The behaviour of granular material in pure shear, direct shear and simple shear

In biaxial compression tests, the stress calculations based on boundary information underestimate the principal stresses leading to a significant overestimation of the shear strength. In direct shear tests, the shear strain becomes highly concentrated in the mid-plane of the sample during the test. Although the stress distribution within the specimen is heterogeneous, the evolution of the stress ratio inside the shear band is similar to that inferred from the boundary force calculations. It is also demonstrated that the dilatancy in the shear band significantly exceeds that implied from the boundary displacements. In simple shear tests, the stresses acting on the wall boundaries do not reflect the internal state of stress but merely provide information about the average mobilised wall friction. It is demonstrated that the results are sensitive to the initial stress state defined by K0 = sh/sv. For all cases, non-coaxiality of the principal stress and strain-rate directions is examined and the corresponding flow rule is identified. Periodic cell simulations have been used to examine biaxial compression for a wide range of initial packing densities. Both constant volume and constant mean stress tests have been simulated. The characteristic behaviour at both the macroscopic and microscopic scales is determined by whether or not the system percolates (enduring connectivity is established in all directions). The transition from non-percolating to percolating systems is characterised by transitional behaviour of internal variables and corresponds to an elastic percolation threshold, which correlates well with the establishment of a mechanical coordination number of ca. 3.0. Strong correlations are found between macroscopic and internal variables at the critical state.

Shear modulus and strength of an acrylic adhesive by the notched plate shear method (Arcan) and the thick adherend shear test (TAST)

In this work, the shear modulus and strength of the acrylic adhesive 3M® DP 8005 was evaluated by two different methods: the Thick Adherend Shear Test (TAST) and the Notched Plate Shear Method (Arcan). However, TAST standards advise the use of a special extensometer attached to the specimen, which requires a very experienced technician. In the present study, the adhesive shear displacement for the TAST was measured using an optical technique, and also with a conventional inductive extensometer of 25 mm used for tensile tests. This allowed for an assessment of suitability of using a conventional extensometer to measure this parameter. Since the results obtained by the two techniques are identical, it can be concluded that using a conventional extensometer is a valid option to obtain the shear modulus for the particular adhesive used. In the Arcan tests, the adhesive shear displacement was only measured using the optical technique. This work also aimed the comparison of shear modulus and strength obtained by the TAST and Arcan test methods.

Desenvolvimento de ferramentas e provetes para o ensaio Thick Adherend Shear Test (TAST).

As estruturas coladas são geralmente projetadas para que o adesivo seja essencialmente sujeito a esforços de corte, pois neste tipo de solicitação o adesivo apresenta melhores caraterísticas mecânicas. A avaliação do comportamento ao corte pode ser realizada com o adesivo no estado maciço ou como camada fina em juntas adesivas. Os métodos que permitem avaliar o comportamento ao corte, quer para o adesivo, quer para as juntas, são: o ensaio Iosipescu ou V-Notched beam shear method, o ensaio de borboleta ou Notched plate shear method (Arcan), o ensaio de torsão, o ensaio de tração numa junta de sobreposição simples e o ensaio Thick Adherend Shear Test (TAST). Os ensaios Arcan e Iosipescu, tal como o ensaio de torção, podem ser realizados em provetes de adesivo maciço ou em juntas. O ensaio de torção é pouco utilizado, porque a aplicação do esforço de corte exige dispositivos e equipamentos de ensaios complexos. Os ensaios Arcan e Iosipescu utilizam provetes com entalhes e podem introduzir alguma dificuldade na medição precisa das deformações. O ensaio de tração numa junta de sobreposição simples é um dos métodos mais usados para caraterizar uma junta adesiva, porque é um método simples, as juntas são de fácil fabrico e pode ser realizado em máquinas universais de ensaios mecânicos. Neste ensaio os aderentes estão sujeitos a uma solicitação de tração, enquanto a camada de adesivo está sujeita a esforços de corte combinados com esforços de arrancamento. Os esforços de arrancamento resultam da própria geometria da junta na qual existe um desalinhamento das forças de tração, mesmo quando são colocados calços (reguladores de espessura) nos locais de amarração. O ensaio TAST é dos mais populares para obtenção das propriedades ao corte, uma vez que tanto as ferramentas de ensaio como o fabrico dos provetes são relativamente simples. Este ensaio é realizado em junta sendo os substratos espessos e de aço que, devido à sua elevada rigidez, contribuem para um esforço de corte praticamente puro no adesivo. Neste trabalho realizou-se o projeto e a fabricação das ferramentas, gabarit e substratos necessários para a execução de provetes TAST e ensaios utilizando diferentes adesivos.

