Indentation hardness tests are used to determine the hardness of a material to deformation. Several such tests exist, wherein the examined material is indented until an impression is formed; these tests can be performed on a macroscopic or microscopic scale.

When testing metals, indentation hardness correlates linearly with tensile strength. This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers. ^[1]

Material hardness[link]

As the direction of materials science continues towards studying the basis of properties on smaller and smaller scales, different techniques are used to quantify material characteristics and tendencies. Measuring mechanical properties for materials on smaller scales, like thin films, can not be done using conventional uniaxial tensile testing. As a result, techniques testing material "hardness" by indenting a material with an impression have been developed to determine such properties.

Hardness measurements quantify the resistance of a material to plastic deformation. Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into two classes: microindentation and macroindentation tests. Microindentation tests typically have forces less than 2 N (0.45 lb_f). Hardness, however, cannot be considered to be a fundamental material property. Instead, it represents an arbitrary quantity used to provide a relative idea of material properties.^[2] As such, hardness can only offer a comparative idea of the material's resistance to plastic deformation since different hardness techniques have different scales.

The main source of error with indentation tests is the strain hardening effect of the process. However, it has been experimentally determined through "strainless hardness tests" that the effect is minimal with smaller indentations.^[3]

Surface finish of the part and the indenter do not have an effect on the hardness measurement, as long as the indentation is large compared to the surface roughness. This proves to be useful when measuring the hardness of practical surfaces. It also is helpful when leaving a shallow indentation, because a finely etched indenter leaves a much easier to read indentation than a smooth indenter.^[4]

The indentation that is left after the indenter and load are removed is known to "recover", or spring back slightly. This effect is properly known as shallowing. For spherical indenters the indentation is known to stay symmetrical and spherical, but with a larger radius. For very hard materials the radius can be three times as large as the indenter's radius. This effect is attributed to the release of elastic stresses. Because of this effect the diameter and depth of the indentation do contain errors. The error from the change in diameter is known to be only a few percent, with the error for the depth being greater.^[5]

Another effect the load has on the indentation is the piling-up or sinking-in of the surrounding material. If the metal is work hardened it has a tendency to pile up and form a "crater". If the metal is annealed it will sink in around the indentation. Both of these effects add to the error of the hardness measurement.^[6]

The equation based definition of hardness is the pressure applied over the contact area between the indenter and the material being tested. As a result hardness values are typically reported in units of pressure, although this is only a "true" pressure if the indenter and surface interface is perfectly flat.^{[citation needed]}

[edit] Macroindentation tests

The term "macroindentation" is applied to tests with a larger test load, such as 1 kgf or more. There are various macroindentation tests, including:

• Vickers hardness test (HV), which has one of the widest scales
• Brinell hardness test (HB)
• Knoop hardness test (HK), for measurement over small areas
• Janka hardness test, for wood
• Meyer hardness test
• Rockwell hardness test (HR), principally used in the USA
• Shore hardness test, for polymers
• Barcol hardness test, for composite materials.

There is, in general, no simple relationship between the results of different hardness tests. Though there are practical conversion tables for hard steels, for example, some materials show qualitatively different behaviors under the various measurement methods. The Vickers and Brinell hardness scales correlate well over a wide range, however, with Brinell only producing overestimated values at high loads.

[edit] Microindentation tests

The term "microhardness" has been widely employed in the literature to describe the hardness testing of materials with low applied loads. A more precise term is "microindentation hardness testing." In microindentation hardness testing, a diamond indenter of specific geometry is impressed into the surface of the test specimen using a known applied force (commonly called a "load" or "test load") of 1 to 1000 gf. Microindentation tests typically have forces of 2 N (roughly 200 gf) and produce indentations of about 50 μm. Due to their specificity, microhardness testing can be used to observe changes in hardness on the microscopic scale. Unfortunately, it is difficult to standardize microhardness measurements; it has been found that the microhardness of almost any material is higher than its macrohardness. Additionally, microhardness values vary with load and work-hardening effects of materials.^[2] The two most commonly used microhardness tests are tests that also can be applied with heavier loads as macroindentation tests:

• Vickers hardness test (HV)
• Knoop hardness test (HK)

In microindentation testing, the hardness number is based on measurements made of the indent formed in the surface of the test specimen. The hardness number is based on the surface area of the indent itself divided by the applied force, giving hardness units in kgf/mm². Microindentation hardness testing can be done using Vickers as well as Knoop indenters. For the Vickers test, both the diagonals are measured and the average value is used to compute the Vickers pyramid number. In the Knoop test, only the longer diagonal is measured, and the Knoop hardness is calculated based on the projected area of the indent divided by the applied force, also giving test units in kgf/mm².

