Assessment of Internal Damping in Uniaxially Stressed Metals: Exponential and Autoregressive Methods

Abstract

When a metallic material is highly stressed, its internal specific damping capacity increases showing a nonlinear behavior. In spite of this, the most part of experimental methods employ nonhomogeneous stress fields measuring only a volumetric average, often called structural damping. To overcome this problem the procedure herein presented extends the applicability of the plain traction or compression methods to higher frequency range (up to 300 Hz). The introduced methodology corrects for elastic energy and dissipated energy relative to the test machine and to the fixtures. The experimental procedure is based on the acquisition of a decay signal when the test machine excitation force has been removed. Two different methods to extract the pattern of internal damping versus material strain have been compared: one is based on least square exponential fitting while the other employs an autoregressive model. Best results have been obtained combining the two techniques taking into account also the variation of Young’s modulus with strain. The resulting curves of the loss factor as a function of strain amplitude for three steels and two cast irons are presented.

Evaluation of the mechanical behaviour of Telemark ski boots: Part I – materials characterization in use conditions

“…In fact, these parameters cannot be compared in absolute value but only in trend, recalling the different experimental conditions, in particular the strain amplitude applied in DMA. 40,41 Moreover, DMA tanδ can provide information on transitions within polymer chains, in the light of which tensile results can be interpreted at different temperatures. In addition, the mechanical behaviour of PEBAs should be interpreted on the basis of physicochemical characterization data in the literature, 18,34,42 thus correlating microscopic chemical and crystalline structure and macro-mechanical features.…”

Fatigue limit estimation of metals based on the thermographic methods: A comprehensive review

“…As already demonstrated by pioneer researchers, 53 it is well-established that fatigue is a dissipative process [54][55][56][57][58] starting at the microscopic level [59][60][61] and culminating in fatigue cracks; as explained in the work of Schijve, 62 the crack onset occurs at stress amplitudes below the yield limit.…”

Research on identification of nonlinear damping based on time frequency analysis

“…But the research on the identification of nonlinear damping is still not enough. Audenino employed the auto-regressive moving average (ARMA) method and the exponent method to compute the nonlinear damping from the free response signal of a single degree of freedom (SDOF) system, 1,2 where the nonlinear relationship between lost factor and strain is obtained. Liu obtained the data of lost factor and strain through the load varying experiments, and the quadratic curve of lost factor versus strain are got by means of the curve fitting.…”

“…While for a high dissipation material, such as damping alloy, damping is related to the stress amplitude, and is always a nonlinear function of strain. 1 Therefore, in this case, a constant damping consideration will lead to big error.…”