Strain Amplitude Dependent Internal Friction Research Articles

Enhancing damping capacity and mechanical properties of Al-Mg alloy by high strain rate hot rolling and subsequent cold rolling

The damping capacity of high Mg alloyed Al-Mg alloy (Al-9.2Mg-0.8Mn-0.2Zr-0.15Ti) prepared by high strain rate hot rolling (HSRR) and subsequent cold rolling (CR) are carefully studied. Both the strain amplitude dependent internal friction (ADIF) at room temperature and the temperature dependent internal friction (TDIF) at elevated temperature are detected by a dynamic mechanical analyzer (DMA). The results indicate that the subsequent cold rolling can significantly improve the damping capacity of the alloy. The as-CRed alloy exhibits higher strength and better damping capacity than the as-HSRRed alloy, with the ultimate tensile strength (UTS) of 606 ± 6 MPa, the elongation to rupture of 11.6 ± 0.6% and the Q-1 value of 0.019 at room temperature with the strain of 1 × 10-3 and the frequency of 1 Hz. The room temperature damping of the as-CRed alloy is mainly ascribed to the low stacking fault energy (SFE), the high dislocation density and the finer broken second phase particles. Moreover, the as-CRed alloy also presents excellent high temperature damping, with the maximum Q-1 value of 0.212 ± 0.003 at 361 ℃ with the frequency of 1 Hz. The relatively high damping capacity of the cold rolled sheet for a given frequency and temperature can be attributable to the special microstructure characteristics including the high dislocation density, the elongated lamellar grains with shear bands and the high fraction of LAGBs.

Measurement of Strain-Amplitude Dependent Internal Friction with Torsion Pendulum and Vibration Reed Methods

Measurement of Strain-Amplitude Dependent Internal Friction with Torsion Pendulum and Vibration Reed Methods

Effect of prior deformation on internal friction in a FeNi based austenitic alloy

Effect of prior deformation on strain amplitude-dependent internal friction has been studied in a FeNi based austenitic alloy subjected to solution and peak-aged treatment. The internal friction initially shows increase and then decreases with pre-strain increase in solution-treated alloy. Nevertheless, it is interesting to find that the internal friction shows continued increase with prior deformation degree in peak-aged alloy. Results could be explained using the breakaway model of dislocation in both state alloys. The discrepancy of internal friction behavior, correlated to dislocation arrangement observation, is discussed in terms of slip mode transition from wavy slip to planar slip with introduction of coherent precipitation particles.

Strain amplitude-dependent internal friction of as-cast high damping magnesium alloy during cyclic vibration

An investigation on strain amplitude-dependent internal friction (IF) of an as-cast high damping Mg-7 wt% Ni alloy was carried out. In the range of our tested strain amplitudes, whether the strain amplitude is increasing or decreasing, the strain amplitude-dependent IF curve can be divided into two stages: one is the strain amplitude weakly dependent part and the other is the strain amplitude strongly dependent part. However, after several cyclic vibrations, the IF values measured during the strain amplitude increasing are smaller than those obtained during the strain amplitude decreasing. The phenomenon is also observed at 100 °C. Partial dislocations generate a short-range slip under the cyclic stress to be responsible for it. At the first certain cycle measurement, it was also found that IF value is completely reversible; no amplitude hysteresis loop appears. During the cycle number increasing, however, it was found that the IF value tested is smaller while increasing the strain amplitude than that obtained while decreasing the strain amplitude.

Damping behavior of Ti50.1Ni49.9 alloy in reverse martensitic transformation region

Damping behavior of Ti50.1Ni49.9 shape memory alloy during reverse martensitic transformation has been investigated by dynamic mechanical analyzer in a dual-cantilever mode. With the increase of strain amplitude, internal friction (IF) of the alloy increases in martensite and austenite states while decreases in transformation region. Based on the regularity of IF attenuation in isothermal condition, IFTr and (IFPT+ IFI) are decomposed from the strain amplitude dependent IF in transformation region. For practical application of shape memory alloys as a damping material, it is significant to evaluate the damping capacity by eliminating the influence of IFTr and consider its time independent real IF (IFPT+ IFI).

Amplitude Dependent Internal Friction of CuAlMn Shape Memory Alloys

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.

