Testing Shore Durometer hardness test

The 30% glass-reinforced polypropylene resin has a unique decrease of approximately 25% in work-to-break with increasing test speed above the 0.05 in./min range (Fig. 3-4). An extremely large work-to-break value is demonstrated by the 40% glass-reinforced polyurethane resin (55D Shore Durometer Hardness Base Resin) at the 0.05 in./min straining rate (Fig. 3-9). 

Vickers and Knoop indentors, Barcol hardness, and Shore durometers (2) (b) to measure the resistance of a material to scratching by another material or by a sharp point, such as the Bierbaum hardness or scratch-resistance test and the Moh one for hardness and (c) to measure rebound efficiency or resilience, such as the various Rockwell hardness tests. The various tests provide different behavior characteristics for plastics, as described by different ASTM standards such as D 785. The ASTM and other sources provide different degrees of comparison for some of these tests. 

The shore durometer is a simple instrument used to measure the resistance of a material to the penetration of a blunt needle. In the Barcol approach, a sharp indentor is used to measure the ability of a sample to resist penetration by the indentor (Figure 14.18). The values given in Table 14.3 are for one specific set of conditions and needle area for the Barcol and Brinell hardness tests. 

The so-called brittle point, associated with sample failure in impact tests, may be determined qualitatively using a penetrometer or a Shore durometer (an instrument used to measure resistance of a sample to penetration by a blunt needle) to measure the change in penetration hardness with temperature. Also, a thin film of a polymer may be readily folded at temperatures above T but may crack when folded at temperatures below Tr... 

The particular case of the hardness of rollers is covered by ISO 726734 36 which is in three parts dealing with the normal dead load method, Shore durometer and the Pusey Jones methods respectively. This last method is a very old hardness test which is now virtually never seen, although it is understood to still be popular in some circles for rollers. It is an amazing brass and chain contraption that uses a 3.175 mm indentor acting under a load of 1kg and without a surrounding foot. 

Hardness tests attract more interest in their accuracy, reproducibiliy and intercomparison than any other test - which is probably a result of them being simple tests which are carried out particularly frequently, and because the situation is confused with several scales. The fact that the situation is far from clear cut owes as much to history as to logic. If the Shore durometers had not been the first hardness meters, it is highly doubtful that we would now have spring loaded instruments mounted on stands or use damage prone indentors. Neither would the IRHD scale have been contrived to mimic the status quo. Such is the effect of powerful established interests. 

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

Durometer hardness is measured on tests specimens that meet specific standards for shape and thickness. Durometer hardness is usually measured using the Shore A scale, which measures relative hardness on a scale of 0 to 100 units. Most rubber components for medical use are found in the 35-60 range with 40-50 typical for rubber vial stoppers. Durometer Hardness may be measured on some actual components if they have a sufficiently large flat surface and thickness, i.e., 28-32 mm IV stoppers. 

The so-called Shore hardnesses are measured differently for metals and plastics. With hard materials (metals), a scleroscope is used to measure the rebound of a small steel ball. This Shore hardness is thus measured by a dynamic method, which yields the rebound hardness (the impact elasticity of the rubber industry). Soft plastics, on the other hand, are tested with a Shore durometer. This measures the resistance to the penetration of the point of a cone through the contraction of a calibrated spring. The durometer thus works according to a static method, and yields the true Shore hardness as understood by the rubber industry. Like the Rockwell hardness, the Shore hardness is given in scale divisions. 

TABLE 3.7 Santoprene Mechanical Property Profile— ASTM Test Methods—Durometer Hardness Range, Shore 55 A to 50 D... 

TABLE 3.10 Geolast Mechanical Property Profile—ASTM Test Methods—Room Temperature—Durometer Hardness Range, Shore 70 A to 45 D... 

Hardness measured with a shore durometer according to standard ASTM D2240, an established standard test method for polymers and rubbers... 

