JB502_CHAPTER_1.0

Diploma in Mechanical Engineering (Material)

JB502 DESTRUCTIVE TESTING

www.pis.edu.my

peneraju ilmu sejagat

Chapter

One (1)

1 pis/yth/jb502/chapter1

CLO 1 : Explain the principle of material testing

and mechanical properties for engineering

material.

2

Week : One (1)

peneraju ilmu sejagat pis/yth/jb502/chapter1


1.1 Understand material testing

1.2 Understand destructive test and non-

destructive test

1.3 Understand material testing selection

1.4 List the three classes of test specimen

1.5 Understand types of loading system using in

universal testing machine

1.6 Understand standard used in material testing

1.7 Understand engineering material

1.8 Understand mechanical properties of materials



material testing destructive test and non-destructive test material testing selection three classes of test specimen

types of loading system using in universal testing machine standard used in material testing

engineering material mechanical properties of materials

INTRODUCTION TO MATERIAL TESTING We select materials for many components and applications by matching the properties

of the material to the service conditions required of the component.

The first step in the selection process requires that we analyze the application to determine the most important characteristics that the material must posses/belongs.

Should the material be strong, or stiff, or ductile ?

Will it be subjected to repeated application of a high force, a sudden intense force, a high stress at elevated temperature, or abrasive condition ?

Once we have determined the required properties, we can select the appropriate material using data listed in handbooks.

However, we must know how the properties listed in the handbook are obtained, know what the properties mean, and realize that the properties listed are obtained from

idealized tests that may not apply exactly to real-life engineering applications.

In this chapter we will study several tests that are used to measure how a material withstands an applied force.

The results of these tests are the mechanical properties of the material.

4

pis/yth/jb502/chapter1





MATERIAL TESTING DEFINITION

The determination of the properties of a substance in comparison with a standard or specification.

PURPOSES OF MATERIAL TESTING

Materials are tested for one or more of the following purposes:

a) To access numerically the fundamental mechanical properties of ductility,

malleability, toughness etc.

b) To check chemical composition.

c) To determine suitability of a material for a particular application.

d) To determine data i.e. force deformation (or stress) values to draw up sets of

specifications upon which the engineer can base his design.

e) To determine the surface defects in raw materials or processed parts.

SIGNIFICANCE OF MATERIAL TESTING

a) To determine the material properties, and

b) To determine the integrity of the material or component






CLASSIFICATION OF TESTS Tests on materials may be classified as;

a) Destructive tests

b) Non-destructive tests

DESTRUCTIVE TESTS

In destructive testing, the component or specimen either breaks or remains no longer useful for further use.

The purpose of destructive testing is to determine the mechanical properties of materials.

Example : Tensile test, impact test, torsion test, etc.

NON-DESTRUCTIVE TESTS

In non-destructive testing, a component does not break and so even after being tested it can be used for the purpose for which it was made.

The purpose of non-destructive testing is to revealing (dedahkan) defects in components that could impair (jejaskan) their performance when put in service

Example : radiography, ultrasonic inspection etc.






DIFFERENCE BETWEEN DESTRUCTIVE AND NON-DESTRUCTIVE TEST

DESTRUCTIVE TEST NON-DESTRUCTIVE TEST

The test-piece is damaged or

broken in the process.

These tests do not damage the

parts being tested.

This test are performed on samples

of a material.

Sampling is not required as, if

necessary, every item can be

checked.

This test is used to determine the

mechanical properties of materials.

This test is used to detect the

presence of internal or surface

flaws in a material, component or

finished product.






ADVANTAGES AND DISADVANTAGES OF DESTRUCTIVE TEST

NO. ADVANTAGES

1 Able to determine the mechanical properties of materials. Example: hardness, tensile strength, toughness, fatigue, ductility, and so on

2 Complete data are available to be analyzed.

3 Permanent record can be kept as a reference. It can be used as a guide in the design and selection of materials in the manufacturing process.

4 Have standard reference for testing. Have coordination in terms of results (machine and test pieces.)

5 A test piece with a limit of a particular geometry and size. Therefore, it is easier for test.

6 Effective and reliable

7 Not require specialist for conduct the testing because machine and equipment is easy to operate.

8 Normally testing is conducted in a laboratory, so it is easier to control the environment in the testing process.

DISADVANTAGES

The sample or test pieces will be destroyed after the test. This will result in increased the cost for testing.

Require competent operator (skilled) to do the test and interpret the data.

Materials testing machines and equipment is big and heavy. So it is not portable. Testing should be done in a specific place.

Require a higher load / forces to do the test. Require a system to produce the force.

