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The liner of a CNG pressure vessel is manufactured by a DDI (deep drawing and ironing) process for the cylinder part, which is a continuous process that includes a drawing process to reduce the diameter of the billet and a subsequent ironing process to reduce the thickness of the billet. A tractrix die used in the 1 st deep drawing allows the blank to flow smoothly by decreasing the punch load and radial tensile stress occurring in the workpiece. It also increases the draw ratio compared to conventional dies, but it causes forming defects. In this study, a shape coefficient ( S c ) is proposed for the tractrix die using the blank diameter ( D 0 ), inflow diameter of the workpiece ( d i ), and inflow angle of the workpiece ( θ ) for design of the tractrix die. The effects of the thickness and inflow angle of the workpiece on wrinkling and folding were investigated through FEA. Also, a discriminant is proposed for the relative radial stress ( σ ~ ) generated during the deep drawing process using the tractirx die and used to predict fracture. Based on the results, the blank thickness, the draw ratio, and the inflow of the workpiece angle in the 1 st deep drawing process are suggested, and the number of operations in the DDI process was reduced from 6 to 4. This improves the productivity and reduces the manufacturing cost.

Environmental stress cracking is a serious problem for polyethylene because it can cause failure without any visible warning due to the slow crack growth accelerated by aggressive agents. Tie molecules and entanglements are the main macromolecular characteristic increasing environmental stress cracking resistance, thus in this work mechanical and thermal properties governed by those macromolecular characteristics are determined by performing simple tests executable in the industrial laboratories for quality control on recycled high-density polyethylene. The mutual relation between the determined properties confirms their dependence on the investigated macromolecular characteristics and allows to predict in a comparative way the expected environmental stress cracking. The mechanical properties related to the environmental stress cracking resistance are the strain hardening modulus and the natural draw ratio. The strain hardening modulus is an intrinsic property that measure the disentanglement capability of the inter-lamellar links and the natural draw ratio is a highly sensitive parameter to the macromolecular network strength via the intercrystalline tie molecules. Since the measurement of these properties according to the standard ISO 18,488 requires a temperature chamber not often available in the industrial laboratories, the tensile test was performed also at room temperature and displacement rate 0.5 mm/min; a proportionality between the data obtained at different test condition emerged. The thermal property related to the environmental stress cracking resistance is the stepwise isothermal segregation ratio that state the chain fraction that generates a high rate of tie molecules responsible of environmental stress cracking resistance.

In this investigation, we assessed the influence of entanglement density on the gel spinning process for producing ultra-high molecular weight polyethylene (UHMWPE) ultrafine fibers with high tensile strength and modulus. Using a semi-dilute solution spinning technique in paraffin oil and including swelling and thermal drawing stages, we discovered that low-entanglement UHMWPE achieves swelling equilibrium more effectively and swells at a faster rate than highly entangled variants, facilitating enhanced drawability, and reduced entanglement. Rheological testing was used to estimate ultimate draw ratios, revealing that low-entanglement UHMWPE could be drawn up to 101 times, which is 1.8 times greater than fibers from highly entangled materials of comparable molecular weight. The fibers spun from low-entanglement UHMWPE demonstrated a tensile strength of 4.2 GPa and an initial modulus of 163.9 GPa, showing improvements of 18% and 68% respectively, compared to their highly entangled counterparts. With a fiber diameter of 7.1 μm, these results show significant enhancements in swelling and thermal drawing processes achievable with low-entanglement UHMWPE, resulting in superior high-performance ultrafine fibers with exceptional processability. Graphical Abstract

The liner of a compressed natural gas pressure vessel is manufactured by D.D.I. (deep drawing and ironing), which is a continuous process that uses deep drawing to reduce the diameter of a billet and ironing to reduce the thickness of the billet. In the second stage of the existing D.D.I. process, drawing and two steps of ironing have been performed separately with different dies, which requires a long processing time, high manufacturing cost, and installation space. To solve the above problems, this study suggests a new second stage using a combined redrawing-ironing die. A theoretical formula to calculate the forming load of the combined redrawing-ironing process was established and verified with finite element analysis results. The forming load, maximum thickness reduction ratio in the second stage, and forming defects in the third stage were analyzed by varying the redrawing-ironing ratio in the second stage. The results show that the number of dyes (3 → 1), punch diameter (394.1 mm → 383 mm), and processing time (39.8 s → 20 s) in the second stage were obtained to save production time and cost.

Compared with conventional monolithic material, an aluminum-polymer sandwich sheet possesses advantageous strength/stiffness versus weight ratio and has received increasing attention in aeronautical, automotive, marine, and civil engineering industries. In the present study, limiting draw ratio (LDR) and other cylindrical cup-drawing characteristics of aluminum-polymer sandwich sheets were investigated by experiments and numerical simulations. Deformation behaviors of skin layer and core polymer layer were analyzed respectively. It was demonstrated that the deformation mode of exterior sheet tends to biaxial tension state and that of interior sheet tend to compression state. The LDR of aluminum-polyethylene sandwich sheet was well predicted, and influences of core layer thickness and mechanical properties of skin sheet on the LDR of sandwich sheet were analyzed. Research results show that the drawability of the aluminum-polymer sandwich sheet becomes poor with increasing the thickness of the polymeric core and the strength of core polymer. The LDR of the sandwich sheet mainly depends on the drawability of the skin sheet.

