Mechanism Of Internal Friction Research Articles

Spectra of Internal Friction in Polyethylene.

The study of spectra of internal friction and temperature dependencies of frequency of freely damped oscillatory process excited in investigated samples of polyethylene with different degree of crystallinity in the temperature range from −150 C to +150 C. It is established that four local dissipative processes of different intensity shown in different temperature intervals are observed on the spectra . These are , , , processes. The theoretical analysis of the relationship between the anomalous changes of the vibrational process frequency and the shift modulus defect and the internal friction mechanisms for each of the dissipative loss processes detected on the spectrum is carried out. The influence of supramolecular structures on local dissipative process in polyethylene is estimated.

Kinetics of phase transitions and amplitude dependences of Q−1 in Na0.875Li0.125NbO3

The temperature and amplitude dependences of internal friction Q−1 and shear modulus G for the Na0.875Li0.125NbO3 solid solution were studied in the temperature range of 300–700 K. It was found that the material undergoes two structural phase transitions near temperatures T1 ≈ 620 K and T2 ≈ 559 K. Both low-temperature phases are ferroelectric one, whereas the phase above the temperature T1 is paraelectric one. It is shown that the main contribution to mechanical losses below T1 is related to the motion of domain walls. The Q−1 maxima observed near temperatures T1 and T2 are satisfactory described within the framework of the low-frequency fluctuation mechanism of internal friction. The amplitude dependences of Q−1 are in agreement with the Friedel dislocation model.

Ultra-Low Friction of Graphene/Honeycomb Borophene Heterojunction

The recently discovered and prepared honeycomb borophene is one of the many forms of borophene. For the first time, we studied the tribological properties of honeycomb borophene based on first principles and found that it has excellent tribological performance. As a two-dimensional material, honeycomb borophene has potential applications in the field of tribology. Correspondingly, we studied interlaminar charge transfer in several common heterojunctions and then explored its internal friction mechanism. The present work indicts that honeycomb borophene, a new type of two-dimensional material, may help broaden the research field of two-dimensional materials in tribology.

Damping Performance of Material Candidates for Service at 350K

Vibration systems require the damping materials operating at high service temperature. In this paper, damping performance of HT100, M2052 and S316L at 350K were evaluated by applying different frequencies, strain amplitudes and heating rates. It is found that the internal friction dependence of frequency of HT100, M2052 and S316L all show a characteristic of Check function, and the resonance frequency has a negative linear correlation with the material physical parameters. The strain amplitude as well as heating rate has no obvious effect on the resonance frequencies of the materials, but significantly enhance the internal friction of the interface damping alloys such as M2052 and HT100, but small on single-phase alloys such as S316L. The internal friction mechanism for HT100 and M2052 are of static hysteresis at 350K, and HT100 and M2052 are applicable candidates for working at temperatures around 350K from the viewpoint of vibration reduction.

Effect of the Secondary Phase on Mechanical and Damping Properties of Mg–Zn–Y–Si Alloy

The Mg–Zn–Y–Si alloy containing the secondary phase is designed by conventional casting. The Mg2Si phase with different volume fractions is obtained by controlling the content of Si (mass fraction: 0%, 0.3%, 1.0%, 3.0%). The effects of Mg2Si phase and LPSO phase on the mechanical properties and damping properties of the alloys are investigated. The results show that due to the addition of Si, the grain of the alloy is refined, and the intergranular secondary phase Mg2Si phase is created. In addition, the addition of Si also causes the bulk LPSO phase inherent in the matrix to transform into a thin-strip LPSO phase, which greatly improves the mechanical properties of the alloys. The damping properties of the alloys have also been improved due to the new internal friction mechanisms in the alloy. Therefore, the overall performance of mechanical and damping of the alloy is greatly improved. Schematic diagram of mechanical properties and damping properties of Mg–Zn–Y–Si alloys

Study on the internal friction mechanism of C/SiC composites in different corrosion stage

