High Draw Ratios Research Articles

Novel Heat Stamping of Ti6Al4V panels with high drawability and low springback

Conventional commonly used titanium stamping techniques like hot forming and superplastic forming each have distinct disadvantages. Hot forming usually leads to limited formability and significant springback, whilst superplastic forming often results in long cycle times, high energy use, and costly tooling. A novel, energy-efficient, and cost-effective Heat Stamping process emerges as a promising solution. Two types of Ti6Al4V components, cup-shaped and U-shaped, were produced using the novel Heat Stamping process, and their properties were examined. A defect-free cup-shaped component achieving a considerably high draw ratio of up to 1.8, was successfully fabricated. A moderate enhancement in the hardness of the component indicated a superior post-form strength achieved by Heat Stamping. Further analysis of the U-shaped components shows that the one produced using the novel method demonstrated a notable reduction in springback angle, from 4.8° to 0.7°, highlighting the potential of H eat Stamping in achieving high shape accuracy for near-net-shape forming.

Formation of highly oriented crystalline structure for polyoxymethylene fiber enables superior intrinsic thermal conductivity

Polyoxymethylene (POM) as an engineering plastic with high performances, has been widely applied, while endowed with superior intrinsic thermal conductivity for POM fibers was conducive to broaden their application in thermal management field, which were usually prepared through melt spinning-hot drawing/heat setting process. In this work, the tension annealing process was further incorporated into fiber production to develop highly orientated crystalline structure of fibers. All fibers have a uniform diameter with axial textures on surface, and the tensile strength/modulus increased remarkably by drawing and annealing process. In melting spinning process, the POM chains pre-oriented under stress, resulting in a slight increase of thermal conductivity. In hot drawing/heat setting process, through stress-induced crystallization of POM fiber, the shish-kebab crystalline structure formed at a low draw ratio (DR), while at high DR, a homogeneous and compact oriented microfibrillar crystalline structure formed. As a result, a significant improvement of crystallinity (Xc: 84.42 %) and orientation degree (fc, fa: 0.94) in crystalline/amorphous region of POM chains contributed to the superior axial thermal conductivity, which increased from 0.286 Wm−1K−1 of bulk POM to 2.131 Wm−1K−1. In annealing process, although Xc increased further to 93.37 % under high temperature, forming a nearly perfect crystal, while the f of annealed fiber remained under tension force but without further increase, the axial thermal conductivity showed no obvious improvement, revealing that orientation of POM chains had a more significant promotion on improving thermal conductivity of POM fibers than crystallization.

Structure and properties of biaxial stretched submicron thin UHMWPE membranes

Producing thinner polymer membranes has been a research hotspot to satisfy the increasing demand from diverse application scenarios in the industry. This work used biaxially stretching with an exceptionally high draw ratio near melting point to thin down the excessively petrolatum-swollen UHMWPE gel from millimeters to hundreds of nanometers. Of which the meso- and micro-structural evolution during stretching processing was systematically investigated, especially within the thickness range from microns to submicrons, threading through the micron-thickness boundary. These membranes consisted of oriented smooth fibrils without identifiable overgrowth lamellae but with two obvious melting points, being different from the conventional bead-fiber shape of the typical shish-kebab super-crystalline structures. Moreover, an ionic rejection phenomenon of submicron UHMWPE was observed, which was attributed to the surface potential that emerged when thinning down PE membrane below the threshold of 800 nm. It is the first report of emerging surface potential for the nonpolar neutral polymers as a function of reduced thickness within the submicron range. This work provides insight into the processing of submicron-thin polymer membranes, with the unique structure and properties distinguished from the bulk revealed and explained. These findings may also help the processing and structure-property analysis of submicron membranes of other polymer materials.

Influence of Deformation of Metal Matrix on the Mechanical Properties of Poly(Ethylene Terephthalate) Inside It

