Microstructure and mechanical performance examination of 3D printed acrylonitrile butadiene styrene thermoplastic parts

Fused filament fabrication (FFF) is a process where thermoplastic materials are heated to its melting point and then extruded, layer by layer, to create a three dimensional printed part. Printing occurs in a layered manner, which leads to creation of voids (air gaps) in the 3D printed parts. These voids act as centers for crack initiation, propagation and therefore resulting bulk mechanical properties are lower. This paper focuses on microstructural characterization and analysis of fused filament fabricated tensile test coupons made from acrylonitrile butadiene styrene polymer, at various design conditions. Comparable tensile modulus with injection molded specimens was obtained for FFF design condition that is, slice height (0.1778 mm), raster width (0.4064 mm), raster to raster air gap (−0.0015 mm), contour to raster air gap (−0.0508 mm) and raster angle (0°). Scanning electron microscope studies provided an understanding as to why FFF processed specimens yielded lower failure strain and an insight into the presence of intralayer voids in specimens having lower tensile modulus. The study confirmed that though bulk mechanicals were affected by the combined effect of inter, intra and interfacial voids, intravoids had a predominant influence.     

Extraction of fibers from saccharum munja grass and its application in composites

With growing environmental awareness, ecological concerns and new legislations, natural fiber‐reinforced plastic composites have received increasing attention during the recent decades. The natural fiber composites have many advantages over traditional glass fiber composites, including lower cost, lighter weight, environmental friendliness, and recyclability. This article reports the findings of the studies done on a new fiber, hitherto unexplored, extracted from Saccharum munja grass. The extracted fibers were further treated using sodium hydroxide to improve its performance in composites. Both treated and untreated fiber‐reinforced composites were prepared by hand lay‐up process using unsaturated polyester resin. Mechanical properties and thermal behavior of the composites were evaluated. The improvement in properties was found for alkali‐treated fiber composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40829.     

Influence of Varying SiO2?% on the Mechanical Properties of Al Based MMC

The current investigation is focused on effective utilization of rice husk ash (RHA) SiO₂??an industrial waste available in abundance, by systematically dispersing into an Al?CMg (0.5, 1.0, 2.5, and 5.0?% by weight) matrix resulting in synthesis of composites via Liquid Metallurgy route. The effect of increasing Mg?% to improve the wettability with the increase in SiO₂?% as reinforcement was studied comparatively. The increase in the percentage of SiO₂ beyond 5?% as reinforcement into Al?CMg alloy increases the agglomeration of SiO₂ particles which creates more sites for crack initiation and hence lowers down the load bearing capacity of the composite while microhardenss and wear testing analysis. For the composite, Al?CMg (2.5?%)?CSiO₂ (5.0?%) the hardness was observed to be maximum corresponding to minimum wear loss. The uniform distribution of maximum amount of hard spinel structure of extremely small size within the matrix confirms maximum wetting characteristic of 2.5 wt% Mg.     

Impedance estimation of photovoltaic modules for inverter start-up analysis

Starting-up of photovoltaic (PV) inverters involves pre-charging of the input dc bus capacitance. Ideally, direct pre-charging of this capacitance from the PV modules is possible as the PV modules are current limited. Practically, the parasitic elements of the system such as the PV module capacitance, effective wire inductance and resistance determine the start-up transient. The start-up transient is also affected by the contactor connecting the PV modules to the inverter input dc bus. In this work, the start-up current and voltages are measured experimentally for different parallel and series connections of the PV modules. These measurements are used to estimate the stray elements, namely the PV module capacitance, effective inductance and resistance. The estimation is based on a linear small-signal model of the start-up conditions. The effect of different connections of the PV modules and the effect of varying irradiation on the scaling of the values of the stray elements are quantified. The System model is further refined by inclusion of connecting cable capacitance and contactor resistance. Dynamics of the resulting fifth-order model are seen to be consistent with those of the simplified third-order model. The analysis of this paper can be used to estimate the expected peak inrush current in PV inverters. It can also be used to arrive at a detailed modelling of PV modules to evaluate the transient behaviour.     

Concatenation of electrochemical grafting with chemical or electrochemical modification for preparing electrodes with specific surface functionality

Surface modified electrodes are used in electro-analysis, electro-catalysis, sensors, biomedical applications, etc. and could also be used in batteries. The properties of modified electrodes are determined by the surface functionality. Therefore, the steps involved in the surface modification of the electrodes to obtain specific functionality are of prime importance. We illustrate here bridging of two routes of surface modifications namely electrochemical grafting, and chemical or electrochemical reduction. First, by electrochemical grafting an organic moiety is covalently immobilized on the surface. Then, either by chemical or by electrochemical route the terminal functional group of the grafted moiety is transformed. Using the former route we prepared lithium alkyl carbonate (–O(CH₂)₃OCO₂Li) modified carbon with potential applications in batteries, and employing the latter we prepared phenyl hydroxyl amine (–C₆H₄NHOH) modified carbon which may find application in biosensors. Benzyl alcohol (–C₆H₄CH₂OH) modified carbon was prepared by both chemical as well as electrochemical route. We report combinations of conjugating the two steps of surface modifications and show how the optimal route of terminal functional group modification depends on the chemical nature of the moiety attached to the surface in the electrochemical grafting step.     

Pattern of change in prolonged exposure and cognitive-processing therapy for female rape victims with posttraumatic stress disorder.

Curve estimation techniques were used to identify the pattern of therapeutic change in female rape victims with posttraumatic stress disorder (PTSD). Within-session data on the Posttraumatic Stres Disorder Symptom Scale were obtained, in alternate therapy sessions, on 171 women. The final sample of treatment completers included 54 prolonged exposure (PE) and 54 cognitive-processing therapy (CPT) completers. For both PE and CPT, a quadratic function provided the best fit for the total PTSD, reexperiencing, and arousal scores. However, a difference in the line of best fit was observed for the avoidance symptoms. Although a quadratic function still provided a better fit for the PE avoidance, a linear function was more parsimonious in explaining the CPT avoidance variance. Implications of the findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermal and mechanical properties of polyisobutylene‐based thermoplastic polyurethanes

We investigated thermal and mechanical properties of thermoplastic polyurethanes (TPUs) with the soft segment comprising of both polyisobutylene (PIB) and poly(tetramethylene)oxide (PTMO) diols. Thermal analysis reveals that the hard segment in all the TPUs investigated is completely amorphous. Significant mixing between the hard and soft segments was also observed. By adjusting the ratio between the hard and soft segments, the mechanical properties of these TPUs were tuned over a wide range, which are comparable to conventional polyether‐based TPUs. Constant stress creep and cyclic stress hysteresis analysis suggested a strong dependence of permanent deformation on hard segment content. The melt viscosity correlation with shear rate and shear stress follows a typical non‐Newtonian behavior, showing decrease in shear viscosity with increase in shear rate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 891‐897, 2013