|
|
|
|
||
|
|
|
Introduction As a marble and granite fabricator it
was very advantageous to determine when a material would fail. Hopefully this determination could be made
prior to investing in a finished, polished piece. Failure of the material was often
catastrophic and befuddling. There was
a very strong motivation to anticipate these failures because although the
material was expensive the labor involved in finishing a piece was the
primary investment. As a fabricator
several rules of thumb developed.
Granite was much more consistent, reliable and stronger than
marble. Marbles might be very strong
in their primary composite, however, they almost always failed along their
veining. Granite was many times
stronger that granite ( I believed about ten times stronger, and it took 10
times the grit to polish: 220-600 grit
for marbles, whereas it was 3,000-5000 grit for granites). Dark stones also were stronger than lighter
stones. |
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
Objective The
goal of this research project, as a high school physics teacher, was to test
these pragmatic assumptions and to attempt to quantify the relative strengths
of marble and granite. I determined to
do a 3-point flexure test (known as modulus of rupture test, I chose seven
samples. I used tile because it was
pre-polished, regular and easily prepared for consistent samples and the 1 cm
thickness, I believed, was in the strength range that I could test with the
testing equipment available to me. I chose a white and black marble, the
whitest granite that I could find, an equally small grained pure black
granite, a larger grained white granite of apparently similar composition to
the light granite, a yellow marble that had significant white “inclusions”
that I expected would act as natural flaws and provide the weakest sample,
and as a last sample I chose a dark granite with obvious differences in
composition to test the further effect of different potential “grain”
boundaries. I cut all of the samples
out of single tiles so that there was a consistency of material. Thus the samples were all out of the same
batch and were located immediately adjacent to each other. Although the rift of the stone could not be
determined on such small samples, this method determined the rift of the
individual samples to all be the same and insured as much consistency among
naturally variable materials as possible.
The variability of natural stone was a huge aspect of this experiment
and it was my intention to limit that variability as much as possible. |
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
Background Stone is a naturally variable
material and it is classified as a brittle material. A brittle material is one that fractures
rather than deforms significantly under stress. In the material science text book, Elements
of Materials Science and Engineering, it indicates that “The ultimate
mechanical failure is fracture. We
commonly categorize fracture as being either ductile or brittle (i.e.
nonductile)…Brittle fracture requires energy to separate atoms and to expose
new surface along the fracture path.” ( Van Vlack, 1989) I tested the compressive and tensile
strength of the stone. Stone is known
to have a very high compressive strength.
Compressive strength is determined by putting a material under a load
which results in compressive stress on the material. A brittle material under compressive
strength deforms little and results in fracture when the tensile stress that
attempts to deform the material outward exceeds the molecular strength of the
material to maintain its structure.
This is associated with the angle of friction at which the materials
fail under compressive load. The
3-point flexure test supports the material at its ends and submits the sample
to the load in the middle. This causes
a compressive stress on the top and a tensile strength on the bottom of the
sample. Since stone has a much higher
compressive than tensile strength, the sample will fail much sooner in the
flexure test, and will fail from the bottom of the sample to the top. Marble is formed by a
metamorphic process. This means that
sedimentary or disintegrated material is put under pressure and heat by being
deeply buried under ground for a long period of time. The pressure and heat transform the
crystalline structure. The bonding
material, which is considerably weaker, gradually becomes a crystal structure
that increases in hardness and strength. Granite is an igneous
material, meaning that it is formed by magma or lava. The slower the lava cools the larger the
crystals that form. From experience
and from my research on flaw sizes, I believed that larger grained granites
would be weaker than smaller grained granites. Larger grains created the beginnings of
larger flaws that would more readily propagate in the various samples. For my samples I chose a
light and black marble and granite. In
the granites I chose small grained granites for consistency in these
samples. I also chose a large grained
white granite with similar coloration of the smaller grained light granite
for comparison. In the marble, instead
of a grain size I chose a black marble with pronounced white veining, which I
considered a natural flaw, and I chose a yellow marble which looked a lot
like a non-metamorphic travertine, which I thought with its variability would
be my weakest sample of all. Van Vlack, |
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
What will you Need? I did additional test,
including a Vickers hardness test, For the lab, the
students will conduct a 3-point flecture test (modulus of rupture, modified For both tests the
students will need :
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
Procedures: 3-Point Flexure Test
– SAFETY FIRST!!! 1.
