Drawing Direction Research Articles

Microstructure, texture, and mechanical properties of multi-pass cold drawn Mg–xZn alloy wire

We performed multiple-pass cold drawing for Mg-4.0 wt%Zn (Z4) and Mg-6.0 wt%Zn (Z6) which showed a preferable drawing deformability of ∼76 and 69 % accumulative true strain (ATS), respectively, at room temperature. Zn addition into pure Mg caused the microstructure refinement and the strengthening of Mg alloy, while the ductility of Mg alloys decreased with increasing Zn content. Moreover, the microstructure of as-drawn Z4 wire with larger ATS showed fibrous morphology, and the grains were elongated along the drawing direction (DD) but the grain boundaries could still be distinguished in wires of Z6 alloy. Based on texture analysis, the non-basal texture of Z4 and Z6 gradually increased with cold drawing. Eventually, the texture component of both Z4 and Z6 wires transformed from as-extruded basal texture to obvious <101¯0> fiber texture with <101¯0> parallel to the DD. The difference was that, besides the formation of a main basal texture, a weaker non-basal texture also appeared in as-extruded Z6 alloy with a higher Zn content. The addition of Zn promoted the formation of non-basal texture.

Approaches to Control Crazing Deformation of PHA-Based Biopolymeric Blends.

The mechanical behavior of polymer materials is heavily influenced by a phenomenon known as crazing. Crazing is a precursor to damage and leads to the formation of cracks as it grows in both thickness and tip size. The current research employs an in situ SEM method to investigate the initiation and progression of crazing in all-biopolymeric blends based on Polyhydroxyalkanoates (PHAs). To this end, two chemically different grades of PHA, namely poly(hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV), were melt-blended with polybutyrate adipate terephthalate (PBAT). The obtained morphologies of blends, the droplet/fibrillar matrix, were highly influenced by the plasticity of the matrices as well as the content of the minor phase. Increasing the concentration of PBAT from 15 to 30 wt.% resulted in the brittle to ductile transition. It changed the mechanism of plastic deformation from single craze-cracking to homogeneous and heterogeneous intensified crazing for PHB and PHBHV matrices, respectively. Homogeneous tensile crazes formed perpendicularly to the draw direction at the initial stages of deformation, transformed into shear crazes characterized by oblique edge propagation for the PHBHV/PBAT blend. Such angled crazes suggested that the displacement might be caused by shear localized deformation. The crazes' strength and the time to failure increased with the minor phase fibers. These fibers, aligned with the tensile direction and spanning the width of the crazes, were in the order of a few micrometers in diameter depending on the concentration. The network of fibrillar PBAT provided additional integrity for larger plastic deformation values. This study elucidates the mechanism of crazing in PHA blends and provides strategies for controlling it.

Elongated liquid metal based self-healing polyurethane composites for tunable thermal conductivity and electromagnetic interference shielding

Materials with desirable properties, including good deformability, high thermal conductivity, and superior electromagnetic interference (EMI) shielding, are in high demand in the modern electronics sector. Here we report, stretching-induced filler alignment method for elongate and align the liquid metal (LM) in the self-healing polyurethane (SPU) matrix along the draw direction, resulting in simultaneous enhancement in in-plane thermal conductivity (λ∥) and the EMI shielding effectiveness (SE) of the composites. LM/SPU composites with 80 wt% filler loading show λ∥ as high as 12.8 W·m-1·K-1 and EMI SE of 72 dB, respectively, at the draw ratio of 3. Excellent deformability of the LM facilitates its alignment in the composites, which improves electron and phonon transmission and allows for multiple reflections and absorption of electromagnetic waves, which greatly enhances λ∥ and EMI shielding. Moreover, LM/SPU composites show excellent healing properties. Thus, this work proposes incorporating multifunctional features into a composite system for flexible electronics.

Structure and Mechanical Behavior of Fully Substituted Acid Starch Esters

AbstractThis study deals with the evolution of structural, thermal, and mechanical properties of a series of fully substituted fatty acid starch esters (FASEs) according to side chain length (from 2 (C2) up to 16 (C16) Carbons). FASEs with C2 to C12 side chains are fully amorphous with a glass transition temperature depending on chain length while in the case of FASE with C16 side chains, a part of side chains is able to crystallize. Thermomechanical behavior depends strongly on both the alkyl chain length and crystallinity of samples. In particular, for FASE‐C16, the presence of crystals leads to a brittle behavior. During stretching, no macromolecular orientation is evidenced for short‐chain FASEs (&lt;C8), whereas, for long‐chain starch ester from C8 to C16 length, an orientation of starch backbone in the drawing direction is observed.

