Conventional Sheet Research Articles

A 0.14 THz Angular Radial Extended Interaction Oscillator

A 0.14 THz angular radial extended interaction oscillator (AREIO) is proposed in this article. The characteristic impedance (<inline-formula> <tex-math notation="LaTeX">${R}/{Q}$ </tex-math></inline-formula>), the normalized equivalent conductance (<inline-formula> <tex-math notation="LaTeX">${g}_{e}$ </tex-math></inline-formula>), and the starting condition of the cavity are calculated and analyzed. When the metal loss is considered, in order to achieve the starting condition, it is necessary to increase the period length (<inline-formula> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula>) to improve <inline-formula> <tex-math notation="LaTeX">$\vert {g}_{e}\vert $ </tex-math></inline-formula>. The performance of the AREIO is simulated by particle-in-cell (PIC). The voltage tuning range and the output performance under different angular angles of the cavity are investigated. Under the condition of lossless and the electron beam of 11.5 kV and 1.5 A, the peak output power and interaction efficiency of the AREIO (8&#x00B0;) are 5.46 kW and 31.7&#x0025;, which have increased by 24.1&#x0025; and 6.2&#x0025; in comparison with conventional sheet beam. When considering the metal loss, the optimal angular angle will decrease to 4&#x00B0;. In addition, the cavity is fabricated and tested, and the results of <inline-formula> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> in operating mode are consistent with the simulation.

Mechanism of dislocation promoting Al13Fe4 precipitation during friction stir-assisted incremental sheet forming in AA5052 sheet

The precipitation behavior of Al13Fe4 in AA5052 sheet during friction stir-assisted incremental sheet forming (FS-ISF) is investigated in the present work. It is found that the sizes of both incoherent and semi-coherent precipitates enlarge, and their contents increase with the increasing temperature caused by the high-speed rotation of the tool. Dense dislocations emerge and interact around these precipitates. Transmission electron microscopy (TEM) analysis reveals that dislocations can induce precipitation through prompting atomic segregations of Fe and Al elements. The strength of FS-ISFed AA5052 is further enhanced compared with conventional incremental sheet forming at room temperature (RT-ISF).

Challenges in Tribometry for Warm and Hot Sheet Metal Forming of High Strength Aluminum with Tool Lubrication

For conventional sheet metal forming at room temperature, numerous tribometers were developed in the 20th century. At the present state of the art, unsolved issues for tribometry remain for temperature-supported forming processes of high strength aluminum (e.g. EN AW-7075), in which the sheet is heated to temperatures between 200 and 480 °C. The tribological design of these processes remains a major challenge, which needs to be addressed by investigations with adapted tribometers. In this study, a recently adapted strip drawing test for aluminum warm and hot forming is presented – including a newly developed strip heating unit, a die lubrication system and a die tempering system for efficient tribological testing. The contribution is completed with both, experimental results and a numerical investigation of temperature gradients in the strip drawing test. Finally, it is discussed whether transient process conditions of non-isothermal forming processes with die lubrication should be considered in tribometers for warm and hot sheet metal forming.

Blast protection of steel reinforced concrete structures using composite foam-core sacrificial cladding

The current investigation presents the effectiveness of a composite foam-core sacrificial cladding for blast protection of steel Reinforced Concrete (RC) structures using explicit finite element analysis in LS-DYNA. Fluid-structure interaction (FSI) methodology was employed to obtain the deformation and damage of steel-reinforced concrete columns under explosive impact. The purpose of this research is to demonstrate the effectiveness of an array of PVC foam cones used as the back layer of a composite sacrificial cladding to protect RC structures from close-in explosions. Simulations were carried out for several blast loading conditions by changing the explosive mass and the stand-off distance. The study was divided into two parts; first, the response of the RC column under blast loading was analyzed and, afterwards, the column was re-examined with the use of composite sacrificial cladding attached on its façade. Based on the analyses, it was proved that the foam conical-array configuration developed in this work that consists the rear layer of the composite sacrificial cladding, reduces the peak force applied on the concrete structure by 50% compared against the same protective configuration, where a uniform rear foam layer of the same thickness was used, whereas it is by 71% lighter than the conventional sheet core.

