微信客服：xiaoxionga100
微信客服：ITCS521
S2098367-无代写
时间：2023-03-10
Materials 2 Lab Report
s2098367 - Yuqing Sun
1
Materials 2 - Wind Turbine Design Lab Report
S2098367 - Yuqing Sun
1. Introduction
This lab is aimed to obtain the properties of each available material (Steel,
Aluminium, 3D-printed PLA, Nylon, Concrete, Gypsum, Timber) by testing
the tensile and compressive strengths and observing the microstructure of
the material. These data were used to select suitable materials for the
turbine towers and foundations of onshore wind turbines that meet Yield
stress > 100 MPa and Yield stress > 20 MPa respectively.
2. Mechanical properties
By performing tensile and compression tests on materials, we use measuring equipment to
record length changes and force changes. We can use these data[1] to calculate strain vs. stress
by:
0
0
A
F
Stress
L
L
Strain
We can plot the stress-strain relationship and analyse the properties of the material by key
features on the graph.
By looking at the data we can see that the stress-strain for each material does not start at (0, 0).
This is probably due to the fact that the Force was not adjusted to 0N when the measuring
instrument was initialised. In addition, when plotting the graph, the front of the graph appears to
have a very small slope. This may be because the measuring device did not fit perfectly to the
experimental target. When the experiment started, this gap caused a smaller rate of stress
growth to appear at the front.
To solve this problem, we identified the 'perfect fit points' and calibrated all the data in the table
(by subtracting the coordinates of the perfect fit points) to ensure that the data started at (0, 0)
and did not have an unexpectedly low slope.
(Figure 2: Original graph and fixed graph)
(Figure 1: Illustration of an onshore wind turbine)[1]
Materials 2 Lab Report
s2098367 - Yuqing Sun
2
Firstly, by plotting the tensile stress-strain relationship for aluminium, we can get:
(Graph 1: stress-strain curve for Aluminium tensile specimen)
From Graph 1, we can see that the strain in aluminium is linear at 0 < stress < 1.1544% and
arcuate at stress > 1.1544%. In this case, there is an accelerated decline when stress > 13.1470%.
Therefore, we determine that yield stress occurs around strain = 1.1544% and also breaks at
approximately σy = 13.1470%.
As aluminium is not brittle[3], we need to move the trend line of the linear part of Graph 1
rightwards by 0.2% and find the intersection point , which will be the 0.2% offset yield point. By
plotting the linear prediction line at 1.358%0.2% offset prediction line with it, and define the 0.2% offset yield point:
342.608
%349.1
331.82 + 799.76 =
59.639 - 29819 =
2.0
2.0
2.02.0
2.02.0
For Graph 1, the closest data is (1.349%, 342.608). Therefore, the 0.2% offset yield point of
aluminium is defined at stress = 342.608 when strain = 1.349%. Yield Stress σ0.2 ≈ 342.608.
On the other hand, we need to find the predicted break point by translating the break point 0.2%
to the left in Graph 1. By calculating the strain of the predicted break point, we can obtain the
elongation of aluminium.
Materials 2 Lab Report
s2098367 - Yuqing Sun
3
For Graph 1, we observed that there’s a sharp decrease at strain = 13.147%. Therefore, the
elongation can be calculated by:
%947.12 predictionoffset 0.2%
0.2%-13.147% predictionoffset 0.2%
13.147%
L L
when
, %100
1
01
00
01
elongation
elongation
strainelongation
LLL
L
L
strain
L
LL
elongation
：
Therefore, the 0.2% offset prediction elongation of aluminium is 12.947%.
Moreover, we can identify the ultimate strength by finding the maximum stress. For Graph 1, we
can write:
Mpa 3103.373
6
4
1.10555
f
2
f
0
max
f
N
A
F
Thus, the ultimate strength of aluminium is 373.3103 MPa.
Then we can calculate the reduction in area by using the equation:
%639.48
9
7523.13
%100
6
4
6
4
3.4
4
%100
2
22
0
01
A
AA
Thus, the reduction in area of aluminium is 46.639%.
In the same way, we can calculate the yield stress, ultimate stress, elongation and reduction in
area for the other two sets of tensile tests (steel and 3D printed PLA) separately.
Materials 2 Lab Report
s2098367 - Yuqing Sun
4
Similarly, by plotting the compression stress-strain relationship for Wood, we can get:
(Graph 2: stress-strain curve for Wood compression specimen)
From Graph 2, we can see that the strain in wood is linear at 0 < stress < 1.9277% and arcuate at
stress > 1.9277%. In this case, there is an accelerated decline when stress > 25.5597%. Therefore,
we determine that yield stress occurs around strain = 1.9277% and also breaks at approximately
σy = 25.5597%.
Also, as wood is not brittle, we need to move the trend line of the linear part of Graph 2
rightwards by 0.2% and find the intersection point , which will be the 0.2% offset yield point:
1301.37
%197.2
64.279 + 277.86 =
7.225 - 3612.4 =
2.0
2.0
2.02.0
2.02.0
For Graph 2, the closest data is (2.197%, 73.1301). Therefore, the 0.2% offset yield point of wood
is defined at stress = 73.1301 when strain = 2.197%. Yield Stress σ0.2 ≈ 73.1301.
On the other hand, we need to find the predicted break point by translating the break point 0.2%
to the left in Graph 2. By calculating the strain of the predicted break point, we can obtain the
elongation of wood.
