Search results for: unconfined compressive strength (USC)

Authors: Jae-Ho Jang, Jung-Soo Kim, Byung-Jun Kim, Dae-Geun Nam, Uoo-Chang Jung, Yoon-Suk Choi

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Low alloy steels are widely used for pressure vessels, spent fuel storage, and steam generators required to withstand the internal pressure and prevent unexpected failure in nuclear power plants, which these may suffer embrittlement by high levels of radiation and heat for a long period. Therefore, it is important to improve mechanical properties of low alloy steels for the integrity of structure materials at an early stage of fabrication. Recently, it showed that a double austenitizing and tempering (DTA) process resulted in a significant improvement of strength and toughness by refinement of prior austenite grains. In this study, it was investigated that the mechanism of improving mechanical properties according to the change of microstructure by the second fully austenitizing temperature of the DAT process for low alloy steel required the structural integrity. Compared to conventional single austenitizing and tempering (SAT) process, the tensile elongation properties have improved about 5%, DBTTs have obtained result in reduction of about -65℃, and grain size has decreased by about 50% in the DAT process conditions. Grain refinement has crack propagation interference effect due to an increase of the grain boundaries and amount of energy absorption at low temperatures. The higher first austenitizing temperature in the DAT process, the more increase the spheroidized carbides and strengthening the effect of fine precipitates in the ferrite grain. The area ratio of the dimple in the transition area has increased by proportion to the effect of spheroidized carbides. This may the primary mechanisms that can improve low-temperature toughness and elongation while maintaining a similar hardness and strength.

Keywords: double austenitizing, Ductile Brittle transition temperature, grain refinement, heat treatment, low alloy steel, low-temperature toughness

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Authors: Masita Mokeira, Kimani Rita, Obonyo Brian, Kwenda Kennedy, Mugambi Purity, Kirui Joan, Chomba Eric, Orwa Daniel, Waiganjo Peter

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Rugby is a highly intense and physical game requiring speed and strength. The need for physical fitness therefore cannot be over-emphasized. Sports are no longer about lifting weights so as to build muscle. Most professional teams are investing much more in the sport in terms of time, equipment and other resources. To play competitively, Kenyan players may therefore need to complement their ‘home-grown’ and sometimes ad-hoc training and nutrition regimes with carefully measured strength and conditioning, diet, nutrition, and supplementation. Nokia Research Center and University of Nairobi conducted an exploratory study on needs and behaviours surrounding sports in Africa. Rugby being one sport that is gaining ground in Kenya was selected as the main focus. The end goal of the research was to identify areas where mobile technology could be used to address gaps, challenges and/or unmet needs. Themes such as information gap, social culture, growth, and development, revenue flow, and technology adoption among others emerged about the sport. From the growth and development theme, it was clear that as rugby continues to grow in the country, teams, coaches, and players are employing interesting techniques both in training and playing. Though some of these techniques are indeed scientific, those employing them are sometimes not fully aware of their scientific basis. A further case study on sports science in rugby in Kenya focusing on physical fitness and nutrition revealed interesting findings. This paper discusses findings on emerging adoption of techniques in managing physiological and nutritional needs of rugby players across different levels of rugby in Kenya namely high school, club and national levels.

Keywords: rugby, nutrition, physiological needs, sports science

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Authors: Bo-Jian Wu, Si-Heng Wu

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Objectives: Frailty is a condition of a person who has chronic health problems complicated by a loss of physiological reserve and deteriorating functional abilities. The frailty syndrome was defined by Fried and colleagues, i.e., weight loss, fatigue, decreased grip strength, slow gait speed, and low physical activity. However, to our best knowledge, there have been rare studies exploring the prevalence of frailty and its association with falls in patients with schizophrenia. Methods: A total of 559 hospitalized patients were recruited from a public psychiatric hospital in 2013. The majority of the subjects were males (361, 64.6%). The average age was 53.5 years. All patients received the assessment of frailty status defined by Fried and colleagues. The status of a fall within one year after the assessment of frailty, clinical and demographic data was collected from medical records. Logistic regression was used to calculate the odds ratio of associated factors. Results : A total of 9.2% of the participants met the criteria of frailty. The percentage of patients having a fall was 7.2%. Age were significantly associated with frailty (odds ratio = 1.057, 95% confidence interval = 1.025-1.091); however, sex was not associated with frailty (p = 0.17). After adjustment for age and sex, frailty status was associated with a fall (odds ratio = 3.62, 95% confidence interval = 1.58-8.28). Concerning the components of frailty, decreased grip strength (odds ratio = 2.44, 95% confidence interval = 1.16-5.14), slow gait speed (odds ratio = 2.82, 95% confidence interval = 1.21-6.53), and low physical activity (odds ratio = 2.64, 95% confidence interval = 1.21-5.78) were found to be associated with a fall. Conclusions: Our findings suggest the prevalence of frailty was about 10% in hospitalized patients with chronic patients with schizophrenia, and frailty status was significant with a fall in this group. By using the status of frailty, it may be beneficial to potential target candidates having fallen in the future as early as possible. The effective intervention of prevention of further falls may be given in advance. Our results bridge this gap and open a potential avenue for the prevention of falls in patients with schizophrenia. Frailty is certainly an important factor for maintaining wellbeing among these patients.

Keywords: fall, frailty, schizophrenia, Taiwan

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Authors: Julie Anne Braun, Leonardo D. da Fonseca, Gerson C. Parreira, Ricardo J. E. Andrade

