This document reports on material tests and analysis conducted by a group to select the most appropriate material for a car body. The group performed tensile and bending tests on various materials and analyzed the results. Based on their findings from the tests and theoretical chapters studied, each group member independently selected the material they found most suitable for a car body and justified their choice.

1. Final report
DG205 – Material Behaviour
Assignor: Dr. Ir. F.L.M.Delbressine
January – March 2012
Eva Palaiologk s112775
Harm van Hoek s106804
Manual Suarez s118705
David E. Dass s110263

2. Table of Contents
Introduction .................................................................................................................................................. 3
Objective ....................................................................................................................................................... 4
Tensile Tests .................................................................................................................................................. 5
Results ....................................................................................................................................................... 5
Analysis ..................................................................................................................................................... 6
Bending Test ................................................................................................................................................. 7
Process ...................................................................................................................................................... 7
Results ....................................................................................................................................................... 9
Error Analysis .......................................................................................................................................... 11
90degree bending test ................................................................................................................................ 12
Studied part ................................................................................................................................................ 16
Chapter 5: Flex, sag and wobble stiffness-limited design. ...................................................................... 16
Chapter 10: Keeping it all together: fracture-limited design. ................................................................. 21
Bibliography ................................................................................................................................................ 24
Appendices.................................................................................................................................................. 25
Bending Tests .......................................................................................................................................... 25
Tensile Tests ............................................................................................................................................ 26
2

3. Introduction
This assignment report comprises the subsequent and structural steps towards selecting the most
appropriate car body material.
In the beginning of the report one is able to review the description of the chapters 5 and 10 from the
book ’Materials Engineering Science Processing and Design” (Michael Ashby, Hugh Shercliff and David
Cebon; 2007, Cambridge University UK ;), this was done as part of the research building activity.
After the description of the chapters, two tests, the tensile and the bending are performed and together
with their results it is possible to understand the behaviour of the materials given. With the two
different graphs that are outcome to the tests, certain conclusions are drawn about the mechanical
properties of the materials given.
To conclude this report, an in depth analysis and selection process of the most suitable car body is given
by each individual of the group. This is based on the knowledge gained from the 2 chapters of the book,
the tests that were conducted and analysed.
3

4. Objective
Within the first part of the assignment we were allocated a predefined set of metals namely; Industrial
Steel, Aluminium 99 Alloy, a precipitate hardened Aluminium, Brass along with an exotic material
known as Polycarbonate (PC).These materials then underwent two tests, a tensile and a bending test,
whose results are illustrated in the appendix of the report.
The main goal of this assignment is to be able as designers to select an appropriate material based on its
behaviour (mechanical properties) to conceptualize our ideas. To practice this aspect, we conducted the
tensile and bending tests of five different materials (St37, Al99, Al51ST, PC, Brass) and based on the
results as well as the CES Edupack database, selected an appropriate metal for a car body.
With the knowledge gained through this selection process as well as the theoretical overviews of the
elastic modulus, stress and strain the group was able to understand basic concepts of elastic
deformation, plastic deformation and failure of the fore mentioned materials and their mechanical
properties i.e., strength, toughness, stiffness and wear. In the following chapters, the tests and their
respective processes, their results and the conclusions are described.
4

5. Tensile Tests
The measurement results of the tensile test performed are displayed in the appendix.
Results
The graph and brief explanations of the tensile behaviours are as follows:
Tensile Test ( Stress against strain)
16000
14000
12000
10000
Standard Force (N)
Industrial Steel
8000 Aluminium
Brass
PC
6000
Al 51 st
4000
2000
0
0 10 20 30 40 50 60 70 80 90
Extension (mm)
5

