12 research outputs found
On the response to hygrothermal aging of pultruded FRPs used in the civil engineering sector
This paper presents the effects of hygrothermal aging on the durability of a pultruded flat sheet, immersed in distilled water at 25oC, 40oC, 60oC or 80oC for a period of 224 days. Elevated temperatures noticeably increase the moisture diffusion coefficient and moisture uptake behaviour. Measured changes in the tensile and in-plane shear mechanical properties were examined after 28, 56, 112 or 224 days. Tensile properties remained practically unaffected by aging whereas matrix dominated shear properties revealed an initial drop which was recovered to a substantial degree after further hygrothermal aging. Visco-elastic property changes due to the superimposing mechanisms of plasticization, additional cross-linking etc. were recorded. Scanning Electron Microscopy micrographs indicate that the fibre/matrix interface remained practically intact, even after the most aggressive hot/wet aging. X-Ray Energy Dispersive Spectroscopy analysis showed no chemical degradation incidents on the fibre reinforcement surfaces and infrared spectroscopy revealed superficial chemical alteration in the aging matrix. Optical microscopy revealed matrix cracking in samples aged at 80oC for 112 days. Lastly, Computed Tomography scans of un-aged material showed internal imperfections that undoubtedly enhanced moisture transport. After aging at 60oC for 112 days, Computed Tomography detected preferentially situated water pockets
Service and maintenance damage assessment of composite structures using various modes of infrared thermography
On the fatigue response of a bonded repaired aerospace composite using thermography
Lock-in thermography was employed to investigate the repair efficiency of a bonded repaired aerospace composite subjected to step-wise cycling mechanical loading. The studied component (substrate) was artificially damaged with a 5âŻmm circular notch and subsequently repaired with a tapered bonded patch. Critical and sub-critical damage of the repaired component was monitored via thermography during 5âŻHz tensionâtension fatigue. The examination of the acquired thermographs enabled the identification of the patch debonding propagation as well as the quantification of the stress magnification at the patch ends and the locus of the circular notch. It was found that fatigue mechanical loading yields both thermoelastic and hysterestic phenomena with the latter being more prominent prior to the failure of the studied repaired component
Polyamide 12/Multiwalled Carbon Nanotube and Carbon Black Nanocomposites Manufactured by 3D Printing Fused Filament Fabrication: A Comparison of the Electrical, Thermoelectric, and Mechanical Properties
In this study, nanocomposites with polyamide 12 (PA12) as the polymer matrix and multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) at different loadings (2.5, 5.0, and 10.0 wt.%) as fillers, were produced in 3D printing filament form by melt mixing extrusion process. The filament was then used to build specimens with the fused filament fabrication (FFF) three-dimensional (3D) printing process. The aim was to produce by FFF 3D printing, electrically conductive and thermoelectric functional specimens with enhanced mechanical properties. All nanocompositesâ samples were electrically conductive at filler loadings above the electrical percolation threshold. The highest thermoelectric performance was obtained for the PA12/CNT nanocomposite at 10.0 wt.%. The static tensile and flexural mechanical properties, as well as the Charpyâs impact and Vickers microhardness, were determined. The highest improvement in mechanical properties was observed for the PA12/CNT nanocomposites at 5.0 wt.% filler loading. The fracture mechanisms were identified by fractographic analyses of scanning electron microscopy (SEM) images acquired from fractured surfaces of tensile tested specimens. The nanocomposites produced could find a variety of applications such as; 3D-printed organic thermoelectric materials for plausible large-scale thermal energy harvesting applications, resistors for flexible circuitry, and piezoresistive sensors for strain sensing
Electromagnetic Shielding for Buildings Using Hybrid Polymer Composites: A Life Cycle Assessment Study
On the Mechanical Recycling of Decommisioned Insulation Polymer Composite Components