Bending properties of sandwich sheets with metallic face sheets and additively manufactured 3D CFRP lattice cores

• Sandwich sheets with representative shell-lattice, truss-lattice and plate-lattice cores are proposed. • Effects of core topologies on mechanical properties and bendability of sandwich sheets are clarified. • Theoretical predictions of failure modes during bending of sandwich sheets with 3D lattice cores. • Bendable sandwich sheets with 3D lattice cores are successfully designed and produced. • Bendable sandwich sheets with multifunctional application potentials. To improve structural performance, bendability and potential functionality of metal-based sandwich sheets, the 3D lattice cores were sandwiched between thin metallic face sheets. The bending properties of sandwich sheets with 3D printed carbon fiber reinforced plastic (CFRP) lattice cores originating from basic topologies of spherical shell, tetrahedral truss and tetrahedral plate were systematically investigated. The effects of core topologies, core relative densities, core heights, face sheet thicknesses on structural properties were clarified. The common failure modes during bending of sandwich sheets, such as face buckling and shear failure of core, were deeply investigated by theoretical models and experimental tests. At a prescribed radius of 60 mm, the sandwich sheets with the bilayered dome, octet truss and plate lattice cores of relative density of 50 %, height of 6 mm and face sheet thickness of 0.5 mm are bendable. This study demonstrates the feasibility of design and production of bendable sandwich sheets with 3D lattice cores based on the theoretical and experimental validations. The designed bendable sandwich sheets can be adopted to replace conventional heavy monolithic metal sheets in various engineering applications, which is anticipated to fulfill the high demand for lightweight functional materials.

Measurement Analysis and Improvement of Vibroacoustic Characteristics of Amorphous Alloy Transformer

The amorphous alloy transformer has a smaller coercive force and lower specific iron loss. It precedes the conventional silicon steel sheet transformer from the perspective of energy conservation. However, amorphous alloy material has a more significant magnetostriction coefficient, resulting in stronger vibration and acoustic noise. This paper investigates the measurement, analysis, and improvement of vibroacoustic characteristics of one three-phase, four-frame amorphous alloy distribution transformer to reduce environment noise pollution. This study adopts a coupling analysis method of magnetic–force–acoustic multi-physical fields to analyze the vibroacoustic characteristics. It then introduces a novel combination method of magnetic field analysis and an electric circuit to improve the efficiency of magnetic field analysis. This new combination method can greatly reduce the solution time of multiple physical fields through comparison with the traditional field-circuit coupling method. Different from other studies, this paper studies the acoustic and vibration characteristics of an amorphous alloy transformer under both no-load and load conditions. It is found that the load vibration noise of an amorphous transformer is more severe than that of a traditional silicon steel transformer. Accordingly, the study measures the vibroacoustic characteristic with different excitations and load levels under different working conditions to verify the numerical analysis method. Furthermore, according to the analysis results, this paper suggests a few vibration and noise control strategies. In conclusion, the paper deduces an essential basis for exploring strategies of vibration reduction and noise control for amorphous alloy distribution transformers.

Finite Element Analysis and Polarization Test of IDEs Piezoelectric Actuator.

A new type of actuator is presented in the paper that integrates the IDEs into a conventional piezoelectric sheet. The electrodes and polarization play a key role in the strain. Adopting constitutive equations of piezoelectric theory and variation principles in elasticity theory, the piezoelectric component dynamic equation was deduced. Several finite element models of the IDEs piezoelectric actuator were established in ANSYS. The effect of branch electrodes on the strain of the actuator was analyzed. The results show that the strain can be bigger than that of the conventional piezoelectric sheet by decreasing the gap and increasing the width of electrodes. According to the FEM result, some IDEs piezoelectric actuators were prepared. The distribution of the static electric field inside the actuator was researched to determine the polarization voltage. The 2671 high voltage power and DU-20 temperature-controlled oil bath was applied to explore the polarization process. The effect of the voltage, time and temperature on the strain of the actuator was researched by a TF2000 and SIOS laser interferometer. The results show that the optimum polarization is 800 V, for 60 min and at 150 °C. The strain of the IDEs piezoelectric actuator is 1.87 times that of the conventional piezoelectric actuator. The actuators could prove to be helpful applications for micro-nano devices.