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Polyurethanes (PU) are multifunctional polymers used across various industries. In construction, thermosetting polyurethanes are applied as coatings for flooring, paints, and waterproofing. They are widely specified in Brazil for waterproofing concrete structures like roof slabs and parking decks. Applied to concrete, they form a fully adhered membrane, providing a protective barrier with low water absorption, high chemical resistance, impermeability to liquids, and low vapor permeability. Their mechanical properties, including tensile strength (1 to 35 MPa) and Shore A hardness (83 to 88), depend on resin molecular weight and functionality, often using Methylene diphenyl diisocyanate. PU production, reliant on fossil-derived isocyanates and polyols, contributes significantly to carbon emissions. Sustainable alternatives, such as biopolyurethanes from renewable sources, are needed. Castor oil is a viable option for synthesizing sustainable polyurethanes. As a bio-based feedstock, castor oil is extensively cultivated in Brazil, making it a feasible option for the national market and ranking third internationally. This study aims to develop and characterize castor oil-based biopolyurethane for high-performance waterproofing and coating applications. A comparative analysis between castor oil-based PU and polyether polyol-based PU was conducted. Mechanical tests (tensile strength, Shore A hardness, abrasion resistance) and surface properties (contact angle, water absorption) were evaluated. Thermal, chemical, and morphological properties were assessed using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results demonstrated that both polyurethanes exhibited high mechanical strength. Specifically, the tensile strength for castor oil-based PU was 19.18 MPa, compared to 12.94 MPa for polyether polyol-based PU. Similarly, the elongation values were 146.90% for castor oil-based PU and 135.50% for polyether polyol-based PU. Both materials exhibited satisfactory performance in terms of abrasion resistance, with mass loss of 0.067% for castor oil PU and 0.043% for polyether polyol PU and Shore A hardness values of 89 and 86, respectively, indicating high surface hardness. The results of the water absorption and contact angle tests confirmed the hydrophilic nature of polyether polyol PU, with a contact angle of 58.73° and water absorption of 2.53%. Conversely, the castor oil-based PU exhibited hydrophobic properties, with a contact angle of 81.05° and water absorption of 0.45%. The results of the FTIR analysis indicated the absence of a peak around 2275 cm-1, which suggests that all of the NCO groups were consumed in the stoichiometric reaction. This conclusion is supported by the high mechanical test results. The TGA results indicated that polyether polyol PU demonstrated superior thermal stability, exhibiting a mass loss of 13% at the initial transition (around 310°C), in comparison to castor oil-based PU, which experienced a higher initial mass loss of 25% at 335°C. In summary, castor oil-based PU demonstrated mechanical properties comparable to polyether polyol PU, making it suitable for applications such as trafficable coatings. However, its higher hydrophobicity makes it more promising for watertightness. Increasing environmental concerns necessitate reducing reliance on non-renewable resources and mitigating the environmental impacts of polyurethane production. Castor oil is a viable option for sustainable polyurethanes, aligning with emission reduction goals and responsible use of natural resources.

Keywords: polyurethane, castor oil, sustainable, waterproofing, construction industry

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Authors: Ahmed Bolaji Alarape, Oluwatobi Damilola Aba, Usman Shehu

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Wood plastic composite boards were made from sawn dust of Cordia alliodora and recycled polyethylene at a mixing ratio of 1.5ratio1, 2.5ratio1 and 3.5ratio1 and nominal densities of 600 kilograms per meter cube, 700 kilograms per meter cube, and 800 kilograms per meter cube, The material was hot pressed at 150-degree celsius to produce board of 250 millimeter by 250 millimeter by 6 millimeter of which 18 boards were produced. The experiment was subject to 3 by 3 factorial experiments in Completely Randomised Design (CRD). Analysis of variance and Duncan Multiple Range Test (DMRT) was adopted by 3 by 3 at 5 percent probability. The strength properties of the boards such as modulus of rupture (MOR) and modulus of elasticity (MOE) were investigated, while the dimensional properties of the board such as the water absorption (WA) and thickness swelling (TS) were as well determined after 12hrs and 24hrs of water immersion. The result showed that the mean values of MOE ranged from 9100.73 Newtons per square millimeters to 12086.96 Newtons per square millimeters while MOR values ranged from 48.26 Newtons per square millimeters to 103.09 Newtons per square millimeters. The values of WA and TS after 12hrs immersion ranged from 1.21 percent to 1.56 percent and 0.00 percent to 0.13 percent, respectively. The values of WA and TS after 24hrs of water immersion ranged from 1.66 percent to 2.99 percent and 0.02 percent to 0.18 percent, respectively. The higher the value of board density and the high-density polythene /sawdust ratio, the stronger, the stiffer and more dimensionally stable the wood plastic composite boards obtained. In addition, as the density of the board increases, the strength property of the boards increases. Hence the board will be suitable for internal construction materials.

Keywords: wood Plastic composite, modulus of rupture, modulus of elasticity, dimensional stability

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Authors: Tengqin Han

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Delinquency has been a crucial factor in economics throughout the years. Commonly seen in credit card and mortgage, it played one of the crucial roles in causing the most recent financial crisis in 2008. In each case, a delinquency is a sign of the loaner being unable to pay off the debt, and thus may cause a lost of property in the end. Individually, one case of delinquency seems unimportant compared to the entire credit system. China, as an emerging economic entity, the national strength and economic strength has grown rapidly, and the gross domestic product (GDP) growth rate has remained as high as 8% in the past decades. However, potential risks exist behind the appearance of prosperity. Among the risks, the credit system is the most significant one. Due to long term and a large amount of balance of the mortgage, it is critical to monitor the risk during the performance period. In this project, about 300,000 mortgage account data are analyzed in order to develop a predictive model to predict the probability of delinquency. Through univariate analysis, the data is cleaned up, and through bivariate analysis, the variables with strong predictive power are detected. The project is divided into two parts. In the first part, the analysis data of 2005 are split into 2 parts, 60% for model development, and 40% for in-time model validation. The KS of model development is 31, and the KS for in-time validation is 31, indicating the model is stable. In addition, the model is further validation by out-of-time validation, which uses 40% of 2006 data, and KS is 33. This indicates the model is still stable and robust. In the second part, the model is improved by the addition of macroeconomic economic indexes, including GDP, consumer price index, unemployment rate, inflation rate, etc. The data of 2005 to 2010 is used for model development and validation. Compared with the base model (without microeconomic variables), KS is increased from 41 to 44, indicating that the macroeconomic variables can be used to improve the separation power of the model, and make the prediction more accurate.

Keywords: delinquency, mortgage, model development, model validation

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Authors: Jong Yeop Kim, Jong Bum Choi, Hyun Jeong Kwak, Sook Young Lee

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Background: Each supraglottic airway requires different anesthetic depth because it has a specific structure and different compressive force in the oropharyngeal cavity. We designed the study to investigate remifentanil effect-site concentration (Ce) in 50% of patients (EC50) for successful insertion of i- gel, and to compare it with that for laryngeal mask airway (LMA) insertion during propofol target-controlled infusion (TCI). Methods: Forty-one female patients were randomized to the i-gel group (n=20) or the LMA group (n=21). Anesthesia induction was performed using propofol Ce of 5 μg/ml and the predetermined remifentanil Ce, and i-gel or LMA insertion was attempted 5 min later. The remifentanil Ce was estimated by modified Dixon's up-and-down method (initial concentration: 3.0 ng/ml, step size: 0.5 ng/ml). The patient’s response to device insertion was classified as either ‘success (no movement)’ or ‘failure (movement)’. Results: Using the Dixon’s up and down method, EC50 of remifentanil Ce for i-gel (1.58 ± 0.41 ng/ml) was significantly lower than that for LMA (2.25 ± 0.55 ng/ml) (p=0.038). Using isotonic regression, EC50 (83% CI) of remifentanil in the i-gel group [1.50 (1.37-1.80) ng/ml] was statistically lower than that in the LMA group [2.00 (1.82-2.34) ng/ml]. EC95 (95% CI) of remifentanil in the i-gel group [2.38 (1.48-2.50) ng/ml] was statistically lower than that in the LMA group [3.35 (2.58-3.48) ng/ml]. Conclusion: We found that EC50 of remifentanil Ce for i-gel insertion (1.58 ng/ml) was significantly lower than that for LMA insertion (2.25 ng/ml), in female patients during propofol TCI without neuromuscular blockade.

