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As zircônias odontológicas são notadamente conhecidas por suas propriedades biomecânicas, e evoluíram de um material branco e opaco para um material com gradiente de translucidez e múltiplas indicações clínicas. Dentre a última geração destes materiais, estão as zircônias multicamadas gradadas, que possuem um gradiente microestrutural com gradação de ítria. A zona de transição, ou interfase, entre essas camadas ainda é pouco descrita pela literatura. O presente estudo se dá diante da hipótese de que a interfase seja uma zona frágil das zircônias multicamadas, e investiga a energia necessária para separá-las, ou seja, a tenacidade à fratura da interfase. Espécimes do tipo Brazil-nut foram confeccionados para o cálculo da energia necessária para a fratura interfásica em diferentes angulações da zircônia multicamadas, verificando modalidades de falhas mistas, por tração ou por cisalhamento em testes de compressão, utilizando 3Y-TZP e 5Y-PSZ puras como controle. Os grupos foram divididos de acordo com a zircônia testada, o ângulo de teste e o envelhecimento hidrotérmico; a tenacidade à fratura da interfase se deu em N/m. Os espécimes fraturados foram submetidos à uma análise fractográfica detalhada, com classificação dos tipos de falha, caracterização em MEV e EDS. Os resultados dos testes da multicamadas foram submetidos ao teste ANOVA de 2 fatores, indicando diferença estatística entre os ângulos, mas não quanto ao envelhecimento. O teste post-hoc de Tukey revelou que a energia para fratura interfásica em 25º, predominantemente por força de cisalhamento, é significativamente maior do que os demais grupos [baseline: 964,74 (± 202,43); envelhecido: 1389,12 (± 978,47) N/m], exceto quando comparado a 15º [baseline: 1006,09 (± 373,13); envelhecido: 798,43 (± 108,67) N/m], que não difere estatisticamente de nenhum dos outros grupos. Os valores da energia interfásica para fratura de uma zircônia multicamadas se mostraram intermediários entre a 5Y-PSZ e a 3Y-TZP, sem diferença significante da multicamadas com a 3Y-TZP e ambas com diferença significativa para a 5Y-PSZ. A tenacidade à fratura da interfase de uma zircônia multicamadas, uma importante propriedade para o bom desempenho clínico do material, não foi afetada pelo envelhecimento hidrotérmico e é menor sob tensões de tração do que de cisalhamento. Os padrões de fratura variaram mas não houve diferenças em comparação aos grupos controle.(AU)
Dental zirconias are well known for their biomechanical properties, and have evolved from a white, opaque material to one with a gradient of translucency and multiple clinical indications. Among the latest generation of these materials are graded multilayer zirconias, which have a microstructural gradient with yttria gradation. The transition zone, or interphase, between these layers is still poorly described in the literature. This study is based on the hypothesis that the interphase is a fragile zone in multilayer zirconias, and investigates the energy required to separate them, i.e. the fracture toughness of the interphase. Brazil-nut specimens were made to calculate the energy required for interphase fracture at different angles of the multilayer zirconia, checking for mixed, tensile or shear failure modes in compression tests, using pure 3Y-TZP and 5Y-PSZ as a control. The groups were divided according to the zirconia tested, the test angle and hydrothermal ageing; the fracture toughness of the interphase was measured in N/m. The fractured specimens were subjected to detailed fractographic analysis, with classification of failure types, SEM and EDS characterization. The results of the multilayer tests were submitted to the 2-way ANOVA test, indicating a statistical difference between the angles, but not in terms of aging. Tukey's post-hoc test revealed that the energy for interphase fracture at 25º, predominantly by shear force, is significantly higher than the other groups [baseline: 964.74 (± 202.43); aged: 1389.12 (± 978.47) N/m], except when compared to 15º [baseline: 1006.09 (± 373.13); aged: 798.43 (± 108.67) N/m], which does not differ statistically from any of the other groups. The interphase energy values for fracture of a multilayer zirconia were intermediate between 5Y-PSZ and 3Y-TZP, with no significant difference between the multilayer and 3Y-TZP and both with a significant difference for 5Y-PSZ. The fracture toughness of the interphase of a multilayer zirconia, an important property for the good clinical performance of the material, was not affected by hydrothermal ageing and is lower under tensile than shear stresses. Fracture patterns varied but there were no differences compared to the control groups (AU)
Subject(s)
Dental Materials , Dental Porcelain , InterphaseABSTRACT
