Delamination in the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of such systems. This is even more pertinent for systems at high temperatures. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory (NPL) is developing multi-layer reference artefacts, including both fully bonded and partially de-bonded systems for validating thermal characterisation of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. The sensitivity studies carried out before creating the partially debonded artefacts have shown that the measurement area of the detector is one the important parameters that affect the accuracy of the thermal characterisation using LFA. However, this parameter is unknown to users of the early version of the Netzsch LFA 427, as it has negligible effect on radially homogenous samples which LFA is typically used for. This paper details the effect of measurement area on thermal characterisation of artefacts with partial debonding in the interface using LFA. For a bi-layer IG-210 grade graphite-hafnium foil system with a 6 mm diameter defect at the centre of the foil interface, variation in the measurement area can change the heat pulse transmission half-rise time by up to ~ 40%. Three methods to determine the system measurement area are discussed. The physical measurement diameter for the LFA 427 at NPL was estimated to be 7.7 mm ± 0.3 mm, independent of temperature. Within the uncertainty range of the measurement diameter, the thermal conductance of the defect region and the average heat transfer coefficient (HTC) can vary by ± 36% and ± 3.5% respectively. It is important to remember that this change is for a defect of 6 mm diameter which is a significant portion of the measurement area. For much smaller defects a much smaller change can be expected.

Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures for both monolayer and multi-layer materials. Although some high-temperature bulk candidate reference materials were developed and studied, e.g., in the European Metrology Research Programme (EMRP) funded Joint Research Project (JRP) ENG08 Metrofission, they were not able to meet the requirements for validating thermal measurements of multi-layer systems using LFA. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory (NPL) is developing multi-layer reference artifacts, including both fully bonded and partially debonded systems for validating thermal characterization of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. This paper details the methodology of production, measurement and validation of silicon carbide and molybdenum foil-based multi-layer systems with, and without, partial debonding. Reproducibility and thermal stability of the artifacts will be discussed, with recommendation on the usage criteria as LFA multi-layer reference artifacts. The multi-layer system was found to be thermally stable for at least ten thermal cycles between room temperature and 1200 °C. The interface thermal conductance of both the bonded and debonded region of the artifacts was calculated using an inverse model and was shown to remain stable with varying temperatures and over five thermal cycles.

Delamination in the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of that system. This is even more pertinent for systems at high temperature. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. Multi-layer reference artefacts, with and without, debonded regions are required for validating the thermal characterization of such systems using LFA. To aid in the design of these reference artifacts a numerical model was developed to simulate LFA of multi-layer systems, with and without, defects. This paper discusses a sensitivity study that was conducted to determine if a defect in the interlayer can be detected and if so what are the most sensitive parameters. It was found that the area and thermal conductance of the defect had the greatest effect on the simulated half-rise time of the system, with shape and radial location having a significant but lesser effect in comparison. To be able to observe a change of 10% in the half-rise time, a circular defect equivalent to 5 μm air gap with an area of 25% of the measurement area in the radial centre of the sample would have to be present.

A novel approach for down-selection of a repaired support structure design produced using Laser Blown Powder – Direct Energy Deposition (LBP-DED) and filled with interstitial Ni-Al powder (∼0.75 area fraction) in a turbine segment was investigated. Simulation of flattening and un-flattening of the segment with implications to degradation of the support structure was quantified using a four-point bend test to identify the role of axial Young’s modulus in out-of-plane flexure. Two markedly different LBP additive structures; Diamond Lattice (DL) - nodal and Continuous Path (CP) – non-nodal, were produced and compared with the un-repaired condition. At room temperature, the forward and rear walls and internal nodes of the original equipment (OE) and DL support structures were found to contribute significantly to the Young’s modulus, with significantly reduced stiffness observed in the CP structures. Oxidation plays a key role in the development of internal compressive stresses within the abradable, with a two-fold increase in elastic modulus in the CP structure, but a smaller increase occurred in OE and DL support structures. A decrease in elastic modulus and concomitant increase in radius of curvature (flattening) occurred with an increasing number of flexural cycles. Cracking is most prominent in the nodal design within the front and rear walls and cracks propagate either to the surface or towards the base of the abradable lattice. No such degradation was observed for equivalent flexural cycles in the original and CP support structures, even up to a significant number of cycles. A criterion for catastrophic failure of the abradable was deduced from a steep decrease in flexural elastic modulus accompanied with a marked change in curvature. A non-nodal design support structure is optimum to counter in- service flattening/un-flattening.