Keywords: i-gel, laryngeal mask airway, propofol, remifentanil

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Authors: S. Amirhossein Tabatabaei, Abdulghader A. Aldaeef, Mohammad T. Rayhani

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As the permafrost continues to melt in the northern regions due to global warming, a soil-water mixture is left behind with drastically lower strength; a phenomenon that directly impacts the resilience of existing structures and infrastructure systems. The frozen soil-structure interaction, which in ice-poor soils is controlled by both interface shear and ice-bonding, changes its nature into a sole frictional state. Adfreeze, the controlling mechanism in frozen soil-structure interaction, diminishes as the ground temperature approaches zero. The main purpose of this paper is to capture the altered behaviour of frozen interface with respect to rising temperature, especially near melting states. A series of pull-out tests are conducted on model piles inside a cold room to study how the strength parameters are influenced by the phase change in ice-poor soils. Steel model piles, embedded in artificially frozen cohesionless soil, are subjected to both sustained pull-out forces and constant rates of displacement to observe the creep behaviour and acquire load-deformation curves, respectively. Temperature, as the main variable of interest, is increased from a lower limit of -10°C up to the point of melting. During different stages of the temperature rise, both skin deformations and temperatures are recorded at various depths along the pile shaft. Significant reduction of pullout capacity and accelerated creep behaviour is found to be the primary consequences of rising temperature. By investigating the different pull-out capacities and deformations measured during step-wise temperature change, characteristics of the transition from frozen to unfrozen soil-structure interaction are studied.

Keywords: Adfreeze, frozen soil-structure interface, ice-poor soils, pull-out capacity, warming permafrost

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Authors: Mahboubeh Kabiri, Saba Aslani

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Among various approaches used for the treatment of cardiovascular diseases, the occlusion of the small-diameter vascular graft (SDVG) is still an unresolved problem which seeks further research to address them. Though autografts are now the gold standards to be replaced for blocked coronary arteries, they suffer from inadequate quality and quantity. On the other hand, the major problems of the tissue engineered grafts are thrombosis and intimal hyperplasia. Provision of a suitable spatiotemporal release pattern of anticoagulant agents such as heparin and aspirin can be a step forward to overcome such issues . Herein, we fabricated electrospun scaffolds from FDA (Food and Drug Administration) approved poly-L-lactic acid (PLLA) with aspirin loaded into the nanofibers. Also, we surface coated the scaffolds with Amniotic Membrane lysate as a source for natural elastic polymers and a mimic of endothelial basement membrane. The scaffolds were characterized thoroughly structurally and mechanically for their morphology, fiber orientation, tensile strength, hydrophilicity, cytotoxicity, aspirin release and cell attachment support. According to the scanning electron microscopy (SEM) images, the size of fibers ranged from 250 to 500 nm. The scaffolds showed appropriate tensile strength expected for vascular grafts. Cellular attachment, growth, and infiltration were proved using SEM and MTT (3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide) assay. Drug-loaded scaffolds showed a sustained release profile of aspirin in 7 days. An enhanced cytocompatibility was observed in AM-coated electrospun PLLA fibers compared to uncoated scaffolds. Our results together indicated that AM lysate coated ASA releasing scaffolds have promising potentials for development of a biocompatible SDVG.

Keywords: vascular tissue engineering, vascular grafts, anticoagulant agent, aspirin, amniotic membrane

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Authors: Saruhan Kartal, Ilker Kalkan

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The present paper reports the cracking moment estimates of a set of steel-reinforced, Fiber Reinforced Polymer (FRP)-reinforced and hybrid steel-FRP reinforced concrete beams, calculated from different analytical formulations in the codes, together with the experimental cracking load values. A total of three steel-reinforced, four FRP-reinforced, 12 hybrid FRP-steel over-reinforced and five hybrid FRP-steel under-reinforced concrete beam tests were analyzed within the scope of the study. Glass FRP (GFRP) and Basalt FRP (BFRP) bars were used in the beams as FRP bars. In under-reinforced hybrid beams, rupture of the FRP bars preceded crushing of concrete, while concrete crushing preceded FRP rupture in over-reinforced beams. In both types, steel yielding took place long before the FRP rupture and concrete crushing. The cracking moment mainly depends on two quantities, namely the moment of inertia of the section at the initiation of cracking and the flexural tensile strength of concrete, i.e. the modulus of rupture. In the present study, two different definitions of uncracked moment of inertia, i.e. the gross and the uncracked transformed moments of inertia, were adopted. Two analytical equations for the modulus of rupture (ACI 318M and Eurocode 2) were utilized in the calculations as well as the experimental tensile strength of concrete from prismatic specimen tests. The ACI 318M modulus of rupture expression produced cracking moment estimates closer to the experimental cracking moments of FRP-reinforced and hybrid FRP-steel reinforced concrete beams when used in combination with the uncracked transformed moment of inertia, yet the Eurocode 2 modulus of rupture expression gave more accurate cracking moment estimates in steel-reinforced concrete beams. All of the analytical definitions produced analytical values considerably different from the experimental cracking load values of the solely FRP-reinforced concrete beam specimens.

