MEMB221 Lab Manual

8/10/2019 MEMB221 Lab Manual

1/66

DEPARTMENT OF MECHANICAL

ENGINEERING

COLLEGE OF ENGINEERING

UNIVERSITY TENAGA NASIONAL


2/66


3/66

Laboratory & Reports: An Overview

Preparations andprocedures

: The experiment is conducted by groups of students under the guidance ofinstructor.

Pre Lab and Quiz,Informal Reports

and FormalReports

: Pre Lab and Quiz - Each student must answer the pre lab/quiz at thebeginning of each session in group. These practices to ensure each student

are fully prepared to conduct the experiment as stated in course schedule.Informal Reports- The informal report report should be submitted by enteringinto a drawer before 5 pm two daysafter the experiment. The informal reportmust have following criteria: date of experiment; title of experiment;objective(s); data and observation; analysis; results and discussion;conclusion; and references.Formal Reports - vital part of good engineering practice. They permit theorganisation, condensation, analysis, interpretation, and transmission of

meaningful result. Two (2) Individual Formal Reports and one (1) GroupFormal report must be submitted once identified by instructor. The reportsare to be handed in at the beginning of the next period unless otherwisedirected by the instructor. No late reports will be accepted. Late submissionwill be subjected to mark deduction penalty. 20 marks will be deducted for oneday late, 40 marks for 2 days, 60 marks for 3 days and no report will beaccepted after that.


4/66

Guidelines for Informal Laboratory Report

General Instructions: Informal Report has to be prepared individually and manually.

No Items Description

1. Cover page 1. Authors name and SID no.

2. Title of experiment

3. Day and date of experiment4. Course and course code

5. Semester and Academic Year (e.g. Sem 2 2014/15)

6. Section and group number

2. Statement of

Purpose /Introduction /

Objective (1%)

This should be a brief description of what the experiment is

demonstrating. Be specific. It should be consistent with the statement ofthe experiment instructions.

3. Data (2%) and

Observations

(1%)

The data and observations obtained in the experiments should be

presented in an orderly formin a data table if possible.

4. Analysis and

Results

The data obtained will be analysed with a view towards fulfilling the

purpose stated at the beginning of the report If there is an accepted or


5/66

(Note: Books

and Journals

are highly

recommended)

1. Book :

a. Author (s). Year. Title. Edition. Place: Publisher. Page

number. (example: L.H. van Vlack. 1989. Elements of

Materials Science and Engineering. 6th Ed. Reading

:Addison-Wesely Publ. pp100-105.)

b. Title. Year. Book Title. Edition. Place: Publisher. Page

number. (Example:Materials Science Handbook. 1986.

20th Ed. Ohio: C.R.C. Press. pp. 1986)2. Journals : Author (s), Year, Article Title; Journal Title, Volume,

Page number. (Example: Brandt, A. 1977. Multtilevel adaptive

solution to boundary value problems. Math of Computation. 31:

333-390)

3. Internet : Title. Year. URL. (Example: Selected encyclopedias

and major reference works in polymer science and technology at

Stanford University. 1998.http://www-

sul.stanford.edu/depts/swain/polymer/encys.html
http://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.html


6/66

Guidelines for Formal Laboratory Report

General Instructions:1. Formal Lab Report has to be preparedindividually or in group andmust be printed

properly.2. Softcopy has to be submitted tohttp://turnitin.com/with similarity checking not exceed

70%.

No Items Description

1. Title page (3%) This page must include:1. Title of experiment2. Course and course code3. Semester and Academic Year (e.g. Sem 2 2014/15)4. Day and date experiment was performed and due date5. (a)* Individual reports: Authors name and matrix no; and Names and

matrix no(s) of group member(b)* Group Reports: Names and matrix no(s) of group member

* Either (a) or (b)6. Section and group number7. Name of the lab instructor

2. Table ofcontent (2%)

This should be placed following the title page (for reports more than 10 pages).It should list up each section of the report and corresponding page number.
http://turnitin.com/http://turnitin.com/http://turnitin.com/http://turnitin.com/


7/66

what was done. Sufficient information should be provided to allow the reader torepeat the experiment in an identical manner.

8. Data (10%) andObservations(5%)

The data and observations obtained in the experiments should be presented inan orderly form in a data table if possible. A spreadsheet would be ideal,especially if there are many repetitive calculations in the analysis of the data.Each table, figure and graph should be labelled and numbered.

9. Analysis andResults

The data obtained will be analysed with a view towards fulfilling the purposestated at the beginning of the report. When possible, part of the analysis maybe combined with the data table in a spreadsheet. If there is an accepted orexpected value for a quantity that is to be obtained by the experiment, thepercentage difference between the expected and experimental value should becalculated. In many cases, another part of the analysis will be the constructionof the graph, which is often a very helpful way of showing the relationship

between two quantities.The graph must have a title, each exist will show scale, units, and a label. Alldata points must have a marking to show that it is an observed data point andall data points must be connected showing the trend of the data. If the studentis using a computer software package to generate graphs, then this packagemust convey the same information as would a hand generated graph.