The effects of microstructure and composites evolution of C/SiC composites after corrosion on the internal friction were investigated and the internal friction mechanisms at different corrosion stages were discussed. The studies presented that the internal friction of C/SiC composites with defects was sensitive to the low frequency and high amplitude. In the initial corrosion stage, there was little change in interface of C/SiC composites and the corrosion under high temperature released the thermal stress at the interface, which decreased the internal friction. As the interface eroded in samples, the weaken interface became the important source of internal friction and improved the internal friction of samples. With the further development of the corrosion, SiC matrix in C/SiC composites was oxidized. The glassy oxide filled the cracks and restrained the matrix deformation, resulting in the little decrease in the internal friction of samples with high content oxide.

Internal Friction in Copolymer Vinylidenefluoride with Trifluoroethylene at Ferroelectric Phase Transition

Temperature dependences of internal friction Q–1, obtained at different heating rates of a copolymer VDF/TrFE (75/25) sample, are studied in the temperature range of 290–420 K at a frequency f ≈ 16 Hz. It is shown that the maximum of Q–1 observed in the vicinity of the ferroelectric phase transition (Tc = 393 K) is related to the motion of interphase boundaries and can be described within the low-frequency fluctuation mechanism of internal friction. The diffusion parameter σ of the ferroelectric phase transition is determined. The obtained σ value significantly exceeds the value that is due to possible microinhomogeneity of the chemical composition.

Effects of microstructure defects on the internal friction of C/SiC composites

The internal friction of C/SiC composites was studied by forced vibration at the frequency and amplitude modes, and the effects of microstructural defects on the internal friction of C/SiC composites were investigated systematically and the internal friction mechanism was also discussed. Test results indicated that the microstructure defects in C/SiC samples improved the internal friction and had greater effects on the internal friction tested at low frequency and high amplitude. The slip friction of weak interphase was the main internal friction mechanism for C/SiC samples with interphase damage, and the internal friction increased slowly with the porosity. As the interphase was corroded completely, the pores in C/SiC composites became the main factor controlling the internal friction, and the internal friction increased rapidly with the porosity.

Low-Temperature Local Dissipative Processes in Polyvinyl Alcohol

The spectra of internal friction and temperature variation in the frequency of free damped torsional vibrations excited in a polyvinyl alcohol (PVA) sample in the temperature range from –150 to 0°C were investigated. Several local dissipative processes of low intensity were detected in the spectrum in the temperature range from –150 to –90°C and one more intense dissipative process in the temperature range from –70 to 0°C. According to these processes, deviations from the linear change in frequency of the vibration process were observed in the temperature-frequency relations in these temperature ranges. The mechanisms of internal friction for each of the dissipative processes are considered, and their probable structural interpretation is proposed. The defects of shear modulus arising in these processes are determined, and their contribution to the shear modulus of the entire PVA system is evaluated.

Origin of Internal Friction in Disordered Proteins Depends on Solvent Quality.

Protein dynamics often exhibit internal friction; i.e., contributions to friction that cannot solely be attributed to the viscosity of the solvent. Remarkably, even unfolded and intrinsically disordered proteins (IDPs) exhibit this behavior, despite typically being solvent-exposed. Several competing molecular mechanisms have been suggested to underlie this phenomenon, in particular dihedral relaxation and intrachain interactions. It has also recently been shown that single-molecule data reflecting internal friction in the disordered protein ACTR cannot be explained using polymer models unless this friction is dependent on protein collapse. However, the connection between the collapse of the chain and the underlying mechanism of internal friction has been unclear. To address this issue, we combine molecular simulation and single-molecule experimental data to investigate how chain compaction affects protein dynamics in the context of ACTR. Chain reconfiguration times and internal friction estimated from all-atom simulations are in semiquantitative agreement with experimental data. We dissect the underlying molecular mechanism with all-atom and coarse-grained simulations and clearly identify both intrachain interactions and dihedral angle transitions as contributions to internal friction. However, their relative contribution is strongly dependent on the compactness of the IDP; while dihedral relaxation dominates internal friction in expanded configurations, intrachain interactions dominate for more compact chains. Our results thus imply a continuous transition between mechanisms and provide a link between internal friction in IDPs and that in more compact and folded states of proteins.