For Graph 2, we observed that there’s a sharp decrease at strain = 25.5597%. Therefore, the
elongation can be calculated by:
%3597.52 predictionoffset 0.2%
0.2%-%5597.52 predictionoffset 0.2%
%5597.52
elongation
elongation
strainelongation
Materials 2 Lab Report
s2098367 - Yuqing Sun
5
Therefore, the 0.2% offset prediction elongation of wood is 25.3597%.
Moreover, we can identify the ultimate strength by finding the maximum stress. For Graph 2, we
can write:
Mpa 759.80
9.10
4
9.7535
f
2
f
0
max
f
N
A
F
Thus, the ultimate strength of wood is 80.759 MPa.
Then we can calculate the reduction in area by using the equation:
%275.25
%100
9.10
4
9.10
4
2.12
4
%100
2
22
0
01
A
AA
Thus, the reduction in area of wood is 25.275%.
In the same way, we can calculate the yield stress and ultimate stress for the other three sets of
compression tests (Concrete, Gypsum and Nylon) separately. We don’t need to calculate the
elongation and reduction in area for compression group.
Then, after repeating the calculations, we summarise the data in the following table:
(Table 1: Summarise of Data)
Materials 2 Lab Report
s2098367 - Yuqing Sun
6
If we plotting the results obtained from all the tensile tests together, we get：
(Graph 3: stress-strain curve for all the tensile specimen)
In tensile tests, we tested 3D printed PLA, aluminium and steel. By looking at Graph 3, we can see
that:
3D printed PLA:
The data obtained from the tensile test of the 3D printed PLA material is linear. And by looking at
it we can see that the ultimate stress and the yield stress of PLA are the same (26.5400 MPa).
This means that the PLA material will fracture as soon as the yield stress is reached.
Aluminium and Steel:
The yield stresses of aluminium and steel are very close, at 342.608 MPa and 338.608 MPa
respectively. (a difference of only 1.30%) Also, the stress-strain relationship between aluminium
and steel is very similar before the yield stress is reached. After the yield stress is reached, the
stress in aluminium shows a slow increase until the ultimate stress (373.3103 MPa) is reached
and then starts to decrease. By contrast, the stress in steel shows a short drop before it starts to
rise slowly in an arc. The ultimate stress of steel occurs at 453.1566 MPa, which is 21.4% higher
than that of aluminium. In terms of elongation figures, steel has a significantly higher elongation
of 26.783%, which is 13.813% higher than aluminium. This means that steel can be stretched
longer without breaking.
Materials 2 Lab Report
s2098367 - Yuqing Sun
7
If we plotting the results obtained from all the compression tests together, we get：
(Graph 4: stress-strain curve for all the compression specimen)
By looking at Graph 4, it is obvious that concrete and gypsum have the lowest yield and ultimate
stresses coMPared to wood and nylon. However, they have the lowest strain, which means that
they are hard and resistant to deformation.
Concrete and gypsum.
CoMPared to gypsum, concrete has a higher yield stress (37.758 MPa) but a lower ultimate stress
(46.796 MPa). This means that concrete can withstand less load than gypsum. On the other hand,
gypsum can withstand a maximum stress of 55.096 MPa, which means it can withstand greater
loads. However, its too small yield stress (9.49 MPa) means that it starts to deform faster at
smaller loads, which is not suitable for jobs that require smaller deflections.
Nylon and wood:
CoMPared to wood, the lower yield stress of nylon (60.890 MPa) represents an earlier onset of
deformation. At the same time, its ultimate stress (244.684 MPa) is significantly higher than that
of wood (80.759 MPa), which means that higher loads can be carried by nylon. Based on the
stress-strain data for nylon shows in Graph 4, we can see that the stress in nylon shows a slow
and accelerating rise trend after yielding. This means that Nylon will bend and yield before it
Materials 2 Lab Report
s2098367 - Yuqing Sun
8
breaks. This is a long process, not instantaneous. In contrast, the difference between the yield
and ultimate stresses in wood is very small (only about 9.6%) and the stresses in wood begin to
show an arc of accelerated decline after the yield stress is reached. This means that wood is
easier to break but harder than nylon.
Thus, through analysis we can know that:
·CoMPared to aluminium and steel, PLA has the lowest yield and ultimate stresses. In addition,
there was not significantly elongated before fracture.
· CoMPared to steel, Aluminium has a slightly higher yield stress. However, aluminium can
withstand lower ultimate stresses and the elongation is almost half that of steel.
·Steel has the highest ultimate stress and is the material with the highest elongation of the three
materials.
·Concrete is the hardest (less deformable) of all the materials involved in the compression test,
but it is also the material with the lowest ultimate stress. It is more suitable for work requiring
less deformation.
·Gypsum has the lowest yield stress, but can withstand higher ultimate stresses.
·CoMPared to wood, nylon can contain higher load, but softer. It is not suitable for work that
requires high precision.
3. Fracture sketches
Aluminium
(Figure 3: Fracture Sketches of Aluminium)
Aluminium becomes smaller in cross-sectional area and longer in length as it is stretched.
After fracture, the fracture surface is inclined, creased and not smooth. There are some
cracks on the fracture surface due to uneven forces. Horizontal stretching patterns can be
seen in the stretched section, which may be due to multiple fracture surfaces occurring
during the stretching process.
