Draw Ratio Research Articles

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.

A rheology and processing study on controlling material and process defects in polymer melt extrusion film casting using polymer blends

The primary objective of this research paper is to control the material and process defects in polymer melt extrusion film casting (EFC) process for linear chain architecture polyethylene (PE) resins through polymer blending methodology. Extrusion film casting is a well-known industrially important manufacturing process that is used to manufacture thousands of tons of polymer/plastic films/sheets and coated products. In this research, the necking defect in an EFC process has been studied experimentally for a linear low density polyethylene (LLDPE) resin and attempts have been made to control its necking by blending in a long chain branched (LCB) low density polyethylene (LDPE) resin. The blending methodology is based on the understanding that a LDPE resin displays enhanced resistance to necking as compared to the LLDPE resin. It is found that added LDPE resin enhances necking resistance for the primary LLDPE resin. Further, as the LDPE concentration increases in the blend formulation, the necking is further reduced as compared to pure LLDPE. Analogous to past studies on EFC of linear and long chain branched architecture containing PEs, it is observed that as the LDPE is increased in the blend formulations, the formulations displayed enhanced melt elasticity and extensional strain hardening in rheological studies. It is concluded from this study that polyethylene resins having linear chain architecture can be made amenable to enhanced resistance to necking using appropriate amount of a long chain branched resins. Finally, process defects such as the draw resonance onset could be shifted to higher draw ratios as the LDPE level is increased in the LLDPE-LDPE blend formulation.

Influence of Spinning Method on Shape Memory Effect of Thermoplastic Polyurethane Yarns.

Shape memory polymers are gaining increasing attention, especially in the medical field, due to their ability to recover high deformations, low activation temperatures, and relatively high actuation stress. Furthermore, shape memory polymers can be applied as fiber-based solutions for the development of smart devices used in many fields, e.g., industry 4.0, medicine, and skill learning. These kind of applications require sensors, actors, and conductive structures. Textile structures address these applications by meeting requirements such as being flexible, adaptable, and wearable. In this work, the influence of spinning methods and parameters on the effect of shape memory polymer yarns was investigated, comparing melt and wet spinning. It is shown that the spinning method can significantly influence the strain fixation and generated stress during the activation of the shape memory effect. Furthermore, for wet spinning, the draw ratio could affect the stress conversion, influencing its efficiency. Therefore, the selection of the spinning process is essential for the setting of application-specific shape-changing properties.

Deep drawability of electron beam welded tailored blanks of commercially pure titanium thin sheets

In this work, commercially pure titanium tailor-welded blanks (TWBs) were fabricated from sheets of thicknesses 1.0 mm (Ti1.0) and 1.2 mm (Ti1.2) using electron beam welding (EBW). It was observed that the titanium base materials had an equiaxed microstructure, whereas the FZ of the weld consisted of coarsened prior β grains with internal α substructures. Transverse and longitudinal tensile tests were conducted to evaluate weld integrity and weld properties, respectively. The deep drawing behaviour of both the base materials and TWB had been investigated by conducting laboratory-scale deep drawing tests. The limiting drawing ratios (LDR) of the Ti1.0 and Ti1.2 base materials were 2.14 and 2.21, respectively. The LDR of TWB was 2.14, which was same as that of the Ti1.0 base material. The CPB06 yield criterion and weld properties were incorporated in the FE modelling to study the deep drawing behaviour of the TWB for the first time. The FE model successfully predicted the non-uniform material flow and thickness distribution in the deep drawn TWB. Moreover, the weld line movement was found to be towards the Ti1.0 side at the cup top region and towards the Ti1.2 side at the cup bottom of the TWB deep-drawn cup.

Optimization of thermoelectric properties of carbon nanotube veils by defect engineering.