Different service conditions can alter test results. Individuals and equipment will have little effect on the test results.

Require a lot of samples according to the type of the testing. This means that sample preparation is required in the testing process.

Test period is quite long. For example, in creep tests, fatigue tests, and tensile the test .

Only able to determine the mechanical properties of materials only. For other defects such as porosity and cracks are not detected.






MATERIAL TESTING SELECTION

MATERIAL TESTING SELECTION PROCEDURE

Material properties to be determined. Example: tensile strength, toughness and hardness.

Type of defects. Example: cracks, porosity and impurities.

The component manufacturing process. Example: welding, machining and casting.

The accessibility of component, that is easy or difficult it is to be tested.

Equipment available, the facilities available.

The desired level of acceptance, the accurate or vice versa.

The cost of testing. Are they commensurate with their capabilities and components that are tested?

The size and geometry of the test piece, which is large or small; the form of simple or complex.






GEOMETRY AND LOADING SITUATIONS

Samples of engineering materials are subjected to a wide variety of mechanical tests to measure their strength or other interest.

Such samples, called specimens, are often broken or grossly deformed in testing. Some of the common forms of test specimen and loading situation are:

a) Tension

b) Compression

c) Indentation

d) Cantilever bending

e) Three-point bending

f) Four-point bending

g) Torsion

The most basic test is simply to break the sample by applying a tensile force. Compression test are also common. In engineering, hardness is usually defined in terms of resistance of the material to

penetration by a hard ball or point.

Various forms of bending test are also often used, as is torsion of cylindrical rods or tubes.






CLASS OF TEST SPECIMEN

There are 3 classes test specimens commonly used in testing:

a) Smooth or un-notched

b) Notched

c) Pre-cracked

The simplest test specimens are smooth (un-notched) ones.

More complex geometries can be used to produce conditions resembling those in actual engineering components.

Notched that have a definite radius at the end may be machined into test specimens.

The term notch is used here in a generic manner to indicate any notch, hole, groove, slot, etc., that has the effect of a stress raiser.

Sharp notches that behave similar to cracks are also used, as well as actual cracks that are introduced into the specimen prior to testing.






LOADING SYSTEM

Equipment of a variety of types is used for applying forces (loads) to test specimens.

Test equipment ranges from very simple devices to complex systems that are controlled by digital computer.

2 common configurations of relatively simple devices called universal testing machines:

a) The mechanical-screw-driven machine

b) The hydraulic system machine

12

pis/yth/jb502/chapter1





a)The mechanical-screw-driven machine a)The hydraulic system machine






These general types of testing machine first became widely used in the period 1900 to 1920, and they are still frequently used today.

The mechanical-screw-driven machine

The hydraulic system machine

Rotation of 2 large threaded posts (screws)

moves a crosshead that applies a load to

the specimen.

Loads is applied using the pressure of oil

pumped into a hydraulic piston.

A simple balance system is used to

measure the magnitude of the force

applied.

The oil pressure provides a simple means

of measuring the force applied.

Testing machines of these types can be used for tension, compression, or bending, and torsion machines.






The closed-loop servo-hydraulic concept is the basic of the most advanced test systems in use today.

Integrated electronic circuitry has increased the sophistication of these system.

Also digital computer control and monitoring of such test systems has steadily developed.

Sensors for measuring loads and displacements using electrical signals are important features of testing machines.

Modern closed-loop servo-

hyraulic testing system.






STANDARD TEST METHODS

The results of materials tests are used for a variety of purposes.

One important use is to obtain values of material properties, such as the materials breaking strength in tension.

Another use in quality control of material that is produced, say plates of steel, to be sure that they meet established requirements.

Such application of measured values of materials properties requires that everyone who makes these measurement do so in a consistent way.

Otherwise, users and producers of materials will not agree as to standards of quality, and much confusion and inefficiency will occur.

Perhaps even more important, safety and reliability of engineering design requires that materials properties be well-defined quantities.

Therefore, materials producers and users, and other involved parties, such as practicing engineers, governmental agencies, and research organizations, have work together to develop standard test methods.

This activity is often organized by professional societies, with the Standards and Industrial Research Institute of Malaysia (SIRIM), British Standard Institute (BSI), American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO) and etc, to coordinates and publishes standards on a worldwide basis.






Example:

The Annual Book of ASTM Standards is published yearly and consists of more than 60 volumes, approximately ten (10) of which include a significant number of standards for mechanical tests.

The details of the test methods differ depending on the general class of materials involved, such as metals, concrete, plastics, rubber, and glass, and ASTM Standards are organized according to such classes of materials.

