Material Formal Report
by: ebrahim
Total views: 54
Word Count: 2312
Abstract
This report is about structure properties in material. We conducted three different experiments to find about properties of materials and how do they change with certain changes in environment for instance change in temperature. When we conducted the tensile test we found ductility of the material, its strength points and other properties. The only error could be systematic from the machine as there was almost no involvement of human in the system, therefore the random error was zero.
In impact testing we found the impact resistivity of the material for different temperatures. By testing a PVC at different materials. It was found that as temperature increase, the impact resistivity of the material increases. Main source of error for this experiment was when we took the readings from the cantilever. There was a possibility of parallax error. And random error was made.
The last test we conducted was about the grain size for a same material after and before annealing. We found the grain size and using the provided picture found out the different properties about both. The error source in this experiment was when we had to count the number of the grains. Mistakes were inescapable. There fore large random error was made.
Introduction
Experiments that were done were the following ,Impact testing, Tensile test, and Grain size. From the results we get from these tests we are going to understand certain concepts. For example the relation between Grain size and ductility. Relation ship between impact resistance and tensile strength.
For Impact testing we will exert force on a PVC from side ways. That is we exert shear stress on the material and we will do it for different temperatures. In order to find the relationship between temperature and Impact resistance.
For tensile test we placed the metal in the tensile test machine.In order to find the properties of the mild steel rod. And also to understand ductility , Yield stress, tensile strength,etc.
Objective of the experiments
In impact testing the objective was to see the effect of temperature on properties of the material.
For tensile testing the objective was to observe the changes in properties of a material under continuous tensile stress and also to find the tensile strength, yield strength, etc.
For the grain size experiment objective was to learn how grain size is calculated.
Experimental Details
Method for Tensile Test
Necking Point
Diagram A
Marked Lines
Diagram B
For tensile test first we marked two lines(Diagram B) on the provided rod. We checked that the lines are at equal distance from centre of the rod using the Venire clipper. Then we measured the distance between the lines. The distance was 33.6mm. We also measured the diameter of the rod using (Vernier clipper meter)The diameter of the rod before test was 12mm. Then the lab demonstrator put the rod in the machine and didn’t let us use it. In the tensile test machine the two heads of the machine were pulled in opposite directions. This I realized because on the monitor there was a negative force and a positive force. As stress was being applied computer measured the strain and the stress and drew the graph for us. Machine pulled the rod until the rod failed(ie.fracture,broke into two pieces.)Then the graph drawn by computer was printed and given to us.
After that I put the metal rods together and measured the distance between the two previously marked lines. The distance was 40.9mm. Then I measured the diameter of the metal rod .The diameter of the metal rod after the test was 8.13mm.
Using the data collected in the lab and the printed stress-strain graph of the test I found other required values using the following formulas.
A=πr^2
E=□(σ/∊)
%EL=(Lf-Li)/Li*100
%RA=(Ai-Af)/Ai*100
Precautions For tensile Test
Do not place your hands near the grip of the Tensile testing machine.
Seek the help of the lab demonstrator and staff who are experienced.
Press the red stop button when something is wrong with the machine.
Error
The source of error in this experiment could be systematic error from the system, and there was no human error during the procedure. Nevertheless there was random error when I took the readings from the graph, It wasn’t precise as the graph wasn’t calibrated for smaller units.
Method for Impact testing
First we were introduced to the Impact testing machine. We put the red pointer down at zero. Then put up the hammer and lock it. First we test our PVC rod at room temperature. By putting the rod in the impact tester machine and releasing the hammer to swing. Then we record the final position of the pointer on the impact tester. We did the same thing for PVC at the temperature of 0℃ by putting the PVC in ice and for PVC at100 by putting the PVC at hot boiling water.
Energy spent to break the rod was calculated by the following
E=mg∂h
Percentage of total energy Cantilever was calculated by the following
Constant E0=mgh
%E=E/E0*100
Precautions
Students shouldn’t stand in front of the cantilever hammer in order to avoid any injuries.
Protective goggles must be worn to avoid the small flying pieces after the impact hit the eyes. Especially as the cantilever we were using had no protective glass door.