Front Cover: Electrospun Tungsten‐Polyurethane Composite Nanofiber Mats for Medical Radiation‐Shielding Applications (ChemNanoMat 2/2022)

An electrospinning strategy was used to manufacture composite mats consisting of nontoxic tungsten powder with a content up to 500 wt% and inexpensive polyurethane (PU) nanofibers for X-ray shielding applications. The electrospun composite mats have X-ray mass attenuation coefficients comparable to conventional sheets prepared by a wet-casting method, but their gas permeability and flexibility are almost two and five times higher, respectively, than those of conventional mats. The successful incorporation of tungsten powder into the electrospun PU nanofibers well beyond their typical limits can allow for the development of nontoxic shielding materials with controlled structural and physical properties. More information can be found in the Full Paper by Hongsik Byun, Sung-Yul Kim et al.

Impact of digital boards on hand and neck muscle activity during online teaching process.

Academicians across the globe due to Covid 19 shifted to online teaching as a mainstream method by replacing the chalk and talk method. The main objective of this study is to find the impact of different sizes of digital boards used for online teaching on muscle activity and muscle fatigue, and then results are compared with conventional writing. Initially, a questionnaire survey is conducted among 100 college professors about the issue they faced while using online teaching methods. Experimental analysis are then conducted using electromyography sensor (sEMG) among ten college professors and their muscle activity on the dominant hand and neck while writing on two commercially available digital boards namely Type 1 (small writing area) and Type 2 (large writing area). Four muscles namely Flexor carpi radialis, Extensor carpi radialis, Biceps brachii, and Sternocleidomastoid (SCM) are chosen for the study. The results are then compared with muscle activity while writing on conventional A4 sheets. Normalized root mean square (RMS) is used to assess the muscle activity and the trend line of MPF value is utilized to assess the muscle fatigue. The results show that SCM muscle has more muscle activation compared to other selected muscles followed by flexor carpi radialis. Subjective analysis is carried out using the Borg scale, which has reported that Type 2 digital board having larger working area was preferred by the participants as it reduces muscle fatigue.

Performance Improvement of Supercapacitor Materials with Crushed 3D Structured Graphene

Electrochemical capacitor devices with conventional 2D-graphene sheets (2D-rGO) often demonstrate poor performance, especially in cyclability due to the lamellar stacking and agglomeration of the electrode materials. Herein, we have proposed that crushed 3D-graphene (c-3D-rGO) can overcome the limitations. A simplistic way to prepare 3D-crushed graphene structures has been presented utilizing metal rGO core–shell (Ni@rGO) followed by acid leaching. The electrochemical performances of the prepared c-3D-rGO were evaluated as capacitor material using a three-electrode system with aqueous 0.5 M Na2SO4 solution through cyclic voltammetry and galvanostatic charge-discharge measurements. In addition, 2D-rGO was separately prepared to compare the performance with 3D-crushed graphene structures. It has been observed that the calculated specific capacitance (C sp) value of the prepared c-3D-rGO was 335 Fg−1 at a current density of 0.15 Ag−1, which was about three times higher than that of the 2D-rGO. Furthermore, the c-3D-rGO electrode retained 100% capacitance of its initial value after 10000 cycles, demonstrating the material’s excellent electrochemical stability. Again, to show the performance in hybrid capacitors, manganese oxide (MnOx) was incorporated onto 2D-rGO and c-3D-rGO. The presence of MnOx significantly improved the capacitive performance of 2D-rGO and c-3D-rGO. The C sp value (532 Fg−1) of the prepared 3D-rGO/MnOx was much higher than that of 2D-rGO/MnOx (284 Fg−1) at a current density of 0.15 Ag−1. The c-3D-rGO/MnOx composite materials also showed good cyclic stability. The high-performance of the c-3D-rGO could be correlated with the structural features of uneven defects and 3D-voids present in the material, which maintained a low level of aggregation. This study is expected to broaden the application of graphene for commercial use.

