Electrically Assisted Research Articles

Design and validation of an electrically assisted modular attachment demonstrator for lightweight cycles

Sustainable transportation solutions are essential for enhancing resource efficiency and reducing greenhouse gas emissions. Significant contributions to this goal have been made by the cycling sector by increasing its presence in urban areas logistics. The primary means for this increase is the usage of cargo cycles. There are numerous advantages associated with it, such as: high versatility, functionality without emissions, lightweight build, and the ability to travel through areas in which conventional vehicles are prohibited. This paper reports the process of designing an experimental demonstrator for an electrically assisted attachment that can be used to convert most cycle vehicles into cargo variants. The attachment is designed to overcome one of the major drawbacks of traditional cargo cycles, namely the lack of modularity. This implies that users previously had to transport the empty cargo area even when not actively involved in delivery tasks. By removing the attachment, the user can convert the cycle for personal use. However, when required, the attachment can be added which, together with the electrical assistance system, can increase delivery efficiency. The paper aims to present the development process of the three-dimensional model of the attachment using computer-aided design techniques, highlighting the universal coupling mechanism and variable storage space. Additionally, vehicle dynamics simulations were performed to evaluate the stability of the system during operation and to ensure the validity of the proposed design.

Decoupling the nonthermal effect of current by electrically assisted crystal plasticity modeling of Ni-based single crystal superalloys

The electrically assisted (EA) deformation process has received considerable attention in recent years, accompanied by research on current-induced deformation mechanisms. However, there are still challenges in eliminating thermal effects, which have prevented a comprehensive understanding of the underlying current-induced mechanisms. Opting for a single crystal (SC) in research provides advantages in decoupling the nonthermal effect of electric current at smaller scales and eliminating the complex interactions that exist in polycrystalline materials. Therefore, the innovation of this work lies in decoupling the nonthermal effect of electric current and conducting a comprehensive analysis of anisotropic deformation and mechanisms within a Ni-based SC with different crystallographic axes and various current directions during electrically assisted tensile simulation. A significant tension axis direction in the SC during EA tension was induced by the combination of a higher current direction factor (|cosθ|) and a dimensionless factor for the current density (|Jα/J0α|) along the [100] axis. The stress drop within the SC due to the nonthermal effect of electric current generally increased with increasing current direction. This was attributed to the increased dislocation density differences and decreased temperature. The increased stress anisotropy of the SC at a current direction of 45° was attributed to fewer activated (111) slip systems and the pinning effect of more dislocations within these systems. This study advances our understanding of the thermal and nonthermal effects of electric current and offers valuable insights for the informed application of EA deformations in industrial and aerospace settings with SC superalloys.

A Case Study: Electrically Assisted Stress Relief Annealing for Cold-Coiled Helical Automotive Springs.

This study experimentally investigated electrically assisted (EA) stress relief annealing for cold-coiled commercial automotive springs. In EA stress relief annealing, the temperature of a spring is rapidly increased to the annealing temperature (400 °C) and is held constant for a specified time using a pulsed electric current. Experimental findings show that the effectiveness of the EA stress relief annealing is superior to that of the conventional stress relief annealing, especially in terms of process time. The present study suggests that EA stress relief annealing, with properly selected process parameters, can effectively substitute for time-consuming conventional stress relief annealing using a furnace for cold-coiled automotive springs.

Temperature-dependent electroplasticity in the Invar 36 alloy

Electroplasticity of the Invar 36 alloy is investigated based on comparisions between warm and electrically-assisted (EA) uniaxial tensions experiments at different temperatures (100–600 °C) and corresponding microstructural characterizations. Under warm deformation (WD), the flow stress decreases with the increase in temperature, which is directly attributed to dynamic recovery and dynamic recrystallization. With the introduction of high electric current during deformation, it shows a temperature-dependent electroplasticity phenomenon. No difference could be observed between WD and EA samples below a critical temperature of 500 °C, above which, an obvious softening behavior takes place in EA samples. This transition in softening respective to deformation temperature clearly demonstrated that it correlates with the intrinsic current-induced dislocation annihilation and recovery rather than the traditional theory of the Joule heating effect. Our findings shed more light on the utilization of EA softening effect on the development of novel forming routines, especially for materials with limited deformability.