The Barcelona method was developed as an alternative to other tests for assessing the post-cracking behavior of fiber-reinforced concrete, with the main advantage being that it uses significantly smaller specimens compared to other methods. For this reason, it can provide a solution for characterizing concrete in hard-to-reach constructions such as roads and tunnels. On the other hand, polypropylene (PP) fibers have gained increased attention in recent years within the scientific community due to their high tensile strength and cost-effectiveness. This research aimed to understand the influence of PP fiber volume, slenderness (l/d), and reinforcement index on post-cracking properties of concrete, including toughness and residual strength (f_res), using the Barcelona method. Three fiber volumes, 0.4%, 0.8%, and 1.2%, and three slenderness ratios, 46.5, 58.1, and 69.8, were employed in normal-strength concrete. In addition to the reference mixture without fibers, 10 mixtures were prepared with 10 specimens each, resulting in a total of 100 specimens. Pearson's hypothesis test was employed to determine the existence of correlations between variables, followed by scatter plots to generate predictive equations between post-cracking properties and fiber attributes. The results indicated no direct correlation between fiber slenderness and post-cracking properties. Regarding fiber volume, there was a correlation with residual strength but not with toughness. However, the combined effect of volume and slenderness, the reinforcement index, correlates with the post-cracking properties of concrete. Finally, four predictive equations for toughness and residual strength were derived based on the reinforcement index. These equations can prove valuable for designing structures made of polypropylene fiber-reinforced concrete.
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Introduction: Self-efficacy is considered a component of mental toughness, but there are few studies investigating the relationship of sport self-efficacy with mental toughness in performance athletes, especially in team sports. Objective: The objective was to examine the impact of sport self-efficacy mediated by mental toughness on the sport performance of Brazilian futsal athletes. Methods: The sample was composed of five adult male teams participating in the National Futsal League 2020, totaling 77 athletes. As instruments, we used: athlete identification sheet, Perceived Self-Efficacy Scale in Sports (PSES), Mental Toughness Index (MTI) questionnaire and the performance data from the National Futsal League 2020 (NFL). The data were analyzed using the Kolmogorov-Smirnov test, Mann-Whitney "U" test, Spearman's correlation, network analysis (LASSO), with the indicators of centrality: strength, proximity and degree of intermediation (p < 0.05). Results: The results showed that the investigated sample presented high levels of Perceived Self-Efficacy Scale in Sports (PSES) (Md = 4.66) and mental toughness (MT) (Md = 6.44). PSES presented a positive relationship with the number of wins, and negative relationships with the number of red cards and wrong passes (r = -0.08). MT indirectly influenced these variables through its connection with PSES (r = 0.30). The best ranked teams presented higher amounts of goals for, fouls, shots on goal, tackles, assists, and wins. The time of practice revealed an inverse relationship with the number of defeats, while age was positively related to the number of wrong passes (r = 0.09). The centrality indicators showed that the number of games stood out as the most central variable in the network, due to its degree of strength, proximity and intermediation. Moreover, the high degree of proximity and intermediation of the tackles made presented a connection with the number of assists (γ = 0.25; n = 77). Conclusion: We can conclude that sport self-efficacy and mental toughness are intervening factors in the sport performance of Brazilian futsal athletes.
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We studied atmospheric corrosion on Rapa Nui Island, using galvanized and non-galvanized SAE 1020 steel samples exposed on racks. We also added Charpy samples of both materials to directly determine the effect of corrosion rate on these materials' impact toughness. The results indicated a correlation between corrosion rate and toughness loss in the studied materials. In the corrosion study, we could also demonstrate the effect from increased insular population growth on contaminants which aid atmospheric corrosivity. Results showed that atmospheric SO2 has tripled compared with similar corrosion studies done 20 years ago (Mapa Iberoamericano de Corrosión, MICAT), increasing corrosion rates. Our results show how human factors can influence changes in environmental variables that strengthen corrosion.
