminium
|
Impact value (J)
Copper
|
Impact value (J)
Mild Steel (0.1% C)
|
|
-200
|
6.1
|
17.6
|
1.1
|
|
-100
|
|
|
4.1
|
|
-50
|
|
|
6.8
|
|
-20
|
|
|
54.9
|
|
0
|
|
|
55.3
|
|
21
|
7.1
|
18.0
|
58.3
|
|
50
|
|
|
54.2
|
|
100
|
6.6
|
15.9
|
54.5
|
Plot a graph of Impact value against temperature for each metal.
Identify with metal(s) that exhibit a ductile/brittle transition temperature. Explain the importance of the ductile/brittle transition temperature and discuss what factors affect the result at which the temperature occurs.
Using the graphs estimate the per cent crystalline fracture appearance at each test temperature as well as the level of plastic deformation.
Discussion of results.
Explain the important differences between ductile and brittle impact failures.
Identify the type of fractures which occur in the metal tested and co-relate that to the testing temperature.
Discuss the significance of your results.
What other factors may influence the transition temperature in the affected metal? Heat treatment and mechanical working?
Illustrate your report with relevant examples.
Attachment:- Brittle Fracture.rar