1,720,976 research outputs found
Investigation on the processing of natural-synthetic hybrid fiber thermoplastic compositions in injection molding
No full textDuring the injection molding of thermoplastics, proper control of shrinkage is critical for developing parts with an acceptable tolerance. This thesis investigated natural-synthetic hybrid fiber reinforced thermoplastic composite (hybrid-NFRC) as a potential alternative to NFRCs in structural designs such as an automotive battery tray.
This research examined the material and process variables of hybrid-NFRCs to control shrinkage during injection molding (IM). Material variables such as melting, shear viscosity, polymer crystallinity and PVT (pressure-volume-temperature) relationship were investigated. Two non-linear models: Cross-WLF viscosity and 2-domain Tait equation were used to investigate the process variables such as shear rates (10s-1 to 5000 s-1), temperature (190 °C to 210 °C), pressure (10 MPa to 200 MPa) and cooling rates (5 °C/min to 20 °C/min). A Taguchi design of experiment and ANOVA (analysis-of-variance) were employed to investigate the influence of fiber hybridization on IM shrinkage.
The analysis of material variables demonstrated that injection molding (IM) of hybrid-NFRCs requires special attention. An incorporation of 10 wt% synthetic fiber in hybrid-NFRCs (at 30 wt% total fiber loading) lowered the shear viscosity by 14.1 Pa.s, polymer crystallinity by 4.5% and volumetric shrinkage by 0.08% (cm3/cm3) relative to NFRCs. A further reduction in shrinkage of hybrid-NFRCs can be realized by lowering the shear viscosity during the filling phase (R2 = 0.56) and crystallinity development during the solidification phase (R2 = 0.67). The findings support the dominance of process variables over the effects of fiber hybridization in determining IM shrinkage.
Overall, fiber hybridization is an effective approach to significantly improve the thermal and dimensional performance (P-valuePh.D
Life Cycle Assessment Based Greenhouse Gas Emission Reductions, Cross Country Analysis and Algorithm Aided Prediction for Lightweighted Composite Auto Parts
Get PDFAlgorithms made our life simpler and enables Machine to learn and predict and seems like a promising revolutionary science of the future. Even though this has been a hotspot in many aspects of science; there are some areas still behind. One of these areas is the Environmental and lifecycle assessments (LCA). The main problem with these areas is that the collected data are not comparable as every research has its own unique details even though LCA has a standard set of guidelines to perform. The second main problem is that we have very limited data avail-able for machines to be able to use in these areas. Here in this thesis, several normalization methods and a coefficient were used to make these data comparable. Also, because we had lim-ited data available, we performed several LCA studies to generate more data to be able to use it in Machine learning algorithms for the purpose of testing, validation and training. One of the advantages of having limited data here was that it enabled us to implement several machine learning algorithms and methods to compare their performances. The results of this study created a powerful tool that can help researchers, original equipment manufacturers, policymakers and automotive companies to make better environmental decisions prior to any design stages just by knowing the percentage of lightweighted automotive parts. This tool is specifically created to work with lightweighting that is resulted from replacing a glass fibre automotive part with natural fibre-reinforced composites. Also, with the developed coefficient of countries, one can transfer the LCA data from one country to another by using a simple equation. These coefficients were developed by using the countries posted total primary energy supply and electricity grid mix. By using these tools, we will have a better understanding of our emissions prior to any design with relatively high accuracy.Ph.D
Study on the Effect of Surface Energy of Polypropylene/Polyamide12 polymer Hybrid Matrix Reinforced with Virgin and Recycled Carbon Fiber
Get PDFThe presented work is focused on characterization of thermal treated recycled and virgin carbon fibers. Their thermal performances, chemical surface composition and its influence on interfacial adhesion phenomena on PP/PA12 hybrid matrix were compared using TGA, FTIR and XPS analysis. Additionally, differences between hybrid matrix structural performances of PP/PA12 using both surface modifiers PMPPIC and MAPP were investigated. Final mechanical properties improvements between 8% up to 17% were reached by addition of PMPPIC in PP/PA12 hybrid matrix. For PP/PA12 matrix reinforcement using virgin and recycled carbon fibers, impact energy was improved up to 98% compared with MAPP modified matrix leading to a novel composite with good energy absorption. Finally, wettability studies and surface free energy analysis of all materials studied support the effect of the addition of PMPPIC, MAPP and carbon fibers in final composite surface thermodynamics bringing important data correlation between
interfacial adhesion mechanisms and final composite performance.M.Sc
Investigation on the processing of natural-synthetic hybrid fiber thermoplastic compositions in injection molding
Get PDFDuring the injection molding of thermoplastics, proper control of shrinkage is critical for developing parts with an acceptable tolerance. This thesis investigated natural-synthetic hybrid fiber reinforced thermoplastic composite (hybrid-NFRC) as a potential alternative to NFRCs in structural designs such as an automotive battery tray.