Set up the
frame and 3-point apparatus 2.
Make sure
that the apparatus and sample are centered 3.
Place the
safety shield in front of the frame (in between you and the frame) 4.
Slowly
engage the hydraulic piston until it is almost touching the sample 5.
Begin
videoing the gauge 6.
Slowly pump
up the pressure 7.
Stop
applying the pressure when the sample fails (there wil be an abrupt drop in
pressure- a dramatic failure!) 8.
Rewind the
viedo and record the maximum pressure on the gauge 9.
Release the
pressure 10. Remove the safely shield 11. Draw a picture of the sample as it is after the
failure. 12. Remove the sample 13. Repeat step 1-12 for each sample Compression Test-
SAFETY FIRST!!! The procedure for the
compression test is the same as for the 3 point flexure test escept for step
1:
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
Lesson Plans Introductory Set: Stone has been utilized as a building
material for thousands of years. There
are many reasons that stone has been used so pervasively, but for our
purposes today we would like to concern ourselves with the properties of
strength that make stone such a good building material. When we talk about strength in stone we are
referring to the materials ability to withstand applied forces. The applied forces, in our case called
load, result in compression and tensile stresses. Compression stresses are forces that push
materials together and tensile stresses are forces that tear materials
apart. In the next few days we will be
considering and testing both compression and tensile stresses on different
types of stone. For our purposes we
will be considering two different types of stone: marbles and granites. Marbles are a metamorphic material
resulting from materials being formed under heat and pressure from being
buried under ground for a long period of time. Granites, which often have a speckled
appearance, are called igneous and are the result of lava cooling at
different rates. What we would like to
find out is, How strong are marbles and granites relative to each other and
to different samples of the same type?
And How much variability is there in the strength of these natural
materials due to natural variability? So our goal is to
determine the relative strength of 7 different samples of stone: 3 marbles
and 4 granites. In the end as a class
we will attempt to answer the questions, Are marbles or granites stronger?
And can we ascertain from a particular sample whether it will be able to
sustain a greater load than another sample of a different stone or even the
same stone? Given this analysis we
will attempt to discuss what variability among natural materials means within
a scientific experiment and how we can design a lab so that we can address
this variability. So now let’s get out our
lab notebooks and begin testing! Using
the scientific method make a hypothesis about which of the seven samples you
believe will be the strongest and why.
Also answer the question whether the strength of the materials will be
the same under compression and under the 3-point tensile test. Which test do you suspect will result in
higher load strengths? Now we are ready to
begin. You will conduct compression
and tensile strength tests.
Compression tests apply stresses that force a material together,
whereas tensile stresses pull a material apart. In stone, do you expect the strength to be
greater in compression or tension? Let’s find out! Begin the procedure for the 3-point flexure
test. Then complete the compression
test. Carefully document all of your
results including your drawings. Begin conducting the
lab. Safety First! If you have any questions ask the teacher
and document all of your questions and findings. When the Lab is
completed… Share your data with the
class. This will give us a larger data
set. How does this help address the
natural variability of our samples. What
did you find? Write up a lab report
about your findings. Make graphs of
your findings. What conclusions can you draw about the relative strengths of
the different stones? Are you
convinced that your findings are accurate?
