Shore durometer - Wikipedia, the free encyclopedia

An automotive tire tread typically ranges from 50A

to 70A, depending on the application.

Shore durometerFrom Wikipedia, the free encyclopedia

Durometer is one of several measures of the hardness

of a material. Hardness may be defined as a material's

resistance to permanent indentation. The durometer

scale was defined by Albert F. Shore, who developed a

measurement device called a durometer in the 1920s.

The term durometer is often used to refer to the

measurement, as well as the instrument itself. Durometer

is typically used as a measure of hardness in polymers,

elastomers and rubbers.[1]

Contents

1 Durometer scales

2 Method of measurement

3 Relation between Shore hardness and elastic

modulus

4 Patents

5 See also

6 References

7 External links

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 D2240 type A and type D scales. The A

scale is for softer plastics, 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.[2]

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 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 6.4 mm (.25 inch) thick.[3]

Test setup for type A & D[3]

Durometer Indenting footApplied

mass [kg]

Resulting

force [ ]

23-01-2011 Shore durometer - Wikipedia, the free …

en.wikipedia.org/wiki/Shore_durometer 1/4

Type A Hardened steel rod 1.1 mm - 1.4 mm diameter, with a truncated

35º cone, 0.79 mm diameter0.822 8.064

Type DHardened steel rod 1.1 mm - 1.4 mm diameter, with a 30º

conical point, 0.1 mm radius tip4.550 44.64

The final value of the hardness depends on the depth of the indenter after it has been applied for 15sec 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. 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.[1]

Durometers of various common

materials

Material Durometer Scale

Bicycle gel seat 15-30 OO

Chewing gum 20 OO

Sorbothane 40 OO

Sorbothane 30-70 A

Rubber band 25 A

Door seal 55 A

Automotive tire tread 70 A

Soft skateboard wheel 75 A

Hydraulic O-ring 70-90 A

Hard skateboard wheel 98 A

Ebonite Rubber 100 A

Solid truck tires 50 D

Hard hat 75 D

Relation between Shore hardness and elastic modulus

A semi-empirical relation between the Shore hardness and the Young's modulus for elastomers has been

derived by Gent[4]. This relation has the form

where E is the Young's modulus in MPa and S is the Shore hardness. This relation gives a value of at

S = 100 but departs from experimental data for S < 40.

Another relation that fits the experimental data slightly better is[5]

where erf is the error function and E is in units of Pa.



A first order estimate of the relation between Shore D hardness and the elastic modulus for a conical indenter

with a 15 degree cone is [6]

where SD is the Shore-D hardness and E is in MPa.

Another linear relation between the Shore hardness and the Young's modulus is applicable over a large range of

Shore A and Shore D hardnesses[6]. This relation has the form

where SA is the Shore A hardness, SD is the Shore D hardness, and E is the Young's modulus in MPa.

Patents

US patent 1770045 (http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=US1770045) , A.F.

Shore, "Apparatus for Measuring the Hardness of Materials", issued 1930-07-08

US patent 2421449 (http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=US2421449) , J.G. Zuber,

"Hardness Measuring Instrument", issued 1947-06-03

See also

Brinell hardness test

Bloom (test)

Hardness

Knoop hardness test

Leeb Rebound Hardness Test

Rockwell hardness test

Vickers hardness test

References

1. ̂a b "Shore (Durometer) Hardness Testing of Plastics" (http://www.matweb.com/reference/shore-

hardness.asp) . http://www.matweb.com/reference/shore-hardness.asp. Retrieved 2006-07-22.

2. ^ "Material Hardness" (http://www.calce.umd.edu/general/Facilities/Hardness_ad_.htm#3.5) . CALCE and the

University of Maryland. 2001. http://www.calce.umd.edu/general/Facilities/Hardness_ad_.htm#3.5. Retrieved

2006-07-22.

3. ̂a b "Rubber Hardness" (http://www.npl.co.uk/server.php?show=ConWebDoc.379) . National Physical

Laboratory, UK. 2006. http://www.npl.co.uk/server.php?show=ConWebDoc.379. Retrieved 2006-07-22.

4. ^ A.N. Gent, (1958), On the relation between indentation hardness and Young's modulus, International Rubber

Institute Transactions, 34 , pp. 46–57.

5. ^ British Standard 903, (1950,1957), Methods of testing vulcanised rubber Part 19 (1950) and Part A7 (1957).

6. ̂a b Qi, HJ and Joyce, K. and Boyce, MC, (2003), Durometer hardness and the stress-strain behavior of

elastomeric materials, Rubber Chemistry and Technology, 76(2), pp. 419-435.



External links

Durometer reference guide (http://www.rexgauge.com/content/tech_reference_guide)

Durometer Hardness Scale Chart (http://www.plasticsintl.com/polyhardness.htm)

Durometer comparison chart (http://www.rexgauge.com/content/tech_comparison_chart)

Durometer range (http://www.worldoftest.com/bareissmain.htm)

Retrieved from "http://en.wikipedia.org/wiki/Shore_durometer"

Categories: Dimensionless numbers | Hardness tests

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Shore durometer - Wikipedia, the free encyclopedia