6. Analysis
The aluminium alloy (combination of aluminium, silicon and magnesium that is precipitated to be
hardened) has a standard force of approximately 12000N, this is particularly high due to the molecular
bonding in metallic structure (lattice)(Neuss, 2010)1, and the magnesium and silicon in this case, filled up
vacant spaces in the lattice to therefore have this high yield strength. Its standard force before fracture
therefore was particularly high reaching an approximate 13000N.The length however on looking to the
x-axis was much less and at the force of 12336.69N it eventually cracked at exactly 10.67mm increment.
Finally this material is very tough of having a very high strain order of 13000N.
Aluminium 99 Alloy displayed tensile behaviours remarkably different to that of the aluminium 51 St
alloy. As one can notice on the graph the standard force is much lower, approximately at 3000N and its
tensile strength considerably lower being about 3250N. This metal had quite an increment in length
before cracking at a length of 28.611mm.
Industrial Steel displayed behaviours quite similar to the pure aluminium however its standard force was
approximately 12500N. Its tensile strength was approximately 12000N and it’s also showed quite a large
extension in length of 26.025mm. This is quite a tough material due to its high strain order of 12000N.
This exotic material had no similarities whatsoever towards the metal behaviours. It had a standard
force of approximately 2350N and a tensile stress of just under 2000N. This metal had an extension of
80.167mm before fracture, clearly a brittle material with having the strain so low.
The last material we did was brass, a combination of copper and zinc. This material had a very strange
final part, and showed a zigzag line before fracture on the graph, the reason still unknown (but possibly
due to the inter-molecular bonding). Brass had high standard force of approximately 14000N and tensile
strength of 12789N before fracture at a length of 39.9mm, proving to be quite a tough material.
From this tensile test it is possible to draw up certain conclusions.
If there is need for selection for tough material, it is important to notice its tensile strength i.e., the
strain order.
1
Neuss, Geoffery. Chemistry: IB Diploman Course Companion. Oxford: Oxford UP, 2010. Print
6

7. F
Bending Test F l3
l f in m
3 E I
f
F l3 N
h E in 2
3 f I m
b
b h3
F [N] f [mm] I in m 4
Elasticity limit 12
Inertia moment
Picture: Calculating the E-modulus
The measurement results of the bending test performed are displayed in the appendix.
Process
The following are steps that we followed to accomplish the bending test:
The first step of the bending test process was to decide which weights would be allocated and at
what increment would they be applied to the material
We then attached the ruler to a box to make sure that when reading the scale of the ruler it was
constant for all materials measured (see picture 1)
After this we measured the initial length (L0) of each material sample
Next with a G clamp and a block piece we clamped the edge of the material tested (picture 1)
The clamped area of the material tested was constant for all the material samples
Started to add different weights at steady increments of all the materials
The next step, was to measure the deflection of the material
This was repeated until the material experienced plastic deformation (in some cases this case
did not occur because of the lack of weights)
7

8. Picture 1: a) Illustrating the mounting of the ruler to the box b) Using a G clamp to hold the material
Picture 2: a) Weights added b) Measurement of deflection
8

9. Results
A graph illustrating Stress [N/m^2] against Strain
[-]
4E+10
3.5E+10
3E+10
2.5E+10
Stress (N/m^2)
St 37
Al 99
2E+10
PC
AL 51 St
1.5E+10 Brass 2mm
Brass 1mm
1E+10
5E+09
0
0 0.1 0.2 0.3 0.4 0.5 0.6
Strain (-)
9

10. From the graph above one can see that the largest gradient is that of St 37; this means that it has the
largest E-modulus compared to the rest of the materials.This can be explained due to the fact that St 37
or Low carbon Steel as it is called has the highest yield stress and the lowest plastic deformation. This is
then followed by Brass 2mm and the value is confirmed by the value in the table below.
After this the graphshould illustrate the E-modulus of Aluminium 51 ST or Al6082-T6 and then Al 99 (we
formulated a hypothesis that Al99 is almost pure Aluminium), which unfortunately cannot be seen in our
graph,this is due to the fact that for Al51st the weights that were applied were too large to start with
and the material sample deformed plastically already at 900 grams. On further discussion, we needed to
have started with low weights.
The most exotic material Polycarbonate displayed the smallest gradient which stayed true when we
compared this to the documented E-modulus.
Brass 1mm showed a large error. It is assumed that the thickness of the material does not affect the E-
modulus, in our graph it did. This may have been due to the positioning of the material when carrying
out the bending test and reading off the deflection. The g-clamp that was holding the material to the
table was not tightened tight and therefore the deflection was added. This was a human error as well as
other uncertainties (refer to error analysis)
Material Calculated E-modulus (Gpa) Actual E-modulus(Gpa)
[found in CES Edupack 2011]
St 37 (Low Carbon Steel) 132 200-215
Al 51 St ( Al 6082 –T6) 69.9 70 -74
Al 99 (Pure Aluminium) 63 69 -72
Brass (Wrought Copper: CuZn30) 114 90 -110
PC (Polycarbonate) 1.95 2 - 2.44
A table illustrating calculated values against documented values
10

