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It seems that so much of modern life is defined by the materials we use. From aircraft to architecture, from cars to communications, from microelectronics to medicine, the development of new materials and the innovative application of existing ones have underpinned the technological advances that have transformed the way we live, work and play.

Recognizing the need for a sound technical basis for drafting codes of practice and specifications for advanced materials, the governments of countries of the Economic Summit (G7) and the European Commission signed a Memorandum of Understanding in 1982 to establish the Versailles Project on Advanced Materials and Standards (VAMAS). This project supports international trade by enabling scientific collaboration as a precursor to the drafting of standards. The VAMAS participants recognized the importance of agreeing a reliable, universally accepted basis for the traceability of the measurements on which standards depend for their preparation and implementation.

Seeing the need to involve the wider metrology community, VAMAS approached the Comité International des Poids et Mesures (CIPM). Following discussions with NMI Directors and a workshop at the BIPM in February 2005, the CIPM decided to establish an ad hoc Working Group on the metrology applicable to the measurement of material properties. The Working Group presented its conclusions to the CIPM in October 2007 and published its final report in 2008, leading to the signature of a Memorandum of Understanding between VAMAS and the BIPM. This MoU recognizes the work that is already going on in VAMAS as well as in the Consultative Committees of the CIPM and establishes a framework for an ongoing dialogue on issues of materials metrology.

The question of what is meant by traceability in the metrology of the properties of materials is particularly vexed when the measurement results depend on a specified procedure. In these cases, confidence in results requires not only traceable calibration of the various instruments and standards used but also the reliable application of an accepted measurement procedure. Nowhere is this more evident than in the use of hardness scales, which are not directly traceable to the SI.

This special issue of Metrologia includes a summary of the findings and conclusions of the Working Group and a further 14 papers covering the full range of properties of interest in science, engineering and standards making. It includes papers by authors at eight national measurement institutes and four other research centres. In addition to mechanical properties, there are papers addressing issues associated with the measurement of electromagnetic, acoustic and optical properties as well as those arising from the specific structural features of many new materials.

As guest editors, we are extremely grateful to all the authors who have contributed to this special issue on the measurement of the properties of materials. We hope it will contribute to a wider appreciation of many of the associated issues and foster a growing understanding of the importance of ensuring that all such measurements are performed in accordance with accepted standards and procedures, with proper attention to the need to establish the traceability of the results. Only in this way can the performance, safety and fitness for purpose of products be guaranteed.

Over the last few years, the need for wider international collaboration in the measurement of materials properties has been under discussion between the Versailles Project on Advanced Materials and Standards (VAMAS) and the Comité International des Poids et Mesures (CIPM) with a view to including materials metrology in the formal international measurement structure established under the Metre Convention. Following a workshop at the BIPM in February 2005 the CIPM established an ad hoc Working Group on the metrology applicable to the measurement of material properties. The Working Group assessed a wide range of properties and explored the role of reference materials in ensuring confidence in measurement data. It also identified a number of different classes of materials that would merit consideration and a wide range of properties that are routinely measured.

The Mutual Recognition Arrangement (MRA) drawn up in 1999 by the CIPM seeks to provide 'a secure technical foundation for wider agreement for measurements related to international trade, commerce and regulatory affairs' and some materials properties are already the subject of study by the CIPM's Consultative Committees.

The Working Group has made a number of recommendations aimed at ensuring an ongoing dialogue between VAMAS and the CIPM. As well as proposing joint activities, underpinned by a Cooperation Agreement which would require VAMAS to report annually to the CIPM on needs for improved materials metrology, there are recommendations which will extend the work of the CIPM's Consultative Committees to ensure that Calibration and Measurement Capabilities (CMCs) for a number of important materials properties are included in the Key Comparison Database in due course.

A schematic traceability chain is proposed similar to the traceability scheme in chemical measurements, in which calibration hierarchy is established by consecutive sets of three components, namely measurement standard, measurement system and measurement procedure. The calibration hierarchy is established among sets of measurement levels, which are characterized by the associated uncertainty that is assigned or achieved to the value assignment process or calibration provided. By taking particle size measurements as an example, a scheme of the implementation of traceability is explained in which proper establishment of three respective elements are illustrated: method or procedure, measurement system and standard or reference material.

