Tensile Test
Tensile test is one of the most common tests for steel. The test is described by standard EN 10 002.
The test involves straining a test piece by tensile force, generally to fracture, for the purpose of
determining tensile strength, yield strength, event. ductility and reduction of area.
16.1.1 Definitions
ƒ
ƒ
ƒ
ƒ
ƒ
gauge length (L) - length of cylindrical or prismatic portion of the test piece on which elongation is
measured at any moment during the test [m]
original gauge length (L0) - gauge length before application of force [m]
final gauge length (Lu) - gauge length after rupture of the test piece [m]
elongation - increase in the original gauge length at the end of the test
ductility – percentage elongation after fracture (A) - permanent elongation of the gauge length
after fracture , expressed as the percentage of the original length:
A=
ƒ
ƒ
[%]
Lu - L0
L0
extension – increase of the original length at a given moment of the test
percentage reduction of area (Z) - maximum change of cross sectional area, which was
occurred during the test, expressed as a percentage of the original cross-sectional area .
Z=
where S0 is
Su
S0 - S u
S0
[%]
original cross-sectional area before testing [m2]
minimum cross-sectional area after fracture [m2]
ƒ
maximum force (Fm) - the greatest force which the test piece withstand during the test [N ]
ƒ
stress (σ) - force at any moment during the test divided by the original cross-sectional area (S0) of
the test piece :
σ=
ƒ
F
S0
tensile strength (Rm) - stress, corresponding to the maximum force Fm :
Rm =
ƒ
Fm
S0
[MPa]
yield strength (Ry) – when metallic material exhibits a yield phenomenon, a point is reached
during the test at which plastic deformation occurs without any increase in the force :
Ry =
where Fy is
ƒ
[MPa]
Fy
S0
[MPa]
force at the point of yield [N]
proof strength (Rp) – stress at which extension is equal to a specified percentage of the gauge
length. the symbol used is followed by a suffix giving the prescribed percentage,for example Rp, 0,2
page 1
Fig.:46 Stress –strain diagram
a) steel with yield point
b) steel with proof strength Rp,0,2
σ [N/mm2]
σ [N/mm2]
( F [N] )
( F [N] )
proof strength
Rp,0,2
tensile strength
Rm
fracture
Ry
yield strenght
elastic limit
proportionality limit
ε [-]
ε [-]
( Δl [mm] )
0,2 %
( Δl [mm] )
16.1.2 Test Pieces
The shape and dimensions of the test pieces depend on the shape and dimensions of the metallic
products the mechanical properties of which are to be determined.
The test piece is usually obtained by machining a sample from the product. However product of
constant cross-section may be subjected to test without being machined. The cross section of the test
pieces may be circular, square, rectangular, annular or, in special cases, of some other shape.
16.1.3 Determination of Original Cross-Section Area
The original cross-section area S0 shall be calculated from measurements of the dimensions of the
test piece.
ƒ for products of circular cross-section and smooth surface S0 may be calculated from formula:
S0 =
π.d 2
4
[mm ]
2
where d is the arithmetic mean of two measurements carried out in two perpendicular direction
ƒ
for products of ribbed surface S0 may be determined from the mass of a known length L and its
density (7850 kg/m3) according the formula :
ρv =
page 2
m
m
=
V
S0 × L
and from it :
S0 =
m
ρv × L
[m ]
2
Vocabulary.
strain
deformace
cold worked steel
ocel tvářená zastudena
ductility
tažnost
elongation
prodloužení
extension
protažení
final gauge length
konečná měřená délka
gauge length
měřená (odměrná) délka
grip
pevně uchytit
jaw
čelist
original gauge length
počáteční měřená délka
percentage elongation after fracture
tažnost
percentage reduction of the area
stažnost (kontrakce)
proof strength
smluvní mez kluzu
reinforcing steel
betonářská ocel
ribbed
žebrovaný, s vroubkovaným povrchem
stress
napětí
stress-strain diagram
pracovní diagram
weldability
svařitelnost
yield
kluz, průtažnost
yield strength
mez kluzu
page 3