Carbon nanotubes (CNTs), with their combination of excellent electrical conductivity, Seebeck coefficient, mechanical robustness and environmental stability are highly desired as thermoelectric (TE) materials for a wide range of fields including Internet of Things, health monitoring and environmental remediation solutions. However, their high thermal conductivity (κ) is an obstacle to practical TE applications. Herein, we present a novel method to reduce the κ of CNT veils, by introducing defects, while preserving their Seebeck coefficient and electrical conductivity. Solid-state drawing of a CNT veil embedded within two polycarbonate films generates CNT veil fragments of reducing size with increasing draw ratio. A successive heat treatment, at above the polycarbonate glass-to-rubber transition temperature, spontaneously reconnects the CNT veils fragments electrically but not thermally. Stretching to a draw ratio of 1.5 and heat repairing at 170 °C leads to a dramatic 3.5-fold decrease in κ (from 46 to 13 W m-1 K-1), in contrast with a decrease in electrical conductivity of only 26% and an increase in Seebeck coefficient of 10%. To clarify the mechanism of reduction in thermal conductivity, a large-scale mesoscopic simulation of CNT veils under uniaxial stretching has also been used. This work shows that defect engineering can be a valuable strategy to optimize TE properties of CNT veils and, potentially, other thermoelectric materials.

The study of correlations among the process condition, structure and property for poly(l-lactide) fibers

This article focus on derive the process-structure-property relationship of Poly(l-lactide) (PLLA) fibers prepared by two-step melt spinning process. The spinning temperature, spinning rate, drawing temperature as well as draw ratio were studied to analyze the influence of process variables on the structure and properties of PLLA fibers. It suggests that the crystallinity, lamellar orientation structure and mechanical properties of fibers are dependent on the spinning conditions, including melt-spinning and hot-drawing process. An approximate linear correlation resulted between the orientation degree and tensile strength of PLLA fibers, which means that the oriented structure plays a dominant role to enhance PLLA fibers. PLLA fibers with high performance of 499 MPa and 5.30 GPa in tensile strength and Young’s modulus separately have been realized by the selected spinning parameters. The results provide a theoretical direction for enhancing PLLA fibers by adjusting the structure characteristic via modifying the spinning parameters.

Calculating the parameters of extrusion of bars from iron-based powder compositions

An algorithm is proposed for calculating the technological parameters of the process of extruding rods from iron-based powder compositions, which makes it possible to predict the density of the rods depending on the initial porosity of the briquette, the drawing ratio, the taper angle of the matrix, and determining the extrusion pressure. Criteria are selected for the selection of conditions allowing one, after extrusion, to obtain a bar suitable for subsequent thermomechanical processing. The obtained data is supposed to be used for technological calculations of the processes for the production of engineering parts by powder metallurgy methods.

底面集合組織の形成を抑制したAZ31Bマグネシウム合金板材の室温深絞り成形性に及ぼすプロセス因子の影響

The effects of process parameters on room-temperature (RT) deep drawability were investigated for AZ31B magnesium alloy sheets, in which the formation of basal texture was suppressed by high-temperature rolling. When the blank holder force was set to the minimum value to prevent wrinkling, high RT drawability was obtained. In particular, a significantly high limiting drawing ratio (LDR) of 1.83 was obtained by the optimization of the process parameters of the servo-press machine. At higher punch speeds, the drawability tended to be deteriorated; however, a high LDR of 1.72 was obtained even at a high punch speed of 50mm/s by the optimization of the process parameters of the servo-press machine. Furthermore, when the punch speed in the initial stage of deep drawing was reduced, it was possible to perform deep drawing without fracture even if the punch speed in the later stages was increased. The results of the study of the effect of lubricants indicated that relatively high RT drawability was obtained when molybdenum disulfide was utilized. It was also suggested to be important to select a lubricant that reduces punch load and does not delaminate during deep drawing.

Estimating Forming Conditions for Deep Drawn SUS304 Square Cups Having no Delayed Cracks Using FE Simulation

Forming conditions for deep drawn SUS304 square cups having no delayed cracks are determined using finite element (FE) simulations based on the threshold % of wall thickening for delay cracking obtained from deep drawing tests of SUS304 cylindrical cups. The maximum drawing ratio and the initial blank thickness are fixed at 1.87 and 0.8 mm, respectively in this study taken into the considerations of the capacity of the press machine i.e., 100 kN. The blank holding forces (BHF), punch corner radius, rp and die corner radius, rd are varied to obtain 75 mm x 75 mm square cups having % of local thickening less than the threshold value i.e., 47% in the cracking zones located adjacent to the top corners of the cups. A quarter 3D FE simulation model of the deep drawing process is constructed, the wall thickness distributions of the cups are calculated. The simulation results showed that the forming conditions for the crack-free cups could be obtained with BHF ≥ 47 kN, rp ≥ 8.5 mm and 6.8 mm ≤ rd ≤ 9.5 mm. A method for designing the forming conditions of deep drawn SUS304 square cups is proposed in this study.

