Technology & Engineering
Hardness Testing
Hardness testing is a method used to determine the resistance of a material to deformation. It is commonly employed in the manufacturing and engineering industries to assess the strength and durability of materials such as metals and polymers. Various techniques, including Brinell, Rockwell, and Vickers hardness tests, are utilized to measure the hardness of different materials.
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12 Key excerpts on "Hardness Testing"
- David C. Jiles(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
7.2 HARDNESS TESTS Hardness is the resistance of a material to plastic deformation. It is usually measured by an indentation test, which consists of applying a known load over a particular geometry and seeing how far the material deforms. There are various forms of the test, ranging from the original Brinell test, which uses a spherical indenter (‘‘ball indenter”), through a variety of cone-shaped indenters used in some of the Rockwell tests, to pyramid-shaped indenters used in the Vickers and Knoop indentation tests. In all cases, the deformation is measured as a result of application of load under standardized conditions. All the indentation tests induce some permanent plastic deformation on the surface of the material under test. This can be thought of as a localized plastic zone. The area of damage varies significantly depending on the type of test. Consequently, these tests are not truly nondestructive. Also, it is known that the resulting calculated hardness varies with load, which can be a problem; so it is best if all hardness tests are conducted under identical standardized conditions. 7.2.1 C OMPARISON OF H ARDNESS T ESTS AND C ONVERSION BETWEEN H ARDNESS S CALES The four main hardness tests have various relative advantages and disadvantages. The Brinell test, which was the first standard hardness test, is hardly used today. It gives a good average value of hardness for the material under test because of the large indentation. However, for the same reason this is not suitable for n K e true e = log log σ ε n K e t e e t = − log log log σ ε n = − − 19 84 20 76 2 30 . . . Mechanical Testing Methods 103 small specimens. The Knoop test is good for brittle materials, and it results in the smallest indentation among the tests that are being considered here. It does, however, require surface preparation. The Rockwell test is very simple and requires no surface preparation; the test is widely used on metals.
eBook - PDF- Mikell P. Groover(Author)
- 2012(Publication Date)
- Wiley(Publisher)
In machining, the material is removed by the mechanism of shear deformation (Section 15.2). 3.2 HARDNESS The hardness of a material is defined as its resistance to permanent indentation. Good hardness generally means that the material is resistant to scratching and wear. For many engineering applications, including most of the tooling used in manufacturing, scratch and wear resistance are important characteristics. As the reader shall see later in this section, there is a strong correlation between hardness and strength. 3.2.1 HARDNESS TESTS Hardness tests are commonly used for assessing material properties because they are quick and convenient. However, a variety of testing methods are appropriate because of differences in hardness among different materials. The best-known hardness tests are Brinell and Rockwell. Brinell Hardness Test The Brinell Hardness Test is widely used for testing metals and nonmetals of low to medium hardness. It is named after the Swedish engineer who developed it around 1900. In the test, a hardened steel (or cemented carbide) ball of 10-mm diameter is pressed into the surface of a specimen using a load of 500, 1500, or 3000 kg. The load is then divided into the indentation area to obtain the Brinell Hardness Number (BHN). In equation form, HB ¼ 2F pD b D b ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi D 2 b D 2 i q (3.19) where HB ¼ Brinell Hardness Number (BHN); F ¼ indentation load, kg; D b ¼ diameter of the ball, mm; and D i ¼ diameter of the indentation on the surface, mm. These dimensions are indicated in Figure 3.14(a). The resulting BHN has units of kg/mm 2 , but the units are usually omitted in expressing the number. For harder materials (above 500 BHN), the cemented carbide ball is used because the steel ball experiences elastic deformation that compromises the accuracy of the reading. Also, higher loads (1500 and 3000 kg) are typically used for harder materials.
