Mechanism Of Internal Friction Research Articles

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.

Atomic mechanism of internal friction in a model metallic glass

Internal friction (IF) describes the ability of materials to damp out mechanical oscillations. It is a crucial engineering parameter and also conveys unique microscopic information about structural defects, transport phenomena, and phase transformations in solids. While IF predominately results from lattice defects in crystalline materials, the origin of IF remains unclear in disordered materials, like metallic glasses. In this paper, we study the atomic rearrangements that govern IF in a model metallic glass, via numerical simulations of dynamical mechanical spectroscopy together with structural analysis. We identify cooperative and avalanchelike thermal-driven excitations as an underlying mechanism and demonstrate a linearlike relation between the concentrations of these excitations and the values of IF. Structurally, these excitations can be hindered, and thus suppress IF, by slow atoms that usually associate with full icosahedral symmetry. Our results also provide practical guides in tuning IF in metallic glasses from atomistic perspectives.

Elastic and Anelastic Behavior of the Relaxor Ferroelectric 0.55SrTiO3-0.45BiScO3

Elastic and anelastic properties of the relaxor 0.55SrTiO3-0.45BiScO3 ceramics were studied. Anomalous behavior of the Young's modulus and the internal friction were observed at cooling below the Burns temperature Td ≈585 K. Both elastic and anelastic anomalies were found to be frequency dependent. Elastic softening is assumed to be due to an electrostriction relationship between spontaneous polarization of polar tetragonal nanoclusters and a strain of unit cell. It was found that the internal friction anomaly observed below Td is in fact superposition of two maxima. Higher temperature maximum is typical for relaxors. Using the special internal friction mechanism for the first order phase transition, the size of the polar tetragonal nanoclusters was estimated to be equal to ∼10 nm. Such sizes of tetragonal islands were found for the sample under study by using the electron backscattered diffraction method.

Concerted dihedral rotations give rise to internal friction in unfolded proteins.

Protein chains undergo conformational diffusion during folding and dynamics, experiencing both thermal kicks and viscous drag. Recent experiments have shown that the corresponding friction can be separated into wet friction, which is determined by the solvent viscosity, and dry friction, where frictional effects arise due to the interactions within the protein chain. Despite important advances, the molecular origins underlying dry friction in proteins have remained unclear. To address this problem, we studied the dynamics of the unfolded cold-shock protein at different solvent viscosities and denaturant concentrations. Using extensive all-atom molecular dynamics simulations we estimated the internal friction time scales and found them to agree well with the corresponding experimental measurements (Soranno et al. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 17800-17806). Analysis of the reconfiguration dynamics of the unfolded chain further revealed that hops in the dihedral space provide the dominant mechanism of internal friction. Furthermore, the increased number of concerted dihedral moves at physiological conditions suggest that, in such conditions, the concerted motions result in higher frictional forces. These findings have important implications for understanding the folding kinetics of proteins as well as the dynamics of intrinsically disordered proteins.

Elastic and anelastic properties of the 0.55SrTiO3–0.45BiScO3 ceramics characteristic for relaxor ferroelectric behavior

The low‐frequency elastic and anelastic properties of the ceramic 0.55SrTiO3–0.45BiScO3 sample have been studied. Anomalous changes of the Young's modulus and the internal friction characteristic for the ferroelectric relaxors were observed at cooling below the Burns temperature at ∼585 K. The relaxor properties of this system are confirmed by dielectric measurements and attributed to the coexistence of the polar tetragonal P4mm phase and the nonpolar cubic Pm3m phase. Elastic anomaly is assumed to be due to electrostriction relationship between spontaneous polarization of polar tetragonal domains and strain of the sample. Using the special internal friction mechanism for the first order phase transition, the size of the polar phase nuclei arising at the Burns temperature was estimated to be equal to ∼20 nm.

