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In the field of ultrasonic-assisted micro-forming, in addition to acoustic softening, impact effects also play a significant role, especially in terms of influencing the deformation behavior of surfaces, such as by generating more deformation on surface asperity. In this study, to understand the mechanisms involved in the effect of an impact, ultrasonic-assisted micro-forging tests were conducted on commercially pure copper, pure aluminum, and pure titanium. A method that can measure the increment in the temperature during ultrasonic vibration was developed. As a result, changes in the surface temperature of the material under the impact effect and acoustic softening were measured. It is indicated that, during ultrasonic vibration, the heat generated through acoustic softening is very limited and the main heat increase occurs after the impact effect. Once the impact effect occurs, the surface temperature increases with increasing amplitude. Nevertheless, for materials with different crystal structures, the influences of the impact effect are also different. The surfaces of copper and aluminum soften, creating more surface deformation, but the exact opposite effect is seen on a titanium surface. Observing the evolution of the microstructure on the material surface with EBSD demonstrates that the impact effect on FCC materials can reach deeper below the surface in terms of temperature diffusion compared to titanium. Meanwhile, the impact effect in the case of titanium causes the regeneration of twinning, which is reduced under the influence of the acoustic softening effect, consequently resulting in strain hardening. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) particle-reinforced aluminum matrix (SiCp/Al) composites are increasingly finding applications across a range of industries due to their exceptional mechanical properties. However, these composites often face challenges in achieving optimal machinability and meeting quality standards, primarily due to the presence of SiC particles, which can hinder their full potential. This study focuses on addressing these challenges through the application of ultrasonic vibration-assisted helical grinding (UVHG) to enhance the efficiency and quality of SiCp/Al composites. To achieve the desired quality and efficiency improvements, a comprehensive methodology involving ultrasonic vibration-assisted helical grinding (UVHG) has been implemented for SiCp/Al composites. A mechanical cutting force model was then developed to accurately predict grinding forces. The grinding force was deconstructed into distinct components: friction force, plastic deformation force, and fracture force, taking into account the underlying material removal mechanisms. To better understand the grinding force associated with a single diamond abrasive grit, parameters such as undeformed chip thickness and cross-sectional area were calculated and subsequently extrapolated to the entire tool. Introducing an innovative approach, the model incorporates the concept of an acoustic softening coefficient, which quantifies the reduction in deformation stress resulting from ultrasonic vibration. This coefficient serves to correct and account for the influence of ultrasonic vibration on the properties of SiCp/Al composites. Experimental machining using the UVHG technique was conducted across various test groups. The experimental outcomes aligned closely with the predicted cutting force values, with a deviation of only 5.07%. This alignment underscores the accuracy of the proposed model and its potential as a guiding framework for optimizing the grinding process of SiCp/Al composites. The newly established predictive cutting force model, coupled with the innovative UVHG machining approach, offers promising avenues for effectively machining SiCp/Al composites on an industrial scale. This advancement not only enhances the application potential of SiCp/Al composites but also paves the way for future research and development in this field. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration (UV)-assisted technology has been widely investigated in metal forming in the past decade. However, the research on ultrasonic-assisted forming of Ti2AlNb alloy has not been reported. To study the flow behavior of Ti2AlNb alloy during ultrasonic-assisted forming and set up the constitutive model that can accurately describe its flow behavior, the room temperature compression test of Ti2AlNb alloy with ultrasonic amplitude range of 0-31 µm and strain rate of 0.001-0.125 s−1 were carried out. Considering the influence of yield strength, strain hardening and strain rate hardening effect, a modified Johnson–Cook (J–C) constitutive model is proposed, which can accurately describe the flow behavior of Ti2AlNb alloy during ultrasonic-assisted compression. The results show that under the studied deformation conditions, the yield strength and strain hardening coefficient of Ti2AlNb alloy decrease with the increase of ultrasonic the amplitude. When the amplitude increases to 31 µm. the yield strength decreases by 42%. The ultrasound provides larger dislocation motion energy, increases dislocation activity, and alleviates dislocation stacking, thus reduce the yield strength. The