Test tools for Flexure Tests
Flexural loading is among the types of loading most frequently occurring in practice and is therefore an important consideration when it comes to testing a wide range of materials. Flexure tests are accordingly used in determining the mechanical properties of steel, plastics, wood, paper, ceramics and other materials.
Characteristic values are generally obtained via 3-point or 4-point flexure tests.
When flexural loading is applied to a symmetrical cross-section, tensile stresses arise in the extreme (outer) fibers along one edge. Compressive stresses arise in the extreme fibers on the opposite side. The stresses on both sides increase with the distance from the neutral axis, so that the highest values in both cases occur in the edge zones. If the tensile or compressive yield point of the material is attained, plastic flow will occur.
During the flexure test shear stresses also arise in the specimen. To keep the shear stress percentage as low as possible during a test, the ratio of the span to the thickness of the specimen must be as high as possible. In most cases the span is specified in the relevant test standard, however.
Specimens with a rectangular cross-section are generally preferred for use in flexure tests.
2-point flexure test kits
The 2-point flexure test kit is suitable for testing of paper, cardboard and films. It is used to determine the bending stiffness (using the beam method) and bending resistance of paper, board and cardboard, e.g. to DIN 53121, ISO 5628 and DIN 19304, plastics to DIN 53350 and coated textiles.
The 3-point flexure test
The loading device consists of two parallel-positioned anvils for the specimen and an upper anvil positioned centrally between the anvils. The upper anvil applies the load to the specimen.
Depending on requirements (standard), the anvils and upper anvils must have fixed, rotating or rocking mountings to enable testing in accordance with specifications.
The test is mainly used for tough and elastic materials.
To minimize frictional influences during testing the anvils can be mounted so as to rotate around their longitudinal axis. Rocking mountings can be used with the upper anvil and anvil supports to ensure that they are parallel to the specimen.
The 4-point flexure test
As with the 3-point flexure test, the 4-point flexure test kit consists of two parallel-positioned anvils which, depending on testing requirements, must have fixed, rotating or rocking mountings.
The difference from the 3-point flexure test lies in the way in which the load is applied to the specimen. This is done via 2 upper anvils located symmetrically to the anvils. The bending moment is then constant between the two force application areas.
This test is primarily used to determine the modulus of elasticity in bending for brittle materials.
Dynstat flexure tool for 4-point flexural loading to DIN 53435 – DB – G
If, for lack of space, only relatively small specimens can be taken from injection-molded parts, the two Dynstat test methods offer interesting options
for the comparative characterization of static and dynamic material properties in quality assurance and product development.
Range of application
The Dynstat flexure tool can be used to determine characteristics of plastics under 4-point flexural loading to DIN 53435 – DB – G. It is used for the characterization of material properties in components made of plastics.
Function description
The Dynstat flexure test is designed as a four-point bending test. With this test fixture, the test can also now be performed on one testing machine. The spans at the start of the test are set to 12 mm and 2 mm. This means a specimen only 15 mm in length can be tested with this method. Flexural deformation is produced by the test fixture's rotational movement. The test result is the maximum flexural stress measured during the test. It is calculated using the bending moment and the resisting moment of the specimen. If the specimen does not break by the time it reaches the Dynstat bending angle defined by the standard, the flexural stress at this point is measured.
Downloads
- Product information: 2-point flexure test kit PDF 518 KB
- Product information: 3-point flexure test kit PDF 246 KB
- Product information: 3- and 4-point flexure test kit PDF 271 KB
- Product information: Dynstat flexure tool for 4-point flexural loading to DIN 53435 – DB – G PDF 6 MB