ISO 844-2014 pdf free.Rigid cellular plastics —  Determination of compression properties.
ISO 844 specifies a method of determining:
a) the compressive strength and corresponding relative deformation,
b) the compressive stress at 10 % relative deformation, and
c) when desired, the compressive modulus of rigid cellular plastics. There are two procedures:
— Procedure A employs crosshead motion for determination of compressive properties. Procedure A is intended to be used when compressive stress at 10 % relative deformation has to be determined.
— Procedure B employs strain measuring devices mounted on the specimen (contact extensometer) or similar device which measures directly sample deformation. Procedure B is intended to be used when compressive modulus has to be determined.
NOTE Compressive strength (at maximum load) can he determined either with Procedure A and B.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1923, Cellular plastics and rubbers — Determination of linear dimensions
3 Terms and definitions
For the purposes ol this document, the lollowing terms and detinitions apply.
relative deformation
ratio of the reduction (in relation to its initial value) in thickness of the test specimen (Procedure A) or of extensometer gauge length (Procedure B)
Note ito entry: It Is expressed as a percentage.
Note 2 to entry: tm Is the relative deformation corresponding to 0m (see 12).
5 Principle
A compressive force is applied in an axial direction to the faces of test specimen.
The maximum stress supported by the test specimen is calculated.
If the value of the maximum stress corresponds to a relative deformation of less than 10%, it is noted as the compressive strength. Otherwise, the compressive stress at 10 % relative deformation is calculated and its value noted as the compressive stress at 10 % relative deformation”.
6 Apparatus
6.1 Compression-testing machine
Use a compression-testing machine suited to the range of force and displacement involved and having two square or circular plane, parallel plates which are polished and cannot be deformed and of which the length of one side (or the diameter) is at least 10 cm. One of the plates shall be fixed and the other movable; the latter shall be capable of moving at a constant rate of displacement in accordance with the conditions laid down in Clause 8. Neither plate shall be self-aligning.
6.2 Devices for measuring displacement and force
6.2.1 Measurement of displacement
Procedure A — The compression-testing machine shall be fitted with a system allowing continuous measurement of the displacement x of the movable plate with an accuracy of ± 5 % or ± 0,1 mm if this latter value is a more accurate measurement (see second paragraph in 6,2.2).
Procedure B — The measure of displacement shall be obtained by attaching an extensometer to the sample or by using similar devices that measure directly the sample deformation, with an accuracy oh I %.
6.2.2 Measurement of force
A force sensor shall be fixed to one of the machine plates in order to measure the force F produced by the reaction of the test specimen upon the plates during the test. This sensor shall be such that its own deformation during the course of the measurement operation is negligible compared with that being measured and, in addition, it shall allow the continuous measurement of the force at any point in time with an accuracyofi 1%.
It is recommended that a device be used for the simultaneous recording of the force Fandthedisplacement x that allows, by obtaining a curve of F = f(x), the graphical determination of the pair of values F. x required in Clause 9 with the accuracy laid down in 62J. and this subclause, and provides additional information on the behaviour of the product.
6.2.3 Calibration
Devices for measuring and, if applicable. recording graphically the force and displacement produced by the test machine shall be checked periodically. The devices shall be checked by using a series of standard weights, the masses of which are known to accuracies better than ± 1 % and which correspond to the forces applied during the test. To check the devices, spacers shall be used which have thicknesses known to accuracies better than either ± 0,5 % or ± 0,1 mm, whichever is more restrictive.
6.3 Instruments for measuring the dimensions of the test specimens These instruments shall be in accordance with ISO 1923.ISO 844 pdf free download.