Introduction To Hardness
Páginas: 19 (4724 palabras)
Publicado: 5 de marzo de 2013
Hardness Testing, 2nd Edition, 06671G Harry Chandler, editor
Copyright © 1999 ASM International ® All rights reserved. www.asminternational.org
1 Introduction to Hardness Testing
Hardness has a variety of meanings. To the metals industry, it may be thought of as resistance to permanent deformation. To the metallurgist, it means resistance to penetration. To the lubrication engineer, it meansresistance to wear. To the design engineer, it is a measure of flow stress. To the mineralogist, it means resistance to scratching, and to the machinist, it means resistance to machining. Hardness may also be referred to as mean contact pressure. All of these characteristics are related to the plastic flow stress of materials.
Measuring Hardness
Hardness is indicated in a variety of ways, asindicated by the names of the tests that follow: • Static indentation tests: A ball, cone, or pyramid is forced into the surface of the metal being tested. The relationship of load to the area or depth of indentation is the measure of hardness, such as in Brinell, Knoop, Rockwell, and Vickers hardness tests. • Rebound tests: An object of standard mass and dimensions is bounced from the surface of theworkpiece being tested, and the height of rebound is the measure of hardness. The Scleroscope and Leeb tests are examples. • Scratch file tests: The idea is that one material is capable of scratching another. The Mohs and file hardness tests are examples of this type. • Plowing tests: A blunt element (usually diamond) is moved across the surface of the workpiece being tested under controlledconditions of load
Hardness Testing, 2nd Edition, 06671G Harry Chandler, editor
Copyright © 1999 ASM International ® All rights reserved. www.asminternational.org
2 / Hardness Testing
• • • •
• •
and shape. The width of the groove is the measure of hardness. The Bierbaum test is an example. Damping tests: Hardness is determined by the change in amplitude of a pendulum having a hard pivot, whichrests on the surface of the workpiece being tested. The Herbert Pendulum test is an example. Cutting tests: A sharp tool of given shape is caused to remove a chip of standard dimensions from the surface of the workpiece being tested. Abrasion tests: A workpiece is loaded against a rotating disk, and the rate of wear is the measure of hardness. Erosion tests: Sand or other granular abrasive isimpinged on the surface of the workpiece being tested under standard conditions, and loss of material in a given time is the measure of hardness. Hardness of grinding wheels is measured by this testing method. Electromagnetic testing: Hardness is measured as a variable against standards of known flux density. Ultrasonic testing: A type of indentation test
In the following chapters, most of thesemethods are covered. However, the focus is on static indentation tests, because they are the most widely used. Rebound testing is also used extensively, particularly for hardness measurements on large workpieces or for applications in which visible or sharp impressions in the test surface cannot be tolerated.
Common Concepts of Hardness
The hardness test is, by far, the most valuable and most widelyused mechanical test for evaluating the properties of metals as well as certain other materials. The hardness of a material usually is considered resistance to permanent indentation. In general, an indenter is pressed into the surface of the metal to be tested under a specific load for a definite time interval, and a measurement is made of the size or depth of the indentation. The principal purposeof the hardness test is to determine the suitability of a material for a given application, or the particular treatment to which the material has been subjected. The ease with which the hardness test can be made has made it the most common method of inspection for metals and alloys. Why so valuable? Principally, the importance of hardness testing has to do with the relationship between hardness...
Copyright © 1999 ASM International ® All rights reserved. www.asminternational.org
1 Introduction to Hardness Testing
Hardness has a variety of meanings. To the metals industry, it may be thought of as resistance to permanent deformation. To the metallurgist, it means resistance to penetration. To the lubrication engineer, it meansresistance to wear. To the design engineer, it is a measure of flow stress. To the mineralogist, it means resistance to scratching, and to the machinist, it means resistance to machining. Hardness may also be referred to as mean contact pressure. All of these characteristics are related to the plastic flow stress of materials.
Measuring Hardness
Hardness is indicated in a variety of ways, asindicated by the names of the tests that follow: • Static indentation tests: A ball, cone, or pyramid is forced into the surface of the metal being tested. The relationship of load to the area or depth of indentation is the measure of hardness, such as in Brinell, Knoop, Rockwell, and Vickers hardness tests. • Rebound tests: An object of standard mass and dimensions is bounced from the surface of theworkpiece being tested, and the height of rebound is the measure of hardness. The Scleroscope and Leeb tests are examples. • Scratch file tests: The idea is that one material is capable of scratching another. The Mohs and file hardness tests are examples of this type. • Plowing tests: A blunt element (usually diamond) is moved across the surface of the workpiece being tested under controlledconditions of load
Hardness Testing, 2nd Edition, 06671G Harry Chandler, editor
Copyright © 1999 ASM International ® All rights reserved. www.asminternational.org
2 / Hardness Testing
• • • •
• •
and shape. The width of the groove is the measure of hardness. The Bierbaum test is an example. Damping tests: Hardness is determined by the change in amplitude of a pendulum having a hard pivot, whichrests on the surface of the workpiece being tested. The Herbert Pendulum test is an example. Cutting tests: A sharp tool of given shape is caused to remove a chip of standard dimensions from the surface of the workpiece being tested. Abrasion tests: A workpiece is loaded against a rotating disk, and the rate of wear is the measure of hardness. Erosion tests: Sand or other granular abrasive isimpinged on the surface of the workpiece being tested under standard conditions, and loss of material in a given time is the measure of hardness. Hardness of grinding wheels is measured by this testing method. Electromagnetic testing: Hardness is measured as a variable against standards of known flux density. Ultrasonic testing: A type of indentation test
In the following chapters, most of thesemethods are covered. However, the focus is on static indentation tests, because they are the most widely used. Rebound testing is also used extensively, particularly for hardness measurements on large workpieces or for applications in which visible or sharp impressions in the test surface cannot be tolerated.
Common Concepts of Hardness
The hardness test is, by far, the most valuable and most widelyused mechanical test for evaluating the properties of metals as well as certain other materials. The hardness of a material usually is considered resistance to permanent indentation. In general, an indenter is pressed into the surface of the metal to be tested under a specific load for a definite time interval, and a measurement is made of the size or depth of the indentation. The principal purposeof the hardness test is to determine the suitability of a material for a given application, or the particular treatment to which the material has been subjected. The ease with which the hardness test can be made has made it the most common method of inspection for metals and alloys. Why so valuable? Principally, the importance of hardness testing has to do with the relationship between hardness...
Leer documento completo
Regístrate para leer el documento completo.