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Search Results: 1 - 10 of 562947 matches for " F. A.;Al-Qureshi "
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Modelo matemático aplicado ao processo de extrus?o de argilas
Andrade, F. A.;Al-Qureshi, H. A.;Hotza, D.;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000200008
Abstract: the clays when mixed with water acquire the property known as plasticity, which plays a key role during processing. the techniques used to characterize the plasticity often do not show quantitative results that allow its application in mathematical models of the forming process of clays. this study aimed to develop a mathematical model for calculating the average pressure of extrusion, evaluating the plasticity through compression tests. then, the theoretical results of the extrusion pressure were compared to experimental results and a good agreement was found between them. it was possible to observe a correlation between effective stress of compression and extrusion pressure. for the extrusion process modeling equation, the effective stress obtained by compression test was a significant parameter that reveals the behavior of the clay during processing.
Alumina-Based Ceramics for Armor Application: Mechanical Characterization and Ballistic Testing
M. V. Silva,D. Stainer,H. A. Al-Qureshi,O. R. K. Montedo,D. Hotza
Journal of Ceramics , 2014, DOI: 10.1155/2014/618154
Abstract: The aim of this work is to present results of mechanical characterization and ballistic test of alumina-based armor plates. Three compositions (92, 96, and 99?wt% Al2O3) were tested for 10?mm thick plates processed in an industrial plant. Samples were pressed at 110?MPa and sintered at 1600°C for 6?h. Relative density, Vickers hardness, and four-point flexural strength measurements of samples after sintering were performed. Results showed that the strength values ranged from 210 to 300?MPa depending on the porosity, with lower standard deviation for the 92?wt% Al2O3 sample. Plates (120?mm × 120?mm × 12?mm) of this composition were selected for ballistic testing according to AISI 1045, using a metallic plate as backing and witness plates in the case of penetration or deformation. Standard NIJ-0108.01 was followed in regard to the type of projectile to be used (7.62 × 51?AP, Level IV, 4068?J). Five alumina plates were used in the ballistic tests (one shot per plate). None of the five shots penetrated or even deformed the metal sheet, showing that the composition containing 92?wt% Al2O3 could be considered to be a potential ballistic ceramic, being able to withstand impacts with more than 4000?J of kinetic energy. 1. Introduction Ceramics have been considered one of the most important materials for lightweight armor applications due to their low density, high compressive strength, and high hardness [1]. Ceramic materials for using as ballistic armor must be sufficiently rigid to fragment the bullet and reduce its speed, transforming it into small fragments that should be stopped by the layer of flexible material that supports the ceramic. Thus, it is necessary that the ceramic material presents high elastic modulus and high hardness [2]. Fracture toughness is also a very important requirement for this application. The main ceramic materials used commercially in the development of ballistic armors are Al2O3, B4C, SiC, and ceramic matrix composites (CMCs) such as Al2O3/ZrO2 system. High cost, processing hindrances, and restrictions to predict ballistic performance from the properties of the material are some drawbacks of ceramic armors [3]. Alumina provides the best cost-benefit ratio among advanced ceramics, featuring high modulus of elasticity, high refractoriness, high hardness, and relatively lower cost. However, because of its low fracture toughness and low flexural strength, ballistic performance of alumina is lower when compared to SiC and B4C [4]. The properties of the alumina may be improved, either by introducing zirconia or by the manufacturing
Estudo da viabilidade de utiliza??o de fibras naturais curtas em matrizes de resina epóxi
Martins, R.R.;Pires, A.T.N.;Al-Qureshi, H.A.;Barra, G.M.O.;
Matéria (Rio de Janeiro) , 2008, DOI: 10.1590/S1517-70762008000400005
Abstract: a novel kind of short natural fiber obtained from mineral resources, which consists mainly of pure amorphous sio2, was characterized and applied as a reinforcing agent in epoxy resin. natural amorphous silica fibers (nasf) were incorporated in epoxy resin and the obtained composites were mechanically tested. the effect of the treatment of nasf chemically modified with aminosilane as well as the aspect ratio of the fibers on the mechanical properties of the composite were evaluated and compared with properties obtained with fnsa without treatment. the results obtained show that these natural fibers are potential candidates for the substitution of short glass fibers as a reinforcement phase in polymer composites, since the mechanical properties obtained were in all cases similar or superior to the ones obtained with commercial short glass fibers.