Fabrication and characterization of chemical crosslinked cellulose fiber by dissolving cellulose in alkali urea aqueous solvent

AbstractSustainable materials fabricated from natural polymers have attracted much attentions because of their multiple advantages like abundant renewable resource, biocompatibility, biodegradability, and nontoxicity, while their actually application often restricted by mechanical properties. Chemical crosslinking method was usually used to improve the mechanical properties of cellulose materials such as hydrogel, film, aerogel, and so forth. Here, cellulose fibers were fabricated from cellulose solution in alkali/urea aqueous solvent by chemical crosslinking with epichlorohydrin in a PVC hose. The chemical crosslinked cellulose fibers exhibited smooth surface and circular cross‐section. Their tensile strength increased from 128 to 368 MPa by adjusting cellulose concentration, ECH concentration, and draw ratio. The crystallinity of the fibers changed from 43.1% to 49.8% after drawing process. Meanwhile, the fibers exhibited a brighter color after dyeing than the viscose rayon. This work promising an avenue for preparation of mechanical strong cellulose fibers.

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.

An investigation on the size-effects on thickness-distribution of directionally rolled multi-stage deep-drawn copper cups through finite element analysis, and its validation through experimentation employed scaling law

Most sectors are moving towards downsizing products that retain high standards of quality and satisfy customer needs. Miniaturisation of components typically makes use of scaling rules. In this work, we use the idea of similarity theory to investigate the micro-and nano-scale thinning behaviours of multi-stage deep-drawn cups. Deep drawing with a limiting draw ratio (LDR) of 1.69 was used to shape ETP copper sheets into cylindrical cups via annealing and directionally rolling. Each rolling pass consists of nine incremental passes that result in a 50% reduction in thickness. The influence of scaling laws for uni and bi-directional rolling was studied, and scaled dies and punch sets were employed to create scaled cups of five different thicknesses, each 50% of the original 6 mm. For this simulation, we used Altair INSPIRE, a sort of explicit finite element analysis that uses real-world material test data. To investigate the impact of thickness variation across all scaled cups, measurements of the thickness were taken at three points on multi-stage deep-drawn cups. Bi-directional rolling produced cups with less thickness variance than uni-directional rolling. All the scaled cups had a consistency greater than the mean at the lip point and less at the cup base for both ways of rolling, it was also noticed. Physical evaluations of the drawn cups for extreme values verified that the inferred variations lie within ±15% of their original thickness for all cups, and the mean thickness likewise has 50% of its multi-stage-drawing, proving the applicability of the scaling rules.

Silk fibroin reinforced graphene fibers with outstanding electrical conductivity and mechanical strength

High-performance graphene fiber with intriguing functionality and mechanical strength is expected for wide potential applications. However, it still demands reliable means to realize the rapid wet-spinning of highly aligned fibers because of the insufficient gel strength of graphene oxide (GO) dope and the possible structural imperfections in the obtained fibers. Here, we demonstrate the fabrication of highly conductive and strong graphene fibers by regulating the rheology and spinnability of trace-carbonyl GO dispersion with silk fibroin (SF). The amphiphilic SF can form hydrogen bonds and π-π interactions with GO sheets to significantly enhance the gel strength of spinning dopes, enabling the conformation adjustment and sheet alignment under large drawing ratio and performance enhancement of the GO/SF fibers. After a chemical reduction, the highly orientated and stacked structure endows the fibers with an exceptional tensile strength of 938.6 MPa and a high electrical conductivity of 1501.7 S cm−1. Even more, the conductivity can be further increased to 2700.7 S cm−1, which is among the highest values for chemically reduced GO fibers. This work offers a promising method to produce strong, flexible, and robust graphene fibers for versatile applications in multifunctional fabrics, energy conversion, and health protection areas.

