?

Plot the engineering stress versus engineering strain graphs in the low strain (<1%) region to

determine Young’s Modulus (E), 0.1% proof stress and

strain at yield.

Note that a linear regression

line can be created easily in Excel for the elastic region by

creating an additional column of strain

values and adding the offset (0.001). By c

licking on the

new

line and selecting the linear fit option

thi

s will produce a regression line

.

The option to display

the regression equation

will provide you

with the slope (E).

?

Plot the engineering stress versus engineering strain and true stress versus engineering strain graphs

from zero strain up to failure.

?

De

termine the ultimate tensile strength, fracture stress

,

ductility

and work to fracture

.

?

Determine the relationship between Vickers hardness and Yield Strength

?

= x (VHN) g.

?

Examine the fracture surfaces and describe the fracture process.

?

Use

CES Edupack (

available in the Mechanical Engineering 5

th

floor cluster under

Programs/Mechanical/ CES Edupack )

to determine which material you have tested for A, B, C

and

discuss your results vs what was expected from the database

.

Deliverables:

–

Each student should p

roduce a

brief but concise

laboratory report

containing an abstract, introduction,

materials and methods, results, discussion and conclusion. Your report should include

results of using

the Materials Selector Database

(CES Edupack)

a

s a means to determine

which materials were used in

the study (A, B, C)

based on their appearance,

fracture

behaviour, and mechanical properties of your

experimental laboratory

.

Introduce all background material

initially

in the Introduction

of your report

.

The

mater

ials and

methods should be as brief as possible

. Y

o

u can include this laboratory procedure in

an appendix and refer to it in your materials and met

hods to keep this section brief. Also include a

brief description of the

on

–

line

Materials

Selector

Database

(CES E

dupack)

.

The

two

required graphs

for each material

in the Results section

are:

(a)

Engineering stress versus engineering strain up to yield.

(b)

Engineering stress versus engineering strain and true stress versus

engineering

strain from the

start up to fra

cture.

These may be presented together in a single figure.

The laboratory report accounts for

1

0

% of the overall module mark.

EXPERIMENTAL METHOD

Follow instructions carefully

–

ask for assistance when you do not understand!

Important Safety Notice:

?

Forc

es may reach in excess of 50kN

–

5Tonnes. Keep your hands clear of the machine

when the load is being applied.

?

Keep clear of the machine. The door is not a safety guard; it is only to stop

d

ebris.

?

Ensure you wear safety glasses at all times.

?

Keep the d

oor closed when the test is running.

?

Following every measurement interval, ensure the door is closed before you continue the

test.

?

If you need to stop the machine in an emergency, press the red stop switch.

Tensile test

protocol

:

1)

Familiarise yourself w

ith the software and the logos below:

Console settings

–

Here, you can reduce the jog speed of the cross head, or return it to

normal

Strain 1 settings

–

the settings for strain gauge, where you can calibrate or balance the

strain gauge.

Load cell

settings

–

The load cell is calibrated and balanced here. You do not need to

do this during this exercise, as it will be done prior to testing for you.

Crosshead settings

–

To balance or set limits on the crosshead. You do not need to do

this during t

his exercise, as it will be done prior to testing for you.

2)

On Bluehill’s first page

(see image below)

,

three boxes display the current status of the machine.

The far left box shows the extension, which needs to be zeroed before start of test. The load i

s

shown in the middle box, and the strain is shown on the right hand side.

click on

Test

.

Laboratory Notes

–

Read after you have completed the lab

In the first part of the lab you measured the initial diameter and the overall gage length. You

measured engineering strain, vs applied load in the elastic region. You then removed the strain gage.

–

from this you can calculate the eng stress, eng strain. Strain was measured directly by the strain

gage; when you removed it this goes to zero or negative, ignore this. You can plot eng stress v eng

strain and solve for the elastic modulus and the yiel

d strength (use a proof str

ess if needed).

In the second part of the lab the machine recorded the deformation. You measured the change in

diameter and load as necking occurred. You measured the final load and final area and final length.

–

you can est

imate the eng stress, eng strain, true stress, true strain. Stress is force/ area, strain is

the change in length / original length. This is an estimate as the change in length used to calculate

strain is measured by crosshead deformation in this part (s

train gage was already removed, ignore

this) and the overall cross sectional shape of the entire specimen is not constant, particularly at the

collars where the specimen is much larger.

You can do the calculations in Microsoft excel or any spreadsheet a

nd paste the results graphs into

microsoft word processor.

If using excel you can do the equations and copy them so the equation is applied to a whole row or

selected column. Look at the cells in the online sample and the equation will be there usually i

n the

form…

=b1*c1 this multiplies two cell locations

=b1/c1 this divides two cells

You can copy this equation down a row or across a column by highlighting the source cell with your

mouse, doing Ctrl C, then highlighting the destination cells and p

ressing Ctrl V.

If you place a $ value in front of any of the characters in the equation it keeps these constant, if you

do not they increment when copied.

To plot data, select the data with the mouse, then click insert a graph by selecting the format

d

esired. If you have the axes mixed up you can simply select the line in the graph and make the

corrections so it picks the right one.

Once you have drawn a line the right mouse button selection allows you to conduct a linear

regression of the line (only

choose the section of the line that is linear for this, you may have to

truncate the data selected for plotting the line to the linear part only) and select the option to show

the equation on the chart, the slope of the equation should be your elastic modu

lus.

To calculate an offset line copy the equation into a cell and vary the values by picking a range of

stress values (in ranges of 50 or 100 MPa for example) and solving for strain or vice versa, you can

then add the offset to the strain column using an

equation like =C4+0.01 this would add a 1% strain

offset value to a cell in c4. if the rest of the values were below you could copy this equation

downwards to get the entire set of new strain data. You then want to plot stress vs the new strain

value

s to get the offset line and then estimate where this crosses the experimental data line, by eye .

Note: spreadsheets like excel plot data, they do not know how one set of data is related to another

even if you have calculated the equation for the line.

Hence excel cannot find the point where two

lines intersect for you.

Learning how to use a spreadsheet

effectively is essential in engineering, and will take a lot of trial

and error to get it right, expect to spend many days on this if you have never used one before. You

do not have to use microsoft products, they are all similar, in fact many are much b

etter (Microcal

Origin for example can do good 3D surface plots, excel can only do 2D and is very poor in this area).

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