Deformation behavior of β titanium alloy tubes in die-less forming with taper shape control

The distributions of the outer and inner radii of die-less drawn β titanium alloy tubes were evaluated in the drawing direction to clarify the effect of the deformation behavior of the tube on taper shape control in the die-less forming. Ti–22V–4Al DAT51 (β Ti alloy) tubes with an outer radius of 0.81 mm were die-less drawn under various heating temperature and taper slope conditions. The outer and inner radius distributions were measured, and the drawing stress was evaluated during the drawing. As a result, a maximum reduction in cross-sectional area of 81% was achieved in a single pass of the die-less forming under a heating temperature of 800 °C and taper slope of −0.005. The outer radius became larger than that with the linear contour theory, which achieved the desired taper slope when the outer radius became smaller than a certain value during drawing. This is because the large slope in the deformation zone caused non-uniaxial tensile deformation dominated by wall thickness reduction. Therefore, the length between the heating and cooling coils should be large such that the slope of the deformation zone becomes small to satisfy uniaxial deformation, which is an assumption of the linear contour theory.

Contribution of grain boundary to strength and electrical conductivity of annealed copper wires

The effect of grain boundaries on the strength and electrical conductivity of annealed copper wires was studied. After annealing at 100 °C for 30 min, the copper wires retained a fiber-like structure. The increase in electrical conductivity is believed to stem from the decrease of crystallographic defects introduced by drawing. Recrystallization occurred when the annealing temperature reached 150 °C. The formation of small recrystallized grains led to the introduction of additional grain boundaries perpendicular to the drawing direction, resulting in a slight decrease in electrical conductivity. When the annealing temperature rose up to 200 °C, complete recrystallization took place in the copper wires. The grain boundaries parallel to the drawing direction play an important role in boundary strengthening, while the grain boundaries perpendicular to the drawing direction play an important role in both boundary strengthening and electron scattering. The electrical resistivity of grain boundaries in fully recrystallized copper wires at room temperature was determined experimentally, and an empirical relation is proposed to quickly determine the electric conductivity of copper wires at room temperature based on the boundary spacing along the drawing direction.

Deformation mechanisms in PBT at elevated temperatures

Plastic deformation mechanisms of Polybutylene terephthalate (PBT) are investigated at 120 °C, 150 °C and 180 °C using tensile experiments, 2D digital image correlation, wide and small angle X-ray scattering measurements.Plots of nominal stress vs true strain (ε), true stress vs ε and Haward-Thackray representation reveal the same I, II, III regimes in strain ranges virtually independent of temperature. Between ε = 0 and the yield strain εY ≈ 0.3 (I) the layer morphology is preserved, the interlamellar distance increases in the drawing direction and the strain is localized in amorphous regions. Between ε ≈ 0.3 and ε ≈ 1.0 (II), amorphous chains remain describable as gaussian coils while transition from spherulitic to fibrillar morphologies occurs. Beyond ε ≈ 1.0 (III) the chains are taut, the fibrillar morphology is established, additional stress causes the transitions between polymorphs, respectively from isotropic amorphous to smectic and from α to β crystalline phases.

Effect of Cold Drawing and Annealing in Thermomechanical Treatment Route on the Microstructure and Functional Properties of Superelastic Ti-Zr-Nb Alloy.

In this study, a superelastic Ti-18Zr-15Nb (at. %) alloy was subjected to thermomechanical treatment, including cold rotary forging, intermediate annealing, cold drawing, post-deformation annealing, and additional low-temperature aging. As a result of intermediate annealing, two structures of β-phase were obtained: a fine-grained structure (d ≈ 3 µm) and a coarse-grained structure (d ≈ 11 µm). Cold drawing promotes grain elongation in the drawing direction; in a fine-grained state, grains form with a size of 4 × 2 µm, and in a coarse-grained state, they grow with a size of 16 × 6 µm. Post-deformation annealing (PDA) at 550 °C for 30 min leads to grain sizes of 5 µm and 3 µm, respectively. After PDA at 550 °C (30 min) in the fine-grained state, the wire exhibits high tensile strength (UTS = 624 MPa), highest elongation to failure (δ ≥ 8%), and maximum difference between the dislocation and transformation yield stresses, as well as the highest superelastic recovery strain (εrSE ≥ 3.3%) and total elastic + superelastic recovery strain (εrel+SE ≥ 5.4%). Additional low-temperature aging at 300 °C for 30-180 min leads to ω-phase formation, alloy hardening, embrittlement, and a significant decrease in superelastic recovery strain.

