ISO 178-2019 – Stanovení ohybových vlastností plastů
Předmluva
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ISO 178-2019 – Stanovení ohybových vlastností plastů
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This document is prepared by ISO/TC 61, Plasty, Podvýbor SC 2, Mechanical Properties.
ISO 178-2019 – Stanovení ohybových vlastností plastů
The sixth edition eliminates and replaces the technically revised fifth edition (ISO 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.
ISO 178-2019 – Stanovení ohybových vlastností plastů
1 Rozsah
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] a ISO 10350-2[6], this document applies to fiber reinforced compounds with fiber length ≤7.5 mm before processing. For fiber length > 7.5 mm long fiber reinforcement (laminate), viz ISO 14125[7].
This method is generally not applicable to rigid porous materials or sandwich structures containing porous materials. V tomto případě, ISO 1209-1[3] and/or ISO 1209-2[4] can be used.
Poznámka 1 For certain types of textile fiber reinforced plastics, a four-point bending test is used. This is described in ISO 14125.
ISO 178-2019 – Stanovení ohybových vlastností plastů
The method is carried out using specimens that may be molded to specified dimensions, processed from the central portion of a standard multipurpose specimen (viz 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.
Poznámka 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.
ISO 178-2019 – Stanovení ohybových vlastností plastů
2 Normativní odkazy
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. Pro datované odkazy, platí pouze citovaná verze. Pro nedatované reference, novou verzi reference (včetně případných revizí) platí.
ISO 291, Plasty — Standard atmosphere for conditioning and testing
ISO 293, Plasty — Compression molding of thermoplastic material specimens
ISO 294-1:2017, Plasty. Injection molding of thermoplastic material samples. Část 1: General principles and molding of general-purpose and bar specimens
ISO 295, Plasty — Compression molding of specimens of thermoset materials
ISO 2602, Statistical interpretation of test results-mean estimates-confidence intervals
ISO 2818, plasty — Preparation of specimens by machining
ISO 750-1, Kovové materiály — Calibration and verification of static uniaxial testing machines — Část 1: Stroje na testování tahem/tlakem — Calibration and verification of force measurement systems
ISO 9513, Kovové materiály — Calibration of extensiometer systems for use in uniaxial testing
ISO 10724-1, Plasty — Injection molding of thermoset powder molded plastics (PMC) specimens — Část 1: General principles and molding of multipurpose specimens
ISO 16012, Plasty — Determination of linear dimensions of specimens
ISO 20753, Plasty — Specimen
ISO 178-2019 – Stanovení ohybových vlastností plastů
3 Terms, definitions and symbols
Pro účely tohoto dokumentu, platí následující termíny a definice.
ISO a IEC udržují terminologické databáze pro standardizaci na následujících adresách:
– ISO online prohlížecí platforma: k dispozici na iso.org/obp
– Elektronická encyklopedie IEC: k dispozici na electropedia.org
3.1 Test speed v
The relative rate of movement between the sample support and the loaded edge
Poznámka 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
Poznámka 1: It is calculated based on the relationship given in Equation (5).
Poznámka 2: It is expressed in megapascals (MPa).
3.3 Bending stress σFB at fracture
Bending stress of the specimen at fracture
Poznámka 1: It is expressed in megabascals (MPa).
Poznámka 2: See Figure 1, curves a and b.
ISO 178-2019 – Stanovení ohybových vlastností plastů
3.4 Flexural strength σfM
Maximum bending stress sustained by the specimen during bending test (3.2)
Poznámka 1: It is expressed in megabascals (MPa).
Poznámka 2: See Figure 1, curves a and b.
3.5 Bending stress σ under conventional deflection
Bending stress at conventional deflection, sC (3.7)
Poznámka 1: It is expressed in megabascals (MPa).
Poznámka 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
Poznámka 1: It is expressed in millimeters (mm).
3.7 Conventional deflection sC
The deflection (3.6) is equal to 1.5 times the sample thickness H
Poznámka 1: It is expressed in millimeters (mm).
ISO 178-2019 – Stanovení ohybových vlastností plastů
Poznámka 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
Poznámka 1: It is expressed as a dimensionless ratio or percentage (%).
Poznámka 2: It is calculated from the relationship given in equations (6) a (7).
Postava 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 |
ISO 178-2019 – Stanovení ohybových vlastností plastů
3.9 Bending strain εFB at fracture
Bending strain of the specimen at fracture
Poznámka 1: It is expressed as a dimensionless ratio or percentage (%).
Poznámka 2: See Figure 1, curves a and b.
3.10 Bending strain εfM under bending strength
Bending strain under maximum bending stress
Poznámka 1: It is expressed as a dimensionless ratio or percentage (%).
Poznámka 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)
Poznámka 1: It is expressed in megabascals (MPa).
Poznámka 2: The bending modulus is only an approximation of Young’s modulus.
Poznámka 3: Please refer to Equation (9).
ISO 178-2019 – Stanovení ohybových vlastností plastů
3.12 Rigid plastics
Plastics with an elastic modulus (3.11) in bending hinges or, if not applicable, in stretching, greater than 700 MPa under the given conditions
[Source: ISO 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) nebo, if this modulus is not applicable, mezi 70 MPa and 700 MPa under tension for the given conditions
[Source: ISO 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
Poznámka 1: It is expressed in millimeters (mm).
Poznámka 2: See Figure 2.
ISO 178-2019 – Stanovení ohybových vlastností plastů
3.15 Bending strain rate r
Rate of increase in bending strain (3.8) during the test
Poznámka 1: It is expressed as a percentage per minute (% ⋅ min−1).
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