The influence of different types of deformation of the metal matrix on mechanical behavior of the amorphous PET film upon its transverse compression in the ductile metal matrix has been investigated. Three deformation modes have been probed. In the first case, a disc-shaped polymer specimen has been put between two 5 mm thick discs of the lead–tin alloy and squeezed in the press. In the second and the third cases, planar elongation has been performed in the so called “dead channel”, i.e., the channel with fixed side walls, the film being elongated due to decrease in the width or thickness, respectively. The plots of true yield stress at different draw ratios have formed a common master curve. At high total draw ratio Λ, the true yield stresses have been close for the considered three types of drawing in the metal. At the draw ratio Λ 2.6, the neck has not appeared, and the specimen has been deformed uniformly. When the film in the channel is elongated due to the decrease in thickness at constant width, the specimen width has been mainly decreased during subsequent elongation in the testing machine. When the film in the channel is elongated due to the decrease in width at constant thickness, further elongation has mainly led to the decrease in the specimen thickness. The true stress Σ has been expressed as Σ = Σ0 + KΛ3, with K being a constant. Deformation of the polymer in the channel occurred with the formation of shear bands. At the preliminary draw ratio Λ = 1.82, the bands have been oriented at the angle 21.5° with respect to the stretching axis. The planar elongation has led to abnormally strong deformation softening of the polymer. The drawing has been accompanied by an increase in the elasticity modulus of the polymer. The obtained results have suggested that the macromolecules orientation is the main reason for strain hardening of the polymer.

Transparent, Heat-Resistant, Ductile, and Self-Reinforced Polylactide through Simultaneous Formation of Nanocrystals and an Oriented Amorphous Phase

Imparting polylactide (PLA) films with great heat resistance, transparency, and balanced mechanical performance simultaneous is a big challenge in academia and industry due to mutual exclusiveness of properties. In this work, a newfound strategy that combines elongational stress field and thermal field is proposed to reorganize the crystalline and amorphous structure of PLA films. It is discovered that the oriented PLA films with high draw ratios form a unique structure of the oriented amorphous phase restricted by the oriented nanosized crystal during thermal treatment at an appropriate temperature. Superb stiffness–toughness balance of the film is achieved as the elongation at break increases from 16 to 91.9% after the thermal treatment at 150 °C, while the yield strength increases from 50.0 to 76.0 MPa. It is worth noting that the PLA film also has excellent transparency, i.e., a transmittance as high as 86.6% (550 nm), owing to crystallites formed on the nanometer scale. Excellent heat resistance is also obtained, with the onset decline temperature increasing from 63.7 (for the unstructured casting film) to 77.1 °C due to increased crystallinity. Furthermore, a new understanding of the orientation of the amorphous phase promoted by the confinement effect to the toughening of PLA is obtained, and a phenomenal model for the thermal-treatment-induced toughening effect is proposed. This work could provide a significant guidance for the facile preparation of a PLA film with promising comprehensive properties of toughness–stiffness balance, high transparency, and good heat resistance.

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.

Structural evolution and related physical properties of machine direction oriented poly(butylene succinate-co-adipate) films

This study sheds light on the microstructural change of uniaxially oriented poly(butylene succinate-co-adipate) (PBSA) copolymer, and the consequent gas permeabilities, as well as tensile and optical properties. Uniaxial stretching at 62 °C takes place by means of a machine direction orientation (MDO) with varied draw ratios and annealing near the melting temperature. The PBSA precursor sheet favorably melt-crystallizes in the form of α-PBS crystals with isotropic in-plane orientation. MDO-PBSA films with and without annealing exhibit preferential orientation of the α-PBS crystal parallel to the stretching direction (MD), with an increased degree of crystallinity according to the increased draw ratio and applied annealing. This was evident from two-dimensional wide-angle X-ray diffraction patterns and X-ray diffraction profiles. Additionally, MDO stretching above the crystallization temperature simultaneously induces rigid amorphous fraction, in particular, by a high draw ratio (5 × ) and chain relaxation during annealing near the melting temperature. From the determined Herman's orientation function, the c-axis of the α-PBS crystal is parallel to the MD, thereby resulting in decreased diffusion path tortuosity. Consequently, oxygen and water vapor permeation are promoted. Furthermore, Young's modulus and tensile strength of MDO-PBSA films drastically increase with high ductility, and are approximately two and four times higher than those of non-oriented PBSA, respectively. MDO-PBSA films exhibit high clarities above 94% while yielding low haze values.

Linear stability analysis of nonisothermal glass fiber drawing

We present a model of the draw resonance instability for glass fiber drawing including inertia, gravity, surface tension, and temperature. Using linear stability analysis, we have evidenced, through an alternative scaling, the crucial role of the fiber aspect ratio as a control parameter. It appears that a strong destabilization of the system occurs as this parameter increases. We also show the significant influence of nonhomogeneous ambient temperature on system stability. Contrary to the film casting problem, the high critical draw ratio in industrial applications could be rationalized only for a heat transfer coefficient dependent on both the velocity and cross-sectional area of the fiber.