The strategic development plan of the national anti-doping agency in the context of current challenges

Optimizing the structure of the National Anti-Doping Agency in the government that would allow the development and implementation of well-thought-out public policies in all related sectors of the Conventions is important for the balanced development of the country in the field of integrity in sports. It is worth noting that optimizing the structure of the National Anti-Doping Agency is a necessity of public administration reform, and is accompanied by important elements of good governance, strengthening the capacities of the services to prevent and combat doping, intelligence and research, and the de facto accountability of employees of the public institution. Therefore, in order to ensure an efficient, democratic, transparent and responsible realization of the national anti-doping program and of the public policies and objectives drawn up by the National Anti-Doping Agency, as well as, by virtue of the cited normative acts, it is necessary to carry out the strategic planning process and the drawing directions of action.

Filler-Enhanced Piezoelectricity of Poly-L-Lactide and Its Use as a Functional Ultrasound-Activated Biomaterial.

Poly-L-lactide (PLLA) offers a unique possibility for processing into biocompatible, biodegradable, and implantable piezoelectric structures. With such properties, PLLA has potential to be used as an advanced tool for mimicking biophysical processes that naturally occur during the self-repair of wounds and damaged tissues, including electrostimulated regeneration. The piezoelectricity of PLLA strongly depends on the possibility of controlling its crystallinity and molecular orientation. Here, it is shown that modifying PLLA with a small amount (1 wt%) of crystalline filler particles with a high aspect ratio, which act as nucleating agents during drawing-induced crystallization, promotes the formation of highly crystalline and oriented PLLA structures. This increases their piezoelectricity, and the filler-modified PLLA films provide a 20-fold larger voltage output than nonmodified PLLA during ultrasound (US)-assisted activation. With 99% PLLA content, the ability of the films to produce reactive oxygen species (ROS) and increase the local temperature during interactions with US is shown to be very low. US-assisted piezostimulation of adherent cells directly attach to their surface (such as skin keratinocytes), stimulate cytoskeleton formation, and as a result cells elongate and orient themselves in a specific direction that align with the direction of PLLA film drawing and PLLA dipole orientation.

Wi-NN: Human Gesture Recognition System Based on Weighted KNN

Gesture recognition, the basis of human–computer interaction (HCI), is a significant component for the development of smart home, VR, and senior care management. Most gesture recognition methods still depend on sensors worn by the user or video-based gestures for recognition, can be used for fine-grained gesture recognition. our paper implements a gesture recognition method that is independent of environment and gesture drawing direction, and it achieves gesture recognition classification by using small sample data. Wi-NN, proposed in this study, does not require the user to wear additional device. In this case, channel state information (CSI) extracted from Wi-Fi signal is used to capture the action information of the human body via CSI. After pre-processing to reduce the interference of environmental noise as much as possible, clear action information is extracted using the feature extraction method based on time domain to obtain the gesture action feature data. The gathered data are integrated with the weighted k-nearest neighbor (KNN) classification recognizer for classification task. The experiment outcomes revealed that the accuracy scores of the same gesture for different users and different gestures for the same user under the same environment were 93.1% and 89.6%, respectively. The experiments in different environments also achieved good recognition results, and by comparing with other experimental methods, the experiments in this paper have better recognition results. Evidently, good classification results were generated after the original data were processed and incorporated into the weighted KNN.

Special-Oriented Annealing-Twins-Induced Orange Peel Morphology of Heat Pipe under Bending Deformation

The thin-wall heat pipe is an efficient heat transfer component that has been widely used in the field of heat dissipation of high-power electronic equipment in recent years. In this study, the orange peel morphology defect of thin-wall heat pipes after bending deformation was analyzed both for the macro-3D profile and for the micro-formation mechanism. The morphology and crystal orientations of the grains and annealing twins were carefully characterized utilizing optical metallography and the electron backscatter diffraction technique. The results show that after high-temperature sintering treatment, the matrix grains of the heat pipe are seriously coarsened and form a strong Goss texture, while certain annealing twins with the unique copper orientation are retained. The distribution of the Schmid factor value subjected to the uniaxial stress indicates that inhomogeneity in the intergranular deformation exists among the annealing twins and matrix grains. The annealing twin exhibits a "hard-oriented" component during the deformation; thus, it plays a role as a barrier and hinders the slipping of dislocation. As the strain accumulates, part of the annealing twins may protrude from the surface of the heat pipe, forming a large-scale fluctuation of the surface as the so-called "orange peel" morphology. The 3D profile shows the bulged twins mostly perpendicular to the drawing direction, about 200-300 in width and 10-20 μm in height.