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It is well known that the use of continuous reinforcing fibers can largely improve the typical low in-plane mechanical properties of 3D-printed parts. However, there is very limited research on the characterization of the interlaminar fracture toughness of 3D-printed composites. In this study, we investigated the feasibility of determining the mode I interlaminar fracture toughness of 3D-printed cFRP composites with multidirectional interfaces. First, elastic calculations and different FE simulations of Double Cantilever Beam (DCB) specimens (using cohesive elements for the delamination, in addition to an intralaminar ply failure criterion) were carried out to choose the best interface orientations and laminate configurations. The objective was to ensure a smooth and stable propagation of the interlaminar crack, while preventing asymmetrical delamination growth and plane migration, also known as crack jumping. Then, the best three specimen configurations were manufactured and tested experimentally to validate the simulation methodology. The experimental results confirmed that, with the appropriate stacking sequence for the specimen arms, it is possible to characterize the interlaminar fracture toughness in multidirectional 3D-printed composites under mode I. The experimental results also show that both initiation and propagation values of the mode I fracture toughness depend on the interface angles, although a clear tendency could not be established.
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The construction industry requires concrete with adequate post-cracking behavior for applications such as tunnels, bridges, and pavements. For this reason, polypropylene macrofibers are used, which are synthetic fibers that fulfill the function of providing residual strength to concrete. In this study, an experimental plan is carried out to evaluate the bending behavior of concrete reinforced with polypropylene fibers using the four-point bending test according to ASTM C1609. Three fiber dosages (3.6, 7.2 and 10.8 kg/m3) and three fiber lengths (40, 50, and 60 mm) were used. The use of macro polypropylene fibers increased the post-cracking behavior of concrete. In addition, based on the experimentally obtained results and available literature data, a multivariable equation was developed to predict the concrete toughness as a function of the volume, slenderness, and modulus of elasticity of the fibers. A Pearson's correlation coefficient, r of 0.90, showed a strong correlation between the developed equation and the experimental data. From this equation, it was possible to determine the participation of the following parameters in calculating toughness. The participation or weight of the fiber's modulus of elasticity on the concrete's tenacity is 26%, the volume of the fiber is 39%, the slenderness is 19%, and the reinforcement index is 16%.
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Hunting impacts tropical vertebrate populations, causing declines of species that function as seed dispersers and predators, or that browse seedlings and saplings. Whether and how the resulting reductions in seed dispersal, seed predation, and browsing translate to changes in the tree composition is poorly understood. Here, we assess the effect of defaunation on the functional composition of communities of tree recruits in tropical rainforests in French Guiana. We selected eight sites along a gradient of defaunation, caused by differences in hunting pressure, in otherwise intact old-growth forests in French Guiana. We measured shifts in functional composition by comparing leaf and fruit traits and wood density between tree recruits (up to 5 cm diameter at breast height) and adults, and tested whether and how these compositional shifts related to defaunation. We found a positive relationship with defaunation for shifts in specific leaf area, a negative relationship for shifts of leaf toughness and wood density, and a weak relationship for shifts in fruit traits. Our results suggest that the loss of vertebrates affects ecological processes such as seed dispersal and browsing, of which browsing remains understudied. Even though these changes sometimes seem minor, together they result in major shifts in forest composition. These changes have long-term ramifications that may alter forest dynamics for generations.
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Forests , Trees , Animals , French Guiana , Vertebrates , Plant Leaves , Tropical Climate , EcosystemABSTRACT
OBJECTIVES: To evaluate the incorporation of repairing capsules containing different monomers and polymerization modulators on the self-healing efficiency of an experimental photopolymerizable resin-based composite. METHODS: Self-healing capsules containing different monomers and polymerization modulators were prepared by emulsion polymerization: TCDHEPT (TEGDMA and DHEPT), BTCDHEPT (Bis-GMA, TEGDMA, and DHEPT), and BTCBPO (Bis-GMA, TEGDMA, and BPO). The capsules were analyzed through Fourier transform infrared spectroscopy and scanning electron microscopy. The capsules were added into experimental photopolymerizable resin composites establishing the following groups: ER (Control without capsules), ER+BPO, ER+BPO+TCDHEPT, and ER+BTCBPO+BTCDHEPT. Filtek Z350 resin composite (3 M ESPE) was used as a commercial reference. The materials were tested for degree of conversion (DC), flexural strength (σf), elastic modulus (Ef), fracture toughness (virgin KIC), self-healing efficiency (healed KIC), and roughness. For statistical analysis, the significance value was established at an a = 0.05 level. RESULTS: When compared to the control material, the incorporation of repairing capsules did not affect DC, σf, and Ef. Fracture toughness was statistically similar between the experimental groups (p ≤ 0.05). Healed KIC was statistically different between the groups ER+TCDHEP and ER+BTCBPO+BTCDHEPT; the self-healing efficiency was higher for ER+TCDHEPT. Surface roughness was statistically similar among all groups. CONCLUSIONS: The use of self-healing capsules promoted repair of the material. Studies with material aging after the self-healing process are necessary to better demonstrate the effectiveness of this system. CLINICAL SIGNIFICANCE: The self-healing system seemed to be a promising technology to be used in self-repaired restorative materials, which may prevent restoration fractures.