The influence of the multi-level structure under high drawing on the preparation of high strength Lyocell fiber

In order to research the multi-level structure of Lyocell fiber at different draw ratios and to reveal the limiting factors for preparing the high strength Lyocell fiber, the paper reports on the effect of draw ratio including low drawing (1–5), high drawing (6–11) and excessive drawing (12–20) on the multi-level structure and the mechanical properties of Lyocell fiber. The structure was determined by wide-angle X-ray diffraction, small-angle X-ray scattering and fibrillation test, and the result showed that, at low draw ratio stage, the breaking strength, yield strength and modulus of the fiber increased with the draw ratio owing to crystallinity as well as orientation increased while the micropore decreased, and there were almost no microfibrils on the fiber surface. At high draw ratio stage, the orientation of amorphous region increasing was the principal reason for the increase of fiber mechanical properties, and the micropores continued to decrease and a few short and thick microfibril was formed. At excessive draw ratio stage, the breaking strength remained constant mainly due to the basically unchanged crystallinity and orientation of the fibers, the yield strength and modulus decreased due to the slip of the highly crystallized and oriented elementary fibril. Meanwhile, the micropores still decreased and became more slender, the number of microfibrils increased and the microfibrils showed tenuous structure. It can be summarized that Lyocell fiber has the characteristics of multi-level structure, and the fundamental reason limiting the improvement of mechanical properties with draw ratio increasing is the slip of elementary fibril.

Orientation of Polylactic Acid-Chitin Nanocomposite Films via Combined Calendering and Uniaxial Drawing: Effect on Structure, Mechanical, and Thermal Properties.

The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio. The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects on solid-state drawn nanocomposites: The highest mechanical properties were achieved for pre-oriented nanocomposites. The stiffness increased from 2.3 to 4 GPa, the strength from 37 to 170 MPa, the elongation at break from 3 to 75%, and the work of fracture from 1 to 96 MJ/m3. This study demonstrates that the pre-orientation has positive effect on the orientation of the nanocomposites structure and that it is an extremely efficient means to produce films with high strength and toughness.

Investigation of consecutive two-stage hydrodynamic deep drawing of aluminum cylindrical cups

In the deep drawing process, achieving a higher drawing ratio has always been considered by researchers. In this study, a new concept of hydrodynamic deep drawing with two consecutive stages without additional operations such as annealing is proposed to increase the limit drawing ratio of the cups. The effective parameters were investigated numerically and experimentally in the forming of Al1200 cylindrical cups. At first, the desired value of punch diameter ratio was determined based on finite element simulation results and was utilized to increase the cup formability. Next, the effects of pressure paths on the cup thickness, separation, and rupture were studied in each forming stage. The cup formability was investigated based on a new proposed framework to obtain the maximum possible limiting drawing ratio, and the desired conditions were determined. Finally, a cup was formed with a high drawing ratio of 3.4 which was a good achievement in comparison with the literature.

Thermal stability enhancement of oriented polyethylene by formation of epitaxial shish-kebab crystalline structure

Oriented polyethylene (PE) products usually exhibit thermodynamic instability in oriented crystalline structure under high temperature during long term service. In this work, self-assembly rare-earth nucleating agent (RENA) was innovatively introduced to fabricate oriented PE and induced PE molecules to form stable epitaxial oriented crystalline structure. Compared with oriented neat PE, oriented PE-RENA showed much higher dimensional/strength retention during aging, which reached as high as 90.13%/86.46% after aging at 100 °C for 1000 h, exhibiting high dimensional/mechanical stability. At low draw ratio, PE-RENA exhibited hybrid oriented shish-kebab structure, for which oriented RENA assembly acted as shish structure and PE lamellae acted as kebab structure, while, after aging, new stable anisotropic shish-kebab crystalline structure formed and the crystallinity (Xc) changed slightly. At high draw ratio, highly oriented shish-kebab structure formed, most of which was retained after aging and the changes of Xc/orientation degree was insignificant, while the molecular mobility in crystalline phase/intermediate phase was weakened, exhibiting enhanced thermal stability in oriented crystalline structure.

Nonmonotonic piezoresistive fibers tuned towards biomechanical sensing

Tuning nonmonotonic piezoresistive materials to detect motions within certain strain limits remains an open challenge. In addition, the origin of this unusual form of piezoresistance is still not properly understood especially for semi conducting polymer nanocomposites containing carbon nanotubes. In this work, we report wet spun nanocomposite fibers based on Poly (ether-block-amide) (PEBA) and multiwalled carbon nanotubes (MWCNT) that show differential sensitivity under uniaxial loading. This nonmonotonic piezoresistance is triggered by yielding of polymer segments which later influences the interaction between the embedded MWCNT at higher draw ratios. We confirmed this observation by correlating the stress – strain curve with the resistance – strain response and further studied its influence on the strain sensing phenomena of PEBA / MWCNT fibers. Moreover, pre-stretched fibers at draw ratios slightly above the yield point produced stable and reproducible sensing signals after applying them as biomechanical sensors for motions associated with small bending radii such as finger-wagging.