Fibre reinforced polymer composites (FRPs) are being increasingly used in aerospace and automotive applications due to their high specific mechanical properties. The construction industry has also started taking advantage of the potential of FRPs for both structural and non-structural purposes. The result of this remarkable absorption of FRPs within the worldwide production market, has led to an immense increase of decommissioned thermoset-matrix components. Nowadays, the majority of the decommissioned FRP components are recovered energy-wise through incineration or simply discarded in landfills around the globe. Within the framework of this paper, we present a solution for the extension of the service life of decommissioned FRP components. Decommissioned electrical insulation FRP pipes were granulated and incorporated as fillers within both cementitious and polymer matrix composites. The effect of FRP granulates on the mechanical performance of cementitious and polymer matrix composites is examined to determine the maximum granulate-filler fraction that can be recycled without compromising the mechanical performance and manufacturing process. © 2020 IOP Publishing Ltd. All rights reserved.Funding details: 2017-001986; Funding text 1: This work was funded by RECYTAL project (Vinnova/Energimyndigheten/Formas (Sweden) - RESource utlysning 2 (2016-2017), Project reference: 2017-001986). Authors are thankful to Marek Machowski (Chalmers University of Technology) and Peter Hellström (Swerea Sicomp) for their contribution to experimental testing. ABB Composites, Sweden, is greatly acknowledged for supplying discarded insulation FRP tubes whereas RAPID Granulator, Sweden, for shredding FRP tubes into fragments.</p
On the Use of Carbon Nanotubes to Develop Durable Structural Electrodes for Self-Sensing Applications
Sustainable Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol over Multiple Recycling Processes
The continuous demand for thermoplastic polymers in a great variety of applications, combined with an urgent need to minimize the quantity of waste for a balanced energy-from-waste strategy, has led to increasing scientific interest in developing new recycling processes for plastic products. Glycol-modified polyethylene terephthalate (PETG) is known to have some enhanced properties as compared to polyethylene terephthalate (PET) homopolymer; this has recently attracted the interest from the fused filament fabrication (FFF) three-dimensional (3D) printing community. PET has shown a reduced ability for repeated recycling through traditional processes. Herein, we demonstrate the potential for using recycled PETG in consecutive 3D printing manufacturing processes. Distributed recycling additive manufacturing (DRAM)-oriented equipment was chosen in order to test the mechanical and thermal response of PETG material in continuous recycling processes. Tensile, flexure, impact strength, and Vickers micro-hardness tests were carried out for six (6) cycles of recycling. Finally, Raman spectroscopy as well as thermal and morphological analyses via scanning electron microscopy (SEM) fractography were carried out. In general, the results revealed a minor knockdown effect on the mechanical properties as well as the thermal properties of PETG following the process proposed herein, even after six rounds of recycling
Synthesis of Bio-based monomers and polymers using microbes for a sustainable bioeconomy
The Two-Sidedness of Society : Actor-structure in the Research Programmes and the Applications of Three Approaches
SamhĂ€llsvetenskapliga portalfigurer som Durkheim, Marx och Weber har medverkat i diskussionen om aktör och struktur. Diskussionen om intentioner; agerande och samhĂ€llsstrukturer pĂ„gĂ„r fortfarande. Om de samhĂ€llsvetenskapliga fenomenen utgĂ„r frĂ„n individen â aktören â och/eller dess omgivning - strukturen - Ă€r en evig frĂ„ga. Denna avhandling Ă€r ett bidrag till den moderna diskussionen om aktör och struktur. Syftet Ă€r att analysera problemkomplexet aktör-struktur. MĂ„nga tidigare studier i genren Ă€r abstrakta och generella. I detta arbete studeras ocksĂ„ samhĂ€llsforskares tillĂ€mpning. Efter analyser av den aktörsteoretiska ansatsen (statsvetaren Axel Hadenius' forskning, den strukturteoretiska ansatsen (sociologen Bruce Mayhews forskning), samt a ansatsen (statsvetaren Bo Rothsteins forskning), samt redovisas ett preciserat förhĂ„llningssĂ€tt till problemkomplexet. Studiens utgĂ„ngspunkt Ă€r att bĂ„de den ensidiga aktörsteoretiska ansatsen och den ensidiga strukturteoretiska ansatsen kommer att uppvisa brister. De respektive ensidiga ansatserna antas inte brista frĂ€mst pĂ„ grund av sin ensidighet, vilket flera företrĂ€dare för den aktör-strukturteoretiska ansatsen hĂ€vdar. UtifrĂ„n avhandlingens vĂ€gledande analysram förvĂ€ntas de respektive ensidiga ansatsernas filosofier, teorier och förklaringar brista pĂ„ sĂ„ sĂ€tt att företrĂ€darnas programförklaringar inte stĂ€mmer överens med företrĂ€darnas tillĂ€mpningar. DĂ€rmed uppfyller de ensidiga ansatsernas företrĂ€dare inte det grundlĂ€ggande kravet pĂ„ vetenskaplig klarhet. Av analysen framgĂ„r att det i den aktörsteoretiska