Influence of processing parameters on forming quality of non-circular spinning

Processing parameters have great influence on forming quality of non-circular spinning. Finite element simulation model of non-circular spinning for the three straight-edge round-corner cross-section (TSRC) hollow-part was established. Variation rules of thickness and springback of TSRC spun workpiece under different processing parameters were obtained by means of orthogonal test as well as the software MSC.MARC. The results show that the influences of the relative clearance ΔC and the feed ratio of roller fz on the maximum wall thickness thinning ratio δt are obvious, and the influences of n and Dr are slight; the influences of the nose radius of roller rρ on the springback angle Δα is the most obvious, and the influences of ΔC and Dr are slight

Measurement of Full-field Ductile Damage based on Resistance Method

AbstractThe measurement of damage evolution in metal materials during plastic deformation accurately and conveniently remains a challenging problem for current research. In this study, a convenient ductile damage measurement procedure is proposed. The damage value can be evaluated by continuous uniaxial tension with the digital image correlation and direct current potential drop techniques. The development of methodology and experimental setups is discussed in details. The ductile damage values obtained by the proposed approach are consistent with those obtained by the micro-hardness method. The full-field damage distribution can also be calculated besides the ductile damage evolution

Electrospun 1D and 2D Carbon and Polyvinylidene Fluoride (PVDF) Piezoelectric Nanocomposites

Piezoelectric nanocomposite fibrous membranes consisting of polymer polyvinylidene fluoride (PVDF) as matrix and incorporating 1D carbon nanotubes (CNTs) and 2D graphene oxide (GO) were prepared using an electrospinning process. The influence of the filler type, loading, and dispersion status on the total PVDF crystallinity (X_{c}); Piezoelectric nanocomposite fibrous membranes consisting of polymer polyvinylidene fluoride (PVDF) as matrix and incorporating 1D carbon nanotubes (CNTs) and 2D graphene oxide (GO) were prepared using an electrospinning process. The influence of the filler type, loading, and dispersion status on the total PVDF crystallinity (F_{β}); the volume fraction of β phase in the samples (v_{β}); and the piezoelectric coefficient d_{33} were investigated. The V_{β} is used to assess the formation of β phase for the first time, which considered the combined influence of fillers on X_{c} and F_{β}, and is more practical than other investigations using only F_{β} for the assessment. The inclusion of all types of carbon fillers had resulted in a considerable reduction in the X_{c} compared with the neat PVDF, and the X_{c} decreased with the CNT loading while increased with the GO loading. The addition of CNT and GO had also reduced the F_{β} compared with the neat PVDF, and F_{β} increased with CNT loading while decreased as GO loading increased. The v_{β} is significantly reduced by the addition of CNT and GO, while v_{β} decreases with CNT and GO loading increases. Since the calculation of V_{β} has considered the combined influence of fillers on X_{c} and F_{β}, both of which were reduced by incorporating CNT and GO, the reduction of v_{β} was expected. The v_{β} of the PVDF/CNT composites were higher than that of the PVDF/GO composites. Although it is generally anticipated that d_{33} increases with v_{β}, it is observed that in the presence of CNT, d_{33} is dominated by the increase in electric conductivity of the composites during and after the electrospinning process, giving rise to transport of charges, produced by β crystals within the fiber to the surface of the sample. In addition, the 1D CNTs may have promoted the orientation of β crystals in the d_{33} direction, therefore, enhancing the d_{33} of the composites despite the hindrance of the β-phase formation (i.e., the reduction of v_{β}). Adding CNTs can also improve piezoelectricity through interfacial polarization, which increases the dielectric constant of composite (mobile charges within CNTs facilitate composite polarization). CNT loadings higher than 0.01 wt.% are sufficient to outperform the neat PVDF, and d_{33} becomes 59.7% higher than the neat PVDF at 0.03 wt.% loading, but only GO loadings of 0.5 wt.% achieved comparable d_{33} to the neat PVDF; further increase in GO loading had resulted in a decline in d_{33}. The low conductivity of GO, the influence of flocculation, and the lower aspect ratio compared with CNT may result in lower electron transfer and less orientation of the β-phase polycrystalline. The d_{33} of the PVDF/CNT composites is higher than that of the PVDF/GO composites despite much higher loading of GO. This study aims to contribute to the development of PVDF nanocomposites in piezoelectric energy harvesting applications (e.g., self-powered biosensors and wireless sensor networks)

New forming method of manufacturing cylindrical parts with nano/ultrafine grained structures by power spinning based on small plastic strains

A new spinning method to manufacture the cylindrical parts with nano/ultrafine grained structures is proposed, which consists of quenching, power spinning and recrystallization annealing. The microstructural evolution during the different process stages and macroforming quality of the spun parts made of ASTM 1020 steel are investigated. The results show that the microstructures of the ferrites and pearlites in the ASTM 1020 steel are transformed to the lath martensites after quenching. The martensite laths obtained by quenching are refined to 87 nm and a small amount of nanoscale deformation twins with an average thickness of 20 nm is generated after performing a 3-pass stagger spinning with 55% thinning ratio of wall thickness, where the equivalent strain required is only 0.92. The equiaxial ferritic grains with an average size of 160 nm and nano-carbides are generated by subsequent recrystallization annealing at 480°C for 30 min. The spun parts with high dimensional precision and low surface roughness are obtained by the forming method developed in this work, combining quenching with 3-pass stagger spinning and recrystallization annealing