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Composite Resins , Polymethacrylic Acids , Bisphenol A-Glycidyl Methacrylate/chemistry , Materials Testing , Composite Resins/chemistry , Polymethacrylic Acids/chemistry , Polyethylene Glycols/chemistry , Dental Materials/chemistry , Capsules/chemistry , Methacrylates/chemistryABSTRACT
The mesocarp ofBertholletia excelsais a rich source of inspiration for strong, stiff and damage-tolerant composites. The bioinspired composites developed here are composed of an epoxy matrix with a 3D printed polylactic acid reinforced with 30% of carbon fiber (PLA-30CF) inspired in fibers, and syntactic foam inspired by sclereids. Monotonic and cyclic four-point bending tests and compact tension fracture toughness tests were carried out assisted by digital image correlation (DIC) to evaluate flexural properties, damage tolerance, and theR-curve of the composite. Its microstructure and fracture surface were analyzed by scanning electron microscopy. The mechanical performance of the bioinspired composite is promising: density of 1.0 g cm-3, flexural apparent elastic modulus of 1.6 GPa, and flexural strength six times higher than the neat epoxy, i.e. 17 MPa. Although the PLA-30CF printed structure led to a risingR-curve, the syntactic foam needs optimization to have a synergistic effect.
Subject(s)
Bertholletia , Flexural Strength , Materials Testing , Polyesters , Surface PropertiesABSTRACT
The use of continuous fiber as reinforcement in polymer additive manufacturing technologies enhances the mechanical performance of the manufactured parts. This is the case of the Carbon-Fiber reinforced PolyAmide (CF/PA) used by the MarkForged MarkTwo® 3D printer. However, the information available on the mechanical properties of this material is limited and with large variability. In this work, the in-plane mechanical properties and the interlaminar fracture toughness in modes I and II of Markforged's CF/PA are experimentally investigated. Two different standard specimens and end-tabs are considered for the in-plane properties. Monolithic CF/PA specimens without any additional reinforcement are used for the interlaminar fracture toughness characterization. Two different mode I specimen configurations are compared, and two different test types are considered for mode II. The results show that prismatic specimens with paper end-tabs are more appropriate for the characterization of the in-plane material properties. The use of thick specimens for mode I fracture toughness tests complicates the characterization and can lead to erroneous results. Contrary to what has been reported in the literature for the same material, fracture toughness in mode I is lower than for mode II, which agrees with the normal tendency of traditional composite materials.
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OBJECTIVES: To evaluate the edge chipping resistance (ReA) and the fracture toughness (KC) of 3Y-TZP bilayers produced with the following materials/processing combinations: fluorapatite glass-ceramic applied on zirconia using the traditional layering and hot-pressing (press-on) techniques; feldspathic porcelain using rapid layer technology (RLT); and lithium disilicate glass-ceramic using CAD-on method. The influence of the cooling rate (slow and fast) was analyzed for layering and hot-pressing. METHODS: Bilayer bars (25x4x2 mm) were made following manufacturers' instructions. The edge chipping test was performed in an universal testing machine, using a coupled Vickers indenter. ReA was calculated dividing the critical load at fracture by the edge distance. Fracture toughness was calculated by a regression fit with a fixed slope of 1.5 correlating the critical chipping load regarding edge distance and also with indentation fracture (IF) method. Data were statistically analyzed using ANOVA and Tukey's test (α = 5%). RESULTS: ReA and KC was significantly higher for the CAD-on bilayers. RLT showed intermediate ReA means, and layering and hot-pressing techniques showed the lowest ReA values. For both processing methods there was no effect of the cooling protocol on the ReA and fracture toughness. CONCLUSIONS: There is a significant effect of the material/processing association on the edge chipping resistance and fracture toughness of the bilayers. There was no effect of the cooling protocol on the edge chipping resistance and fracture toughness for the specimens processed by both the layering and hot-pressing techniques.