10. Discussions This section should tie the results of the experiments to the purpose. Sources or

d i ti d t i t h ld b di d d h th i ht ff t


8/66

Basic Laboratory Safety Rules

Each and every students taking MEMB221 (Mechanics and Material Laboratory) areexpected to follow these requirements in order to ensure the safety throughout thesemester:

GENERAL GUIDELINES1.

Do not enter laboratory until you are instructed to do so.2. Conduct yourself and your experiment in a responsible manner at all times in thelaboratory.

3. When first entering laboratory do not touch any equipment, chemicals, or other materials inthe laboratory area until you are instructed to do so.

4. All personal belonging, which you do not need during the experiments, must be placed inthe cupboard.

5. Perform only those experiments authorized by your instructor. Unauthorized experiments

are not allowed.6. Follow all written and verbal instructions carefully.7. Never work alone in the laboratory. No student may work in the laboratory without the

presence of the instructor or technician.8. Do not eat sweets, drink beverages, or chew gum in the laboratory.9. Be prepared for your work in the laboratory. Read all procedures thoroughly before

entering the laboratory remember you have to answer pre lab questions beforeperforming the experiments!N f l d i th l b t


9/66

Experiment 1

Tensile Testing (Universal Tester)

Objectives

1. To understand the principles of tensile testing.2. To determine the stress-strain relationship for two types of material3. To determine the values of:

i. elongation at fractureii. tensile strength (UTS)iii. yield strength (offset of 0.2%)iv. Modulus of Elasticity

Theory

If a load is static or changed relatively slowly with time and is applied uniformly over a crosssection /surface of a member, the mechanical behaviour may be ascertained by a simple stress-strain test. These tests are most commonly conducted for metals at room temperature. There arethree principal ways in which the load may be applied: tension, compression and shear.

Tension is one of the most common mechanical stress-strain tests. The stress-strain diagram

h th diff t b h i f th i di id l t i l ti l l l l E h t i l h


10/66

Basic

In its basic form, the unit does not require anyexternal connections. The test force is generatedvia a manually actuated hydraulic system anddisplayed via a large, easily legible displayinstrument with a trailing pointer. Elongation of thesamples is recorded via a dial gauge. All

accessories are screwed to the cross members.This means that the test unit can be quickly andeasily refitted for various tests.

The basic unit essentially consists of the followingelements:

machine base (1) with handgrip (11)

support with cross-head (2)

load frame with upper (3) and lower cross-member (4)

hydraulic system consisting of a main cylinder(5) and a master cylinder with hand wheel (6)

force display (7)

elongation display via a dial gauge (8)

gripping heads (9) with sample (10)


11/66

Support

The posts (1) and cross-head (2) form fixed support of the testunit. The various fixed sample receptacles are fastened to thecross-head. The mobile load frame is also mounted on it low-friction linear ball bearings.

Load Frame

The load frame consists of the upper (1) and lower cross-member (2) and the guide rod (3). The load frame transmitsthe test force from the hydraulic main cylinder to the relevantsample. The load frame is slide-mounted in the cross-head ofthe support. Tensile samples are clamped between the upper

cross-member and the cross-head, whilst compressivesamples are clamped between the lower cross-member and

the cross-head.

Hydraulic system

Th t t f i t d b h d li A


12/66

Gripping heads

Tensile sample

P d

The gripping heads are designed for tensile sampleswith an M10 threaded head. In addition, flatcompression pads can easily be inserted in the cross-head and cross-member and are held by nut.

Round samples with an M10 threaded head in accordancewith DIN 50125 made of aluminium, copper, brass andsteel are supplied with the machine.

Tensile sample B6 x 30 DIN 50125

This is a short proportional test bar with a measuring lengthof 30 mm and a diameter of 6 mm.


13/66

Slowly and constantly loaded by rotating the hand wheel.

Application of the force should spread over a time interval of 5-10 minutes

It is essential to avoid sudden, jerky force application.

Observe the dial gauge and the sample.

For the first 1 mm extension, record the force value for every 0.1 mm extension.

Above 1 mm extension, record the force value for every 0.2 mm extension

Monitor the sample and note when constriction begins. From now on, the force will be nolonger increase, but instead, will tend to decrease.

ATTENTION: dont be startled! Particularly with some material, fracture will occur with a loudbang.

Remove the sample from the gripping heads

T i t b k th h d h l th t li d f it ill d th l d f

.

Adjust the dial gauge

Push the dial gauge upwards on the support baruntil the tracer pin is touching the drive.

Set the rotating scale on the dial gauge to zero.

Set the maximum pointer on the force display tozero.


14/66

Experiment 2

Torsion Test

Objectives

1. To understand the principle of torsion test.

2. To determine the modulus of shear, G through measurement of the applied torque and angleof twist.

Theory

Torsion is a variation of pure shear wherein a structural member is twisted, torsional forces

produce a rotating motion about the longitudinal axis of one end of the member relative to theother end. Torsion tests are normally performed on cylindrical solids shaft or tube. Most of thesetests are performed according to ASTM Standard E 143, Standard Test for Shear Modulus.

In each test, torque and twisting angle are measured to determine the shear modulus, G.