strain hardening exponent and strain rate hardening coefficient increase with the increase of amplitude. The results, obtained from the quantitative analysis of the optimized J–C model, show that the prediction results are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Metallic bipolar plates (BPPs) are key components in the proton-exchange membrane fuel cell (PEMFC), which can replace traditional fossil fuels as a kind of clean energy. However, these kinds of plates, characterized by micro-channels with a high ratio between depth and width, are difficult to fabricate with an ultra-thin metallic sheet. Then, ultrasonic-vibration-assisted stamping is performed considering the acoustic softening effect. Additionally, the influence of various vibration parameters on the forming quality is analyzed. The experimental results show that ultrasonic vibration can obviously increase the channel depth. Among the vibration parameters, the vibration power has the maximum influence on the depth, the vibration interval time is the second, and the vibration duration time is the last. In addition, the rolling direction will affect the channel depth. When the micro-channels are parallel to the rolling direction, the depth of a micro-channel is the largest. This means that the developed ultrasonic-vibration-assisted stamping process is helpful for improving the forming limitation of micro-channels used for the bipolar plates in PEMFC. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration-assisted deformation (UVAD) technology has been widely utilized in the metallic materials forming and manufacturing process owing to its advantages of effectively reducing deformation stress. However, the intrinsic mechanism of UVAD involved in Ti3Al intermetallics has not yet been clarified. In this research, an ultrasonic vibration tension device for Ti3Al was designed. The mechanical properties under ultrasonic vibration-assisted tension (UVAT) were investigated. Subsequently, the rheological behavior under the effect of ultrasound was analyzed. The influences of the vibration amplitudes and vibration modes on the microhardness and microstructure were explored. The results indicated that Ti3Al behaved obviously an acoustic softening after introducing ultrasonic energy, and the degree of softening was positively correlated with amplitude. There was a “competitive” relationship between the acoustic softening and acoustic residual hardening effects. The maximum stress and microhardness reductions were 206.13 MPa and 6 % when the amplitude was 6.55 μm and 1.31 μm, respectively. The fracture mode evolved from ductility dimple fracture to a mixed-mode of cleavage pattern and brittle fracture. The metallographic organization revealed a “defective phase” structure in the α2 phase and B2 matrix. The amounts of defective phases enlarged with amplitude increasing and extended away from the vicinities of the fracture cross-section.

The deformation capacity of foils deteriorates rapidly due to the appearance of size effects. In this study, the mechanism of ultrasonic vibration affecting the tensile deformation behavior of pure titanium foil was investigated using the developed ultrasonic-assisted tensile forming platform. The results showed that the energy of ultrasonic vibration during foil tensile deformation was mainly consumed by acoustic softening and mechanical vibration, and the energy consumed by acoustic softening was less than 20% of the total energy. When the percentage of grain boundary region is less than the critical value, increasing the ultrasonic amplitude results in a slight increase in the percentage of acoustic softening energy, but a sharp decrease in elongation. The digital image correlation results showed that the acoustic softening effect promoted the dispersion of local concentrated deformation of foils, resulting in more uniform deformation. Mechanical vibration could accelerate the formation and propagation of microcracks, which makes the fracture morphology of foils exhibit brittle fracture characteristics. Foil grain refinement is a useful method to enhance the acoustic softening effect during the tensile deformation process of foils. This work provides a basis for investigating the mechanism of ultrasonic vibration affecting the tensile deformation behavior of foils. [Display omitted] • The energy of ultrasonic vibration in the foils tensile process was mainly consumed by acoustic softening and mechanical vibration. • Ultrasonic amplitude hardly affects the absorption efficiency of acoustic softening energy when the grain boundary region proportion is small. • Acoustic softening can promote the dispersion of local concentrated deformation of foils for more uniform deformation. • Mechanical vibration can accelerate the formation and propagation of micro-cracks, resulting in the brittle fracture characteristics of fracture morphology. • Grain refinement is a useful method to enhance the acoustic softening effect during the tensile deformation process of foils. [ABSTRACT FROM AUTHOR]