YbPO4 crystals in as-drawn silica-based optical fibers

MCVD germanosilica glass embedded with YbPO4 crystals were for the first time drawn into optical fibers. Solution doping was used to embed the crystals in the silica soot prior to the collapsing step. We demonstrate, using scanning/transmission electron microscopes and confocal Raman microscope, that YbPO4 crystals survive not only the MCVD process but also the drawing process despite the high temperature involved (up to 2100 °C) during fabrication processes. The fiber contains 100 nm-crystals with the same composition and structure as the as-prepared crystals. During the drawing process, these crystals tend to have a preferential orientation of their c-axis along the drawing direction. These results open a new route to fabricate glass-based composite fibers containing crystalline particles without additional post heat-treatment.

Increasing Electrical Conductivity of Bacterial Cellulose/Polypyrrole Bio Composite Films Prepared Using the Pulling Technique

This research has found a new approach to improving the conductivity of bacterial cellulose BC/Ppy bio composite films prepared using pulling. A wet BC pellicle is immersed in a liquid Ppy semiconductor for 30 minutes. The wet films was pulled out using a tensile testing machine. The results show that, after pulling, the conductivity of the films became better parallel to the sample drawing direction. Compared to the non-pulled out film, the pulled out film had higher conductivity (σ = 19.2 x 10-3 S/cm), increasing by 153%. The conductivity of films can still improve significantly because deformation during sample preparation in wet conditions.

Construction of a Highly Oriented Poly(lactic acid)-Based Block Polymer Foam and Its Self-Reinforcing Mechanism

Developing poly(lactic acid) (PLA)-based biodegradable polymer foams with high performance is crucial for sustainable energy conservation and the ecological environment. In this work, by applying poly(lactide-co-caprolactone) (PLCL) as a compatibilizer, the block polymer of poly(l-lactic) acid (PLLA)-b-polycaprolactone (PCL) with a long-chain branched structure was prepared by reactive processing. By utilizing the difference between the glass-transition temperature (Tg) and melting temperature (Tm) of PLA and PCL, PLLA-b-PCL-PLCL foams with a PCL chain as the foaming phase and an oriented PLLA chain as the enhancing phase were prepared by establishing a solid-phase hot drawing@supercritical CO2 foaming method. The incorporation of PLCL links significantly improved the interfacial compatibility between PLLA and PCL phases and chain entanglements, exhibiting strain-hardening behavior and leading to an improvement in the stretchability of the block polymer. In the hot drawing process in the range of Tg(PLA)–Tm(PLA), both PLLA and PCL phases were elongated along the drawing direction, and with an increasing draw ratio, the orientation factor and the crystallinity of the two phases increased evidently, accompanied by the formation of a shish–kebab crystalline structure. In the subsequent foaming process in the range of Tg(PCL)–Tm(PCL), the molecular chains of the PLLA phase were frozen and the retention of the orientation factor reached over 90%, while under CO2, crystallinity and crystallite size increased and a more perfect crystalline structure formed for the PCL phase. With an increasing draw ratio, the saturated dissolved amount of CO2 increased and the cell density and cell size of foam reached 5.13 × 109 cells/cm3 and 4.06 μm, respectively. The fibrillar structures of the PLLA phase appeared on the cell wall, while the tensile strength and modulus of foam reached as high as 65.9 MPa and 1.01 GPa, respectively. As a result, a super-strong PLA-based microcellular foam with dense micropores and highly oriented microfibrillar structures was constructed.

Partial Thinning Method for Steel Sheets by Bending-Assisted Compression Drawing

Tailored blanks with in-plane differential thickness are required to reduce automobile body weight and satisfy two or more strength requirements in one panel. We developed a method of partial thinning in the width direction of steel sheets by bending-assisted compression drawing. This method reduces shear deformation energy by combining bending deformation and compression deformation, which can lead to a reduction in forming load. In this study, we conducted an experiment to partially reduce the thickness about 10 mm from the width edge of the mild steel sheet by the proposed method. We found that this method enables us to partially reduce the mild steel sheet thickness by 30% on the blank edge side. Furthermore, we combined the proposed method with a continuous stretch-bending method that can partially reduce the thickness in the longitudinal direction (drawing direction). As a result, a tailored blank with in-plane differential thickness was demonstrated experimentally.

