Rubber hardness tests

As the rubber hardness is a measurement of almost completely elastic deformation, it can be related to elastic modulus. Most rubber hardness tests measure the depth of penetration of an inden-tor under either a fixed weight or a spring load, and when rubber is assumed to be an elastic isotropic medium, the indentation obtained at small deformation depends on the elastic modulus, the... 

International Rubber Hardness. The International rubber hardness test (ASTM D1415) (2) for elastomers is similar to the Rockwell test in that the measured property is the difference in penetration of a standard steel ball between minor and major loads. The viscoelastic properties of elastomers require that a load application time, usually 30 seconds, be a part of the test procedure. The hardness number is read direcdy on a scale of 0 to 100 upon return to the minor load. International mbber hardness numbers are often considered equivalent to Durometer hardness numbers but differences in indenters, loads, and test time preclude such a relationship. 

Soden A L. A Practical Manual of Rubber Hardness Testing, Maclaren and Sons, 1951. 

The normal tests use indentors with dimensions of the order of mm, but there are also micro tests that are scaled down by approximately an order of magnitude and allow thinner test pieces to be used and, on rigid materials, produce less damage. With rubbers hardness test are essentially nondestructive. A review of micro tests has been given by-Lopez [5]. 

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

Recommended Practice for Scleroscopic Hardness Testing of Metallic Materials Test Method for Rubber Property International Hardness Test Method for Rubber Property Durometer Hardness... 

This is an instrument for hardness testing and not a plastometer. The Pusey and Jones tester is used for determining hardness particularly on curved surfaces, such as rubber-covered rolls. It operates on a dead-weight principle. 

The most practical tests specifically followed for rubber lining are hardness test, spark test and immersion test. Hardness test is invariably the most frequently prescribed test for rubber lining quality by clients, though it is an inadequate test. The term hardness is a vague one the different expressions such as "Scratch Hardness","Cutting Hardness" "Abrasion Hardness" etc. illustrate that different concepts of hardness exist. 

The standard briefly covers the significance of hardness in terms of its relation with modulus, and the practical use of hardness tests. The hardness tests for rubber that are standardized by ISO are introduced and the distinction between dead load and durometer type instruments is explained to help with selection of a test method for particular circumstances. The effect of test piece, use of standard hardness blocks and comparison of hardness scales is also outlined. 

It would appear that the common standard low temperature tests are not thought totally suitable for measuring effects of crystallisation because a hardness tests has been standardised for this purpose, even although hardness tests are not so commonly used for measuring the immediate effect of low temperature. The international method ISO 338733 and the British method BS 903 Part A6334 are the same and are applicable to unvulcanised as well as vulcanised rubber. This is probably one reason why the hardness test has been introduced because the other methods would not be satisfactory... 

Standard test method for rubber property Durometer hardness Shore A and Shore D hardness testing of rubber Physical testing of rubber Part A57... 

With the second category of hardness tests the measurement is carried out after the load is removed. This is the case with Rockwell R, S, V. L, M and P under a small prestress the position of the sphere is measured, so the permanent penetration depth, h (mm). The sphere diameter isy or j inch, the load is 60, 100 or 150 kg force, dependent on which of the six types of test is chosen. The hardness is defined as HR = 130 - hi0.002. This hardness value has no relation at all to the modulus of elasticity the permanent deformation after recovery is being measured (such a type of test would result in a very high value for rubbers ). 

Test method for indentation hardness of rubbers, international hardness Test for Durometer hardness of rubbers... 

The hardness measured with the small pocket type of hardness meter is associated with the durometer tests. Although there is not an international standard [1] that covers durometers, there is one for plastics, ISO R868 [10], which was used [9]. The two durometers specified are the Shore A and D which are also described in ASTM D2240 [11] where they are intended to cover both rubbers and plastics. The A scale corresponds approximately to the IRHD (International Rubber Hardness Degrees) scale and the D scale can be conveniently be used for hard rubbers above about 90 IRHD. 

Although hardness tests are applied to most classes of polymer materials, they are far more common or important for some materials than for others. Hardness is almost inevitably included in properties of rubbers, fairly often for plastics, and only rarely for composites. With cellular materials a test more equivalent to compression stiffness is termed hardness, while the indentation of fabrics is not practical. Because of the range of stiffness involved across these materials, the methods applied vary considerably. 

In his 1950 review of the history of rubber testing, Buist (IJ observed that prototypes of many of the tests then in use had been tried with varying degrees of success before 1900. and there is no doubt that technologists of that period would still recognize many of the features of the present-day rubber laboratory. The value of tensile stress-strain properties as control measures was appreciated in the late nineteenth century the principles of the indentation hardness test were established before the First World War and the accelerated air-oven aging test dates back at least 80 years. 

Although hardness is much less used in the characterization of plastics than it is for rubbers, there are, nevertheless, several methods of test frequently encountered. The principles behind hardness testing have been considered in Chapter 9. 

Rubber, vulcanized or thermoplastic - Determination of indentatimi hardness - Part 2 IRHD pocket meter method Hardness testing of plastics and mbber... 

VD1 Guideline VDl/VDE 2616-2 Hardness Testing of Plastics and Rubber. VDl/VDE-Gesellschaft Mess- und Automatisierungstechnik, Diisseldorf, 2012. 

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