How would you continue this laboratory exploration? Educational Standards Used and/ or Met Content Standard A:
Science As Inquiry A1: Abilities necessary
to do scientific inquiry:
A2: Understanding about
scientific inquiry:
Content Standard B:
Physical Science B2: Structure and
properties of matter Content Standard G:
Science as Inquiry G1. Science as a human
endeavor:
G2. Nature of scientific
knowledge
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
Lesson Plans Introductory Set: Stone has been utilized as a building
material for thousands of years. There
are many reasons that stone has been used so pervasively, but for our
purposes today we would like to concern ourselves with the properties of
strength that make stone such a good building material. When we talk about strength in stone we are
referring to the materials ability to withstand applied forces. The applied forces, in our case called
load, result in compression and tensile stresses. Compression stresses are forces that push
materials together and tensile stresses are forces that tear materials
apart. In the next few days we will be
considering and testing both compression and tensile stresses on different
types of stone. For our purposes we
will be considering two different types of stone: marbles and granites. Marbles are a metamorphic material
resulting from materials being formed under heat and pressure from being
buried under ground for a long period of time. Granites, which often have a speckled
appearance, are called igneous and are the result of lava cooling at
different rates. What we would like to
find out is, How strong are marbles and granites relative to each other and
to different samples of the same type?
And How much variability is there in the strength of these natural
materials due to natural variability? So our goal is to
determine the relative strength of 7 different samples of stone: 3 marbles
and 4 granites. In the end as a class
we will attempt to answer the questions, Are marbles or granites stronger?
And can we ascertain from a particular sample whether it will be able to
sustain a greater load than another sample of a different stone or even the
same stone? Given this analysis we
will attempt to discuss what variability among natural materials means within
a scientific experiment and how we can design a lab so that we can address
this variability. So now let’s get out our
lab notebooks and begin testing! Using
the scientific method make a hypothesis about which of the seven samples you
believe will be the strongest and why.
Also answer the question whether the strength of the materials will be
the same under compression and under the 3-point tensile test. Which test do you suspect will result in
higher load strengths? Now we are ready to
begin. You will conduct compression
and tensile strength tests. Compression
tests apply stresses that force a material together, whereas tensile stresses
pull a material apart. In stone, do
you expect the strength to be greater in compression or tension? Let’s find out! Begin the procedure for the 3-point flexure
test. Then complete the compression
test. Carefully document all of your
results including your drawings. Begin conducting the
lab. Safety First! If you have any questions ask the teacher
and document all of your questions and findings. When the Lab is completed… Share your data with the
class. This will give us a larger data
set. How does this help address the
natural variability of our samples. What
did you find? Write up a lab report
about your findings. Make graphs of
your findings. What conclusions can you draw about the relative strengths of
the different stones? Are you
convinced that your findings are accurate?
How would you continue this laboratory exploration? EDUCATIONAL STANDARDS USED and / or Content Standard A: Science As Inquiry A1: Abilities necessary
to do scientific inquiry:
A2: Understanding about scientific inquiry:
Content Standard B:
Physical Science B2: Structure and properties of matter Content Standard G:
Science as Inquiry G1. Science as a human endeavor:
G2. Nature of scientific knowledge
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
||||||||||||||||||||||||||||||||||||||
|
|
|
Other Data- Experimental Results Blkgrn 3386.5 3114.1 3284.5 ubtgrn 1098 1085.9 569.13 whtgrn 750.33 853.69 782.6 Whtgrnlg 488.59 775.83 595.97 blkmrb 1926.1 1783.9 1214.7 Whtmrb 617.45 546.31 702.01 Ylwmrb 1562.4 1681.9 1864.4
ylwmrb 19060 31548 19308 blkmrb 18888 8500 15792 blkgrn 14342 32656 32108 lgwhtgrn 7000 20704 17800 whtgrn 9000 6636 8560 whtmrb 6818 5980 7005 ubtgrn 6528 7500 8560
|
|
||||||||||||||||||||||||||||||||||||||
|
|
|
|
|
||||||||||||||||||||||||||||||||||||||
|
|
|
||||||||||||||||||||||||||||||||||||||||