Grain‐boundary relaxation peak correlated to the precipitation in Cu–20.4Al–8.7Mn shape‐memory alloy

AbstractThe grain‐boundary relaxation as well as corresponding internal friction (IF) mechanism in Cu‐based shape‐memory alloy was investigated taking Cu–20.4Al–8.7Mn (at%) as an example. A relaxational IF peak was found at around 214 °C during the heating process, whereas the peak completely disappears during the subsequence cooling process. The IF peak with the activation energy and pre‐exponential factor of 1.60 eV and 3.8 × 10−18, respectively, shifting towards higher temperature as the measuring frequency increased indicates that the peak correlates to a thermal‐activation process. The results obtained revealed that the viscous sliding of the grain boundaries should be the operative mechanism for the appearance of the peak. However, the appearance of the γ2 precipitate particles formed during the heating process provides a reverse contribution to the peak, leading to the disappearance of the peak due to their pinning effect on the grain boundaries.

Internal friction mechanism of Fe–19Mn alloy at low and high strain amplitude

Fe–Mn damping alloy, which can decrease the vibrating and noise effectively, will be widely applied to household appliances, automobiles, industrial facilities, etc. In this paper, the internal friction mechanism of Fe–19Mn alloy at low strain amplitude (10−5 range) and high strain amplitude (10−4 range) was investigated. The internal friction was measured using multifunction internal friction equipment and reversal torsion pendulum. The microstructure was observed using scanning electron microscopy. The phase transformation temperatures were determined using differential scanning calorimetry. The results indicated that the internal friction of Fe–19Mn alloy after solution treating was related to strain amplitude. The internal friction mechanism was believed to the movements of four damping sources (ε-martensite variant boundaries, stacking fault boundaries in ε-martensite and γ-austenite, γ/ε interfaces), which could be explained using the interactive movements of Shockley partial dislocations and point defects. At low strain amplitude (10−5 range), the bowing out movements of Shockley partial dislocations are the main moving mode of generating internal friction. At high strain amplitude (10−4 range), however, the breaking away movements of Shockley partial dislocations are the high internal friction mechanism of Fe–19Mn alloy.

Analysis of inelasticity in high-damping Zn – Al alloys, gray irons, and iron alloys with internal friction of a magnetomechanical nature

Results are presented from a comparative analysis of the main mechanisms of internal friction in high-damping alloys based on the Zn – Al system, cast iron with flaked graphite, and iron alloys that exhibit internal friction of a magnetomechanical nature. A study is made of the damping capacity of alloys Zn – 26% Al, SCh25, and Fe – 5% Cr – 3% Al and steel 45, which are typical representatives of the types of materials in question. Their set of physico-mechanical properties is determined with allowance for damping capacity.

Improved mechanical property and internal friction of pure Mg processed by ECAP

Equal channel angular pressing was performed on the extruded pure Mg. The elongation to failure of the ECAPed pure Mg is enhanced to 27% without sacrificing the strength, which is mainly resulted from both the effective refinement of grain size and the weakening of the basal plane texture. The internal friction mechanisms of magnesium at room and elevated temperature were studied by dynamic mechanical analyzer (DMA). The strain independent internal friction is increased after ECAP processing, while the strain dependent part is obviously decreased. Three internal friction peaks were observed in the temperature dependent internal friction curves. The activation energy is 105kJ/mol for P1 peak, which may be related to the basal dislocation glide controlled by climb of jogs and diffusion of vacancies along dislocations. The activation energy of P2 peak is in the range from 95 to 181kJ/mol, and this obviously broadened peak is associated with grain boundary relaxation. The P3 peak is related to recrystallization.

Quantifying internal friction in unfolded and intrinsically disordered proteins with single-molecule spectroscopy

Internal friction, which reflects the "roughness" of the energy landscape, plays an important role for proteins by modulating the dynamics of their folding and other conformational changes. However, the experimental quantification of internal friction and its contribution to folding dynamics has remained challenging. Here we use the combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, and microfluidic mixing to determine the reconfiguration times of unfolded proteins and investigate the mechanisms of internal friction contributing to their dynamics. Using concepts from polymer dynamics, we determine internal friction with three complementary, largely independent, and consistent approaches as an additive contribution to the reconfiguration time of the unfolded state. We find that the magnitude of internal friction correlates with the compactness of the unfolded protein: its contribution dominates the reconfiguration time of approximately 100 ns of the compact unfolded state of a small cold shock protein under native conditions, but decreases for more expanded chains, and approaches zero both at high denaturant concentrations and in intrinsically disordered proteins that are expanded due to intramolecular charge repulsion. Our results suggest that internal friction in the unfolded state will be particularly relevant for the kinetics of proteins that fold in the microsecond range or faster. The low internal friction in expanded intrinsically disordered proteins may have implications for the dynamics of their interactions with cellular binding partners.

