Acoustoplastic Effect Research Articles

On possible mechanisms of the acoustoplastic effect

On possible mechanisms of the acoustoplastic effect

Flow stress behavior of polycrystalline Ni under combined magneto- and acousto-plastic effects

The effects of an alternating magnetic field (50 Hz, 6.4 × 10 4 A/m) and an ultrasonic deformation (2 × 10 4 Hz, 5 × 10 −5) on the flow stress of polycrystalline nickel during unidirectional tension at 290 K have been investigated in detail. Special attention is paid to clarify the mechanism of the magneto-plastic (MPE) and acousto-plastic (APE) joint effects. The combined MPE + APE effect is found to be smaller than the sum of the individual ones. An experimental procedure allowed synchronization and consecutive shifts in phase between beginning of the application of the magnetic field period and the initiation of the ultrasonic deformation. The combined MPE + APE is found to be dependent on the phase shift with extremes at 170° and 350°. Considering both magnetically and thermally activated dislocation motion, a differential equation is proposed describing the deformation process in magnetically and ultrasonically induced stress fields. Calculated dependencies of stress on time and strain correlate well with experimental results and clarify the revealed extremes.

Modelling of acousto-plastic effect in TiNi alloy

An acousto-plastic effect expressed in a drastic flow stress change under ultrasonic vibrations was simulated for the TiNi alloy in the range of martensitic transformation temperatures. The structure-analytical theory of strength was used for the computer simulation. It was assumed that the main factors of the ultrasound effect on the flow stress are a temperature increase and an oscillating stress of the ultrasound wave. Diagrams of the quasistatic deformation of a TiNi specimen at different temperatures corresponding to the martensitic, austenitic and two-phase states were calculated. The temperature is taken to change linearly: abruptly rise after vibration start and smoothly fall after vibration finish. It was found that the temperature change may lead either to the rise or to the drop of the flow stress depending on the material structure state. An oscillating stress applied during the quasistatic deformation leads to material softening during loading and to the rise of the stress during unloading. At joint action of oscillating stress and temperature variation in the course of the quasistatic deformation one can observe both material softening and a complicated flow stress evolution: a decrease of the stress followed by its rise. All results are consistent with the available experimental data on the action of ultrasound on TiNi shape memory alloys.

Towards understanding anelasticity of the β 1′ martensitic phase of Cu–Al–Ni

The present work continues the series of experimental investigations undertaken in order to elucidate the mechanisms controlling elastic and anelastic properties of the β 1′ martensitic phase of Cu-based shape memory alloys. The paper reports an attempt to distinguish between ‘dislocation’ and ‘interface’ mechanisms of the internal friction in the β 1′ martensitic phase of Cu–Al–Ni single crystals. Two types of experiments have been performed. First, the ultrasonic strain amplitude-independent and amplitude-dependent internal friction (ADIF) of a monovariant specimen for temperatures 90–300 K is carefully re-examined. Second, in situ measurements of the ADIF and of the influence of ultrasonic oscillations on the plastic deformation (acoustoplastic effect) were carried out during quasistatic deformation of a quenched polyvariant specimen. Experimental results support a dislocation rather than an interface mechanism of anelasticity, at least at ultrasonic frequencies and moderate strain amplitudes.

Motion of dislocations and interfaces during deformation of martensitic Cu–Al–Ni crystals