Global comparability of the measured values of material properties is based on some fundamental metrological concepts. These concepts are either already widely implemented in current procedures for materials testing or they are being further developed and increasingly accepted and used. An important aspect of the comparability of measurement results is metrological traceability. This paper aims at illustrating with practical examples how to apply the concept of metrological traceability as defined in ISO/IEC Guide 99:2007, known also as the VIM (International Vocabulary of Metrology), in the field of engineering material properties. VIM distinguishes three different types of references for traceability: either to a system of units, such as the SI, to a measurement procedure or to a physical measurement standard. For each approach, an example is given in the field of engineering material properties, including appropriate traceability statements and means to achieve the traceability. The role of certified reference materials is highlighted, as well as practical consequences of traceability requirements for the design of reference material certification projects.

Many important mechanical properties of materials including tensile strength are procedure dependent. This means that test results are traceable to standard test procedures rather than SI base units. However, most of the test procedures described in the current international standards such as ISO and ASTM are not suitable to be adopted as a primary standard procedure since they were developed to be used at industrial sites as well as testing laboratories. The Working Group on Hardness under CCM is working to develop a primary standard procedure to establish traceability for hardness measurement through key comparison among NMIs. These kinds of activities are necessary for other properties such as tensile strength, impact strength, creep and fatigue for the establishment of a traceability system. KRISS has been trying to establish a traceability chain in the measurement of materials' mechanical properties through international round-robin tests, the development of certified reference materials and uncertainty evaluation. In this paper, the activities of KRISS for establishing traceability and those of related ISO technical committees are described.

Elastic modulus is an intrinsic material property and a key parameter in engineering design and materials development. A wide range of test methods is available for measuring modulus, but there is currently some uncertainty within parts of the user community about the reliability of modulus data, particularly from the tensile test, to the extent that many use standard handbook values in their calculations and designs. This is not recommended and can be addressed through good experimental practice and careful measurement.

The paper discusses some of the key practical issues associated with the tensile test that need to be considered to obtain reliable values for Young's modulus such as strain measurement, alignment, data analysis methods, software validation, uncertainty budgets and the use of reference materials.

With the emergence of international standards for the instrumented indentation test, an international comparison on nanoindentation, sponsored by The International Academy for Production Engineering (CIRP), was performed. The objective of the comparison was to determine how well the ISO standards adopted in October 2002 (ISO 14577-1, -2, -3) could be realized. The exercise involved 12 participants throughout Europe, Asia and the USA. Results for hardness and elastic modulus of (1 0 0)Al were collected and analysed. A comparison of the results obtained by this exercise with those obtained from the first CIRP international comparison on ultra-microhardness and elasticity measurement held from 1993 to 1997 was made.

The measurement of hardness has been and continues to be of significant importance to many of the world's manufacturing industries. Conventional hardness testing is the most commonly used method for acceptance testing and production quality control of metals and metallic products. Instrumented indentation is one of the few techniques available for obtaining various property values for coatings and electronic products in the micrometre and nanometre dimensional scales. For these industries to be successful, it is critical that measurements made by suppliers and customers agree within some practical limits.

To help assure this measurement agreement, a traceability chain for hardness measurement traceability from the hardness definition to industry has developed and evolved over the past 100 years, but its development has been complicated. A hardness measurement value not only requires traceability of force, length and time measurements but also requires traceability of the hardness values measured by the hardness machine. These multiple traceability paths are needed because a hardness measurement is affected by other influence parameters that are often difficult to identify, quantify and correct. This paper describes the current situation of hardness measurement traceability that exists for the conventional hardness methods (i.e. Rockwell, Brinell, Vickers and Knoop hardness) and for special-application hardness and indentation methods (i.e. elastomer, dynamic, portables and instrumented indentation).

Measurement of microstructural parameters is essential for both controlling and modelling properties of and production processes for advanced materials. In the past decade new techniques such as electron backscatter diffraction have enabled a considerable increase in the amount of data and degree of detail in microstructural measurements of, for example, the extent of recrystallization in a metal deformed at high temperatures. However, the many parameters involved and automated nature of the methods can lead to artefacts and bias in calculated values, and increased resolution will lead to disagreement with more conventional methods. Examples are given of the range of microstructural measurements possible by new techniques and how different results can be obtained from the same underlying data. The need is stressed for interlaboratory comparisons to enable underpinning data to be derived on the validity, repeatability and reproducibility of measurements of key microstructural parameters.

The current status and future needs of nanoparticle metrology are discussed, particularly with respect to measurements of size, size distribution and number concentration of airborne and liquid-borne nanoparticles. Possible classification of types of measurement standards is proposed, and the role of each type of standard, including the feasibility of its establishment, is examined. A desirable interplay between measurement standards and documentary standards in establishing the traceability chain in particle measurements is suggested. Particle-related calibration services currently provided by our laboratory at the National Institute of Advanced Industrial Science and Technology are also described.

