BS ISO 21971:2019 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) – Mechanical properties of ceramic composites at ambient temperature in air atmospheric pressure – Determination of hoop tensile properties of tubes
1 Scope
This document specifies the conditions for the determination of hoop tensile properties of ceramic matrix composite (CMC) tubes with continuous fibre-reinforcement at ambient temperature in air atmospheric pressure. This document is specific to the tubular geometries since fibre architecture and specimen geometry factors in composite tubes are distinctly different from those in flat specimens. This document provides information on the hoop tensile properties and stress-strain response, such as hoop tensile strength, hoop tensile strain at failure and elastic constants. The information can be used for material development, control of manufacturing (quality insurance), material comparison, characterization, reliability and design data generation for tubular components. This document addresses, but is not restricted to, various suggested test piece fabrication methods. It applies primarily to ceramic and/or glass matrix composite tubes with a continuous fibrous- reinforcement: unidirectional (1D filament winding and tape lay-up), bi-directional (2D braid and weave) and tri-directional (xD, with 2 < x < 3), subjected to an internal pressure. Values expressed in this document are in accordance with the International System of Units (SI).
4 Principle
A prepared tubular test specimen of specified dimensions is inserted into an appropriate test fixture assembly and subjected to monotonic loading via indirect internal pressure up to fracture. Uniform radial pressure is produced using hydraulic oil injection with a piston through an elastomeric bladder located inside the tubular test specimen. The elastomeric bladder mates to the inner diameter of the tubular test specimen, thus causing its expansion under pressure. The test is performed at constant piston displacement or constant strain (or constant loading rate). Both the applied pressure and resulting hoop tensile strain are measured and recorded simultaneously. The hoop tensile strength and corresponding strain are determined from the burst pressure while the various other hoop tensile properties are determined from the stress-strain response data. Generally, the test is carried out under conditions of ambient temperature and environment. NOTE 1 The resulting force from internal pressure loading is applied in the radial direction. Monotonic refers to a continuous non-stop test rate with no reversals from test initiation to final fracture. NOTE 2 The method described in this document does not cover the possibility of applying pressurization via a dense rubber material in compressive without fluid.
5.2 Test specimen gripping and end closure
The gripping device shall be able to maintain the tubular test specimen in position to withstand internal pressure induced by the expansion of the elastomeric bladder while allowing it to move radially. An example of construction detail is shown in Figure 2 for which the tubular test specimen is mounted on a spacer flange. A cover plate is clamped on the flange with two screws to obtain a correct alignment. The brittle nature of the CMCs requires particular attention to minimize crack initiation and fracture. Therefore, it is recommended that the attachment screws are released and then the adjustment screw adjusted to push the mating flanges back slightly until they come into contact with the tube, but without applying any axial force to it.