Effects of macroscopic pores on the damping behavior of foamed commercially pure aluminum
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I. INTRODUCTION
DURING the last 2 decades, cellular materials were developed and are currently growing in use as new engineering materials. These exceptionally lightweight materials possess unique combinations of properties, such as impact energy absorption capacity, air and water permeability, unusual acoustic properties, low thermal conductivity, and good electrical insulating properties.[1] Materials with a cellular structure are increasingly used in engineering applications, which requires an understanding of their damping behavior. Although there have been many studies on the damping behavior of cellular materials using various techniques,[2,3,4] studies using the internal friction (IF) have hardly appeared in the literature. Hence, it is important to measure the IF of the FA. In the present article, we measure the dependence of IF of open-celled FA with macroscopic pores on its porosity, pore sizes, the applied low frequency, and the amplitude of vibration. There are many methods available to produce metallic foams: casting, powder metallurgy, and metallic deposition. During powder metallurgy, metallic foams are prepared by adding a foaming agent to the molten metal after carefully adjusting the viscosity of the metal. Because one gas is released instantaneously as soon as the foaming agent comes into contact with the melt, this process is very difficult to control and leads to undesirable large cell sizes.[5] In this article, an air pressure infiltration process for the preparation of the FA specimen is discussed, which allows the production of highly porous parts. The FA specimen prepared by an air pressure infiltration process has uniform macropores and density distribution. Since macropore structures in the FA processed J.N. WEI, Doctor, and H.F. CHENG, C.L. GONG, F.S. HAN, and J.P. SHUI, Professors, are with the Laboratory of Internal Friction and Defects in Solids, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei Anhui 230031, P.R. China. Contact e-mail: [email protected] or [email protected] Manuscript submitted August 31, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
infiltration process are very different from those of traditional porous materials, the damping of the FA will also have unique features. On the basis of damping measurements conducted on the multifunction internal friction apparatus (MFIFA), the present article reports on the results of a systematic study of the macrosized pores on the damping behavior of the FA. Commercially pure aluminum is chosen as the matrix of the FA specimens. Macroscopic pores with a size on the order of a millimeter are used. Experimental results showed that the IF of the FA obviously increases with an increase in porosity and a decrease in pore size and typically depends on the frequency and strain amplitude. The TEM observations showed that dislocation substructures exist near the grain boundaries in the FA. Finally, the possible operative damping mechanisms in the FA are discussed in light of IF measurements and TEM observations,
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