Toolpath Planning for Manufacturing of Complex Parts Through Incremental Sheet Forming

Abstract Incremental sheet forming (ISF) offers great flexibility in producing complex sheet parts as compared with conventional sheet forming processes where part-specific die sets are required to form a product. While there are many potential applications of ISF in various industries, toolpath planning for multifeature parts remains a leading challenge hindering the wide adoption of ISF. In this study, a criterion based on the gradient of the target surface was established for determining the appropriate feature forming sequence. Based on the analysis of the gradients of the surface, multifeature geometries were separated into two categories: “plane-referenced” and “surface-referenced.” Experimental investigations of forming a multifeature air intake as an example were carried out to demonstrate the proposed criterion and feature forming sequence. The results show that the choice of the optimal sequence depends on the type of geometry formed. The proposed criterion extends existing toolpath strategies for relatively regular geometries, where features are formed from flat or inclined bases to more complex geometries with features on a curved basis. This work will be of interest to both design and manufacturing communities.

Formability analysis on titanium grade2 sheets in multi point incremental forming process

Single point incremental forming (SPIF) is found to be a good alternative to the conventional sheet metal forming techniques and is suitable for the production of small batch and custom made parts. The major disadvantage of the SPIF process is the time required to complete the job. In this work, a multipoint incremental forming (MPIF) tool which gives better contact on the workpiece and completes the job in less time compared to SPIF is used. The present work investigates the formability and failure mechanism of titanium grade 2 sheets in MPIF process. The major operating parameters selected for the study are step depth, feed rate and speed. Formability of titanium grade 2 sheets increases with decrease in speed and step depth while keeping the feed rate constant. Based on the results it was found that the MPIF process can be effectively utilized for forming sheet metal parts.

A Comparative Investigation of Conventional and Hammering-Assisted Incremental Sheet Forming Processes for AA1050 H14 Sheets

Incremental Sheet Forming (ISF) is emerging as one of the popular dieless forming processes for the small-sized batch production of sheet metal components. However, the parts formed by the ISF process suffer from poor surface finish, geometric inaccuracy, and non-uniform thinning, which leads to poor part characteristics. Hammering, on the other hand, plays an important role in relieving residual stresses, and thus enhances the material properties through a change in grain structure. A few studies based on shot peening, one of the types of hammering operation, revealed that shot peening can produce nanostructure surfaces with different characteristics. This paper introduces a novel process, named the Incremental Sheet Hammering (ISH) process, i.e., integration of incremental sheet forming (ISF) process and hammering to improve the efficacy of the ISF process. Controlled hammering in the ISF process causes an alternating motion at the tool-sheet interface in the local deformation zone. This motion leads to enhanced material flow and subsequent improvement in the surface finish. Typical toolpath strategies are incorporated to impart the tool movement. The mechanics of the process is further explored through explicit-dynamic numerical models and experimental investigations on 1 mm thick AA1050 sheets. The varying wall angle truncated cone (VWATC) and constant wall angle truncated cone (CWATC) test geometries are identified to compare the ISF and ISH processes. The results indicate that the formability is improved in terms of wall angle, forming depth and forming limits. Further, ISF and ISH processes are compared based on the numerical and experimental results. The indicative statistical analysis is performed which shows that the ISH process would lead to an overall 10.99% improvement in the quality of the parts primarily in the surface finish and forming forces.