Modelamento para previs o de propriedades mecanicas no processo de trefila o aplicado a tubos de a o com costura
Fernando Augusto Andrade,Hazim Ali Al-Qureshi
Exacta , 2009,
Abstract: This work carried out a study of the mechanical properties of two common steels used for the manufacture of cold drawing welded steel tubes, SAE 1012 and ST-52.3. The tubes were submitted to chemical and thermal treatment and then were drawn. Properties such as hardness and tensile strength had been evaluated in each stage of the process. Incremental reductions of 5% were made in the tube in order to investigate the behavior of its properties. An estimation of the maximum reduction allowed without necessity of intermediate annealing for two models, considered for Sachs and Baldwin, and another one for Backofen were also discussed. Equations obtained from the curves will be the base to estimate the final properties desired for a specific reduction of the tube. They will also help in the selection of different steels, by making a relation between reduction and its properties.
Measuring and Modeling the Plasticity of Clays
Andrade, Fernando Augusto de;Al-Qureshi, Hazim Ali;Hotza, Dachamir;
Materials Research , 2010, DOI: 10.1590/S1516-14392010000300019
Abstract: the measurement of plasticity in clay bodies is crucial in order to get products free of defects and with less processing time. however, tests which simulate the behavior of the clay during processing and the mathematical modeling of some of its characteristics, particularly the plasticity, become difficult because many variables are involved and there is no consensus on the choice of method to be used. this study aimed to develop a mathematical model based on compression test to evaluate the plasticity of clays. three types of clays were studied with different levels of moisture and their indices of plasticity were also characterized by the atterberg's and pfefferkorn's methods. the experimental data were well fitted by the theoretical curves for a wide range of clay plasticity. moreover, it was possible to observe a correlation between effective stress of compression and paste moisture within each group of clay.
Caracteriza o da tenacidade à fratura de materiais de fric o e critérios de projetos
Alexandre Casaril,Carlos Henrique Selle Pereira,Carlos Pérez Bergmann,Hazim Ali Al-Qureshi
Exacta , 2011,
Abstract: The purpose of this study was to characterize friction materials currently used in heavy vehicles for assembly lines and replacement parts. Five different friction materials were evaluated through mechanical tests based on the ASTM D5045-99 (Reapproved 2007) Standard - Plane Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials. Results of KIC for the five materials were on the order 1 MPa.m1/2, corroborating values expected for phenolic matrix materials. In addition, KIC results are representative of the fragility of friction materials. A statistical analysis was conducted using the Weibull methodology, allowing to establish occurrence probabilities of KIC lower than a randomly chosen value. Consequently, from a design point of view, it is possible to establish failure criteria and avoid investing resources in prototypes that may come to fail in field tests.
Modelling of Ballistic Impact over a Ceramic-Metal Protection System
Leandro Neckel,Dachamir Hotza,Daniel Stainer,Rolf Janssen,Hazim Ali Al-Qureshi
Advances in Materials Science and Engineering , 2013, DOI: 10.1155/2013/698476
Abstract: The behavior of ceramic-metal protection against a projectile impact is modeled. The model takes into account the mass and velocity for each stage of the phenomenon. A former model was modified considering more realistic parameters such as geometries and deformation profile. To analyze the model, simulations on different parameters have been run. The impact results of different ballistic projectiles were simulated, and the movement was plotted. In addition, a deterministic simulation on the mechanical properties of the back metal plate properties was done. 1. Introduction Gon?alves et al. [1] have developed a mathematical approach to the behavior of a two-layer system protection of ceramic-metal system against high speed impact. The scheme of the protection is presented in Figure 1. The ceramic layer erodes the projectile, and the back metal plate is responsible for absorbing the remaining energy by plastic deformation. The mathematical model separates the penetration into three different stages and proposes a deterministic equation that explains the deflection of the metal plate. The movement equations were manipulated to find a single problem for velocity and mass separately for each stage. The data and initial parameters provided by the original work [1] were used for the differential equations found. The metal deformity was reevaluated by deducing the deterministic equation. A more realistic shape parameter was considered for the postimpact curvature, and the volume approach was improved. Finally, the solution was plotted and compared to former results [1]. Figure 1: Proposal of a two-layer protection made by Gon?alves et al. [ 1]. The model was better understood once the solutions were used to simulate different impacts over the system. Initially, properties of some ballistic projectiles were used to prevent the shock absorption. In addition, the mechanical properties of the metallic plate were modified intending to observe the effect on the final deformation. A previous work [2] has focused on the study of the movement evolution of the projectile. This work has continued to analyze the penetration of the projectile searching for the understanding of the final deformation. The set of data generated in the simulations together with the newly developed equations for impact and shock absorption were, in conclusion, observed as an advance for the understanding of high speed impact phenomena. 2. Materials and Methods The software Maplesoft Maple V12 was used to solve the system. Gon?alves et al. work [1] provided all materials, constant values, and
