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Ultra-high molecular weight polyethylene (UHMWPE) acquires excellent properties while possessing poor processability. Blending low molecular weight polyethylene disentangles the molecular chain of UHMWPE and improves its processability, improving fiber productivity. In the present study, UHMWPE and its HDPE-blended fibers were produced by a high-temperature electrospinning process, and the effect of HDPE content on fiber properties was investigated in depth. Analysis of fiber surface morphology revealed the formation of uniformly distributed nano- to microscopic pores/pits, wrinkles, and grooves on the surface of blended fibers, unlike neat UHMWPE fibers containing irregular surface bulges and pits. It suggested that the blending of HDPE affected the surface topography and the thermal and mechanical properties of electrospun fibers. The tensile strength and Young's modulus of UHMWPE fiber improved by 142 and 102% at a 67:33 mass ratio of UHMWPE and HDPE and by 84 and 132% in the case of a 50:50 composition ratio, respectively. [ABSTRACT FROM AUTHOR]

Defence structures are under high threat of blast loading in recent years due to rising terrorist activities. Protection of defence structures against blast conditions has received a huge interest in the past few years. Blast mitigation requires to study the behavior of various metals under supersonic shock loading. An experimental study was carried out using in-house developed shock tube apparatus to understand effect of shock loading on mild steel and aluminum sheets. A limitation of current study is 1-D loading occurring in shock tube which is unlike 3-D loading occurring in a blast event. Experiments reveal that the properties of thin sheets in through-thickness direction plays an essential role in the shock transfer, which affects considerably the failure and final deformed shape of the sheet. The study showed that metallic thin sheets absorbed shock energy via plastic deformation and failed via a tensile failure mode. Results from this study indicate that aluminum sheets and mild steel sheets can offer shock-resistant properties and mitigate more energy via absorption and plastic deformation. Aluminum and mild steel sheets can therefore be used as a face and back sheet for the development of any sandwich composites. [ABSTRACT FROM AUTHOR]

Nano-micron size fiber formation of UHMWPE (ultra-high molecular weight polyethylene) can be carried out by a high temperature (130 °C) electrospinning method. In this work, the effect of solution parameters on fiber formation by the electrospinning method is discussed. Two different grades of UHMWPE having a molecular weight (Mw) of 2.21 million g/mole (UM2.21) and 4.43 million g/mole (UM4.43) were chosen for the analysis. The solution properties of UHMWPE were investigated via rheology, which allowed the identification of the entanglement concentration before conducting the electrospinning process. The entanglement concentration (ce) for UM2.21 was 1.5 wt.%, while that for UM4.43 was 0.8 wt.%, respectively. The concentration exponent in semi dilute unentangled, and semi dilute entangled regimes was 1.23 and 2.59 for UM2.21 and 0.45 and 2.57 for UM4.43, respectively, in-line with de-Gennes's scaling theory. SEM of the electrospun product revealed that defect-free smooth fiber morphology could only be obtained when the concentration of the solution is around 1.5-2.5 times the entanglement concentration. [ABSTRACT FROM AUTHOR]

The demand of high-speed wireless communication has increased, which need the data rate to be in the order of Terabyte per second (Tbps) in the near future. Terahertz (THz) band communication is a key wireless communication technology to satisfy this future demand. This would also reduce the spectrum scarcity and capacity limitation of current wireless systems. Microfabricated Folded Waveguide TWTs are the potential compact sources of wide band and high-power terahertz radiation. This study primarily focuses on machining technology for THz waveguide components requiring ultra-high precision micromachining. Rectangular waveguides, especially Folded Waveguides (FW), are even more difficult to manufacture using conventional machining techniques due to their small size and very tight tolerances. The criticalities in micromachining of FW for 0.22 THz have been addressed in this article. Half hard free cutting Brass IS 319-H2 was used as a work material due to its electrical and mechanical properties. Waveguide size of 0.852 × 0.12 mm was machined within ± 3–5 μm linear tolerances, surface roughness in the order of 45 nm Ra, and flatness less than half of wavelength (< λ/2). The split top and bottom blocks of the folded waveguide were aligned by dowel pins which matched within a tolerance of ± 5 μm. The perpendicularity and parallelism were maintained within 5 μm tolerance. This work explored and established the application of micromilling as reasonably suitable for the THz waveguides followed by ultrasonic cleaning as deburring. It also investigated the measured folded waveguide losses which were close to simulated values. [ABSTRACT FROM AUTHOR]