The numbers identifying some of the major standards for mechanical testing are given in table below:






MALAYSIAN STANDARDS (MS)

The Department of Standards Malaysia (STANDARDS MALAYSIA) is an agency under the ambit (control) of Ministry of Science, Technology and Innovation (MOSTI).

STANDARDS MALAYSIA was officially launched on 28 August 1996 following the incorporation of Standards and Research Institute of Malaysia (SIRIM) into SIRIM Berhad.

STANDARDS MALAYSIA took over the statutory (berkanun) roles in standardization, formerly carried out by SIRIM.

In addition, STANDARDS MALAYSIA is also entrusted with the responsibilities of accreditation. In performing its duties and functions, STANDARDS MALAYSIA is governed by Standards of Malaysia

Act 1996 (Act 549).

OBJECTIVES

The Objectives of establishment of STANDARDS MALAYSIA are as follows: a) To promulgate and promote the national standards. (untuk menyebarluaskan dan menggalakkan

piawaian kebangsaan)

b) To manage the national accreditation schemes in accordance to the international practices (Untuk menguruskan skim akreditasi kebangsaan selaras dengan amalan antarabangsa)

c) To maintain the credibility, integrity and competency of the national standardisation and accreditation systems (Untuk mengekalkan kredibiliti, integriti dan kecekapan bagi penstandardan kebangsaan dan sistem akreditasi)

d) To safeguard the interest of Malaysia at regional and international level in the fields of standardisation and accreditation. (Untuk melindungi kepentingan Malaysia di peringkat serantau dan antarabangsa dalam bidang standardisasi dan akreditasi.)

EXAMPLE:

Tensile test : MS ISO 6892 : 2002

[Metallic Material-Tensile Testing At Ambient Temperature)






BRITISH STANDARDS (BS)

History

BSI Group began in 1901 as the Engineering Standards Committee, led by James Mansergh, to standardise the number and type of steel sections, in order to make British manufacturers more

efficient and competitive.

Over time the standards developed to cover many aspects of tangible (nyata) engineering, and then engineering methodologies including quality systems, safety and security.

British Standards are the standards produced by BSI Group which is incorporated under a Royal Charter (piagam diraja) (and which is formally designated as the National Standards Body (NSB)

for the UK).

The BSI Group produces British Standards under the authority of the Charter, which lays down as one of the BSI's objectives to:

Set up standards of quality for goods and services, and prepare and promote the general

adoption of British Standards and schedules in connection there with and from time to time

to revise, alter and amend such standards and schedules as experience and circumstances

require.

(Menetapkan standard kualiti bagi barangan dan perkhidmatan, dan menyedia dan menggalakkan penggunaan umum Piawaian British dan jadual yang berkaitan di sana dan dari masa ke masa untuk mengkaji

semula, mengubah dan meminda apa-apa piawaian dan jadual sebagai pengalaman dan keadaan memerlukan)

EXAMPLE:

Tensile test : BS 18 : 1987 [British Standard Method for Tensile Testing of Metals)






ASTM (American Society for Testing and Materials) History ASTM was formed in 1898 by chemists and engineers from the Pennsylvania Railroad. At the time of its establishment, the organization was known as the American Section of the

International Association for Testing and Materials. Charles B. Dudley, Ph.D., a chemist with the Pennsylvania Railroad, was the driving force behind

the formation of the Society. In 2001, the Society became known as ASTM International.

OVERVIEW ASTM International, formerly known as the American Society for Testing and Materials (ASTM), is

a globally recognized leader in the development and delivery of international voluntary consensus standards.

Today, some 12,000 ASTM standards are used around the world to improve product quality, enhance safety, facilitate market access and trade, and build consumer confidence.

ASTMs leadership in international standards development is driven by the contributions of its members: more than 30,000 of the worlds top technical experts and business professionals representing 135 countries.

Working in an open and transparent process and using ASTMs advanced electronic infrastructure, ASTM members deliver the test methods, specifications, guides, and practices that support industries and governments worldwide.

EXAMPLE:

Tensile test : ASTM E 8M-91[Standard test Methods for Tension Testing of Metallic Material)






SIGNIFICANCE OF STANDARD

a) To protect the consumer rights

b) To protect the safety of consumer






ENGINEERING MATERIAL

The material used to resist the mechanical force/load. They are formed from elements and fall into 4 groups: a) metals

b) ceramics

c) polymers and

d) composites

METAL

In chemistry, a metal is defined as an element with a valence of 1, 2, or 3.

All metals possess metallic properties such as luster (kilau), opacity (legap-tidak lutsinar), malleability,

ductility and electrical conductivity.