Acoustic softening is a phenomenon where metals exhibit a lower flow stress when excited by a vibration at ultrasonic frequencies. This softening effect has been well documented in the literature, however, there are two areas that require further in-depth analysis. The first relates to the wide range of reported softening responses for the same alloy. The second relates to the use of coefficients and compensation factors when modeling the acoustic softening phenomenon in a complex forming processes. This study investigates the changes in softening response when altering specimen dimensions in ultrasonic assisted compression tests. Aluminum alloys (AA) 2024-O and AA7075-O were machined to different dimensions and compressed with ultrasonic assistance, to investigate the relationship between specimen volume and softening response. An inverse relationship between softening magnitude and sample volume was found. When relating this to acoustic energy density and stress, the values are invariant because the standard acoustic equations cannot account for changes in specimen height. The amplitude strain parameter, amplitude divided by the current specimen height, is introduced, and shown to account for changes in specimen dimensions. In addition, the softening effect diminishes relative to the state of strain. The results suggest acoustic softening is a function of the amplitude strain parameter and strain history. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on the wave equation and the resonance theory of non-uniform material, a uniaxial tension device with ultrasonic vibration assistance for Ti 3 Al intermetallic compounds was designed. • The acoustic residual hardening induced by a small amplitude was dominant, while a large amplitude led to acoustic softening. • As ultrasonic vibration was applied, the fracture mode of Ti 3 Al evolved from the ductility dimple fracture to the mixed mode of cleavage pattern and brittle fracture. • The "defective phase" structure in the α 2 phase and B2 matrix was discovered and it extended from the vicinities of the fracture cross-section to the area away from the fracture cross-section as vibration amplitude was enlarged. Ultrasonic vibration-assisted deformation (UVAD) technology has been widely utilized in the metallic materials forming and manufacturing process owing to its advantages of effectively reducing deformation stress. However, the intrinsic mechanism of UVAD involved in Ti 3 Al intermetallics has not yet been clarified. In this research, an ultrasonic vibration tension device for Ti 3 Al was designed. The mechanical properties under ultrasonic vibration-assisted tension (UVAT) were investigated. Subsequently, the rheological behavior under the effect of ultrasound was analyzed. The influences of the vibration amplitudes and vibration modes on the microhardness and microstructure were explored. The results indicated that Ti 3 Al behaved obviously an acoustic softening after introducing ultrasonic energy, and the degree of softening was positively correlated with amplitude. There was a "competitive" relationship between the acoustic softening and acoustic residual hardening effects. The maximum stress and microhardness reductions were 206.13 MPa and 6 % when the amplitude was 6.55 μm and 1.31 μm, respectively. The fracture mode evolved from ductility dimple fracture to a mixed-mode of cleavage pattern and brittle fracture. The metallographic organization revealed a "defective phase" structure in the α 2 phase and B2 matrix. The amounts of defective phases enlarged with amplitude increasing and extended away from the vicinities of the fracture cross-section. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration assisted metal forming is a promising technology, but the microscopic mechanism of the ultrasonic effect on metal deformation has not been fully understood yet. In this paper, by molecular dynamics simulation, the microscopic mechanism behind the acoustic softening effect of ultrasonic vibration was studied. The stress superposition and acoustic softening can be simulated simultaneously by molecular dynamics method, and the stress–strain response of the polycrystalline copper simulations agrees well with the experimental results. Based on the analysis of atomic kinetic energy and dislocation density, it is found that ultrasonic vibration increases the atomic kinetic energy and promotes the generation, multiplication, motion, and annihilation of dislocations in the plastic deformation process, resulting in a reduction of dislocation tangles and pile-ups. Therefore, the hindrance to crystal sliding is significantly decreased, which promotes the plastic deformation accompanied by a macroscopic reduction in flow stress of copper. As for different ultrasonic parameters, the influence laws of ultrasonic amplitude and frequency on the deformation behaviors of coppers are different. These findings play an essential role in revealing the mechanism of ultrasonic vibration assisted plastic forming. [Display omitted] • Based on analysis of atomic kinetic energy and dislocation density, the micro-mechanism of acoustic softening was revealed. • The stress superposition and acoustic softening can be simulated simultaneously by molecular dynamics method. • The stress–strain response of the polycrystalline copper simulations agrees well with the experimental results. • The influence laws of ultrasonic amplitude and frequency on the deformation behaviors of coppers are different. [ABSTRACT FROM AUTHOR]