Subject(s)
Ceramics , Zirconium , Dental Porcelain , Dental Stress Analysis , Dental Veneers , Materials Testing , Phase TransitionABSTRACT
Molecular dynamics simulations of cracked nanocrystals of aluminum were performed in order to investigate the crack length and grain boundary effects. Atomistic models of single-crystals and bi-crystals were built considering 11 different crack lengths. Novel approaches based on fracture mechanics concepts were proposed to predict the crack length effect on single-crystals and bi-crystals. The results showed that the effect of the grain boundary on the fracture resistance was beneficial increasing the fracture toughness almost four times for bi-crystals.
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This study has assessed the psychometric proprieties of the Mental Toughness Inventory (MTI) within the context of Brazilian sports. About 12 professionals participated in the process of adapting and translating the scale to Brazilian Portuguese. Subjects were 575 athletes (23.54 ± 5.79 years old; 58% males) who answered the MTI and the 10-item Connor-Davidson Resilience Scale (CD-RISC-10). Data were analyzed through confirmatory factor analysis (CFA), Cronbach's alpha (α), composite reliability (CR), average variance extracted (AVE), Spearman correlation, and model invariance tests. Results from CFA showed adequate fit for the original 8-item structure of the scale [Chi-square (χ2) = 27.041; p = 0.078; normalized chi-square (χ2/df) = 1.50; comparative fit index (CFI) = 0.988; Tucker-Lewis Index (TLI) = 0.981; root mean square error of approximation (RMSEA) = 0.03 [0.00-0.05]; standardized root mean residual (SRMR) = 0.030] assessing mental toughness (MT) as a single factor and the scale presented satisfactory internal consistency (CR = 0.81; α = 0.82). MT was correlated with resilience (r = 0.607), age (r = 0.276), and time of experience in the sport (r = 0.215). The MTI has also shown partial measurement invariance for sex and complete invariance across sport types. It was concluded that the MTI is a suitable tool for assessing MT in the present sample of Brazilian athletes; this instrument has potential practical application for researchers and sports psychologists who seek to develop the well-being and performance of athletes.
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In this publication, molecular dynamics simulations are used to investigate the fracture behavior of single-crystal aluminum. The stress intensity factor is estimated by means of four different methods, the accuracy is assessed for each approach and the fracture toughness is estimated. The proposed methodology is also applied to estimate the fracture toughness for graphene and diamond using published data from other scientific articles. The obtained fracture toughness for the single-crystal aluminum is compared with other nanomaterials that have similar microstructures. Dislocation emission during the fracture simulation of the cracked nano-crystal of aluminum is analyzed to study the fracture behavior. Brittle fracture behavior is the predominant failure mode for the nanomaterials studied in this research.
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Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred.
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Dental interfaces are subject to mixed-mode loading. This study provides practical guidance for determining interfacial fracture toughness of dental ceramic systems. We address interfacial fracture of a composite resin cement sandwiched between two dental ceramic materials. Emphasis is placed on sandwich disc specimens with cracks originating from elliptical-shaped flaws near the center, for which analytical fracture mechanics methods fail to predict. The interaction integral method is used to provide accurate finite element solutions for cracks with elliptical-shaped flaws in a Brazil-nut-sandwich specimen. The developed model was first validated with existing experimental data and then used to evaluate the three most widely used dental ceramic systems: polycrystalline ceramics (zirconia), glass-ceramics (lithium disilicate), and feldspathic ceramics (porcelain). Contrary to disc specimens with ideal cracks, those with cracks emanating from elliptical-shaped flaws do not exhibit a monotonic increase in interfacial toughness. Also, interfacial fracture toughness is seen to have a direct relationship with the aspect ratio of elliptical-shaped flaws and an inverse relationship with the modulus ratio of the constituents. The presence of an elliptical-shaped flaw significantly changes the interfacial fracture behavior of sandwich structures. Semi-empirical design equations are provided for fracture toughness and stress intensity factors for interfacial cracks. The developed design equations provide practical guidance for determining interfacial fracture toughness of selected dental ceramic material systems. Those equations take into account four critical factors: size of the elliptical flaw, modulus ratio of constituent materials, loading angle, and applied load.
