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The aim of this work was to develop a calibration procedure to cover the production of static and continuous forces by industrial machines, used for both materials testing and in the larger scale testing of components, products, and structures – this second application incorporated the use of multiple force sensors, reversal of loading direction, and novel transducer design. The calibration procedure can be generally used without any limit of the nominal load range, so the typical force range for material tests from 1 N to 1 MN can be served., The ComTraForce project 18SIB08 has received funding from the European Metrology Programme for Innovation and Research (EMPIR) as well as the European Association of National Metrology Institutes (Euramet).

In the framework of EMPIR project ComTraForce, the Digital Twin (DT) concept of force measurement device is developed. DT aims to shade static, continuous as well as dynamic calibration processes, preserving data quality and collecting calibration data for improved Decision-making. To illustrate the developed DT concept, a prototype realisation for static and continuous force calibration processes is developed, involving simulation with ANSYS engineering software. The focus of the current work is placed on the data connection between the physical device and the DT. The DT model is validated using traceable measurements.

In the last few decades, many researchers have been studying how hardness measurements can be affected by possible influence variables (i.e. velocity of the indenter, dwell times, temperature, etc). This interest is particularly motivated by the newly adopted international definitions for the realization of Rockwell superficial hardness scales (HR45N, HR30N and HR15N) provided by the Consultative Committee for Mass and Related Quantities of Bureau International des Poids et Mesures, which deal with all the above-mentioned parameters. In this paper, the effect of two such parameters, namely the velocity of the final load application and the time interval of the force variation from the preliminary force value to the total force value, on superficial Rockwell hardness scales at different levels is studied and the related sensitivity coefficients are determined. The coefficients obtained are in the order of 10−3 HR s μm−1 and 10−2 HR s−1, respectively, in agreement with other National Metrology Institutes (NMIs), i.e. NIST and NPL. However, the uncertainties associated by the other NMIs are usually underestimated since they are simply given as the standard deviation calculated from the ordinary least squares method for the multiple linear regression, or, in other cases, not reported. For this reason, we propose a methodology for calculating the uncertainties of the sensitivity coefficients via a Monte Carlo method applied to multiple linear regression in order to consider the variability of both input and output quantities: with this method, the squared uncertainties are given as the squared sum of the standard deviation calculated from the ordinary least squares method and the uncertainty contribution due to the repeatability obtained via the proposed Monte Carlo method. The proposed method yields uncertainties of about 10−2 HR, while the uncertainties reported in other related published papers are in the order of 10−3 HR.

The aim of this report is to describe the preliminary version of a digital metrological twin (DMT) of a force measuring device for static, continuous and dynamic forces. In almost all major manufacturing industries such as aerospace, automobile, and construction, one of the most important activities is material/mechanical testing. Material/mechanical testing allows the manufacturer to understand, quantify and check whether their product is suitable for a particular application. This process involves the measurement of force/s acting on a product usually by means of a force measuring instrument called a load cell. With the inevitability of the fourth industrial revolution, coined as Industry 4.0, virtual tools and models of measuring instruments called digital twins (DT) will be required in manufacturing and inspection processes. A DT is generally defined as “a virtual model used to facilitate detailed analysis and monitoring of physical or psychological systems”. DT’s purpose is not to mirror but rather to ensure the “health,” integrity and reliability through monitoring, prediction and optimisation of its physical asset using data analytics, artificial intelligence, machine learning, among others., The ComTraForce project 18SIB08 has received funding from the European Metrology Programme for Innovation and Research (EMPIR) as well as the European Association of National Metrology Institutes (Euramet).

In recent years a growing need in naval acoustics for the characterization of low frequency materials below 100 Hz and particularly from 50 Hz has been observed. The problem related to airborne and impact acoustic insulation at low frequencies is becoming more and more relevant due to the considerable impact of sound sources at these frequencies, such as audio-video systems in theaters and discos as well as TV systems inside cabins. Current measurement procedures for identifying the sound insulation properties of bulkheads and floors are not sufficient to ensure repeatable and reproducible measurements, as accuracy and precision values are too low to be accepted when applied at frequencies below 100 Hz. In fact, at low frequencies and in ordinary laboratory or room volumes between 40 m3 and 80 m3, the acoustic field is no longer diffuse due to the dominant presence of standing waves or modes, which result in large fluctuations of the sound pressure level in space and frequency. In the present study, an experimental methodology based on the modal approach is proposed and applied for the study of low-frequency sound insulation phenomena below 100 Hz in the naval field. An extensive experimental activity has been conducted at CETENA laboratories in Riva Trigoso, which has allowed to validate the measurement procedure and compare it with classical theories of sound transmission. The development of this approach seems to be able to provide significant support in the design phase for the optimization of shipboard sound insulation performances.

