ISO 14125 pdf download.Fibre-reinforced plastic composites — Determination of flexural properties
1 Scope
1.1 This International Standard specifies a method for determining the flexural properties of fibre- reinforced plastic composites under three-point (Method A) and four-point (Method B) loading. Standard test specimens are defined but parameters included for alternative specimen sizes for use where appropriate. A range of test speeds is included.
1.2 The method is not suitable for the determination of design parameters, but may be used for screening materials, or as a quality-control test. NOTE – For example, the flexural modulus is only an appropriate value of the tensile Young’s modulus of elasticity as the test is not for the additional deflection due to the shear stress which leads to a lower value of the flexural modulus but uses test span/specimen thickness ratios that minimise this effect. Differences between tensile and flexural properties are also caused by the material structure/lay-up.
1.3 The method is suitable for fibre-reinforced thermoplastic and thermosetting plastic composites. Unreinforced and particle-filled plastics and plastics reinforced with short (i.e. less than 1 mm length) fibres are covered by ISO 1 78.
1.4 The method is performed using specimens which may be moulded to the chosen dimensions, machined from the central portion of the standard multi-purpose test specimen (see ISO 31 67) or machined from semi-finished or finished products such as mouldings or laminates.
1.5 The method specifies preferred dimensions for the specimen. Tests which are carried out on specimens of other dimensions, or on specimens which are prepared under different conditions, may produce results which are not comparable. Other factors, such as the speed of testing and the conditioning of the specimens can influence the results. For materials which are not homogeneous through the section, or above the linear-elastic response region, the result applies only to the thickness and structure tested. Consequently, when comparative data are required, these factors must be carefully controlled and recorded.
3 Principle
The test specimen, supported as a beam, is deflected at a constant rate until the specimen fractures or until the deformation reaches some pre-determined value. During this procedure, the force applied to the specimen and the deflection are measured. The method is used to investigate the flexural behaviour of the test specimens and for determining 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 in three- or four-point flexure. The test geometry is chosen to limit shear deformation and to avoid an interlaminar shear failure. NOTE – The four-point loading geometry provides a constant bending moment between the central loading members. The compressive contact stresses due to the two central loading members are lower in comparison with the stresses induced under the single loading member of the three-point test. The four-point geometry is chosen so that the centre span equals one-third of the outer span. The distance between the outer support points is the same as in the equivalent three-point loading case, therefore the same specimen can be used.
6.2 Specimen preparation
6.2.1 Moulding and extrusion compounds Specimens shall be prepared in accordance with the relevant material specification. When none exists, or when otherwise specified, specimens shall be either directly compression moulded or directly injection moulded from the material in accordance with ISO 293, ISO 294-1 or ISO 295, as appropriate. 6.2.2 Plates Specimens shall be machined from plates in accordance with ISO 281 8.6.2.3 Long-fibre-reinforced plastic materials Specimens shall be machined from a panel prepared in accordance with ISO 1 268 or another specified or agreed-upon procedure. Guidance on machining of plastics is given in ISO 281 8. 6.3 Checking the test specimens The specimens shall be free of twist and shall have mutually perpendicular pairs of parallel surfaces. The surfaces and edges shall be free from scratches, pits, sink marks and flashes. The specimens shall be checked for conformity with these requirements by visual observation against straight-edges, squares and flat plates, and by measuring with micrometer callipers. Specimens showing measurable or observable departure from one or more of these requirements shall be rejected or machined to the required size and shape before testing.