This International Standard specifies a method for determining
the flexural properties of rigid (see 3.12) and semi-rigid plastics
under defined conditions. A standard test specimen is defined, but
parameters are included for alternative specimen sizes for use
where appropriate. A range of test speeds is included.
The method is used to investigate the flexural behaviour of the
test specimens and to determine the flexural strength, flexural
modulus and other aspects of the flexural stress/strain
relationship under the conditions defined. It applies to a freely
supported beam, loaded at midspan (three-point loading test).
The method is suitable for use with the following range of
- thermoplastic moulding, extrusion and casting materials,
including filled and reinforced compounds in addition to unfilled
types; rigid thermoplastics sheets;
- thermosetting moulding materials, including filled and
reinforced compounds; thermosetting sheets.
In agreement with ISO 10350-1 and ISO
10350-2, this International Standard applies to
fibre-reinforced compounds with fibre
lengths ≤ 7,5 mm prior to processing.
For long-fibre-reinforced materials (laminates) with fibre lengths
> 7,5 mm, see ISO 14125.
The method is not normally suitable for use with rigid cellular
materials or sandwich structures containing cellular material. In
such cases, ISO 1209-1 and/or ISO
1209-2 can be used.
NOTE For certain types of textile-fibre-reinforced plastic, a
four-point bending test is preferred. This is described in ISO
The method is performed using specimens which may be either
moulded to the specified dimensions, machined from the central
section of a standard multipurpose test specimen (see ISO 20753) or
machined from finished or semi-finished products, such as
mouldings, laminates, or extruded or cast sheet.
The method specifies the preferred dimensions for the test
specimen. Tests which are carried out on specimens of different
dimensions, or on specimens which are prepared under different
conditions, can produce results which are not comparable. Other
factors, such as the test speed and the conditioning of the
specimens, can also influence the results.
NOTE Especially for semi-crystalline polymers, the thickness of
the oriented skin layer, which is dependent on the moulding
conditions, also affects the flexural properties.
The method is not suitable for the determination of design
parameters but can be used in materials testing and as a quality
For materials exhibiting non-linear stress/strain behaviour, the
flexural properties are only nominal. The equations given have been
derived assuming linear elastic behaviour and are valid for
deflections of the specimen that are small compared to its
thickness. With the preferred specimen (which measures 80 mm × 10
mm × 4 mm) at the conventional flexural strain of 3,5 % and a
span-to-thickness ratio, L/h, of 16, the deflection is
1,5h. Flexural tests are more appropriate for stiff and
brittle materials showing small deflections at break than for very
soft and ductile ones.
Contrary to the previous editions of this International
Standard, this edition specifies two methods, method A and method
B. Method A is identical to the method in previous editions of this
International Standard, i.e. it uses a strain rate of 1 %/min
throughout the test. Method B uses two different strain rates: 1
%/min for the determination of the flexural modulus and 5 %/min or
50 %/min, depending on the ductility of the material, for the
determination of the remainder of the flexural stress-strain
Order online or call: Americas: +1 800 854 7179 | Asia Pacific: +852 2368 5733 | Europe, Middle East, Africa: +44 1344 328039