Fatigue failure analysis of vibrating screen spring by means of finite element simulation: a case study

Vibrating screens are often used in the mining industry to separate mineral particles by size. In many designs, spring arrays are used to provide the system with the necessary stiffness for screens to vibrate in a controlled manner. Naturally, these springs are subjected to varying loading cycles, which can cause their premature fatigue failure. This behavior has been studied by means of finite element analysis and compared with data obtained from a real case scenario, in which a helical spring failed. The 3D computational model was developed using the geometric characteristics and material properties of a fractured spring, as well as the loading characteristics of a specific vibrating screen. The meshing and the simulation tasks were performed in the general purpose software ANSYS Mechanical. Given the nature of the helical springs and the high-cycle loading conditions, for the fatigue analysis it was determined that a stress-life approach with constant amplitude and non-proportional loading best fit the investigated phenomenon. In solving the nonproportional loading case, stress values of two static scenarios were required to determine the upper and lower limits. Then, to perform the fatigue calculations a solution combination was used. In addition, in order to correct the effect of mean stress and calculate the stresses component respectively the Goodman and Von Mises theories were employed. Simulation results showed that spring would present failure below the second turn of the coil when working with the full nominal load during nearly forty million cycles. These results strongly agreed with the data extracted from a vibrating screen where fractured spring had been working. Fatigue analysis also predicted that the nominal load should be reduced to 90% in order for the spring to meet the minimum life requirements before failure occur

A one way coupled thermo-mechanical model to determine residual stresses and deformations in butt welding of two ASTM A36 steel plates

To simulate the gas metal arc welding (GMAW) process in two ASTM A36 steel plates a finite element numerical model was developed, to obtain the corresponding residual stresses and deformations. The welding process was simulated as a one way coupled thermo-structural problem, considering that the structural field has very little influence in the thermal field, which is widely accepted in the specialized literature. To solve the thermal field, a nonlinear transient problem was created using finite second order elements that have temperature as the only degree of freedom in their nodes. The thermal properties of material were defined as a function of temperature and a combined convection-radiation coefficient was used as boundary condition. The double ellipsoidal model presented by Goldak was used to simulate the heat source and its dimensions were determined from the expressions developed by Christensen. To solve the structural field another nonlinear transient problem was created, considering the same mesh and the same time step of the thermal problem, using finite second order elements that have three displacements as degrees of freedom in their nodes. The mechanical properties of material were defined as a function of temperature, a thermo-elasto-plastic material model was used and the necessary displacement constraints were applied as boundary conditions. The temperature distribution obtained by solving the thermal field at each time step was transferred as a load to the structural problem. In both problems the “birth and death” technique was used to simulate the material deposition, which is implemented in the ANSYS software used in the present study. The activation of “dead” elements of the weld bead in the thermal analysis was performed simultaneously with the passage of the heat source, while in the structural analysis “dead” elements were activated as a function of their temperature. Different activation temperatures of “dead” elements were tested in the structural analysis, obtaining the best results when this temperature takes a value of 80% of material solidification temperature. The model used in this study was validated experimentally, taking as reference the residual displacements in several points of the welded plates. It was verified that there is a good correspondence between numerical and experimental results, with an error of less than 10%

Prediction of Gas Chromatographic Retention Indices of Coumarins

Quantitative structure-retention relationships (QSRR) were used in this study to relate the chromatographic retention of different substituted coumarins to molecular structure. Different structural parameters were selected, such as topological, geometric, electronic, quantum-chemical and physico-chemical descriptors, in order to find an equation that fitted the chromatographic retention of these compounds. The method proposed by Dimov that classifies the descriptors in different groups in agreement with their values of correlation coefficients was analysed. Significant correlation equations were obtained with the following molecular descriptors: the total surface area (A T), the electrotopological state index (S(-o-)) of the oxygen in position 1 of coumarin, and the highest occupied molecular orbital energy (E HOMO), showing that the experimental retention, using stationary phases with low polarity, was related with the shape and electronic factors of the solutes. The models found have a good predictive ability as established by cross-validation r²cv values and thus, can be used to aid in the elucidation of the structure or the chromatographic retention of similar coumarins. O estudo de correlação entre estrutura-retenção (QSRR) foi usado para relacionar a retenção cromatográfica de diferentes cumarinas substituídas as suas características estruturais. Diferentes parâmetros estruturais foram selecionados tais como: descritores topológicos, geométricos, eletrônicos, químico-quânticos e físico-químicos para encontrar uma equação que melhor explique o comportamento cromatográfico destes compostos. O método proposto por Dimov que classifica os descritores em diferentes grupos de acordo com seus valores de coeficientes de correlação foi utilizado neste estudo. As melhores equações de correlação linear múltipla foram obtidas com os seguintes descritores: área total (A T), índice do estado eletrotopológico (S-O-) e orbital molecular ocupado de maior energia (E HOMO), mostrando que a retenção experimental, usando fase estacionária de baixa polaridade está relacionada principalmente com fatores relacionados a forma e também eletrônicos. Os modelos selecionados apresentaram uma boa predictabilidade, a qual foi estabelecida através dos valores do coeficiente de correlação de validação cruzada (r²cv). As equações encontradas podem ser utilizadas para auxiliar na elucidação da estrutura ou retenção cromatográfica de cumarinas similares às estudadas

