Characteristics of plastic deformation under the action of ultrasound

Tyapunina, N. A.; Blagoveshchenskii, V. V.; Zinenkova, G. M.; Ivashkin, Yu. A.

doi:10.1007/bf00898751

Cited by 19 publications

(11 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In Fig. 3(a), it can be seen that the curve with circular symbols catches up with the curve with square symbols at strain of about 0.5 and exceeds the latter beyond this strain, and so this case corresponds to a small extent of residual hardening [13,34,35]. Fig.…”

Section: Resultsmentioning

confidence: 71%

“…(iii) However, not withstanding (ii) above, residual softening or hardening compared to the state before ultrasound excitation may happen after the ultrasound has been switched off. Residual softening is more often observed [29][30][31][32][33], whereas residual hardening can sometimes be observed if the ultrasonic intensity is high [13,34,35].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Understanding acoustoplasticity through dislocation dynamics simulations

Siu

Ngan

2011

Philosophical Magazine

View full text Add to dashboard Cite

The acoustoplastic effect in metals is routinely utilized in industrial processes involving forming, machining and joining, but the underlying mechanism is still not well understood. There have been earlier suggestions that dislocation mobility is enhanced intrinsically by the applied ultra-sound excitation, but in subsequent deliberations it is routinely assumed that the ultra-sound merely adds extra stresses to the material without altering its dislocation density or intrinsic resistance to deformation. In this study, dislocation dynamics simulation is carried out to investigate the interactions of dislocations under the combined influence of quasistatic and oscillatory stresses. Under such combined stress states, dislocation annihilation is found to be enhanced leading to larger strains at the same load history. The simulated strain evolution under different stress schemes also resembles closely certain experimental observations previously obtained. The discovery here goes far beyond the simple picture that the ultra-sound effect is merely an added-stress one, since here, the intrinsic strain-hardening potency of the material is found to be reduced by the ultra-sound, through its effect on enhancing dislocation annihilation.

show abstract

Section: Resultsmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Understanding acoustoplasticity through dislocation dynamics simulations

Siu

Ngan

2011

Philosophical Magazine

View full text Add to dashboard Cite

show abstract

“…Residual hardening has also been found experimentally especially after the application of sufficiently large vibration intensities [16]. Tanibayashi's equivalence principle (eqn.…”

Section: Discussionmentioning

confidence: 88%

“…However, overwhelming experimental evidences have shown that acoustoplasticity is far from a merely extrinsic effect. First, it is well known that residual softening or hardening may occur in metals after application, and then removal, of ultrasound irradiation [1,[14][15][16], suggesting that the vibrations can induce permanent changes in the deformation microstructure of the material. This has been recently confirmed by Siu, Ngan and Jones [9], who observed extensive dislocation annihilation and subgrain formation in Al, Cu and Mo samples accompanying ultrasound irradiation in macroindentation experiments.…”

Section: Introductionmentioning

confidence: 99%

Strength of metals under vibrations – dislocation-density-function dynamics simulations

Cheng

Leung

Ngan

2014

Philosophical Magazine

View full text Add to dashboard Cite

It is well-known that ultrasonic vibration can soften metals, and this phenomenon has been widely exploited in industrial applications concerning metal forming and bonding. Recent experiments show that the simultaneous application of oscillatory stresses from audible to ultrasonic frequency ranges can lead to not only softening but also significant dislocation annihilation and subgrain formation in metal samples from the nano-to macro-size range. These findings indicate that the existing understanding of ultrasound softeningthat the vibrations either impose additional stress waves to augment the quasi-static applied load, or cause heating of the metal, whereas the metal's intrinsic deformation resistance or mechanism remains unalteredis far from complete. To understand the softening and the associated enhanced subgrain formation and dislocation annihilation, a new simulator based on the dynamics of dislocation-density functions is employed. This new simulator considers the flux, production and annihilation, as well as the Taylor and elastic interactions between dislocation densities. Softening during vibrations as well as enhanced cell formation are predicted. The simulations reveal the main mechanism for subcell formation under oscillatory loadings to be the enhanced elimination of statistically stored dislocations (SSDs) by the oscillatory stress, leaving behind geometrically necessary dislocations with low Schmid factors which then form the subgrain walls. The oscillatory stress helps the depletion of the SSDs, because the chance for them to meet up and annihilate is increased with reversals of dislocation motions. This is the first simulation effort to successfully predict the cell formation phenomenon under vibratory loadings.

show abstract

“…It is well known that residual softening or hardening compared to the state before ultrasound excitation may occur in metals after application, and then removal, of ultrasound irradiation [6,[32][33][34][35][36][37], suggesting that the vibrations can make permanent changes in the microstructure of the material. Siu et al [27] observed extensive dislocation annihilation and subgrain formation in Al, Cu and Mo samples while applying ultrasonic vibrations in macro indentations experiments.…”

Section: Introductionmentioning

confidence: 99%