Papers by Keyword: High Damping Materials

Abstract: The mechanical and fatigue properties of Cu - Al - Mn shape memory alloys with different phase fractions at room temperature were investigated. The specimens with different chemical compositions (Al: 8.9 - 12.5 wt. % and Mn: 3.3 - 9.3 wt. %) were tensile loaded with 10-3 s-1 tensile strain rate. Austenitic specimens have the highest tensile strength and fracture strain. Yield strength, tensile strength and elongation of martensitic alloys were lower compared with austenitic alloys. Fracture strain of martensitic alloys depend only little on the chemical composition. Specimens of martensitic, austenitic and three different multiple phase specimens were tested in the high cycle fatigue range at room temperature. The Woehler curves for multiple specimens depend on the phase fraction at testing temperatures. Different elements as Co, Ni, Fe and Si were alloyed to CuAl11.6Mn5. All decreased the ductility of the specimens, and their fatigue properties. Maxima could be detected in the strain amplitude dependence of damping for multiple phase specimen. These maximum are shifted to lower damping and to higher strains with increasing number of mechanical cycles, compared to the as cast condition for not cycled specimen. The strain amplitude dependence of damping in martensitic and austenitic Cu – Al – Mn shape memory alloys does not change much during mechanical cycling.

Abstract: A new algorithm OMI (Optimization in Multiple Intervals) for the computation of the logarithmic decrement from exponentially damped harmonic oscillations is described. This method is shown to be effective and computationally compact for high damping materials. A comparison between the OMI algorithm and the four classical methods usually used in the computation of the logarithmic decrement is reported. The OMI algorithm yields high precision in the computation of the logarithmic decrement and the smallest dispersion of experimental points on the plots of mechanical loss spectra. The effect of the acquisition parameters and the experimental conditions on the results of computations of the logarithmic decrement and the relative error is discussed.

Abstract: Different viewpoints at high damping materials - from engineering needs to physical mechanisms are discussed. It is suggested that only several mechanisms in metallic materials can lead to high intrinsic damping capacity while some other “peak-like” effects are not sufficient to make high damping materials.

Abstract: We have subjected Zr59Cu20Al10Ni8Ti3 glassy sample to internal friction thermal cycle (IFTC) measurements under various conditions involving changes in heating/cooling rate, strain amplitude and frequency. Additional low temperature internal friction peaks (ALTIFP) were found to occur with the characteristic low temperature internal friction peak (CLTIFP) observed for some glassy alloys. The ALTIFP were enhanced on heating and reduced on cooling. Their strength increase following the number of IFTC can be related to a stress concentration in some zones of the glassy structure, which is abruptly relaxed by the viscous flow creating interfaces in the glassy structure. These interfaces are likely to be formed between atomic clusters. The growth of the ALTIFP increases significantly the whole IF level (IFL) from 10-4 to 10-2 enhancing the damping capacity of the glassy sample.

Abstract: The strain amplitude dependent internal friction at room temperature and the transition temperatures of CuAlMn-shape memory alloys with Al contents from 8.9 wt.% to 12.7 wt.% and Mn contents from 4.7 wt.% to 9.3 wt.% were investigated. The investigated strain range was 10-6 - 10-3. Rods of various compositions were die cast and machined to single clamped damping bars. Their transition temperatures and amplitude dependent damping was determined in as cast and homogenized state. The damping in the investigated shape memory alloys was found to be generally much higher than in metals without martensitic transition. In as cast state some alloys exceeded the damping of a Sonoston type alloy measured in comparison for strains higher than 3 x 10-5. The influence of grain size on damping was investigated by additional sand casting and the use of Boron for grain refinement. It was found that only the material with the biggest grains had a noticeable higher damping over the whole measured strain range. Homogenization heat treatment can still extremely increase the damping of CuAlMn alloys. After homogenization this extremely high damping decreases slowly to medium values in the order of as cast alloys.