ISO 75-1:2020 pdf free download.Plastics — Determination of temperature of deflection under load — Part 1: General test method.You can download it here.
ISO 75-1:2020 gives a general test method for the determination of the temperature of deflection under load (flexural stress under three-point loading) of plastics. Different types of test specimen and different constant loads are defined to suit different types of material.
ISO 75-2 gives specific requirements for plastics (including filled plastics and fibre-reinforced plastics in which the fibre length, prior to processing, is up to 7,5 mm) and ebonite, while ISO 75-3 gives specific requirements for high-strength thermosetting laminates and long-fibre-reinforced plastics in which the fibre length, prior to processing, is greater than 7,5 mm.
ISO 75-1:2020 specified are suitable for assessing the relative behaviour of different types of material at elevated temperature under load at a specified rate of temperature increase. The results obtained do not necessarily represent maximum applicable temperatures because, in practice, essential factors, such as time, loading conditions and nominal surface stress, can differ from the test conditions. True comparability of data can only be achieved for materials having the same room-temperature flexural modulus.
The methods specify preferred dimensions for the test specimens.
ISO 75-1:2020 is commonly known as the heat deflection temperature or heat distortion temperature (HDT) test, although there is no official document using this designation.
4 Principle
A standard test specimen is subjected to three-point bending under a constant load in the flatwise raised at a uniform rate, and the temperature at which the standard deflection corresponding to the specified increase in flexural strain, occurs is measured.
5.1 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- arrying 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.
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 specime 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 addin it algebraically to the reading of the apparent deflection of the test specimen.