This review gives a brief introduction to the principles of microwave measurements of the complex permittivity of materials. The fundamentals of reflection, transmission and resonant methods are summarized and examples of sample cell design and measurement systems are presented for each category. The frequency domain and the fast response time domain methods are discussed in view of their merits and limitations. Accuracy aspects and reference materials for calibration procedures are mentioned briefly. Selected examples of applications indicate the diverse usability spectrum of microwave dielectric measurements in basic research and in the characterization of materials in manufacturing processes as well as monitoring and control routines.

Major methods to measure the magnetic properties of materials are systematically discussed in the light of the general phenomenology of magnetism in matter and its physical interpretation. Attention is paid to the problems of measurement traceability and reproducibility and the related standards. While the discussion is focused on the characterization of the soft and hard ferromagnetic materials relevant for electromagnetic applications, brief consideration is given to the special problems posed by measurements on feebly magnetic materials. It is stressed how geometrical and physical properties can often combine to make the determination of the true magnetic properties of materials a somewhat elusive goal. Measurement reproducibility can nevertheless be attained under the guidance provided by written standards. Recent evolution of the magnetic measuring techniques has occurred in response to the digital revolution and the development of novel high-performance materials (e.g. extra-hard rare-earth based magnets, multilayers, micro/nanostructures, etc). It is stressed, however, that the drive to progress in measurements ultimately stems from the search for new fundamental phenomena in materials and their understanding.

In order to improve the performance of devices, components and systems, where heat is generated, transported, stored or converted to other types of energy, reliable thermal design and simulation are required using reliable thermophysical property data. In order to produce reliable thermophysical property data systematically and continually, the international and national standards of thermophysical properties must be established and the measurement methods should be evaluated and standardized, and the measuring instruments must be calibrated by reference materials traceable to the international or national standard.

Users search for and purchase a particular grade of material which satisfies the properties, performances and technical specifications required. In order to guarantee fair commerce and trade, values of thermophysical properties should be measured traceable to the national standard. Thus, the establishment of an international standard is required satisfying the global CIPM MRA under the metric convention, and then, the global and regional framework to examine calibration and measurement capability of national metrology institutes (NMIs). A domestic traceability system in each country should be established and the quality management system of the NMI and calibration laboratories should be constructed based on ISO 17025.

A review is presented of methods of measurement for a range of key acoustic properties of materials, spanning three application areas: airborne sound, underwater acoustics and ultrasound. The acoustic properties considered, primarily transmission loss (damping) and echo-reduction, are specifically important to the end application of any material. The state-of-the-art in measurement and likely future challenges are described in detail.

The instrumentation of the Physikalisch-Technische Bundesanstalt (PTB) for the measurement of the directional spectral emissivity in air in the temperature range from 80 °C to 400 °C and wavelength range from 4 µm to 40 µm and the subsequent procedures for data evaluation are described. Special emphasis is placed on the calculation of the uncertainty of the directional spectral emissivity and of the uncertainty of the sample surface temperature. For samples with typical emissivities of about 0.6, absolute expanded uncertainties (k = 2) of 0.01 can be reached at a surface temperature of 200 °C in the spectral range from 5 µm to 40 µm. However, it is also shown that—due to the complex dependence of the uncertainty on the sample and the conditions of measurement—general statements about the uncertainty cannot be given. The uncertainty of the emissivity has to be calculated for each individual case of sample and temperature.

This paper reviews the basic concepts, metrological requirements and approaches for the precise and accurate measurement of photoluminescent materials. These fluorescence measurements offer significant advantages in terms of sensitivity and selectivity, finding wide use in a range of applications in bioanalytical, analytical chemistry and colour technology. Depending upon the specific metrological requirement, different properties of the photoluminescent material are of interest and different measurement techniques and instrumentation have been developed. The optical properties of interest for both analytical and colorimetric applications are defined along with their basic measurement principles. However, many problems are associated with the comparability of these measurements due to their dependence on both instrument and sample parameters. These considerations and measurement problems are identified and the impacts of standardization methods are illustrated in two typical applications. The paper also gives a detailed description of both the physical transfer standard and chemical transfer standard approaches for obtaining reliable, traceable fluorescence data. However, for many applications, the robust standardization of these measurements and availability of appropriate transfer standards are still in their infancy. This paper concludes with a brief discussion of the state-of-the-art uncertainties in the metrology of photoluminescence.