322

,44 dr

J

L

G

J

T

Where;T = torque

J l t f i ti


15/66

Figure 2.1: Layout of the torsion apparatus

Technical data


16/66

Loading Device

Torque measurement unit

The torsional loading is transmitted to the specimen by aworm gear (1) and a hand wheel (4). The twisting angle at

the output and the input is read off by two 360 scales(2,3).

At the input side of the gear there is in addition a 5-digitrevolution counter (5) which shows the input revolutions1:1.

The worm gear has a reduction ratio of 62. The specimenshexagon ends are set into an axial moveable socket (6) atthe worm gear output end.

In this testing the torque will be measured by a referencetorsion rod and strain gauges. The specimen is mounted onone side to the loading device and on the other side to thetorque measurement device.

The load torque applied to the specimen produce shear

t i th t t i d Th h


17/66

To reject this error, the specimen holder of thetorque measurement unit is turnable.

The deformation can be compensated by alever and a threaded spindle at the fixed side ofthe torsion rod.

The compensation can be controlled by a dialgauge at the side of the specimen holder.

The output signal of the strain gauge bridge isconditioned in a measurement amplifier with a

di it l di l (Att ti t i i it


18/66

Procedure

a) Calibration

For calibration of the torque measurement unit adefined load torque is used as reference. Thisreference load torque is generated by acalibration unit. The calibration unit mainlyconsists of a lever and a load weight. The weightof the lever is balanced by a certain counterweight. By that the load torque only depends onthe load weight.

A wide range of torque between 0 and 30 Nmcan be set thanks a division into weight discs.The resolution is 2.5 Nm. The calibration unitmust be clamped near by the specimen holder of

the torque measurement unit. To connect bothunits use the 15 mm hexagon socket.

To calibrate the torque measurement unit:

Set the read out of the amplifier to zero.

Connect the torque measurement unit to the


19/66

b) Performing the test

Mounting the specimen

1. In this test the short specimen is used.2. Mount the specimen between the loading device and the torque-measuring unit.3. Use the 19 mm hexagon socket.4. Make sure the shifting holder of the load device is in the mid position.

5. Make sure that there is no preload on the specimen. If necessary turn the hand wheel at theinput of the worm gear until the read out of the amplifier is zero.

6. Set both indicators at the input and at the output shaft of the worm gear to zero.7. Set the dial gauge of the compensation unit to zero. Therefore turn the turnable scale.8. Reset revolution counter.

Loading the specimen

1. Turn the hand wheel at the input of the gear clockwise to load the specimen. Turn it only for adefined angle increment.

2. For the first rotation choose an increment of a quarter rotation (90 ), for the second and third

rotation of a half-quarter (180) and for the 4thto 10throtation of one rotation (360).3. To calculate the twist angle at the specimen (output angle of the gear) divide the rotations at

the input by the reduction ratio of 62.4. Fracture will occur between 100 and 200 rotations.

5 C t th d f ti f th i t i d ft h l i t


20/66

Experiment 3

Bending testtensile strength (OPEN-ENDED LAB)

Objectives

1. To investigate the relationship between load, span, width, height and deflection of a beam,

placed on two bear affected by a concentrated load at the center.

2. To ascertain the coefficient of elasticity for steel, brass, aluminum and wood.

Theory

The stress-strain behavior of brittle materials (e.g. ceramic, low toughness composite material) isnot usually ascertained by tensile tests as outline in Exp. 1. A more suitable transverse bending

test is most frequently employed, in which a rod specimen either a circular or rectangular crosssection is bent until fracture using a three- or four-point loading technique. The assessments areconducted according to ASTM Standard C 1161, Standard Test Method for Flexural Strength of

Advanced Ceramics at Ambient Temperature.

In this module, the apparatus has been design to enable students to carry out experiments onsimply supported and cantilever beams in order to investigate:-


21/66

where12

3

bdI

beam compliance3

3

4Ebd

l

W

Determination of coefficient of elasticity

Calculations:Deflection formula for the load given above:

I

FLE

EI

FL

4848

33

A d t i ti f th fl l t i ld


22/66

Procedure

Task 1: To investigate the relationship between load, span, width, height and deflection ofa beam, placed on two bear affected by a concentrated load at the center.

a): Investigate the relationship between load and deflection

b): Investigate relationship between span and deflection

c): Investigate the relationship between width and deflection of the test specimen.

d): Investigate the relationship between the height and deflection of the test specimen.

Task 2: To ascertain the coefficient of elasticity for steel, brass, aluminum and wood.

When E is calculated, the initial load caused by the load device has no significance since thegauge has been set at zero with the device in place. However, when calculating flexural stress, F1is included.

Questions


23/66

Experiment 4

Buckling Test

Objectives

1. To determine critical buckling loads for columns with support.

2. To examination the Euler theory of buckling.3. To investigate the influence of different material parameters.

Introduction

All relevant buckling problems can be demonstrated with the WP 120 test stand.

