ИСО 178-2019 – Determination of bending properties of Plastics
А Префаце
ИСО (Међународна организација за стандардизацију) је глобални савез националних тела за стандардизацију (Тела чланица ИСО). Развој међународних стандарда се обично спроводи преко ИСО техничких комитета. Свака институција чланица заинтересована за предмет за који је основан технички комитет има право да буде заступљена у комитету. У овај посао су укључене и владине и невладине међународне организације које су у вези са организацијама за стандардизацију. ИСО блиско сарађује са Међународном електротехничком комисијом (ИЕЦ) о свим питањима електричне стандардизације.
The procedures used to develop this document as well as those used for further maintenance are described in Part 1 ИСО/ИЕЦ директиве. Нарочито, треба обратити пажњу на различите критеријуме одобрења који су потребни за различите типове ИСО докумената. Овај документ је састављен у складу са уређивачким правилима Дел 2 ИСО/ИЕЦ директиве (види исо.орг/дирецтивес).
ИСО 178-2019 – Determination of bending properties of Plastics
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Any trade names used in this document are provided as information for the convenience of the user and do not constitute an endorsement.
Voluntary, related standards and conformity assessment related ISO specific and express the meaning of terminology as well as in relevant ISO technical barriers to trade (ТБТ) adhere to the principle of the world trade organization (WTO) information, please refer to the following URL:iso.org/iso/foreword.html.
This document is prepared by ISO/TC 61, Пластика, Subcommittee SC 2, Mechanical Properties.
ИСО 178-2019 – Determination of bending properties of Plastics
The sixth edition eliminates and replaces the technically revised fifth edition (ИСО 178:2010). It also incorporates amendments to ISO 178:2010 / Amd.1:2013. Compared with the previous edition, the main changes are as follows:
– Differentiation of calibration requirements according to test type;
– Introduction of deflectometer;
– Resumption of compliance correction procedures;
— A new annex D has been added, showing the relationship between tensile modulus and bending modulus.
Any feedback or questions regarding this document should be directed to the user’s national standards body. A full list of these agencies can be found at iso.org/members.html.
ИСО 178-2019 – Determination of bending properties of Plastics
1 Обим
This document specifies a method for determining the bending properties of rigid and semi-rigid plastics under specified conditions. The preferred sample selection was defined, but parameters for the size of the standby sample were included for use where appropriate. Includes a series of test speeds.
This method is used to study the bending behavior of the specimen and to determine the bending strength, bending modulus and other aspects of the bending stress/strain relationship under defined conditions. It is suitable for free support beams loaded at mid-span (three-point loading test).
The method is applicable to the following material ranges:
– Thermoplastic forming, extrusion and casting materials, including filled and reinforced compounds in addition to unfilled types; Rigid thermoplastic sheet;
– Thermoset molding materials, including filling and reinforcing compounds; Thermoset sheet.
According to ISO 10350-1[5] и ИСО 10350-2[6], this document applies to fiber reinforced compounds with fiber length ≤7.5 mm before processing. For fiber length &гт; 7.5 mm long fiber reinforcement (laminate), see ISO 14125[7].
This method is generally not applicable to rigid porous materials or sandwich structures containing porous materials. In this case, ИСО 1209-1[3] and/or ISO 1209-2[4] can be used.
Белешка 1 For certain types of textile fiber reinforced plastics, a four-point bending test is used. This is described in ISO 14125.
ИСО 178-2019 – Determination of bending properties of Plastics
The method is carried out using specimens that may be molded to specified dimensions, processed from the central portion of a standard multipurpose specimen (see ISO 20753) or processed from finished or semi-finished products, such as moulds, laminated plates or extruded or cast plates.
This method specifies the selected size of the sample. Tests performed on specimens of different sizes or prepared under different conditions can yield incomparable results. Other factors, such as the speed of the test and the conditioning of the specimen, can also affect the results.
Белешка 2 Especially for injection molded semi-crystalline polymers, the thickness of the oriented skin layer depends on the forming conditions and also affects the bending performance.
This method is not suitable for the determination of design parameters, but it can be used for material testing and quality control testing.
ИСО 178-2019 – Determination of bending properties of Plastics
2 Normative references
The following documents are referenced in the text in such a way that some or all of their contents constitute the requirements of this document. За датиране референце, примењује се само наведена верзија. For undated references, the new version of the reference (укључујући све ревизије) примењује.