Delamination of the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of that system. This is even more pertinent for systems at high temperature. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. Multi-layer reference artefacts, with and without, debonded regions are required for validating the thermal characterisation of such systems using LFA. Although some high-temperature bulk candidate reference materials were developed and studied, e.g. in the European Metrology Research Programme (EMRP) funded Joint Research Project (JRP) ENG08 Metrofission, they were not able to meet the requirements for validating thermal measurements of multi-layer systems using LFA. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory is developing multi-layer reference artefacts, including both fully bonded and partially de-bonded systems for validating thermal characterisation of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. This paper details the methodology of production, measurement and validation of isotropic graphite and hafnium based multi-layer systems with, and without, partial debonding. Reproducibility, thermal stability and sensitive parameters concerning the thermal response of the artefacts will be discussed, with recommendation on the usage criteria as LFA multi-layer reference artefacts.

Due to the depletion of the thermal conductivity reference materials, the National Physical Laboratory (NPL) has certified a new thermal conductivity reference material, NPL code 2I09 that is based on Inconel 600. This batch of material has been thermally and electrically characterised over the temperature range 100 °C to 500 °C. The primary thermal conductivity measurements used to generate the certified values were carried out in the NPL Axial Heat Flow apparatus, which is a UK national standard measurement facility. It is based on a steady-state absolute technique and is suitable for measuring specimens with thermal conductivities in the range 10 W·m−1·K−1 to 240 W·m−1·K−1. Comparisons were made between the reference thermal conductivity values and the derived thermal conductivity values obtained from two indirect methods based upon electrical resistivity and thermal diffusivity measurements, respectively. The reference thermal conductivity values of NPL 2I09 compare with those calculated from the measurements of electrical resistivity within 2 % and those calculated from the measurements of thermal diffusivity, specific heat capacity, density and thermal expansion better than 4 %. In addition, the certified thermal conductivity values of the new batch of Inconel 600, the NPL code 2I09, were compared with the representative reference thermal conductivity values of Inconel 600 reported by J Clark and R Tye, and the agreement is within 2 %. The new reference material NPL 2I09 is available from NPL and can be used to calibrate or check apparatus that provides measurements of thermal conductivity which includes the range 14 W·m−1·K−1 to 22 W·m−1·K−1 covering the temperature range from 100 °C to 500 °C. The overall uncertainty on the certified values is estimated to be within ± 4.8 %, based on a standard uncertainty multiplied by a coverage factor k = 2, providing a level of confidence of approximately 95 %.

The goal of this research is to fabricate pure transparent yttria ceramics through gel casting and vacuum sintering. A specific processing method has been used and optimized for this purpose. A pure yttria nanopowder was synthesized as the starting material to produce pure transparent ceramics through a low-temperature sintering process. It was attempted to minimize the undesirable nanopowder hydration by using the as-synthesized yttria nanopowder and a rapid deagglomeration and slurry preparation process. The synthesized nanopowders were deagglomerated to enhance the efficiency of both powder shaping and sintering stages. Carrageenan was used as the gelling agent because it is a low-cost and abundant material, and because the temperature is the only catalyst needed for its gelation; therefore, it is possible to control its gelation to obtain high-density and pure optical ceramics. The effect of the deagglomeration method and the processing parameters, including the amounts of dispersant, gelling agent, solid loading, pH, and deagglomeration time, on the rheology of slurry, density, and microstructure of the obtained green yttria ceramics was examined and optimized in order to obtain high solid loading nanoyttria suspensions of 38 vol%, which is more than those obtained in many of the previous investigations. The precise gelling temperature and time were measured, and green gel cast ceramics with a density of 63 % of the theoretical density were produced. A rapid deagglomeration and slurry preparation method was used instead of using a conventional planetary ball-milling approach to minimize the risk of the hydrolysis of yttria nanopowder. No sintering aid was necessary, and transparent yttria ceramics with 99 % of the theoretical density were produced after vacuum-furnace sintering at 10-2 mbar and 1715 °C.