Buckling, as opposed to simple strength problems such as drawing, pressure, bending andshearing, is primarily a stability problem. Buckling plays an important role in almost every field oftechnology. Examples of this are:

- Columns and supports in construction and steel engineering- Stop rods for valve actuation and connecting rods in motor construction- Piston rods for hydraulic cylinders and- Lifting spindles in lifting gear


24/66

b) Euler Formula

Buckling occurs suddenly and without warning when a certain limit load is attained. It is thereforean extremely dangerous type of failure, which must be avoided by all means. As soon as a rodbegins to buckle, it will become deformed to the point of total destruction. This is typical unstablebehavior. Buckling is a stability problem. The critical limit load F krit, above which buckling canoccur is dependent on both the slenderness of the rod, i.e. influence of length and diameter, and

the material used. In order to define slenderness the slenderness ratio will be introduced here.

i

lk

In this case l kis the characteristic length of the rod. It takes both the actual length of the rod and

the mounting conditions into consideration.


25/66

c) Influencing Factors

Below the influence of various characteristic values such as the E modulus, geometric moment ofinertia, length and the type of mounting on buckling behavior will be examined using the Eulerformula.

E modulus

The E modulus is a measure of the rigidity of a material. A stiff material is sensible for highresistance to buckling. Since strength has no influence on buckling, materials with as high an Emodulus as possible should be used. For example, in the case of buckling strength a simpleconstructive steel St37 with a tensile strength of only 370 N/mm should be given preference overa high strength titanium allow TiAI6Zr5 with 1270 N/mm.Whereas the constructive steel has an E modulus of 210 kN/mm, the titanium alloy only features

105 kN/mm.

Geometric moment of inertia

The geometric moment of inertia indicates the resistance against deflection resulting from thecross-sectional shape of the rod. Since a rod buckles in the direction of least resistance, theminimum geometric moment of inertia is the decisive factor. The table contains the geometricmoment of inertia for several cross-sectional shapes. Here, hollow sections with small wall


26/66

due to buckling. If the admissible compressive strain is used as the normal compressive strain,the critical slenderness ratio critat which buckling occurs can be calculated.

For constructive steel St37 with p=192 N/mm the crit= 104. Above critbuckling according toEuler can be expected. The buckling strain curve can be seen in Diagram 3.10.

p

crit

E

2


27/66

Technical Description of Unit

a) Layout of Test Device

The test device mainly consists of a basic frame, theguide columns and the load cross bar.

The basic frame contains the bottom mounting for the

rod specimen, consisting of a force-measuring devicefor measuring the testing force and an attachmentsocket which can hold different pressure pieces forrealizing various storage conditions.

The height of the load cross bar can be adjusted alongthe guide columns and it can be clamped in position.This allows rod specimens with different buckling

lengths to be examined.

The load cross bar features a load spindle forgenerating the test force. Using the load nut, the testforce is applied to the rod specimen via guided thrustpieces. An axial mounting between the load nut and thethrust piece prevents torsional stresses from being


28/66

c) Specimen Holders

d) Deformation Measurement

Bottom specimen holderTwo different mounting options are available:

For articulated mountingThrust piece with V notch for knife-edge mounting

For clamped mountingA thrust piece, which is firmly connected to the rod specimen

The thrust pieces are inserted in the attachment socket and are

clamped firmly with a screw.

Top specimen holderTwo different mounting options are available:

For articulated mountingLong thrust piece with V notch for knife-edged

mounting

For clamped mounting

Short adapter and thrust piece firmly attached to the rodspecimen. The thrust pieces are inserted into the guide bush ofthe load cross bar


29/66

f) Device Technical Data

Dimensions

Length: 620 mmWidth: 450mmHeight: ll50 mm

Weight: 35 kg

Max. test force: 2000NMax. lateral load: 20N

Max. lateral deflection: 20 mmMax. rod specimen length: 700mmMax. load spindle stroke: l0 mmRod specimen hole: 20 mm dia.

Rod Specimens


30/66

b) Accessories Set WP 120.01

No. Material Diametermm

Lengthmm

Mounting

SZ1 Alu. AlMgSiO.5 F22 25 x 6 500 knife-edge/knife-edge (e=0 mm)

SZ2 Alu. AlMgSiO.5 F22 25 x 6 500 Knife-edge/knife-edge (e=1 mm)

SZ3 Alu. AlMgSiO.5 F22 25 x 6 500 Knife-edge/knife-edge (e=3mm)

SZ4 Alu. AlMgSiO.5 F22 40 x 6 500 knife-edge/knife-edgeSZ5 Fieberline 25 x 10 700 knife-edge/knife-edge

SZ6 PVC 1 6 x 2 400 knife-edge/knife-edge

SZ7 PVC 20 x 1.5 400 knife-edge/knife-edge

SZ8 Alu. AlMgSiO.5 F22 20 x 10 x 2 700 knife-edge/knife-edge

SZ9 Alu. AlMgSiO.5 F22 1 5 x 2 700 knife-edge/knife-edge

SZ10 Alu. AIMgSiO.5 F22 1 4 700 knife-edge/knife-edge

Procedure

1) Introductory Test


31/66

b) Testing

1. Set up the test device in vertical or horizontal position. The force gauge can be turned 90 ofor

this purpose


32/66

8. Align the measuring gauge to the middle of the rod

specimen using the support clamps. The measuring

gauge must be set at a right angle to the direction of

buckling.

5. The load cross-bar must be clamped on the guide column in

such a manner that there is still approx. 5 mm for the top

thrust piece to move.

