memb221 lab manual sem 2 2015 2016 - updated 19 oct 2015

7/23/2019 Memb221 Lab Manual Sem 2 2015 2016 - Updated 19 Oct 2015

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DEPARTMENT OF MECHANICAL

ENGINEERING

COLLEGE OF ENGINEERING

UNIVERSITY TENAGA NASIONAL



TABLE OF CONTENTS

Section: Page No.

A. Laboratory & Reports: An Overview 3

B. Guidelines for Informal Laboratory Report 4

C. Guidelines for Formal Laboratory Report 6

D. Basic Laboratory Safety Rules 8

Experiment 1 Tensile Test 9

Experiment 2 Torsion Test 14

Experiment 3 Bending Test – Open Ended Lab 20

E periment 4 B ckling Test 21



A. Laboratory & Reports: An Overview

Preparations andprocedures

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

Pre Lab Quizzes,

Informal Reportsand FormalReports

: Pre Lab Quiz - Each student must answer the pre lab quiz at the beginning of

each session in group. These practices to ensure each student are fullyprepared to conduct the experiment as stated in course schedule.

Individual Informal Report - The informal report report should be submittedbefore 5 pm two days after the experiment. The informal report must havefollowing criteria: date of experiment; title of experiment; objective(s); data andobservation; analysis; results and discussion; conclusion; and references.

Group Formal Report – Report is a vital part of good engineering practice.The reports permit organisation, condensation, analysis, interpretation, andtransmission of meaningful result. The reports are to be handed in at thebeginning of the next period unless otherwise directed by the instructor. No latereports will be accepted. Late submission will be subjected to mark deductionpenalty. 20 marks will be deducted for one day late, 40 marks for 2 days, 60marks for 3 days and no report will be accepted after that.



received in writing. If conditions develop which may cause a student to missany laboratory work, the student must inform their lab instructor as soon aspossible in advance of the scheduled laboratory.

Plagiarism : Student must not adopt or reproduce idea words or statements of anotherperson without an appropriate acknowledgement. Copying someone else’swork or facilitating academic dishonesty constitutes plagiarism. Plagiarism willbe heavily penalized and the student will receive zero marks for that report.

Students must submit Group Formal Report in Microsoft Word format tohttp://turnitin.com/ for similarity checking. Class details (class section/ID andenrolment password) will be informed by respective instructor. The similaritychecking must not exceed 70%. Special highlight will be given to summary,discussion and conclusion.

B. Guidelines for Informal Laboratory Report

General description: Informal Report is an individual and manual report.

No Items Description

1. Cover page Cover page is compulsory and complete with following information:

1. Author’s name and SID no.

2. Title of experiment

3 Day and date of experiment



data.

5. Discussions

(4%)

This section should tie the results of the experiments to the purpose.

Sources or error, deviations and uncertainty should be discussed and

how they might affect the results. Any points that are specifically asked

for in experiment instructions should be discussed in this section.

6. Conclusions

(3%)

This section summarizes the lab report. Any conclusions drawn from the

results should be given in this section. Express the implication of the

results. Examine the outcome in the light of the stated objectives.

7. References

(1%)

A list of all references used in writing the report should be included in this

section. Use the following format:

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)



No Items Description1. Title page

(3%)This page must include:1. Title of experiment2. Course and course code3. Semester and Academic Year (e.g. Sem 2 2015/16)4. Day and date experiment was performed and due date5. Names and SIDs of group member

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). Itshould list up each section of the report and corresponding page number

3. Summary /

Abstract(10%)

This should encapsulate the major portion of the report and provides a concise

overview of the work. The length should be no more than 200-300 words or 2-3paragraphs. It should highlight the objectives, results and conclusions of theexperiment.

4. Statement ofPurpose /Introduction /Objective

(5%)

This should be a brief description of what the experiment is demonstrating. Bespecific. It should be consistent with the statement of the experiment instructions.Some experiments have one or more parts and each part demonstrates adifferent aspect. Be sure to include all objectives of the experiment in this section.