The Vickers microindentation test is carried out in a similar manner to the Vickers macroindentation tests, using the same pyramid. The Knoop test uses an elongated pyramid to indent material samples. This elongated pyramid creates a shallow impression, which is beneficial for measuring the hardness of brittle materials or thin components. Both the Knoop and Vickers indenters require prepolishing of the surface to achieve accurate results.^{[citation needed]}

Scratch tests at low loads, such as the Bierbaum microcharacter test, performed with either 3 gf or 9 gf loads, preceded the development of microhardness testers using traditional indenters. In 1925, Smith and Sandland of the UK developed an indentation test that employed a square-based pyramidal indenter made from diamond.^[7] They chose the pyramidal shape with an angle of 136° between opposite faces in order to obtain hardness numbers that would be as close as possible to Brinell hardness numbers for the specimen. The Vickers test has a great advantage of using one hardness scale to test all materials.The first reference to the Vickers indenter with low loads was made in the annual report of the National Physical Laboratory in 1932. Lips and Sack describes the first Vickers tester using low loads in 1936.^{[citation needed]}

There is some disagreement in the literature regarding the load range applicable to microhardness testing. ASTM Specification E384, for example, states that the load range for microhardness testing is 1 to 1000 gf. For loads of 1 kgf and below, the Vickers hardness (HV) is calculated with an equation, wherein load (L) is in grams force and the mean of two diagonals (d) is in millimeters:

Failed to parse (Missing texvc executable; please see math/README to configure.): HV=0.0018544\times\tfrac{L}{d^2}

For any given load, the hardness increases rapidly at low diagonal lengths, with the effect becoming more pronounced as the load decreases. Thus at low loads, small measurement errors will produce large hardness deviations. Thus one should always use the highest possible load in any test. Also, in the vertical portion of the curves, small measurement errors will produce large hardness deviations.

Nanoindentation tests[link]

See also[link]

• Meyer's law
• Leeb rebound hardness test

References[link]

Notes[link]

External links[link]

• "Pinball Tester Reveals Hardness." Popular Mechanics, November 1945, p.75.

Bibliography[link]

• Tabor, David (2000), The Hardness of Metals, Oxford University Press, ISBN 0-19-850776-3, http://books.google.com/?id=b-9LdJ5FHXYC .

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2010)

Dr Sunilam, birth name Sunil Mishra (27 July 1961– ) is a social activist, politician, writer, and former physicist.

Early life[link]

Sunil Mishra was born on 27 July 1961, at Govt. Sultaniya Hospital in Bhopal, India.

His primary to higher-secondary studies were carried out in Kendriya Vidyalaya, Gwalior. He graduated from Govt. Science College, Gwalior and completed his post-graduate Msc Applied Physics from M.I.T.S., Gwalior's engineering college. Sunilam received a PhD in Bio-Medical Electronics from Delhi University. He was Research Associate with CISR. After returning from Burn's Institute, Melbourne, Australia, he became a full-time political worker.

Sunilam also took the responsibility of editing Georage Fernandez' Pratipaksha newspaper. He also managed the editorial work of Nayachakra Magazine of Shri Ram Vilas Paswan.

Through Samajwadi Yuvjan Sabha, he as a schoolchild, participated in a rally demonstration against emergency events. He was district president of Yuva Janata Dal. Later he was the National General Secretary of Yuva Janta for 10 years.

Sunilam was elected International Vice President of International Union of Socialist Youth (an organization of socialist youths of 120 countries connected to Socialist International) in Milan, Italy. He travelled widely to represent the youth of India, in 60 countries of the world, and he kept his analysis in front of the world during presentations.

