Technology & Engineering
Hardness
Hardness refers to the resistance of a material to deformation, scratching, or abrasion. In engineering, it is an important property for materials used in various applications, as it can indicate the material's durability and ability to withstand wear and tear. Hardness is often measured using standardized tests such as the Mohs scale for minerals or the Rockwell scale for metals.
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10 Key excerpts on "Hardness"
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 - 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 - 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 - 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- John J. Gilman(Author)
- 2009(Publication Date)
- Wiley-Interscience(Publisher)
PREFACE xi For the structural applications of materials, there is no more useful measurable property than mechanical Hardness. It quickly and conveniently probes the strengths of materials at various scales of aggregation. Firstly, it does this at the human scale (Brinell Hardness—millimeters to centimeters). Secondly, it does so at a microscopic scale (Vickers microHardness—1 to 100 microns). And thirdly, it does so at a “nanoscale” (nanoindentation—10 to 1000 nanometers). For millenia, Hardness has been used to characterize materials; for example, to describe various kinds of wood ranging from soft balsa wood to hard maple and ironwood. Mineralogists have used it to characterize differing rocks, and gemologists for the description of gems. Ceramists and metallurgists depend on it for classifying their multitude of products. Hardness does not produce a complete characterization of the strengths of materials, but it does sort them in a general way, so it is very useful for “quality control”; for the development of new materials; and for developing prototypes of devices and processes. Furthermore, mechanical Hardness is closely related to chemical Hardness, which is a measure of chemical bond stability (reactivity). In the case of metals the connection is somewhat indirect, but nevertheless exists. The principal intention of the present book is to connect mechanical Hardness numbers with the physics of chemical bonds in simple, but definite (quantitative) ways. This has not been done very effectively in the past because the atomic processes involved had not been fully identified. In some cases, where the atomic structures are complex, this is still true, but the author believes that the simpler prototype cases are now understood. However, the mechanisms change from one type of chemical bonding to another. Therefore, metals, covalent crystals, ionic crystals, and molecular crystals must be consid- ered separately.
Available until 4 Dec |Learn moreManufacturing Technology
Materials, Processes, and Equipment
- Helmi A. Youssef, Hassan A. El-Hofy, Mahmoud H. Ahmed(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
Hardness ,.which.is.a.measure.of.material. resistance.to.localized.plastic.deformation . .Therefore,.both.tensile.strength.and.Hardness.are.indi-cators.of.a.metal’s.resistance.to.plastic.deformation . .Consequently,.they.are.roughly.proportional,. as.shown.in.Figure.2 .5, .for.tensile.strength.(TS).as.a.function.of.the.Brinell.Hardness.number. (HB) for.cast.iron,.steel,.and.brass . .The.same.proportionality.relationship.does.not.hold.for.all. Brittle Ductile B B' C' C A Strain Stress FIGURE 2.3 Stress–strain.curves.for.brittle.and.ductile.materials.loaded.to.fracture.(with.brittle.material. fracture.usually.terminated.before.necking) . Impact force Impact force (b) (a) FIGURE 2.4 Test.specimens.and.methods.of.applying.energy.for.(a).Charpy.and.(b).Izod.impact.tests . 22 Manufacturing Technology: Materials, Processes, and Equipment metals,.as.Figure.2 .5 .indicates . .As.a.rule.of.thumb,.for.most.steels,.the.HB.and.TS.are.related. according.to:. . TS.(MPa).=.3 .5 .×.HB. (2 .3) Over.the.years,.various.techniques.have.been.developed.in.which.a.small.indenter.is.forced.into.the. surface.of.the.material.to.be.tested,.under.controlled.conditions.of.load.and.rate.of.application . .The. depth.or.size.of.the.resulting.indentation.is.measured,.which.in.turn.is.related.to.a.Hardness.num-ber;.the.softer.the.material,.the.larger.and.deeper.the.indentation,.and.the.lower.the.Hardness.index. number. .Among.the.most.common.standardized.Hardness.tests.are.Brinell,.Rockwell,.Vickers,.and. Knoop.(Figure.2 .6). . Measured. Hardness. values. are. only. relative. (rather. than. absolute),. and. care. should.be.exercised.when.comparing.values.determined.by.different.techniques . Hardness.tests.are.performed.more.frequently.for.several.reasons . . 1 . .They.are.simple.and.inexpensive . . 2 . .The.test.is.nondestructive . . 3 . .Other.mechanical.properties.often.may.be.estimated.from.Hardness.data,.such.as.yield.and.
eBook - PDFFundamentals of Modern Manufacturing
Materials, Processes, and Systems
- Mikell P. Groover(Author)
- 2016(Publication Date)
- Wiley(Publisher)
Key: HB = Brinell Hardness number, HR = Rockwell Hardness a HR values are given in the B or C scale as indicated by the letter designation. Missing values indicate that the Hardness is too low for Rockwell scales. b HB values given are typical. Hardness values will vary according to composition, heat treatment, and degree of work hardening. Section 3.3 | Effect of Temperature on Properties | 57 these hard materials. Table 3.7 lists Hardness values for several ceramics and hard materials. For comparison, the Rockwell C Hardness for hardened tool steel is 65 HRC. The HRC scale does not extend high enough to be used for the harder materials. POLYMERS Polymers have the lowest Hardness among the three types of engineering materials. Table 3.8 lists several of the polymers on the Brinell Hardness scale, although this testing method is not normally used for these materials. It does, however, allow comparison with the Hardness of metals. Temperature has a significant effect on nearly all properties of a material. It is important for the designer to know the material properties at the operating temperatures of the product when in ser- vice. It is also important to know how temperature affects mechanical properties in manufacturing. At elevated temperatures, materials are lower in strength and higher in ductility. The general rela- tionships for metals are depicted in Figure 3.15. Thus, most metals can be formed more easily at elevated temperatures than when they are cold. HOT Hardness A property often used to characterize strength and Hardness at elevated tem- peratures is hot Hardness, which is simply the ability of a material to retain Hardness at elevated temperatures. It is usually presented as either a listing of Hardness values at different temperatures or as a plot of Hardness vs. temperature, as in Figure 3.16. Steels can be alloyed to achieve signifi- cant improvements in hot Hardness, as shown in the figure.