Mechanical Spectroscopy of Ti-15Zr-based Alloys with Mo Addition

In this paper, the effect of substitutional Mo amounts in internal friction and interstitial diffusion mechanisms was analyzed in Ti-15Zr-based alloys. Mechanical spectroscopy was obtained from room temperature up to 730 K with frequencies between 1 Hz and 40 Hz. Internal friction spectra were composed by anelastic relaxation peaks in β-type alloys (metastable and stable), due to stress-induced ordering of oxygen and nitrogen interstitially in octahedral sites of the bcc crystalline structure. Peak decomposition analysis exhibited interactions between matrix-interstitial (Ti-O and Ti-N), substitutional-interstitial (Zr-O, Mo-O and Mo-N), and clusters (Ti-O-O and Zr-O-O). The diffusion results showed that the introduction of Mo facilitates the diffusion of interstitial elements in the metallic matrix.

Dislocation contribution to hysteresis mechanism of internal friction at homological temperatures below 0.2

The computations of the internal friction background arising due to the hysteresis mechanism of dislocation mobility in metallic systems at low temperatures carried out by different model representations are presented. It is shown that the general background of internal friction contains not only the losses due to hysteresis mechanism of oscillatory motions but also the losses due to other mechanisms of the structure defect mobility.

Linking Internal Dissipation Mechanisms to the Effective Complex Viscoelastic Moduli of Ferroelectrics

Microstructural mechanisms such as domain switching in ferroelectric ceramics dissipate energy, the nature, and extent of which are of significant interest for two reasons. First, dissipative internal processes lead to hysteretic behavior at the macroscale (e.g., the hysteresis of polarization versus electric field in ferroelectrics). Second, mechanisms of internal friction determine the viscoelastic behavior of the material under small-amplitude vibrations. Although experimental techniques and constitutive models exist for both phenomena, there is a strong disconnect and, in particular, no advantageous strategy to link both for improved physics-based kinetic models for multifunctional rheological materials. Here, we present a theoretical approach that relates inelastic constitutive models to frequency-dependent viscoelastic parameters by linearizing the kinetic relations for the internal variables. This enables us to gain qualitative and quantitative experimental validation of the kinetics of internal processes for both quasistatic microstructure evolution and high-frequency damping. We first present the simple example of the generalized Maxwell model and then proceed to the case of ferroelectric ceramics for which we predict the viscoelastic response during domain switching and compare to experimental data. This strategy identifies the relations between microstructural kinetics and viscoelastic properties. The approach is general in that it can be applied to other rheological materials with microstructure evolution.

Influence of Thermomechanical Treatment on the Damping Capacity of Selected Magnesium Alloys

In the paper the temperature and amplitude dependence of internal friction in the AZ31, AZ63 and AZ91 alloys is reported. A rapid increase in internal friction with increasing temperature was estimated. Internal friction peaks were observed in AZ63 and AZ91 alloys. Position and height of the peaks in the temperature scale depends on the heating rate. Simultaneously, microstructural observations were performed in the selected points of the temperature scale. The amplitude dependence of internal friction in an AZ31 alloy, prepared by rolling, was measured. A significant influence of the rolling texture has been estimated. Main mechanisms of internal friction are connected with precipitation, dislocation motion and twinning.

Correlation between the internal friction and fracture mechanism in quenched and tempered carbon steels

The mechanical behavior of quenched and tempered steels is analyzed by mechanical spectroscopy (internal friction), hardness measurements, Charpy impact and tensile mechanical tests. In quenched steels, the high dislocation density leads to a stress relaxation mainly based on the Snoek-Köster relaxation, and inhibits the plastic deformation, leading to a predominantly intergranular mechanism of fracture. During tempering, the martensite decomposition decreases the dislocation density and hardness. This leads to a stress relaxation based on both dislocation-enhanced Snoek and Snoek-Koster relaxations, and promotes the fracture mechanism transition from brittle to ductile. This suggests that the Snoek-Köster and dislocation-enhanced Snoek relaxations are correlated with the intergranular and ductile fracture mechanisms, respectively. Nevertheless, the tempered martensite embrittlement cannot be detected by means of internal friction since the strain rate associated to this technique is more similar to the strain rate observed in tensile mechanical test than that observed in Charpy impact test. On the other hand, the risk of embrittlement is increased when the retained austenite is thermally instable.