Keywords: polymer reinforcement, four-point bending, hybrid use of reinforcement, cracking moment

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Authors: Mohammed Ghazwani, Shyma Ali Alshahrani, Zahra Abdu Yousef, Taif Torki Asiri, Ghofran Abdur Rahman, Asma Ali Alshahrani, Umme Hani

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Background and introduction: Piroxicam is a nonsteroidal anti-inflammatory drug characterized by low solubility-high permeability used to reduce pain, swelling, and joint stiffness from arthritis. Hydrotropes are a class of compounds that normally increase the aqueous solubility of insoluble solutes. Aim: The objective of the present research study was to formulate and optimize Piroxicam hydrotropic starch gel using sodium salicylate, sodium benzoate as hydrotropic salts, and potato starch for topical application. Materials and methods: The prepared Piroxicam hydrotropic starch gel was characterized for various physicochemical parameters like drug content estimation, pH, tube extrudability, and spreadability; all the prepared formulations were subjected to in-vitro diffusion studies for six hours in 100 ml phosphate buffer (pH 7.4) and determined gel strength. Results: All formulations were found to be white opaque in appearance and have good homogeneity. The pH of formulations was found to be between 6.9-7.9. Drug content ranged from 96.8%-99.4.5%. Spreadability plays an important role in patient compliance and helps in the uniform application of gel to the skin as gels should spread easily; F4 showed a spreadability of 2.4cm highest among all other formulations. In in vitro diffusion studies, extrudability and gel strength were good with F4 in comparison with other formulations; hence F4 was selected as the optimized formulation. Conclusion: Isolated potato starch was successfully employed to prepare the gel. Hydrotropic salt sodium salicylate increased the solubility of Piroxicam and resulted in a stable gel, whereas the gel prepared using sodium benzoate changed its color after one week of preparation from white to light yellowish. Hydrotropic potato starch gel proposed a suitable vehicle for the topical delivery of Piroxicam.

Keywords: Piroxicam, potato starch, hydrotropic salts, hydrotropic starch gel

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Authors: Amani Alotaibi

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3D printing has emerged as a pivotal technique for scaffold development, particularly in the field of bone tissue regeneration, due to its ability to customize scaffolds to fit complex geometries of bone defects. Among the various methods available, fused deposition modeling (FDM) is particularly promising as it avoids the use of solvents or toxic chemicals during fabrication. This study investigates the effects of three key parameters, extrusion temperature, screw rotational speed, and deposition speed, on the crystallization and mechanical properties of polycaprolactone (PCL) scaffolds. Three extrusion temperatures (70°C, 80°C, and 90°C), three screw speeds (10 RPM, 15 RPM, and 20 RPM), and three deposition speeds (8 mm/s, 10 mm/s, and 12 mm/s) were evaluated. The scaffolds were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and tensile testing to assess changes in crystallinity and mechanical properties. Additionally, the scaffolds were analyzed for crystal size and biocompatibility. The results demonstrated that increasing the extrusion temperature to 80°C, combined with a screw speed of 15 RPM and a deposition speed of 10 mm/s, significantly improved the crystallinity, compressive modulus, and thermal resistance of the PCL scaffolds. These findings suggest that by fine-tuning basic 3D printing parameters, it is possible to modulate the structural and mechanical properties of the scaffold, thereby enhancing its suitability for bone tissue regeneration.

Keywords: 3D printing, polymer, scaffolds, tissue engineering, crystallization

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Authors: E. Nakamachi, S. Tanaka, K. Yamamoto, Y. Morita

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In this study, we developed a three-dimensional (3D) direct current electric field (DCEF) stimulation bio-reactor for axonal outgrowth enhancement to generate the neural network of the central nervous system (CNS). By using our newly developed 3D DCEF stimulation bio-reactor, we cultured the rat pheochromocytoma cells (PC12) and investigated the effects on the axonal extension enhancement and network generation. Firstly, we designed and fabricated a 3D bio-reactor, which can load DCEF stimulation on PC12 cells embedded in the collagen gel as extracellular environment. The connection between the electrolyte and the medium using salt bridges for DCEF stimulation was introduced to avoid the cell death by the toxicity of metal ion. The distance between the salt bridges was adopted as the design variable to optimize a structure for uniform DCEF stimulation, where the finite element (FE) analyses results were used. Uniform DCEF strength and electric flux vector direction in the PC12 cells embedded in collagen gel were examined through measurements of the fabricated 3D bio-reactor chamber. Measurement results of DCEF strength in the bio-reactor showed a good agreement with FE results. In addition, the perfusion system was attached to maintain pH 7.2 ~ 7.6 of the medium because pH change was caused by DCEF stimulation loading. Secondly, we disseminated PC12 cells in collagen gel and carried out 3D culture. Finally, we measured the morphology of PC12 cell bodies and neurites by the multiphoton excitation fluorescence microscope (MPM). The effectiveness of DCEF stimulation to enhance the axonal outgrowth and the neural network generation was investigated. We confirmed that both an increase of mean axonal length and axogenesis rate of PC12, which have been exposed 5 mV/mm for 6 hours a day for 4 days in the bioreactor. We found following conclusions in our study. 1) Design and fabrication of DCEF stimulation bio-reactor capable of 3D culture nerve cell were completed. A uniform electric field strength of average value of 17 mV/mm within the 1.2% error range was confirmed by using FE analyses, after the structure determination through the optimization process. In addition, we attached a perfusion system capable of suppressing the pH change of the culture solution due to DCEF stimulation loading. 2) Evaluation of DCEF stimulation effects on PC12 cell activity was executed. The 3D culture of PC 12 was carried out adopting the embedding culture method using collagen gel as a scaffold for four days under the condition of 5.0 mV/mm and 10mV/mm. There was a significant effect on the enhancement of axonal extension, as 11.3% increase in an average length, and the increase of axogenesis rate. On the other hand, no effects on the orientation of axon against the DCEF flux direction was observed. Further, the network generation was enhanced to connect longer distance between the target neighbor cells by DCEF stimulation.

Keywords: PC12, DCEF stimulation, 3D bio-reactor, axonal extension, neural network generation

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Authors: Engang Wang

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The Cu-alloy composites are a kind of high-strength and high-conductivity Cu-based alloys, which have excellent mechanical and electrical properties and is widely used in electronic, electrical, machinery industrial fields. However, the solidification microstructure of the composites, such as the primary or second dendrite arm spacing, have important rule to its tensile strength and conductivity, and that is affected by its fabricating method. In this paper, two kinds of directional solidification methods; the exothermic powder method (EP method) and liquid metal cooling method (LMC method), were used to fabricate the Cu-alloy composites with applied different magnetic fields to investigate their influence on the solidifying microstructure of Cu-alloy, and further the fabricated Cu-alloy composites was drawn to wires to investigate the influence of fabricating method and magnetic fields on the drawing microstructure of fiber-reinforced Cu-alloy composites and its properties. The experiment of Cu-Ag alloy under directional solidification and horizontal magnetic fields with different processing parameters show that: 1) For the Cu-Ag alloy with EP method, the dendrite is directionally developed in the cooling copper mould and the solidifying microstructure is effectively refined by applying horizontal magnetic fields. 2) For the Cu-Ag alloy with LMC method, the primary dendrite arm spacing is decreased and the content of Ag in the dendrite increases as increasing the drawing velocity of solidification. 3) The dendrite is refined and the content of Ag in the dendrite increases as increasing the magnetic flux intensity; meanwhile, the growth direction of dendrite is also affected by magnetic field. The research results of Cu-Ag alloy in situ composites by drawing deforming process show that the micro-hardness of alloy is higher by decreasing dendrite arm spacing. When the dendrite growth orientation is consistent with the axial of the samples. the conductivity of the composites increases with the second dendrite arm spacing increases. However, its conductivity reduces with the applied magnetic fields owing to disrupting the dendrite growth orientation.