Materials 2 Lab Report
s2098367 - Yuqing Sun
9
3D printed PLA
(Figure 4: Fracture Sketches of PLA)
The PLA is barely deformed during the stretching process and the mere 0.05 mm length
variation is indistinguishable. the fracture surface of the PLA is spirally patterned, probably
because the 3D printing technology has enabled the PLA interior to be covered with layers
and layers of spiral structures. The layered structure makes the PLA easy to break, with the
fracture at the centre being the strongest part of this structure.
Wood
(Figure 5: Fracture Sketches of Wood)
In the compression test of the wood we can clearly see the grain of the wood fibres all over
the cracks of the wood. As Wood is a porous and fibrous structural tissue [4], the fracture
surfaces are longitudinal and straight, as the fibre structure is not damaged. Due to the
softness of the wood, a large number of cracks appear when it is compressed.
Materials 2 Lab Report
s2098367 - Yuqing Sun
10
Nylon
(Figure 6: Fracture Sketches of Nylon)
During the compression of the nylon, we can clearly see that the nylon is compressed and
grows in diameter. However, the nylon does not break but is strongly plastically deformed.
After compression, the surface of the nylon is smooth. We presume that since moisture has a
plasticizing effect on nylons that increases flexibility and iMPact resistance [5], this nylon
cylinder should be moist.
Concrete
(Figure 7: Fracture Sketches of Concrete)
As concrete is a ceramic, it is very brittle and hard. In the experiments, the cement barely
deforms, but breaks into several irregular fragments the moment the ultimate stress is
reached. The fracture surface is very uneven and covered with a mixture of different
materials. There are some small pores inside, which may have contributed to the uneven
stresses.
Materials 2 Lab Report
s2098367 - Yuqing Sun
11
Gypsum
(Figure 8: Fracture Sketches of Gypsum)
Plaster is also a ceramic and as such it is also fragile. Its fractured surface is full of large air
pockets and cracks and has an uneven surface. This may be the result of uneven forces. The
excessive porosity makes it difficult for the plaster to withstand excessive stresses, but it also
provides greater scope for elastic deformation.
Steel
(Figure 9: Fracture Sketches of Steel)
Steel stretches much like aluminium, becoming longer in length and smaller in diameter. However,
steel stretches without folds, probably because the forces between the steel molecules are
greater, making it difficult to produce deformation. In addition, the fracture surface of steel is
very rough and horizontal stretching cracks can be seen on the sides.
Materials 2 Lab Report
s2098367 - Yuqing Sun
12
Tensile test
Aluminium and steel fracture very similarly, both having a rough fracture surface, increased
length and reduced cross-sectional area. The difference, however, is that the fracture surface of
steel is not folded and is not inclined. This is probably due to the fact that steel has greater
hardness and stronger molecular interactions. This makes it difficult for the steel to deform
significantly during tension.
PLA materials, which have very low ultimate stresses, are also the most susceptible to fracture.
This is not only because it is not a metal, but also because of its layered structure.
Compression test
Concrete and plaster have the lowest ultimate stresses, but they are the hardest. The difference
is that plaster has a greater elastic deformation due to its more porous nature.
The fibrous structure of wood causes it to be softer and easier to break than nylon. The plastic
deformation of nylon, on the other hand, makes it less prone to fracture and instead produces
deformations of great magnitude.
4. Materials selection
When choosing materials for the towers and
foundations of wind turbines, we should first
consider the scenario of the application. By
analysing the forces on the wind turbine during
operation we find that the foundations are
primarily responsible for supporting the heavy
wind turbine tower and therefore need to be
strong and resistant to compression. On the
other hand, the wind generates lateral forces
that subject the wind turbine tower to a
moment and generate a tensile force.
Therefore, the material of the tower needs to
be very resistant to tensile forces.
#The assumptions of this experiment ignore
the tensile forces acting on the foundations
due to the tilt of the tower.
If we look at the material requirements, we can see that the Wind turbine tower material
requires Yield stress > 100 MPa, while the Foundation material requires Yield stress > 20 MPa. we
therefore filter out the materials that meet the requirements as follows:
Wind turbine tower (Tensile):
• Aluminium (342.6 MPa)
• Steel (338.2 MPa)
Foundation (Compression):
• Concrete (37.8 MPa)
• Wood (73.7 MPa)
• Nylon (60.9 MPa)
(Figure 10: FBD Sketches of Wind Turbine)
Materials 2 Lab Report
s2098367 - Yuqing Sun
13
We can choose the right material for Tower by comparing the different properties of Aluminium
and Steel:
Name of
material
yield stress ultimate stress elongation (%) reduction in area (%)
σy (Mpa) σult (Mpa) δL / L0 δA / A0
Aluminium 342.608 373.3103 12.947% 48.639%
Steel 338.208 453.1566 26.783% 65.972%
(Table 2: Compare Tensile Material options for Tower)
For wind power towers, the most important property when selecting materials is the
ultimate stress. This not only represents greater tensile resistance, but also symbolises greater
durability. In addition to this, a higher elongation is also an important indicator, as this indicates
that the material will not break over a wider range.
In table 2, we can clearly see that the properties of steel are much higher than those of
aluminium, with the exception of yield stress. 453.16 MPa of ultimate stress represents a higher
tensile strength, and wind towers made from this material can withstand greater wind resistance.
At the same time, the higher elongation (26.783%, almost 2.2 times that of aluminium) and
cross-sectional area variation represent greater scope for deformation and are less likely to break.
