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Submitted on 1 Jan 1987
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WHERE TO GO WITH HIGH DAMPING MATERIALS (HIDAMETS) ?
J. van Humbeeck, M. Wuttig
To cite this version:
J. van Humbeeck, M. Wuttig. WHERE TO GO WITH HIGH DAMPING MATERI- ALS (HIDAMETS) ?. Journal de Physique Colloques, 1987, 48 (C8), pp.C8-581-C8-583.
�10.1051/jphyscol:1987891�. �jpa-00227195�
JOURNAL DE PHYSIQUE
Colloque C8, suppl6ment au n012, Tome 48, dkcembre 1987
WHERE TO GO WITH HIGH DAMPING MATERIALS (HIDAMETS) ?
J. VAN HUMBEECK and M. WUTTIG*
Department MTM, K.U. Leuven, de Croylaan 2, B-3030 Heverlee, Be1 glum
* ~ e p a r t m e n t of Chemical and Nuclear Engineering, University of Maryland, College Park, MD 20742-2111, U.S.A.
The existence of materials showing a high damping capacity under appropriate conditions is very well known, especially by metallurgical engineers. In addition, the industrial interest in these materials has increased during the last years. As a consequence, the study of high damping materials by research specialised in the field of internal friction should be stimulated. The workshop on high damping materials held in conjunction with the ECIFUAS-5 was convened as part of this stimulation effort. It had an attendence of 60 % of all the participants of the conference, which indicates a general interest in the subject.
The following topics received most of the interest during the two-hour workshop :
Application of existing sufficiently well-documented high damping materials : It was pointed out by many that a successful application of known high Q-1 materials is critically dependent on a close interaction between the design- and metallurgical engineers. It is essential that an analysis of the "eigenmodes" of the structural member is performed so that the exact conditions under which the material must perform, are exactly known. Particular attention should be given to the change of modes under stress, as most likely the materials will be expected to retain their high Q-1 capacity under load. The discussion also made it clear that quite a few materials, already known as high damping materials, must be better documented in order to facilitate their industrial use.
Turning now to the materials aspects of high damping materials, the following observations were made :
It is easy the prepare high damping materials, if one remembers that : 8 - 1 'J &/E
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987891
C8-582 JOURNAL DE PHYSIQUE
The above relation shows that mechanically soft materials are good candidates for HIDAMETS, however, they are equally impractical. It will also be fruitful to search for HIDAMETS in the vicinity of second and also first order transformations. In general, a compromise has to be found between the desirable mechanical properties and the damping capacity (excluding for the moment other properties, e.g. corrosion resistance, etc. ). Figure 1 shows how this compromise can be achieved conceptually : one has to identify a defect mechanism which operates in a mechanically sufficiently strong material and yields the desirable characteristics. From this figure follows that ALL mechanisms are candidates and that one should strive to understand how different mechanisms couple the acoustical energy to be absorbed to the lattice vibrations, i.e. convert into heat. Such an understanding will show the limits of high damping materials.
A second general point concerns the use of inhomogeneous materials for high Q - l . It was pointed out that earlier studies concentrated on homogeneous materials whereas it appears that inhomogeneous materials are excellent candidates for high Q - 1 . The inhomogeneities can microscopically be such as in partial spinodally decomposed materials or they can microscopically be such as in gradiated powder metallurgic alloys or multiphase materials. In this context it was pointed out that complicated materials deserve more attention than they have been given
in the past.
Another general point which was discussed in some detail concerns the classification of HIDAMETS, such as linear and non-linear damping materials or materials sollicited such that an open or closed stress- strain loop is formed. Here, the question of reversibility arose and it was mentioned that reversibility should be taken in a larger context than it has been until now. Doing that would easily include the high damping lead-based shock absorbers developed by Robinson (ref. 1).
The conference showed that the understanding of one and zero dimensional defects and the damping mechanisms based on them or their interaction, has reached a high degree of sophistication. This is not the case for two-dimensional defects which are responsible for much of the damping in copper-based shape memory alloys. Studies of the motion of interfaces were encouraged during the workshop in order to determine their limitations.
It is clear that all damping must come from non-linearities in the material as no modes could couple without them. Consequently, it was
pointed out in the workshop that the non-linearities, which are so prominent in the vicinity of first order structural phase transformations should be more systematically explored and exploited.
The soliton paradigm is well-suited to describe many of the pertinent phenomena quantitatively.
Finally, the workshop called for an extension of internal friction studies to materials other than metals and alloys. These include ceramics, polymers as well as composites of various kinds. From the experimental point of view one has to extend the present techniques, especially to higher deformation amplitude ranges (10-5 to 10-3) which are normally encountered in engineering constructions. A special field of interest will also be the stability of the damping, either as a function of (ageing) time, or as a function of the number of vibration cycles. Measurements at T = 0 will thus be as important as these for T = 0.
To conclude, it was clear that the study of hidamets needs and deserves more attention than presently given. This research work is necessary in order to understand the properties, defects and defect interactions in multi-compound and many times multi-phase inhomogeneous materials.
Consequently, the understanding of these properties can lead to the development of specific industrial materials.
Ref. 1 : W.H. Robinson, Journ. de Phys., 1985, Tome 46, pp. 10-421-424.
t Q-I
Figure 1 : concept for ,act* material : ... ... " ...
a high-damping mechanism related to the existence of a defined defect in an
engineering material
