BS EN ISO 20504:2016 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for compressive behaviour of continuous fibre- reinforced composites at room temperature (ISO 20504:2006)
5.2Load train
The load train is composed of movable and fixed cross-heads, the loading rods and the grips or platens. Loadtrain couplers may additionally be used to connect the grips or platens to the loading rods.
The load train shall align the test specimen axis with the direction of force application without introducingbending or torsion in the test specimen. The misalignment of the test specimen shall be verified anddocumented in accordance with the procedure described in Annex B. The maximum percent bending shall notexceed 5 % at an average axial strain of 500× 10-6.
There are two alternative means of force application:
a) Compression platens are connected to the force transducer and the moving cross-head.The parallelism
of these platens shall be better than 0,01 mm, in the loading area and the faces of the platens shall beperpendicular to the force application direction.
NOTE1 The use of platens is not recommended for compression testing of 1D and 2D materials with smallthicknesses because of buckling.
NOTE2 A compliant interlayer material (composed only of paper or cardboard), between the test specimen andplatens, can be used for testing macroscopically inhomogeneous materials to ensure uniform contact pressure.
When the dimensions of the test specimen are such that buckling may occur, it is recommended to useantibuckling devices similar to those described in lSO 14126.These devices should not introduceparasitic stresses (i.e.stresses other than the uniform , axial stress) during loading of the test specimen.
b) Grips are used to clamp and load the test specimen. The grip design shall prevent the test specimen from
slipping and the grips shall align the test specimen axis with that of the applied force.
Alignment shall be verified and documented in accordance with, for example,the procedure described inAnnex B.
5.3Strain measurement
5.3.1 General
For continuous measurement of the longitudinal deformation as a function of the applied force, either straingauges or a suitable extensometer may be used.Use an extensometer that meets the requirements of at leastclass 1 in ISO 9513.Measurement of longitudinal deformation over a length as long as possible within thegauge section length of the test specimen is recommended.
5.3.2Strain gauges
Strain gauges are used for the verification of the alignment on the test specimen. They may also be used todetermine longitudinal deformation during testing. In both cases, the length of the strain gauges shall be suchthat the readings are not affected by local features on the surface of the specimen, such as fibre crossovers.Unless it can be shown that strain gauge readings are not unduly influenced by localized strain events, suchas fibre crossovers, strain gauges should be not less than 9 mm to 12 mm in length for the longitudinaldirection and not less than 6 mm in length for the transverse direction. The strain gauges, surface preparationand bonding agents/adhesives should be chosen to provide adequate performance on the subject materials.
Suitable strain-conditioning and recording equipment should be used.Care shall be taken to ensure that thestrain gauge readings are not influenced by the surface preparation and the adhesive used.
5.3.3 Extensometry
The linearity tolerance of the extensometer shall be less than 0,15 % of the extensometer range used.Extensometers shall meet the requirements of at least class 1 in accordance with ISO 9513.
Types of commonly used extensometers are described in and Mechanical extensometer
For a mechanical extensometer, the gauge length corresponds to the longitudinal distance between the twolocations where the extensometer contacts the test specimen.Mounting of the extensometer to the testspecimen shall prevent slippage of the extensometer at the contact points and shall not initiate failure underthe contact points.Any extensometer contact forces shall not introduce bending greater than that allowedin 5.2. Electro-optical extensometer
Electro-optical measurements of strain require reference marks on the test specimen. For this purpose,fiducial marks such as rods or flags are attached to the test specimen surface perpendicular to the longitudinalaxis of the test specimen.The gauge length corresponds to the longitudinal distance between the two fiducialmarks.
NOTE The use of integral flags as part of the test specimen geometry is not recommended,because of stressconcentrations induced by such features.
5.4Data recording system
A calibrated recorder may be used to record force-deformation curves. The use of a digital data recordingsystem combined with an analog recorder is recommended.
5.5Dimension measuring devices
Devices used for measuring linear dimensions of the test specimen shall be accurate to ±0,1 mm.Micrometers shall be in accordance with lsO 3611.
6Test specimens
The choice of test specimen geometry depends on several parameters:
— the nature of the material and of the reinforcement structure;
— the type of testing system.BS EN ISO 20504 pdf download.