ISO 178-2019 – Determination of bending properties of Plastics
Isang Paunang Salita
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ISO 178-2019 – Determination of bending properties of Plastics
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This document is prepared by ISO/TC 61, Mga plastik, Subcommittee SC 2, Mechanical Properties.
ISO 178-2019 – Determination of bending properties of Plastics
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. Kumpara sa nakaraang edisyon, 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.
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ISO 178-2019 – Determination of bending properties of Plastics
1 Saklaw
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] at 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), tingnan ang ISO 14125[7].
This method is generally not applicable to rigid porous materials or sandwich structures containing porous materials. Sa ganitong sitwasyon, ISO 1209-1[3] and/or ISO 1209-2[4] pwedeng gamitin.
Tala 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 – 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 (tingnan ang 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.
Tala 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 – Determination of bending properties of Plastics
2 Mga reperensyang normatibo
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. Para sa mga petsang sanggunian, ang binanggit na bersyon lamang ang nalalapat. Para sa mga walang petsang sanggunian, ang bagong bersyon ng sanggunian (kasama ang anumang mga rebisyon) angkop.
ISO 291, Mga plastik — Standard atmosphere for conditioning and testing
ISO 293, Mga plastik — Compression molding of thermoplastic material specimens
ISO 294-1:2017, Mga plastik. Injection molding of thermoplastic material samples. Bahagi 1: General principles and molding of general-purpose and bar specimens
ISO 295, Mga plastik — Compression molding of specimens of thermoset materials
ISO 2602, Statistical interpretation of test results-mean estimates-confidence intervals
ISO 2818, mga plastik na — Preparation of specimens by machining
ISO 750-1, Metallic materials — Calibration and verification of static uniaxial testing machines — Bahagi 1: Tensile/compression testing machines — Calibration and verification of force measurement systems
ISO 9513, Metallic materials — Calibration of extensiometer systems for use in uniaxial testing
ISO 10724-1, Mga plastik — Injection molding of thermoset powder molded plastics (PMC) specimens — Bahagi 1: General principles and molding of multipurpose specimens
ISO 16012, Mga plastik — Determination of linear dimensions of specimens
ISO 20753, Mga plastik — Specimen
ISO 178-2019 – Determination of bending properties of Plastics
3 Terms, definitions and symbols
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3.1 Test speed v
The relative rate of movement between the sample support and the loaded edge
Tala 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
Tala 1: It is calculated based on the relationship given in Equation (5).
Tala 2: It is expressed in megapascals (MPa).
3.3 Bending stress σFB at fracture
Bending stress of the specimen at fracture
Tala 1: It is expressed in megabascals (MPa).
Tala 2: Tingnan sa Larawan 1, curves a and b.
ISO 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)
Tala 1: It is expressed in megabascals (MPa).
Tala 2: Tingnan sa Larawan 1, curves a and b.
3.5 Bending stress σ under conventional deflection
Bending stress at conventional deflection, sC (3.7)
Tala 1: It is expressed in megabascals (MPa).
Tala 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
Tala 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
Tala 1: It is expressed in millimeters (mm).
ISO 178-2019 – Determination of bending properties of Plastics
Tala 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
Tala 1: It is expressed as a dimensionless ratio or percentage (%).
Magsalita 2: It is calculated from the relationship given in equations (6) at (7).
Larawan 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 – Determination of bending properties of Plastics
3.9 Bending strain εFB at fracture
Bending strain of the specimen at fracture
Tala 1: It is expressed as a dimensionless ratio or percentage (%).
Tala 2: Tingnan sa Larawan 1, curves a and b.
3.10 Bending strain εfM under bending strength
Bending strain under maximum bending stress
Tala 1: It is expressed as a dimensionless ratio or percentage (%).
Tala 2: Tingnan sa Larawan 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)
Tala 1: It is expressed in megabascals (MPa).
Magsalita 2: The bending modulus is only an approximation of Young’s modulus.
Tala 3: Please refer to Equation (9).
ISO 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, greater than 700 MPa under the given conditions
[Pinagmulan: ISO 472:2013, 2.884, binago ang — entry comments have been omitted.
3.13 Semi-rigid plastics
A plastic with an elastic modulus in a bending hinge (3.11) o, if this modulus is not applicable, between 70 MPa and 700 MPa under tension for the given conditions
[Pinagmulan: ISO 472:2013, 2.909, binago ang – 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
Tala 1: It is expressed in millimeters (mm).
Tala 2: Tingnan sa Larawan 2.
ISO 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
Magsalita 1: It is expressed as a percentage per minute (% ⋅ min−1).
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