Dislocation mechanisms of low-temperature internal friction in nanostructured materials

A new method of statistically describing the dislocation component of low-temperature internal friction in nanostructured materials. The latter term is applied to ultrafine polycrystals with high density intragranular and grain boundary dislocations, the lines of which are divided into nanometer-scale fragments (dislocation relaxants) with random geometrical and energy parameters. The resonant interaction of elastic vibrations and thermally activated excitations of such relaxators are examined, and the maxima caused by these relaxators along the internal friction temperature dependence are analyzed. It is shown that at low temperatures, the shape of the peaks and the region of their localization along the temperature axis are largely determined by the dispersion of the relaxator activation energy. An algorithm is written in order to analyze the internal friction recorded in the experiment, allowing us to identify the physical model corresponding to the relaxator, and obtain empirical estimates of its parameters.

Internal friction mechanisms in xMn0.4Zn0.6Fe2O4–(1–x)PbZr0.53Ti0.47O3 composites near the ferroelectric phase transition temperature

The internal friction in mixed magnetoelectric composites xMn0.4Zn0.6Fe2O4–(1‒x) PbZr0.53Ti0.47O3 (x = 0.1, 0.2, 0.4) prepared by the ceramic technology has been studied near the ferroelectric phase transition temperature at a frequency of 30 Hz. The contributions to the internal friction due to the kinetics of the phase transition and due to the interaction between the domain walls and point defects have been separated.

Change of Internal Friction on Magnesium Alloy Depending on the Temperature and the Use of Mathematical Methods in the Evaluation of This Property

The article is aimed on present research of internal friction mechanisms that are responsible for the temperature behaviour of AZ91 magnesium alloys. These mechanisms have been studied by ultrasonic resonant apparatus at a frequency close to 20470 Hz and in a temperature range from 50 °C up to 400 °C. The specimen on internal friction measurement has an hour glass shape. The specimens were in the as cast state and after measurement showed dendritic structure. Structure of magnesium alloys AZ91 was carried out after the homogenization annealing at temperature 390 °C. It was also used application of mathematical calculations for a more accurately experimental measurement of internal friction depending on the temperature.

First-principles calculations of internal friction of a Gaussian chain

We consider internal friction of a Gaussian chain placed in vacuum. Dynamics of a single chain can be described by Langevin equation where the random force term comes from the random collisions of monomers among themselves. To nd the moment of these random forces, Gaussian distribution for chain conformation is used . Since collisions between monomers cause these forces, random forces on two monomers can be equal and opposite at the same time. Such correlation is exploited to nd friction constant for Fourier mode p. We show that this same mechanism of internal friction is also applicable for polymers in solution.

An ultrasonic internal friction study of ultrafine-grained AZ31 magnesium alloy

Internal friction in ultrafine-grained AZ31 magnesium alloy is investigated by resonant ultrasound spectroscopy. It is shown that the internal friction signifi- cantly increases at elevated temperatures (J100 C), and that this increase can be attributed to grain boundary slid- ing (GBS). The evolution of this phenomenon with grain refinement is studied by comparing the results obtained for an extruded material and for materials after additional one, two, and four passes of equal channel angular pressing. It is observed that the activation energy for diffusive GBS significantly decreases with decreasing grain size, and so does also the threshold temperature above which this internal friction mechanism is dominant. The results prove that the ultrafine-grained AZ31 alloys exhibit diffusive GBS at temperatures close to the ambient temperature, which is an interesting finding with respect to the possible applications of these alloys in superplastic forming technologies.