ansatsens tillĂ€mpning ocksĂ„ Ă„terfinns strukturfaktorer av ett slag som ansatsens företrĂ€dare programmatiskt vill utesluta. I den tillĂ€mpade strukturteoretiska ansatsen Ă„terfinns aktörsfaktorer. OcksĂ„ den aktör-strukturteoretiska ansats som analyseras uppvisar brister i överensstĂ€mmelse mellan programförklaring och tillĂ€mpning. Resultaten tas till intĂ€kt för att överge bĂ„de den individualism som den aktörsteoretiska ansatsen vilar pĂ„ och den strukturalism sĂ€tts i detta arbete den filosofiska antagande att den samhĂ€lleliga verkligheten innehĂ„ller bĂ„de aktör och struktur, Antagandet om samhĂ€llets tvĂ„sidighet utgör en viktig grund för den preciserande aktör-strukturteoretiska ansats som Ă€r studiens övergripande slutsats.This thesis is a contribution to the age-old discussion in the social sciences about actor and structure. From the outset it is argued that the question of actor and structure constitutes a complexity of problems which contains philosophical, theoretical and explanatory elements. Different ways of comprehending the complexity of problems constitute a watershed between research approaches. The three main approaches are the actor theoretical approach, the structural theoretical approach and 1he actor-structural theoretical approach. The purpose of this study is to analyse these three approaches and thereby present a fruitful approach to the complexity of problems. The author adopts the combined actor-structural theoretical approach from the start, but not in an uncritical and self-evident manner. This study is based on two lines of argumentation. Firstly, it is stipulated that a social scientist's research programme on actor and structure should be consistent With the researcher's application. Secondly, it is stipulated that social reality consists of both actor and s1ructure, and that actor and structure do not mean the same thing. The author's suggestion is that this idea about the two-sidedness of soc iety is a prerequisite for interna! consistency. Hence, traces of both actor and structure should a lso be found in the applications of the two one-sided approaches. In order to discern the one-sided actor theoretical approach, three ideas are stipulated as philosophy, theory and explanation in a specified ideal type: methodological individualism, instrumental rationality and intentional explanation. These ideas are present in the research programme of the chosen representative of the actor theoretical approach, the Swedish political scientist Axel Hadenius. It is found that Hadenius' application does not correspond with his research programme. In his application. factors occur that are not totally reducible to facts aboul separale or aggregated individuals. In order to discern the one-sided sructural theoretical approach, three ideas are stipulated as philosophy. theory and explanation in a specified ideal type: structuralism, theoretical relations between structures and nomothetical-deductive explanations with structures. These ideas are present in the research programme of the chosen representative of the structural theoretical approach, the American sociologi st Bruce Mayhew. It is found that Mayhew's application does not correspond with his research programme. In his application, fac1s about separate or aggregated individuals occur. The three ideas behind the ideal type actor-structural theoretical approach are two-sided level realism, theoretical actor-structural relations and actor-structural explanation. These ideas are present in the research programme of the chosen representative of the actor-structural theoretical approach, the Swedish political scientist Bo Rothstein, even if there are also traces leading off in other directions. Finally, the testing of the occurrence of the preliminary actor-structural approach in the three research approaches is combined with the elabora1ion of philosophy, theory and explana1ion in the specified actorstructural theoretical approach. The latter approach constitutes the author's stand on the complexity of problems of actor and structure. The philosophy in the specified approach, two-sided leve! realism, is allegedly composed of three closely related ideas: actual closeness between actor and structure, situational irreducibility, and the relational concept of social structure. The idea of the theoretical relation between actor and structure is allegedly composed of three closely related ideas: empirical openness, analytical dualism and generative mechanisms. All are, in tum, closely related to the three ideas of the two-sided leve! realism, as well as to the idea of actor-structural explanation. The specified approach lays the foundations for clarity in terms of internat logical congruence between research programme and application