3D printing by fused filament fabrication (FFF) provides an innovative manufacturing method for complex geometry components. Since FFF is a layered manufacturing process, effects of process ...parameters are of concern when plastic materials such as polylactic acid (PLA), polystyrene and nylon are used. This study explores how the process parameters, e.g. build orientation and infill pattern/density, affect the mechanical response of PLA samples produced using FFF. Digital image correlation (DIC) was employed to get full-field surface-strain measurements. The results show the influence of build orientation and infill density is significant. For on-edge orientation, the tensile strength and Young’s modulus were 55 MPa and 3.5 GPa respectively, which were about 91% and 40% less for the upright orientation, demonstrating a significant anisotropy. The tensile strength and Young’s modulus increased with increasing infill density. In contrast, different infill patterns have no significant effect. Considering the influence of build orientation, based on the experimental results, a constitutive model derived from the laminate plate theory was employed. The material parameters were determined by tensile tests. Results demonstrated a reasonable agreement between the experimental data and the predictive model. Similar anisotropy to tension was observed in shear tests; shear modulus and shear strength for 45° flat orientation were about 1.55 GPa and 36 MPa, whereas for upright specimens they were about 0.95 GPa and 18 MPa, respectively. The findings provide a framework for systematic mechanical characterisation of 3D-printed polymers and potential ways of choosing process parameters to maximise performance for a given design.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
How Technology is Changing Retail Shankar, Venkatesh; Kalyanam, Kirthi; Setia, Pankaj ...
Journal of retailing,
03/2021, Volume:
97, Issue:
1
Journal Article
Peer reviewed
Retailing is undergoing a remarkable transformation brought by recent advances in technology. In this paper, we provide a deep discussion of and look ahead on how technology is changing retail, ...starting with a classification of technologies that impact retailing, in particular, in the COVID-19 and beyond world. We discuss different theoretical frameworks or lenses to better understand the role of technology in retailing. We identify and elaborate on the drivers and outcomes of technology adoption by shoppers, retailers, employees, and suppliers. We speculate on future retail scenarios and outline future research avenues on technology and retailing. We close by concluding that technology is not only reshaping retailing, but also allowing retailing to pivot in the face of new and unforeseen circumstances.
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CEKLJ, GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
3.
Nanoindentation of coatings Bull, S J
Journal of physics. D, Applied physics,
12/2005, Volume:
38, Issue:
24
Journal Article
Peer reviewed
A range of mechanical properties of a coating/strate system may be obtained using indentation tests, and with the emergence of continuously recording indentation testing with nanometre penetration ...(often called nanoindentation) the mechanical properties of very thin coatings ( < 1 mum) and surface treated layers may be measured. This paper reviews the deformation mechanisms which occur and the methods for extracting mechanical properties of coatings from nanoindentation load-displacement curves and introduces the differences observed when compared with the testing of bulk materials. The importance of the relative hardness of coating and substrate on the response of the system is highlighted, and the use of energy-based models for the prediction of the performance of single and multilayered systems is discussed.
The fundamental property which often dictates the performance of a coating is its adhesion to the substrate and thus there are many techniques to measure adhesion. The choice of methods is dependent ...on many factors such as the mechanical properties of the coating and substrate, the interface properties, the microstructure of the coating/substrate system, residual stress, coating thickness and the intended application. Most tests aim to introduce a stable interfacial crack and make it propagate under controlled conditions and model this process to determine adhesion. The corresponding models are either stress analysis-based or energy-based. With the advent of miniature systems and very thin functional coatings, there is a need for characterization of adhesion at small length scales and some specific tests have been developed which are not appropriate for thicker coatings. Among these, indentation and scratch methods have the widest range of applicability but it is necessary to analyse the failure mechanisms before choosing an appropriate model to extract adhesion parameters. This paper reviews the main quantitative adhesion tests for coatings and highlights the tests which can be used to assess submicrometre coatings and thin films. The paper also highlights the modelling and analysis methods necessary to extract reliable adhesion properties illustrating this with examples for submicrometre coatings on silicon and architectural glass.
Kinetics of the homogeneous freezing of water Murray, B. J; Broadley, S. L; Wilson, T. W ...
Physical chemistry chemical physics : PCCP,
01/2010, Volume:
12, Issue:
35
Journal Article
Peer reviewed
Rates of homogeneous nucleation of ice in micrometre-sized water droplets are reported. Measurements were made using a new system in which droplets were supported on a hydrophobic substrate and their ...phase was monitored using optical microscopy as they were cooled at a controlled rate. Our nucleation rates are in agreement, given the quoted uncertainties, with the most recent literature data. However, the level of uncertainty in the rate of homogeneous freezing remains unacceptable given the importance of homogeneous nucleation to cloud formation in the Earth's atmosphere. We go on to use the most recent thermodynamic data for cubic ice (the metastable phase thought to nucleate from supercooled water) to estimate the interfacial energy of the cubic ice-supercooled water interface. We estimate a value of 20.8 ± 1.2 mJ m
−2
in the temperature range 234.9-236.7 K.
Temperature dependent nucleation rates of ice in water are analysed assuming the metastable cubic phase of ice nucleates.