Acoustic metamaterials (AMMs) offer innovative solutions for physics and engineering problems, allowing lighter, multiphysics, and sustainable systems. They are usually studied analytically or numerically and then tested on prototypes. For this reason, additive manufacturing (AM) techniques are a popular way of quickly realising AMMs' innovative geometrical designs. However, AM parameters are often standardised without considering the specific issues of each AMM geometrical shape, leading to a possible mismatch between the analytical (or numerical) and experimental results. In this study, a simple AMM—a coiled-up resonator—has been produced with different AM technologies [fused deposition modeling (FDM), stereolithography (SLA), and selective laser melting and materials (polylactic acid, polyethylene terephthalate glycol, resin, flexible resin, and stainless steel). The sound absorption performance of these samples has been measured in two research labs in Italy and compared with the analytical and numerical calculations. This permitted the identification of the best combinations of AM technologies, their setup, and materials matching the expected results. The SLA/resin combination performed better overall; however, cheaper and more easily manageable samples made with FDM and polyethylene terephthalate glycol can achieve the same acoustic performance through the optimal AM printing setup. It is expected that this methodology could also be replicated for other AMMs.

Mechanical calibration and traceability of seismometers in operating conditions are still a technical challenge, since very low-frequency ranges (below 0.1 Hz) are involved, and sensors under investigation are generally heavy and bulky. Recently, within the vibration metrology field, some pioneering works proposed to evaluate the seismometers’ sensitivity by applying laboratory mechanical calibration procedures, against primary or secondary standards, according to the ISO 16063 methods. By following this path, at INRIM, it has been developed a suitable system for short period horizontal and vertical ground velocity calibration of 3-axis seismometers. The calibration system allows to directly evaluate the sensitivities of the 2 axes perpendicular to the gravity field, with respect to the horizontal ground velocity (S-waves), and to derive the sensitivity of the vertical axis, parallel to the gravity field, with respect to the vertical ground velocity (P-waves), in the frequency range between 0.03 Hz and 30 Hz.

Accurate characterization of coil springs, typically in terms of axial and transverse stiffness, is crucial in many applications, in particular in automotive engineering, such as suspensions, vibration reduction, seating, exhaust valves, gear engagement controls, transmission hose, fuel panels, car trunks, and engine hoods. These measurements are usually performed in spring testing machines along the vertical axis in quasi-static conditions. However, when springs are stressed along the main vertical axis, side forces, bending and torsion moments are generated, thus have to be evaluated. For this reason, a hexapod-shaped multicomponent force and moment transducer has been recently devised, realized and integrated into standard spring testing machines capable to measure the displacement along the main and transverse axes. In this way, forces, moments and displacement components generated by the springs can be measured and axial and transverse stiffness derived. In this work, two multicomponent spring testing machines with the hexapod-shaped force and moment transducer are described and measurements on different large coil springs are presented.

Natural stone masonry is a building technology largely used all over the world, since the dawn of humankind. At present day stone masonry buildings, beyond being naturally characterized by intrinsic building physics performances, allow to reconsider the use of natural stone masonry (together with new technological supports, components and materials), as a promising “new trend” for both newly developed buildings and renovation of existing buildings, in particular where it is a priority to retrieve the historical identity of the urban landscape. In this paper, energy performance and structural-acoustic properties of stone masonry buildings, in compliance with seismic safety criteria, are investigated and discussed on the basis of current technical standards and scientific literature. Related performances are evaluated by means of accurate calculation models. The results show that stone masonry buildings can offer often higher performance than those normally attributed to it.