Keywords: Cu-Ag composite, magnetic field, microstructure, solidification

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Authors: Riaz A. Agha, Ishani Barai, Shivanchan Rajmohan, Seon Lee, Mohammed O. Anwar, Alex J. Fowler, Dennis P. Orgill, Douglas G. Altman

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Introduction: Medical knowledge is growing fast. Evidence-based medicine works best if the evidence is reported well. Past studies have shown reporting quality to be lacking in the field of surgery. Reporting guidelines are an important tool for authors to optimize the reporting of their research. The objective of this study was to analyse the frequency and strength of recommendation for such reporting guidelines within surgical journals. Methods: A systematic review of the 198 journals within the Journal Citation Report 2014 (surgery category) published by Thomson Reuters was undertaken. The online guide for authors for each journal was screened by two independent groups and results were compared. Data regarding the presence and strength of recommendation to use reporting guidelines was extracted. Results: 193 journals were included (as five appeared twice having changed their name). These had a median impact factor of 1.526 (range 0.047 to 8.327), with a median of 145 articles published per journal (range 29-659), with 34,036 articles published in total over the two-year window 2012-2013. The majority (62%) of surgical journals made no mention of reporting guidelines within their guidelines for authors. Of the journals (38%) that did mention them, only 14% (10/73) required the use of all relevant reporting guidelines. The most frequently mentioned reporting guideline was CONSORT (46 journals). Conclusion: The mention of reporting guidelines within the guide for authors of surgical journals needs improvement. Authors, reviewers and editors should work to ensure that research is reported in line with the relevant reporting guidelines. Journals should consider hard-wiring adherence to them. This will allow peer-reviewers to focus on what is present, not what is missing, raising the level of scholarly discourse between authors and the scientific community and reducing frustration amongst readers.

Keywords: CONSORT, guide for authors, PRISMA, reporting guidelines, journal impact factor, citation analysis

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Authors: Beenish Saba, Ann D. Christy

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Modern day municipal solid waste landfills are operated and controlled to protect the environment from contaminants during the biological stabilization and degradation of the solid waste. They are equipped with liners, caps, gas and leachate collection systems. Landfill gas is passively or actively collected and can be used as bio fuel after necessary purification, but leachate treatment is the more difficult challenge. Leachate, if not recirculated in a bioreactor landfill system, is typically transported to a local wastewater treatment plant for treatment. These plants are designed for sewage treatment, and often charge additional fees for higher strength wastewaters such as leachate if they accept them at all. Different biological, chemical, physical and integrated techniques can be used to treat the leachate. Treating that leachate with simultaneous power production using microbial fuel cells (MFC) technology has been a recent innovation, reported its application in its earliest starting phase. High chemical oxygen demand (COD), ionic strength and salt concentration are some of the characteristics which make leachate an excellent substrate for power production in MFCs. Different materials of electrodes, microbial communities, carbon co-substrates and temperature conditions are some factors that can be optimized to achieve simultaneous power production and treatment. The advantage of the MFC is its dual functionality but lower power production and high costs are the hurdles in its commercialization and more widespread application. The studies so far suggest that landfill leachate MFCs can produce 1.8 mW/m2 with 79% COD removal, while amendment with food leachate or domestic wastewater can increase performance up to 18W/m3 with 90% COD removal. The columbic efficiency is reported to vary between 2-60%. However efforts towards biofilm optimization, efficient electron transport system studies and use of genetic tools can increase the efficiency of the MFC and can determine its future potential in treating landfill leachate.

Keywords: microbial fuel cell, landfill leachate, power generation, MFC

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Authors: M. Mischopoulou, P. Naidis, S. Kalamaras, T. Kotsopoulos, P. Samaras

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The treatment of high strength wastewater by an Upflow Anaerobic Sludge Blanket (UASB) reactor has several benefits, such as high organic removal efficiency, short hydraulic retention time along with low operating costs. In addition, high volumes of biogas are released in these reactors, which can be utilized in several industrial facilities for energy production. This study aims at the examination of the application potential of anaerobic treatment of wastewater, with high molasses content derived from yeast manufacturing, by a lab-scale UASB reactor. The molasses wastewater and the sludge used in the experiments were collected from the wastewater treatment plant of a baker’s yeast manufacturing company. The experimental set-up consisted of a 15 L thermostated UASB reactor at 37 ◦C. Before the reactor start-up, the reactor was filled with sludge and molasses wastewater at a ratio 1:1 v/v. Influent was fed to the reactor at a flowrate of 12 L/d, corresponding to a hydraulic residence time of about 30 h. Effluents were collected from the system outlet and were analyzed for the determination of the following parameters: COD, pH, total solids, volatile solids, ammonium, phosphates and total nitrogen according to the standard methods of analysis. In addition, volatile fatty acid (VFA) composition of the effluent was determined by a gas chromatograph equipped with a flame ionization detector (FID), as an indicator to evaluate the process efficiency. The volume of biogas generated in the reactor was daily measured by the water displacement method, while gas composition was analyzed by a gas chromatograph equipped with a thermal conductivity detector (TCD). The effluent quality was greatly enhanced due to the use of the UASB reactor and high rate of biogas production was observed. The anaerobic treatment of the molasses wastewater by the UASB reactor improved the biodegradation potential of the influent, resulting at high methane yields and an effluent with better quality than the raw wastewater.

Keywords: anaerobic digestion, biogas production, molasses wastewater, UASB reactor

Procedia PDF Downloads 271

Authors: J. Ptačinová, J. Ďurica, P. Jurči, M Kusý

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Ledeburitic tool steel Vanadis 6 has been subjected to sub-zero treatment (SZT) at -140 °C and -196 °C, for different durations up to 48 h. The microstructure and hardness have been examined with reference to the same material after room temperature quenching, by using the light microscopy, scanning electron microscopy, X-ray diffraction, and Vickers hardness testing method. The microstructure of the material consists of the martensitic matrix with certain amount of retained austenite, and of several types of carbides – eutectic carbides, secondary carbides, and small globular carbides. SZT reduces the retained austenite amount – this is more effective at -196 °C than at -140 °C. Alternatively, the amount of small globular carbides increases more rapidly after SZT at -140 °C than after the treatment at -140 °C. The hardness of sub-zero treated material is higher than that of conventionally treated steel when tempered at low temperature. Compressive hydrostatic stresses are developed in the retained austenite due to the application of SZT, as a result of more complete martensitic transformation. This is also why the population density of small globular carbides is substantially increased due to the SZT. In contrast, the hardness of sub-zero treated samples decreases more rapidly compared to that of conventionally treated steel, and in addition, sub-zero treated material induces a loss the secondary hardening peak.