Abstract 9483: Detection of Lipids by Near-infrared Spectroscopy in Calcified Coronary Plaques Containing Nodular Calcification: Insights from Multimodality Imaging and Histopathologic Assessment

Introduction: Detection of lipids in coronary plaques by near-infrared spectroscopy (NIRS) is based on the absorbance of NIR light and can predict future coronary events. It remains unclear whether the ability of NIRS can be applied to calcified lesions containing nodular calcification (Ca), which potentially scatters NIR light. Hypothesis: We hypothesized that detection of lipids by NIRS is overestimated in calcified coronary plaques containing nodular Ca compared with those with conventional sheet Ca. Methods: We investigated a total of 322 culprit lesions from 283 patients with CAD who underwent both NIRS-IVUS and OCT. After identifying nodular and sheet Ca on cross-sectional images in both IVUS and OCT, the presence of NIRS signals behind Ca was determined and quantified as lipid arc divided by Ca arc. In addition, consecutive 30 autopsy cases with CAD were pathologically assessed for the prevalence of lipids within nodular and sheet Ca. Results: Among 8850 cross-sections in vivo, 382 nodular and 1190 sheet Ca were identified. Generalized estimating equation modeling showed the presence of NIRS signals was more frequent in nodular Ca (79% vs. 64%, p=0.001) and the extent of NIRS signals was greater in nodular than sheet Ca (70% vs. 23%, p&lt;0.001, Figure). Multivariate analysis identified nodular Ca as an independent determinant of positive NIRS signals (Table). Among 2467 histologic coronary sections evaluated, 55 nodular and 456 sheet Ca were identified. In contrast to imaging assessment, pathology showed that the prevalence of lipids within nodular Ca was extremely low; only 4%, and less than that in sheet Ca (20%, p=0.015). Conclusions: Majority of nodular Ca exhibited positive NIRS signals, whereas lipids within nodular Ca was extremely rare in pathologic assessment. The discrepancy suggests that NIR light-based detection of lipids is overestimated in nodular Ca, which needs to be considered when interpreting co-localized lipids in calcified coronary plaques.

Ohmic Contact to Two-Dimensional Nanofabricated Silicon Structures with a Two-Probe Scanning Tunneling Microscope.

We used multiprobe scanning tunneling microscope (STM) to fabricate and electrically characterize nanostructures on Si surfaces. We overcame resistive contacts by using field evaporation to clean tip apexes in order to create Ohmic contact with the Si surface states on a Si substrate. A two-probe (2P-) STM with Ohmic contact allowed for measurement at very low bias, limiting conduction through space-charge layer and bulk states. The Ohmic 2P-STM measurement clarified the surface conductivity of the Si(111)-(7 × 7) surface. We also confirmed that Ohmic 2P-STM can be replaced with more convenient Ohmic one-probe STM for the conductance measurements on the Si surface. We prepared nanostructures using STM lithography to define electronically isolated two-dimensional (2D) regions with various aspect ratios. Their surface conduction properties are described well by the conventional sheet model, proving the diffusive 2D conduction on the Si surface. Constrictions and breaks in 2D structures were also evaluated. Ohmic 2P-STM will be helpful for the investigation of exploratory atomic-scale circuitry or cutting-edge materials sciences.

Geometric mechanics of folded kirigami structures with tunable bandgap

We study the geometric mechanics and tunable band structures of a recently developed new class of folded kirigami structures through experiments, theoretical modeling, and numerical simulation. The folded kirigami structures with square and triangular cut patterns are constructed by replacing the point hinge in conventional kirigami sheets with a 3D folding hinge. We find that the folded design can effectively overcome the polarization constraint in the conventional kirigami sheets without folds. Specially, as the creases continue to fold from 0° to 180°, the folded design achieves a unique polarization switch, i.e., the structure expands first and then shrinks to be even smaller than that before folding. Geometric mechanics models are developed to predict how the geometry of the folding hinges determines both the shape changes and structural responses, including nominal strains, polarization switch, Poisson’s ratio, folding rate, surface porosity, and structural stiffness. The models are validated through related experiments. We find that the observed polarization switch corresponds to both the peak nominal strains and stiffness singularity in the structures. Lastly, we numerically explore its shape change induced tunable phononic bandgap structures. We find that for special designs with polarization switch, it leads to symmetric bandgap structures changing with the folding angle. This work could find potential applications in designing kirigami metamaterials, shape-morphing materials, and phononic materials with tunable band structures.