Investigations of the ultrasonic strain amplitude-dependent internal friction (ADIF) and of the influence of ultrasonic vibrations on the macroplastic strain (the acoustoplastic effect) have been performed in situ during deformation of quenched Cu–Al–Ni single crystals in the β′ 1 martensitic phase. The effect of the macroscopic plastic strain rate on the ADIF and acoustoplastic effect as well as the kinetics of the acoustoplastic effect has been studied. The results of in situ ADIF measurements are compared with data on the ADIF temperature dependence. Observed regularities are attributed to differences in the mechanisms of the macroplastic deformation of the martensitic phase, related to the motion of intervariant interfaces, and of the reversible anelastic strain, which, at ultrasonic frequencies and moderate strain amplitudes, is largely due to the oscillatory motion of the partial dislocations. The conclusion has been drawn that the dynamics of partial dislocations at temperatures of 210–300 K is to a great extent determined by their interaction with atmospheres of mobile pinners with saturated density. Simultaneous measurements of the ADIF and acoustoplastic effect allows the conclusion that, for high oscillatory strain amplitudes, the breakthrough of partial dislocations beyond the mobile atmospheres of pinners initiates the step-like accumulation of the macroplastic strain due to the motion of intervariant boundaries.

Theory of amplitude-dependent internal friction and acoustoplastic effect in shape memory alloys

Mechanisms of amplitude-dependent internal friction and the acoustoplastic effect in shape memory alloys are discussed in terms of the previously developed theory of diffuse thermoelastic martensitic transformations. The amplitude dependences of these effects are found for different temperatures and applied stresses.

Acoustoplastic effect and the stress superimposition mechanism

The mechanism of the acoustoplastic effect is discussed which arises when an oscillatory stress of an acoustic frequency is superimposed during quasi-static deformation of a crystal. The kinetics of the acoustoplastic effect and its dependence on the amount of plastic deformation, amplitude of acoustic-frequency stresses, temperature, and strain rate are investigated in terms of the stress superimposition mechanism by a computer simulation method.

Frequency Dependence of Acoustoelastic and Acoustoplastic Effects.

Ulrrasonic wave velocities propagating in a plastically deformed medium are known to be dependent upon its microstructural properties (e.g., crystallinestructure, distributions of micro cracks, residual stresses and texture, etc). The authors have proposed the theoretical modeling for an ultrasonic nondestructive evaluation method of the microstructural property of the materials under the plastic deformation. Generally, wave propagating characteristics are also dependent upon the propagating wave frequency. hence to accomplish a precise evaluation of material property changes it is necessary to examine an influence of frequency dependence on the propagating wave veloclties. In the present paper, frequency dependence of acoustoelastic and acoustoplastic effects, which correspond to wave velocity changes due to the stress and material property changes. respectively, are studied experimentally on the longitudinal and Rayleigh surface waves and also are simulated using our proposed theory via Granato Lucke's model for dislocation damping.

Acoustoplastic effect in the shape memory alloy Ni–Ti–Re at ultrasonic frequency

The influence of ultrasonic vibrations on the deformation and phase transformation in the shape memory alloy Ni–Ti–Re was studied. The decrease in the sample's length under superimposed ultrasonics in the interval of phase transformation temperatures was measured. Acoustoplastic effect in the shape memory alloy was investigated. The increase in the hardening coefficient and the decrease in the stage of the pseudoelastic deformation under superimposed ultrasonics was found.

Influence of impurity content on the acoustoplastic effect, internal friction, and Young's modulus defect during deformation of Cu-Ni single crystals

Abstract Oscillatory stress amplitude dependences of the acoustoplastic effect, absorption of ultrasonic vibrations (frequency of about 100 kHz) causing this effect, and Young's modulus defect were simulataneously measured in situ during quasistatic deformation of Cu-1·3–7·6 at.% Ni single crystals. The time dependences of the magnitude of the acoustoplastic effect at constant oscillatory stress amplitudes were also obtained. The amplitude-dependent internal friction and Young's modulus defect diminish drastically with increasing Ni content. The dependence of the magnitude of the acoustoplastic effect on the Ni concentration is much less pronounced and is reversed with increase in oscillatory stress amplitude. Data on the kinetics of the acoustoplastic effect revealed ‘instant’ (time-independent) and ‘relaxational’ (time-dependent) components. Both components show a similar dependence on Ni concentration, thus indicating their common origin. It is concluded that, while the amplitude—dependent internal friction is largely due to dislocation—point-defect interactions, the acoustoplastic effect originates mainly from dislocation—dislocation interactions.

