1.1 This Standard specifies a method for determining the fiexural properties of rigid
and semi-rigid plastics by three point loading test (it applies to a freely supported beam,
loaded at midspan) and specifies the specimens to be tested.
1.2 The method is used to investigate the fiexural behaviourlit of the test specimens
and for determining the fiexural strength, fiexural modulus and other aspects of the
fiexural stress/strain relationship under the conditions defined.
1.3 The method is suitable for use with the following range of materials:
-- thermoplastics moulding and extrusion materials, including filled and reinforced
compounds in addition to unfilled types; rigid thermoplastics sheets;
-- thermosetting moulding materials, including filled and reinforced compounds; ther-
mosetting sheets.
In agreement with JIS K 7140-1 and JIS K 7140-2, this 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 bibliography [2].
The method is not normally suitable for use with rigid cellar materials and sand-
wich structures containing cellular material.
NOTE: For certain types of textile-fibre-reinforced plastics, a four-point bend-
ing test is preferred. It is described in bibliography [2].
1.4 The method is performed using specimens which may be moulded to the speci-
fied dimensions, machined from the central portion of a standard multipurpose test specimen (see JIS K 7139) or machined from finished or semi-finished products such
as mouldings, or extruded or cast sheet.
1.5 The method specifies preferred dimensions for the test specimen. Tests which
are carried out on specimens of different dimensions, or on specimens which are pre-
pared under different conditions, may produce results which are not comparable. Other
factors, such as the test speed and the conditioning of the specimens, can also influ-
ence the results. Especially for semi-crystalline polymers, the thickness of the oriented
skin layer, which is dependent on moulding conditions and thickness, affects the flex-
ural properties. Consequently, when comparable data are required, these factors must
be carefully controlled and recorded.
1.6 Flexural properties can only be used for engineering design purposes for materi-
als with linear stress/strain behaviour. For non-linear behaviour, the flexural prop-
erties are only nominal. The bending test should preferentially be used with brittle
materials, for which tensile tests are difficult.
NOTE ~ The International Standard corresponding to this Standard is as follows.
ISO 178: 2001 Plastics--Determination offlexural properties (IDT) and
Amendment I (2004)
In addition, symbols which denote the degree of correspondence in the
contents between the relevant International Standard and JlS are IDT
(identical), MOD (modified), and NEQ (not equivalent) according to ISO/
IEC Guide 21.
JIS K 7171:2008 Referenced Document
ISO 2602 Statistical interpretation of test results; estimation of the mean; confidence interval
ISO 295 Plastics - Compression moulding of test specimens of thermosetting materials
JIS K 6272 Rubber -- Tensile, flexural and compression test equipment (constant rate of traverse) -- Specification
JIS K 7100 Plastics -- Standard atmospheres for conditioning and testing
JIS K 7139 Plastics -- Test specimens*， 2009-12-21 Update
JIS K 7140-1 Plastics -- Acquisition and presentation of comparable single-point data -- Part 1: Moulding materials
JIS K 7140-2 Plastics -- Acquisition and presentation of comparable single-point data -- Part 2: Long-fibre-reinforced plastics
JIS K 7144 Plastics -- Preparation of test specimens by machining
JIS K 7151 Plastics -- Compression moulding test specimens of thermoplastic materials
JIS K 7152-1 Plastics -- Injection moulding of test specimens of thermoplastic materials -- Part 1: General principles, and moulding of multipurpose and bar test specimens
JIS K 7154-1 Plastics -- Injection moulding of test specimens of thermosetting powder moulding compounds (PMCs) -- Part 1: General principles and moulding of multipurpose test specimens
JIS K 7171:2008 history
2022JIS K 7171:2022 Plastics -- Determination of flexural properties
2016JIS K 7171:2016 Plastics -- Determination of flexural properties
2008JIS K 7171:2008 Plastics -- Determination of flexural properties
1994JIS K 7171:1994 Plastics -- Determination of flexural properties