6. Align the rod specimen in such a manner that its buckling

direction points in the direction of the lateral guide columns.

Here, the edges must be perpendicular to the load cross-bar.

7. Pretighten the rod specimen with low, non-measurable force.


33/66

Safety

DANGER!

The load cross arm can drop of the clamping screws are loosened!

A drop could damage parts of the testing machine located underneath the cross arm.

Carefully support the cross arm by hand when loosening the clamping screws!

Before removing a rod specimen make sure that the clamping screws are tightenedsecurely! Pay attention to the top thrust piece when removing the rod specimen!

The hazards mentioned do not apply when the test device is set up horizontally.

Caution when working with brittle materials!

The rod specimen could break suddenly in this case. Pieces of specimen could fly aroundand cause injuries!

This hazard is not posed with original G.U.N.T. rod specimens, since they are made


34/66

Experiment 5

BRINELL HARDNESS TESTING

Objectives:1. To study the hardness of different material.2. To understand the principles of Brinell Testing method.

Theory

Brinell Fundamental principles

Hardness refers to the resistance, which a body has to the penetration of another. Accordingly, incommon hardness testing methods, a hard test body is pressed into the sample perpendicular toits surface.

A three-dimensional stress forms in the sample beneath the penetrating test body. Lasting im-pressions can be achieved in very hard and brittle materials without resulting in cracks. Thisdistinguishes hardness testing from tensile testing in which only a mono-axial stress is generatedin the sample and no plastic deformation is possible with hard materials.


35/66

Brinell Hardness

The factor 0.102 is an historical one and takes into account the conversion from kp/mm 2 toN/mm2.

If the impression from the ball is not circular, the average from two vertically superimposedmeasurements should be used.

To ensure that the hardness numbers for various materials, sample forms and ball diameters arecomparable, certain rules must be observed.

Brinell hardness is calculated from the test force F and thesurface area of the Impression AB caused by the ball. Withthe ball diameter D and the diameter of the impression d thisthen produces

225.0102.0102.0

dDDD

F

A

FHB

B


36/66

Load Factor2

102.0

D

Fx depending on material

Load factor x 30 10 5 2.5 1.25 0.5

Measurablehardnessrange HB

67.400 22315 11158 6...78 3...39 1...15

Material Iron

materialsSteelCast steelCast iron

Light metals

Copper BrassGunmetalNickel

Pure

aluminumMagnesium

Bearing

metals

Lead

TinSoft solder

Soft metals at

highertemperatures

Technical description

The WP300 materials testing device is a robust unit designed specifically for technical

instruction and is one of the classical materials testing devices in materials science. The flexible

design of the unit permits a wide range of different tests requiring tensile or compressive

forces. Thanks to its clear, simple layout, the unit is ideally suited for both student experiments

and for demonstrations.

Its compact dimensions and relatively low weight permit mobile use and erection on all


37/66

Machine base

Support

The rigid machine base made of cast iron forms the

foundation and ensures stability of the test unit in connection

with 4 rubber feet. The machine base supports the hydraulicsand the frame.

The posts (1) and cross-head (2) form the fixed support of the

test unit. The various fixed sample receptacles are fastened to


38/66

Force display and elongation measurement. The force-

Hydraulic system

The test force is generated by hydraulic means. A piston in the

master cylinder (2) actuated via the hand wheel (1) and the

threaded spindle creates a hydrostatic pressure, which

induces the test force in the main cylinder (3). The hydraulic

transmission ratio is 2.77:1, whilst the mechanical

transmission ratio hand wheel/spindle is 503 : 1. Excludingfriction losses, this would correspond to a manual force of 1 N

per 1.3 kN test force. The full stroke of the main cylinder of 45

mm requires 83 revolutions of the hand wheel.


39/66

Hardness test

Set up

The hardness-testing device is mounted in the compression zone ofthe test unit.

The basic unit includes a device for hardness testing according to

Brinell. Hardness testing is performed with a hardened steel ball

with a diameter of 10 mm.

Metal plates 10 x 30 x 30 mm made of the materials aluminum,

copper, brass and steel are used as samples.

The hardness testing device (1) is inserted in the compression zone

of the test device between the cross-head (2) and the lower cross-

member (3). The sample (4) is placed on the compression pad (5)

of the lower cross-member.


40/66

Procedure

Samples of 4 different materials are tested. For all materials, a loadfactor of 10 is selected. For the steel sample, a load factor of 30 is

recommended in accordance with the table on page 38. However, thenecessary test force of 29 kN cannot be applied with the WP3OO. Asthe Brinell hardness of the steel sample is undoubtedly less than HB315, the load factor of 10 is still permissible.

(Part A)- 1. Position the test piece on the lower pressure plate so that the

center of the test ball is at least 20 mm from the edge.

- 2. Carefully lower the test ball onto the sample by rotating the handwheel.

- 3. Smoothly apply the test force of 10 kN with the hand wheel. Donot apply the force too quickly. The increase to the maximum levelshould take at least 5 seconds.