Traceability of multicomponent force and moment transducers (MCFMTs) is a metrological priority as stated within the document of future strategy 2017–2027 of the Consultative Committee of Mass and Related Quantities of Bureau International des Poids et Mesures (BIPM). In this paper, a calibration system using force standard machines (FSMs) integrated with tilted plates is described. The main advantage of this method is the possibility to apply force and moment components using existing uniaxial FSMs without the necessity to modify them or to develop specific ones. On the other hand, force and moment components cannot be fully independently applied. Expanded uncertainties of the applied side forces and moments are in the order of around 5%, acceptable for several industrial applications. A procedure for the calibration and the uncertainty assessment of MCFMTs is also provided. Calibration results, in terms of main and cross-talk sensitivities, of a six-components transducer are shown. This method is easily implementable and can be adopted to improve the current standard.

The value of the acceleration due to gravity is of interest in a wide range of fields, from geophysics, geodesy, water-floor monitoring, and hazard forecasting to oil, gas and mineral exploration. For this purpose, relative or absolute gravimeters have been developed and used for decades. While absolute gravimeters are mainly used in monitoring stations or as reference, relative gravimeters are those actually used to determine the relative variations of the local gravitational field given their smaller dimension, lighter weight, and better reading resolution, despite the high costs and the difficulty in being used under severe environmental conditions. In the last years, the advent of micro-electromechanical-systems (MEMS), in particular MEMS accelerometers, has opened up the doors to new measuring possibilities at very low-costs. As a consequence, different international research groups focused their efforts to develop relative MEMS gravimeters and showed that this technology might be really useful for monitoring the gravitational field. However, their current production is limited to a few specimens and prototypes that cannot be exploited on a large scale at the present day. For this reason, this work investigates the possibilities and the limits in the use of commercial digital MEMS accelerometers as relative gravimeters. The digital MEMS accelerometers investigated in this work are two commercial low-cost digital MEMS accelerometers (STM, model LSM6DSR, and Sequoia, model GEA). The first is composed of an accelerometer sensor, a charge amplifier, and an analog-to-digital converter and is connected by a serial cable to a separated external microcontroller (ST, model 32F769IDISCOVERY), in which other electronic components are integrated. The second is composed of the sensing element and the analog-to-digital converter. Both are connected to the computer via USB cable. The two devices are included in a thermally insulated case, in which a resistive heater and a resistance thermometer (PT1000), connected in loop, are placed in order to guarantee temperature stability during use. The system, installed on a tilting table to ensure higher accuracy in the evaluation of local g, is calibrated in static conditions by comparison to the absolute gravimeter IMGC-02 at a specific measurement location at INRIM. Calibration is repeated several times over a period of a few weeks in order to evaluate repeatability, reproducibility and stability over time. Despite the promising future prospects of this technology, at present, the levels of precisions are low compared to the ones required by most of geodynamics applications.

The use of sensors with digital interface, within large or dense sensor networks, is nowadays widespread in many scientific and technological applications: from more traditional applications, such as infrastructure monitoring and predictive maintenance, up to the advanced ones, such as smart manufacturing, IoT, Machine Learning, and other emerging fields of fast-real-time interconnections, within the framework of digitalization. The technical and functional performance of these sensing infrastructures, if accurately identified, allows to enhance the trustworthiness, safety, and accuracy of the managed processes; based on metrological characterizations and calibration, it is possible to provide the actual sensitivity of digital sensors with respect to reference physical stimuli, within the proper uncertainty budgets and suitable covering factors. At present days, metrological characterization and proper calibration of digital sensors is still a technical and methodological challenge and several studies are oriented along with this perspective. In this paper, the sampling rate variability – depending on MEMS analog-to-digital converter, external microcontroller internal clock and their interaction – of digital MEMS accelerometers in dynamic calibration is investigated. The sampling rate variability is evaluated among 25 sensors of the same batch, and within every single sensor in time, and methods to manage the associated uncertainty and to avoid mismatches in calibration, are proposed and discussed.

Traceability of digital 3-axis MEMS accelerometer networks is often disregarded by manufacturers and end-users due to the lack of suitable calibration procedures and to the complexity in managing a large number of sensitivities. To overcome these problems, two traceable independent accelerometer calibration systems and methods using inclined planes have been recently developed by a national metrology institute and a calibration laboratory at an uncertainty level of 2 %. In this work, main and transverse magnitude sensitivities of 25 digital 3-axis MEMS accelerometers, part of a sensor network prototype conceived for structural monitoring at low-frequencies, are evaluated at three low-frequencies by the two laboratories. Comparison shows compatible results. Furthermore, a method for decreasing the number of sensitivity and uncertainty data to be managed by sensor network end-users is also proposed. It is shown that its number can be reduced preserving the required traceability at the expense of higher uncertainties up to 4.5 %.