Atividade antimicrobiana do australato de metila de Ganoderma australe

In addition to nine known steroidal compounds, australic acid and the new methyl australate have been isolated from the Brazilian fungus Ganoderma australe. Both methyl australate and its corresponding acid were shown to be active against fungi and Gram-positive bacteria, the methyl ester being also active against Gram-negative bacteria. Do fungo brasileiro Ganoderma australe foram isolados o ácido austrálico e o novo composto australado de metila, além de outros 9 compostos já conhecidos. Tanto o australado de metila quanto o ácido correpondente foram ativos contra fungos e bactérias Gram-positivas, sendo o éster metílico ainda ativo contra bactérias Gram-negativas

Chemical composition and biological activities of the leaves of Cynara scolymus L. (artichoke) cultivated in Brazil

The present paper describes the chemical composition and biological activities of artichoke cultivated in Brazil. Our studies demonstrated that glycosyl flavonoids (cynaroside and scolymoside), are the major constituents, along with cynaropicrin, a sesquiterpene lactone, and the triterpene lupeol. Cynarin, which is the main compound described for artichoke, was detected in very low concentration. Hexanic fraction exhibited considerable cytotoxicity and diuretic activities

Pharmacological and Phytochemical Evaluation of Adiantum cuneatum Growing in Brazil

This work describes the phytochemical analysis and analgesic activity of a non polar fraction obtained from Adiantum cuneatum grown in Brazil. The results showed that the hexane fraction as well as two pure compounds, identified as filicene (1) and filicenal (2), given intraperitoneally, exhibited potent analgesic activity when evaluated in two models of pain in mice, writhing test and formalin-induced pain. Compound 1 presented a calculated ID50 value of 19.5 μmol/kg body weight, when evaluated in writhing test, being about 7-fold more active than some reference drugs, like as acetyl salicylic acid and acetaminophen. It also inhibited both phases (neurogenic and inflammatory) of the formalin test at 10 mg/kg (24 μmol/kg). The chemical composition of the plant grown in Brazil is similar to that grown in other countries. The results confirm and justify the popular use of this plant for the treatment of dolorous processes

Cortes selectos de la canal de corderos cruzados katahdín × pelibuey alimentados con Medicago sativa L.

Objective: To evaluate the effect of alfalfa (Medicago sativa L.) forage (AF) in diet and sex on yield of select cuts of crossed (F1) Katahdin × Pelibuey lambs (Kt × Pb). Design/methodology/approach: Thirty-four male and twenty-one female lambs were distributed in a completely randomized design with 2 x 2 factorial arrangement: two diets (with and without AF) and two sexes (male and female). Results: No significant effect of diet on select cuts of carcass was detected (P > 0.05). Male lambs had a greatest live weight (LW) at slaughter, hot carcass weight and yield of selects cuts, though the female lambs had a higher weight of Rack (P ? 0.01; P ? 0.05). The effect of the diet was independent of the type of sex of the lambs in all the variables evaluated (P > 0.05). Limitations on study/implications: In Mexico there are more farms and companies that are interested in the market of lamb cuts, because they have a great potential for developing. However, it is necessary to establish its characteristics and differentiate the quality standers that market demands. Findings/conclusions: Lambs fed with alfalfa forage have a yield of selected cuts of carcass similar to those that received concentrated feed, so it is possible to obtain meat cuts of excellent characteristics, using diets with good quality forage, like alfalfa.Objetivo: Evaluar el efecto del forraje de alfalfa (Medicago sativa L.) (FA) en la dieta y el sexo sobre el rendimiento de cortes selectos de corderos cruzados (F1) Katahdín × Pelibuey (Kt × Pb). Diseño/metodología/aproximación: Treinta y cuatro corderos machos y veintiuna hembras fueron distribuidos mediante un diseño completamente al azar con un arreglo factorial 2 × 2: dos dietas (con y sin FA) y dos sexos (Machos y Hembras). Resultados: No se encontró un efecto significativo de la dieta sobre los cortes selectos de la canal de corderos (P > 0.05). Los corderos machos tuvieron un mayor peso vivo (PV), peso de la canal caliente (CC) y un rendimiento superior en la mayoría de los cortes selectos, a excepción del corte Rack (Costillar), en el cual las hembras registraron un mayor peso (P ? 0.01; P ? 0.05). El efecto de la dieta se mostró independiente del tipo de sexo de los corderos en todas las variables evaluadas (P > 0.05). Limitaciones del estudio/implicaciones: En México son cada vez más la explotaciones y empresas que se interesan en el mercado de cortes de cordero, debido a tienen un gran potencial para desarrollarse. Sin embargo, es necesario establecer sus características y diferenciar sus estándares de calidad que el mercado demanda. Hallazgos/conclusiones: Los corderos alimentados con dietas a base de forraje de Alfalfa tienen un rendimiento de cortes selectos de la canal similar a los que recibieron alimento concentrado, por lo que es posible obtener cortes finos de excelentes características, utilizando dietas con forrajes de buena calidad, como la alfalfa