Being the founder President of Kisan Sangharsh Samiti (Farmers Struggle Committee), he offered his leadership for Kisan Andolans.^[1] He was sent to prison for three months, after his arrest in Kisan Andolan at Multai, M.P, where 24 innocent farmers/kisans were shot dead and 250 injured under police firing on 12 January 1998. Congress Government has lodged 66 false cases against Dr Sunilam and his associate farmers in one single incident of police firing in Multai. Every month, Kisan sangharsh Samiti, Madhya Pradesh organises the Kisan Mahapanchayat (General Meeting of Farmers). On 12 January 2011, the 175th Kisan Mahapanchayat was organized.

In 1998, Sunilam won the legislative assembly seat of Multai, by a margin of 50% votes. He contested this seat as People's candidate of farmers community (Jan Ummidawar of Kisan community) in Kisan mahapanchayat. Later, with the help of various Madhya Pradesh kisan sangathans, he made Kisan-Mazdoor-Adiwasi Kranti Dal, which merged with the Samajwadi Party; he again won the Multai assembly seat in 2003, with 60% of polled votes. He was made the Leader of the Samajwadi Legislative Party of Madhya Pradesh, by party president Shri Mulayam Singh Yadavj, and he was also appointed as National Secretary of Samajwadi Party.

Publication work[link]

Dr. Sunilam published and co-authored two books. In Samajwadi Andolan ke Dastavej (in Hindi with Prof. Vinod Prasad Singh), he collected various facts and papers relating to Samajwadi Andolan. In English he prepared a book with Shri Surendra Mohan, the late shri HariDev Sharma and Prof. V.P. Singh titled "Evolution of Socialist Policy in India". Sunilam also compiled a book on Urvasiam lohia of the northeastern frontier. Sunilam continues to write articles in national newspapers and local dailies.^[2]

Offices[link]

Sunilam is a managing trustee of Lohiya’s Samta Adivasi kendra at the village Urdan, Panchayat Jamadhi, Betul. For almost a decade, he was monitor for CAPART, evaluating various projects. He is active with many kisan and Jan sangathans (social groups), like INSAF, NAPM, Coordination Committee of farmers organization, collision for GM free India, Yusuf Meher Ali yuva biradari, Rastriya Seva dal Sangathan, and Socialist Front.

Travels[link]

Sunilam has travelled the length and breadth of Madhya Pradesh states three times, covering 15,000 kilometres (9,000 mi) for various campaigns. During Dr Ram Manohar's birth-centenary year, Sunilam travelled by road through 21 states and completed 20,000 kilometres (12,000 mi). Saptakranti Vichar yatra was organized by Rastriya Seva Dal and Yusuf Meher ali yuva Biradari. On the occasion of the birth-centenary year of Mama Baleshwar dayal, Sunilam started from Nivarikala (Etawa,U.P) and travelled in Samta yatra to Jhabua.^[3] The next month, Sunilam has undertaken Saptakranti Vichar yatra to northeastern states.

He is also National Secretary of the Indian solidarity committee for Freedom Democracy and Human Rights^[4] and National President of Bhutan Solidarity, which is fighting for Democracy in Bhutan. He is also supporting the movement for restoration of Democracy in Burma and Freedom of Tibet,^[5] In the last nineteen years, Sunilam has organized 150 youth camps in various parts of India, for training young socialists.

Different governments have imposed 132 court cases against him. He has been arrested more than 125 times.^[6] Still he is fighting for the cause. He is regularly writing articles for Hindi daily Jansatta, Aaj Samaj, People's Samachar, Khabaryaar weekly, Sputanik weekly, Mahabeer Samata Sandesh Weekly, in Hindi and English, Janta weekly and English monthly The Otherside.

References[link]

External links[link]

• http://www.tribuneindia.com/2009/20090927/bathinda.htm
• http://eci.nic.in/archive/website_2/S12/138/Dr_Sunilam/Dr_Sunilam.htm
• http://www.hindu.com/2009/08/16/stories/2009081653860400.htm
• http://www.hindustantimes.com/StoryPage/Print/714395.aspx