(15%) 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 construction ofthe graph, which is often a very helpful way of showing the relationship betweentwo quantities.The graph must have a title, each exist will show scale, units, and a label. All datapoints must have a marking to show that it is an observed data point and all data

points must be connected showing the trend of the data. If the student is using acomputer software package to generate graphs, then this package must conveythe same information as would a hand generated graph.

10. Discussions(15%)

This section should tie the results of the experiments to the purpose. Sources orerror, deviations and uncertainty should be discussed and how they might affectthe results. Any points that are specifically asked for in experiment instructionsshould be discussed in this section.

11. Conclusions(10%)

This section summarizes the lab report. Any conclusions drawn from the resultsshould be given in this section. Express the implication of the results. Examinethe outcome in the light of the stated objectives.

12. References(5%)

A list of all references used in writing the report should be included in this section.Use the following format:

B k



D. 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 the

laboratory.3. When first entering laboratory do not touch any equipment, chemicals, or other materials in

the laboratory area until you are instructed to do so.4. All personal belonging, which you do not need during the experiments, must be placed in

the cupboard.5.

Perform only those experiments authorized by your instructor. Unauthorized experimentsare 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 before

f i th i t !



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 materials3. 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



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)



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



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 Material A and Material B.

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.



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: don’t be startled! Particularly with some material, fracture will occur with a loudbang.

R th l f th i i h d

.

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 to

zero.



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 d r

J

L

G

J

T

Where;T = torque

J l t f i ti



Figure 2.1: Layout of the torsion apparatus

Technical data



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 specimen’shexagon 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



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



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



b) Performing the test

Mounting the specimen

1. In this test the short specimen is used.2. Mount thee specimen between loading device and 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 4th to 10th rotation 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



Experiment 3

Bending test – tensile strength (OPEN-ENDED LAB)

Bending test – tensile strength (OPEN-ENDED LAB)

DescriptionIn a group design a simple and cost effective experimental set-up to study bending behaviour ofnon-metallic material. The material must be prepared as beam with various dimensions. Theexperimental setup must be able to study the bending behaviour and also must be able todetermine the modulus of elasticity of the material. The loading shall be made of string andvarious numbers of nail.

Objectives1. To design a simple bending testing set-up for beams with concentrated loading2. To investigate the bending behavior a non-ferrous material placed on two support with

concentrated load at the center.3. To determine the Modulus of Elasticity of non-ferrous material

Time Frame:

Di i P ti d P t t W2 W11



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



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 Fkrit, 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

l k

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

the mounting conditions into consideration.



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 features105 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 wallthickness are more favorable at the same weight as solid cross sections. For example, the ratio of

f f ( ) f ( )



the critical slenderness ratio crit at which buckling occurs can be calculated.

For constructive steel St37 with p =192 N/mm the crit = 104. Above crit buckling according to

Euler can be expected. The buckling strain curve can be seen in Diagram 3.10.

p

crit

E

2



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



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



f) Device Technical Data

Dimensions

Length: 620 mmWidth: 450 mmHeight: ll50 mm

Weight: 35 kg

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

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

Rod specimen hole: 20 mm dia.

Rod Specimens



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



b) Testing

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

this purpose

2. Insert thrust piece with V notch into attachment socket



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.



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 madeof ductile material.



Experiment 5

BRINELL HARDNESS TESTING

Objectives:1. To understand the principles of Brinell Testing method.2. To study the hardness of High Density Polyethylene and Low Density Polyethylene.

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.