At the same time, the yield stress of aluminium is only 4.4 MPa higher than that of steel, which is
almost negligible. Therefore, steel is the perfect choice of material for the tower.
Similarly, we can use a table to compare wood, nylon and concrete for material of foundation:
Name of material
yield stress ultimate stress Reduction in length (%)
σy (Mpa) σult (Mpa) δL / L0
Concrete 37.758 46.7963 0.357%
Wood 73.660 80.7592 32.197%
Nylon 60.890 244.6843 60.011%
(Table 3: Compare Compression Material options for Foundation)
For the foundations of wind power towers, the most important material property is the
pressure resistance, as this is the criterion by which the weight of the foundation is considered. A
higher pressure resistance means that it can withstand more weight, making the foundation
stronger. However, length variation is also an essential property of foundation materials.
Excessive length variation can lead to a shift in the centre of gravity and tipping, which can be
disastrous for wind power towers. In addition, excessive length variation can lead to significant
rocking, which can affect the efficiency of wind power generation. Therefore, foundations require
a material with minimal variation in length.
Looking at the table 3 of data from the compression tests, we find that wood has the highest
yield stress (73.660 MPa), which means that it has the highest resistance to compression. In
addition, nylon has the highest ultimate stress (244.684 MPa), which means that it can withstand
the greatest force before breaking. However, for both nylon and wood, they have too much
variation in length, 32% and 60% respectively. For a large and heavy wind turbine tower, such a
large deformation could lead to a terrible collapse. When too much deformation causes the wind
turbine tower to tilt at too large an angle, the shifted centre of gravity causes the tensile forces
acting on the foundations to increase rapidly and directly leads to the fracture of the foundations.
For this reason, we have chosen to use concrete for the foundations with a deflection of only
Materials 2 Lab Report
s2098367 - Yuqing Sun
14
0.357%. This is because it not only makes the tower more stable, but also minimises the wind
turbulence and ensures a stable power output.
In addition to the data covered in this experiment, there are many important indicators for
the choice of materials for the tower and foundations.
Wind power towers:
1. they need to be easy to manufacture. This is because the fan blades of wind turbine towers are
complex and twisted in shape. Materials that are difficult to shape can lead to increased
construction costs. (e.g. wood)
2. Light weight. Due to the high heights required for wind turbines, wind power towers are
commonly around 70 metres. Lighter materials reduce weight and wear and tear on the
foundations. In addition to this, lighter materials have less inertia and can easily be driven by
the wind, increasing the efficiency of power generation.
Foundations.
1. Apart from the properties of the foundation, the most important property of the material used
for the foundation is that it is heavy, as a heavy foundation ensures the stability of the wind
power tower.
2. Non-corrosiveness is also an important property. As a foundation, durability and ease of
maintenance allow the foundation to provide better support for the wind turbine tower. The
lack of damage also reduces the cost of wind power generation.
Even though other materials are not used in this report, they have a lot of scope for application in
other areas.
Nylon: can be drawn to fibers as fine as silk, and was widely used as a substitute for it.
Gypsum:When mixed with water it rehydrates and sets to a hard, white solid. It is used to make
molds and casts for ceramics and sculptures, to make pre-cast ornamental plasterwork on ceilings
and cornices, and for orthopedic bandages or casts.
Aluminium: light and tough, a structural material used in the manufacture of aircraft, rockets and
cars.
Wood: readily available, easy to work with and widely used as a material for agricultural tools.
PLA: its biodegradability makes it the recyclable material of choice and is used in areas such as
making video packaging.
For other applicable materials, two alloys
were selected, Cast Al-alloys and Tungsten
alloys, both of which have in common the
characteristics of exhibiting adapted or
higher performance at both high and low
temperatures, high tensile strength and
very low cost. The difference is that
Tungsten alloys are relatively slightly more
expensive but have higher tensile strength.
(Graph 5: Materials suitable for Wind Turbine Tower)
Materials 2 Lab Report
s2098367 - Yuqing Sun
15
5. Conclusion
Tensile and compressive strength tests were carried out on seven different materials to obtain
the properties of the different materials and to serve as a reference for the selection of materials
for the construction of wind turbines. A comprehensive analysis of yield stress, ultimate stress,
elongation, area change and length change led to the selection of steel as the material for the
wind turbine tower and concrete as the material for the foundation. In this experiment, I
understood the process of material selection and the measurement of properties such as yield
stress of different materials.
6. References
1. Materials 2 Laboratory Handout, version 1.1, University of Edinburgh, 2022.
2. What it's like to use PLA biodegradable straws, Nanjing Jieyang Straw Machine, 2021, Baidu.
https://baijiahao.baidu.com/s?id=1711020262038165015&wfr=spider&for=pc
3. Is aluminium brittle?, Jim Bandstra, 2020, quora.
https://www.quora.com/Is-aluminium-brittle#:~:text=Pure%20aluminum%20is%20not%20b
rittle,are%20harder%20to%20slide%20along.
4. Wood, Wikipedia, 2021.
https://en.wikipedia.org/wiki/Wood#:~:text=Wood%20is%20a%20porous%20and,trees%20
and%20other%20woody%20plants.