Characterization of stress drop and strain localization for titanium alloy subjected to electrically-assisted tension

The stress drop and strain localization behaviors of Ti–6Al–4V titanium alloy under the action of single pulse were investigated using electrically-assisted (EA) tension tests in this study. It is found that the flow stress drop gradually increases with the increase of current density and pulse width during EA tension. The digital image correlation (DIC) technology was adopted to analyze the strain distribution evolution and fracture regulation in EA micro-tension process. It turn out that the EA tensile sample will suddenly form two new intersecting high-strain bands at the moment of applying a pulse. With the increase of strain, the two high-strain bands converge toward the center and gradually evolve into a crossed localized flow zone, which makes the EA tensile sample exhibit a high local plastic deformation compared with room temperature tension. Furthermore, with the increase of current density, the temperature gradient in the tensile direction of the sample increases gradually, resulting in the narrowing of localized flow zone. The transformation of the localized flow zone eventually leads to the increase of fracture angle and the formation of a sawtooth shape fracture morphology. Finally, a material flow model for the single-pulse EA tension process was established. The calculation results show that about 11 % of the stress drop comes from the contribution of non-thermal electroplastic, the main mechanism of stress drop is thermal softening and thermal expansion induced by Joule heat during EA tension.

Examining the Efficiency of Electric-Assisted Mountain Biking across Different Types of Terrain

Mountain bikes with electric assistance (e-bikes) have gained popularity recently by allowing riders to increase their pedaling power through an electric motor. This innovation has raised questions about how e-bikes compare to traditional mountain bikes regarding physical effort, speed, and physiological demands. By examining these factors, the study aims to compare and characterize differences in performance-related parameters when using an electric-assisted mountain bike compared to a conventional mountain bike on different types of terrain (uphill, downhill, flat section, technically demanding terrain) concerning power output, velocity, cardiorespiratory parameters, and energy expenditure. Six experienced mountain bikers (mean age: 44.6 ± 6.4 years, mean body height: 173.3 ± 5.6 cm, mean body weight: 70.6 ± 4.9 kg) cycled 4.5 km on varying off-road terrain at their own race pace, once with and once without electrical assistance, in randomized order. The results of the study indicate significantly faster (24.3 ± 1.85 to 17.2 ± 1.22 km/h (p < 0.001)) cycling on an electric-assisted mountain bike, which reduces cardiorespiratory parameters and metabolic effort as well as results in less demanding workload (138.5 ± 31.8 W) during the cycling with an electric-assisted mountain bike in comparison to a conventional mountain bike (217.5 ± 24.3 W (p < 0.001)). The results indicate significant differences especially when riding uphill. The performance advantage of an electrically assisted mountain bike diminishes compared to a conventional mountain bike on downhill, flat, or technically challenging terrain. The highlighted advantages of electric-assisted mountain bikes could represent a novel strategy for cycling in different terrains to optimize efficiency.

Bonding evolution of composites fabricated via electrically assisted press bonding

Reducing fuel consumption and increasing efficiency is one of the solutions that humanity has adopted to reduce costs caused by fuel consumption in all industries, including the transportation industry. An effective solution to improve practical fuel consumption is to reduce weight. In principle, press bonding (PB), which is done using a press and is a solid-state welding process, can create a bond between parts with different materials and produce materials with lighter weight and more strength. But it should also be noted that the plasticity of some materials is very low, and these materials are incapable of machinability. Electrical assistance is a potential solution that can solve this problem by increasing the flow tension and reducing the forming force. In this study, aluminum alloy 1060 bars were electrically press bonded at electricity current levels 0 Å up to 300 Å. The effect of pressing parameters on the bonding strength, such as amount of electricity current level and plastic strain, was investigated using a peeling test. Results show that more adhesive among the layers (bonding strength) was attained by growing current and reducing thickness. Scanning electron microscope (SEM) was investigated the peeling surface of samples versus the different thickness reduction ratios and electric currents. The Joule heating effect in the electrically-assisted in press bonding (EAPB) process decreases the forming strength of bars and increases the bond strength of bonded bars by about three times. Using SEM, the peeling surface of samples and the fracture surface around the interface after the tensile test were studied to investigate the bonding quality.

