Dynamic tensile tests with superimposed ultrasonic oscillations for stainless steel type 321 at room temperature

Acoustic softening and stress superposition in ultrasonic vibration assisted uniaxial tension of copper foil: Experiments and modeling

“…In addition, an S-shaped increase of the stress related to the vibration duration was observed after vibration is removed. For the acoustic softening effect, however, investigations also illustrate that no significant temperature rise is observed during vibration assisted experiments [17,21,28]. As reported in quite a few literatures, the flow stress decrease due to acoustic softening is proportional to the vibration amplitude (acoustic energy density) [2,29].…”

“…13. Assuming the elastic-plastic material is rate-independent characterized by perfect elastic unloading in stress-strain curve, the specimen will be deformed elastically first and followed by plastic deformation during one period of oscillation [17]. During the tension assisted with ultrasonic vibration, the oscillation displacement of the ultrasonic horn tip that transmitted to the tension specimen will lead to additional periodic strain in the deformation area of the specimen, i.e., the vibration amplitude is roughly equivalent to the strain amplitude in the specimen.…”

“…The stress superposition mechanism could be depicted by the correlation between stress-strain curve and time-strain curve [17,18], based on a rate-independent elastic-plastic material in an idealized condition.…”

Thermally Activated Jamming in Ultrasonic Powder Compaction

“…Proposed mechanisms of acoustic softening include thermal softening due to frictional heating between the ultrasonic actuator and the test specimen [ 95 ] ; dislocation‐based effects related to dislocation annihilation [ 100–103 ] and to unlocking of pinned dislocations; [ 93,104–106 ] and stress superposition, [ 95,107 ] which holds that the peak stress in each oscillation cycle still equals the conventional flow stress even though the mean stress appears lower. The thermal softening hypothesis conflicts with in situ temperature measurements that reveal a lack of heating [ 108 ] and with the nearly instantaneous recovery of strength when the ultrasonic excitation stops. Dislocation‐based explanations of acoustic softening are similarly inconsistent with the reversible nature of acoustic softening.…”

Investigations on the material property changes of ultrasonic-vibration assisted aluminum alloy upsetting

“…Explanations on the effects of ultrasonic vibration include the superposition of stress [1,2,5,[11][12][13][14], increased temperatures [1,2,15], energy absorption of dislocation [3,4], and the effects of interface friction [7][8][9][10][11][12][13]. These factors are usually coupled, which makes them difficult to understand.…”