ISO 75-1:2020 pdf download.Plastics ‑ Determination of temperature of deflection under load ‑ Part 1: General test method (ISO 75‑1:2020)
4 Principle
A standard test specimen is subjected to three-point bending under a constant load in the flatwise position to produce one of the flexural stresses given in the relevant part of ISO 75. The temperature is raised at a uniform rate, and the temperature at which the standard deflection, corresponding to the specified increase in flexural strain, occurs is measured.
5 Apparatus
5.1 Means of producing a flexural stress The apparatus shall be constructed essentially as shown in Figure 1. It consists of a rigid metal frame in which a rod shall move freely in the vertical direction. One end of the rod is fitted with a weight- carrying plate and the other end is equipped with a loading edge. The base of the frame is fitted with test‑specimen supports. These supports and the vertical members of the frame are made of a material having the same coefficient of linear expansion as the rod. The test‑specimen supports consist of metal pieces that are cylindrical in the contact area and with their lines of contact with the specimen in a horizontal plane.
The size of the span, i.e. of the distance between the contact lines, is given in ISO 75‑2 or ISO 75‑3. The supports are fitted to the base of the frame in such a way that the vertical force applied to the test specimen by the loading edge is midway (±1 mm) between them. The contact edges of the supports are parallel to the loading edge and at right angles to the length direction of the test specimen placed symmetrically across them. The contact edges of the supports and loading edge have a radius of (3,0 ± 0,2) mm and shall be longer than the width of the test specimen.
Unless vertical parts of the apparatus have the same coefficient of linear thermal expansion, the difference in change of length of these parts introduces an error in the reading of the apparent deflection of the test specimen. A blank test shall be made on each apparatus using a test specimen made of rigid material having a low coefficient of expansion and a thickness comparable to that of the specimen under test.
The blank test shall cover the temperature ranges to be used in the actual determination, and a correction term shall be determined for each temperature. If the correction term is 0,01 mm or greater, its value and algebraic sign shall be recorded, and the term applied to each test result by adding it algebraically to the reading of the apparent deflection of the test specimen.
NOTE Invar and borosilicate glass have been found suitable as materials for the test specimen in the blank test.
5.2 Heating equipment
The heating equipment shall be a heating bath containing a suitable liquid, a fluidized bed or an air oven. For heat transfer media other than gas (air) the test specimen shall be immersed to a depth of at least 50 mm. An efficient stirrer or means to fluidize a solid heat transfer medium shall be provided. If liquids are used for heat transfer, it shall be established that the liquid chosen is stable over the temperature range used and does not affect the material under test, for example causing it to swell or crack.
The method using a liquid heat transfer medium shall be considered a reference method in case of doubts or conflicts, if possible, in the temperature range under consideration. The heating equipment shall be provided with a control unit so that the temperature can be raised at a uniform rate of (120 ± 10) °C/h.
The heating rate shall be verified periodically either by
— checking the automatic temperature reading, or
— manually checking the temperature at least every 6 min.ISO 75-1 pdf dowload.ISO 75-1 pdf dowload