Keywords: microstructure, Vanadis 6 tool steel, sub-zero treatment, carbides

Procedia PDF Downloads 162

Authors: M. J. Kang, Y. N. Jo, H. H. Yoo

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Pendulum tests were used to identify a stretch reflex and diagnose spasticity. Some researches tried to make a mathematical model to simulate the motions. Thighs are subject to compressive forces due to gravity during a pendulum test. Therefore, it affects knee trajectories. However, the most studies on the pendulum tests did not consider that conditions. We used Kelvin-Voight model as compression model of skin and muscles. In this study, we investigated viscoelastic behaviors of skin and muscles using gelatin blocks from experiments of the vibration of the compliantly supported beam. Then we calculated a dynamic stiffness and loss factors from the experiment and estimated a damping coefficient of the model. We also did pendulum tests of human lower limbs to validate the stiffness and damping coefficient of a skin model. To simulate the pendulum motion, we derive equations of motion. We used stretch reflex activation model to estimate muscle forces induced by the stretch reflex. To validate the results, we compared the activation with electromyography signals during experiments. The compression behavior of skin and muscles in this study can be applied to analyze sitting posture as wee as developing surgical techniques.

Keywords: Kelvin-Voight model, pendulum test, skin and muscles under compression, stretch reflex

Procedia PDF Downloads 446

Authors: Helan Gethse J., Dhanya K., Muthuselvi G., Diana Hyden N., Samuel Pakianathan P.

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Transformer oil is mostly used to keep the transformer cool. It functions as a cooling agent. Mineral oil has long been used in transformers. Mineral oil has a high dielectric strength, which allows it to withstand high temperatures. Mineral oil's main disadvantage is that it is not environmentally friendly and can be dangerous to the environment. The features of breakdown voltage (BDV), viscosity, flash point, and fire point are measured and reported in this study, and the characteristics of olive oil are compared to the characteristics of mineral oil.

Keywords: antioxidants, transformer oil, mineral oil, olive oil

Procedia PDF Downloads 150

Authors: Farusil Najeeb Mullaveettil, Rolanas Dauksevicius

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Cellular structures produced by additive manufacturing have earned wide research attention due to their unique specific strength and energy absorption potentiality. The literature review concludes that pattern type and density are vital parameters that affect the mechanical properties of parts formed by additive manufacturing techniques and have an influence on printing time and material consumption. Fused deposition modeling technique (FDM) is used here to produce Polyvinylidene fluoride (PVDF) parts. In this work, patterns are based on triply periodic minimal surfaces (TPMS) produced by PVDF-based filaments using the FDM technique. PVDF homopolymer filament Fluorinar-H™ and PVDF copolymer filament Fluorinar-C™ are printed with three types of TPMS patterns. The patterns printed are Gyroid, Schwartz diamond, and Schwartz primitive. Tensile, flexural, and compression tests under quasi-static loading conditions are performed in compliance with ISO standards. The investigation elucidates the deformation mechanisms and a study that establishes a relationship between the printed and nominal specimens' dimensional accuracy. In comparison to the examined TPMS pattern, Schwartz diamond showed a higher relative elastic modulus and strength than the other patterns in tensile loading, and the Gyroid pattern showed the highest mechanical characteristics in flexural loading. The concluded results could be utilized to produce informed cellular designs for biomedical and mechanical applications.

Keywords: additive manufacturing, FDM, PVDF, gyroid, schwartz primitive, schwartz diamond, TPMS, tensile, flexural

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Authors: Sandeep Goyal, Sandeep Saluja

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Natural antioxidants have major role in maintenance of health. Green tea extract principally contains epigallocatechin-3-gallate (EGCG), as its abundant antioxidant constituent. Green tea is consumed daily worldwide as antioxidant to combat CNS diseases and has traditional importance also. EGCG has neuroprotective potential in various animal models of Parkinson disease, Alzheimer’s disease etc. but its exact mechanism has not been ruled out. The present study has been designed to investigate the anti-inflammatory, antioxidant and mitochondrial modulating mechanism of neuroprotective effect of epigallocatechin-3-gallate against rodent model of rotenone induced Parkinson’s disease (PD). The behavioural alterations were assessed by using open field test apparatus, Chatilon’s grip strength test apparatus and elevated plus maze for determining the locomotor activity, grip strength and cognition respectively. Biochemically, various parameters to assess oxidative stress, neuroinflammation and neurochemical estimations were performed on rat brain homogenates. A histological examination of rat brain striatum was done to check the neurodegeneration. Epigallocatechin-3-gallate (EGCG) at 10 & 20 mg/kg, were investigated for their neuroprotective potential along with levodopa as a standard agent. Minocycline, a microglial activation inhibitor, was administered alone and in combination with EGCG. EGCG and minocycline produced ameliorative effect against rotenone induced PD like symptoms by significantly reduced behavioral, biochemical and histological alterations. Results of our study reveal the neuroprotective effect of EGCG and minocycline against rotenone induced PD. Results of our study indicate that EGCG exerted neuroprotective effect against rotenone induced PD via its antioxidant, anti-inflammatory and mitochondrial modulating mechanisms and substantiate its previously reported and traditional claims for its use in CNS diseases.