Ice internal friction: Standard theoretical perspectives on friction codified, adapted for the unusual rheology of ice, and unified

Sea ice contains flaws including frictional contacts. We aim to describe quantitatively the mechanics of those contacts, providing local physics for geophysical models. With a focus on the internal friction of ice, we review standard micro-mechanical models of friction. The solid's deformation under normal load may be ductile or elastic. The shear failure of the contact may be by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models. When the material under study is ice, several of the rheological parameters in the standard models are not constant, but depend on the temperature of the bulk, on the normal stress under which samples are pressed together, or on the sliding velocity and acceleration. This has the effect of making the shear stress required for sliding dependent on sliding velocity, acceleration, and temperature. In some cases, it also perturbs the exponent in the normal-stress dependence of that shear stress away from the value that applies to most materials. We unify the models by a principle of maximum displacement for normal deformation, and of minimum stress for shear failure, reducing the controversy over the mechanism of internal friction in ice to the choice of values of four parameters in a single model. The four parameters represent, for a typical asperity contact, the sliding distance required to expel melt-water, the sliding distance required to break contact, the normal strain in the asperity, and the thickness of any ductile shear zone.

Snoek Relaxation in bcc Metals and High Damping β-Ti Alloys

The Snoek relaxation, a specific point-defect induced anelastic relaxation phenomenon, is characteristic of an internal friction peak in bcc metals with interstitial solutes. Such internal friction mechanism has not been applied in the development of high damping alloy while grain boundary and twin boundary featured anelastic relaxations are applied in some high damping alloys. In this paper, the fundamental principles and experimental results concerning the Snoek relaxation are reviewed, and the feasibility to apply the Snoek relaxation mechanism into high damping alloys is discussed. Due to the peak-shape behavior in the Snoek relaxation type damping, composition design of a high damping alloys should takes temperature position, broadness and also peak height into account. Ti-Nb-O and Ti-V-Cr-O alloys are designed and fabricated by CCLM casting in our laboratory. It is conformed that the damping behaviors of the alloys are of Snoek relaxation type showing obvious frequency and temperature dependence. While the broadened damping peak caused by the substitutional solutes is advantage to improve the temperature stability of damping capacity, a large concentration of interstitial solute and texture control are required to improve the reduced damping capacity.

Thermoelastic Dissipation in MEMS/NEMS Flexural Mode Resonators

Understanding the energy dissipation mechanisms in single-crystal silicon MEMS/NEMS resonators are particularly important to maximizing an important figure of merit relevant for miniature sensor and signal processing applications: the Quality factor (Q) of resonance. This paper discusses thermoelastic dissipation (TED) as the dominant internal-friction mechanism in flexural mode MEMS/NEMS resonators. Criteria for optimizing the geometrical design of flexural mode MEMS/NEMS resonators are theoretically established with a view towards minimizing the TED for single-crystal silicon MEMS/NEMS flexural mode resonators.

Development of a semi-empirical friction model in automotive driveshaft joints

High speed and sport utility vehicles with large joint articulation angle demand lower friction in automotive driveshaft joints to meet noise and vibration comfort levels. Thus a more thorough understanding of internal friction characteristics and mechanisms is required. In this paper, a friction model in automotive driveshaft joints was developed through the use of test data from an instrumented Constant Velocity (CV) joint friction apparatus with actual driveshaft assemblies. Experiments were conducted under different realistic operating conditions of oscillatory speeds, CV joint articulation angles, lubrication, and torque. The experimental data was used to develop a physics-based semi-empirical CV joint internal friction model as a function of different CV joint operating parameters. It was found that the proposed friction model captures the experimental results well. Also the friction model estimates the generated axial force (GAF) in tripod CV joints well, which is the main source of force that causes vehicle vibration problems.

Mechanism of internal friction in Cu–Al–Mn shape memory alloy

Electrical resistivity and low frequency internal friction (IF) measurements have been performed during constant heating rate. At low frequency, a high IF peak is observed which is in good accordance with the hump appearing in electrical resistivity. It is shown that this IF is not proportional to (where is the temperature rate and f is the vibration frequency). This behavior is systematically investigated.