41/66

Experiment 6

THIN CYLINDER

Objective

1. Determination of circumferential stress under open condition, and analysis of combined andcircumferential stress.

Theory

a) Complex Stress System

The diagrams in Figure 4.1 represent (a) the stress and (b) the forces acting upon an element ofmaterial under the action of a two-dimensional stress system.


42/66

Assuming (b) to be a 'wedge' of material of unit depth and the side AB to be of unit length:

Resolving along will give:

2sin2cos2

1

2

1

2sin

2

2cos1

2

12cos

cossin2sincos

cossinsincossinsincoscos

22

xyxy

xy

xy

xy

Resolving along will give:

2cos2sin2

1

cossin2

2sin

2

2sin

coscossinsincossinsincos

22

xy

xy

xy

From equation 2 it can be seen that there are values for e for which is zero and the planes onwhich the shear component is zero are called 'Principal Planes'.

(1)

(2)


43/66

From the diagram:

)4(

4

22sin

22

xy

and

)5(

42cos

22

xy

xy

The stresses on the principal planes are normal to these planes and are called principal stresses.

From equation 1 and substituting the above values:

Principal stresses are the maximum and minimum values of normal stress in the system. Thesign will denote the type of stress.

i.e Negative sign - Compressive Stress

)6(421

2

1 22

xyxy


44/66

Therefore the maximum shear stress occurs on planes at 450to the principal planes, and

or (using equation 6)

b) Two Dimensional Stress System

)8(2

112

)9(4 22 xy


45/66

Figure 6.5: Representation of strain on a Mohr circle

In the usual manner, referring to Figure 4.5:

OR is the maximum principal strain.


46/66

Theory as Applied to the Thin Cylinder

Because this is a thin cylinder, i.e. the ratio of wall thickness to internal diameter is less than

about 1/20, the value of H and Lmay be assumed reasonably constant over the area, i.e.throughout the wall thickness, and in all subsequent theory the radial stress, which is small, willbe ignored. I symmetry the two principal stresses will be circumferential (hoop) and longitudinaland these, from elementary theory, will be given by: -

tpd

H2

(14)

and

t

pdL

4 (15)

As previously stated, there are two possible conditions of stress obtainable; 'open end' and

'closed ends'


47/66

and these are the two principal strains. As can be seen from equation 17, in this condition Lwillbe negative quantity, i.e. the cylinder in the longitudinal direction will be in compression.

b) Closed Ends Condition

By constraining the ends, a longitudinal as well as circumferential stress will be imposed upon thecylinder. Considering an element of material:

Hwill cause strains of:-

EH

H

(18)

and

E

v HL

1 (19)

Lwill cause strains of:-

E

L

L

(20)

and

E

v LH

(21)


48/66

Description of the apparatus

Figure 6.7: Thin cylinder SM1007

Figure 6.7 shows a thin walled cylinder of aluminum containing a freely supported piston. The


49/66

the locking screw and the hand wheel. The hand wheel sets the cylinder for open and closed

ends conditions.When the hand wheel is screwed in, it forces the piston away from the end plate and the entireaxial load is taken on the frame, thus relieving the cylinder of all longitudinal stress. This createsopen ends experiments as shown in Figure 6.9. Pure axial load transmission from the cylinderto frame is ensured by the hardened steel rollers situated at the end of the locking screw andhand wheel.


50/66

Strain Gauges

Figure 6.11; strain gauges positions

Six active strain gauges are cemented onto the cylinder in the position shown in Figure 6.11;these are self-temperature compensation gauges and are selected to match the thermalcharacteristics of the thin cylinder. Each gauge forms one arm of a bridge, the other three armsconsisting of close tolerance high stability resistors mounted on a p.c.b. Shunt resistors are used


51/66

Thin cylinder technical information

Items DetailsDimensions 370 mm high x 700 mm long x 380 mm

front to back

Nett weight 30 kg

Electrical supply 85 VAC to 264 VAC 50 Hz to 60HzFuse 20 mm 6.3 A Type F

Maximum cylinder pressure 3.5 MNm-2Set by a pressure relief valveon the hand pump

Strain gauges Electrical resistance self-temperaturecompensation type

Cylinder oil Shell Tellus 37 (or equivalent)

Total oil capacity Approximately 2 litres

Cylinder dimensions 80 mm internal diameter3mm wall thickness359 mm length

Cylinder material Aged aluminium alloy 6063

Youngs modulus (E) 69 GN/m2

Poissons ratio 0.33


52/66

condition, the value of Young's Modulus for the cylinder material may be determined and also thevalue for Poisson's Ratio.

To obtain the biaxial stress system: - (refer to Figure 6.10)

Ensure that the return valve on the pump is fully unscrewed. Unscrew the hand wheel and pushthe crosspiece to the left until it contacts the frame end plate. Now close the return valve andoperate the hand pump to pump oil into the cylinder and push the piston to the end of the

cylinder.

Thus, when the cylinder is pressurized, both longitudinal and circumferential stresses are set upin the cylinder. Before any test, and at zero pressure, each strain gauge channel should bebrought to zero or the initial strain readings recorded as appropriate.

This equipment is equipped with VDAS (Versatile Data Acquisition System), however, forteaching purposes, students are encouraged to conduct the experiment manually.

