Topic: ENGINEERING MATERIALS ,Practicals
PRACTICAL 2: EFFECT OF COLD WORKING ON MECHANICAL PROPERTIES
This practical should be read prior to your practical session.
ROOM, Rear Lab in Northern part of Mechanical Engineering Building M at mawson Lakes.
To investigate the influence of room temperature deformation on the mechanical properties of metals
A strip of copper had been previously softened (annealed) by heating in a furnace at 500°C for
1 hour (OS 100 temper, 100µm average grain size).
Measure the thickness and width of the strip and perform two Rockwell Hardness HRF tests using the Rockwell
Your staff supervisor will demonstrate and roll at room temperature (cold rolling) the annealed copper at
various stages to an initial reduction in thickness of between 1 and 2%.
If necessary front tension is maintained on the copper strip using pliers as the copper strip exits the rolls.
Between each pass the copper strip is inverted to assist in reducing the curling of the copper strip.
Once the initial target reduction of between 1 and 2% has been reached, record the precise thickness and
width of the sample on the results spreadsheet.
Then measure the Rockwell hardness of the sample and record the values on the supplied table.
Other samples will then be rolled in stages to achieve reduction in thickness of approximately 5,
10, 20, 30, 40 and 60%.
Measure the Rockwell hardness, in duplicate for each of the copper strips after each
of the chosen reduction stages. It is critical that each time hardness measurements
are taken, then the thickness and width of the strip is measured accurately and recorded.
All dimensions and hardness measurements should be recorded on the table supplied.
Information below is from ASM Handbook, volume 2, and is to be used so that published
data from literature can be plotted on the graph.
Description H Temper approx. % red. description H temper approx. % red.
in thickness in thickness
1/8 hard H00 spring hard H08 ????
1/4 hard H01 ???? extra spring hard H10 ????
1/2 hard H02 ???? special spring hard H12 ????
3/4 hard H03 ???? ultra spring hard H13
hard H04 ???? super spring hard H14 ????
extra hard H06 ????
Plot the results according to the instructions supplied in the Table Data Document supplied.
(a) What property must be exceeded for rolling to successfully change a materials shape? (4%)
Give the reason for your answer.
(b) How would you expect the grain structure of the copper to change during the rolling process.
(provide labelled sketches, giving the rolling direction, and give reference used)? (10%)
Mark the rolling direction on your sketches.
(c) Describe what is happening to the grains, grain boundaries and dislocations during the
cold rolling process. Note, the starting copper does not have porosity and therefore the
copper does not get denser nor do the atoms or grains get closer together. (4%)
(d) Investigate similar data for copper (eg C 11000) in literature and compare to practical results by
plotting on the graph. See instruction in the Data File.
In the box below comment on the results and trends. Are the results consistent with the expected
change in grain structure and dislocation behaviour?
Some references will describe cold working in terms of 1/4 hard, 1/2 hard, 3/4 hard, fully hard,
extra hard etc. Others may give it an H number such as H00, H01 etc.
Relate actual published hardness data, (with the same scale as the practical results), for the different levels
of reduction in thickness to the practical results. Annealed condition is one of the 0 temper
designations. Only consider copper and NOT copper alloys.
These should then be superimposed on the graph plot of the prac values.
Description approx. % Hardness Comments:
of Temper reduction Brinell
(e) By investigating published data for different levels of cold working suggest how the
reduction of thickness affects various mechanical and physical properties. (6%)
(f) What material property limits the amount of reduction possible, giving your reasons? (4%)
REFERENCES used in this practical, including full details. ASM Handbook, 10th Edition,
Volume 2, Properties and Selection of Non ferrous Alloys and Special Purpose Materials, R669 A512 is one
of many good references for properties (i.e. part for (d) above). The 9 edition is a similar reference. (12%)
part (b) & (c)