Study of a Regional Turboprop Aircraft with Electrically Assisted Turboshaft

Hybrid-Electric Propulsion (HEP) could be part of the solution to decrease emissions associated with regional commercial aviation. This study presents results for the aircraft level fuel reduction potential of a regional turboprop concept with an HEP architecture and Entry-Into-Service (EIS) in 2035+. The configuration specifically tackles the elaborated challenges of introducing an additional electrical energy source to the configuration by employing a twofold electrical assistance to a turboshaft engine in combination with an innovative thermal management concept. Relevant components and disciplines were modeled and incorporated into an integrated aircraft design environment. The behavior and interaction of the HEP architecture with the aircraft was thoroughly investigated. A best-performing configuration was derived and compared with a conventional reference configuration following a State-of-the-Art (SoA) reference aircraft approach. For a typical mission with 200 nmi range, a block fuel reduction of 9.6% was found. However, the assumed battery performance characteristics limited the reduction potential and led to a fuel burn increase for the 600 nmi design mission. Furthermore, sourcing the non-propulsive subsystems directly from the on-board battery was detrimental. The innovative Thermal Management System (TMS) located in the propeller slipstream showed a synergistic effect with the investigated configuration.

Thermal and non-thermal effects of Cu/Al laminated composite during electrically assisted tension

The electrically assisted (EA) forming technology is expected to further explore the forming potential of Cu/Al laminated composite (LC). However, the current action mechanism in the forming process of Cu/Al LC is still unclear. In this paper, the influence mechanism of thermal effect and non-thermal effect on the dislocation structure of Cu/Al LC during EA tensile process was mainly studied. The results demonstrated that there was an obvious non-thermal effect in EA tensile Cu/Al LC. The flow stress reduction of EA tensile specimens was more significant than that of thermal assisted tensile specimens at the matching temperature. At the same time, the dislocation generated by the Frank-Read dislocation source and the Lattice distortion degree near the Frank-Read source was decreased by electric current. The decrease of dislocation density caused by the annihilation of the dislocations in the EA tensile process leads to the reduction of flow stress in the Cu/Al LC. In addition, the Cu matrix and the interface region dislocation lines of the EA tensile specimen were rearranged along the direction of electron movement and the crack tip healing in the intermetallic compound layer was promoted. What is more, the junction of phase layer becomes a new crack source due to the resistance being higher at the heterogeneous junction.

The anomalous negative electric current sensitivity of a precipitation hardened Al alloy during electrically-assisted forming

It has been known for decades that the formability of metal sheets can be improved effectively by electrically-assisted (EA) forming. However, it remains controversial as to the detailed mechanisms and the manifestation of electrical effects can vary in different materials. In this paper, the EA flow behavior and mechanism of a precipitation hardened AA7075-T6 were studied. The term “electric current density sensitivity” (ECDS) was introduced to describe the athermal effect. The results show that Joule heating is the main influence factor, while the athermal effect varies with the electric–thermal parameters. Here, we report an anomalous negative electric current sensitivity in AA7075-T6, i.e. the flow stress increases with current density under the same temperature and strain rate when the temperature is ≤ 150 °C and strain rate is ≥ 0.005/s. The above phenomena are attributed to the local Joule heating and promoted atom diffusion under the action of the current, leading to the dissolution of GPZ, the formation of fine precipitate and Cr segregation-induced vacancies. Further, an extended dislocation density based constitutive model was proposed to cover the ECDS and softening effect, which could predict the flow behavior of 7075-T6 under EA forming, including the negative electric current sensitivity. The above work provides a viable method to simultaneously control both the shape and performance of the metal part. Meanwhile, the corresponding mechanism shed new light into the understanding of electroplasticity.