Post-buckling behaviour of slender structures with a bi-linear bending moment–curvature relationship

Certain classes of slender structures of complex cross-section or fabricated from specialised materials can exhibit a bi-linear bending moment–curvature relationship that has a strong influence on their global structural behaviour. This condition may be encountered, for instance, in (a) non-linear elastic or inelastic post-buckling problems if the cross-section stiffness may be well approximated by a bi-linear model; (b) multi-layered structures such as stranded cables, power transmission lines, umbilical cables and flexible pipes where the drop in the bending stiffness is associated with an internal friction mechanism. This paper presents a mathematical formulation and an analytical solution for such slender structures with a bi-linear bending moment versus curvature constitutive behaviour and subjected to axial terminal forces. A set of five first-order non-linear ordinary differential equations are derived from considering geometrical compatibility, equilibrium of forces and moments and constitutive equations, with hinged boundary conditions prescribed at both ends, resulting a complex two-point boundary value problem. The variables are non-dimensionalised and solutions are developed for monotonic and unloading conditions. The results are presented in non-dimensional graphs for a range of critical curvatures and reductions in bending stiffness, and it is shown how these parameters affect the structure's post-buckling behaviour.

Relaxation processes in glasses of the Ge-As-S system

The internal friction in GexAs40 − xS60 glasses is investigated in the temperature range 100 K-Tg at infralow frequencies (10−3−10−1 Hz). It is shown that the concentration dependence of the internal friction of these materials changes as a result of the transformation of the dominant kinetic unit in dissipative processes of the relaxation and nonrelaxation types. It is established tha the change in the mechanism of internal friction in the GexAs40 − xS60 glasses leads to a jump in the activation energy of the α relaxation and to a local minimum in the frequency factor τ0.

DAMPING PERFORMANCE AND MECHANISM OF HIGH STRENGTH ALUMINUM ALLOY PREPARED BY RAPIDLY SOLIDIFIED/POWER METALLURGY PROCESS

The investigation of damping property, microstructure and damping mechanism of High Strength Aluminum Alloy (HSAA) prepared by rapid solidified/powder metallurgy (RS/PM) process were conducted by means of Dynamic Mechanical Thermal Analyzer (DMTA) and Transmission Electron Microscopy (TEM) in the paper. The damping capacity (Q-1) of the HSAA was (0.5~3.1)×10-2 in the temperature range of 20~250°C, reaching to the level of high damping alloys. It was found that grain boundaries in the alloy became clear and sharp in high temperature and contributed to the total damping capacity. The analysis results show that at low temperature, the main internal friction mechanism was dislocation damping which was induced by large extrusion deformation, while in the high temperature region, the influence of interface damping increased gradually.

Basic mechanism of grain-boundary internal friction revealed by a coupling model

By taking into account the mutual interaction among relaxation species, the data of grain boundary (GB) internal friction of Al bicrystals obtained in our previous works [Phys. Rev. B 71, 060101(R) (2005); Phys. Rev. B 72, 174118 (2005)] are further analyzed based on a coupling model. It is found that the high-angle GBs exhibit a strong coupling; while the low-angle GBs exhibit a weak coupling. It is shown that the basic mechanism of GB internal friction is GB diffusion for high-angle GBs, and dislocation climb for low-angle GBs. The previously puzzling behaviors (measured high activation energy and broad peak width) of GB internal friction in bicrystals with high-angle GBs and in polycrystals are satisfactorily explained in the light of the coupling model.

Internal friction and dynamic modulus of three-dimensional silicon carbide-matrix composites

The internal friction and dynamic modulus of 3D C/SiC and SiC/SiC composites were investigated by means of forced vibration at elevated temperatures from room temperature to 600 °C, and the relationship between the microstructural defects in the composites and the internal friction mechanism was also discussed. It was found that the microstructural defects, which are produced by the mismatch of the coefficient of thermal expansion (CTE) between the fiber and matrix, have an important effect on the internal friction behavior and dynamic modulus of 3D C/SiC and SiC/SiC composites. C/SiC composites have a higher internal friction and lower dynamic modulus than SiC/SiC composites in the same testing conditions because of the damage.