Precaution: NEVER pump the oil pressure higher than 3.1 MN/m2

a) Experiment 1Open ends


53/66

Data

Cylinder Condition: OPEN ENDS

ReadingPressure(MN.m-2)

DirectHoopStress

(MN.m-2)

Strain

Gauge1

Gauge2

Gauge3

Gauge4

Gauge5

Gauge6

1

23

4

5

6

7

Values from actual MohrsCircle (at 3 MN.m-2)

Values from theorethicalMohrs Circle (at 3 MN.m-2)

Data Table 6.1: Open Ends Results


54/66

Questions:

Open Ends Conditions1. Plot a graph of Hoop Stress against Hoop Strain. Find the Youngs Modulus for the

cylinder material. Compare your result.2. Plot a Longitudinal Strain against Hoop Strain. Find the Poissons ratio for the cylinder

material. Compare your result.

3. Draw the Mohrs Circle at 3 MN/m2

. Identify the Principles Strains for Open EndsConditions. Compare the values with theoretical Mohrs Circle (Hint: to construct thetheoretical Mohrs Circle, consider Poissons Ratio and Youngs Modulus given intechnical details, use these values with the Principal Strain equations 16 and 17 tocalculate theoretical principal strain with calculated Hoop Stress at 3 MN/m2pressure).

Closed Ends Conditions1. Draw the Mohrs Circle at 3 MN/m2. Identify the Principles Strains for Closed Ends

Conditions.2. Compare the values with theoretical Mohrs Circle (Hint: to construct the theoretical

Mohrs Circle, consider Poissons Ratio and Youngs Modulus given in technical details,use these values with the Principal Strain equations 22 and 23 to calculate theoreticalprincipal strain with calculated Hoop Stress at 3 MN/m2pressure).


55/66

Experiment 7

IMPACT TEST

Objective

To investigate the impact strength of polymers

Theory

Impact testing

For determination of both tensile strength and hardness testing, the test piece is loaded

continuously and slowly. How a material reacts to a sudden tension due to a quick blow or impact

is shown by means of an impact tester.The test is conducted according to D6110-06 StandardTest Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics.


56/66

Fig 8.2: Charpy method Fig 8.3: Izod Method

Test pieces

Charpy test-pieces see fig. 8:4 can have slightly different instruction as to how the test isconducted.

Keyhole and U test-pieces give equally good results. The specific impact energy or impact unitKCU is measured in kj /m2. For U test-pieces the impact energy or impact strength kV, ismeasured in j (joules). There is no sure method of calculation of impact energy for test pieces, fortests carried out with different instructions on the test piece


57/66

Impact Strength

LR = Reduced length of pendulum= distance to center of impact

Fig.8.5: Pendulums potential


58/66

The impact tester has maximum impact energy of 1 joule, each scale division being 0.1 joules.Test pieces suitable for the tester are 6 x 6 x 44 mm. The reduced length of the pendulumrequires a test piece smaller then standard.

The impact tester weights 30 kg and has dimensions of 195 x 315 x 590 mm.The weight of the pendulum is 2 kg.


59/66

Method:

1. Set the pointer to 1 5 joules (straight down).

2. Raise the pendulum to the start point. Release the pendulum by means of the black knob.

KEEP FINGERS AND HANDS CLEAR OF THE PENDULUM MOTION THUS

AVOIDING JAMMING ACCIDENTS.

3. Stop the pendulum using the friction brake. Take the reading of the pointer. The pointershould point to zero (0) if the impact tester is properly set.

4. If the pointer shows more than zero, fixed impact testers should be angled slightly byinserting a spacer (washer) under the pendulum side. For the freestanding model, screwdown the allen screw using an MOO allen key.

If the pointer shows less than zero, i.e. the pointer is over the scale, then the spacer(washer), shall be placed under the back edge for fixed models end the allen screw in thefree standing model, turned anti clockwise (upwards).

5. Check the setting with an unloaded test. Complete further adjustment until exactly zero isregistered.


60/66

4. Release the pendulum by turning the black knob, top right. KEEP HANDS CLEAR. The testpiece is broken off.

5. Stop the pendulum by lifting the friction brake. Be sure that the pendulum is at standstillbefore removing the test pieces.

6. The energy consumed when breaking the test piece can now be read directly from the scale,

indicated by the pointer.

7. Read and note the value of the impact energy. Calculate the fracture area andsubsequently the impact strength.

Data

Test FractureArea(cm2)

ImpactEnergy(joule)

ImpactStrength

(joule/cm2)

HDPE

LDPE


61/66

Experiment 8

Microstructure Analysis

Objective:

1. To be familiar with metallography techniques such as grinding, polishing and etching.

2. To be familiar with metallurgy microscope3. To investigate the microstructure of metal and alloy.

Theory

Metallurgy is the study of microstructural features of materials. The structure studied by

metallography are indicative of the properties and hence the performance of material in service.

Typical application of metallography techniques in research centres and industry may include:a. To monitor metal alloy heat treatmentb. To measure the thickness of coatingc. To evaluate/examine the weld or brazed. To evaluate corrosion, etc.


62/66

Samples for microstructure evaluation are typically encapsulated in a plastic mount for handling

during sample preparation. Large sample or samples for macrostructure evaluation can beprepared without mounting.

