The standard “EN ISO 14125 Fiber-reinforced plastic composites – Determination of flexural properties”, developed by the International Organization for Standardization (ISO) and later published as a European standard within the scope of harmonization efforts, describes a method for determining the flexural properties of fiber-reinforced plastic composites under three-point (Method A) and four-point (Method B) loading. Standard test specimens are defined, but parameters for alternative specimen sizes are added for use where appropriate. This standard also includes a range of test speeds.
This method is not suitable for determining design parameters, but it can be used for screening materials or as a quality control test. For example, the flexural modulus is simply a suitable value of the tensile Young's modulus of elasticity because the test is not for the additional deflection due to shear stress that leads to a lower flexural modulus value, but uses test aperture/sample thickness ratios that minimize this effect. Differences between tensile and flexural properties also arise from the material structure and layering.
This method is suitable for fiber-reinforced thermoplastic and thermoset plastic composites. Unreinforced and particle-filled plastics, as well as short (i.e., less than 1 mm) fiber-reinforced plastics, are covered by ISO 178.
This method is performed using samples machined from the middle section of a standard multipurpose test specimen that can be molded to selected dimensions (ISO 3167 standard), or samples machined from semi-finished or finished products such as molds or laminates.
This method specifies the preferred dimensions for the sample. Tests performed on samples of different dimensions or samples prepared under different conditions may yield incomparable results. Other factors, such as test speed and sample conditioning, can also affect the results. For materials that are not homogeneous along the cross-section or above the linear elastic response zone, the result is only valid for the thickness and structure being tested. Therefore, these factors must be carefully controlled and recorded when comparative data are needed.
EN ISO 14125 is based on ISO 178 but specifically addresses fiber-reinforced plastic composites. Therefore, it retains the applicable test conditions for glass fiber reinforced systems. The test conditions have been expanded to include both three-point (Method A) and four-point (Method B) loading geometries, as well as conditions for composites based on newer fibers such as carbon and aramid fibers, in accordance with the ISO 178 standard.
In principle, the test specimen, supported as a beam, is deflected at a constant rate until the specimen fractures or the deformation reaches a predetermined value. During this process, the force applied to the specimen and the deflection are measured.
This method is used to study the bending behavior of test specimens and to determine the bending strength, bending modulus, and other aspects of the bending stress/strain relationship under defined conditions. It is applicable to a freely supported beam loaded with three or four-point bending. The test geometry is chosen to limit shear deformation and prevent interlayer shear fracture.
The four-point loading geometry provides a constant bending moment between the central loading elements. The compressive contact stresses resulting from two central loading elements are lower compared to the stresses generated under a single loading element in a three-point test. The four-point geometry is chosen such that the central span is equal to one-third of the outer span. Since the distance between the outer support points is the same as in the equivalent three-point loading case, the same specimen can be used.
In short, EN ISO 14125 is an international standard that defines methods for determining the flexural properties (flexural strength and modulus) of fiber-reinforced plastic composites. This standard applies to both unidirectional and multidirectional fiber-reinforced thermoset and thermoplastic composites, including laminates, molded sheets, and pultrusion profiles.
Bending (three-point or four-point bending) testing is one of the most frequently performed mechanical tests on composites because,
The EN ISO 14125 standard covers composites reinforced with glass, carbon, aramid, or other fibers as follows:
This standard explicitly excludes thick-core sandwich structures (these are covered by ISO 14125 for surfaces only, or by separate standards such as ISO 1922 or ASTM C393 for the entire sandwich).
The EN ISO 14125 standard defines three classes of test methods depending on the expected failure mode and sample geometry:
Class I is the most commonly used. Class II is chosen when the transverse shear stiffness of the material is low (e.g., thick laminates or low-modulus matrices). Classes III and IV provide a closer approximation of the true tensile/compressive modulus in bending by eliminating most of the shear effect.
When performing EN ISO 14125 tests,
For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "EN ISO 14125 Fiber-reinforced plastic composites - Determination of bending properties" standard.
To get an appointment, to get more detailed information or to request an evaluation, you can ask us to fill in our form and reach you.