Design and Validity of a Smart Healthcare and Control System for Electric Bikes.

This paper presents the development of an electronic system that converts an electrically assisted bicycle into an intelligent health monitoring system, allowing people who are not athletic or who have a history of health issues to progressively start the physical activity by following a medical protocol (e.g., max heart rate and power output, training time). The developed system aims to monitor the health state of the rider, analyze data in real-time, and provide electric assistance, thus diminishing muscular exertion. Furthermore, such a system can recover the same physiological data used in medical centers and program it into the e-bike to track the patient's health. System validation is conducted by replicating a standard medical protocol used in physiotherapy centers and hospitals, typically conducted in indoor conditions. However, the presented work differentiates itself by implementing this protocol in outdoor environments, which is impossible with the equipment used in medical centers. The experimental results show that the developed electronic prototypes and the algorithm effectively monitored the subject's physiological condition. Moreover, when necessary, the system can change the training load and help the subject remain in their prescribed cardiac zone. This system allows whoever needs to follow a rehabilitation program to do so not only in their physician's office, but whenever they want, including while commuting.

Enhanced salt rejection of hydroxylated BaTiO3/Ti3C2Tx@polyvinyl alcohol composite nanofiltration membranes under electrochemical assistance

The influence of surface charge density of nanofiltration (NF) membranes could due to enhanced electrostatic interaction through electrically assisted. In this study, the hydroxylated BaTiO3/Ti3C2Tx (HBT)@polyvinyl alcohol (PVA) (HBTA) composite NF membranes were prepared by crosslinking HBT on the surfaces of NF membranes. The optimized HBTA-0.06 sample exhibited a water contact angle of 43.7°, zeta potential of −13.73 mV (pH = 6.5), average effective pore size of 0.319 nm, and pure water permeance of 55.1 L·m–2·h–1. At an applied electric field of 3 V, the rejection rates of LiCl, NaCl, KCl, RbCl, and MgCl2 determined for HBTA-0.06 reached 73.3%, 60.1%, 53.6%, 49.4%, and 59.8%, respectively. HBTA-0.06 has good stabilization properties that are especially advantageous for water purification, indicating good long-term filtration stability within 168 h. Furthermore, HBT doping significantly increased the charge density of the HBTA membranes and the rejection efficiency of chloride salts, both chlorine radicals (·Cl) and hydroxyl radicals (·OH) generation pathways were proposed under electrochemical assistance. Hence, electrical assistance represents a novel and effective technique for enhancing the salt rejection properties of multifunctional composite NF membranes.

Effect of Pulsed Current-Assisted Tension on the Mechanical Behavior and Local Strain of Nickel-Based Superalloy Sheet

Electrically assisted (EA) forming is a plastic forming technique under the coupling action of multiple energy fields, such as force field, temperature field, and electric field. It is suitable for the forming of difficult-to-deform materials such as nickel-based superalloys. In this paper, uniaxial tensile tests on nickel-based superalloy sheets were carried out using the pulsed current assisted with different parameters. The experimental results show that the flow stress of the material decreased with the increase in the current density under a high-frequency pulsed current, and the Joule heating effect explains the flow stress drop. In the pulsed current application process, the different types of Portevin-Le Chatelier phenomena appeared with the increase in the current density. The decrease in elongation assisted by the pulsed current was explained by analyzing the inhomogeneity of the maximum Joule heating temperature distribution. In addition, the digital image correlation (DIC) analysis was used to analyze the local strain behavior of the pulsed current-assisted tensile process. Under the application of a high-frequency pulse current, the specimen exerted an inhomogeneous temperature increase and local hot pressing stress, which resulted in the inhomogeneous distribution of the local strain.

