Durometer hardness measures the flexibility of materials like rubber and plastics. The scale ranges from 0 (softest) to 100 (hardest). Two main scales, Shore A and Shore D, are used, with different testing tools and methods. The testing apparatus is called a hardness tester, and the test method involves applying a predetermined force for 15 seconds to determine the depth of penetration. The D-type tester requires more force and is preferred for harder materials. Standards are determined by ASTM and ISO.
Durometer hardness is used to describe both the hardness of a material and the instrument used to measure it. Typically used for rubber, plastics, and other polymers, hardness test results apply a specific value to a material’s hardness. Many people use these results to gauge the strength of a product, but this test wasn’t designed for that. Rather than strength or durability, the hardness scale of the durometer measures the flexibility of the tested specimen. This can be useful when selecting the best material for a particular project.
The durometer hardness scale, developed by Albert Shore in the 1920s, refers to a material’s resistance to permanent indentation when a specific amount of pressure is applied. A deeper indentation indicates a softer material and a lower durometer number. The softest material would have a durometer value of zero, but the scale goes up to 100 for the hardest plastics. Using a numerical scale like this makes it easy to tell the difference between various products, even when you don’t know what the specific numbers mean.
A total of 12 Shore durometer hardness scales have been developed over the years, but only two are in widespread use today. Shore A chart, normally used for softer plastics, and Shore D chart, reserved for stiffer materials. According to the American Society for Testing and Materials (ASTM), both scales use the same 0-100 scale, but are based on slightly different durometer hardness testing tools and methods.
The actual testing apparatus is called a hardness tester or hardness tester. They come in many styles, but they all use the same basic mechanism to get the test result. The mechanism in question is a hardened steel rod attached to a caliper.
The difference between the durometers for the Shore A and D charts is found right at the tip of the steel rod. The shaft for the graph A hardness tester tapers to a point, at an angle of 35°. Graphic tester D is tapered at a 30° angle and is slightly larger in diameter.
Durometer hardness testing standards in North America are determined by ASTM DD2240 00 test method and worldwide by ISO 7619 and ISO 868. According to these standards, the Shore A chart test method consists of ‘Apply the rod, also called the indenter, to the material with a predetermined force for 15 seconds. The depth of penetration determines the durometer number. If there is no penetration, that material would be said to have a durometer of 100. An indentation of 09 inches (2.5 mm), on the other hand, would show a durometer of 0.
The D-type tester is used in the same way. The biggest difference, aside from the size and shape of the indenter, is that the durometer hardness test for chart D requires more than 5 times as much force as the same test for chart A. That’s why this is the preferred method for the hardest materials.
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