11. Error Analysis
The uncertainties that occurred during the bending test were the following:
The ruler
The weight piece
The vision of the measurer
Picture 3: Vision of the measurer was an error
The perpendicularity of the ruler
The positioning of the weight
The positioning of the material when measuring the deflection
The amount of pressure while clamping the material
The value of the gravitational constant
In our opinion these were the most crucial uncertainties to be mentioned and may have largely
contributed to the values of shown on the graph; however there are many more errors that could have
contributed to the results.
11

12. 90degree bending test
As an added part to the bending test, we tried to bend the material to 90degrees with a force; this was
to notice which material bent to 90degrees and underwent plastic deformation and what effects this
had; below are the results and images.
Material Results
St 37 Maximum force needed to bend showing
High strength
Material does not bend back
Al 99 Not enough force to bend it
Very high strength
Material does not bend back
Al 51 St 5725 g of weight
Material bends back to 40degrees when force
is removed
Cracks appear in the material
PC Force used for 28 degrees plastic deformation
5340 g
Brass 1mm Force used for 90 degrees plastic deformation
ERROR of how much force was used
Brass 2mm Force used for 90 degrees plastic deformation
4890 g of weight used
No cracks / breaks
A table illustrating the 90degrees scale test
The results seen in the table above showed that St
37 and Al 99 needed a high amount of force to cause
plastic deformation, however Poly carbonate
underwent plastic deformation at 28 degrees and
not at 90 degrees, this was due to its lowest elastic
modulus as compared to the other 6 materials.
Picture 4: Tool for carrying 90degree testing
12

13. Picture 5 :Polycarbonate
Picture 6: Aluminium 99
13

14. Picture 7: Brass 1mm
Picture 8: Steel 37 2mm
14

15. Picture 9: Aluminium 51 ST
Picture 10: Brass 2mm
15

16. Studied part
Chapter 5: Flex, sag and wobble stiffness-limited design.
This chapter starts with the standard solutions to elastic problems in five different forms.
Standard solutions to elastic problems.
Elastic extension or compression.
In this example, a tensile or compressive stress ς applies to a tie. The stiffness S can be calculated with
S =F/δ,
With F being the load and δ the deflection.
2
(M. Ashby, 2007)
The stress is uniform over the whole section A, as can be seen in the graph on the right.
Elastic bending of beams.
For the bending of beams, the neutral axis becomes a curved axis. The lower part of the beam is loaded
in compression, where the top part is loaded in tension. At the neutral axis is the point where
compression changes into tension. This result is moment M
3
(M. Ashby, 2007)
2
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 83.
16

17. Torsion of shafts.
In the third example the torsion of shafts is described. Again, there is a neutral axis at which the stress is
neutral. Moving outward from this axis along the radial r, the shear stress increases, with the opposite
direction of r having a negative shear stress, working in the opposite direction.
4
(M. Ashby, 2007)
Buckling of columns and plate.
There is a critical load at which a column or plate will fail, which is Fcrit. This critical load can be calculated
with the following formula:
Fcrit = (n2π2EI) / L2
With L being the length of the column or plate, El the flexural rigidity and n the number of half
wavelengths of the object that is buckled. For instance, for the first situation in the picture below, n = ½ ,
because the shape shows a quarter wavelength.
3
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of Cambridge.
2007. First edition. p. 83.
4
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 83.
17

18. 5
(M. Ashby, 2007)
Vibrating beams and plates.
When a system is vibrating in one of its natural frequencies, it can be depicted as a mass m attachted to
a spring with stiffness k. The lowest natural frequency can be calculated with:
f = (1 / 2π) (k / m)1/2.
In the following picture you can see three situations with different end constraints and their lowest
natural frequencies. C2 is a constant depending on the end constraints.
(M. Ashby, 2007)
5
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 87.
18