eBook - ePub- Ammar Grous(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
Canada, specifically, is experiencing a particularly growing interest because of harsh climates and “potholes” in Montreal and Ottawa. Depending on the circumstances, measuring the hardness value may help in assessing the effectiveness of heat or chemical treatment of a workpiece (e.g. cementation), to characterize its coating (e.g. paint, varnish), to evaluate its resistance to wear, or to better understand its mechanical behavior and its aging (possible cracks or hardening, or even damage in whole bridges). Among so many processes, we can distinguish the most common.The hardness tests which have been long reserved for the strength of materials – non-destructive and destructive testing – are in fact a discipline in the field of metrology; the test depends on the means of measurements, calibration, and readings related to errors and other uncertainties. We will not explore in detail the properties of materials if it does not involve intrinsic factors of the material or other factors that would influence the measurement such as the fatigue or the flow of the material. Material characteristics, as we know, influence the choice of measurement and control method. Hardness is primarily an intuitive notion characterizing the resistance that a body offers to local strains. The main methods of measuring the hardness of a material can be classified into three categories: static penetration, rebounding/bouncing, and impact penetration.Unlike minerals whose hardness is historically characterized by the scratch test (e.g. Mohs scale), the hardness of metals is generally characterized by using rebounding/bouncing or penetration tests. We consider the materials studied here as homogeneous and isotropic, and assume that the state of the material depends only on the values of constraints which are applied at a given time.Tests commonly used in metrology laboratories to study the behavior of metals under the effect of mechanical stress are of varying importance, depending on their use. Therefore, we can be satisfied with a limited number of selected tests to be sufficient for the understanding of the most important dimensional factors. The methods on which we focus here are: Brinell method (steel ball), the Vickers method (diamond pyramid), and the Rockwell method (steel ball and/or diamond cone). We will also discuss other methods, without going into much detail.
- Yichun Zhou, Li Yang, Yongli Huang(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
How do we describe the feeling of "soft" or "hard"? First, we will name it "hardness" so that we can quantify it. The higher the hardness value is, the harder the material will be, and vice versa. How do we define this "hardness" value? Currently, there is no overall consensus on the definition. From a practical point of view, it can be defined as "a measure of the degree that a material is capable of resisting deformation produced by another material." In deformation mechanics, hardness could be defined as "the ability to resist elastic deformation, plastic deformation, and fracture," or "the ability of a material to resist residual deformation and fracture." However hardness is defined, it is always measured by applying a certain amount of pressure on the surface of the solid sample being tested by using a harder object of definite shape and size, that is, an indenter. The measured hardness value not only depends on the elastic modulus, yield strength, tensile strength, and other mechanical properties but also is heavily influenced by the test instrument and the test conditions. Therefore, the hardness is a measure of bulk characteristics from the combined effects of local mechanical properties under a specific set of conditions. For example, if we indent and apply the same force on the surfaces of copper and iron with indenters of the same material properties and then measure the depth of penetration from each surface, we will find that the indentation depth taken from copper is a lot deeper than that of iron. This indicates that copper’s deformation resisting strength is greater than that of iron, which means that copper is softer than iron and has a lower hardness value. In reality, this comparison also reflects the differences in elastic and plastic anti-resistance capabilities between the two metals.4.1.2 Material Hardness Testing
The hardness of a material is determined by Hardness Testing. In order to compare the hardness between a wild variety of materials, various testing methods and hardness standards were developed. These include static indentation hardness, dynamic or rebound hardness, and scratch hardness. Static indentation hardness is determined by applying pressure on the sample surface using a ball-or diamond-shaped indenter. For a given applied load, a hardness value can be obtained from the area and depth of the indentation. Dynamic or rebound hardness uses a standardized object of a given weight and shape and drops it upon the sample surface from a given height. The height of the rebound is then measured and a hardness value is determined from that measurement. Scratch Hardness Testing applies a normal load on a tip with a radius of curvature. The tip is then dragged across the surface resulting in a scratch that is used to determine hardness. Depending on the applied load of the hardness tests, hardness values are separated into different categories: macrohardness (over10 Nin Japan, the United States, Russia, and over2 Nin the EU), microhardness (below 10-2 N but above10 m N), and nanohardness (lower than700 m N). During nanohardness tests, materials are observed to have increasing hardness with a decrease in size, showing signs of “size effect” [1 –3
eBook - PDFEngineering Materials
Research, Applications and Advances
- K.M. Gupta(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
249 10 Superhard Materials 10.1 Introduction Hardness is a surface property . It is defined as the resistance of a material against permanent deformation of the surface in the form of scratch, cutting, indentation or mechanical wear. Diamond is the hardest known material. 10.1.1 Need of Hardness Test The need of hardness test arises from the fact that in numerous engineering applications, two components in contact are made to slide or roll over each other. In due course, their surfaces are scratched and they may fail due to mechanical wear. This results in not only a quick replacement of both parts but also incurs a big loss in terms of money. For example, piston rings of an IC engine remain in sliding contact with the cylinder body when the piston recip-rocates within the cylinder. If proper care is not taken in selection of materials for them, the piston rings and cylinder will wear soon. In this case, the replace-ment or repairing of cylinder block will involve much time, trouble and money. Therefore, the materials of piston rings and cylinder block should be taken such that the wear is least on the cylinder. Thus, in case of repairing, compara-tively cheaper piston rings can be easily replaced. This envisages that material of cylinder block should be harder than the material of piston rings so that the cylinder wears the least. This can be ascertained by conduct of a hardness test. That is why it is essential to know as to how this test can be conducted. 10.1.2 Different Types of Hardness Tests In various hardness tests, the indentors are used to introduce indentation on the surface. The shape of indentors may be a spherical ball, a cone or a pyra-mid. Various hardness test methods are as follows: 1. Mohs hardness test with scale range 0–10 2. Brinell hardness test with scale range 0–3000 3. Rockwell hardness test with scale range 0–1000 250 Engineering Materials: Research, Applications and Advances 4.
