Ultimate tensile
strength:
Ultimate tensile strength (UTS), often shortened to tensile strength (TS) or ultimate strength, is the maximum stress that a
material can withstand while being stretched or pulled before failing or
breaking. Tensile strength is not the same as strength
and
the values can be quite different.
Some materials will break sharply, without plastic deformation, in what is called a brittle
failure. Others, which are more ductile, including
most metals, will experience some plastic deformation and possibly necking before
fracture.
The UTS is usually found by performing a tensile
test and
recording the engineering stress versus strain. The highest point of the stress–strain curve (see
point 1 on the engineering stress/strain diagrams below) is the UTS. It is an intensive property;
therefore its value does not depend on the size of the test specimen. However,
it is dependent on other factors, such as the preparation of the specimen, the
presence or otherwise of surface defects, and the temperature of the test
environment and material.
Tensile strengths are rarely used in the design of ductile members, but they are important in brittle
members. They are tabulated for common materials such as alloys, composite materials, ceramics, plastics, and wood.
Tensile strength is defined as a stress, which is measured as force per unit area. For
some non-homogeneous materials (or for assembled components) it can be reported
just as a force or as a force per unit width. In the SI system, the
unit is the pascal (Pa)
(or a multiple thereof, often megapascals (MPa), using the mega- prefix); or, equivalently to pascals, newtons per
square metre (N/m²). AUnited States customary unit is pounds-force per square inch (lbf/in² or psi), or kilo-pounds per square
inch (ksi, or sometimes kpsi), which is equal to 1000 psi; kilo-pounds per square
inch are commonly used when measuring tensile strengths.