19. Material indices for elastic design.
The next part of this chapter is about ranking based on objectives, which are criterion which must either
be minimized (like costs or weight) or maximized (such as energy storage). With this criterion, a list of
objectives can be made.
As an example, a panel must be constructed with the objective to be as light as possible, while the
deflection does not exceed δ under load F. The thickness h is free. h can be minimized in order to make
the panel lighter, but this goes at the cost of the deflection exceeding δ while under the load F.
The weight m of the panel can be calculated with
m=ALρ=bhLρ
Again, for the stiffness S can be calculated with
S =F/δ,
but this stiffness must be at least equal to S* in the formula:
S* = (C1EI) / L3
C1 is a constant which depends on the way that the force is distributed over the cross-section. The
height of the panel was free, but we can use the stiffness constraint to eliminate this undefined variable.
6
(M. Ashby, 2007)
Minimizing material cost
6
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 89.
19

20. When cost is the factor that must be minimized, C, the total material cost, is the result of:
C = mCm = ALCmρ
where Cm is the material price.
However, for a complete product, not only material costs, but also manufacturing costs for shaping,
joining and finishing the product must be made.
Plotting limits and indices on charts.
Screening: attribute limits on charts.
Other than constraints that certain designs imply, there are also constraints caused by materials
themselves. To make a selection of effective materials for a design, these limitations can be plotted on
the axes of a chart. By applying the requirements of the design, are window within the chart can be
formed, and all the materials within this window meet the constraints of the design. This is called
Screening. Then, a more detailed material selection can be made. This is called Ranking.
Ranking: indices on charts.
The next step in selecting the right material is choosing from the screened materials the one that will
offer maximum performance.
Computer-aided selection.
Because of the sheer number of material, selecting them by hand can be quite unpractical. Different
kinds of software are available to ease the process of selecting the right material. By entering limitations
for the material chose, it is possible to filter out all the materials that fall outside of these limits.
20

21. Chapter 10: Keeping it all together: fracture-limited design.
Standard solutions to fracture problems
Tensile stress intensity k1 caused by a crack depends on crack length, component geometry and the way
the component is loaded. Cracks will not expand if k1 is kept below the fracture toughness k1c of the
material of the structure.
7
We can manipulate geometry and points of pressure in a component design in order to avoid future
fractures. The non-destructive testing (NDT) to make sure there are no cracks which have wrong values,
this way we can choose materials with adequate fracture toughness.
7
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 205.
21

22. Material indices for fracture-safe design
Load limited design
Materials with highest values of fracture toughness k1c can support larger loads. If the fracture
toughness is below M1, it may fail in a brittle way if the stress exceeds.
8
Energy limited design
Examples of designs that are energy limited instead of load limited are springs and containment systems
for turbines and flywheels.
9
8
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 207.
9
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 207.
22

23. Displacement limited design.
Displacement limited designs must allow enough elastic displacement to allow flexure or snap-action
with no failure. Materials with large values of M3 are the best for displacement limited designs.
10
Case study
Forensic fracture mechanics: pressure vessels.
11
Pressure vessels’s purpose is to contain a gas under pressure. Their failure can mean a catastrophe.
A filled truck-mounted propane tank exploded when its driver left it in the sun with the engine running.
The tank’s longitudinal weld’s surface had a crack of 10 mm that was growing slowly by fatigue every
time it was emptied and refilled. This was the apparent cause of the failure. According to this, the
pressure needed to generate the explosion was 3,8MPa, while the safety limit was of 1,5 MPa.After
further tests, heat from the sun and from the exhaust system of the truck where proved as the cause of
the high temperature of the tank. This made the crack propagate by a pressure higher than 3,8 needed
for it to fail. In normal circumstances the crack would not have propagated.
10
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 207.
11
Ashby, M.; Shercliff, H.; Cebon, D. Materials Engineering, Science, Processing and Design. University of
Cambridge. 2007. First edition. p. 209.
23

24. Bibliography
Granta Design Limited. (2011). Edupack 2011. Cambridge, United Kingdom.
Houtzger, Overbeeke, & Vennix. (1999). Matbase. Retrieved March 11, 2012, from www.matbase.com.
M. Ashby, H. S. (2007). Materials, Engineering, Science, Processing and Design. London: Elsevier.
Neuss, G. (2010). Chemistry: IB Diploma Course Companion. Oxford: Oxford.
24

25. Appendices
Bending Tests
25

26. Tensile Tests
See C. Meesters Tensile Tests results
26