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Uniaxial material damping measurements using a fiber optic lattice: a discussion of its performance envelope
KTH, Superseded Departments, Materials Processing.
KTH, Superseded Departments, Casting of Metals.
2004 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 44, no 1, 33-36 p.Article in journal (Refereed) Published
Abstract [en]

Damping is the internal transfer of kinetic energy to other forms of energy. Today, most methods use either bending or torsional vibration to measure damping. This means that the strain field in the specimen is nonhomogeneous. If the damping of the tested material is linear, strain-independent, the values acquired with these traditional methods will be equal to the intrinsic material damping of the material. If, however, the damping is strain-dependent, nonlinear, the measured value will be an average of the damping of the specimen, and not equal to its intrinsic material damping. To address this problem, a method is required to experimentally determine the damping in uniaxial tension in order to produce the same strain level in all parts of the test specimen and hence obtain a measurement of the intrinsic material damping. Using such a method, it is possible to view the material damping as the phase angle between the stress and the strain in a harmonic oscillation. In this paper, a method is suggested for measuring this phase shift in uniaxial tension to determine the material damping properties. It uses a tensile test machine, an optical fiber Bragg grating technique and a lock-in amplifier. Measurements with the phase shift technique have been suggested previously, but its performance envelope has been overestimated. In this paper, the performance envelope is discussed and restricted. It is shown that the envelope depends on the specimen length, loss factor and test frequency. An optical strain measurement method is also believed to help avoid many electrical measurement problems seen with the originally proposed method.

Place, publisher, year, edition, pages
2004. Vol. 44, no 1, 33-36 p.
Keyword [en]
ntrinsic, material, damping, phase lag, experimental measurement, optical strain gage, Bragg grating, optic sensor
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-5953DOI: 10.1177/0014485104039746ISI: 000188607100005Scopus ID: 2-s2.0-1342329587OAI: oai:DiVA.org:kth-5953DiVA: diva2:10501
Note
QC 20100929Available from: 2006-06-02 Created: 2006-06-02 Last updated: 2010-09-29Bibliographically approved
In thesis
1. On the Experimental Determination of Damping of Metals and Calculation of Thermal Stresses in Solidifying Shells
Open this publication in new window or tab >>On the Experimental Determination of Damping of Metals and Calculation of Thermal Stresses in Solidifying Shells
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis explores experimentally and theoretically two different aspects of the properties and behaviour of metals: their ability to damp noise and their susceptibility to crack when solidifying.

The first part concerns intrinsic material damping, and is motivated by increased demands from society for reductions in noise emissions. It is a material’s inherent ability to reduce its vibration level, and hence noise emission, and transform its kinetic energy into a temperature increase. To design new materials with increased intrinsic material damping, we need to be able to measure it. In this thesis, different methods for measurement of the intrinsic damping have been considered: one using Fourier analysis has been experimentally evaluated, and another using a specimen in uniaxial tension to measure the phase-lag between stress and strain has been improved. Finally, after discarding these methods, a new method has been developed. The new method measures the damping properties during compression using differential calorimetry. A specimen is subjected to a cyclic uniaxial stress to give a prescribed energy input. The difference in temperature between a specimen under stress and a non-stressed reference sample is measured. The experiments are performed in an insulated vacuum container to reduce convective losses. The rate of temperature change, together with the energy input, is used as a measure of the intrinsic material damping in the specimen. The results show a difference in intrinsic material damping, and the way in which it is influenced by the internal structure is discussed.

The second part of the thesis examines hot cracks in solidifying shells. Most metals have a brittle region starting in the two-phase temperature range during solidification and for some alloys this region extends as far as hundreds of degrees below the solidus temperature. To calculate the risk of hot cracking, one needs, besides knowledge of the solidifying material’s ability to withstand stress, knowledge of the casting process to be able to calculate the thermal history of the solidification, and from this calculate the stress. In this work, experimental methods to measure and evaluate the energy transfer from the solidifying melt have been developed. The evaluated data has been used as a boundary condition to numerically calculate the solidification process and the evolving stress in the solidifying shell. A solidification model has been implemented using a fixed-domain methodology in a commercial finite element code, Comsol Multiphysics. A new solidification model using an arbitrary Lagrange Eulerian (ALE) formulation has also been implemented to solve the solidification problem for pure metals. This new model explicitly tracks the movement of the liquid/solid interface and is much more effective than the first model.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xii, 41 p.
Series
Trita-MG, ISSN 1104-7127 ; 2006:03
Keyword
material damping, measurement methods, calorimetric methods, optical strain gauge measurements, hot cracking, stress in solid shells, ALE
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4038 (URN)91-7178-377-6 (ISBN)
Public defence
2006-06-15, M3, Brinellvägen 68, 100 44 Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100929Available from: 2006-06-02 Created: 2006-06-02 Last updated: 2010-09-29Bibliographically approved

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