Influence of impurity content on the acoustoplastic effect, internal friction, and Young's modulus defect during deformation of Cu-Ni single crystals

Abstract Oscillatory stress amplitude dependences of the acoustoplastic effect, absorption of ultrasonic vibrations (frequency of about 100 kHz) causing this effect, and Young's modulus defect were simulataneously measured in situ during quasistatic deformation of Cu-1·3–7·6 at.% Ni single crystals. The time dependences of the magnitude of the acoustoplastic effect at constant oscillatory stress amplitudes were also obtained. The amplitude-dependent internal friction and Young's modulus defect diminish drastically with increasing Ni content. The dependence of the magnitude of the acoustoplastic effect on the Ni concentration is much less pronounced and is reversed with increase in oscillatory stress amplitude. Data on the kinetics of the acoustoplastic effect revealed ‘instant’ (time-independent) and ‘relaxational’ (time-dependent) components. Both components show a similar dependence on Ni concentration, thus indicating their common origin. It is concluded that, while the amplitude—dependent internal friction is largely due to dislocation—point-defect interactions, the acoustoplastic effect originates mainly from dislocation—dislocation interactions.

Effect of temperature on the amplitude dependences of the acoustoplastic effect and internal friction during deformation of crystals

Abstract Oscillatory strain amplitude dependences of the acoustoplastic effect and absorption of ultrasonic vibrations (frequency of about 100 kHz) causing this effect were measured in a wide temperature range in situ during quasistatic deformation of NaCl and Al single crystals. An increase in efficiency of the ultrasonic effect on the plastic deformation process has been found with an increase in temperature. The data obtained provide evidence for the distinction in basic mechanisms of the acoustoplastic effect and amplitude-dependent internal friction. The absorbtion of ultrasound is largely due to dislocation-point-defect interactions under reversible movement of mobile dislocations. Mechanical activation of irreversible movement of the same mobile dislocations through long-range internal stress fields of other dislocations and dislocation pileups is suggested as the basic mechanism of the acoustoplastic effect. Mechanisms are discussed determining the temperature dependences of the acoustoplastic eff...

Acoustoplastic effect and internal friction of aluminum single crystals in various deformation stages

The dependences of the acoustoplastic effect and the internal friction on the oscillatory strain amplitude are measured in various deformation stages of low-purity aluminum single crystals. It is discovered that the acoustoplastic effect is observed not only in the macroscopic plastic region of the stress-strain diagram, but also for microplastic deformation in the “elastic” loading and unloading stages. The sign of the effect reverses during unloading. An increase in the strain rate leads to enhancement of the acoustoplastic effect and the absorption of the energy of ultrasonic vibrations causing this effect with a frequency of about 100 kHz. It is concluded that the acoustoplastic effect observed during both macro-and microplastic deformation is caused by the irreversible high-speed motion of dislocations through the long-range stress field of the other dislocations after breaking through the Cottrell atmospheres.

Acoustoplastic Effect and Amplitude-Dependent Internal Friction During Deformation of Impure Aluminium Single Crystals

Time, temperature, plastic strain, strain rate and oscillatory stress amplitude dependences of the acoustoplastic effect and dislocation amplitude-dependent absorption of ultrasound causing this effect have been studied during three-point bending of aluminium single crystals. The acoustoplastic effect was observed not only during macroplastic deformation, but during microplastic deformation on elastic loading and during strain recovery on unloading as well. The time dependence of the acoustoplastic effect shows two components: fast (time-independent) and slow (time-dependent). Data obtained evidence for the distinction in defect structure levels responsible for the acoustoplastic effect and amplitude-dependent internal friction. Dislocation - dislocation interaction is suggested as a basic source of the acoustoplastic effect. Dislocation - point defect interaction plays a secondary part in mechanism of the acoustoplastic effect, even in case of dynamic strain ageing.