Bionic structure and blood compatibility of highly oriented homo-epitaxially crystallized poly(l-lactic acid)

A highly oriented poly(l-lactic acid) (PLLA), with a blood vessel-like biomimetic structure, was fabricated using solid-phase hot drawing technology and homo-epitaxial crystallization to improve the mechanical properties and biocompatibility of PLLA. Long chain branched PLLA (LCB-PLLA) was prepared through a two-step ring-opening reaction, and a consequent draw as high as 1000 % was achieved during the hot drawing. The modulus and tensile strength were found to have increased through the formation of oriented shish-kebab like crystals along the drawing direction during processing. Furthermore, PLLA nano-lamellae were formed on the surface of the oriented plates via the introduction of homo-epitaxial crystallization. The high degree of orientation and epitaxial crystallization substantially enhanced the biocompatibility of the PLLA by prolonging clotting time, decreasing the rate of hemolysis, and increasing the cell growth and reproduction of the osteoblasts.

Chitosan grafting coumarin-3-carboxylic acid fluorescent fiber with enhanced strength prepared by in-situ wet-spinning

Chitosan grafting coumarin-3-carboxylic acid (CS-g-CCA) fiber with fluorescent function and enhanced tensile strength was successfully prepared by in-situ wet-spinning. FTIR and NMR results demonstrate that CCA is successfully grafted onto the CS molecule chains. As the grafting rate increases from 4.2 to 15.8 %, the spinning solution viscosity increases from 22 to 54 Pa·s. SEM observations show that the CS and CS-g-CCA fiber surfaces and cross-sections exhibit homogeneity and smoothness. Likewise, as the drawing ratio increases from 1.0 to 1.4, 2D WAXS patterns illustrate the molecular chain oriented significantly along the drawing direction. The CS-g-CCA fiber (the grafting rate of 15.8 %) exhibits a maximum breaking strength of 1.06 cn/dtex, increasing by 20 % more than the CS fiber. Meanwhile, it has a peak fluorescence intensity of around 480 nm. In addition, the continuous preparation process simplifies the technological route and improves the preparation efficiency of CS-g-CCA fiber. As-prepared CS-g-CCA fiber with enhanced tensile strength and elevated fluorescence efficiency lays the foundation for potential application in fluorescent probes, anti-counterfeiting, and biomedicine fields.

Evolutions of microstructure and texture of Mg-Gd alloy wires processed by cold drawing

High-performance Mg-4.7Gd (wt%) alloy wires were prepared by large-strain multiple-pass cold drawing process. The maximum accumulative true strain (ATS) of Mg-4.7Gd alloy reached as high as 165%, indicating an excellent formability of Mg alloy at room temperature. Evolutions of microstructure and texture as well as mechanical properties of Mg-4.7Gd (wt%) alloy wires were studied in as-extruded and as-drawn condition. A small amount of grain with nano-sizes were observed by transmission electron microscope in the microstructure of as-drawn alloy wires with large ATS. The weak texture components with ∼45° to the transverse direction (TD) drawing direction (DD) instead of the basal texture formed in as-extruded Mg-4.7Gd alloy wire, which was beneficial to the subsequent cold drawing. As ATS increased, grains rotated around the DD and gradually approached the TD. And, the non-basal texture of G4.7 gradually increased with cold drawing due to the addition of Gd, constrained inclined compressive stress, twinning and large strain. This evolution in texture leaded to the formation of <101¯0> fiber texture with <101¯0> parallel to the DD and consequently contributed an extraordinary drawing deformability to Mg alloy.

Texture Evolution of a Single Crystal Cu-8% at. Al Subjected to the Drawing Process

Single crystals of Cu-8.% at. Al were subjected to cold drawing up to 1.1 true strain. Development of the crystallographic texture was analysed at various stages of the drawing process. Investigations revealed significant crystal rotation and reorientation due to a twinning process, while general 4-fold symmetry around the drawing direction was preserved. Local texture analysis performed on cross-sections perpendicular to the drawing direction showed that due to crystal rotation, the original crystal was initially fragmented into four quadrants. However, within the volume near the central axis the initial cubic orientation was preserved. Subsequent deformation within dominating twinning systems led to further fragmentation which divided the crystal into sectors one eighth the size of the full circular cross-section. The obtained results also indicate that approximation of the drawing process stress state by the tensor having only normal components cannot be used during analysis of the activation of deformation systems.