Transformation temperatures, elastic and anelastic properties of Cu-Al-Ni crystals subjected to impact loading

Experimental investigations of the influence of impact loading on properties of Cu-Al-Ni single crystals have been performed. Crystals in the β 1 phase were impacted with pulses of a uniaxial plane strain wave with a duration of about 2×10 -6 s. A normal component of stress in the direction of the pulse propagation ranged from 0.5 to 5.4 GPa. For as-quenched and impacted crystals martensitic transformation temperatures were determined, the Young's modulus (YM), strain amplitude-independent and strain amplitude-dependent internal friction were measured at a frequency of about 100 kHz over the temperature range of 300-90 K for strain amplitudes of 10 -7 -2×10 -4 , Experimental results indicate that β 1 →γ 1 ' martensitic transformation (MT) and plastic deformation of the martensite are induced by the impact. The impact loading generates a « structure memory effects: the YM in the austenite is not sensitive to the impact, but the consequent temperature-induced MT reveals a dramatic influence of the impact on the YM of the γ 1 ' martensite. The conclusion is drawn that the observed effect is fundamentally similar to the two-way memory effect, but is extremely sensitive to the impact stress. The origin of this phenomenon is attributed to the internal stresses, created by impact, which control the nucleation of preferentially oriented anisotropic martensitic variants during temperature-induced MT in impacted crystals. No influence of the impact loading on the transformation temperatures was detected for β 1 →γ 1 ' MT, in contrast to elastic properties of the martensitic phase, indicating that structural changes due to the high-velocity impact do not affect appreciably the thermoelastic equilibrium and hysteretic motion of parent- martensite boundaries during the MT.

Structural and transient internal friction due to thermal expansion mismatch between matrix and reinforcement in Al–SiC particulate composite

Microyield phenomena during thermocycling of Al 7075 alloy/15 vol.% SiC metal-matrix composite due to mismatch of the thermal expansion coefficients of the matrix and the SiC particles are studied over the temperature range from ∼50 to 300 K by means of internal friction techniques. The transient component of the internal friction is measured in the infrasonic frequency range, whereas the structural strain amplitude-independent and strain amplitude-dependent internal friction is investigated at ultrasonic frequencies. Combining the two techniques enables us to follow the variation of the defect structure during thermocycling as well as to evaluate basic contributions to the microyield phenomenon. The following conclusions are drawn: (1) thermal stresses are responsible for creation of fresh, i.e. mobile dislocations, whose density does not differ significantly, for the same temperature, during heating and cooling or in consecutive thermocycles; (2) yielding is much more pronounced during the first cooling from a stress-free state than in the consecutive thermocycles; this pronounced yielding is due to long-range motion of approximately the same amount of fresh dislocations as in consecutive thermocycles; and (3) during thermocycling, the matrix undergoes dynamic strain ageing; its intensity depends strongly on temperature and therefore varies continuously in a thermocycle.

Origin of the low-frequency internal friction background of gold

The internal friction (IF) background of gold is studied in the kHz frequency range. Systematic measurements of IF as a function of frequency, strain amplitude, and temperature show that the IF is due to the superposition of two contributions: the thermoelastic effect and a dislocation effect. The thermoelastic effect is responsible for the IF background observed when the strain amplitude tends to zero. It is the only contribution to the IF background which is strain amplitude independent. On the contrary, the dislocation effect contributes only to the strain amplitude-dependent IF background. This effect is proportional to the strain amplitude. In particular, it is zero when the strain amplitude tends to zero. Furthermore, the dislocation contribution is frequency independent. The experimental results show that the dislocation effect cannot be explained by a viscous damping of dislocation motion, but must be related to an hysteretic and athermal motion of dislocations.

Ａｌ‐Ｃｕ共晶合金の超塑性変形と室温内部摩擦

Interrelation between superplastic deformation and internal friction was investigated using an Al-Cu eutectic alloy. The increment of internal friction at room temperature due to deformation, ΔQ-1, increased with the amount of strain under non-superplastic deformation conditions, while under superplastic conditions the change in ΔQ-1 was relatively small. Strain amplitude dependence was observed in ΔQ-1 of specimens deformed at lower temperatures or higher strains. An analysis of the strain amplitude dependent internal friction was carried out by using Granato-Lücke theory. It was found that ΔQ-1 was proportional to the dislocation density ∧. It was also found that the strain rate sensitivity of flow stress m (σ=kεm, σ: flow stress, ε: strain rate, k: constant) was proportional to the negative value of ΔQ-1 or ∧. Changing characteristics of ΔQ-1 for various strains and deformation conditions showed a good correspondence to the results of the direct observation of dislocation structures.These results are consistent with the superplastic deformation mechanism proposed previously, which involves the grain boundary sliding compensated by the diffusional process predominantly and the dislocation motion acting to decrease the m value.

The effect of hydrostatic pressure on the strain amplitude dependent internal friction in aluminum

Strain amplitude dependent internal friction in zone-refined aluminum, containing silver and copper as impurities, was measured as a function of hydrostatic pressure with cold-work as an additional parameter. Using a modification of the torsional pendulum apparatus, the measurements were conducted at room temperature under forced vibrations with a frequency of 8.3 × 10 −3Hz. For a given strain amplitude the damping was found to decrease as pressure increased, the magnitude of the drop being dependent on the strain amplitude. At a strain of approximately 10 −5 damping changes of the order of −10 −4 kbar −1 were observed. The dislocation damping theory by Granato and Lücke, well suited to describe the strain amplitude dependence at constant pressure, is used to predict the pressure dependence of the damping. The theory predicts the observed trends of the damping changes due to pressure, if it is assumed that the pressure response of the impurity atoms is governed by the bulk modulus of the impurity material. The measured changes, however, were two to three times larger than the predicted ones. It is suggested that the lack of treatment of thermally activated depinning in the theory is a possible reason for these discrepancies. The cold-work condition of the specimens also appears to have affected the magnitudes of the changes in internal friction, but the data is not conclusive in this regard.