An evaluation of the direct agglutination test to diagnose "Mal de Caderas" disease

Se evaluó la utilidad de la prueba de aglutinación directa (AD) para diagnosticar el Mal de Caderas. Se emplearon cuarenta y cuatro sueros provenientes de dos lotes de equinos naturalmente infectados con el Trypanosoma evansi (Lote 1 y Lote 2). La AD fue positiva (Aglutinación > 1:512) en 13 de 16 equinos (81.2%), de los que se aislaron los parásitos. En doce de estos animales (92%) se detectaron IgM anti T. evansi mediante la AD realizada con 2-mercaptoetanol (AD + 2-ME). La AD fue positiva en 17 de los 28 equinos que resultaron negativos al diagnóstico parasitológico. Un tercer lote de cinco equinos infectados con T. evansi que presentaba elevados títulos de AD, fue tratado con Suramina Sódica (Nagano1-Bayer). La AD + 2-ME evidenció en cuatro animales que, gran parte de estos anticuerpos se ubicaban en la fracción IgM. Posterior al tratamiento farmacológico y, en concordancia de la negativización de la parasitemia, la detección de la IgM anti T. evansi no fue posible, mientras que los anticuerpos IgG continuaron detectándose a los doce meses post-tratamiento en valores de 1:512, en tres animales. Cincuenta sueros de equinos de una zona libre del parásito, que se emplearon como controles, fueron negativos a la AD. Se recomienda la utilización de la AD y AD + 2-ME para el uso de rutina en el diagnóstico del Mal de Caderas de los equinos, en combinación con otros métodos parasitológicos sensibles.

Direct Sensitivity Test of the MB/BacT System

In order to evaluate the direct-method test of sensitivity to drugs used in the principal tuberculosis treatment regimes, in the Organon Teknika MB/BacT system, we tested 50 sputum samples positive to microscopy taken from patients with pulmonary tuberculosis and with clinical indications for an antibiogram, admitted sequentially for examination during the routine of the reference laboratory. The material was treated v/v with 23% trisodium phosphate solution, incubated for 24 h at 35°C, and neutralized v/v with 20% monosodium phosphate solution. The material was then centrifuged and the sediment inoculated into flasks containing Rifampin - 2 µg/ml, Isoniazid - 0.2 µg/ml, Pyrazinamide - 100 µg/ml, Ethambutol - 2.5 µg/ml, Ethionamide - 1.25 µg/ml, and Streptomycin - 2 µg/ml. The tests were evaluated using the indirect method in the BACTEC 460 TB (Becton Dickinson) system as the gold standard. The results showed that the Rifampin test performed best, i.e., 100% sensitivity at 95% Confidence Interval (82.2-100) and 100% specificity at 95% Confidence Interval (84.5-100), followed by Isoniazid and Pyrazinamide. In this experiment, 92% of the materials showed a final reading in 30 days; this period represents the time for primary isolation as well as the results of the sensitivity profile, and is within Centers for Disease Control and Prevention recommendations regarding time for performance of the antibiogram. The inoculated flasks showed no contamination during the experiment. The MB/BacT is shown to be a reliable, rapid, fully automated nonradiometric system for the tuberculosis antibiogram.