La modellazione dell’isolamento acustico di una partizione con i modelli SEA, adottati nelle ISO 12354, ha fra le ipotesi la diffusione del campo di vibrazione nell’elemento in esame. Per quanto riguarda i pannelli in XLAM, quest’ipotesi è senz’altro una delle più stringenti e non sempre verificate nelle frequenze utilizzate per la modellazione. Il presente lavoro riguarda quindi lo studio della transizione fra regime modale e regime diffuso negli elementi in XLAM attraverso il confronto fra misure sperimentali e modelli analitici.

In this work two calibration methodologies, able to characterize the digital sensitivity of MEMS accelerometers, are presented and compared, to identify the contributions for the evaluation of the reproducibility in the low frequency range. The methodologies are different from the point of view of test bench, test procedure and data processing method. In particular, different vibration actuators are used, a linear slide and an electro-dynamic shaker, different sensors as a reference for the calibration, piezoelectric accelerometers and a Laser Doppler Vibrometer (LDV). A group of 5 accelerometers is tested for the purpose of developing the calibration techniques and evaluate a first reproducibility estimate. The experimental results provided by the two calibration procedures show significant differences. Some elements that could explain these differences have been identified, and will be further investigated in future work.

The internationally recognized procedure ISO 354:2003 for measuring sound absorption coefficients under diffuse field conditions is now under revision. The main reason for this revision is the limited reproducibility of absorption coefficients measured in different laboratories that may have significant implications spanning from room acoustic design to material selection. A network of Italian laboratories have come together to carry out an Inter-Laboratory Test (ILT) to assess and compare the measurement uncertainties resulting from the application of the current version of ISO 354:2003 and of the new ISO/CD 354:2019. After detailing the methodological aspects, the paper presents the results of the measurements, discussing the compliance of the laboratories to the standard requirements and new qualification tests, and, more importantly, providing a quantitative estimation of their effects on measurement uncertainty and accuracy. (C) 2020 Elsevier Ltd. All rights reserved.

ISO 4545-2 and 4545-3 of Knoop hardness tests require the geometrical verification of the indenter. INRiM hardness laboratory developed a specific measuring system, commercialized by Galileo- LTF (R) as Gal-Indent optical system, which is used for the verification of Vickers indenters. This system is able to measure the vertex angles of the indenter between two opposite faces, and the four quadrilateral base angles. Using such quantities as inputs of a suitable geometrical model, the geometry of Knoop indenters can be verified. This work deals with the description of the system and the geometrical model.

The research and development phase of sound absorptive building materials by designers, engineers, acoustic consultants and architects need tools for fast, inexpensive preliminary comparison tests on products or acoustic systems. The existing methods exhibit some drawbacks: the impedance tube (IT) is not suitable for 3D systems, while the full-scale reverberation room (FSRR) requires test samples of large dimensions. To overcome these limitations, this work aims to explore the capabilities of small-scale reverberation rooms (SSRR) of about 3 m3 located at Politecnico di Torino in evaluating the random-incidence sound absorption coefficient. In order to define the range of application and reliability of the method, the considered factors are the sample area and its orientation on the room floor. Four different materials have been tested by applying IT, FSRR and SSRR. The absorption coefficients data obtained with SSRR are compatible with the FSRR benchmarking in the 400–5000 Hz frequency range for three porous materials, and in the range 1000–5000 Hz for the thin rigid material. Therefore, the SSRR can be considered as a reliable alternative for the sound absorption characterization in these ranges for this kind of materials, leading to several benefits. Among them, samples with reduced size can be evaluated with a cheaper equipment in a short time, increasing the overall economical sustainability of the measurement process; in turn, this can encourage designers and architects to perform acoustical measurements since the very early research and development phase, leading to an overall reduction of design costs and improved product quality.