Typical examples of metallic materials are iron, copper, aluminium, zinc, etc., and their alloys.






CERAMIC

A ceramic can defined as a combination of one or more metals with a non-metallic element.

Hence, metal oxides, carbides, nitrides, borides and silicates are considered as ceramics.

They are characterised by high hardness, abrasion resistance, brittleness and chemical inertness

(lengai), and are poor conductors of electricity.

Typical examples of ceramics include refractories glasses, abrasives, clays and cements.

POLYMERS

Polymers are organic substances and derivatives of carbon and hydrogen.

They are also known as plastics.

Most plastics are light in weight and are soft as compared to metals.

They possess/are high corrosion resistance and can be moulded into various shapes by the application of heat and pressure. Typical examples of polymers are polyester, phenolics, polyethylene, nylon and rubber.






COMPOSITES

A composite is a combination of two or more materials that has properties different from its

constituents (juzuk/kandungan).

Typical examples of composites are wood, clad metals, fibre glass, reinforced plastics,

cemented carbides, etc.

Composites as a class of engineering material provide almost an unlimited potential for higher

strength, stiffness, and corrosion resistance

over the pure material systems of metals, ceramics and polymers.

They will probably be the steel of the next century.






MECHANICAL PROPERTIES

Mechanical properties are the characteristics of a material that are displayed when a force (load) is applied to the material, OR

Mechanical properties are the properties that describe how a material will respond to applied loads (or forces) OR

The mechanical properties of a material are those properties that involve a reaction to an applied load.

These mechanical properties are determined by subjected prepared specimens to standard laboratory tests designed to evaluate the materials reaction to applied force.

The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected.

Mechanical properties are also used to help classify and identify material.

They usually relate to the elastic and plastic behavior of the material.

(Elastic deformation = recovered immediately upon unloaded, Plastic deformation = not recovered upon unloaded and is therefore

permanent.)

The most common properties considered are strength, hardness, ductility, modulus of elasticity, yield strength, tensile strength, percent elongation, reduction in area, impact, fracture toughness, fatigue, creep strengths and etc.






The application of a force to an object is known as loading. Materials can be subjected to many different loading scenarios and a materials

performance is dependant on the loading conditions.

There are five fundamental loading conditions; 1) tension,

2) compression,

3) bending,

4) shear, and

5) torsion.

Tension is the type of loading in which the two sections of material on either side of a plane tend to be pulled apart or elongated.

Compression is the reverse of tensile loading and involves pressing the material together.

Loading by bending involves applying a load in a manner that causes a material to curve and results in compressing the material on one side and stretching it on the other.

Shear involves applying a load parallel to a plane which caused the material on one side of the plane to want to slide across the material on the other side of the plane.

Torsion is the application of a force that causes twisting in a material.






Strength

The strength of metal is its ability to withstand various forces to which it is subjected during a test or in service, or

Ability of a material to resist applied forces without yielding or fracturing

It is usually defined as tensile strength, compressive strength, proof stress, shear strength, etc.

Strength of materials is a general expression for the measure of capacity of resistance possessed by solid masses or pieces of various kinds to any cause tending to produce in them a permanent. and disabling change of form.






Elasticity

This is the ability of a material to deform under load and return to its original size and shape when the load is

removed.

A material is said to be perfectly elastic if the whole of the stress produced by a load disappears completely on the

removal of the load, the modulus of elasticity of Youngs modulus (E) is the proportionally constant between stress and

strain for elastic materials.

Figure below shows a tensile test specimen:

If it is made from an elastic material it will be the same length before and after the load is applied.

All materials possess elasticity to some degree and each has its own elastic limit.

If stressed beyond this limit, permanent deformation (plastic deformation), and ultimately fracture, occurs.

At stress levels below the elastic limit the amount of deformation is directly proportional to the applied force which

may be tensile or compressive.






Youngs modulus is the indicative of the property called stiffness; small values of E indicate flexible materials and large value of E stiffness and rigidity. The property of

spring back is a function of modulus of elasticity and refers to the extent to which metal

spring back when an elastic deformation load is removed.

In metal cutting, modulus of elasticity of the cutting tools and tool and holder affects their rigidity.

Values of modulus of elasticity for some important metals are given in table below:






Plasticity

Plasticity is the property that enables the formation of permanent deformation in a material.

It is the state of a material which has been loaded beyond its elastic limit so as to cause the material to deform permanently. Under such conditions the material

takes a permanent set and will not return to its original size and shape when the

load is removed.

It is reverse of elasticity; a plastic material will retain exactly the shape it takes under load, even after load is removed.