A counterbalanced reed pendulum apparatus for internal friction studies

A counterbalanced reed pendulum apparatus, using a noncontacting optical transducer, is described. It is particularly suited to the study of strain amplitude dependent internal friction of single crystals of ceramics in the temperature range ambient to 800 degrees C, and at frequencies in the range 1-30 Hz. The apparatus can also be used for the study of sheet metal or foil specimens. The importance of using a counterbalanced system when studying amplitude dependent dislocation phenomena is discussed. Logarithmic decrement values in the range 5*10-5 to 8*10-2 have been observed with the apparatus.

Internal Friction Measurements on Neutron- Irradiated Fe-3.48% Ni Alloy

The Snoek peak and the strain-amplitude dependence of internal friction were measured in order to gain further information on the behavior of interstitial solute atoms in Fe-3.48%Ni alloy which had been neutron-irradiated and annealed. This alloy contained 37 ppm N and 7 ppm C. Interstitial solute N and C atoms were trapped by irradiation-induced defects and released by annealing at above 250°C. The Snoek peak and the slops of Granato-Lucke plots which latter is proportional to 1/Lc (Lc being the dislocation loop length between impurity atoms) increased with annealing temperature. The binding energy of interstitial solute N atoms to dislocations in the irradiated and annealed specimen was obtained from the strain-amplitude dependent internal friction. The value was about 16, 500 cal/mol.

The effects of interrupted neutron irradiation on strain amplitude dependent internal friction in NaCl

NaCl single crystals have been subjected to fast neutron irradiations during which the neutron beam was interrupted for a specific time interval. The variation of crystal decrement with strain amplitude (for strain amplitudes between 5*10-8 and 5*10-6) was measured at a series of times during the interrupted irradiations. Similar experiments were carried out at a number of temperatures between -16 and 22 degrees C. The results were analysed in terms of the theory of strain amplitude dependent internal friction developed by Granato and Lucke (1956). This theory yielded the variation with time in the number of pinning points added to each original dislocation loop. When the irradiation was interrupted, a decrease occurred in the pinning point number. This decrease reached completion within 1 minute at temperatures below 17 degrees C but required about 4 minutes to reach completion at higher temperatures. An explanation for this effect is offered which involves recombination of the pinning point parts.

Effects of neutron irradiation on strain-amplitude dependent internal friction in sodium chloride single crystals

A method has been developed which allows the dependence of internal friction on strain amplitude for a crystal to be measured in a period of 30 s. This method was used to study the variation of internal friction with strain amplitude in sodium chloride single crystals as a function of neutron irradiation. The results were found to agree with the Granato- Lucke theory of strain-amplitude dependent internal friction and this theory was used to examine the variation of pinned dislocation loop length with irradiation time. It was found that the loop-length variation from amplitude-dependent results was different to that from amplitude- independent results. An explanation is offered for this difference.

Time-Dependent Internal Friction in Deformed Alkali Halide Crystals

Time-dependent properties of the strain amplitude dependent internal friction in alkali halide crystals were systematically investigated. The measurement technique more reliable than the conventional one was established, and repeatable enhancement and recovery of the internal friction due to external excitation was discovered. A new procedure for the Granato-Lucke plot was derived from recovery of the internal friction. At the same time, this procedure itself shows validity of the Granato-Lucke theory. The enhancement and recovery was interpreted in terms of the diffusion process of pinning elements during breakaway and the counter-diffusion process of pinning elements during resting of the dislocation-motion. The nature of hysteresis phenomena in internal friction measurements in NaCl crystals was also interpreted by the same mechanism.

Strain-Amplitude Dependent Internal Friction Studies of Dilute Alloys of Copper

This paper presents an investigation of the room temperature decrement in dilute polycrystalline alloys of copper as a function of strain amplitude and annealing at a frequency of about 1 cps. The characteristics of the internal friction measured are: (1) The internal friction and strain amplitude dependence of the internal friction decreases with increasing solute content. (2) The internal friction is reversibly dependent upon the preanneal temperature. (3) The internal friction is hysteretic with strain amplitude. From the effect of the solute concentration and annealing temperature on the decrement, values for the binding energy for Al and Si solute atoms to dislocations in copper were calculated. These values are compared to theoretical values calculated on the basis of strain and electrical interaction energies. The experimental binding energy is in good enough agreement with the theoretical values to conclude that the onset of a strain amplitude dependence of the internal friction is caused by the freeing of sufficient dislocations from their pinning solute atoms.