For the measurement of the acceleration due to gravity, INRiM developed a transportable ballistic rise-and-fall absolute gravimeter, the IMGC-02. It uses laser interferometry to measure the symmetrical free rising and falling motion of a test mass in the gravity field. The launch system is composed of a moveable carriage fixed to two pairs of springs loaded by an electric stepper motor, which vertically throw up a corner cube retroreflector in vacuum. The interferometer system is a modified Mach-Zehnder interferometer where the launched corner cube acts as the reflector in one of the optical arms of the interferometer and the other retroreflector acts as inertial reference during the measurement. However, both systems entail some practical problems and uncertainty contributions that need to be reduced. In particular, the current launch system might cause beam shear and rotational effects due to unavoidable small different loadings of the springs, while the current interferometer system poses problems in the alignment of the mirrors, which is a highly time-consuming procedure and has to be performed before and, sometimes, during the measurement session. For this reason, a new launch system consisting of an electric linear motor which produces a linear force along its length, and a modified Jamin interferometer system entailing a simpler alignment and a better stability in time, have been designed. This works deals with the description of these new systems.

The modelling of vibro-acoustic properties of plates usually requires the hypothesis of diffuse conditions of the vibrational field. For heavy-weight homogeneous isotropic plates, this condition is met starting from low frequencies. Nevertheless, the same hypotheses do not hold when applied to stiff, inhomogeneous and non-isotropic materials, like wood, thus its modal behavior needs to be addressed with more detail. The aim of the work is to benchmark theoretical methods and experimental measurements that allow to estimate when the transition from modal to diffuse field occurs in Cross Laminated Timber (CLT) elements. For this purpose, the diffuseness of the vibrational field has been investigated through the experimental evaluation of the mode count and the modal overlap factor on a pilot CLT panel. Measurements of the spatial distribution of modes, impulse responses, dispersion relations and driving point admittance were conducted in laboratory on an 8 m2 CLT plate. The analysis of the results allowed, on the one hand, to directly estimate the two parameters, and on the other, to provide input data necessary to evaluate and compare different theoretical models. Results of direct measurements, performed up to 550 Hz, show that the number of modes occurring in one-third octave bands exceeds the standard threshold of 5 only at 500 Hz, whereas the modal overlap factor is lower than the standard threshold of 1 for most of the modes. This indicates that the vibrational field is mainly non-diffuse in the mid-low frequency range, due to the small number of modes combined with a low damping of the CLT plate. Nonetheless, measurements of modal reverberation time and structural reverberation time in one-third octave band provided consistent results, implying that modal decays are the major contributors to the one-third octave band decay. Furthermore, comparisons with theoretical models show that the driving point admittance proved to be the best method of analysis, requiring simple measurement setup and signal processing, whereas the ISO 10848-4 is affected by the thin plate hypothesis and underestimates the mode count at mid-high frequencies.

Indoor working and living environments are increasingly exposed to low-frequency noise sources. The well-known relationship between noise conditions and effects on human health requires the development of a proper procedure to evaluate the stress due to acoustical factors. For this purpose, an experiment, based on Soft Metrology principles, was designed to measure the changes of cognitive and physiological parameters (response time and heart rate) on a sample of 25 male and female volunteers, aged 19–29 years, exposed to three types of noise in a hemi-anechoic room. Participants were involved in a cognitive task (Stroop effect) for 10 min in four different conditions: silence, stochastic broadband multi-tonal noise (BBN), stochastic low-frequency multi-tonal noise (LFN1), and low-frequency stationary noise with regular amplitude modulation (LFN2). All sounds were reproduced by two loudspeakers at equivalent sound pressure level of 93 dB. Results showed that in noise conditions, subjects reduced their response times. This is an evidence of growing stress, according to arousal theory. In particular, LFN1 and LFN2 produced cognitive stress comparable to stochastic broadband multi-tonal noise. Furthermore, subdividing the subjects in extroverts and introverts through the Eysenck Personality Questionnaire–Revised psychological test, it was shown that LFN1 and LFN2 produced higher stress effects than stochastic broadband multi-tonal noise on the cognitive performances and a physiological stress comparable to stochastic broadband multi-tonal noise in introverts, whereas no effects were observed in extroverts, as hypothesized by Eysenck. This result highlights the necessity in the future to consider the personality parameter as a key factor in the evaluation of the effects of noise on humans.