Error
When the reading is being taken there are some random errors, due to parallax error. In order to minimize this random error, the experiment must be repeated few times and different people should take the reading and the the average must be taken. However this error was very little as the cantilever was well calibrated.
Method for Grain Size
The picture of Extruded and recrystallized magnesium alloy AZ31 and extruded magnesium alloy Az31 was taken by computer and provided to us by lab demonstrator. I drew 10 squares of size of 1 inch length on the provided pictures of the Extruded and recrystallized magnesium alloy AZ31 and extruded magnesium alloy AZ31 .
First I counted the whole grains in the square and recorded the number in a table. Then I counted all the grains which weren’t completely in the square and then recorded in the table as a different variable. Then I divided the grains which weren’t fully in the square by two and then added to the full grain number. This can be demonstrated more frequently below:
A=Number of grains completely in the table
B= Number of grains not completely in the table
C=0.5 x B
N=Total Number of grain per square inch=A+C
N is the average number of grains per square inch at a magnification of 100X
This was repeated for 10 different squares and then the values were tabulated.
Using the following formula the grain size was measured.
n=logN/log2 +1
Pre caution
There was no precaution for this method as the lab process was done for us.
Error
As the squares were hand drawn, could be different sizes therefore the number of grains could be inaccurate. Errors could be made while counting the grains. However this error was minimized as you can see in the table below that 10 different readings were taken and then the average was taken.
Results and Analysis
For Tensile test
Yield Stress
The yield stress is the point of the stress where the rod is going into a plastic deformation. This stress level for this metal rod was measured to be 570 N
Tensile Strength
Tensile strength is the highest stress that the material can take. On the stress-strain graph it is the highest level of stress. From graph Tensile Strength was measured to be 640 MPa.
Young’s modulus
Young’s modulus is how much a material is strained with respect to the applied stress and it only applies when material is elastic. It is the slope of the stress-strain curve in the graph in the elastic region. The young modulus for our rod was calculated using the formula and the graph
E=□(σ/∊)=(570-0)/0.56=1018Nm^(-2)
Uniform Elongation
Uniform elongation is the total strain that can a graph achieve before necking. To find this point we look at the graph, it is the the strain from 0 to the point where there is ultimate stress. In the computer cross section area is taken to be constant but there is a necking point where by the cross sectional area reduces. Hence stress increases as the cross sectional area decreases and there fore the slope must be positive all the way through. But since the computer takes the same cross sectional area then it calculates that less force and hence stress is necessary to elongate the rod. This mistake in the graph lets us find the Uniform elongation. As we know when the slope changes sign, the cross sectional area has reduced and the rod has necked. We can find uniform elongation by taking the area from the point 0 to the point where it has necked.(i.e. Slope changed sign)
Cross Sectional Area
There was a reduction in cross sectional area due to slipping of the atom planes. The diameters were measured therefore the cross sectional area could be calculated.
A=πr^2
Ai=π〖〖(6*10〗^(-3))〗^2=1.13*〖10〗^(-4)
Af=π〖(4.1*〖10〗^(-3))〗^2=5.28*〖10〗^(-5)
The cross sectional area was reduced from Ai=1.13*〖10〗^(-4) to Af=5.28*〖10〗^(-5). The percentage change in cross sectional area was calculated also.
%RA=(Ai-Af)/Ai*100
%RA=(1.13*〖10〗^(-4) -5.28*〖10〗^(-5))/(1.13*〖10〗^(-4) )*100
%RA=53.2%
Therefore cross sectional area was changed by 53.2%
Ductility
“It is a measure of the degree of plastic deformation that has been sustained at fracture.” pg 147WilliamDcallister,Material Science and Engineering. In simple words ductility is how much a material can deform before it breaks. There are two ways articulate ductility quantitatively.