Keywords: antioxidants, neurotoxicity, rotenone, EGCG

Procedia PDF Downloads 354

Authors: Syed Ibrahim, Syed Muneer Ahmed

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It is a global phenomenon that fitness is a pre-requisite to the desired end of optimum efficiency in elite class basketballers achieved through appropriate conditioning program. This study was undertaken to find out the effect of gymnastic oriented training program on the physical fitness and the level of technical performance of basketball players. Method: 27 basketballers were divided into 12 experimental and 15 control groups aged between 19 to 25 years. Physical fitness tests comprising of vertical jump, push-ups, chin ups, sit ups, back strength, 30 m sprint, boomerangs test, 600 m run, sit and reach, bridge up and shoulder rotation and technical skill tests like dribbling, layup shots and rebound collection were used for the study. A pre- and post-test was conducted before and after the training program of 6 weeks. Results: The results indicated no significant difference in the anthropometric measurements of age, height and weight between the experimental and control group as the ‘t’ values observed were 0.28, 1.63 and 1.60 respectively . There were significant improvements in vertical jump, push-ups, sit-ups, modified boomerang test, bridge test and shoulder rotation index with the ‘t’ values being 2.60, 3.41, 3.91, 4.02, 3.55 and 2.33 respectively. However, no significant differences existed in chin-ups, back strength, 30 m sprint and 6000 m run with the ‘t’ values being 2.08, 1.77, 1.28 and 0.80 respectively. There was significant improvement in the post-test for the technical skills tests in the experimental group with ‘t’ values being 3.65, 2.57, and 3.62 for the dribble, layup shots and rebound collection respectively. There was no significant difference in the values of the control group except in the rebound collection which showed significant difference. Conclusion: It was found that both the physical fitness and skill proficiency of the basketballers increased through the participation in the gymnastics oriented program.

Keywords: gymnastic, technical, pre-requisite, elite class

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Authors: Ana Lucia Molina

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Introduction: Fine motor skills refer to the use of the hands and coordination of the small muscles that control the fingers. A deficiency in fine motor skills is as important as a change in global movements, as fine motor skills directly affect activities of daily living. Fine movements are involved in some functions, such as motor control of the extremities, sensitivity, strength and tonus of the hands. A growing interest in the effects of non-invasive neuromodulation, such as transcranial stimulation technologies, through transcranial magnetic stimulation (TMS), has been observed in the scientific literature, with promising results in fine motor rehabilitation, as it provides modulation of the corresponding cortical activity in the area primary motor skills of the hands in both hemispheres (according to the International System 10-20, corresponding to C3 and C4). Objectives: to carry out a literature review about the effects of TMS on the cortical motor area corresponding to hand motricity. Methodology: This is a bibliographic survey carried out between October 2022 and March 2023 at Pubmed, Google Scholar, Lillacs and Virtual Health Library (BVS), with a national and international database. Some books on neuromodulation were included. Results: 28 articles and 5 books were initially found, and after reading the abstracts, only 14 articles and 3 books were selected, with publication dates between 2008 and 2022, to compose the literature review since it suited the purpose of this study. Conclusion: TMS has shown promising results in the treatment of fine motor rehabilitation, such as improving coordination, muscle strength and range of motion of the hands, being a complementary technique to existing treatments and thus providing more potent results for manual skills in activities of daily living. It is important to emphasize the need for more specific studies on the application of TMS for the treatment of manual disorders, which describe the uniqueness of each movement.

Keywords: transcranial magnetic stimulation, fine motor skills, motor rehabilitation, non-invasive neuromodulation

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Authors: Linyu Wang, Furui Huo, Jianhong Xiang

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The Doppler shift generated by high-speed movement and multipath effects in the channel are the main reasons for the generation of a time-frequency doubly-selective (DS) channel. There is severe inter-carrier interference (ICI) in the DS channel. Channel estimation for an orthogonal frequency division multiplexing (OFDM) system over a DS channel is very difficult. The simultaneous orthogonal matching pursuit algorithm under distributed compressive sensing theory (DCS-SOMP) has been used in channel estimation for OFDM systems over DS channels. However, the reconstruction accuracy of the DCS-SOMP algorithm is not high enough in the low SNR stage. To solve this problem, in this paper, we propose an improved DCS-SOMP algorithm based on the inner product difference comparison operation (DCS-DCSOMP). The reconstruction accuracy is improved by increasing the number of candidate indexes and designing the comparison conditions of inner product difference. We combine the DCS-DCSOMP algorithm with the basis expansion model (BEM) to reduce the complexity of channel estimation. Simulation results show the effectiveness of the proposed algorithm and its advantages over other algorithms.

Keywords: OFDM, doubly selective, channel estimation, compressed sensing

Procedia PDF Downloads 95

Authors: Khawlh A. Alzubaidi, Khadijah B. Alziyadi, Amor M. Alsayari

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The discovery of a dilute magnetic semiconductor (DMS) in which ferromagnetism is carrier-mediated and persists above room temperature is a major step toward the implementation of spintronic devices for processing, transferring, and storing of information. Among the many types of DMS materials which have been investigated, Mn-doped GaAs has become one of the best candidates for technological application. However, despite major developments over the last few decades, the maximum Curie temperature (~200 K) remains well below room temperature. In this work, we have studied the effect of Mn content and strain on the GaMnAs effective masses of electron, heavy and light holes calculated in the different crystallographic direction. Also, the Curie temperature in the DMS GaMnAs alloy is determined. Compilation of GaMnAs band parameters have been carried out using the 8-band k.p model based on Lowdin perturbation theory where spin orbit, sp-d exchange interaction, and biaxial strain are taken into account. Our results show that effective masses, calculated along the different crystallographic directions, have a strong dependence on strain, ranging from -2% (tensile strain) to 2% (compressive strain), and Mn content increased from 1 to 5%. The Curie temperature is determined within the mean-field approach based on the Zener model.

Keywords: diluted magnetic semiconductors, k.p method, effective masses, curie temperature, strain

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Authors: Gökhan Karhan, Yavuz Elitok

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Nowadays, inequality between developing and underdeveloped countries has a rapid increment. Developed countries impress the underdeveloped countries to become dependent through them. For that reason, Turkey has to increase its capability of making technological innovations. It has tried to be identified by examining the expenses of R&D in public, mercantile establishments and universities in Turkey that which expense is not enough and which expense should be doubled. As a result, developing new resolution strategies will be easier.