Back in 1986, investigating the Space Shuttle Challenger disaster, famous physicist Richard Feynman clearly showed how viscoelastic behavior of a polymeric material is of paramount importance in practical engineering. At present day a definitive universal rheological law is not yet available for polymers, as a consequence both theoretical models and experimental investigations of viscoelastic behavior must be necessarily focused independently on each single polymer or, at least, on well-defined classes of polymers. Accurate experimental evidences are needed in order to properly evaluate the mechanical properties of a polymeric material, as a function of its particular applications. In this paper measurements of the stress relaxation behavior of six polymeric materials under uniaxial tension and uniaxial unconfined compression tests, are performed and experimental results are modelled using a stretched exponential function, known as Kohlraush-Williams-Watts time-decay function. In particular the short-term stress relaxation is investigated, as a function of typical environmental temperature range, in order to assess viscoelastic behavior of tested polymeric materials for peculiar industrial and biomedical applications.

Several studies have shown so far that poor acoustics inside classrooms negatively affects the teaching and learning processes, especially at the lowest grades of education. However, the extent to which noise exposure or excessive reverberation affect well-being of children at school in their early childhood is still unanswered, as well as their awareness of noise disturbance. This work is a pilot study to investigate to which extent classroom acoustics affects the perceived well-being and noise disturbance in first graders. About 330 pupils aged from 6 to 7 years participated in the study. They belonged to 20 classes of 10 primary schools located in Torino (Italy), where room acoustic measurements were performed and where noise level was monitored during classes. The school buildings and the classrooms were balanced between socioeconomic status and acoustic conditions. Trained experimenters administered questionnaires in each class, where pupils answered all together during the last month of the school year (May). Questions included the happiness scale, subscales assessing self-esteem, emotional health, relationship at home and with friends, enjoyment of school, intensity and noise disturbance due to different sound sources, and quality of voice. The findings of the study suggest that long reverberation times, which are associated with poor classroom acoustics as they generate higher noise levels and degraded speech intelligibility, bring pupils to a reduced perception of having fun and being happy with themselves. Furthermore, bad classroom acoustics is also related to an increased perception of noise intensity and disturbance, particularly in the case of traffic noise and noise from adjacent school environments. Finally, happy pupils reported a higher perception of noise disturbance under bad classroom acoustic conditions, whereas unhappy pupils only reported complaints in bad classroom acoustics with respect to the perception of pleasances with himself or herself and of fitting in at school. Being a mother tongue speaker is a characteristic of children that brings more chances of attending classes in good acoustics, of being less disturbed, and of having more well-being, and richer districts presented better acoustic conditions, in turn resulting in richer districts also revealing a greater perception of well-being.

The use of digital sensors in engineering applications and monitoring systems is widely increased in the last years, in particular in the context of smart manufacturing, Industry 4.0, Internet of Things (IoT) sensors networking, as well as in environmental and infrastructural monitoring. Nevertheless, digital MEMS accelerometers and microphones are currently not reliable to quantify with adequate accuracy the vibratory phenomena and the sound pressure fluctuations, in terms of amplitude and frequency, due to the lack of metrological traceability and suitable sensitivity parameters for digital sensors. This paper presents two calibration procedures, recently realized at INRiM, suitable to characterize digital MEMS accelerometers and microphones. In particular, the possibility to provide a proper sensitivity for digital signal outputs, in order to ensure traceability to primary standard, is addressed.

This study aims to characterize the sound insulation properties of a two-layers innovative facade made by a Structural Concrete Wall with Thermal Insulation Properties (SCWTIP). The sound reduction index of the wall has been evaluated through analytical calculation, software simulation and laboratory measurement on a 10 m2 real sample, according to EN ISO 10140-2. Results showed that analytical calculation matches laboratory measurements in terms of sound reduction index, while 1 dB increase has been found with software simulation. Software simulations have also been carried out in order to compare the sound insulation index of the tested wall with walls in which the mechanical properties or the thicknesses of the concrete layers have been varied, in consideration of the commercially available options. Calculation of the standardized sound level difference of facade according to EN ISO 12354-3 for a typical dwelling room showed that a lightweight concrete facade made with this technology satisfies the requirements of the higher class set by the COST Action TU0901 for sound insulation of dwellings. The requirement set by French laws, which is not included in the Action framework, has been also accomplished.