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The Shore durometer is a device for measuring the
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
of a material, typically of
polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s. Higher numbers on the scale indicate a greater resistance to indentation and thus harder materials. Lower numbers indicate less resistance and softer materials. The term is also used to describe a material's rating on the scale, as in an object having a "'Shore durometer' of 90." The scale was defined by
Albert Ferdinand Shore Albert Ferdinand Shore (September 4, 1876 – January 17, 1936) was an American metallurgist who invented the Shore durometer. He won the Elliott Cresson Medal. Shore was born in New York City. He invented the first quadrant durometer in 1915 to ...
, who developed a suitable device to measure hardness in the 1920s. It was neither the first hardness tester nor the first to be called a ''durometer'' ( ISV '' duro-'' and '' -meter''; attested since the 19th century), but today that name usually refers to Shore hardness; other devices use other measures, which return corresponding results, such as for
Rockwell hardness The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). Th ...
.


Durometer scales

There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the
ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
D2240 type A and type D scales. The A scale is for softer ones, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use: types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in a value between 0 and 100, with higher values indicating a harder material.


Method of measurement

Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its
viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly wi ...
properties, the shape of the presser foot, and the duration of the test. ASTM D2240 durometers allows for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock, and measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6 mm (0.25 inches) thick. Theoretical background of the test is considered in Stoßprobleme in Physik, Technik und Medizin by Grundlagen und Anwendungen The ASTM D2240 standard recognizes twelve different durometer scales using combinations of specific spring forces and indentor configurations. These scales are properly referred to as durometer types; i.e., a durometer type is specifically designed to determine a specific scale, and the scale does not exist separately from the durometer. The table below provides details for each of these types, with the exception of Type R. Note: Type R is a designation, rather than a true "type". The R designation specifies a presser foot diameter (hence the R, for radius; obviously D could not be used) of 18 ± 0.5 mm (0.71 ± 0.02 in) in diameter, while the spring forces and indenter configurations remain unchanged. The R designation is applicable to any D2240 Type, with the exception of Type M; the R designation is expressed as Type xR, where x is the D2240 type, e.g., aR, dR, etc.; the R designation also mandates the employment of an operating stand. Some conditions and procedures that have to be met, according to DIN ISO 7619-1 standard are: * For measuring Shore A the foot indents the material while for Shore D the foot penetrates the surface of the material. * Material for testing needs to be in laboratory climate storage at least one hour before testing. * Measuring time is 15s. * Force is 1 kg +0.1 kg for Shore A, and 5 kg +0.5 kg for Shore D. * Five measurements need to be taken. * Calibration of the Durometer is one per week with elastomer blocks of different hardness. The final value of the hardness depends on the depth of the indenter after it has been applied for 15 seconds on the material. If the indenter penetrates 2.54 mm (0.100 inch) or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. But if the hardness is <10 °Sh or >90 °Sh the results are not to be trusted. The measurement must be redone with adjacent scale type. Durometer is a dimensionless quantity, and there is no simple relationship between a material's durometer in one scale, and its durometer in any other scale, or by any other hardness test.


ASTM D2240 hardness and elastic modulus

Using linear elastic indentation hardness, a relation between the
ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
D2240 hardness and the
Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied leng ...
for
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
s has been derived by GentA. N. Gent (1958), On the relation between indentation hardness and Young's modulus, Institution of Rubber Industry -- Transactions, 34, pp. 46–57. .Gent's relation has the form E = \frac, where E is the Young's modulus in MPa and S is the ASTM D2240 type A hardness. This relation gives a value of E = \infty at S = 100 but departs from experimental data for S < 40 . Mix and Giacomin derive comparable equations for all 12 scales that are standardized by ASTM D2240.A. W. Mix and A. J. Giacomin (2011), Standardized Polymer Durometry, ''Journal of Testing and Evaluation'', 39(4), pp. 1–10. Another relation that fits the experimental data slightly better isBritish Standard 903 (1950, 1957), Methods of testing vulcanised rubber Part 19 (1950) and Part A7 (1957). S = 100 \operatorname(3.186\times10^~ E^), where \operatorname is the
error function In mathematics, the error function (also called the Gauss error function), often denoted by , is a complex function of a complex variable defined as: :\operatorname z = \frac\int_0^z e^\,\mathrm dt. This integral is a special (non-elementary ...
, and E is in units of Pa. A first-order estimate of the relation between ASTM D2240 type D hardness (for a conical indenter with a 15° half-cone angle) and the elastic modulus of the material being tested isQi, H. J., Joyce, K., Boyce, M. C. (2003), Durometer hardness and the stress-strain behavior of elastomeric materials, ''Rubber Chemistry and Technology'', 76(2), pp. 419–435. S_\text = 100 - \frac, where S_\text is the ASTM D2240 type D hardness, and E is in MPa. Another Neo-Hookean linear relation between the ASTM D2240 hardness value and material elastic modulus has the form \log_ E = 0.0235 S - 0.6403, \quad S = \begin S_\text & \text~20 < S_A < 80, \\ S_\text + 50 & \text~30 < S_D < 85, \end where S_\text is the ASTM D2240 type A hardness, S_\text is the ASTM D2240 type D hardness, and E is the Young's modulus in MPa.


Patents

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See also

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Brinell hardness test The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science. History Proposed by Swe ...
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Bloom (test) Bloom is a test to measure the strength of a gel or gelatin. The test was originally developed and patented in 1925 by Oscar T. Bloom. The test determines the weight in grams needed by a specified plunger (normally with a diameter of 0.5 inch) to ...
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Knoop hardness test The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed i ...
* Leeb Rebound Hardness Test *
Rockwell hardness test The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). The ...
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Vickers hardness test The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness t ...


References

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External links


Comparison Chart

Reference Guide

Растеряев Ю.К., Агальцов Г.Н. Связь между твёрдостью и модулем упругости резин (Connection between hardness and a modulus of gums)
Dimensionless numbers Hardness tests Rubber properties