Análise micromecanica dos compósitos com fibras curtas e partículas
Casaril, Alexandre;Gomes, Eduardo Rovaris;Soares, Marcos Roberto;Fredel, Márcio Celso;Al-Qureshi, Hazim Ali;
Matéria (Rio de Janeiro) , 2007, DOI: 10.1590/S1517-70762007000200019
Abstract: the present work presents the investigation of the mechanical behavior of the composite materials, strengthened with short fibers and particles. a simple model is presented, with purpose for prediction of the breaking stress of this class of composite material. the model consists in the modification of the rule of mixture, with the introduction of a term, referring to the particle phase, present in the composite material. it is introduced and investigated a correction factor (g), to adjust the magnitude of the phase particle contribution to composite material strength. it is developed, still, a simplified equation to correct the factor (b) - of fiber alignment - present in the equation of the rule of mixtures. this correction needs to be made because of the preferential alignment of the fibers that occurs in the stage of material compaction process. three different composite materials were produced, varying only the ratios of materials, maintaining the raw materials. the composite materials produced were tested by the three-point flexural method, in order to determine their mechanical properties. the comparison between mechanical properties obtained experimentally and the theoretical results demonstrate good agreement with the real behavior of the composite material strengthened with short fibers and particles.
α-Synuclein Levels in Blood Plasma from LRRK2 Mutation Carriers
Ana Gorostidi, Alberto Bergareche, Javier Ruiz-Martínez, José F. Martí-Massó, María Cruz, Shiji Varghese, Mohamed M. Qureshi, Fatimah Alzahmi, Abdulmonem Al-Hayani, Adolfo López de Munáin, Omar M.A. El-Agnaf
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0052312
Abstract: The diagnosis of Parkinson’s disease (PD) remains primarily a clinical issue, based mainly on phenotypic patterns. The identification of biomarkers capable of permitting the preclinical detection of PD is critically needed. α-Synuclein is a key protein in PD, with missense and multiplication mutations in the gene encoding α-synuclein (SNCA) having been reported in familial cases of PD, and accumulation of the protein identified in Lewy bodies (LBs) and Lewy neurites (LNs) in affected brain regions. With the objective of validating the use of α-synuclein as a clinical or progressive biomarker in an accessible tissue, we used an enzyme-linked immunosorbent assay (ELISA) to measure α-synuclein levels in the peripheral blood plasma of idiopathic PD and LRRK2 mutation carrier patients and compared our findings with healthy control subjects. Compared to healthy controls, we found a significant decrease in plasma total α-synuclein levels in idiopathic PD (iPD) patients (n = 134, p = 0.010). However, the reduction was less significant in patients who were LRRK2 mutation carriers (n = 32, p = 0.133). This lack of significance could be due to the small number of individuals employed in this group. No predictive value of total α-synuclein in the diagnosis of PD was found in a receiver operating characteristic (ROC) curve analysis. Although this is a pilot study requiring corroboration on a larger cohort of patients, our results highlight the possible use of plasma α-synuclein as a biomarker for PD.
Studies on Colorectal Cancer in The Kingdom of Saudi Arabia: A Portrait Through Pre and Post-Millennium
Abdurrahman Al Diab,S. Qureshi,Khalid A. Al Saleh,Farjah H. Al Qahtani,Aamer Aleem,Mohammad Farhan Qureshi,Viquar Fatima Qureshi,Mohammad Rehan Qureshi
Research Journal of Medical Sciences , 2012, DOI: 10.3923/rjmsci.2012.203.207
Abstract: Literature reports suggest a tremendous decline in the global incidence, mortality and morbidity of Colorectal Cancer (CRC) during the post-millennium as compared to the pre-millennium. These developments are attributed to the advancement in technicalities and researches. The status of CRC in the Kingdom of Saudi Arabia (KSA) during the pre-millennium restricted to most of the etiological, histological and epidemiological researches while progress around the world had already begun studies on molecular level. During the third millennium, there are active genome level researches in addition to the development of the link of MicroRNAs with progression of cancer. Although, research on gene expression began in KSA but its involvement in the discovery of newer compounds is still a vision. Furthermore, the researches in KSA lag behind in the new developed era of MicroRNAs. This review on the development of research activities on CRC has revealed that researches in KSA are slow and late but do not lag behind in the global scientific maneuvers taking place in the third millennium.
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