A Consideration of the Measurement of Macro-Stresses in Non-Metallic Materials

Abstract

In this paper the challenges associated with the determination of within section macrostresses in the non-metallic materials porous reactor core graphites, glasses and thermally grown oxides, will be considered, with respect to the length-scale over which such measurements are required. Examples are briefly presented to demonstrate the capability of the methods selected, which include deep hole drilling and photoluminescence and Raman spectroscopy. These techniques span the length-scale from micro-metres to tens of millimetres. The measured values will be discussed with respect to the confidence with which these techniques may be applied and hence benefits for life/integrity evaluation.

In-situ neutron diffraction measurement and numerical modelling of macro- and micro-strains in two porous synthetic graphites

“…These values are compared with the porous graphite modulus of elasticity in Table 3. The different values of ND micro-strains measured of IMI-24 and PG25 graphite, Table 3, can be attributed to the fact that these two grades of graphite have been prepared by different manufacturing processes and have different microstructure [4,10]. These values agree with the graphite elastic modulii measured at smaller length-scales [29].…”

“…where E p is the macroscopic modulus of elasticity, F is applied load, A is area of the cross-section and ε is the strain. The measured macroscopic modulus of elasticity, E p , with the experimentally determined uncertainty for both IMI-24 graphite and PG25 graphite are compared with reported pseudo-static values [4] in Table 2.…”

“…However, an important factor controlling the properties is the level of porosity within the material. For example in the case of Gilsocarbon graphite, tensile/compression tests reveal linear elastic deformation followed by inelastic behaviour leading to permanent strain [3,4]. The latter was attributed to the development of localised damage zones [5][6][7].…”

“…A series of laboratory experimental techniques have been developed to measure internal and surface strains in different grades of graphite [4][5][6][19][20][21][22]. While many report fracture of polygranular graphite under different loading conditions [23][24][25][26], only a few provide experimental evidence that link microscale properties to the macroscopic properties.…”

“…Graphite is the stable form of solid carbon, which has a pseudo hexagonal close-packed crystal structure and can be found as the natural mineral as well as an artificially manufactured material [1]. Graphite has widespread applications and many industries uses including a dry lubricant, a refractory, electrodes for steel production [2], and a moderator and structural material for selected power generation plants [3,4]. For the latter graphite has a polygranlar microstructure and preserves strength at high temperature in a harsh environment.…”