Here, a new accurate approach is presented to quantify the degree of crystallinity of regenerated cellulose textile fibers using wide-angle X-ray scattering. The approach is based on the observation that the contributions to the scattering from crystalline and amorphous domains of the fibers can be separated due to their different degree of orientation with respect to the fiber direction. The method is tested on Ioncell-F fibers, dry jet wet spun with different draw ratios from an ionic liquid solution. The analysis output includes, apart from an accurate estimate of the fiber crystallinity, the degrees of orientation of the cellulose nanocrystals and the cellulose chains in the amorphous domains.

Four kinds of polypropylene (PP) cast films with different die draw ratios (DDR) were prepared. The impact of different DDR on the crystalline and oriented properties of PP cast films and annealed films was explored herein. Wide angle X-ray diffraction (WAXD) and fourier transform infrared (FTIR) methods were adopted to examine the orientation degree of crystalline and amorphous phases. Long period distance ( L p ) of the crystalline structure was tested by small angle X-ray scattering (SAXS). Crystallization was determined by differential scanning calorimeter (DSC). The oriented and crystalline behaviors of the samples were carried out by the elastic recovery (ER) testing. Then, samples after being annealed were examined by the same methods. The influence of annealing process on the films’ structures and properties was explored. Besides, the final stretched microporous membranes manufactured via stretching the annealed films along machine direction were examined by scanning electronic microscope (SEM). No matter for cast films or for annealed films, it is found that the films’ orientation degree of crystalline and amorphous phases, as well as L p and crystallinity are larger at higher DDR and relatively lower at lower DDR. When the DDR is overly high (DDR = 170), both the oriented and crystalline properties will decline. Elastic recovery testing indicates that a film with better orientation of the crystalline and the amorphous phases as well as with higher crystallinity can be obtained at an appropriate DDR. SEM images show that stretched membranes with better microporous structure can be obtained when the precursor film is prepared at a proper DDR.

For application of polymer nanofibers (e.g., sensors, and scaffolds to study cell behavior) it is important to control the spatial orientation of the fibers. We compare the ability to align and pattern fibers using shear force fiber spinning, i.e. contacting a drop of polymer solution with a rotating collector to mechanically draw a fiber, with electrospinning onto a rotating drum. Using polystyrene as a model system, we observe that the fiber spacing using shear force fiber spinning was more uniform than electrospinning with the rotating drum with relative standard deviations of 18% and 39%, respectively. Importantly, the approaches are complementary as the fiber spacing achieved using electrospinning with the rotating drum was ~10 microns while fiber spacing achieved using shear force fiber spinning was ~250 microns. To expand to additional polymer systems, we use polymer entanglement and capillary number. Solution properties that favor large capillary numbers (>50) prevent droplet breakup to facilitate fiber formation. Draw-down ratio was useful for determining appropriate process conditions (flow rate, rotational speed of the collector) to achieve continuous formation of fibers. These rules of thumb for considering the polymer solution properties and process parameters are expected to expand use of this platform for creating hierarchical structures of multiple fiber layers for cell scaffolds and additional applications.

Forming of pure molybdenum crucible is greatly demanded for its broad application in production of single crystal sapphire. To fabricate molybdenum crucible and other sheet metal products of molybdenum, it is necessary to determine the limiting draw ratio and frictional data with the aid of finite element analysis to reduce the massive experiments. To ensure the accuracy of finite element analysis, it is crucial to determine the reproducible frictional data. In this study, an evaluation methodology combined hot deep-drawing test with numerical simulation used to investigate the formability and tribological behavior of pure molybdenum at elevated temperature. For calculation of friction coefficient, the isothermal deep-drawing tests were carried out at the temperature ranging from 993 to 1143 K under lubricated and dry conditions. According to the predicted relation between frictional coefficient and forming temperature, the influences of forming temperature, lubrication, and blank diameter on friction are discussed, and the limiting draw ratios of molybdenum sheet at various temperatures are obtained. It is found that there is a significant improvement in drawability of pure molybdenum from 1.2 at room temperature to 1.98 at 1143 K by using boron nitride lubricant. However, the effect of forming temperature on the formability of molybdenum sheet is not significant under dry friction condition. Compared with the experimental results, the method used for evaluation of the formability and friction characteristic in hot deep drawing of molybdenum sheet is verified efficiently.

We report the preparation of polybenzoxazole (PBO) fiber from polyhydroxyamide (PHA) precursor fiber which is free from strong acid such as polyphosphoric acid. We prepared the PHA fibers with different spin-draw ratios (SDRs) using a wet-spinning method and the PBO fibers with an SDR of 3.5 (SDR-3.5 PBO fibers) were prepared by various heat-treatment temperatures, and investigated their morphology, crystalline structure, and mechanical properties. The simultaneous thermogravimetric analysis-mass spectrometry (STA-MS) and field-emission scanning electron microscopy (FE-SEM) results confirmed that the diameter of the SDR-3.5 PBO fiber was much smaller than that of the SDR-3.5 PHA fiber, due to the release of water during the thermal cyclization reaction which forms the PBO structure. The wide-angle Xray diffraction (WAXD) pattern of the SDR-3.5 PBO fiber heat-treated at 350 °C (SDR-3.5 PBO 350 fiber) showed two peaks, at 2θ=14.83 ° and 24.38 °, and the diffraction angles dropped with increasing heat-treatment temperature. In addition, the initial modulus and tensile strength of the SDR-3.5 PBO fiber heat-treated at 550 °C (SDR-3.5 PBO 550 fiber) were found to be 19.1 GPa and 449.2 MPa, which were much higher than those of the SDR-3.5 PHA fiber, 9.3 GPa and 227.0 MPa, respectively.