eBook - ePub- J Martin(Author)
- 2006(Publication Date)
- Woodhead Publishing(Publisher)
height of rebound of a ball or hammer dropped from a given distance.2.5.1 Indentation hardness tests
There are two types of indentation hardness test. The first type (Brinell and Vickers) measures the size of the impression left by an indenter of prescribed geometry under a known load whereas the second type (Rockwell) measures the depth of penetration of an indenter under specified conditions.2.5.2 The Brinell test
The surface of the material is indented by a hardened steel ball (whose diameter D is usually 10 mm) under a known load (L ) (e.g. 3000 kg for steel) and the average diameter of the impression measured with a low-power microscope. The Brinell number (H B ) is the ratio of the load to the contact surface area of the indentation. Most machines have a set of tables for each loading force, from which the hardness may be read in units of kgf mm−2 .If other sizes of indenter are used, the load is varied according to the relation: L /D 2 = constant in order to obtain consistent results. The constant is 30 for steel, 10 for copper and 5 for aluminium.2.5.3 The Vickers test
A diamond square-based pyramid of 136° angle is used as the indenter, which gives geometrically similar impressions under differing loads (which may range from 5 to 120 kg). A square indent is thus produced, and the user measures the average diagonal length and again reads the hardness number (H V ) from the tables. The Brinell and Vickers hardness values are identical up to a hardness of about 300 kgf mm−2 , but distortion of the steel ball occurs in Brinell tests on hard materials, so that the test is not reliable above values of 600 kgf mm−2
eBook - ePubStructural Components
Mechanical Tests and Behavioral Laws
- Dominique Francois(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
Chapter 5Hardness Tests 1
5.1. Introduction
Tests known as “hardness tests” measure the average contact pressure of materials when an indenter (conical, pyramidal or spherical) is pressed into a flat surface. After the withdrawal of the indenter, hardness is calculated by measuring the dimension of the indentation made by the indenter, or during the test, with the help of a penetration curve, which relates the depth of penetration to the applied load.When hardness is measured on a ductile material under the conditions defined by the standards [MAT 94a, 94b, 98], it can be regarded as an intrinsic material parameter. Although the result obtained is pressure, it is expressed without dimension since the measured pressure depends on the geometry of the indenter. Thus, the value of hardness is a number (average contact pressure expressed in kgf/mm2 ) followed by H (for hardness) and an index which indicates the type of indenter used (V for Vickers or B for Brinell, for example).The main advantage of this test is that it can be performed on very small-sized samples without any preparation except polishing of the surface. This allows us to test the success of a surface treatment over a few hundred micrometers in depth, or the quality of surface coating, or the size of the zone affected by the welding of two sheets, etc. It is preferentially used when the removal of conventional tensile test pieces is difficult. Micro-hardness and nano-hardness tests were developed in order to test smaller and smaller zones down to surfaces of a few micrometers square.In addition, when compared with tensile tests, the hardness test has the advantage of being more or less non-destructive, easy to implement and inexpensive. It is a method of inspection commonly used to establish cartographies of hardness on sections of massive parts after heat treatments and forming.