5. Drying Nylon, Plastics Auxiliaries, 1999, Tidewater Publications Services, Inc.
http://cometpe.com/html/pr_nylon.htm
6. World’s Largest Wind Turbine Would Be Taller Than the Empire State Building, Annie Sneed,
2017, Scientific American.
https://www.scientificamerican.com/article/world-rsquo-s-largest-wind-turbine-would-be-t
aller-than-the-empire-state-building/
s2098367 - Yuqing Sun
1
Materials 2 - Wind Turbine Design Lab Report
S2098367 - Yuqing Sun
1. Introduction
This lab is aimed to obtain the properties of each available material (Steel,
Aluminium, 3D-printed PLA, Nylon, Concrete, Gypsum, Timber) by testing
the tensile and compressive strengths and observing the microstructure of
the material. These data were used to select suitable materials for the
turbine towers and foundations of onshore wind turbines that meet Yield
stress > 100 MPa and Yield stress > 20 MPa respectively.
2. Mechanical properties
By performing tensile and compression tests on materials, we use measuring equipment to
record length changes and force changes. We can use these data[1] to calculate strain vs. stress
by:
0
0
A
F
Stress
L
L
Strain
We can plot the stress-strain relationship and analyse the properties of the material by key
features on the graph.
By looking at the data we can see that the stress-strain for each material does not start at (0, 0).
This is probably due to the fact that the Force was not adjusted to 0N when the measuring
instrument was initialised. In addition, when plotting the graph, the front of the graph appears to
have a very small slope. This may be because the measuring device did not fit perfectly to the
experimental target. When the experiment started, this gap caused a smaller rate of stress
growth to appear at the front.
To solve this problem, we identified the 'perfect fit points' and calibrated all the data in the table
(by subtracting the coordinates of the perfect fit points) to ensure that the data started at (0, 0)
and did not have an unexpectedly low slope.
(Figure 2: Original graph and fixed graph)
(Figure 1: Illustration of an onshore wind turbine)[1]
Materials 2 Lab Report
s2098367 - Yuqing Sun
2
Firstly, by plotting the tensile stress-strain relationship for aluminium, we can get:
(Graph 1: stress-strain curve for Aluminium tensile specimen)
From Graph 1, we can see that the strain in aluminium is linear at 0 < stress < 1.1544% and
arcuate at stress > 1.1544%. In this case, there is an accelerated decline when stress > 13.1470%.
Therefore, we determine that yield stress occurs around strain = 1.1544% and also breaks at
approximately σy = 13.1470%.
As aluminium is not brittle[3], we need to move the trend line of the linear part of Graph 1
rightwards by 0.2% and find the intersection point , which will be the 0.2% offset yield point. By
plotting the linear prediction line at 1.358%
342.608
%349.1
331.82 + 799.76 =
59.639 - 29819 =
2.0
2.0
2.02.0
2.02.0
For Graph 1, the closest data is (1.349%, 342.608). Therefore, the 0.2% offset yield point of
aluminium is defined at stress = 342.608 when strain = 1.349%. Yield Stress σ0.2 ≈ 342.608.
On the other hand, we need to find the predicted break point by translating the break point 0.2%
to the left in Graph 1. By calculating the strain of the predicted break point, we can obtain the
elongation of aluminium.
Materials 2 Lab Report
s2098367 - Yuqing Sun
3
For Graph 1, we observed that there’s a sharp decrease at strain = 13.147%. Therefore, the
elongation can be calculated by:
%947.12 predictionoffset 0.2%
0.2%-13.147% predictionoffset 0.2%
13.147%
L L
when
, %100
1
01
00
01
elongation
elongation
strainelongation
LLL
L
L
strain
L
LL
elongation
：
Therefore, the 0.2% offset prediction elongation of aluminium is 12.947%.
Moreover, we can identify the ultimate strength by finding the maximum stress. For Graph 1, we
can write:
Mpa 3103.373
6
4
1.10555
f
2
f
0
max
f
N
A
F
Thus, the ultimate strength of aluminium is 373.3103 MPa.
Then we can calculate the reduction in area by using the equation:
%639.48
9
7523.13
%100
6
4
6
4
3.4
4
%100
2
22
0
01
A
AA
Thus, the reduction in area of aluminium is 46.639%.
In the same way, we can calculate the yield stress, ultimate stress, elongation and reduction in
area for the other two sets of tensile tests (steel and 3D printed PLA) separately.
Materials 2 Lab Report
s2098367 - Yuqing Sun
4
Similarly, by plotting the compression stress-strain relationship for Wood, we can get:
(Graph 2: stress-strain curve for Wood compression specimen)
From Graph 2, we can see that the strain in wood is linear at 0 < stress < 1.9277% and arcuate at
stress > 1.9277%. In this case, there is an accelerated decline when stress > 25.5597%. Therefore,
we determine that yield stress occurs around strain = 1.9277% and also breaks at approximately
σy = 25.5597%.
Also, as wood is not brittle, we need to move the trend line of the linear part of Graph 2
rightwards by 0.2% and find the intersection point , which will be the 0.2% offset yield point:
1301.37
%197.2
64.279 + 277.86 =
7.225 - 3612.4 =
2.0
2.0
2.02.0
2.02.0
For Graph 2, the closest data is (2.197%, 73.1301). Therefore, the 0.2% offset yield point of wood
is defined at stress = 73.1301 when strain = 2.197%. Yield Stress σ0.2 ≈ 73.1301.
On the other hand, we need to find the predicted break point by translating the break point 0.2%
to the left in Graph 2. By calculating the strain of the predicted break point, we can obtain the
elongation of wood.