Air gap spinning of a cellulose solution in [DBNH][OAc] ionic liquid with a novel vertically arranged spinning bath to simulate a closed loop operation in the Ioncell® process

AbstractA novel, small‐volume vertically arranged spin bath was successfully developed for an air gap lyocell‐type spinning process. A maximum regeneration bath length with a minimum free volume characterizes the concept of the new spin bath. Using the ionic liquid (IL) 1,5‐diazabicyclo[4.3.0]non‐5‐enium acetate [DBNH][OAc], the spin bath showed very good spinning performances of IL‐cellulose dopes at high draw ratios and spinning duration for single filament spinning experiments. Using this new device, it was possible to get a step further in the optimization of the Ioncell® process and simulate a process closed loop operation by performing single filament spinning in IL/H2O mixtures. Good dope spinnability and preserved fibers mechanical properties were achieved in a coagulation bath containing up to 30 wt% IL. It is only at 45 wt% of IL in the bath that the spinnability and fibers mechanical properties started to deteriorate. The fibers fibrillar structure was less pronounced in IL‐containing spinning bath in comparison to a pure water bath. However, their crystallinity after washing was preserved regardless of the spinning bath composition. The results presented in this work have a high relevance to the upscaling of emerging IL‐based cellulose dissolution and spinning processes.

Nanocomposites of Au/Disentangled UHMWPE: A Combined Optical and Structural Study.

The term disentangled refers to polymers with fewer entanglements in the amorphous regions, a metastable condition that can significantly affect the material’s properties and processing behavior. The lower entanglement density in ultra-high molecular weight polyethylene (dis-UHMWPE) facilitates the solid-state processability into uniaxially-oriented specimens reaching very high draw ratios and crystallinities. In this study, Au/dis-UHMWPE nanocomposites were formulated and processed at variable draw ratios. Polarized light microscopy suggests gold nanoparticles are oriented in arrays following the drawing of polymer chains. The structural features, upon orientation, are studied by means of Raman spectroscopy, wide- and small-angle X-ray scattering, and near-infrared spectrophotometry. Crystallinity is found to increase by 15%, as calculated by wide-angle X-ray scattering. The change in optical absorbance in the visible spectrum indicates that, with orientation, the average size of gold aggregates increases, supported quantitatively by small-angle X-ray scattering. Since the gold nanoparticles are expected to be found within amorphous chain segments, the aforementioned findings are attributed to the increase of crystallinity and thus the decrease of available (amorphous) space.

Potential Application of Nanocellulose for Filaments Production: A Review

Some researchers have reported the successful experiments to produce nanocellulose-based filaments by several spinning methods, including wet spinning and dry spinning. The addition of nanocellulose to the composites was found to improve the mechanical and thermal properties of produced filaments or continuous fibers. However, there are several parameters of spinning that needs to be considered to achieve better quality of filaments, including high aspect ratio of nanocellulose, low viscosity of dope (low solid content), high shear rate in the spinneret, and high draw ratio. This review article focuses on brief explanation of cellulose structure and how to isolate nanocellulose, nanocellulose-based filaments by wet spinning and dry spinning methods, characteristics of wet and dry spun fibers, as well as parameters that affect spinning process. For example, the strength of filament was attributed to the aspect ratio or slenderness and crystallinity of nanocellulose. Further details of the potential application of nanocellulose for filament production is presented here as the reference for application in textile, medical, and other fields.

Impact of the wet spinning parameters on the alpaca‐based polyacrylonitrile composite fibers: Morphology and enhanced mechanical properties study

AbstractThe study examined the effect of different wet spinning parameters (e.g., total solid content, coagulation bath concentration, drawing, and stretching) on the morphology and mechanical properties of the wet spun alpaca/polyacrylonitrile (PAN) composite fibers. The alpaca/PAN composite fibers were wet spun using 10, 20, and 30% of alpaca particles along with the PAN polymer. The shear‐thinning or non‐Newtonian flow behavior was observed among the dope solutions with different solid content. The cross‐sectional fiber morphology showed the bean‐shaped characteristic for the control PAN fibers, whereas the alpaca/PAN composite fibers exhibited almost circular shape. “Cavity healing” was observed, where noticeable voids and porous areas were demolished in the cross section of the composite fibers, by changing the total solid content and coagulation bath concentration. Although the control PAN fibers exhibited the highest tenacity with lower fiber diameter, the alpaca/PAN composite fibers showed a gradual deterioration in tenacity while adding alpaca particles into the PAN polymeric matrix. Nevertheless, due to the increment in the total solid content, higher draw ratio, and stretching of the fibers, the tenacity, molecular orientation, and the crystallinity of the composite fibers were increased.