Influence of Surface-profile and Movement-path of Roller on Thickness Thinning during Multi-pass Deep Drawing Spinning

Over thinning is a serious defect influencing the forming quality of spun workpiece during multi-pass deep drawing spinning. Surface-profile and movement-path of roller are the key factors influencing the thinning ratio of wall thickness of spun workpiece. The influence of surface-profile and movement-path of roller on thickness thinning were studied based on numerical simulation and experimental research, four groups of forming experiments were carried out under the combination of the different surface-profile of roller (R12 and R25-12) and movement-path of roller (spinning from the bottom of the blank and spinning from the middle of the blank). The results show that both the surface-profile and movement-path of roller have great influence on wall thickness thinning during multi-pass deep drawing spinning; and compared with the movement-path of roller, the influence of surface-profile of roller is more significant. The experimental results conform well to the simulation ones. It indicates that the FEA model established is reasonable and reliable

Vibration Control of a High-Speed Precision Servo Numerically Controlled Punching Press: Multidomain Simulation and Experiments

A three-degree-of-freedom mathematical vibration model of a high-speed punching press was developed in order to explore the vibration modes of the punching press. A multidomain model of the punching press was established to predict the kinematic state during different conditions, as well as the effects of load fluctuation on the motor speed. Experimental measurements of the acceleration of the punching press were carried out. The results comparison reveals that the multidomain model is consistent with the vibration model and the experimental measurements. Modal analysis and structure modification of the punching press were conducted. The foundation at the base of the punching press was improved against excess of vibration. The effects of the dimensions of the foundation on the vibration were discussed with the aid of the multidomain model. Finally, proper foundation design, able to reduce the vibration, was obtained

Influence of Surface-profile and Movement-path of Roller on Thickness Thinning during Multi-pass Deep Drawing Spinning

Over thinning is a serious defect influencing the forming quality of spun workpiece during multi-pass deep drawing spinning. Surface-profile and movement-path of roller are the key factors influencing the thinning ratio of wall thickness of spun workpiece. The influence of surface-profile and movement-path of roller on thickness thinning were studied based on numerical simulation and experimental research, four groups of forming experiments were carried out under the combination of the different surface-profile of roller (R12 and R25-12) and movement-path of roller (spinning from the bottom of the blank and spinning from the middle of the blank). The results show that both the surface-profile and movement-path of roller have great influence on wall thickness thinning during multi-pass deep drawing spinning; and compared with the movement-path of roller, the influence of surface-profile of roller is more significant. The experimental results conform well to the simulation ones. It indicates that the FEA model established is reasonable and reliable

Research on Formation Conditions of the Ultrafine-Grained Structure of the Cylindrical Parts Manufactured by Power Spinning Based on Small Strains

Two different methods, power spinning and annealing (PSA), quenching and power spinning followed by annealing (QPSA), for manufacturing the cylindrical parts with ultrafine-grained (UFG) structure were reviewed, the dislocation density and microstructural evolution during the two different processes of PSA and QPSA were further studied. The results show that the required strains for obtaining the UFG structure by power spinning is only 0.92 when the initial microstructure of the material is in the phase of lath martensite. The dislocation density and storage energy are increased to 10 times that of the blank after quenching and power spinning and decreased to the level of the blank after recrystallization annealing. Microstructures with fine grain size after quenching, storage energy of 1.8 × 105 kJ/m3 obtained after power spinning and second phase particle with nano-scale precipitated during annealing are the necessary formation conditions for manufacturing the cylindrical parts with UFG structure based on small strains. Compared with the original tubular blank, the mechanical properties of the spun parts with UFG structure improves significantly. The tensile strength and hardness of the spun parts manufactured by QPSA method is 815 MPa and 305 HV, respectively, and the elongation is 17.5%

Investigation on dimensional accuracy and mechanical properties of cylindrical parts by flow forming

The high dimensional accuracy and excellent mechanical properties have become two most important requirements for structural components. In this paper, experiments using two spinning methods, stagger spinning and counter-roller spinning, were carried out under different thinning ratio of wall thickness of spun parts. The influence of spinning methods and total thinning ratio of wall thickness on the dimensional accuracy and mechanical properties of the!spun parts were studied. It shows that the wall thickness deviation and ovality of the spun parts are closely related to the spinning method and the total thinning ratio of wall thickness. The hardness of the spun parts increases with the increasing of the total thinning ratio, and the hardness along the thickness direction of the spun parts manufactured by counter-roller spinning is more homogeneous than that of the stagger spinning. The strength and the elongation of the spun parts are mainly influenced by the total thinning ratio, with little relevance to the spinning method

The complete chloroplast genome of Aster sampsonii (Hance) Hemsl, a perennial herb

Aster sampsonii (Hance) Hemsl is endemic to China. The complete chloroplast genome of Aster sampsonii was studied here. The genome was 152,686 base pair (bp) in length, containing a large single-copy (LSC) region of 84,345 bp, a small single-copy region (SSC) of 18,249 bp and a pair of inverted repeats (IRs) of 25,046 bp. It contains 132 unique genes, including 86 protein-coding genes, 36 transfer RNA (tRNA) genes, and eight ribosomal RNA (rRNA) genes. The GC content of the complete chloroplast genome sequence was 37.3%. Phylogenetic analyses using complete chloroplast genomes showed that Aster sampsonii is most closely related to Aster hypoleucus (NC_046503.1)