Brinell Hardness

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

225.0

102.0102.0

d D D D

F

A

F HB

B



Load Factor2

102.0

D

F x depending on material

Load factor x 30 10 5 2.5 1.25 0.5

Measurablehardnessrange HB

67….400 22…315 11…158 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 Universal Hardness Tester is provided with a backlit, LCD display. It is used to displaymeasured hardness results, to monitor the progress of the test and to display information thatmay be required when setting up the machine for a variety of parameters



Experiment procedure:

A. Changing ScaleThe hardness scale is determined by the indenter and the test load.First select the indenter to be used for a measurement which will in turn define the modeof operation (Rockwell, Vickers or Brinell). Press the menu key once and then scrollthrough the available indenter options using the

and keys. When the desired

indenter is dispayed, press the Enter key. The machine will, if necessary “change mode”to itself to the appropriate test start condition.

B. Fitting the IndenterLower the anvil, then push the indenter into the indenter sleeve from below and hold inposition with the M3 contersink screw. After that, lock the indenter screw tightly with the2 mm Allen key.

C. Moving the IndenterThe indentation is made by lowering the indenter onto the test surface. The indenter isfitted into a moveable sleeve, which is advanced to a fixed forward position when theimpression is made and retracted to a rear fixed position after the completion ofindentation, to allow viewing of the impression through the built-in microscopeassembly.The sleeve is moved by a means of a small handlever on the right –hand side of themachine. The angular position of the hand lever can be adjusted by pressing the button



F. Making Brinell Impression

1. Put HDPE specimen on stage. 2. Rotate the handwheel clockwise to bring specimen close to indenter.3. Movement of the indenter is displayed by a bar graph and the correct pre-load is

indicated when the horizontal bar touches the end of the fixed bar. 4. When this point is reached, an audible bleep will be heard, and vertical movement of the

indenter should stop. 5. The rest of the loading cycle is automatic.

6. At the end of the load cycle, the hardness number will be displayed on the screen. 7. Turn the stage counter clock wise to release the specimen.8. Take five readings for each sample.9. Repeat steps 1-8 with LDPE.

Questions:1. Record the data of HDPE and LDPE in a table completely.2. Compare the hardness properties of HDPE and LDPE.

3. HDPE and LDPE have different polymeric chain. Explain how it affects thehardness properties.

4. What are the important samples preparations need to be considered beforeconducting hardness test?

5. Give two examples regarding the importance of hardness test.6. What is the advantage of hardness testing in contrast to tensile testing?



Experiment 6

THIN CYLINDER

Objective

1. To determination the behaviour of aluminium alloy 6063 in open ends condition andclosed ends condition.

2. To determine the principle plane in open ends and closed ends condition.

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.



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

x y x y

x y

x y

x y

Resolving along will give:

2cos2sin2

1

cossin2

2sin

2

2sin

coscossinsincossinsincos

22

x y

x y

x y

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)



From the diagram:

)4(

4

22sin

22

x y

and

)5(

42cos

22

x y

x y

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(42

1

2

1 22

x y x y



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

or (using equation 6)

b) Two Dimensional Stress System

)8(2

112

)9(4 22 x y



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.

/2



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 L may 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: -

t pd

H 2

(14)

and

t

pd L

4 (15)

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

'closed ends'



and these are the two principal strains. As can be seen from equation 17, in this condition L willbe 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:

H will cause strains of:-

E H

H

(18)

and

E

v H

L

1 (19)

L will cause strains of:-

E

L

L

(20)

and

E

v L H

(21)



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



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 creates‘open 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.



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



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-2 Set 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

Young’s modulus (E) 69 GN/m2

Poisson’s ratio 0.33



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 1 – Open ends



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

Values from actual Mohr’sCircle (at 2.5 MN.m-2)

Values from theorethical

Mohr’s Circle (at 2.5 MN.m-2)

Data Table 6.1: Open Ends Results



Questions:

A. Open Ends Conditions1. Plot a graph of Hoop Stress against Hoop Strain. Find the Young’s Modulus for the

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

material. Compare your result.3. Draw the Mohr’s Circle at 2.5 MN/m2. Identify the Principles Strains for Open Ends

Conditions. Compare the values with theoretical Mohr’s Circle (Hint: to construct thetheoretical Mohr’s Circle, consider Poisson’s Ratio and Young’s Modulus given intechnical details, use these values with the Principal Strain equations 16 and 17 tocalculate theoretical principal strain with calculated Hoop Stress at 2.5 MN/m2 pressure).