1.Ductility as percent elongation
%EL=(Lf-Li)/Li*100
∴ %EL=(40.9-33.6)/33.6*100
=21.7%
2.Ductility as percentage of reduction in Area(Pasted from last section)
%RA=(Ai-Af)/Ai*100*100
%RA=(1.13*〖10〗^(-4) -5.28*〖10〗^(-5))/(1.13*〖10〗^(-4) )*100
%RA=53.2%
Results and Analysis for Impact Testing
Sample Temperature(°C) Initial Height(m) Final Height(m) Energy(J) Energy Used(%)
Room Temperature 24 1.5 1.36 4.04 9.32
Hot Water 98 1.5 0.42 31.2 72.1
Ice Water 0 1.5 1.42 2.31 5.33
Diagram C
As it can be seen from the diagram b, it can be seen that more energy is required to break the rod. My analysis was that heat supplied to the rod makes the rod more ductile. And ductile are tougher and they absorb energy. Rise in temperature causes the grain size to increase, as the smaller grains join together. According to hall petch slope(Diagram 2) as grain size increases its yield stress decreases.ie.the material deforms more easily.
It was concluded that ductile materials are tougher as they can absorb more energy. More strain energy is required to induce ductile fracture inasmuch ductile materials are generally tougher.(pg 209,callister)
Results and Analysis for Grain Size
Data for Extruded and recrystallized magnesium alloy AZ31
Test No. No. of grains inside
Square(A) No.of grains Intersected
by the circumference C=Bx0.5 Total Number of
grains per square inch
1 21 15 7.5 28.5
2 12 15 7.5 19.5
3 24 18 9 33
4 27 26 13 40
5 19 11 5.5 24.5
6 21 14 7 28
7 19 13 6.5 25.5
8 17 13 6.5 23.5
9 27 16 8 35
10 19 17 8.5 27.5
Average number of grains per square inch 28.5
Diagram D
Data for Extruded magnesium alloy AZ31
Our N could be inaccurate due to human error.Therefore our n could be inaccurate as well. This problem could be solved by using a software to count the number of grains.Or this random error could be reduced by asking few people to do the experiment and then taking the average.
Discussion
The relation ship between grain size and yield stress can be seen on the hall petch formula.
Diagram E
From the graph above can be seen that how grain size affects the yield stress. As grain size decreases the yield stress increases. That is it can be deformed elastically more and it takes more stress to deform it.
Different materials have different Hall Petch slope. This slope indicates how much yield stress changes by the change in grain size. If the slope is very steep it shows that by little change in grain size the yield stress changes a lot. But if the hall Petch slope is very low and flat it shows that a large change in grain size wouldn’t make much or as much difference in yield stress of the material.
So if the hall petch slope is high and steep then it is worth it to use refining strategy for material but if the hall petch slope is low and flat then it is not worth it to use refining strategy as it wont make much difference.
Both impact resistance and tensile strength are dependent upon how brittle or ductile a material is. The more ductile the material the higher the impact resistance and higher the yield strength of the material. So these two quantities are directly proportional to ductility of the material.This is because when the grain size is increased the dislocation density in the material is lower therefore ductility is
If the Hall petch slope is high and then it is effective to anneal the material as it will increase the grain size and will increase its ductility, When it is more ductile it will go under plastic deformation for a longer time,during plastic deformation there is energy absorption, therefore more energy is needed to break the rod,hence we can conclude that annealing will increase the impact resistance of the material.
Conclusion and References
From Impact testing we conclude that the as temperature increases the impact resistance increases. As temperature increases the material becomes more ductile as grain size increases. When ductility increase the strength of the material increase. As plastic deformation absorbs energy.
From tensile test we learn about the properties of mild steel. We learn after material reaches yield stress that it will start deforming plastically and then when it reaches the maximum stress level,it will neck as shown in diagram A. and then it will break.
From grain size we learn how to calculate the grain size. And what is the microstructural changes during annealing. We learn that grains start to grow and dislocation density reduce which will make the material more ductile. We also see that grains are oriented in one direction and that’s another reason why it will become more ductile as stress is one direction and it is easier to deform rather than smaller grains which have border and bonds with many other grains.
References
William D.Callister
www.TheWritersOnline.com
(Read or Write Your Way to Big Success)
About the Author
William D.Callister
Rating: Not yet rated