eBook - PDFSteel and Its Heat Treatment
Bofors Handbook
- Karl-Erik Thelning(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
2 Materials testing The properties conferred on steel as a result of heat treatment need to be tested and verified. There are many testing methods available but only those that are standardized and widely used are considered here. (Before reading this chapter further consideration of the section 'International Designations and Symbols' on p. vii is recommended.) 2.1 T H E H A R D N E S S T E S T After heat treatment a steel component is usually hardness tested, and the value obtained is a good indication of the effectiveness of the treatment. The hardness test is carried out by pressing a ball or point with a predetermined force into the surface of the specimen. The hardness figure is a function of the size of the indentation for the Brinell (HB) and Vickers (H V), tests and of the depth of the penetration for the Rockwell (HRC) test. These three methods are the most commonly used tests and each has its special range of application and between them they cover almost the whole of the hardness field that is of interest to the steel producer and user. 2.1.1 The Brinell test In the Brinell test a ball of hardened steel or sintered carbide is pressed into the surface of the specimen to be tested (Figure 2.1). Depending on the material to be tested and the ball diameter, a load up to 3000 kp may be used. For steel the following discrete ball diameters and loads have been standardized: Diameter of ball mm 2-5 5 10 Load kp 187-5 750 3000 The diameter of the impression is measured and the Brinell hardness, which is the quotient of the load divided by the spherical area of the impression, is read off from a table. The unit, kgf/mm 2 or kp/mm 2 , is not recorded after the hardness number. 42 MATERIALS TESTING 43 The piece to be tested should have a thickness of at least 8 times the depth of the impression. The minimum distance between the centres of two adjacent impressions or from any edge should be 4 and 2^ times the impression diameter, respectively.
eBook - PDF- T. W. Clyne, J. E. Campbell(Authors)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
There are procedures and protocols in which they are accorded a higher significance than this, but this is an unsound approach. 7.1 Concept of a Hardness Number (Obtained by Indentation) Reviews are available [1, 2] that summarize the historical development of Hardness Testing. Systematic attempts to characterize the hardness (resistance to plastic deform- ation) of materials can be traced back [2] to the proposal in 1812 by the Austrian mineralogist Friedrich Mohs that the capacity of one material to scratch another could be used as a basis for a ranking order (see §7.4.2). Suggestions of using a single hard indenter on a range of metals date back [2] to the work of William Wade in 1856, oriented towards optimizing materials for production of cannons. Commercial set-ups for testing hardness in this way started to become available around the beginning of the twentieth century. It was, however, several decades before serious attempts were made to establish a sound theoretical background to this type of testing [3–5], with the work of David Tabor being particularly notable [6, 7]. A small number of handbooks 123 on Hardness Testing are also available, such as the compilation of chapters on individ- ual tests edited by Herrmann [8]. Hardness is a measure of the resistance that a material offers to plastic deformation. It’s of interest to have information, not only about the yield stress, but also about the subsequent work hardening characteristics. The hardness number provides a yardstick that incorporates both, although not in a well-defined manner. In view of the com- plexity of what it represents, it’s unsurprising that hardness is not a simple, well- defined parameter and there are several different hardness measurement schemes, each giving different numbers. The idea, however, is the same for all of these schemes. A specified load is applied to an indenter, which penetrates into the specimen, causing plastic deformation and leaving a permanent depression.
eBook - PDF- Karl-Erik Thelning(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
2 Materials testing The properties conferred on steel as a result of heat treatment need to be tested and verified. There are many testing methods available but only those that are standardized and widely used are considered here. (Before reading this chapter further consideration of the section 'International Designations and Symbols' at the beginning of the book is recommended.) 2.1 The hardness test After heat treatment a steel component is usually hardness tested, and the value obtained is a good indication of the effectiveness of the treatment. The hardness test is carried out by pressing a ball or point with a predetermined force into the surface of the specimen. The hardness figure is a function of the size of the indentation for the Brinell (HB) and Vickers (H V), tests and of the depth of the penetration for the Rockwell (HRC) test. These three methods are the most commonly used tests and each has its special range of application and between them they cover almost the whole of the hardness field that is of interest to the steel producer and user. 2.1.1 The Brinell test In the Brinell test a ball of hardened steel or sintered carbide is pressed into the surface of the specimen to be tested (Figure 2.1). Depending on the material to be tested and the ball diameter, a load up to 3000 kp may be used. For steel the following discrete ball diameters and loads have been standardized: Diameter of ball mm 2-5 2 10 Loadkp 187-5 270 3000 The diameter of the impression is measured and the Brinell hardness, which is the quotient öf the load divided by the spherical area of the impression, is read off from a table. The unit, kgf/mm 2 or kp/mm 2 , is not recorded after the hardness number. The piece to be tested should have a thickness of at least 8 times the 48 The hardness test 49 depth of the impression. The minimum distance between the centres of two adjacent impressions or from any edge should be 4 and 2^2 times the impression diameter, respectively.