For Graph 2, we observed that there’s a sharp decrease at strain = 25.5597%. Therefore, the
elongation can be calculated by:
%3597.52 predictionoffset 0.2%
0.2%-%5597.52 predictionoffset 0.2%
%5597.52
elongation
elongation
strainelongation
Materials 2 Lab Report
s2098367 - Yuqing Sun
5
Therefore, the 0.2% offset prediction elongation of wood is 25.3597%.
Moreover, we can identify the ultimate strength by finding the maximum stress. For Graph 2, we
can write:
Mpa 759.80
9.10
4
9.7535
f
2
f
0
max
f
N
A
F
Thus, the ultimate strength of wood is 80.759 MPa.
Then we can calculate the reduction in area by using the equation:
%275.25
%100
9.10
4
9.10
4
2.12
4
%100
2
22
0
01
A
AA
Thus, the reduction in area of wood is 25.275%.
In the same way, we can calculate the yield stress and ultimate stress for the other three sets of
compression tests (Concrete, Gypsum and Nylon) separately. We don’t need to calculate the
elongation and reduction in area for compression group.
Then, after repeating the calculations, we summarise the data in the following table:
(Table 1: Summarise of Data)
Materials 2 Lab Report
s2098367 - Yuqing Sun
6
If we plotting the results obtained from all the tensile tests together, we get：
(Graph 3: stress-strain curve for all the tensile specimen)
In tensile tests, we tested 3D printed PLA, aluminium and steel. By looking at Graph 3, we can see
that:
3D printed PLA:
The data obtained from the tensile test of the 3D printed PLA material is linear. And by looking at
it we can see that the ultimate stress and the yield stress of PLA are the same (26.5400 MPa).
This means that the PLA material will fracture as soon as the yield stress is reached.
Aluminium and Steel:
The yield stresses of aluminium and steel are very close, at 342.608 MPa and 338.608 MPa
respectively. (a difference of only 1.30%) Also, the stress-strain relationship between aluminium
and steel is very similar before the yield stress is reached. After the yield stress is reached, the
stress in aluminium shows a slow increase until the ultimate stress (373.3103 MPa) is reached
and then starts to decrease. By contrast, the stress in steel shows a short drop before it starts to
rise slowly in an arc. The ultimate stress of steel occurs at 453.1566 MPa, which is 21.4% higher
than that of aluminium. In terms of elongation figures, steel has a significantly higher elongation
of 26.783%, which is 13.813% higher than aluminium. This means that steel can be stretched
longer without breaking.
Materials 2 Lab Report
s2098367 - Yuqing Sun
7
If we plotting the results obtained from all the compression tests together, we get：
(Graph 4: stress-strain curve for all the compression specimen)
By looking at Graph 4, it is obvious that concrete and gypsum have the lowest yield and ultimate
stresses coMPared to wood and nylon. However, they have the lowest strain, which means that
they are hard and resistant to deformation.
Concrete and gypsum.
CoMPared to gypsum, concrete has a higher yield stress (37.758 MPa) but a lower ultimate stress
(46.796 MPa). This means that concrete can withstand less load than gypsum. On the other hand,
gypsum can withstand a maximum stress of 55.096 MPa, which means it can withstand greater
loads. However, its too small yield stress (9.49 MPa) means that it starts to deform faster at
smaller loads, which is not suitable for jobs that require smaller deflections.
Nylon and wood:
CoMPared to wood, the lower yield stress of nylon (60.890 MPa) represents an earlier onset of
deformation. At the same time, its ultimate stress (244.684 MPa) is significantly higher than that
of wood (80.759 MPa), which means that higher loads can be carried by nylon. Based on the
stress-strain data for nylon shows in Graph 4, we can see that the stress in nylon shows a slow
and accelerating rise trend after yielding. This means that Nylon will bend and yield before it
Materials 2 Lab Report
s2098367 - Yuqing Sun
8
breaks. This is a long process, not instantaneous. In contrast, the difference between the yield
and ultimate stresses in wood is very small (only about 9.6%) and the stresses in wood begin to
show an arc of accelerated decline after the yield stress is reached. This means that wood is
easier to break but harder than nylon.
Thus, through analysis we can know that:
·CoMPared to aluminium and steel, PLA has the lowest yield and ultimate stresses. In addition,
there was not significantly elongated before fracture.
· CoMPared to steel, Aluminium has a slightly higher yield stress. However, aluminium can
withstand lower ultimate stresses and the elongation is almost half that of steel.
·Steel has the highest ultimate stress and is the material with the highest elongation of the three
materials.
·Concrete is the hardest (less deformable) of all the materials involved in the compression test,
but it is also the material with the lowest ultimate stress. It is more suitable for work requiring
less deformation.
·Gypsum has the lowest yield stress, but can withstand higher ultimate stresses.
·CoMPared to wood, nylon can contain higher load, but softer. It is not suitable for work that
requires high precision.
3. Fracture sketches
Aluminium
(Figure 3: Fracture Sketches of Aluminium)
Aluminium becomes smaller in cross-sectional area and longer in length as it is stretched.
After fracture, the fracture surface is inclined, creased and not smooth. There are some
cracks on the fracture surface due to uneven forces. Horizontal stretching patterns can be
seen in the stretched section, which may be due to multiple fracture surfaces occurring
during the stretching process.