Under such conditions the material takes a permanent set and will not return to its original size and shape when the load is removed.

Gold and lead are the highly plastic materials.

It is because of this property that certain synthetic materials are given the name plastics.

These materials can be changed into required shape easily.

Example : When a piece of mild steel strip is bent at right angles into the shape of bracket, it shows the property of plasticity since it does not spring back straight again.






Example : When a piece of mild steel strip is bent at right angles into the shape of bracket, it shows the property of plasticity since it does not spring back straight again.






Ductility

It is the ability of a metal to withstand elongation or bending, or

A material that can undergo large plastic deformation without fracture / before fracture occurs by applying a tensile load.

A ductile material allows a useful amount of plastic deformation to occur under tensile load before fracture.

Due to this property, wires are made by drawing out through a hole.

Example: A material is manipulated by processes such as wire drawing, tube drawing, and cold pressing low-carbon steel sheets into motor car body panels.

The material shows a considerable amount of plasticity during the ductile extension.

This is a valuable property in chains, rope etc., because they do not snap off, while in service, without giving sufficient warning by elongation.






Malleability

This is the property by virtue of which a material may be hammered or rolled into thin sheets without rupture.

Ability of material allows a useful amount of plastic deformation to occur under compressive loading before fracture occurs.

Such a material is required for manipulation by such processes as forging, rolling, and rivet heading.

This property generally increases with the increase of temperature.

The metals in order of their ductility and malleability (at room temperature) are given

in table below:






Toughness (Impact resistance or Tenacity)

Toughness is the strength with which the material opposes/resists rupture, or

Ability or capacity of a material to absorb energy during plastic deformation or

Ability of a material to withstand shatter.

If a material shatters it is brittle (Ex : glass)

Rubber and most plastic materials do not shatter, therefore they are tough.

Example : A metal rod in a vice being broken by impact loading.

a) If the rod is made from a piece of high-carbon-steel, example silver steel in the annealed (soft condition), it will have only a moderate tensile strength, but under the impact of the hammer it will bend without breaking, therefore it is TOUGH.

b) If a similar specimen is made hard by making it red hot and quenching it (cooling it quickly in water), it will now have a very much higher tensile strength, although it is now stronger it will prove to be brittle and will break off easily when struck with a hammer. So, it is now LACKS TOUGHNESS.






It is due to the attraction which the molecules have for each other; giving them power to resist tearing apart.

The area under the stress-strain curve indicates the toughness (i.e. energy which can be absorbed by the material upto the point of rupture.

Toughness is expressed as energy absorped (Nm) per unit volume of material participating in absorption or Nm/m3 .

Brittleness

It is the property of a material that shows little or no plastic deformation before fracture when a force is applied.

It is usually regarded as the opposite of ductility and malleability.

Lack of ductility is brittleness

When a body breaks easily when subjected to shocks it is said to be brittle.

For example : A steel rod can be bent but a grey cast iron rod snaps when you try to bent it. Therefore grey cast iron is a brittle material.






Hardness

Hardness is usually defined as resistance of material to penetration.

Ability of a material to withstand scratching (abrasion) or indentation by another hard body.

It is an indication of the wear resistance of the material

Hard material resist scratches or being worn out by friction with another body.

Example : A hardened steel ball being pressed first into a had material and then into a soft material by the same load. The ball only makes a small indentation in the hard material, but it makes a very much deeper impression in the softer material.

Hardness is primarily a function of the elastic limit (i.e. yield strength) of the material.

The modulus of elasticity also exerts a slight effect on hardness.

In the most generally accepted test, an indentor is pressed into the surface of the material by slowly applied known load, and the extent of the resulting impression is measured mechanically or optically.

A large impression for a given load and indentor indicates soft material, and the opposite is true for small impression.

The converse of hardness is known as softness.






Fatigue

Failure in metals that are subjected to many reversed or repeated stresses.

When subjected to fluctuating or repeated loads (or stress), material tend to develop a characteristic behavior which is different from that (or materials) under steady loads.

Fatigue is the phenomenon that leads to fracture under such conditions.

Fracture takes place under repeated of fluctuating stresses whose maximum value is less than the tensile strength of the materials (under steady load).

Fatigue fracture is progressive, beginning as minute cracks that grow under the action for the fluctuating stress.






Creep

The slow and progressive deformation of a material with time under a constant stress.

Creep is the slow plastic deformation of metals under constant stress or under prolonged loading usually at high temperature.

It can take place and lead to fracture at static stresses much smaller than those which will break the specimen by loading it quickly.

Creep is specially takes care of while designing engines, boilers and turbines.


Documents

JB502_CHAPTER_1.0