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

Abstract

Ultrasonic vibration is widely utilized in manufacturing processes mainly because acoustic field could significantly affect the metal plasticity leading to stress reduction. However, viewpoints on the influence mechanism have not reached a consensus yet. In this paper, an ultrasonic vibration assisted uniaxial tension experiment with copper foils is carried out using a specially-developed device. The results show that the extent of stress reduction increases with the increase of the vibration amplitude. Acoustic softening and stress superposition are both considered in a developed model to describe the stress reduction due to ultrasonic excitation during metal forming process. Considering ultrasonic vibration provides the energy for dislocation sliding, acoustic softening is analyzed based on crystal plasticity theory considering ultrasonic intensity. Stress superposition, mostly induced by the additional periodic strain, is included by taking account of its proportional relationship with vibration amplitude. The calculation results from the numerical model show a good agreement with those from the experiment. These findings provide an instructive understanding of mechanism of stress reduction in ultrasonic vibration assisted metal deformation and is especially helpful for pro-actively designing ultrasonic vibration assisted metal forming processes.

Fatigue Behaviour of 7N01-T4 Aluminium Alloy Welded by Ultrasonic-Assisted Friction Stir Welding

“…From the local view of metal flow, the tool and the material were in a state of repeated contact and separation; hence, the superposition of the oscillating and axial stresses of the tool (steady stress) led to a reduction in the average stress and internal strain (stress superposition). The ultrasonic energy introduced into the weld was preferentially absorbed by defects, such as dislocations and grain boundaries in the material, which reduced the maximum shear stress required for the dislocation movement and resulted in a decrease in the material shear stress (acoustic softening) [ 40 ]. Shi et al [ 41 ] believed that ultrasonic energy reduced the flow stress and viscosity of the metal near the pin, which led to the increase in the flow velocity and strain rate of the SZ metal.…”

Ultrasonic Vibration Facilitates the Micro-Formability of a Zr-Based Metallic Glass

“…αt=4ρnormalH13cnormalH13ρZr35cZr35false(ρnormalH13cnormalH13+ρZr35cZr35false)2 where C H13 and C Zr35 are the longitudinal vibration wave velocities of H13 die steel and MG samples, respectively. According to the material properties of H13 steel [26] and Zr35 [27], the value of C Zr35 is 2861.5 m/s and the value of C H13 is 6072 m/s. Therefore, the value of α t is 0.739.…”

Research on the Micro-Extrusion Process of Copper T2 with Different Ultrasonic Vibration Modes

“…Referring to the researches on ultrasonic micro plastic forming process with tool vibration mode [17,18], the effect of ultrasonic tool vibration on metal plastic deformation can be explained by stress superposition, acoustic softening and friction decrease. Furthermore, the model for predicting reduction of yield stress under the excitation of ultrasonic tool vibration can be supposed as follows:…”

“…where β and m are parameters to be determined in experiments, M is the Taylor factor, ̂ is the mechanical threshold of material, E is the acoustic energy density, can be expressed as follows [18]:…”

“…where ∆σ s is the total reduction of yield stress, ∆σ t is the yield reduction due to acoustic softening, ∆σ p is the yield reduction due to stress superposition, ∆σ f is the yield reduction due to friction decrease. The stress reduction due to acoustic softening ∆σ t can be expressed as [18]:…”