BS EN 820-5:2009 pdf free download – Advanced technical ceramics一 Thermomechanical properties of monolithic ceramics Part 5: Determination of elastic moduli at elevated temperatures.
4.3 Test pieces
Test pieces shall be rectangular section bars selected and prepared by agreement between parties. They may be directly prepared close to final dimensions or machined from larger blocks. This test measures Young’s modulus parallel to the length of the test piece. If the test material is likely to be elastically anisotropic, care shall be taken in selection of the test piece orientation and in the interpretation of the test results.
The length of the test pieces shall be at least 10 mm longer than the test-jig span. The width of the test piece shall be in the range 4 mm to 10 mm. For method 1, the thickness of the test piece shall be in the range 0,8 mm to 1,5 mm. For method 2, the test piece may be up to 3 mm thick, but preferably should be in the range 1 mm to 2 mm thick. The test pieces shall be machined to final dimensions. They shall be flat and parallel-faced to better than ± 0,5 % of thickness on the faces to be placed on the loading rollers of the test jig. They shall similarly be machined flat and parallel-faced to better than ± 0,5 % of width on the side faces. For method 1 they shall not be chamfered. For method 2 they may be chamfered as specified in EN 843-1.
At least three test pieces shall be prepared.
4.4 Procedure
Measure the width and thickness of the test pieces at several places and record the average values.
Insert a test piece in the test-jig and centralise it in accordance with the requirements of EN 843-1. Select a maximum force to be applied to the test piece which will avoid fracture.
NOTE 1 The upper level of force can be estimated by employing the strength calculation in EN 843-1:2006, Clause 8, and inserting a stress level of no more than 0,5 at, where a is the mean fracture stress expected at the test temperature.
Heat the thermal enclosure to the required test temperature and allow the temperature to stabilize such that the thermocouple recording test piece temperature varies by no more than 2 °C in a 15 mm period up to 1 000 °C, and by no more than 4 °C at higher temperatures.
Apply a steadily increasing force to the test jig at a constant test machine cross-head displacement rate in the range 0,001 mm/mm to 0,5 mm/mm. Record the load and displacement (either cross-head displacement, or transducer displacement output) continuously. When the maximum selected force is achieved, reverse the direction of the machine and reduce the load to zero. Repeat the cycle at least twice more to the same peak load, or until repeatable results are obtained. Repeat the test on each test piece. If the machine displacement is to be employed (method 1) or if the transducer method is employed using a support roller as one of the defined points (method 2), replace the test piece with the thick parallel-sided steel (for use to 300 °C) or ceramic bar and repeat the loading cycles to the same peak load, recording load and displacement.
NOTE 2 The use of both loading and unloading cycles is required in order to take into account machine hysteresis in method 1, transducer hysteresis in method 2.
4.5 Calculation of results
4.5.1 From cross-head displacement (Method 1)
Inspect the recordings of load and displacement for the test piece and the thick steel or ceramic bar for uniformity and linearity. Select a region of the recordings from a minimum load of not less than 10 % of peak load or 0,2 N, whichever is the greater, to a maximum load of not more than 90 % of the peak load applied. The same load range shall be selected for each loading cycle on the test piece and the thick bar.