Materials 2 Lab Report
s2098367 - Yuqing Sun
9
3D printed PLA
(Figure 4: Fracture Sketches of PLA)
The PLA is barely deformed during the stretching process and the mere 0.05 mm length
variation is indistinguishable. the fracture surface of the PLA is spirally patterned, probably
because the 3D printing technology has enabled the PLA interior to be covered with layers
and layers of spiral structures. The layered structure makes the PLA easy to break, with the
fracture at the centre being the strongest part of this structure.
Wood
(Figure 5: Fracture Sketches of Wood)
In the compression test of the wood we can clearly see the grain of the wood fibres all over
the cracks of the wood. As Wood is a porous and fibrous structural tissue [4], the fracture
surfaces are longitudinal and straight, as the fibre structure is not damaged. Due to the
softness of the wood, a large number of cracks appear when it is compressed.
Materials 2 Lab Report
s2098367 - Yuqing Sun
10
Nylon
(Figure 6: Fracture Sketches of Nylon)
During the compression of the nylon, we can clearly see that the nylon is compressed and
grows in diameter. However, the nylon does not break but is strongly plastically deformed.
After compression, the surface of the nylon is smooth. We presume that since moisture has a
plasticizing effect on nylons that increases flexibility and iMPact resistance [5], this nylon
cylinder should be moist.
Concrete
(Figure 7: Fracture Sketches of Concrete)
As concrete is a ceramic, it is very brittle and hard. In the experiments, the cement barely
deforms, but breaks into several irregular fragments the moment the ultimate stress is
reached. The fracture surface is very uneven and covered with a mixture of different
materials. There are some small pores inside, which may have contributed to the uneven
stresses.
Materials 2 Lab Report
s2098367 - Yuqing Sun
11
Gypsum
(Figure 8: Fracture Sketches of Gypsum)
Plaster is also a ceramic and as such it is also fragile. Its fractured surface is full of large air
pockets and cracks and has an uneven surface. This may be the result of uneven forces. The
excessive porosity makes it difficult for the plaster to withstand excessive stresses, but it also
provides greater scope for elastic deformation.
Steel
(Figure 9: Fracture Sketches of Steel)
Steel stretches much like aluminium, becoming longer in length and smaller in diameter. However,
steel stretches without folds, probably because the forces between the steel molecules are
greater, making it difficult to produce deformation. In addition, the fracture surface of steel is
very rough and horizontal stretching cracks can be seen on the sides.
Materials 2 Lab Report
s2098367 - Yuqing Sun
12
Tensile test
Aluminium and steel fracture very similarly, both having a rough fracture surface, increased
length and reduced cross-sectional area. The difference, however, is that the fracture surface of
steel is not folded and is not inclined. This is probably due to the fact that steel has greater
hardness and stronger molecular interactions. This makes it difficult for the steel to deform
significantly during tension.
PLA materials, which have very low ultimate stresses, are also the most susceptible to fracture.
This is not only because it is not a metal, but also because of its layered structure.
Compression test
Concrete and plaster have the lowest ultimate stresses, but they are the hardest. The difference
is that plaster has a greater elastic deformation due to its more porous nature.
The fibrous structure of wood causes it to be softer and easier to break than nylon. The plastic
deformation of nylon, on the other hand, makes it less prone to fracture and instead produces
deformations of great magnitude.
4. Materials selection
When choosing materials for the towers and
foundations of wind turbines, we should first
consider the scenario of the application. By
analysing the forces on the wind turbine during
operation we find that the foundations are
primarily responsible for supporting the heavy
wind turbine tower and therefore need to be
strong and resistant to compression. On the
other hand, the wind generates lateral forces
that subject the wind turbine tower to a
moment and generate a tensile force.
Therefore, the material of the tower needs to
be very resistant to tensile forces.
#The assumptions of this experiment ignore
the tensile forces acting on the foundations
due to the tilt of the tower.
If we look at the material requirements, we can see that the Wind turbine tower material
requires Yield stress > 100 MPa, while the Foundation material requires Yield stress > 20 MPa. we
therefore filter out the materials that meet the requirements as follows:
Wind turbine tower (Tensile):
• Aluminium (342.6 MPa)
• Steel (338.2 MPa)
Foundation (Compression):
• Concrete (37.8 MPa)
• Wood (73.7 MPa)
• Nylon (60.9 MPa)
(Figure 10: FBD Sketches of Wind Turbine)
Materials 2 Lab Report
s2098367 - Yuqing Sun
13
We can choose the right material for Tower by comparing the different properties of Aluminium
and Steel:
Name of
material
yield stress ultimate stress elongation (%) reduction in area (%)
σy (Mpa) σult (Mpa) δL / L0 δA / A0
Aluminium 342.608 373.3103 12.947% 48.639%
Steel 338.208 453.1566 26.783% 65.972%
(Table 2: Compare Tensile Material options for Tower)
For wind power towers, the most important property when selecting materials is the
ultimate stress. This not only represents greater tensile resistance, but also symbolises greater
durability. In addition to this, a higher elongation is also an important indicator, as this indicates
that the material will not break over a wider range.
In table 2, we can clearly see that the properties of steel are much higher than those of
aluminium, with the exception of yield stress. 453.16 MPa of ultimate stress represents a higher
tensile strength, and wind towers made from this material can withstand greater wind resistance.
At the same time, the higher elongation (26.783%, almost 2.2 times that of aluminium) and
cross-sectional area variation represent greater scope for deformation and are less likely to break.
At the same time, the yield stress of aluminium is only 4.4 MPa higher than that of steel, which is
almost negligible. Therefore, steel is the perfect choice of material for the tower.
