The Dynamometry Department carries out researches and technical activities in the field of mechanics. It is devoted to the study and dissemination of primary standards of force and torque, high-medium-low pressures and hardness. Other topics of interest are primary techniques and in-struments for dynamic acceleration and absolute gravimetry, both for measurements and calibrations. The Department also carries out experimental and theoretical activities aiming at a kilogram realization based on the mass of the 28Si atom.
The continuous expansion system is a primary standard based on the dynamic expansion of a pure gas which is pumped through a conductance. The gas flow is generated and measured by a constant-pressure, variable-volume flow-meter. Several manual operations have been automated: the start-up of the two pistons of the flow meter, temperature acquisition in the key places of the system, with real time measurement results. A bilateral comparison with NPL has been activated (EUROMET project 855). An experimental study has started in order to evaluate the influence of the configuration used for mounting the spinning rotor gauges to the calibration chamber. The gas flow meters are also used for calibration of standard leaks. Three gas-flow-meters are available and have been used in the bilateral comparison with Giessen University (Germany).
Continuous expansion system, pressure range from 1·10-6 Pa to 9·10-2 Pa.
The performances of the two interferometer manometers HG5 and MM1 have been improved throug the adoption of a new type of cat's eyes floating, especially for low pressure.With the aim to perform cycles of measurements at increasing and decreasing pressure with devices which are gas-dependent (air and N2), a circuit for gas regulation has been prepared for the connection of up four barometers.
The pressure balances under investigation operate up to 200 MPa (free deformation and controlled clearance types). All FEM numerical results are compared to the experimental characteristics of the piston-cylinders. This work shows that the determination of the deformation coefficient using FEM methods implies very good knowledge, not only of the dimensional parameters, but also of the elastic properties of the specific piston and cylinder material used and the boundary conditions (stress and pressure) applied on the cylinder.
FEM calculated values of piston fall rates (for the free deformation unit) compared with experimental values of different units. Good agreement between predicted results and experimental values, within the imposed ± 0.1 µm variation of the piston-cylinder radial clearance.
The commitment to long-term basic research and to ensuring solid foundations to metrology is illustrated by the involvement in an international cooperation programme aimed at realizing the kilogram on the basis of the 28Si mass. The basic concept is to count the number of atoms in a 1 kg crystal 28Si sphere. An essential step is to measure atom spacing with ten decimal digits; this leading-edge experiment relies on combined X-ray and optical interferometers to observe and to count the atoms in a crystal part of known length. To this end, Si crystal is cut into two parts which are reassembled in such a way that atoms refill the same lattice locations as in the initial single-crystal. The two crystals are slid one against the other by about 1 mm while the passing atoms are counted and crystal displacement is measured to within picometer accuracy. Crystal displacement is a formidable challenge. Not only were vibrations eliminated down to picometers, but also electronic control of the crystal attitude and location was achieved, over six degrees of freedom and commensurate with the requirement of atomic-scale positioning. Parallel studies aimed to develop theoretical models and numerical methods, which are necessary to understand the underlying physical phenomena, to explain the experimental observations, and to compress the huge amount of data generated by each measurement run. The most exact spacing measurement achieved is 0.192015569(6) nm.
Device used for the alignment and translation of a scanning X-ray interferometer.
The measurement capabilities of the transportable absolute gravimeter IMGC-02 have been improved with the complete automation of the apparatus and with a new software for statistical analysis of the results. The procedure used for the verticality of the laser beam and the model equation used to reconstruct the test-mass trajectory have been upgraded. The present instrument adopts an innovative fringe-processing technique. The relative instrumental expanded uncertainty (p=95%) is 8.2·10-9. Noteworthy measurement activities are the participation in the international comparison ICAG-2005, held at the BIPM, and monitoring the volcanic area of Colli Albani in Lazio (Italy). In dynamic accelerations, a high stability signal conditioning to be used for international comparison has been produced. A portable vibrating table for low frequencies (2-8) Hz has been studied and a new program for vibration measurements of buildings (UNI 9614) has been developed.
New transportable absolute gravimeter IMGC-02.
The new definition of the Rockwell C scale has been finalized and proposed at international level (CCM-WGH). New studies on the influence of the numerical aperture in Brinell measurements has been carried out, as well as a new procedure for the performance test of Rockwell diamond indenters has been developed and proposed at international level. The metrological characterization of the primary hardness standard machine and indentation measuring system for INMETRO (Brazil) and their installation have been performed, as well as the metrological characterization of the measuring system for diamond indenters of UME (Turkey).
Primary Hardness Standard Machine in-stalled at INMETRO (Brazil).
A broad internal campaign of comparison among the primary force standard machines has been carried out to assure continuity of the national force scale and for participation in the 500 kN and 1 MN CCM Key-Comparisons. A new 1.2 kN dead weight force standard machine has been designed. In stress analysis at cryogenic temperatures, some preliminary tests on Al-Li at 17 K have been carried out for space mission applications.