Strength and Testing of Materials

Laboratory

ENGR 229 - 86

Fall 2013

Report # 3

Experiment: Compression

Dr. Mohamed Darwish

Mostafa Madkor900113463

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Table of ContentsAbstract....................................................................................................3

Introduction............................................................................................. 4

Objectives................................................................................................ 5

Theory......................................................................................................6

Procedures............................................................................................... 7

Equipment and specimens........................................................................7

i. Equipment.......................................................................................7A) Universal Testing Machines............................................................................................7

B) Vernier Caliper................................................................................................................9

Results....................................................................................................12

Cast iron........................................................................................12

Lead...............................................................................................15I. Without Grease.............................................................................................................15

II. With Grease..................................................................................................................16

Mechanical Properties of the Lead.................................................17

Conclusion..............................................................................................19

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Abstract

This experiment mainly aimed to study the study the properties of different

materials by conducting the compression test on them in order to know how each of the

material will behave under this condition. In this experiment three different materials

were tested. These materials are wood, Cast iron and Lead. The experiment starts at

measuring the initial for each of the materials. Each of these materials was tested using

the universal testing machine. Each of them was put between the two plates of the

machine then; a compressive force was applied to each of them. For the cast iron, the

compressive load was applied until the specimen broke while for the lead it was tested

under 750 kN (maximum compressive load) without grease firstly and then with grease

for another specimen. For the wood, the testing process was also done two times.

Firstly when the fiber is parallel to the plate of the machine and secondly when the

fibers are perpendicular to the plate of the machine. This is because wood is an isotropic

material which means that it acts differently in different orientations (directions). The

results of this experiment indicated that cast iron broke into two pieces with an angle of

45 degrees between them. The wood when it was tested in the perpendicular

orientation, the piece of the wood broke while when it was tested in the parallel

orientation, the piece of wood compressed the height of it decreased. For the lead, the

first test done on it indicated that when the specimen is tested without grease the

specimen compressed and it make a barreling shape while in the second the test which

was done with putting some grease between the specimen of lead and the plate, the

results showed a homogeneous compression without barreling in the shape. The

specimen after the test became tilted to a certain direction because the grease made

the specimen to move, so it was compressed with an inclination.

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Introduction

A compression test is a method for determining the behavior of materials under

a compressive load. Compression tests are conducted by loading the test specimen

between two plates and then applying a force to the specimen by moving the

crossheads together. A compressive force is applied so that the two ends of the

specimen are pushed together. The shape of the specimen used is a cylinder with the

restriction that its length-to-diameter ratio is less than 2 to avoid buckling. The

cylindrical specimen is pressed between flat platens so that no special grips are needed.

As the compressive load is increased, the length of the cylinder decreases while its

diameter increases. The compression test is used to determine elastic limit,

proportionality limit, yield point, yield strength and compressive strength.

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Objectives

1- Neatly plot the Engineering Stress vs. Engineering Strain Diagram for cast iron.

2- Determine the following Mechanical Properties for cast iron:

a. Elastic Strength;

b. Yield Strength;

c. Compressive Strength (σmax);

d. Modulus of Elasticity;

e. Modulus of Toughness;

f. Malleability (percentage change in length and area).

3- Determine the following Mechanical Properties for the other Specimens:

a. Compressive Strength (σmax);

b. Malleability. (not for wood)

4- Compare the malleability of the lead specimen with and without grease.

5- Compare the behavior of the wood specimen when the load is applied parallel

to its fibers.

6- Examine the Surface of Fracture for the tested Specimens (cast iron, lead with

Grease, lead without grease, wood with parallel load, and wood with

Perpendicular load) and Plot a schematic for their shape.

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Theory

This is the test performed to determine the strength of a material under

compression. Generally the compression test is carried out to know either simple

compression characteristics of material or column action of structural members. It has

been observed that for varying heights of members, keeping the cross sectional and the

load applied constant, there is an increased tendency towards bending of a member.

Members under compression usually bend along the minor axis, i.e, along least lateral

dimension. According to the column theory slenderness ratio has more functional value.

If this ratio goes on increasing, axial compressive stress goes on decreasing and the

member buckles more and more. End conditions at the time of test have a pronounced

effect on compressive strength of materials. The effective length must be taken

according to end conditions assumed, at the time of the test.

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Procedures

1. Measure the initial values of the specimens using the vernier caliper

2. Place the specimen in position between the compression pads.

3. Switch on the UTM

4. Remove the specimen and measure the final dimensions

5. Repeat the above steps on the other materials

6. In the case of the lead specimen, do the experiment with grease and without

grease

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Equipment and specimens

i. Equipment

A)Universal Testing Machines

1.

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Load cell

Movable cross-head

Two Plates

Test specimen

This machine is used for testing one the most significant mechanical properties

of the material which compression. It consists of a movable crosshead that moves along

the side frames. It also contains two plates in which the material specimen is positioned.

The lower plate is fixed while the upper plate is movable. There is also a load cell of

capacity 50 KN. This load cell provides an electrical circuit for measuring the

instantaneous load along the loading axis.

2.

This machine is the one that was used to test the greased and non-greased lead

Specimens. It contains two parallel plates that apply a force to compress the specimen.