- Mahmood Aliofkhazraei(Author)
- 2016(Publication Date)
- IntechOpen(Publisher)
Based on the aforementioned reasons, nowadays, hard thin films have a significant place in coating. In the abstract, we have underlined that Hardness is one of the most important mechanical characteristics of a material. You can get insights about other characteristics of the material by © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. measuring its Hardness. Hardness is an indicator of the material's resistance against scratching, cutting, abrasion, and puncture. Table lists the Hardness of some materials in terms of absolute Hardness ( Table 1 ). Mineral Absolute Hardness Talk: Mg 3 Si 4 O 10 (OH) 2 1 Gypsum: CaSO 4 .2H 2 O 2 Calcite: CaCO 3 9 Fluorite: CaF 2 21 Quartz: SiO 2 100 Topaz: Al 2 SiO 4 (OH,F) 2 200 Ruby or Sapphire: Cr–Al 2 O 3 400 Diamond: C 1500 Table 1. Absolute Hardness of some materials. Nanoscale, that is, a few hundred nanometers in size, materials are called nanomaterials. Thanks to nanomaterials, the technology has made great progress. The properties of a mate‐ rial in nanoscale are very different than the ones in the bulk form, which created great ad‐ vantages for the technology. Especially, coating these materials to the surface as a thin film has added new properties to the base material. However, there is very little information in the literature on the mechanical properties of thin films [1]. After coating process, the coated material can gain electrical, optical, corrosive, and cracking resistance, depending on the thickness of the film. A material with such properties will be very handy in space research, astronomy, automobile industry, and in many other areas of engineering. For example, imagine that you can cover any surface with a heat‐resistant ma‐ terial.
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Hardness test Measures the resistance of a material to penetration by a sharp object. Common Hardness tests include the Brinell test, Rockwell test, Knoop test, and Vickers test. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 219 Glossary Hooke’s law The linear relationship between stress and strain in the elastic portion of the stress strain curve. Impact energy The energy required to fracture a standard specimen when the load is applied suddenly. Impact loading Application of stress at a high strain rate (, . 100 s 21 ). Impact test Measures the ability of a material to absorb the sudden application of a load without breaking. The Charpy and Izod tests are commonly used impact tests. Impact toughness Energy absorbed by a material, usually notched, during fracture, under the conditions of the impact test. Kinematic viscosity Ratio of viscosity and density, often expressed in centiStokes. Load The force applied to a material during testing. MacroHardness Bulk Hardness of materials measured using loads . 2 N. MicroHardness Hardness of materials typically measured using loads less than 2 N with a test such as the Knoop. Modulus of elasticity Young’s modulus, or the slope of the linear part of the stress strain curve in the elastic region. It is a measure of the stiffness of the bonds of a material and is not strongly dependent upon microstructure. Modulus of resilience The maximum elastic energy absorbed by a material when a load is applied. Nanoindentation Hardness testing performed at the nanometer length scale.
eBook - PDF- Michael D. Holloway, Emma Holloway(Authors)
- 2020(Publication Date)
- Wiley-Scrivener(Publisher)
Chemical Engineering Hardness, permanent The Hardness that cannot be removed from water by precipitation reactions. Essentially, the same thing as the non-carbonate Hardness. Chemical Engineering Hardness, temporary The Hardness that can be removed from water by precipitation. Essentially, the same as the carbonate Hardness. Chemical Engineering Hardness, total The sum of the calcium and the magnesium Hardness. Also the sum of the per- manent Hardness and temporary Hardness. The U.S. Geological Survey hard- ness criteria for potable water are: soft water 0-60 ppm, moderately hard water 61-120 ppm, hard water 121-180 ppm, very hard water >180 ppm. Chemical Engineering Hards coals of a hard and closed-grained character. (Mids.); or the name given to large pieces of best quality coal. (Som.). Mining Hardstand A hard-surfaced area on which heavy vehicles or airplanes can be parked Civil Engineering Hardstop cement-like material for sealing stoppings. Mining Hardware The electrical, mechanical and electromechanical equipment and parts associ- ated with a computing system, as opposed to its firmware or software. Electrical Hardwired To be physically interconnected and intended for a specific purpose. Hardwired logic is essentially unalterable. Electrical Engineering Hardwood Relatively high strength wood from deciduous trees with covered seeds. Material Process Hardwoods (deciduous trees) Trees with broad, flat leaves shed on an annual basis whose wood Hardness var- ies among individual species. Forestry Hare Core of Unemployment that group in the labor market which is able and willing to work but which, even in periods of short labor supply, still remain unemployed. Industrial Relations Harflex 300X Trade name for a high molecular weight polymeric type plasticizer. Very vis- cous, light yellow liquid, odorless, low volatility, heat and light resistant, high compatibility for vinyl resins.
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