Keywords: competitive strength, research and development, technological innovation, Turkey

Procedia PDF Downloads 364

Authors: Martin Alexander Eder, Sergei Semenov

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Many glass-epoxy composite structures, such as large utility wind turbine rotor blades (WTBs), comprise of adhesive joints with typically thick bond lines used to connect the different components during assembly. Performance optimization of rotor blades to increase power output by simultaneously maintaining high stiffness-to-low-mass ratios entails intricate geometries in conjunction with complex anisotropic material behavior. Consequently, adhesive joints in WTBs are subject to multiaxial stress states with significant stress gradients depending on the local joint geometry. Moreover, the dynamic aero-elastic interaction of the WTB with the airflow generates non-proportional, variable amplitude stress histories in the material. Empiricism shows that a prominent failure type in WTBs is high cycle fatigue failure of adhesive bond line interfaces, which in fact over time developed into a design driver as WTB sizes increase rapidly. Structural optimization employed at an early design stage, therefore, sets high demands on computationally efficient interface fatigue models capable of predicting the critical locations prone for interface failure. The numerical stress-based interface fatigue model presented in this work uses the Drucker-Prager criterion to compute three different damage indices corresponding to the two interface shear tractions and the outward normal traction. The two-parameter Drucker-Prager model was chosen because of its ability to consider shear strength enhancement under compression and shear strength reduction under tension. The governing interface damage index is taken as the maximum of the triple. The damage indices are computed through the well-known linear Palmgren-Miner rule after separate rain flow-counting of the equivalent shear stress history and the equivalent pure normal stress history. The equivalent stress signals are obtained by self-similar scaling of the Drucker-Prager surface whose shape is defined by the uniaxial tensile strength and the shear strength such that it intersects with the stress point at every time step. This approach implicitly assumes that the damage caused by the prevailing multiaxial stress state is the same as the damage caused by an amplified equivalent uniaxial stress state in the three interface directions. The model was implemented as Python plug-in for the commercially available finite element code Abaqus for its use with solid elements. The model was used to predict the interface damage of an adhesively bonded, tapered glass-epoxy composite cantilever I-beam tested by LM Wind Power under constant amplitude compression-compression tip load in the high cycle fatigue regime. Results show that the model was able to predict the location of debonding in the adhesive interface between the webfoot and the cap. Moreover, with a set of two different constant life diagrams namely in shear and tension, it was possible to predict both the fatigue lifetime and the failure mode of the sub-component with reasonable accuracy. It can be concluded that the fidelity, robustness and computational efficiency of the proposed model make it especially suitable for rapid fatigue damage screening of large 3D finite element models subject to complex dynamic load histories.

Keywords: adhesive, fatigue, interface, multiaxial stress

Procedia PDF Downloads 169

Authors: Daniel Botero, Oscar Rubiano, Pedro P. Barragan, Jaime Baron, Leonardo Rodriguez Perdomo, Jaime Rodriguez

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In the last decade interval training (IT) has gained importance when is compare with strength training (ST). However, there are few studies analyzing the impact of these training over the autonomic nervous system (ANS). This work has aimed to compare the activity of the autonomic nervous system, when is expose to an IT or ST indoor cycling mode. After approval by the ethics committee, a cross-over clinical trial with 22 healthy participants (age 21 ± 3 years) was implemented. The selection of participants for the groups with sequence force-interval (F-I) and interval-force (I-F) was made randomly with assignation of 11 participants for each group. The temporal series of heart rate was obtained before and after each training using the POLAR TEAM® heart monitor. The evaluation of the ANS was performed with spectral analysis of the heart rate variability (HRV) using the fast Fourier transform (Kubios software). A training of 8 weeks in each sequence (4 weeks with each training) with an intermediate period of two weeks of washout was implemented for each group. The power parameter of the HRV in the low frequency band (LF = 0.04-0.15Hz related to the sympathetic nervous system), high frequency (HF = 0.15-0.4Hz, related to the parasympathetic) and LF/HF (with reference to a modulation of parasympathetic over the sympathetic), were calculated. Afterward, the difference between the parameters before and after was realized. Then, to evaluate statistical differences between each training was implemented the method of Wellek (Wellek and Blettner, 2012, Medicine, 109 (15), 276-81). To determine the difference of effect over parasympathetic when FT and IT are used, the T test is implemented obtaining a T value of 0.73 with p-value ≤ 0.1. For the sympathetic was obtained a T of 0.33 with p ≤ 0.1 and for LF/HF the T was 1.44 with a p ≥ 0.1. Then, the carry over effect was evaluated and was not present. Significant changes over autonomic activity with strength or interval training were not observed. However, a modulation of the parasympathetic over the sympathetic can be observed. Probably, these findings should be explained because the sample is little and/or the time of training was insufficient to generate changes.

Keywords: autonomic nervous, force training, indoor cycling, interval training

Procedia PDF Downloads 225

Authors: Daniel Sava, Dragos Gudovan, Iulia Alexandra Gudovan, Ioana Ardelean, Maria Sonmez, Denisa Ficai, Laurentia Alexandrescu, Ecaterina Andronescu

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Graphene and graphene oxide have been intensively studied due to the very good properties, which are intrinsic to the material or come from the easy doping of those with other functional groups. Graphene and graphene oxide have known a broad band of useful applications, in electronic devices, drug delivery systems, medical devices, sensors and opto-electronics, coating materials, sorbents of different agents for environmental applications, etc. The board range of applications does not come only from the use of graphene or graphene oxide alone, or by its prior functionalization with different moieties, but also it is a building block and an important component in many composite devices, its addition coming with new functionalities on the final composite or strengthening the ones that are already existent on the parent product. An attempt to improve the mechanical properties of polyamide elastomers by compounding with graphene oxide in the parent polymer composition was attempted. The addition of the graphene oxide contributes to the properties of the final product, improving the hardness and aging resistance. Graphene oxide has a lower hardness and textile strength, and if the amount of graphene oxide in the final product is not correctly estimated, it can lead to mechanical properties which are comparable to the starting material or even worse, the graphene oxide agglomerates becoming a tearing point in the final material if the amount added is too high (in a value greater than 3% towards the parent material measured in mass percentages). Two different types of tests were done on the obtained materials, the hardness standard test and the tensile strength standard test, and they were made on the obtained materials before and after the aging process. For the aging process, an accelerated aging was used in order to simulate the effect of natural aging over a long period of time. The accelerated aging was made in extreme heat. For all materials, FT-IR spectra were recorded using FT-IR spectroscopy. From the FT-IR spectra only the bands corresponding to the polyamide were intense, while the characteristic bands for graphene oxide were very small in comparison due to the very small amounts introduced in the final composite along with the low absorptivity of the graphene backbone and limited number of functional groups. In conclusion, some compositions showed very promising results, both in tensile strength test and in hardness tests. The best ratio of graphene to elastomer was between 0.6 and 0.8%, this addition extending the life of the product. Acknowledgements: The present work was possible due to the EU-funding grant POSCCE-A2O2.2.1-2013-1, Project No. 638/12.03.2014, code SMIS-CSNR 48652. The financial contribution received from the national project ‘New nanostructured polymeric composites for centre pivot liners, centre plate and other components for the railway industry (RONERANANOSTRUCT)’, No: 18 PTE (PN-III-P2-2.1-PTE-2016-0146) is also acknowledged.

Keywords: graphene, graphene oxide, mechanical properties, dopping effect

Procedia PDF Downloads 314