The metallography specimen mounting is done by encapsulating the specimen into:1. A compression/hot mounting compound (thermosets e.g. phenolics, epoxies or

thermoplasticse.g. acrylics)2. A castable resin/cold mounting (e.g. acrylics resins, epoxy resins and polyester resins)

c) Grinding

Grinding is required to ensure the surface is flat & parallel and to reduce the damage createdduring sectioning. Grinding is accomplished by decreasing the abrasive grit size sequentially toobtain the required fine surface finish prior to polishing.

It is important to note that the final appearance of the prepared surface is dependent on the

machine parameters such as grinding/polishing pressure, relative velocity distribution and thedirection of grinding/polishing.

d) Polishing

For microstructure examination a mirror/reflective finish is needed whereas a finely ground finishis adequate for macrostructure evaluation. Polishing can be divided into two main steps:


63/66

g) Equipment, Apparatus and Sample

1. Abrasive cutter machine 8. Grinder2. Polisher 9. Silicon carbide paper (4 different mesh)3. Lubricant 10. Diamond spray (6 micron and 1 micron)4. Ultra sonic cleanser 11. Dryer5. Soapy water 12. Cotton6. Nital solution (2% HNO3) 13. Alcohol

7.

Metallurgy microscope 14. Samplemild steel

Procedure

1. Grinding is done using rotating discs covered with silicon carbide (SiC) paper and water. Inthis operation four different grade of paper is used. Starts with the smallest grit number;which represents coarse particles.

2. During grinding apply light pressure on the centre of the sample. Continue grinding until allthe blemishes have been removed, the sample surface is flat, and all starches are directed inone direction.

3. Wash the sample in water and move to the next grit, orienting the starches from the previousgrade normal to the rotation direction.


64/66

Questions

1. Label the microstructure obtained.

2. Discuss the difference between before- and after- etching process.

3. Discuss the effect of etching process. What will happen if the process is too long (more than


65/66

Lab Schedule

Mechanics and Materials Laboratory Schedule (MEMB221)

S1 (Mon, 2-5 pm), S2 (Wed, 9-12 pm), S3 (Fri, 8-11 am), S4 (Mon, 9-12 pm), S5 (Thu, 8-11 am), S6 (Tue, 3-6 pm), S7 (Tue, 10-1 pm) & S8 (Thu (2-5 pm)

Semester 2 2014/2015

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14

W15 W16-

W17

27-31Oct2014

3-7Nov 2014

10-14Nov 2014

17-21Nov 2014

24-28Nov 2014

1-5Dec2014

8-12Dec2014

15-19Dec 2014

22-26Dec2014

29 Dec-2 Jan2015

4-9Jan2015

11-16Jan2015

18-23Jan2015

25-30Jan2015

2-6Feb2014

7-18Feb2015

G1

AddandDropWeek

Introduction

1 2 3 4 5 6

MidSemesterBreak

7 8

Examweek

G2 8 1 2 3 4 5 6 7

G3 7 8 1 2 3 4 5 6

G4 6 7 8 1 2 3 4 5

G5 5 6 7 8 1 2 3 4

G6 4 5 6 7 8 1 2 3

G7 3 4 5 6 7 8 1 2G8 2 3 4 5 6 7 8 1

Note

Sultan

Selangors

Birthday

Christmas

New

Year

Thaipusam

Exp No.:

1 Tensile test (Universal Tester) 4 Buckling Test 7 Impact test

2 Torsion Test 5 Hardness Test 8 Microstructure Analysis

3 Bending Test 6 Thin Cylinder


66/66

66

Lab Schedule

Mechanics and Materials Laboratory Schedule (MEMB221)

S1 (Mon, 2-5 pm), S2 (Wed, 9-12 pm), S3 (Fri, 8-11 am), S4 (Mon, 9-12 pm), S5 (Thu, 8-11 am), S6 (Tue, 3-6 pm), S7 (Tue, 10-1 pm) & S8 (Thu (2-5 pm)

Semester 2 2014/2015

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 W15 W16-W17

27-31Oct2014

3-7Nov2014

10-14Nov2014

17-21Nov2014

24-28Nov2014

1-5Dec2014

8-12Dec2014

15-19Dec2014

22-26Dec2014

29 Dec-2 Jan2015

4-9Jan2015

11-16Jan2015

18-23Jan2015

25-30Jan2015

2-6Feb2014

7-18Feb2015

G1

AddandDropWeek

Introduction

1/5 2 3 4 7 6

MidSemesterBreak

8

Examweek

G2 2 3 4 7 6 8 1/5

G3 3 4 7 6 8 1/5 2

G4 4 7 6 8 1/5 2 3

G5 7 6 8 1/5 2 3 4

G6 6 8 1/5 2 3 4 7

G7 8 1/5 2 3 4 7 6

G8

Note

Sultan

Selangors

Birthday

Christmas

New

Year

Thaipusam

Exp No.:

1 Tensile test (Universal Tester) 4 Buckling Test 7 Impact test

2 Torsion Test 5 Hardness Test 8 Microstructure Analysis

3 Bending Test 6 Thin Cylinder

Documents

MEMB221 Lab Manual