Stress and strain measurements by image correlation and Thermoelasticity
In this paper image correlation and thermoelaticity are proposed as joint measurement techniques to perform a “full field” characterization of materials and mechanical components. The very interesting possibilities offered by using both these non contact measurements techniques is the ability to obtain, by measuring both stress and strain, distributions of mechanical parameters on the surface of a dynamically loaded mechanical component, made, in general, of any material. This kind of results can be very useful for non homogeneous, composite or complex materials, or for complex shapes or loading conditions of the mechanical component under analysis, nowadays largely used for machine and structure realizations. In the work a proper coating, useful to perform measurements by both the techniques, is developed and tested. The coating act as a stressstrain distributed gauges.
Development of a non-contact torque transducer based on the laser speckle contrast method
Abstract. When a torque measurement is required, torque transducers show many drawbacks during their use: the usual limits are the need for contact and the effects on shaft line parameters. A new approach is proposed in this work: a non-contact torque meter for a machine shaft has been developed. It carries out torque measurements evaluating the torsional displacement between two distinct sections of the shaft, through the monitoring of their roughness. The sensing principle employed is the classical laser speckle contrast method. The outcoming intensity scattered by the rough surface is processed by a cross-correlation function. In this way, the angular torsion of two distinct sections is obtained. It is therefore possible to point out the applied torque knowing the shaft torsional stiffness.
A Coupled Fluid-Structure Analysis for 3D Flutter in Turbomachines
A three-dimensional nonlinear time-marching method and numerical analysis for aeroelastic behaviour of oscillating blade row has been presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural equations are integrated simultaneously in time. In this formulation of a coupled problem, the interblade phase angle at which a stability (or instability) would occur, is a part of the solution. The ideal gas flow through multiple interblade passage (with periodicity on the whole annulus) is described by the unsteady Euler equations in the form of conservative laws, which are integrated by use of the explicit monotonous second order accurate Godunov-Kolgan volume scheme and a moving hybrid H-H (or H-O) grid. The structure analysis uses the modal approach and 3D finite element model of the blade. The blade motion is assumed to be a linear combination of modes shapes with the modal coefficients depending on time. The influence of the natural frequencies on the aerodynamic coefficient and aeroelastic coupled oscillations for the Fourth Standard Configuration is shown. The stability (instability) areas for the modes are obtained. It has been shown that interaction between modes plays an important role in the aeroelastic blade response. This interaction has essentially nonlinear character and leads to blade limit cycle oscillations.Copyright © 2000 by ASME