Indentation Hardness n Resistance to penetration by an indenter. The hardness of a material as determined by either the size of an indentation made by an indenting tool under a fixed load, or the load needed to produce penetration of an indenter to a predetermined depth. The instruments commonly used with plastics are the Shore Durometer (indenter A for soft resins and elastomers, D for hard materials) described in ASTM D 2240, and the Barcol Impressor, ASTM D 2583. In D 2240, the authors say, No simple relationship exists between indentation hardness determined by this method and any fundamental property of the material tested. For specification purposes it is recommended that Test Method D 1415 (section 09.01) be used for soft materials and method A of D 530 or Test D 785 be used for hard materials. D 530 and D 785 use the Rockwell test in which a ball of suitable diameter is pressed into the... 

The hardness of plastics (and coatings may be considered to be very thin plastics) is most commonly measured by the Shore (durometer) test or Rockwell hardness test. Both of these hardness methods measure the resistance of plastics toward indentation. This provides an empirical hardness value. Shore hardness most often uses either the Shore A or the Shore D scale. These methods are best used for rubbers or elastomers and are also commonly used for softer plastics such as polyolefins, lluoropolymers, and polyvinyls. The Shore A scale is used for softer rubbers while the Shore D scale is used for harder ones. This method works better for thicker coatings, as with all hardness tests on coatings. The hardness of thin coatings can be influenced by the substrate, that is, an artificially hard measure may be measured. A picture of a durometer is shown in Fig. 2.23. 

The hardness range of this class of materials is from 60 Shore A to 60 Shore D. Hardness, modulus and tensile strength all increase as the PP content increases. (The hardness of rubber compounds is typically measured by the Shore Durometer test an indentor is pressed into the material, under a specified load, and the amount of penetration determines the hardness. A circular tip is used for the A scale and a pointed tip is used for the D scale. D means harder materids.)... 

For thermoplastic materials, hardness is often described using the term durometer. A common test is the Shore durometer test, with some of the common test protocols being A, B, C, and D. A comparison of hardness data for some common materials are given in the graph below (Figure 7.22). 

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. 

Figure 7-10 shows durometer scale relationships and hardness ranges. The letter designations refer to the Shore hardness test (Chapter 5, MECHANICAL PROPERTY, Hardness). 

Although not greatly influenced by the mixing ratio of prepolymer and curatives, hardness is one of the most frequently specified and carried-out tests. The two main handheld units are the Shore A and D range Durometers. 

Mechanical Tests. Hardness measurements taken with a Shore A durometer are reported every time a pad specimen has been removed from its water bath for compression-deflection tests. Separate flat slabs, 0.12 and 0.50 in. thick, of polyurethane elastomer, which were cast from the same batch of material and given identical exposure to water as the pads, were employed for the hardness tests. 

Shore hardness (Durometer) is another standard test—ASTM D1706... 

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. 

The two most common types of durometers used for plastics are the Shore Type A and Shore Type D. They differ in the spring force and the geometry of the indentor, as shown in Figure 3.45. Due to creep, readings should be taken after a fixed time interval, often chosen as 10 sec. Typical hardness values of some of the common plastics measured by different test methods are shown in Table 3.4. 

Shore hardness Procedure for determining the indentation hardness of a material by means of a durometer. Shore designation is given to tests made with a specified durometer instrument. 

Hardness measure of a rubber s relative resistance to an indenter point on a testing device. Shore A durometers gauge soft to hard rubber. Shore D durometers are more accurate for samples of ebonite. 

Tests for indention under load are performed basically like the ASTM tests used to measure the hardness of other materials, such as metals and ceramics. There are at least four popular hardness scales in use. Shore A and Shore D are for soft to relatively hard plastics and elastomers. Barcol is used from the mid-range of Shore D to above it. Rockwell M is used for very hard plastics. Figure 3-107 shows the relative ranges covered by these durometers. This diagram does not correlate the different systems in Chapter 2. 

---