STRENGTH OF MATERIALS

STRENGTH OF MATERIALS
Elastic limit is the maximum stress to which a test specimen may be subjected and still
return to its original length upon release of the load. A material is said to be stressed within
the elastic region when the working stress does not exceed the elastic limit, and to be
stressed in the plastic region when the working stress does exceed the elastic limit. The
elastic limit for steel is for all practical purposes the same as its proportional limit.
Yield point is a point on the stress-strain curve at which there is a sudden increase in strain
without a corresponding increase in stress. Not all materials have a yield point. Some representative
values of the yield point (in ksi) are as follows:
Yield strength, Sy, is the maximum stress that can be applied without permanent deformation
of the test specimen. This is the value of the stress at the elastic limit for materials for
which there is an elastic limit. Because of the difficulty in determining the elastic limit, and
because many materials do not have an elastic region, yield strength is often determined by
the offset method as illustrated by the accompanying figure at (3). Yield strength in such a
case is the stress value on the stress-strain curve corresponding to a definite amount of permanent
set or strain, usually 0.1 or 0.2 per cent of the original dimension.
Ultimate strength, Su, (also called tensile strength) is the maximum stress value obtained
on a stress-strain curve.
Modulus of elasticity, E, (also called Young's modulus) is the ratio of unit stress to unit
strain within the proportional limit of a material in tension or compression. Some representative
values of Young's modulus (in 106 psi) are as follows:
Modulus of elasticity in shear, G, is the ratio of unit stress to unit strain within the proportional
limit of a material in shear.
Poisson's ratio, μ, is the ratio of lateral strain to longitudinal strain for a given material
subjected to uniform longitudinal stresses within the proportional limit. The term is found
in certain equations associated with strength of materials. Values of Poisson's ratio for
common materials are as follows:
Compressive Properties.—From compression tests, compressive yield strength, Scy, and
compressive ultimate strength, Scu, are determined. Ductile materials under compression
Aluminum, wrought, 2014-T6 60 Titanium, pure 55–70
Aluminum, wrought, 6061-T6 35 Titanium, alloy, 5Al, 2.5Sn 110
Beryllium copper 140 Steel for bridges and buildings,
ASTM A7-61T, all shapes
33
Brass, naval 25–50
Cast iron, malleable 32–45 Steel, castings, high strength, for structural
purposes, ASTM A148.60 (seven grades)
40–145
Cast iron, nodular 45–65
Magnesium, AZ80A-T5 38 Steel, stainless (0.08–0.2C, 17Cr, 7Ni) 1⁄4 78
Aluminum, cast, pure 9 Magnesium, AZ80A-T5 6.5
Aluminum, wrought, 2014-T6 10.6 Titanium, pure 15.5
Beryllium copper 19 Titanium, alloy, 5 Al, 2.5 Sn 17
Brass, naval 15 Steel for bridges and buildings,
ASTM A7-61T, all shapes
29
Bronze, phosphor, ASTM B159 15
Cast iron, malleable 26 Steel, castings, high strength, for structural
purposes, ASTM A148-60 (seven grades)
29
Cast iron, nodular 23.5
Aluminum 0.334 Nickel silver 0.322
Beryllium copper 0.285 Phosphor bronze 0.349
Brass 0.340 Rubber 0.500
Cast iron, gray 0.211 Steel, cast 0.265
Copper 0.340 high carbon 0.295
Inconel 0.290 mild 0.303
Lead 0.431 nickel 0.291
Magnesium 0.350 Wrought iron 0.278
Monel metal 0.320 Zinc 0.331