Study of the limiting parameters of deep drawing of sheet blanks made of heat-resistant copper alloys

This article studies the mechanism of thin-walled workpiece deep drawing in the mould with a conical die and determines the forming limit state that occurs at the time of the bottom detachment in the radius part of the punch when stresses in the meridional direction reach their maximum value. This condition is determined by a decrease in the workpiece edge size at the stage of slow material hardening and a decrease in the workpiece flange area that are main factors hindering the process. This condition makes it possible to establish a criterion used to determine the limiting drawing ratio (ratio of the diameter of the workpiece to the diameter of the part), namely: equality of meridional stresses in the punch radius rounding area and the material tensile strength. The paper establishes the effect of the workpiece material strength properties, friction and die taper on the limiting drawing ratio. A change in the plastic and strength properties of the BrKh08 heat-resistant copper alloy (tensile strength, yield strength) does not affect the material hardening constant values and practically does not affect the limiting drawing ratio. The paper uses a comprehensive research method including theoretical analysis and modeling in the ANSYS/LS-DYNA software with input data for the 1.35 mm thick workpiece 100 mm in diameter made of BrKh08. The article presents computer simulation stages indicating main process parameters such as the workpiece material model, mechanical properties, type of elements, kinematic loads, conditions of contact interaction between elements, etc. Process simulation results confirmed theoretical conclusions necessary for the process implementation without part defects.

Exploration of disentangled UHMWPE tape as a soft body armour material

Disentangled ultrahigh molecular weight polyethylene (UHMWPE) is a very promising material with extremely high tenacity and modulus. In this work, the effect of drawing on the morphological, physical, and mechanical properties of disentangled UHMWPE tapes was studied. The tapes were characterised by using the density gradient column method , wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), polarised optical microscopy and scanning electron microscopy (SEM). The density and crystallinity of tape improved after each stage of drawing. The unoriented crystalline structure of the as-prepared UHMWPE tape gradually transformed into an oriented crystalline structure on drawing as confirmed by WAXD patterns. As the draw ratio increased, concomitant increase in birefringence, and tensile properties were also noticed. The tape obtained after the final stage of drawing had tensile properties similar to that of gel spun UHMWPE fibres. Hence, this tape was used to make prototype of soft armour panel (SAP) that stopped all the bullets fired when subjected to ballistic test and yielded very low back face signature (BFS) justifying the potential of disentangled UHMWPE tape as a ballistic material.

Effect of drawing on mechanical properties, degradation and drug release of dexamethasone-loaded polydioxanone monofilaments

• Dexamethasone-loaded polydioxanone monofilaments were developed through melt spinning process. • Drawing process mechanically reinforces dexamethasone-loaded polydioxanone monofilaments. • Drawing process retards release of dexamethasone from polydioxanone monofilaments. • Drawing process could control hydrolytic degradation of polydioxanone monofilaments. A series of dexamethasone (DEX)-loaded polydioxanone (PDO) monofilaments drawn at different draw ratios through a melt spinning process was developed to investigate changes in drug release behavior, mechanical properties, and biodegradation. Drawn PDO monofilaments presented decreased diameters, increased tensile strengths, and reduced elongation at break. The XRD analysis of DEX-loaded PDO monofilament showed changes in crystallinity due to the drawing process. The drawing process also changed behaviors of degradation and drug release, showing reduced degradation rates and long-term sustained release rates at higher draw ratios. Taken together, obtained characteristic properties and their controllability are expected to be favorable for practical applications requiring invasive and longer implantation such as non-vascular stents, surgical sutures, and face-lifting materials.

