BS ISO 21713:2020 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of elastic modulus of ceramics at high temperature by thin wall C-ring method
5.2 Heating system
5.2.1 General A furnace shall be capable of heating the test fixture and test piece as well as maintaining a uniform and constant temperature during the test, by which a vacuum environment shall be available for test requirements. If a vacuum chamber is used, and it is necessary to transmit the load through a seal, bellows or a fitting, it shall be verified that load losses or errors are less than 1 % of the applied loads.
5.2.2 Test piece temperature stability The furnace shall be controlled by a device for maintaining a constant temperature within ±2 °C or better within the working space of the furnace, during the time that the test piece is loaded in the range of elasticity.
5.2.3 Test temperature uniformity The furnace shall be capable of maintaining the test piece at a uniform temperature. The temperature of the test piece shall not vary by more than 10 °C after a 15-min holding time at the required temperature.
5.2.4 Furnace heating rate The furnace control device shall be capable of controlling the heating rates of the furnace and preventing temperature overshoots.
5.2.5 Furnace stability The time for the system to reach thermal equilibrium at the test temperature shall be determined.
5.3 Temperature-measuring and indicating instruments
5.3.1 General The thermocouple temperature-measuring equipment shall have a resolution of at least 1 °C and an accuracy of 5 °C or better. The optical pyrometer, if used, shall have a resolution of at least 5 °C and an accuracy of 10 °C or better.
5.3.2 Thermocouples Thermocouples in accordance with IEC 60584-1 shall be used. The thermocouples shall exhibit low thermal inertia (the diameter of the wires shall be not greater than 0,5 mm). The thermocouples shall have a sufficient length within the furnace (with respect to heat conduction along the wires). The measuring thermocouple tip shall be as close as possible to the test piece.
5.3.3 Verification of the thermocouple temperature-measuring system Thermocouples shall be checked periodically as their output may drift with usage or contamination.
5.4 Vacuuming machine A suitable vacuuming machine capable of applying a suitable vacuum environment shall be used. The low vacuum degree (<10 Pa) shall be accomplished by a mechanical pump, while the high vacuum degree (<0,1 Pa) shall be accomplished by a molecular pump. 5.5 Data acquisition Obtain records of the applied load versus crosshead displacement or testing time.
Use either analogue chart recorders or digital data acquisition systems. Recording devices shall be accurate to within 1 % of the selected range of the test equipment, including the readout unit, and shall have a minimum data acquisition rate of 10 Hz, with a response of 50 Hz deemed more than sufficient.
5.6 Dimension-measuring device Micrometers and other devices with a precision of 0,01 mm according to ISO 3611 shall be used to measure the linear dimensions of the test piece. Alternative dimension-measuring instruments may be used, provided they have a resolution of 0,01 mm or finer.
6 Test pieces
6.1 Test piece size and preparation 6.1.1 General Test piece geometry shall be 0,8 ≤ r/R ≤ 0,95 for the validity of the calculation formulae for the thin-wall ring. The gap of the C-ring shall be sufficiently large so that the ring does not close during the test, but less than one half of the inner diameter, as shown in Figure 1. The width (axial length) of the C-ring shall satisfy two conditions: 0,2 ≤ b/R ≤ 1,0 and 1,0 ≤ b/(R − r) ≤ 5,0. This document permits two options for the radius and surface treatment of the test piece. a) Existing tubes: if r and R of these tubes satisfy the requirements above, cut the tube into several rings. Grind and polish the cutting section surfaces of each ring to a parallelism of 0,02 mm or better. Clean the test pieces with alcohol or pure water, then cut a slot with a width from 0,2 r to 0,5 r using a ceramics cutting machine. b) Other-shaped materials: machine a ring with R = 15 mm, r = 13 mm and b = 8 mm. Grind and polish the cutting section surfaces of the ring to a parallelism of 0,02 mm or better. Clean the test piece with alcohol or pure water, then cut a slot with a width from 0,2 r to 0,5 r using a ceramics cutting machine.