Structure and performance of electroblown PVDF‐based nanofibrous electret filters

AbstractPoly(vinylidene fluoride) (PVDF)‐based nanofibrous mats were produced via electrically assisted solution blowing (electroblowing). Morphology and filtration properties of the nanofibrous mats were investigated as a function of polymer concentration and applied voltage. The average fiber diameter was reduced from 727 ± 366 nm to 408 ± 143 nm and from 424 ± 233 nm to 328 ± 105 nm, using 16 wt% and 12 wt% concentrations, respectively, with an increase of electric voltage from 0 to 30 kV. In addition, the pore size of the mats produced from 12 wt% concentration decreases with the increase of electric voltage. Results showed that electroblown mats possess high filtration properties and performance. Enhancement of mechanical capturing efficiency is attributed to the reduction in fiber diameter and pore size. The enhancement of electrostatic capturing efficiency is thought to be from the improved electret property of the mats, which eliminates the need for a second step to polarize nanofibrous mats. As a result, both mechanical and electrostatic capture efficiency of the mats is enhanced compared to solution blown PVDF mats. The emerging electret property might be due to the accumulation of the electrostatic charges at high voltage and the enhanced polarized β phase, which is the result of the high drawing ratio applied to the polymer jet during the spinning process.

Вплив орієнтаційного витягування на властивості сумішей поліефірів ПЕТg/ПЕТ

Rational conditions for orientational drawing of PETg/PET polyester blend during processing into tape products are established. Tensile strength and elongation at break for all test specimens were determined according to ISO 527-2: 2012. Tensile modulus - ISO 527-1: 2019, specimen density - PN-EN ISO 1183-1, change of linear dimensions of specimens - ISO 16012: 2015. It was found that the introduction of PET into PETg leads to an increase in tensile strength of the blend, which is probably due to the process of orientational crystallization of PET. When the orientations are higher than 5.5 times in the PETg /PET mixtures, cavitation foaming occurs, which leads to a decrease in the blend density, its turbidity and a decrease in tensile strength. Blends with a high content of PETg have a significant thermal shrinkage, which should be taken into account when processing and applying these polymers. Physical and mechanical properties of PETg/PET polyesters blend with different ratio in the process of orientational stretching are established. The tensile strength increases with the increase drawing ratio for blends with high PET content due to its orientation crystallization. The phenomenon of cavitation foaming in polyester blend with draw ratio more than 5.5 times is found, which is accompanied by a decrease in the density of the samples and their tensile strength. Presence of PETg in PET matrix decrease tensile strength and elongation and significantly increase thermal shrinkage. Low elongation at break found for PETg/PET blend specimen without orientation which increases dramatically with low draw ratios and then decrease with higher drawing ratio. The technological modes of realization of cavitation foaming for the PETg/PET mixture at orientation drawing ratio above 5.5 due to the different phase structure of the components of the mixtures have been established. The introduction of PETg into PET leads to a significant increase in thermal shrinkage and reduces the physical and mechanical performance of oriented products.

Local process-dependent structural and mechanical properties of extrusion blow molded high-density polyethylene hollow parts

Although applied for several decades, production of hollow plastic parts by extrusion blow molding (EBM) is still over-dimensioned. To overcome this issue, a thorough investigation of the process-structure-property relationship is required. In this study, the local process-structure-property relationship for high-density polyethylene EBM containers is analyzed with differential scanning calorimetry and dynamic mechanic analysis microindentation. Local process-dependent crystallinity and complex modulus data at various processing conditions are supplemented with wide-angle X-ray diffraction and transmission electron microscopy (TEM). The crystallinities and the complex moduli clearly show lower values close to the mold side than at the inner side and the middle of the cross-section, which reflects the temperature gradient during processing. Additionally, the orientation of the polymer chain (c-axis) reveals a low level of biaxiality with a slight tendency towards transverse direction. The biaxiality increases for low mold temperature and high draw ratio. Finally, biaxiality is confirmed with TEM, which reveals no preferred lamellar orientation.