Three-Point Bending

In the three-point bending test, the specimen is placed on two supports and pressed at its centre by a single loading nose. Load and deflection are recorded to obtain the flexural stress–strain curve. The maximum moment concentrates at a single cross-section, so fracture usually occurs beneath the loading nose.

The purpose is to determine the material's strength and stiffness under bending. In quality control, batch-to-batch consistency is monitored; in design, comparable data is produced for material selection.

• Thermoplastic and thermoset plastic parts
• Fibre-reinforced composite panels
• Wood and wood-based panels
• Ceramic and glass materials
• Welded metal specimens (as a bend test)

• ISO 178 (plastics — determination of flexural properties)
• ASTM D790 (plastics and electrical insulating materials)
• ISO 14125 (fibre-reinforced plastic composites)
• EN 843-1 (advanced technical ceramics — flexural strength)

Setup

Two supports and a single loading nose; support span from the standard, per specimen thickness

Test speed

The speed given by the standard for the material class

Environment

After conditioning in the standard laboratory atmosphere

Quantities measured

Flexural strength, flexural modulus, strain at break

• Universal tension-compression machine
• Three-point bend fixture and adjustable supports
• Load cell and deflection extensometer
• Conditioning chamber
• Specimen measurement equipment (micrometer, calipers)

• Specimen dimensions must be prepared per the standard applied.
• No nicks must form on the edges during cutting and machining.
• Plastic specimens are conditioned in the standard atmosphere before testing.
• Multiple specimens are usually tested; the number is defined in the standard.
• For anisotropic materials, the specimen orientation must be reported.

A single specimen's test takes minutes. Total duration depends on specimen preparation and conditioning; conditioning often takes longer than the test itself.

1. 1The specimen is measured and conditioned if required.
2. 2The support span is set per the standard.
3. 3The specimen is centred on the supports.
4. 4Loading is applied at the defined speed.
5. 5Load and deflection are continuously recorded.
6. 6The test is stopped at fracture or on reaching the defined deformation.
7. 7Flexural strength and modulus are calculated.

The method standard defines how the test is performed, not what the result should be. The acceptance limit comes from the material standard, the product specification or the customer's technical drawing; this page therefore gives no numerical limit.

Results are assessed together with the specimen set's average and spread. A fracture location not beneath the loading nose, or shear-induced damage in the specimen, requires review of the setup geometry.

• Specimen identification, material type and cast/batch number, if any
• Specimen geometry, dimensions and preparation method
• Standard and test conditions applied
• Test temperature and ambient conditions
• Measured values and calculated quantities
• Fracture surface or indentation photographs (where applicable)
• Measurement uncertainty (if requested)
• A statement that the result applies only to the specimen submitted for testing

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

• EN 10204 (inspection documents for metallic products)
• EU 305/2011 Construction Products Regulation (for products used in construction)
• Harmonised standards applied according to the product family

The section below describes the field that the Three-Point Bending test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

• Four-Point Bending
• Tensile Test
• Compression Test
• Bending Test
• Bend Test
• Shear Test
• Torsion Test
• Peel Test
• Adhesion Test
• Break Test
• Puncture Test
• Crush Test