Hardness numbers range

Durometer. The Durometer hardness test was developed for and is used for determining the hardness of elastomers. The Durometer is a hand-held, spring-loaded instrument which when pressed against the sample forces a conical steel indenter into the surface. Durometer hardness numbers range from 0 to 100 and are read directly from the attached dial indicator. Several load scales are available, but the A scale (8 N = 822 gf) and the D scale (44.5 N = 4.54 kgf) are most common. Specifics of the test procedure are discussed in ASTM D2240 (2). Lighter load scales and larger diameter indenters are available for very soft materials such as foam. 

In the Rockwed test a spheroconical diamond (Brale) indenter or a hardened steel bad is used with various load ranges to achieve a series of scales identified by a suffix letter (Table 3). The suffix letter defines both load and indenter. The most popular scales used are "C" for hard materials and "B" for soft materials. A Rockwed hardness number is meaningless without the letter suffix, eg, HRC 54 or HRB 95. 

The chemistry of Th(IV) has expanded greatly since the mid-1980s (14,28,29). Being a hard metal ion, Th(IV) has the greatest affinity for hard donors such as N, O, and light haUdes such as F and CF. Coordination complexes that are common for the t7-block elements have been studied for thorium. These complexes exhibit coordination numbers ranging from 4 to 11. 

Fuzzy logic gets around this difficulty by replacing hard boundaries between sets with soft divisions. Objects are allocated to fuzzy sets, which are sets with fuzzy boundaries. The membership value of an object within a fuzzy set can lie anywhere within the real number range of 0.0 to 1.0 (Figure 8.4). 

The range of hardness numbers, measured in kilograms per square millimeter, is large. It runs from one for a soft material like KI to about ten thousand for the hardest material—diamond. In other words, it has a range of about four orders of magnitude. 

A fixed force is applied to the axis of the indenter which makes an irreversible indentation into the specimen s surface. The projected length, or area, of this indentation is measured, and the ratio of the applied load to this projection is formed to obtain the hardness number which has the dimensions of stress (also expressable as energy/volume).The sizes of the indentations vary, depending on the indenter s shape and the amount of load applied to it. The size range is from macro- (millimeters), through micro- (microns), to nano-(nanometers). 

The elastic modulus, measured in units of pressure (1 gigapascal = 1 GPa = 10 1 Pa) indicates the stiffness of a material when it is subjected to a load. The larger the value, the stiffer the material. Numbers on the Mohs hardness scale range from 1 for talc, a very soft material, to 10 for diamond, the hardest known substance. 

Branched paraffins (collectively referred to as "isoparaffins ) generally have high octane numbers normal paraffins have low octane numbers Normal paraffins of carbon numbers of seven or fewer are particularly hard to reform to aromatics and relatively hard to isomerize Therefore, the target selectivity was a maximum production of isoparaffins and a minimum production of normal paraffins, particularly in the lower carbon number range (C4-C7) ... 

Hardness. The Brinell hardness number HB ranges from 15 for unalloyed A1 in the soft tender to about 140 for an artificially aged Al—Zn—Mg—1.5 wt%Cu alloy. 

Tyler sieve (Box 4.5) and weighed. Twice the weight is the Hardness Number. Values should range from 90 to less than lOO . ... 

Fully annealed bar stock has a typical hardness of 60 HRA. Vicker numbers range fi"om 190 HV in the annealed condition to 240 HV after 15% cold work (Ref 3). 

Brinell hardness number A measure of the hardness of metals and alloys. It involves pressing a small, hardened steel ball into the surface of the metal being tested by a known loading force. The number is the ratio of the mass of the load in kilograms to the area of the depression created by the ball in square millimetres. Typical numbers range from 60 (soft) to 800 (hard). It is named after Swedish metallurgist J. A. Brinell (1849-1925). 

Another mechanical property that may be important to consider is hardness, which is a measure of a material s resistance to localized plastic deformation (e.g., a small dent or a scratch). Early hardness tests were based on natmal minerals with a scale constructed solely on the ability of one material to scratch another that was softer. A qualitative and somewhat arbitrary hardness indexing scheme was devised, termed the Mohs scale, which ranged from 1 on the soft end for talc to 10 for diamond. Quantitative hardness techniques have been developed over the years in which a small indenter is forced into the surface of a material to be tested under controlled conditions of load and rate of application. The depth or size of the resulting indentation is measured and related to a hardness number the softer the material, the larger and deeper the indentation, and the lower the hardness index number. Measured hardnesses are only relative (rather than absolute), and care should be exercised when comparing values determined by different techniques. 

Silcones are important products of silicon. They may be prepared by hydrolyzing a silicon organic chloride, such as dimethyl silicon chloride. Hydrolysis and condensation of various substituted chlorosilanes can be used to produce a very great number of polymeric products, or silicones, ranging from liquids to hard, glasslike solids with many useful properties. 

There is hardly a metal that cannot, or has not, been joined by some welding process. From a practical standpoint, however, the range of alloy systems that may be welded is more restricted. The term weldability specifies the capacity of a metal, or combination of metals, to be welded under fabrication conditions into a suitable stmcture that provides satisfactory service. It is not a precisely defined concept, but encompasses a range of conditions, eg, base- and filler-metal combinations, type of process, procedures, surface conditions, and joint geometries of the base metals (12). A number of tests have been developed to measure weldabiHty. These tests generally are intended to determine the susceptibiHty of welds to cracking. 

---