eBook - ePubHeat-Treatment of Steel: A Comprehensive Treatise on the Hardening, Tempering, Annealing and Casehardening of Various Kinds of Steel
Including High-speed, High-Carbon, Alloy and Low Carbon Steels, Together with Chapters on Heat-Treating Furnaces and on Hardness Testing
- Erik Oberg(Author)
- 2017(Publication Date)
- Owen Press(Publisher)
CHAPTER XIII
TESTING THE HARDNESS OF METALS
Importance of Hardness Tests. —Few properties of iron and steel are of more importance than that of hardness. In some cases, as with a cutting tool or a pressure die, the metal is practically valueless unless it can retain a sharp edge; while in other instances, where the material has to be machined or cut or trued to shape, even a relatively slight increase of hardness is the cause of much inconvenience and expense. In a third class of material a good wearing surface is of prime importance; while, lastly, hardness may often serve as an indication of a degree of brittleness and untrustworthiness which might perhaps be otherwise unsuspected.Definition of Hardness. —Hardness may be defined as the property of resisting penetration, and, conversely, a hard body is one which, under suitable conditions, readily penetrates a softer material. There are, however, in metals various kinds or manifestations of hardness according to the form of stress to which the metal may be subjected. These include tensile hardness, cutting hardness, abrasion hardness, and elastic hardness; doubtless other varieties could also be recognized when the experimental conditions are modified so as to bring into operation properties of the material in addition to that of simple, or what may be conveniently called mineralogical hardness. This has been defined by Dana as “the resistance offered by a smooth surface to abrasion.”The usual quantitative tests for hardness are static in character, but the conditions are profoundly modified when the penetrating body is moving with greater or less velocity. The resistance to the action of running water, to the effect of a sandblast, or to the pounding of a heavy locomotive on a steel rail, affords examples of what might perhaps for purposes of distinction be called dynamic hardness, which is a branch of the subject that has received little attention.
eBook - PDFAn Introduction to Metallurgical Laboratory Techniques
Pergamon Series of Monographs in Laboratory Techniques
- P. G. Ormandy, K. Guy(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
This definition may be calculated from the T ri~rv% u ln Testing of Materials the ball usually deforms slightly. The amount of deformation is dependent upon the hardness of the metal and the magnitude of the applied load. A Brinell hardness number of approximately 525 is the upper limit that may be used with an ordinary steel ball, but by using a Hultgen ball, the hardness number may be increased to 600. By using a tungsten ball the hardness number may be increased to 725. ROCKWELL TEST In the standard Rockwell test, which originated in the United States of America, the specimen is placed surface uppermost on an anvil which is slowly raised by way of a handwheel until the surface of the specimen just touches an indenter. By raising the anvil still further, a minor load is applied, causing an indentation in the specimen. This load of approximately 10 kg is indicated on a dial indicator, and also sets the dial to zero. Whilst this minor load is in operation, it is augmented by a major load by operating a suitable lever which will slowly move in a downwards direction. This operates the mechanism in the machine and in-creases the depth of penetration of the indenter. The rate of loading is controlled by a dashpot, and when the lever applying the major load has completely descended, the reading on the indicator becomes steady and indicates the total load that has been applied to the specimen. The major load is then removed, still retaining the minor load as illustrated in Fig. 4.23. Hence the Minor Minor and major Major load only load load removed FIG.4.23. Demonstrates the principle of the Rockwell hardness test. 135 Metallurgical Laboratory Techniques 136 specimen is allowed to recover elastically.
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