The different indentation fracture mechanisms of coated glass caused by a sharp tip (cube corner) at low loads ( < 4 mN) and a blunt tip (Berkovich) at high loads (up to 500 mN) have been analysed in ...this study. Existing indentation methods to estimate fracture toughness are unsuitable for very thin coatings ( < 500 nm). An alternative energy-based method can successfully be applied in the assessment of the ultra-small cracks produced in coated glass based on excursions in the load-displacement curve caused by indentation with a sharp tip. However, it was found that no excursions were observed associated with picture-frame cracks produced by a blunt tip in the same coatings; this is not unusual in other coated systems and makes the existing energy-based models invalid. Therefore, a new energy-based model is developed here to solve this problem and good results have been obtained. The existing models cannot be applied to the analysis of the indentation-induced interfacial failure in this study; therefore, new approaches have also been developed to assess the interfacial toughness and again reasonable results are obtained.
Depression and fatigue are frequent side effects of interferon-alpha (IFN-alpha) treatment, and there is compelling evidence that the inflammatory response system (including interleukin-6, IL-6) and ...the serotonergic system is important in the pathophysiology of such symptoms. Functional polymorphisms in the promoter region of the IL-6 gene (rs1800795) and serotonin transporter gene (5-HTTLPR) have been identified as regulating these systems. The present study aimed to determine if these polymorphisms were associated with the development of depression and fatigue during IFN-alpha and ribavirin treatment. Ninety-eight Caucasian patients receiving pegylated IFN-alpha and ribavirin treatment for chronic hepatitis C virus at King's College Hospital, London, and Emory University Hospital, Atlanta, participated in this prospective cohort study. Symptoms of depression and fatigue were measured before treatment and at weeks 4, 8, 12 and 24 during treatment. The 'low IL-6' synthesizing genotype (CC) was associated with significantly fewer symptoms of depression (effect size = 0.7 at week 24; F = 9.4, d.f. = 436, P = 0.002). The 'high transcription' serotonin transporter (5-HTT) genotype (LL) was also associated with significantly fewer symptoms of depression, but with a much smaller effect (effect size = 0.2 at week 24; F = 4.5, d.f. = 436, P = 0.03). Neither polymorphisms were associated with symptoms of fatigue (IL-6: F = 1.2, d.f. = 430, P = 0.2; 5-HTT: F = 0.5, d.f. = 430, P = 0.5). The smaller effects of the 5-HTT polymorphism on depression may be explained by an interaction between the genes (F = 5.0, d.f. = 434, P = 0.02): the 'protective' effect of the 5-HTTLPR polymorphism was evident only in the presence of the 'low IL-6' genotype (F = 5.4, d.f. = 64, P = 0.02), not in the presence of the 'high IL-6' genotype (F = 2.2, d.f. = 369, P = 0.1). The association between the IL-6 polymorphism and reduced risk of depressive symptoms confirms the role of the inflammatory response system in the pathophysiology of IFN-alpha-induced depression; in contrast, the effect of the 5-HTT gene was small and perhaps dependent on the status of the inflammatory response.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The scratch test has been used to assess the adhesion of thin hard coatings for some time now and is a useful tool for coating development or quality assurance. However, the test is influenced by a ...number of intrinsic and extrinsic factors which are not adhesion-related and the results of the test are usually regarded as only semi-quantitative. The stress state around a moving indenter scratching a coating/substrate system is very complex and it is difficult to determine the stresses which lead to detachment. Furthermore, the interfacial defect state responsible for failure is unknown. However, by a careful analysis of the observed failure modes in the scratch test (not all of which are related to adhesion) it is possible to identify adhesive failures and in some cases these occur in regions where the stress state is relatively simple and quantification can be attempted.
Ideally engineers would like a material parameter (such as work of adhesion or interfacial toughness) which can be used in an appropriate model of the coating-substrate system stress state to determine if detachment will occur under the loading conditions experienced in service. This data is not usually available and the development of such models must be seen as a long-term goal. In modern indentation and scratch systems the work of friction (or indentation) can be directly measured and the relationship between this parameter and adhesive failure can be demonstrated in some cases. This paper reviews the main adhesion-related failure modes and the stresses responsible for them and indicates where quantification is possible illustrating this with results from hard coatings on steel, thermally grown oxide scales and optical coatings on glass. The use of empirical calibration studies, directly measured work of friction and quantification by finite element methods is discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SBCE, SBJE, UPUK
Various indentation models have been developed to measure the toughness of bulk materials and coatings. Most of them are based on the formation of well-developed cracks. However, in order to ...eliminate the influence of elastic–plastic deformation in the substrate, it is preferable to perform small indentations in thin coatings and thus the cracks may not be well-developed compared to the indentation size. Relatively little work has been done to investigate this kind of small cracks. The ultra small cracks (<
500 nm in length) in thin coatings (∼
500 nm in thickness) confined to indentation zone are investigated here. A new method to assess the toughness of the main components of solar control coatings such as SnO
2, TiO
x
N
y
and ITO deposited on soda–lime glass is proposed here. This method is able to separate the energy contributions from other deformation mechanisms from that dissipated in the fracture event. The energy release rate of these ceramics coating are in the range 15–45 J/m
2 by this method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
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