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Load counter

Two Plates

Load Controller

On/Off arm

B)Vernier Caliper

Material Length (initial)(mm) Diameter (initial)(mm)

Lead without grease 20.1 12.1

Lead with grease 20.2 12

Cast Iron Specimen

Material Length (initial)(mm)

Diameter (initial)(mm)

Cast Iron 19.9 10.1

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Wood Specimen

Table (1) wood Dimensions

Orientation Height (initial)(mm)

Thickness (initial)(mm)

Width (initial)(mm)

parallel 46.2 45.1 45.2

Perpendicular

45.2 45.1 46.3

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Results

Cast iron

Material Final Length (mm) Final Diameter (mm)

Cast Iron 16 11

In this experiment, the compressive load was applied to the cast iron until it

broke suddenly. This showed

the difference between

the brittle and the ductile

material when they are

exposed to

compressive load. Cast iron which is a brittle material broke suddenly into two pieces.

The angle between these two pieces is 45 degrees while ductile material increases in its

diameter as we will discuss in the below lines for the lead.

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Load (KN) Compressive extension (mm)

Stress (MPa) Strain

0 0 0 010 0.15 125 0.0075420 0.25 250 0.0125630 0.5 374 0.0215340 0.6 499 0.0301550 0.95 624 0.0477460 1.4 749 0.0703565 1.75 811 0.0879470 2.2 874 0.1105575 4 936 0.20101

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0 0.05 0.1 0.15 0.2 0.250

100

200

300

400

500

600

700

800

900

1000

Strain

Stress Mpa

Requirements Values

Elastic strength 624 MPa

Yield Strength 750 MPa

Compressive strength 936 MPa

Modulus of elasticity 13.82 GPa

Modulus of toughness 147.45155 Mpa

Percent of change in length 19.598 %

Percent of change in area 18.6096 %

In this part of the experiment the specimen of wood was positioned parallel to the force of the machine. The fibers of the wood were parallel as shown in figure (8). The piece of wood

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broke as shown. This position make the specimen take more load and it keeps in taking loads also after part of it is fractured.

Table Requirements Values

Compressive Strength (maximum load/ area) 52 Mpa

In this part of the experiment, another specimen of wood was positioned between the two plates of the machine. But the fibers of the specimen were perpendicular to the force as shown in figure (9). The piece of wood compressed as shown and it has a fracture from the side. This orientation can’t take high loads and it seems from the results for the ultimate strength that the wood in parallel orientation is about 5 times the wood in perpendicular orientation.

Requirements Values

Compressive Strength (maximum load/ area) 6.6 Mpa

Lead In this experiment, lead was tested under two conditions; firstly with grease and

secondly without grease.

I. Without Grease

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The shape as shown in figure (11) has the barreling shape Figure (12). This shape

always happen because without using grease the molecules of the specimen are in

contact with plate and they can’t move so the molecules that are inside the specimen

are the only molecules moving under compression. These molecules always move to the

edges of the specimen and finally this shape occurs. The final result of this part indicated

that the area of the ductile material increase and the length will decrease.

Table (2) Lead without grease final dimensions

Material Diameter (final) (mm) Length (Final) (mm)

Lead without grease 15.5 12.4

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II. With Grease

The shape as shown in figure (13) has a compressed homogeneous shape as in

figure (14). This is because with grease the molecules are not in touch with the plate, so

they move freely and this shape happens. In figure (13) the shape seems to be tilted to

the right and this is because the grease causes a slight slipping between the plate and

the specimen so the specimen compression becomes tilted.

Table (3) Lead with grease final dimensions

Material Diameter (final) (mm) Length (Final) (mm)

Lead with grease 16.4 11.5

Mechanical Properties of the Lead

Requirements Lead without grease Lead with grease

Compressive strength 6.087 6.189

Percent change in Area 64.09 % 86.77 %

Percent change in length 38.31% 43.07 %

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Conclusion

Examining the effect of grease on the malleability of lead showed that when a

compressive load is applied on a lead specimen with grease the specimen has different

behavior compared to its behavior without grease under the same compressive load.

The grease applied on the specimen decreases the friction force between the specimen

and the machine surface. Accordingly, the surface layer will have more area to move

and deform. Also the use of grease on the specimen has resulted in decrease of

malleability. The specimen without grease did withstand more plastic deformation than

the one with grease. But here we have an error because the deformation in the

specimen without grease is much more than the one with grease. This error maybe that

the grease used was not enough, or the material was not pure, or their initial dimension

was not the same.

For the wood in this experiment, we find out that wood is composed of fibers on

top of each other. The two wooden blocks under compressive forces applied parallel

and perpendicular to the wood fibers, show different deformity behaviors. In the

perpendicular test the extension was far greater than the parallel test. Also the

perpendicular test showed that the wooden block needed very small load for the block

to deform compared to the parallel test.

For the cast iron in this experiment, due to the brittle nature of the cast iron

specimen it breaks at 45 degrees into two pieces after the machine reached a certain

load applied on it. In each of the two pieces broken, we found out that the surface are

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rough after breaking and this is due to the friction that the material experiences while

the forces are applied to break it.

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