Owing to its excellent mechanical and thermal properties such as high strength, high hardness, and good thermal shock resistance, silicon nitride is a material suitable for forming tools. This work analyses the failure of a compaction roll made of Si3N4. One of the two ceramic rings broke during the compaction rolls' operation. Fractographic examinations have shown that very high tensile stresses occurred in the ceramic material during operation. These stresses first led to the formation of cracks and then to the total failure of the roll ring. Failure analysis has shown that roll design and clamping are of major importance. Causes for the generation of tensile stresses are shown and suggestions are made on how to ensure a safe operation of the rolls.

Edge flaking of WC-based hardmetals has been examined in detail. So-called “edge toughness”, the load at which a flake will form under load vs. displacement from the specimen edge has been correlated with more commonly used toughness parameters; Palmqvist toughness, plane strain fracture toughness (KIC) and critical strain energy release rate (GIC). KIC and GIC showed better correlations than Palmqvist, though coarser grained hardmetals, exhibiting rising R-curves, were consistently found to be outliers. It is thought that this behaviour is consistent with far more pronounced crack bridging in these materials in the edge fracture mode. Mechanical property data were complimented by SEM microscopy to examine fracture behaviour in more detail.

The simulation modelling of metal processes requires realistic, accurate and self-consistent thermophysical properties as input data. In particular, solidification models have been shown to be sensitive to small changes in the density of the liquid alloy. This paper compiles experimental data for the density of selected liquid aluminium, magnesium and nickel-base alloys at their liquidus temperatures. These data are drawn from the published literature and some of our own previously unpublished results. Comparison with ideal mixing calculations for the selected aluminium and magnesium alloys shows reasonable agreement between the calculations and the experimental results within the experimental measurement uncertainties. For aluminium alloys, the composition limits in Cu; Ni and Ag additions required to produce a 1% deviation from ideal behaviour are calculated allowing for the binary interactions between these elements and aluminium. For a selection of nickel based super alloys the ideal model predicts lower densities than the experimental measured values. These differences are interpreted mainly in terms of the published experimental non-ideality of mixing of the Ni-Al system and to a lesser extent reported binary interactions for other systems. Correction for these effects results in significantly improved agreement between the density predicted by the non-ideal model and experimental values.

The National Physical Laboratory (NPL) has developed a new thermal conductivity reference material, NPL code 2S09 that is based on Stainless Steel 304. This batch of material has been thermally and electrically characterised over the temperature range 100 degrees C to 500 degrees C. The primary thermal conductivity measurements used to generate the certified values used the NPL Axial Heat Flow apparatus, which is based on a steady-state absolute technique and is suitable for measuring specimens with thermal conductivities in the range 10 W m(-1) K-1 to 240 W m(1) K-1. Comparisons were made between the reference thermal conductivity values and derived thermal conductivity values obtained from two indirect methods based upon electrical resistivity and thermal diffusivity measurements respectively. The reference thermal conductivity values of NPL 2S09 compare with those calculated from the measurements of electrical resistivity within 2 % and those calculated from the measurements of thermal diffusivity, specific heat capacity, density and thermal expansion better than 4 %. The new reference material NPL 2S09 is available from NPL and can be used to calibrate or check apparatuses that provide measurements of thermal conductivity from 16 W m(-1) K-1 to 22 W m(-1) K-1 covering the temperature range 100 degrees C to 500 degrees C. The overall uncertainty on the certified values is estimated to be within +/- 4.8 %, based on a standard uncertainty multiplied by a coverage factor k = 2, providing a level of confidence of approximately 95 %.

