Iio Table 47 



MECHANICAL PROPERTIES: INTRODUCTION AND DEFINITIONS 



(Compiled from various sources by Harvey A. Anderson, C.E., Assistant Engineer Physicist, U. S. 

 Bureau of Standards.) 



The mechanical properties of most materials vary between wide limits; the following figures ars given as 

 being representative rather" than what may be expected from an individual sample. Figures denoting such 

 properties are commonly given either as specification or experimental values. Unless otherwise shown, the 

 values below are experimental. Credit for information included is due the U. S. Bureau of Standards; the 

 Am. Soc. for Testing Materials; the Soc. of Automotive Eng.; the Motor Transport Corps, U. S. War Dept.; 

 the Inst, of Mech. Eng.; the Inst, of Metals; Forest Products Lab.; Dept. of Agriculture (Bull. 556); Moore's 

 Materials of Engineering; Hatfield's Cast Iron; and various other American, English and French authorities. 



The specified properties shown are indicated minimums as prescribed by the Am. Soc. for Testing Materials, 

 U. S. Navy Dept., Panama Canal, Soc. of Automotive Eng., or Intern. Aircraft Standards Board. In the 

 majority of cases, specifications show a range for chemical constituents and the average value only of this 

 range is quoted. Corresponding average values are in general given for mechanical properties. In gen- 

 eral, tensile test specimens were 12.8 mm (0.505 in.) diameter and 50.8 mm (2 in.) gage length. Sizes of 

 compressive and transverse specimens are generally shown accompanying the data. 



All data shown in these tables are as determined at ordinary room temperature, averaging 20 C (68° F.). 

 The properties of most metals and alloys vary considerably from the values shown when the tests are con- 

 ducted at higher or lower temperatures. 



The following definitions govern the more commonly confused terms shown in the tables. In all cases the 

 stress referred to in the definitions is equal to the total load at that stage of the test divided by the original 

 cross-sectional area of the specimen (or the corresponding stress in the extreme fiber as computed from the 

 flexure formula for transverse tests). 



Proportional Limit (abbreviated P-limit). — Stress at which the deformation (or deflection) ceases to be 

 proportional to the load (determined with extensometer for tension, compressometer for compression and 

 deflectometer for transverse tests). 



Elastic Limit. — Stress which produces a permanent elongation (or shortening) of 0.001 per cent of the 

 gage length, as shown by an instrument capable of this degree of precision (determined from set readings with 

 extensometer or compressometer). In transverse tests the extreme fiber stress at an appreciable permanent 

 deflection. 



Yield Point. — Stress at which marked increase in deformation (or deflection) of specimen occurs without in- 

 crease in load (determined usually by drop of beam or with dividers for tension, compression or transverse tests). 



Ultimate Strength in Tension or Compression. — Maximum stress developed in the material during test. 



Modulus of Rupture. — Maximum stress in the extreme fiber of a beam tested to rupture, as computed 

 by the empirical application of the flexure formula to stresses above the transverse proportional limit. 



Modulus of Elasticity (Young's Modulus). — Ratio of stress within the proportional limit to the corre- 

 sponding strain, — as determined with an extensometer. Note: All moduli shown are obtained from tensile 

 tests of materials, unless otherwise stated. 



Brinell Hardness Numeral (abbreviated B. h. n.). — Ratio of pressure on a sphere used to indent the 

 material to be tested to the area of the spherical indentation produced. The standard sphere used is a 10- 

 mm diameter hardened steel ball. The pressures used are 3000 kg for steel and 500 kg for softer metals, and 

 the time of application of pressure is 30 seconds. Values shown in the tables are based on spherical areas 

 computed in the main from measurements of the diameters of the spherical indentations, by the following 



formula: 



B. h. n. = P + irtD = P -T- ttD(D/2 - y/D'-U - d 2 /d- 

 P — pressure in kg, / = depth of indentation, D = diameter of ball, and d = diameter of indentation, — all 

 lengths being expressed in mm. Brinell hardness values have a direct relation to tensile strength, and hardness 

 determinations may be used to define tensile strengths by employing the proper conversion factor for the ma- 

 terial under consideration. 



Shore Scleroscope Hardness. — Height of rebound of diamond pointed hammer falling by its own weight 

 on the object. The hardness is measured on an empirical scale on which the average hardness of martensitic 

 high carbon steel equals 100. On very soft metals a " magnifier" hammer is used in place of the commonly 

 used "universal" hammer and values may be converted to the corresponding "universal" value by multi- 

 plying the reading by $. The scleroscope hardness, when accurately determined, is an index of the tensile 

 elastic limit of the metal tested. 



Erlchsen Value. — Index of forming quality of sheet metal. The test is conducted by supporting the 

 sheet on a circular ring and deforming it at the center of the ring by a spherical pointed tool. The depth of 

 impression (or cup) in mm required to obtain fracture is the Erichsen value for the metal. Erichsen standard 

 values for trade qualities of soft metal sheets are furnished by the manufacturer of the machine corresponding 

 to various sheet thicknesses. (See Proc. A. S. T. M. 17, part 2, p. 200, 1017.) 



Alloy steels are commonly used in the heat treated condition, as strength increases are not commensurate 

 with increases in production costs for annealed alloy steels. Corresponding strength values are accordingly 

 shown for annealed alloy steels and for such steels after having been given certain recommended heat treat- 

 ments of the Society of Automotive Engineers. The heat treatments followed in obtaining the properties 

 shown are outlined on the pages immediately following the tables on steel. It will be noted that considerable 

 latitude is allowed in the indicated drawing temperatures and corresponding wide variations in physical prop- 

 erties may be obtained with each heat treatment. The properties vary also with the size of the specimens 

 heat treated. The drawing temperature is shown with the letter denoting the heat treatment, wherever the 

 information is available. 