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Herein, poly (N-(4-aminophenyl) methacrylamide))-carbon nano-onions (PAPMA-CNOs = f-CNOs) and anilinated-poly (ether ether ketone) (AN-PEEK) have synthesized, and AN-PEEK/f-CNOs composite thin films were primed via layer-by-layer (LbL) self-assembly for stimuli-responsive drug release. The obtained thin films exhibited pH-responsive drug release in a controlled manner; pH 4.5 = 99.2% and pH 6.5 = 59.3% of doxorubicin (DOX) release was observed over 15 days. Supramolecular π-π stacking interactions between f-CNOs and DOX played a critical role in controlling drug release from thin films. Cell viability was studied with human osteoblast cells and augmented viability was perceived. Moreover, the thin films presented 891.4 ± 8.2 MPa of the tensile strength (σult), 43.2 ± 1.1 GPa of Young's modulus (E), and 164.5 ± 1.7 Jg-1 of toughness (K). Quantitative scrutiny revealed that the well-ordered aligned nanofibers provide critical interphase, and this could be responsible for augmented tensile properties. Nonetheless, a pH-responsive and mechanically robust biocompatible thin-film system may show potential applications in the biomedical field.
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Introducción: En los sistemas fluviales colombianos ha sido poco estudiada la fragmentación del material alóctono por parte de los insectos acuáticos. Uno de los organismos trituradores más abundantes en las corrientes tropicales de América es el tricóptero del género Phylloicus (Calamoceratidae). Objetivo: El presente estudio tuvo como objetivo evaluar el efecto de los atributos químicos (nitrógeno, fósforo y lignina) y físicos (dureza) de las hojas de tres especies ribereñas (Ficus tonduzii, Zygia longifolia y Clusia multiflora) dominantes en la parte media del río Gaira, sobre la preferencia de hojas y el crecimiento de larvas de Phylloicus sp. Métodos: Se realizaron experimentos de multiselección de alimento en campo, en los que se ubicaron cámaras experimentales dentro del río por 21 días. Para la valoración de la calidad foliar se recolectaron hojas del río, las cuales se secaron y se pulverizaron para realizar los análisis químicos. Resultados: No se presentaron diferencias significativas en los porcentajes de lignina y fósforo entre las hojas de las tres especies de árboles, pero si en su dureza y en el contenido de nitrógeno. Las hojas de C. multiflora fueron más suaves (180.1± 53.9 g) que las de F. tonduzii (285.3 ± 88.4 g) y Z. longifolia (232.3 ± 60.8 g), pero sin diferencias entre las dos últimas especies. Las hojas de Z. longifolia también tuvieron más nitrógeno (1.9 ± 0.0%) que las de hojas de las otras especies (1 ± 0.0 %). En cuanto a la preferencia de hojas, las larvas de Phylloicus sp. utilizaron en mayor proporción las hojas de C. multiflora. Aunque las hojas de C. multiflora no tuvieron diferencias significativas en el contenido de lignina y fósforo, presentaron valores menores de dureza, lo que podría hacerlas más palatables para Phylloicus sp. Por otra parte, el crecimiento específico diario de las larvas fue mayor cuando usaron hojas de F. tonduzii. Conclusiones: Nuestros resultados parecen indicar que las hojas más preferidas no son necesariamente las de mejor calidad nutricional y sugieren que la dureza de las hojas es la variable más importante en la selección de la hojarasca por parte de las larvas de Phylloicus sp.
Introduction: Fragmentation of allochthonous material by aquatic insects is a functional process that has been little studied in Colombian rivers. One of the most abundant shredder genus in American tropical stream ecosystems is the caddisfly genus Phylloicus (Calamoceratidae). Objective: In this study we evaluate the effect of chemical (nitrogen, phosphorus and lignin) and physical (toughness) attributes of leaves of three dominant tree species (Ficus tonduzii, Zygia longifolia and Clusia multiflora) in the riverine area of the middle section of the Gaira river, on leaf preferences and larval growth of a species of Phylloicus. Methods: Multiple food selection field experiments were performed, in which experimental chambers were located in the river for twenty-one days. For the assessment of leaf quality, leaves were collected in the river, dried and pulverized to perform chemical analyzes. Results: There were no significant differences in lignin and phosphorous percentages between the leaves of the three species, but nitrogen content and leaf toughness differed among them. The leaves of C. multiflora were softer (180.1± 53.9 g) than those of F. tonduzii (285.3 ± 88.4 g) and Z. longifolia (232.3 ± 60.8 g), but without differences between the last two species. The Z. longifolia leaves also had more nitrogen (1.9 ± 0.0 %) than those of the other species (1 ± 0.0 %). Regarding leaf selection, Phylloicus sp. larvae used in greater proportion the leaves of C. multiflora. Although lignin and phosphorous differences were not significant, the leaves of C. multiflora had lower toughness, which could make them more palatable for Phylloicus sp. On the other hand, the daily specific growth of the larvae was higher when they used leaves of F. tonduzii. Conclusions: Our findings seem to indicate that the most preferred leaves were not necessarily those of better nutritional quality and suggest that leaf toughness was the most important variable in the selection of leaf litter by the larvae of Phylloicus sp.
