ISO 178:2010 pdf free download – Plastics一Determination of flexural properties.
When determining the flexural modulus, the deflection-measuring system shall be capable of measuring the change in deflection to an accuracy of 1 % of the relevant value or better, corresponding to ±3,4 pm for a support span, L, of 64 mm and a specimen thickness, Ii, of 4,0 mm (see Figure 3). Other support spans and specimen thicknesses will lead to different requirements for the accuracy of the deflection-measuring system.
Any deflection indicator capable of measuring deflection to the accuracy specified above is suitable.
NOTE The crosshead displacement includes not only the specimen deflection but also the indentation of the loading edge and the supports into the specimen and deformation of the machine. The last of these is machine-dependent as well as load-dependent. Results determined on different types of machine are therefore not comparable.
In general, measurement of crosshead displacement is not suitable for modulus determination unless a compliance correction is applied.
5.5 Equipment for measuring the width and thickness of the test specimens
5.5.1 Rigid materials
5.5.1.1 Specimen thickness
Measure the thickness using a micrometer, at points lying within ±2 mm of the centre of the specimen, in accordance with ISO 16012, but using a micrometer that has an accuracy of ±0,01 mm as opposed to the accuracy of ±0,02 mm specified in ISO 16012. The presser foot shall have a flat, circular contact face with a diameter of 4 mm and the anvil shall have a spherical contact face of radius 50 mm to avoid errors caused by misalignment with the test piece.
5.5.1.2 Specimen width
Measure the width in accordance with ISO 16012, using a micrometer that has an accuracy of ±0,02 mm as specified in ISO 16012. The presser foot shall have either a flat contact face which is circular with a diameter of 1 mm or a rectangular contact face with the side which will be parallel to the specimen thickness direction 1 mm long.
In any one test specimen, the thickness within the central third of the length shall not deviate by more than 2 % from its mean value. The width shall not deviate from its mean value within this part of the specimen by more than 3 %. The specimen cross section should preferably be rectangular, with no rounded edges, except as noted in 6.4.
The preferred specimen may be machined from the central part of a multipurpose test specimen complying with ISO 20753.
6.1.3 Other test specimens
When it is not possible or desirable to use the preferred test specimen, use a specimen with the dimensions given in Table 2.
NOTE Certain specifications require that test specimens from sheets of thickness greater than a specified upper limit be reduced to a standard thickness by machining one face only. In such cases, it is conventional practice to place the test specimen such that the original surface of the specimen is in contact with the two supports and the force is applied by the central loading edge to the machined surface of the specimen.