Similarly, we can use a table to compare wood, nylon and concrete for material of foundation:
Name of material
yield stress ultimate stress Reduction in length (%)
σy (Mpa) σult (Mpa) δL / L0
Concrete 37.758 46.7963 0.357%
Wood 73.660 80.7592 32.197%
Nylon 60.890 244.6843 60.011%
(Table 3: Compare Compression Material options for Foundation)
For the foundations of wind power towers, the most important material property is the
pressure resistance, as this is the criterion by which the weight of the foundation is considered. A
higher pressure resistance means that it can withstand more weight, making the foundation
stronger. However, length variation is also an essential property of foundation materials.
Excessive length variation can lead to a shift in the centre of gravity and tipping, which can be
disastrous for wind power towers. In addition, excessive length variation can lead to significant
rocking, which can affect the efficiency of wind power generation. Therefore, foundations require
a material with minimal variation in length.
Looking at the table 3 of data from the compression tests, we find that wood has the highest
yield stress (73.660 MPa), which means that it has the highest resistance to compression. In
addition, nylon has the highest ultimate stress (244.684 MPa), which means that it can withstand
the greatest force before breaking. However, for both nylon and wood, they have too much
variation in length, 32% and 60% respectively. For a large and heavy wind turbine tower, such a
large deformation could lead to a terrible collapse. When too much deformation causes the wind
turbine tower to tilt at too large an angle, the shifted centre of gravity causes the tensile forces
acting on the foundations to increase rapidly and directly leads to the fracture of the foundations.
For this reason, we have chosen to use concrete for the foundations with a deflection of only
Materials 2 Lab Report
s2098367 - Yuqing Sun
14
0.357%. This is because it not only makes the tower more stable, but also minimises the wind
turbulence and ensures a stable power output.
In addition to the data covered in this experiment, there are many important indicators for
the choice of materials for the tower and foundations.
Wind power towers:
1. they need to be easy to manufacture. This is because the fan blades of wind turbine towers are
complex and twisted in shape. Materials that are difficult to shape can lead to increased
construction costs. (e.g. wood)
2. Light weight. Due to the high heights required for wind turbines, wind power towers are
commonly around 70 metres. Lighter materials reduce weight and wear and tear on the
foundations. In addition to this, lighter materials have less inertia and can easily be driven by
the wind, increasing the efficiency of power generation.
Foundations.
1. Apart from the properties of the foundation, the most important property of the material used
for the foundation is that it is heavy, as a heavy foundation ensures the stability of the wind
power tower.
2. Non-corrosiveness is also an important property. As a foundation, durability and ease of
maintenance allow the foundation to provide better support for the wind turbine tower. The
lack of damage also reduces the cost of wind power generation.
Even though other materials are not used in this report, they have a lot of scope for application in
other areas.
Nylon: can be drawn to fibers as fine as silk, and was widely used as a substitute for it.
Gypsum:When mixed with water it rehydrates and sets to a hard, white solid. It is used to make
molds and casts for ceramics and sculptures, to make pre-cast ornamental plasterwork on ceilings
and cornices, and for orthopedic bandages or casts.
Aluminium: light and tough, a structural material used in the manufacture of aircraft, rockets and
cars.
Wood: readily available, easy to work with and widely used as a material for agricultural tools.
PLA: its biodegradability makes it the recyclable material of choice and is used in areas such as
making video packaging.
For other applicable materials, two alloys
were selected, Cast Al-alloys and Tungsten
alloys, both of which have in common the
characteristics of exhibiting adapted or
higher performance at both high and low
temperatures, high tensile strength and
very low cost. The difference is that
Tungsten alloys are relatively slightly more
expensive but have higher tensile strength.
(Graph 5: Materials suitable for Wind Turbine Tower)
Materials 2 Lab Report
s2098367 - Yuqing Sun
15
5. Conclusion
Tensile and compressive strength tests were carried out on seven different materials to obtain
the properties of the different materials and to serve as a reference for the selection of materials
for the construction of wind turbines. A comprehensive analysis of yield stress, ultimate stress,
elongation, area change and length change led to the selection of steel as the material for the
wind turbine tower and concrete as the material for the foundation. In this experiment, I
understood the process of material selection and the measurement of properties such as yield
stress of different materials.
6. References
1. Materials 2 Laboratory Handout, version 1.1, University of Edinburgh, 2022.
2. What it's like to use PLA biodegradable straws, Nanjing Jieyang Straw Machine, 2021, Baidu.
https://baijiahao.baidu.com/s?id=1711020262038165015&wfr=spider&for=pc
3. Is aluminium brittle?, Jim Bandstra, 2020, quora.
https://www.quora.com/Is-aluminium-brittle#:~:text=Pure%20aluminum%20is%20not%20b
rittle,are%20harder%20to%20slide%20along.
4. Wood, Wikipedia, 2021.
https://en.wikipedia.org/wiki/Wood#:~:text=Wood%20is%20a%20porous%20and,trees%20
and%20other%20woody%20plants.
5. Drying Nylon, Plastics Auxiliaries, 1999, Tidewater Publications Services, Inc.
http://cometpe.com/html/pr_nylon.htm
6. World’s Largest Wind Turbine Would Be Taller Than the Empire State Building, Annie Sneed,
2017, Scientific American.
https://www.scientificamerican.com/article/world-rsquo-s-largest-wind-turbine-would-be-t
aller-than-the-empire-state-building/