Effect of electric current on mechanical properties and microstructure of Ti/Al laminated composite during electrically assisted tension

Electrically assisted (EA) forming technology is often applied to difficult to form materials for its convenience and efficiency. As one of the common metal clad plates, explosive welded Ti/Al laminated composite (LC) is hard to form at room temperature (RT). EA forming provides a new idea for Ti/Al LC forming. Explosive welded Ti/Al LC was used as the experimental material to conduct EA tensile experiments with different parameters in this paper. The mechanical properties and microstructure evolution of Ti/Al LC during EA tension were investigated. The flow stress of Ti/Al LC during EA tension was reduced, but the elongation of Ti/Al LC was less than that tension at RT. The reason that induced the fracture in advance was that the local Joule heat temperature was too high. The Ti/Al LC microstructure characterization results showed that dislocation density of matrix diminished, the recrystallization in matrix and atomic diffusion in interface were facilitated. Besides, the high frequency current promoted the transition of Al matrix from ductile fracture to brittle fracture. The primary reason for the decrease of Ti/Al LC flow stress is the decrease of dislocation density in the matrix, and the change of microstructure is also due to dislocation evolution.

Macro-micro behaviors of Ti–22Al–26Nb alloy under near isothermal electrically-assisted tension

To reveal the non-thermal effect of electric current in macro-micro behaviors Ti–22Al–26Nb alloy sheet with bimodal initial structure, electrically-assisted (EA) near isothermal tensile tests and thermally-assisted (TA) tensile tests have been conducted comparatively at equivalent temperatures by adjusting the applied current-time curve. The stress responses, morphological evolution of constituent phases and the phase transformation behaviors have been characterized by means of EBSD and TEM. Result shows that EA tension is more effective in reducing deformation resistance, while TA tension plays a more important role in plasticity enhancement. The overall electrically-induced stress drop in EA tension increases monotonically with current density, but its non-thermal component first decreases with current density and then increases significantly from the critical value of 12.40A/mm2 in EA tension. The variation of the non-thermal stress drop during EA deformation is attributed to the competition between softening effect and strengthening effect of the electric current, viz. electric current causes softening effect by activating dislocation slip and inducing dislocation annihilation on one hand, and the electrically-driven dynamic precipitation of nanoscale O laths and dynamic globularization of O lamellae leads to additional strengthening effect on the other hand. Moreover, electric current promotes the process of O→B2 phase transformation from both thermodynamic and kinetic at 16.01–20.87 A/mm2.

Deformation characteristics and performance evolution of superalloy capillary drawn by electrically assisted microforming

Thin-walled superalloy capillaries are considered the core components of the heat exchanger in the hypersonic vehicle. To achieve the precise and efficient fabrication of capillaries, this study proposes an electrically assisted (EA) microforming process and investigates the deformation characteristics and performance evolution of capillaries under electric current. Experimental results show the EA drawing at 600 °C enhances the grain coordinated deformation capacity and dislocation recovery, while the ultrafast complete recrystallization and gradient grain microstructure are achieved by the EA annealing above 800 °C for 15 s. The microstructural evolution improves ductility and avoids macro defects, which is related to the reduction of activation energy of dislocation and grain boundary motion under the electroplastic mechanisms. In addition, the inhibition of the electric current on the increase in wall thickness is attributed to the increase in friction coefficient and the shedding of the oxide layer, while the electric current improves surface quality by forming ultrafine grains, oxidizing peaks, and healing troughs. Compared with the conventional manufactured capillaries, the surface quality, tensile strength, and elongation of the EA manufactured capillaries with the size of φ0.9 mm × 58 μm are increased by 129.0%, 31.1%, and 9.4%, respectively. A heat exchanger module integrated by the EA manufactured capillaries can cool the 25 m/s airflow from 1000 to 672 °C within 1 ms.