Subject(s)
Plant Leaves/chemistry , Diet, Food, and Nutrition , Insecta , Analysis of Variance , ColombiaABSTRACT
The present study evaluated the mechanical behaviour of thin high-performance cementitious composite slabs reinforced with short steel fibres. For this purpose, slabs with 1%, 3% and 5% vol. of steel fibres were moulded using the slurry infiltration method. Fibres concentrated in the region subjected to traction during bending stresses. After curing for 28 days, all slabs underwent flexural testing. The slabs with 5% fibre showed significantly higher flexural strength, deflection and toughness compared to those of the control group without reinforcement. The dense fibre distribution, resulting from the production process, led to profiles with multiple random cracks in the region of failure of the slabs as the fibre content increased. The results of the statistical analysis showed the intensity of the correlation between the variables and revealed that the increase of the fibre content significantly influenced the parameters of mechanical behaviour (load, flexural strength, deflection, toughness and toughness factor). Images obtained by optical microscopy aided in understanding the fibre-matrix interface, showing the bonding surface between the constituents of the composite.
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OBJECTIVES: The properties of lithium-silicate dental glass-ceramics are very sensitive to heat treatments which are conducted after CAD/CAM (Computer Aided Design/Computer Aided Machining) processing. In particular, temperature variations inside the furnace chamber which may occur between different models of furnaces may result in altered mechanical properties of these materials. In this work, the effect of thermal treatment parameters on the transformation of lithium metasilicate (Li2SiO3) into lithium disilicate (Li2Si2O5) and on the resulting mechanical properties has been investigated. METHODS: Lithium metasilicate samples. containing 59â¯vol% of amorphous phase, were thermal treated under vacuum at 820⯰C for up to 9â¯min or at 840⯰C for 7min (as control group). The samples were characterized by X-ray diffraction analysis using the Rietveld refinement and scanning electron microscopy. Hardness and fracture toughness (nâ¯=â¯30 indentations/group) were evaluated by the Vickers indentation technique. The elastic properties were measured by the Impulse Excitation Technique and the flexural strength (nâ¯=â¯15/group) was measured using the piston-on-three-ball (P-3B) testing assembly. Complementary Weibull statistic were conducted as statistical analysis. RESULTS: The results indicate a progressive reduction of the Li2SiO3 phase with increasing isothermal holding time at 820⯰C until the conversion into Li2Si2O5, is completed for treatments longer than 7â¯min. A complete transformation of Li2SiO3 into Li2Si2O5 has also been observed for the control group of samples treated at 840⯰C for 7min. Samples of the control group exhibited hardness, fracture toughness, Young's modulus and Poisson ratio 5.76⯱â¯0.17â¯GPa, 1.60⯱â¯0.03â¯MPaâ¯m1/2, 100.3â¯GPa e 0.21, respectively. The reduction of the thermal treatment temperature to 820⯰C reduced the fracture toughness and the Young's modulus between 5-10%. Furthermore, the fracture strength was significantly reduced by approximately 71%, because of the lower amount of elongated Li2Si2O5 grains and higher amount of residual amorphous phase. CONCLUSION: In general, the glass-ceramic material containing residual amorphous phase associated with various crystalline phases, presented a reduction of its mechanical properties in relation to the lithium disilicate glass-ceramic. The reasons for these differences in the mechanical behavior are discussed by analyzing the influences of different phenomena such as thermal expansion anisotropy, residual stresses, amorphous phase content and microstructure on the properties.