Influence of Ni Content on Internal Friction and Acoustoplastic Effect in Cu-Ni Single Crystals

Influence of Ni content in a range 1.3 - 7.6 at.% on amplitude-dependent internal friction and Young's modulus defect of Cu-Ni single crystals oriented for single slip has been studied by composite oscillator technique at frequencies of about 100 kHz in a wide strain amplitude range before, during, and after plastic deformation. The acoustoplastic effect was registered simultaneously with in situ internal friction measurements. Effects of the composition and temperature ranging from 6 to 255 K on damping and anelastic strain was studied and allowed to suggest multicomponent strain amplitude-temperature spectra of the amplitude dependent internal friction. A functional form of the amplitude dependence of the internal friction and Young's modulus defect is discussed. Data on in situ measurements allow to associate the amplitude-dependent internal friction and acoustoplastic effect with different mechanisms: dislocation - point obstacle and dislocation - dislocation interactions, respectively.

On the additivity of acoustoplastic and electroplastic effects

The influence of high density current pulses (approximately 10 3 A mm −2 for 25–80 μs) and the ultrasonic deformation (2 × 10 4 Hz) on the flow stress of Cu tested in uniaxial tension at 300 K were investigated with the objective of determining the mechanisms of the joint action of electroplastic (EPE) and acoustoplastic (APE) effects. The experimental procedure used allows synchronization of the current pulse and the ultrasonic deformation and allows the current pulse and the ultrasonic deformation to be shifted in phase. It was found that the combined APE + EPE is smaller than the sum of separate effects and depends on the phase shift between the current pulse and the ultrasonic deformation. An extremum of the combined APE + EPE at a certain phase shift between the current pulse and the ultrasonic deformation was detected. An increase in the EPE after prior action of ultrasonic deformation was detected. Employing the thermally activated plastic flow concept, a differential equation for combined APE + EPE is proposed.

Dynamics of dislocations in InSb and GaAs crystals

Abstract An asymmetry of the mobility of 60° α and screw dislocations in nominally pure InSb and GaAs single crystals has been studied as a function of shear stress (τ ≈ 1–50MPa) and temperature (T ≈ 323–773 K). The observed synchronous decrease in the mean free path length and the mean number of mobile dislocations under periodic tensile-compressive and monotonic multiple-tension loadings are most clearly manifested for dislocations prone to a noticeable cross-slip (screws containing β partials). It has been found that variations in the dislocation stacking fault width with increasing shear stress τ under compression and extension affect the dislocation velocity in InSb and GaAs in different manners. An estimation of the Peierls stress τP shows that τP≤10 −6μ (μ is the shear modulus) in A3B5 covalent compounds, whereas τP≤10−5μ in the elemental semiconductors Si and Ge. The data on acoustoplastic, electroplastic and photoplastic effects in semiconductors may be unambiguously explained using a universal m...

Kinetics of the acoustoplastic effect

The acoustoplastic effect (APE) as a function of time is considered. The causes of the spread of APE experimental data are revealed. Effects unobserved previously by experiment are predicted. The influences of machine stiffness and material dislocation structure variation on the APE are investigated. The stress relaxation associated with the APE is studied and an anomalous behaviour of the APE at high temperatures is predicted.

Peculiarities in the plastic deformation of crystals subjected to the acoustoplastic effect

A decrease in the stress of unidirectional plastic deformation during the superposition of oscillations was observed at high ultrasonic frequencies. In a recently published paper, this effect was experimentally studied at low frequencies (about 1 Hz). Such low frequencies allowed the process kinetics to be studied in a sufficiently detailed manner. However, no satisfactory explanation was given for the effects observed. In the present study a model is proposed which describes the process of plastic deformation of a crystal in the field of alternating stresses; this model correlates fairly well with the experimental results obtained both at low frequencies and at higher frequencies.