Effect of electric current on formability and microstructure evolution of Cu/Al laminated composite

Cu/Al laminated composite is a kind of material with wide application value, which has attracted the interest of many researchers. Improving the formability of Cu/Al laminated composite is a hot research topic. Electrically assisted manufacturing technology can improve the formability of metal materials, and its application to Cu/Al laminated composite plate is anticipated to improve its formability. In this work, the mechanical properties of Cu/Al laminated composite during electrically assisted (EA) tension were studied, and the effect of electric current on the microstructure evolution of Cu/Al laminated composite was characterized. The results showed that the forming force of Cu/Al laminated composite decreased significantly with the increase of current when the frequency is constant, but the forming limit decreased. The reason was that the increase in current density led to local overheating, which eventually led to premature fracture of the specimen. Under low frequency conditions, the elongation of Cu/Al laminated composite decreased moderately, but the forming force decreased obviously. The microstructure characterization results showed that the electric current circulated only in the Cu matrix during the EA tension. The electric current lowered the dislocation density of Cu layer and promoted dislocation unwinding. The proportion of recrystallized grains in the Cu layer increased slightly under the action of current. In addition, the current accelerated the change of texture type of Cu layer and the texture strength decreased.

An experimental and modelling study of cyclic tension-compression behavior of AA7075-T6 under electrically-assisted condition

Electrically-assisted (EA) forming is an effective method to improve forming quality of sheet metal. In order to reveal the effects of current on material flow behavior under complex strain paths and develop corresponding constitutive model, the EA tension-compression cyclic loading tests with particularly designed setup were carried out. Then, the effects of current on the elastic modulus degradation and cyclic deformation were investigated. Further, corresponding modulus degradation model and constitutive model were developed. The results showed that the flow stress under EA uniaxial tension was lower than that under warm uniaxial tension. Moreover, the current-induced growth of precipitate and the decrease of dislocation occur under EA uniaxial tension. Regarding the EA cyclic deformation behavior, the elastic modulus decreases with the increase of plastic strain, temperature and current density, which is described by a proposed modified modulus degradation model. The Bauschinger effect and permanent softening effect are weakened with the increase of temperature and current density. The asymmetric tension-compression behavior becomes more obvious with the increase of temperature and current density. Based on above results, a modified Y-U model was established and verified with EA draw-bending process. The above research work can provide some research basis for the application of electrically-assisted forming.

Experimental Investigation on the Effect of Electrically Assisted Rapid Heating in Bulk Metal Forming

Many industries utilize hot metal forming to reduce forming forces and material flow issues. In this study, electrically assisted (EA) rapid heating is used in direct comparison to conventional heating methods. Three materials were investigated: AISI 4340, Al-7075-T6, and Ti-6Al-4V. Samples were heated at an approximate rate of 100 °C/s before applying compressive loads, simulating forging or other bulk deformation processes. Afterwards, samples were prepared for further microstructure evaluation. It was observed that high-rate temperature increase resulted in some developments in the microstructure and phases, as seen in AISI 4330, for example. Additionally, the effect of electricity was noticed to have a significant impact on flow stresses, as observed in many of the compression tests, immediately following the rapid heating process. Experiments and images from optical microscopy show that samples experienced drastic and immediate decrease in flow stress at all temperatures when using the EA rapid heating method versus the conventional method with seemingly no change to the material microstructure. This may be explained by the lack of phase changes at lower temperatures combined with the effect of electricity. Further investigation into the changes in micro-porosity, intermetallic phases, and changes in precipitates are suggested to supplement the current understanding of the drastic stress drop caused by passing electrical currents through metals.

Fracture mechanism of electrically-assisted micro-tension in nanostructured titanium using synchrotron radiation X-ray tomography

A coarse-grained (CG) Ti with an average grain size of ∼50 μm was processed by high-pressure torsion (HPT) under a pressure of 6.0 GPa through 10 turns at room temperature (RT) to produce nanostructured titanium (Nano-Ti) with an average grain size of ∼95 nm. Electrically-assisted (EA) micro-tensions of CG-Ti and Nano-Ti were performed using pulsed unidirectional current with a current density of 750 A/mm2, pulse width of 10−4 s. The stress drop is higher for Nano-Ti compared with CG-Ti. The results of fractograph observations show many cleavage steps in Nano-Ti while the CG-Ti is dominated by dimples. The spatial distribution of voids in tensile specimens was revealed after testing using synchrotron radiation X-ray tomography. The results demonstrate that applying a pulse current can effectively reduce the number and volume of voids before fracture. A model is presented describing the fracture mechanism of CG-Ti and Nano-Ti during EA micro-tension.