For the characterization of material specific properties of plastics the bend testing amongst others is used. Normally test pieces are produced out of the materials, which should be tested in the injection molding and are tested according to DIN 178 with a 3 point- or 4 point picture. Alternatively test pieces with an appropriate size can be taken from finished parts.
DIN EN ISO 178
Bending experiments with metals are performed for the determination of the bending strength and the maximum bending in case of fracture. For this quasi-static experiment the bending over the traverse way is measured and the bending angle at the first crack determined.
The test procedure is illustrated with a tension-extension-graph. Additionally there is the possibility to capture the experiment with a video camera. Hereby a stamp is pressing centered and parallel to the bearings on the test object.
The average bearing distance is standard-compliant or individually adjusted for the experiment. The bearing radius can come to R2 or R5. Commonly 3-point bend tests are performed.
At the 4-point bend test the charge is produced by a double stamp. By this the force is produced without additional shear forces, what leads to a constant bending moment between the bearing points.
For the statistic characterization of fiber-reinforced plastics we offer next to tensile tests also 3- and 4-point-bend tests. At the 3-point bend test the deflection is determined by the traversal pick-up.
The advantage of the 4-point bend test is the shear force free area between the force application points of the double stamp. The deflection is determined with a direct measurement in the middle of the sample between the bearings. Hereby an extensometer with an accuracy class of 0.5 according to EN ISO 9513 is used.
Norm: DIN EN ISO 14125, ASTM D 790,, ASTM D 7264, BMW: PR 544, PR500, AA-0630
The platelet bending test according to VDA 238-100 is used to determine the bending angle with the aim of drawing conclusions about the deformation behaviour and the susceptibility to failure of metallic materials in forming processes with dominant bending proportions or under crash loading.
In the platelet bending test, a bending specimen is bent in the test facility without lubricants and on rotatably mounted support rollers until the strength shut-off threshold is reached. Stamp travel and force are measured on the machine side. The bending angle can either be calculated from the feed movement of the bending punch or determined by manual remeasurement.