Structure evolution and performance of poly (vinyl alcohol) fibers with controllable cross-section fabricated using a combination of melt-spinning and stretching

Profiled fibers are gained potential applications in the fields of both functional textiles and cements reinforcements. While the commercial Poly (vinyl alcohol) (PVA) fibers are generally produced by solution spinning, which is difficult to prepare profiled PVA fiber with controllable cross-section because of bidirectional mass transfer in coagulation bath. In this work, based on intermolecular complexation and plasticization, water was adopted to improve the thermal-processing of PVA, the special-shaped PVA fibers such as triangular, trilobal, cruciform and wavy cross-sections were prepared by melt-spinning. The crystallinity of profiled as-spun PVA fibers was lower than 32%, and their elongation at break was higher than 400%, resulting in good stretch-ability for hot-drawing. During the hot-drawing of profiled PVA fibers, the circular trend of the characteristic sections can be controlled, and the reduction in profile degree was lower than 9.4%. Hot-drawing improved the crystalline structure of PVA, and increased the crystallinity, orientation, tensile strength, and melting point of profiled fibers. When the draw ratio was 9, the tensile strength of triangular, cruciform, trilobal and wavy fibers were 585 MPa, 559 MPa, 481 MPa and 585 MPa, respectively, which proposed a new processing technology of special-shaped PVA fiber and enriched the kinds of special-shaped fibers.

Fundamental Structural and Kinetic Principals of High Strength UHMWPE Fibers Production by Gel-Technology.

One of the main research work in the field of polymeric materials was, is and always will be the improvement of their mechanical properties. Comprehensive structural studies of UHMWPE reactor powder, the features of its dissolution and the formation of a gel-state, as well as UHMWPE films oriented up to various draw ratios, were carried out using scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. For comparison, decalin and vaseline oil were chosen as solvents. The mechanical properties of oriented UHMWPE films were also studied. In the process of orientation drawing, basing on the developed structural-kinetic principles of strengthening for highly oriented speciments gel-cast from UHMWPE powders, the average values of tensile strength of 4.7 GPa (about 6% of the samples had strength values up to 6.0 GPa) and an Young's modulus of 170 GPa (about 6% of the samples had Young's modulus values of 200 GPa). These values are among the highest according to the world scientific literature. A significant increase in the mechanical characteristics of highly oriented UHMWPE films was achieved using experimentally confirmed scientific approaches to revealing the structure-property relationship at each stage of the gel process.

Study on the microfiber attenuation in melt-blowing airflow field

Melt blowing (MB) is a process for producing microfiber or nanofiber using high-velocity air to attenuate the polymer jet. Compared to research on the melt-blowing airflow field analysis, the melt blown die optimization, and new materials development, little work has been done on fiber attenuation and whipping in the melt-blowing process. In this study, the airflow field distribution and turbulence fluctuation of the melt-blowing die are investigated using numerical simulation. The fiber motion process is simulated with the bead-viscoelastic element model and obtained using the high-speed camera. The underlying mechanisms leading to melt-blowing fiber attenuation have been discussed. The results show that the airflow field can be separated into three regions. The turbulent fluctuations in Regions I are related to the fiber whipping in the melt-blowing process. The fiber motion in Regions II and III are unsteady, resulting in higher fiber attenuation. Region II is the main zone of fiber attenuation where the fiber whipping increases and the drawing ratio is the largest. The fluctuation of air velocity causes fiber whipping which plays an important role in fiber attenuation. Experimental results of fiber diameter reduction and fiber motion are consistent with the simulation results.

Strip Casting of Al-4.7%Mg with Impurity Fe Using a Single Roll Caster with a Scraper

Fe was added to Al-4.7%Mg to make model alloys of recycled Al-Mg alloy. The effect of Fe addition on the mechanical properties of the Al-4.7%Mg strip cast using a single-roll caster equipped with a scraper was investigated. The added Fe content was 0.2, 0.4, 0.6, and 0.8%. The as-cast strip cast at 30 m/min was cold rolled down to a thickness of 1 mm thick annealed to conduct a tensile test and a cup test. The as-cast strip could be cold rolled without cracking. The tensile stress and the 0.2% proof stress were only slightly affected by the addition of Fe. The elongation gradually decreased as the Fe content increased. When the Fe content was 0.8%, the elongation in the casting direction was 27.7%. The limiting drawing ratio did not deteriorate until the Fe content was 0.4%. When the Fe content was 0.4% and 0.8%, the limiting drawing ratios were 2.0 and 1.7, respectively.