In our technology-intensive world, manufacturing is transforming rapidly and is now driven by personalized demand. To deal with the modern manufacturing challenges, one requires an inclusive approach and therefore, a new paradigm has evolved shifting the manufacturing closer to the customer. This paper highlights the need for inclusive manufacturing along with its important aspects of automation, workforce diversity, and environment-friendly manufacturing operations. Variables pertaining to an inclusive manufacturing system were identified from the literature and were shortlisted based on the opinion of domain specialists. The causal relations among the variables are modeled using Bayesian network. The overall focus of the study lies in evaluating the impact of identified variables affecting product quality through the lens of an inclusive manufacturing system. Cascading effect of variables and the sensitivity analysis further build this study to conclude important observations and managerial insights. [ABSTRACT FROM AUTHOR]

Microcellular injection molding (MIM) of thermoplastics is a challenging molding process compared to conventional injection molding (IM) process because of its narrow processing window. As far as microcellular molding of open-celled foam is concerned, it is much more difficult because of extremely narrow processing window for open-cell foam and transient nature of melt temperature and pressure inside cavity during the molding process. However, it is expected that molding of open-celled microcellular foam may open many new areas such as tissue engineering, drug delivery, reverse osmosis, dialysis membranes, and fuel cell. The production cost may also be reduced manifolds. In present work a novel expandable cavity mold (EC mold) was designed and fabricated. EC mold has some nonconventional features like pneumatically actuated gate seal, mechanism for cavity expansion, and arrangement for cyclic heating-cooling of core and cavity blocks. In present study polylactic acid (PLA), a biodegradable polymer, was used and expandable cavity molding (EC molding) variables, namely, cavity expansion rare (mm/s), cavity expansion distance (mm), and cavity expansion-compression-expansion (ECE) profile mode, were studied. The results confirm molding of PLA foams with very high cell density and impinged structure. The micrographs and open-cell ratio confirm the formation of PLA foam with ~40% open-cell content. [ABSTRACT FROM AUTHOR]

This review focuses on contemporary metal foams, their fabrication techniques and commercial applications. Different type of foam synthesis techniques like open cell and closed cell foams using solid, liquid, ions or vapor metals are discussed along with their characteristic process parameters. A vast body of research has been established for producing metallic foams for many decades. Space holder methods, sponge replication method, vapor deposition method, hot isostatic pressing as well as powder metallurgy process have been extensively reported in available literature. Techniques like sponge replication have the capability to produce up to 98% porosity with considerable amount of strength. However, metallic foam fabrication of certain metals still poses many challenges, which need to be explored. Metallic foams have enormous industrial applications, like closed cell foams have structural applications, open cell foams can be used for structural as well as biomedical applications. Often open cell metal foams have encountered low fatigue strength that might need alloying as well heat treatment operations for strengthening. Moreover, it is important to understand the physics and techniques of foaming for fabricating a good quality foam, which is also discussed in this article. The focus of the review finally shifts to open cell metallic foams for biomedical applications. [ABSTRACT FROM AUTHOR]

Shear thickening is a non-Newtonian flow behavior characterized by the increase in apparent viscosity with the increase in applied shear rate, particularly when the shear rate exceeds a critical value termed as the critical shear rate (CSR). Due to this remarkable property of shear-thickening fluids (STFs), they are extensively used in hip protection pads, protective gear for athletes, and more recently in body armor. The use of STFs in body armor has led to the development of the concept of liquid body armor. In this study, the effect of particle size is explored on the low and high strain rate behavior of nanosilica dispersions, so as to predict the efficacy of STF-aided personal protection systems (PPS), specifically for ballistic applications. The low strain rate study was conducted on cone and plate rheometer, whereas the high strain rate characterization of STF was conducted on in-house fabricated split Hopkinson pressure bar (SHPB) system. Spherical nanosilica particles of three different sizes (100, 300, and 500 nm) as well as fumed silica particles of four different specific surface areas (Aerosil A-90, A-130, A-150, and A-200), respectively, were used in this study. The test samples were prepared by dispersing nanosilica particles in polypropylene glycol (PPG) using ultrasonic homogenization method. The low strain rate studies aided in determining the CSR of the synthesized STF dispersions, whereas the high strain rate studies explored the impact-resisting ability of STFs in terms of the impact toughness and the peak stress attained during the impact loading of STF in SHPB testing. [ABSTRACT FROM AUTHOR]

The monomer of poly(lactide), i.e. lactic acid is an optically active compound and thus renders optical activity in the polymer itself. In the present studies highly crystalline and low crystalline grades of poly(lactide) were used to prepare blends with different d- and l-ratios to explore the relation between d- and l-content and various properties of poly(lactide). Optical rotation was measured by Polarimetry to analyse d-content in the blends which was found to vary from 0.05 to 4.14 %. Polarized light microscopy revealed that both the growth rate and final average size of the spherulites increased with the decrease of d-content. The crystallinity was measured by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) methods. It was noticed that a small change in d-content produced remarkable changes in crystallinity and other properties of the blends. The mechanical properties were slightly modified with the decrease in d-content. [ABSTRACT FROM AUTHOR]