Some WC/Co hardmetal dies used for the high-temperature, high-pressure fabrication of polycrystalline diamond have been subjected to fractographic investigation after service failure. In each die a number of flat plate-like fragments have been found showing an unusual fountain-like appearance to the fracture surface markings. Despite extensive probing, discrete fracture origins could not be found. Instead, from the evidence of the microcracking found in the die bore region and the recognised development of deformations during a campaign, it was concluded that microstructural damage was developed under the complex non-equitriaxial compression stresses which are developed during the duty cycles. When the propagation of this damage reached the axial tensile zone that exists in the cooler regions of the die, the plate-like, more-brittle failure pattern developed.

Ceramic components will be used for electrical insulation and optical transparency on the heating and diagnostic systems of fusion reactors. As these form the boundary for the radioactive confinement, a defined procedure is required to demonstrate structural integrity. The established design codes are incompatible with ceramic materials for various reasons, predominantly the brittle nature of ceramics. CCFE and others have started to develop an in-house design code for the use of brittle materials in pressure vessels, this paper discusses the rationale behind the rules. The difficulty of reconciling the statistical nature of failure in ceramics with the deterministic nature in codes is addressed and it is suggested that the only way to achieve this is by a proof testing approach. The inherent weakness of the proof testing methodology, quantifying the strength loss during the qualification test is discussed. Further work is required to determine the validity of the rules experimentally. Crown Copyright (C) 2017 Published by Elsevier B.V. All rights reserved.

Measurement of residual stresses in FRP composites is by no means a trivial task and there are no commonly applied or standardised methods currently available. As a result, characterisation of residual stresses is often avoided, resulting in the use of conservative safety margins, which has consequently resulted in structures being overdesigned. In the work described here, the incremental slitting method has been demonstrated to be a technique suitable for measuring residual stress in thin (∼0.3mm) plies of a [0°2/90°2]4s carbon fibre-reinforced epoxy laminate. The stresses measured using a constant stress approximation approach provided the best agreement with measurements obtained using the layer removal technique and stresses predicted using a semi-coupled transient-thermal and structural model.

The coefficient of thermal expansion (CTE) of nickel-based superalloys and bond coat layers was modelled by considering contributions from their constituent phases. The equilibrium phase composition of the examined materials was determined using thermodynamic equilibrium software with an appropriate database for Ni-based alloys, whereas the CTE and elastic properties of the principal phases were modelled using published data. The CTEs of individual phases were combined using a number of approaches to determine the CTE of the phase aggregate. As part of this work, the expansion coefficients of the superalloy IN-738LC and bond coat Amdry-995 were measured as a function of temperature and compared with the model predictions. The predicted values were also validated with the published data for the single-crystal superalloy CMSX-4 and a number of other Ni-based alloy compositions at 1000 K. A very good agreement between experiment and model output was found, especially up to 800 \(^\circ \)C. The modelling approaches discussed in this paper have the potential to be an extremely useful tool for the industry and for the designers of new coating systems.

Residual stresses are those stresses present in a material in the absence of any external loading. For fibre-reinforced plastic (FRP) composites, residual stress development during processing can cause significant fabrication and in-service performance problems resulting in part distortion, matrix cracking, delamination, adverse effects on the stress-strain behaviour of the material [1-5], and reduction in fracture toughness [6], impact and environmental resistance. In this paper, measurements of residual stress in [0 degrees(2)/90 degrees(2)](4s) laminates fabricated from SE84 LV carbon fibre-reinforced epoxy have been undertaken using the incremental slitting approach. The technique involves machining a slit of increasing depth in a rectangular coupon such that stresses normal to the plane of the slit are relieved. The resultant back-face deformation is used to determine the residual stresses in the coupon prior to machining. Residual stresses from incremental slitting measurements have been compared to measurements made using the layer removal technique and predictions using a semi-coupled transient-thermal and structural analysis. The incremental slitting technique has been demonstrated to be a technique suitable for measuring residual stress in thin (similar to 0.3 mm) plies of a [0 degrees(2)/90 degrees(2)](4s) laminate. Results derived using a constant stress approximation approach were in good agreement with residual stresses predicted using a semi-coupled transient-thermal and structural model and measured using the layer removal technique. Although the incremental slitting technique requires a computationally intensive data reduction methodology, once the methodology has been established it is easy to modify for different laminate configurations and is not restricted by the geometric limitations stipulated by classical laminate theory. Experimentally, accurate machining of thin plies in their entirety without over or under machining is virtually impossible to perform and is a severe limitation of the layer removal method. Incremental slitting overcomes this limitation by only requiring a narrow slit of material to be removed, which can be performed much more accurately.