B. Closed Ends Conditions1. Draw the Mohr’s Circle at 2.5 MN/m2. Identify the Principles Strains for Closed Ends

Conditions.

2. Compare the values with theoretical Mohr’s Circle (Hint: to construct the theoreticalMohr’s Circle, consider Poisson’s Ratio and Young’s 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 2.5 MN/m2 pressure).

C. State one example of real engineering application using open ends condition and



Experiment 7

IMPACT TEST

Objective

To investigate the impact strength of High Density Polyethylene and Low Density Polyethylene.

Theory

Impact testing

For determination of both tensile strength and hardness testing, the test piece is loadedcontinuously and slowly. How a material reacts to a sudden tension due to a quick blow or impactis 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 Test pieces of Plastics.

Impact Strength

In impact testing, the pendulum is released from a known height strikes the test piece once it isreleased and fracture the test piece. By knowing the mass of the pendulum, the original positionof the pendulum, and final position of the pendulum; the potential energy when released, the



Two methods of impact testing techniques are applicable namely Charpy Test and IzodTest.Figure 8.2 shows the Charpy method, which consists of placing the test piece between twosupports. Fig. 8:3 shows the Izod method. This entails fixing the test-piece and allowing thependulum to break off a piece of the test-piece.

Fig 8.2: Charpy method Fig 8.3: Izod Method

Test pieces



DESCRIPTION OF APPARATUS

This section describes on the Impact tester.

(a) Overview of the equipment.



Charpy Impact Testing

i. Charpy Impact Fixture

Figure 8.6. Charpy Impact Fixture



b)Pendulum



Safety Measures:.

(a) Protection screen of the equipment



1 Centering pin2 Test piece with a V or U notch3 Hand wheel



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.



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

thermoplastics – e.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:



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. Sample – mild steel

Procedure

1. Grinding is done using planar grinding machine covered with silicon carbide (SiC) paper andwater. In this 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 planar direction.



Question:

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 (morethan 3 seconds)?



Lab Schedule

Mechanics and Materials Laboratory Schedule (MEMB221)

Semester 2 2015/2016

Time table

Section 1 2 3 4 5 6 7 8 9

Lecturer Rogemah Siti Zubaidah Siti Zubaidah Nuraslinda Nuraslinda NuraslindaAP. Dr.Shahida Siti Zubaidah Siti Zubaidah

Day Monday Wednesday Tuesday Wednesday Thursday Tuesday Thursday Tuesday Friday

Time 1700-2000 1100-1400 900-1200 1700-2000 1900-2200 1700-2000 1600-1900 1300-1600 800 - 1100

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14 W15W16-W17

19 -23Oct2015

26-30Oct2015

2-6Nov2015

9-13Nov2015

16-20Nov2015

23-27Nov2015

30Nov-4Dec2015

7-11Dec2015

14-18Dec2015

21-25Dec2015

28Dec-1Jan2016

4-8Jan2016

11-15Jan2016

18-22Jan2016

25-29Jan2016

1-17Feb2016

G1

AddandDrop

Week

Introduction

1 2 4 7

5 8 -

Replacem

ent

MidSemesterBreak

Replacem

ent

3 6

Examwe

ek

G2 2 4 7

5 8 - 1 3 6

G3 4 7 5 8 - 1 2 3 6

G4 7 5 8 - 1 2 4 3 6

G5 8 - 1 2 4 7 5 3 6

G6 - 1 2 4 7 5 8 3 6

Note 10/11-Deepavali

11 Dec –

SultanSelangor’s

Birthday

24/12 – Maulidur

Rasul,

24/12 -Christmas

1/1 – New Year

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

memb221 lab manual sem 2 2015 2016 - updated 19 oct 2015

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