ИСО 291, Пластика — Standard atmosphere for conditioning and testing
ИСО 293, Пластика — Compression molding of thermoplastic material specimens
ИСО 294-1:2017, Пластика. Injection molding of thermoplastic material samples. Парт 1: General principles and molding of general-purpose and bar specimens
ИСО 295, Пластика — Compression molding of specimens of thermoset materials
ИСО 2602, Statistical interpretation of test results-mean estimates-confidence intervals
ИСО 2818, пластике — Preparation of specimens by machining
ИСО 750-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Парт 1: Tensile/compression testing machines — Calibration and verification of force measurement systems
ИСО 9513, Metallic materials — Calibration of extensiometer systems for use in uniaxial testing
ИСО 10724-1, Пластика — Injection molding of thermoset powder molded plastics (PMC) specimens — Парт 1: General principles and molding of multipurpose specimens
ИСО 16012, Пластика — Determination of linear dimensions of specimens
ИСО 20753, Пластика — Specimen
ИСО 178-2019 – Determination of bending properties of Plastics
3 Terms, definitions and symbols
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for standardization at the following addresses:
– ISO online browsing platform: available at iso.org/obp
– IEC Electronic Encyclopedia: available at electropedia.org
3.1 Test speed v
The relative rate of movement between the sample support and the loaded edge
Белешка 1: It is expressed in millimeters per minute (mm/min).
3.2 Bending stress σf
Nominal stress on the outer surface of the specimen at the middle span
Белешка 1: It is calculated based on the relationship given in Equation (5).
Белешка 2: It is expressed in megapascals (МПа).
3.3 Bending stress σFB at fracture
Bending stress of the specimen at fracture
Белешка 1: It is expressed in megabascals (МПа).
Белешка 2: See Figure 1, curves a and b.
ИСО 178-2019 – Determination of bending properties of Plastics
3.4 Flexural strength σfM
Maximum bending stress sustained by the specimen during bending test (3.2)
Белешка 1: It is expressed in megabascals (МПа).
Белешка 2: See Figure 1, curves a and b.
3.5 Bending stress σ under conventional deflection
Bending stress at conventional deflection, sC (3.7)
Белешка 1: It is expressed in megabascals (МПа).
Белешка 2: See also Figure 1, Curve c.
3.6 Deflection s
The distance of the top or bottom surface of the mid-span specimen from its original position during bending
Белешка 1: It is expressed in millimeters (мм).
3.7 Conventional deflection sC
The deflection (3.6) is equal to 1.5 times the sample thickness H
Белешка 1: It is expressed in millimeters (мм).
ИСО 178-2019 – Determination of bending properties of Plastics
Белешка 2: Using a 16-h span L, the conventional deflection corresponds to a flexure strain of 3.5% (3.8).
3.8 Bending strain εf
Nominal fractional change in wafer length on the outer surface of the specimen at the mid-span
Белешка 1: It is expressed as a dimensionless ratio or percentage (%).
Remark 2: It is calculated from the relationship given in equations (6) и (7).
Figure 1 — Typical curves of bending stress σf versus bending strain εf and deflection s
| Curve a | A specimen that breaks before yielding |
| Curve b | The specimen that gives the maximum value then breaks before the conventional deflection, sC |
| Curve c | Specimens that neither give a maximum nor break before the conventional deflection, sC |
ИСО 178-2019 – Determination of bending properties of Plastics
3.9 Bending strain εFB at fracture
Bending strain of the specimen at fracture
Белешка 1: It is expressed as a dimensionless ratio or percentage (%).
Белешка 2: See Figure 1, curves a and b.
3.10 Bending strain εfM under bending strength
Bending strain under maximum bending stress
Белешка 1: It is expressed as a dimensionless ratio or percentage (%).
Белешка 2: See Figure 1, curves a and b.
3.11 Flexural modulus Flexural modulus Ef
Ratio of the stress difference σf2 − σf1 to the corresponding strain difference εf2 (= 0,002 5) − εf1 (= 0,000 5)
Белешка 1: It is expressed in megabascals (МПа).
Remark 2: The bending modulus is only an approximation of Young’s modulus.
Белешка 3: Please refer to Equation (9).
ИСО 178-2019 – Determination of bending properties of Plastics
3.12 Rigid plastics
Plastics with an elastic modulus (3.11) in bending hinges or, if not applicable, in stretching, веће од 700 MPa under the given conditions
[Извор: ИСО 472:2013, 2.884, modified — entry comments have been omitted.
3.13 Semi-rigid plastics
A plastic with an elastic modulus in a bending hinge (3.11) или, if this modulus is not applicable, between 70 MPa and 700 MPa under tension for the given conditions
[Извор: ИСО 472:2013, 2.909, modified – entry comments have been omitted.
3.14 Span L between sample supports
The distance between the contact point between the specimen and the specimen holder
Белешка 1: It is expressed in millimeters (мм).
Белешка 2: See Figure 2.
ИСО 178-2019 – Determination of bending properties of Plastics
3.15 Bending strain rate r
Rate of increase in bending strain (3.8) during the test
Remark 1: It is expressed as a percentage per minute (% ⋅ min−1).
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