Cylindrical and bamboo-like boron nitride nanotubes (BNNTs) have been used to reinforce brittle amorphous borosilicate glass matrix materials prepared by spark plasma sintering. The mechanical properties, such as hardness, Young's modulus, fracture toughness, and scratch resistance of the materials have been investigated. The fracture toughness of the composites showed an improvement of ∼30% compared to the pure amorphous glass. BNNTs pull-out, crack bridging, stretching, and crack deflection toughening mechanisms were observed in the reinforced glass matrix composites. Extensive pull-out of the BNNTs (>400 nm) was observed in the form of the telescopic “sword-in-sheath” mechanism, resulting in poor energy dissipation due to the weak Van der Waals force between the inner walls of the BNNTs. The scratch resistance was significantly improved (∼26%) after the addition of the BNNTs, and the results correspond well with the brittleness index of the materials.

The strength of ceramic materials is limited by flaws which are distributed in the volume or on the surface of the material. Commonly, fractographic investigations are performed after the strength tests to interpret the strength values.The relatively new Ball-on-Three Balls (B3B)-bending test applies a biaxial stress state (which is more searching for cracks than a uniaxial stress state) on the specimen. To identify typical fracture initiating flaws and to get a better understanding of the fracture behaviour of B3B-specimens a systematic fractographic investigation was performed on 260 silicon nitride specimens divided into batches with different surface qualities. It could be shown that in most cases (at least those in which origins could be clearly identified) surface or near surface located defects were responsible for failure. On specimens with poor surface qualities, surface defects were introduced through machining. On specimens with a better surface quality, volume defects, which were exposed on the surface by polishing, could be identified as fracture origins. In only a few cases defects in the bulk were fracture origins. (C) 2014 Elsevier Ltd. All rights reserved.

Abstract The accurate measurement of modulus is not an issue specific to high modulus steels, but is still a challenge for the wider engineering and materials community. Inherently, the measurements should not offer significant problems, but results from a series of interlaboratory validation exercises and data on representative high modulus steels are included to illustrate some of the practical issues associated with the static and dynamic techniques. Dynamic methods probably offer the potential for the most accurate measurements due to the simple geometry and test set-up. Results show that a well set up test could be expected to give modulus values with an uncertainty of ±1–2%. Comparable levels can be achieved from the tensile test, but only through the use of a separate and dedicated test, where loading is carried out below the elastic limit, using averaging strain measurement, careful alignment and robust data analysis procedures. La mesure précise du module d’élasticité n’est pas un problème spécifique aux aciers à module d’élasticité élevé, mais c’est quand même un défi pour la grande communauté d’ingénierie et des matériaux. Fondamentalement, les mesures ne devraient pas offrir de problèmes importants, mais on inclut les résultats d’une série d’exercices de validation entre laboratoires et les données d’aciers représentatifs à module d’élasticité élevé pour illustrer certains des problèmes pratiques associés aux techniques statiques et dynamiques. Il est probable que les méthodes dynamiques offrent le potentiel de mesures les plus précises grâce à la géométrie et au montage d’essai simples. Les résultats montrent qu’on peut s’attendre à ce qu’un essai bien monté donne des valeurs du module d’élasticité avec une incertitude de ±1–2%. On peut obtenir des niveaux comparables pour l’essai de traction, mais seulement au moyen de l’utilisation d’un essai séparé et dédié, où la mise sous contrainte est effectuée sous la limite d’élasticité, en utilisant la mesure moyenne de la déformation, un alignement diligent et des procédures robustes d’analyse de données.