Design for FDM of flexible tooling for manufacturing aeronautical components by incremental sheet forming

Nowadays, industrial production is required to reduce industrialization times and development costs for new products while maintaining high quality standards. In this context, the development of new flexible manufacturing technologies has gained relevance in the last few years. The use of Fused Deposition Modelling (FDM) additive technique has been recently proposed in different industrial sectors for manufacturing rapid tooling (dies) to be used in conventional sheet metal stamping or stretching processes with a significant decrease in costs and time savings. On the other hand, Incremental Sheet Forming (ISF) technology is characterized by an enhanced formability of the parts thus manufactured as well as for the need of a small number of tooling, reducing costs compared to conventional processes such as hydroforming or stamping. In particular, its simplest variant, Single-Point Incremental Forming (SPIF) requires the use of backing plates, which do not require tight tolerances as their only function is to collaborate in the deformation process acting as a support point. Furthermore, the strength requirements are also not a limitation since the forces involved in SPIF are very small given the local nature of the deformation. In this context, the main objective of this work is the design of a modular tooling system, manufactured using the FDM additive technique, that allows the flexible manufacturing of different aeronautical components by SPIF.

Impact of radiation to the eye of operators during endo-cardiovascular surgery and the importance of protection

To verify the amount of radiation exposure to the eye of operators during endocardiovascular surgery (ECVS) in hybrid operating room (HOR), which increases the risk of cataracts in surgeons. Fifty cases of ECVS (including 36 transcatheter aortic valve implantation and 14 thoracic endovascular repair) using the transfemoral approach performed from February 2020 to July 2020 were included. A measurement device was attached to the left side of the head of the operators and their assistants to measure the cumulative dose (CD) of intraoperative radiation exposure. The subjects were divided into the control group (Group C, n = 26), received conventional protection using the protective curtain in HOR and the protected group (Group R, n = 24), received conventional protection and protection sheet. The normalized CD by dose area product (CD/DAP) was evaluated. The CD/DAP of the surgeons was significantly decreased in Group R, averaging at 5.97 μSV/Gycm2 in Group C group and 4.40 μSV/Gycm2 in Group R (p < 0.01). Moreover, CD/DAP of the assistant was significantly reduced in the Group R, with an average of 1.87 μSV/Gycm2 in the Group C and 1.01 μSV/Gycm2 in Group R (p < 0.01). The radiation exposure to the surgeon's eye could be significantly reduced by protection sheet.

PEEK based cranial reconstruction using thermal assisted incremental sheet forming

Compared to conventional sheet forming operations, incremental sheet forming (ISF) is a flexible forming technique that can achieve higher formability in terms of localized deformation. Due to excellent mechanical properties and X-ray penetration, polyether-ether-ketone (PEEK) is an ideal alternative to titanium alloy and stainless steel in orthopedic applications. In this study, a 3-axis desktop manufacturing system has been fabricated to investigate the temperature-dependent formability of PEEK in terms of manufacturing the cranial plate by using the ISF technique. Meanwhile, the forming force, temperature distribution, geometrical accuracy, and thermal properties were obtained and analyzed. The findings indicate that the ISF technique provides technological and economic advantages in cranial reconstruction by using PEEK.

Design and Microfabrication of an Interaction Circuit for a 0.3-THz Sheet Beam Extended Interaction Oscillator With Multiple-Mode Operation

Normally, the conventional sheet beam extended interaction oscillator (SB-EIO) operates in a single mode and has a narrow tunable bandwidth. To broaden the tunable bandwidth, the concept of multiple-mode operation is proposed and a 0.3-THz ladder-shaped interaction circuit is designed as described in this article. The interaction circuit was manufactured by using the computer numerical control milling technique and cold tested by using a vector network analyzer. Measured and simulated results were in good agreement with each other. Beam-wave interaction simulations with the ohmic loss being taken into account verified the feasibility of the multiple-mode operation and demonstrated that the SB-EIO produced an output power of >91 W in the frequency range of 293.7–294.9 GHz. Compared with the single-mode SB-EIO, the tunable bandwidth of the multiple-mode SB-EIO has increased from 0.3 to 1.2 GHz.