This research examined the material and process variables of hybrid-NFRCs to control shrinkage during injection molding (IM). Material variables such as melting, shear viscosity, polymer crystallinity and PVT (pressure-volume-temperature) relationship were investigated. Two non-linear models: Cross-WLF viscosity and 2-domain Tait equation were used to investigate the process variables such as shear rates (10s-1 to 5000 s-1), temperature (190 °C to 210 °C), pressure (10 MPa to 200 MPa) and cooling rates (5 °C/min to 20 °C/min). A Taguchi design of experiment and ANOVA (analysis-of-variance) were employed to investigate the influence of fiber hybridization on IM shrinkage.
The analysis of material variables demonstrated that injection molding (IM) of hybrid-NFRCs requires special attention. An incorporation of 10 wt% synthetic fiber in hybrid-NFRCs (at 30 wt% total fiber loading) lowered the shear viscosity by 14.1 Pa.s, polymer crystallinity by 4.5% and volumetric shrinkage by 0.08% (cm3/cm3) relative to NFRCs. A further reduction in shrinkage of hybrid-NFRCs can be realized by lowering the shear viscosity during the filling phase (R2 = 0.56) and crystallinity development during the solidification phase (R2 = 0.67). The findings support the dominance of process variables over the effects of fiber hybridization in determining IM shrinkage.
Overall, fiber hybridization is an effective approach to significantly improve the thermal and dimensional performance (P-valuePh.D
Study on the Effect of Surface Energy of Polypropylene/Polyamide12 polymer Hybrid Matrix Reinforced with Virgin and Recycled Carbon Fiber
No full textThe presented work is focused on characterization of thermal treated recycled and virgin carbon fibers. Their thermal performances, chemical surface composition and its influence on interfacial adhesion phenomena on PP/PA12 hybrid matrix were compared using TGA, FTIR and XPS analysis. Additionally, differences between hybrid matrix structural performances of PP/PA12 using both surface modifiers PMPPIC and MAPP were investigated. Final mechanical properties improvements between 8% up to 17% were reached by addition of PMPPIC in PP/PA12 hybrid matrix. For PP/PA12 matrix reinforcement using virgin and recycled carbon fibers, impact energy was improved up to 98% compared with MAPP modified matrix leading to a novel composite with good energy absorption. Finally, wettability studies and surface free energy analysis of all materials studied support the effect of the addition of PMPPIC, MAPP and carbon fibers in final composite surface thermodynamics bringing important data correlation between
interfacial adhesion mechanisms and final composite performance.M.Sc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Rheological Characteristics of Pulp-fibre-reinforced Polyamide Composite
Get PDFRecently, there has been increasing interest in utilizing pulp-fibre–reinforced, higher-melting–temperature engineering thermoplastics, such as polyamide 11 and polyamide 6 in the automotive, aerospace and construction industries. Moreover, the rheological characteristics of those composites were not fully investigated in relation to processing approaches and pulp-fibre aspect ratio. Two processing approaches were used in this thesis: the extrusion compounding process and the Brabender mixer technique using inorganic salt lithium chloride (LiCl). The fibre-length distribution and content, and the densities of the PA11 and modified bio-based PA11 after compounding, were investigated and found to coincide with the final properties of the resultant composites. The effects of fibre content, fibre aspect ratio, and fibre length on rheological properties were studied. The rheological properties of high-yield–pulp (HYP) –reinforced bio-based Polyamide 11 (PA11) composite (HYP/PA11) were experimentally investigated using a capillary rheometer. Experimental test results showed a steep decrease in shear viscosity with increasing shear rate; this melt-flow characteristic corresponds to shear-thinning behavior in HYP/PA11. The morphological properties of HYP/PA11 composite were examined using SEM: no fibre pullout was observed. This was due to the presence of the hydrogen bond, which created excellent compatibility between high-yield pulp fibre and bio-based Nylon 11. The viscoelastic characteristics of biocomposites derived from natural-fibre–reinforced thermoplastic polymers and of predictive models were reviewed to understand their rheological behavior. Novel predicted multiphase rheological-model–based polymer, fibre, and interphasial phases were developed. Rheological characteristics of the composite components influenced the development of resultant microstructures; this in turn affected the mechanical characteristics of a multiphase composite. Experimental and theoretical test results of HYP/PA11 showed a steep decrease in apparent viscosity with increasing shear rate; this melt-flow characteristic corresponds to shear-thinning behavior in HYP/PA11.The nonlinear mathematical model to predict the rheological behavior of HYP/PA11was validated experimentally at 200˚C and 5000S-1 shear rate.Ph.D
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