Evaluation of the direct agglutination test and the rK39 dipstick test for the sero-diagnosis of visceral leishmaniasis

The direct agglutination test (DAT) based on a freeze-dried antigen and the rK39 dipstick test were evaluated for the sero-diagnosis of visceral leishmaniasis (VL). The sensitivity and specificity of both tests were determined using sera from confirmed VL patients (n = 21), healthy controls (n = 19) and from patients with other confirmed infectious diseases (n = 42). The DAT had a sensitivity and a specificity of 100%. The rK39 had a sensitivity of 85.7% and a specificity of 82%. Both tests were also used to screen blood samples of confirmed VL patients (n = 15) and serum samples of VL suspects (n = 61). The DAT found all blood samples of confirmed VL patients positive and tested 98.4% of the serum samples of the VL suspects positive. In contrast, rK39 detected in 9/15 blood samples (60%) antibodies against Leishmania chagasi and found 85.3% of the serum samples of the suspected patients positive. Although the rK39 dipstick is more rapid and user friendlier than the DAT, the latter has a superior sensitivity and specificity. Furthermore, the reagents used for DAT do not require cold storage, whereas the buffer of the rK39 must be stored at 4ºC. Therefore, the DAT is the most suitable test for the sero-diagnosis of VL under field conditions.

Effect of testing methods on the bond strength of resin to zirconia-alumina ceramic: microtensile versus shear test

This study tested the bond strength of a resin cement to a glass-infiltrated zirconia-alumina ceramic after three conditioning methods and using two test methods (shear-SBS versus microtensile-MTBS). Ceramic blocks for MTBS and ceramic disks for SBS were fabricated. Three surface conditioning (SC) methods were evaluated: (1) 110-mu m Al(2)O(3)+Silanization; (2) Chairside silica coating+silanization: (3) Laboratory silica coating+silanization. Following surface conditioning, the resin cement (Panavia F) was bonded to the conditioned ceramics. Although no statistically significant differences (p=0.1076) were seen between the test methods, results yielded with the different surface conditioning methods showed statistically significant differences (p<0.0001) (SC2=SC3>SC1.). As for the interaction between the factors, two-way ANOVA showed that it was not statistically significant (p=0.1443). MTBS test resulted in predominantly mixed failure (85%), but SBS test resulted in exclusively adhesive failure. on the effects of different surface conditioning methods, chairside and laboratory tribochemical silica coating followed by silanization showed higher bond strength results compared to those of aluminum oxide abrasion and silanization, independent of the test method employed.

Hygrotermal effects evaluation using the losipescu shear test for glare laminates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Coeficientes de presión intersticial en el aparato de corte simple = Pore pressure coefficients for simple shear test

La actuación de cargas sobre un suelo saturado, produce, en función de la naturaleza de la solicitación, del tipo de suelo y de las condiciones de drenaje del terreno, un incremento de la presión sobre el agua de los intersticios. Se ha abordado el estudio de la generación de dicha presión intersticial a partir de muestras de suelo blando, normalmente consolidadas, procedentes del subsuelo del Puerto de Barcelona. Para ello se han utilizado los datos de una completa campaña experimental utilizando la máquina de ensayo de corte simple, y tras la adecuada interpretación del ensayo, se identifican los aspectos que se consideran clave para el proceso de generación de presión intersticial en el suelo, según las diferentes situaciones de carga actuante. Como conclusión, se plantea la generalización de la clásica ecuación que Skempton formuló hace casi 60 años y que permite interpretar la generación de presión intersticial para el aparato de ensayo triaxial. ncrease in pore pressure depending on the nature of the excitation, the type of soil and the drainage conditions of the ground are generated by loads acting on a saturated soil. It has approached the study of the generation of the pore pressure from usually consolidated soft soil samples from the basement of the Port of Barcelona. Data from an adequate experimental campaign using simple shear machine have been used, and the aspects that are considered key to the process of generation of pore pressure in the soil under different loading conditions acting have been identified. In conclusion, the generalization of Skempton's classical equation (formulated almost 60 years ago) and the interpretation of the pore pressure generation for triaxial test apparatus have been proposed.

RNA virus error catastrophe: Direct molecular test by using ribavirin

RNA viruses evolve rapidly. One source of this ability to rapidly change is the apparently high mutation frequency in RNA virus populations. A high mutation frequency is a central tenet of the quasispecies theory. A corollary of the quasispecies theory postulates that, given their high mutation frequency, animal RNA viruses may be susceptible to error catastrophe, where they undergo a sharp drop in viability after a modest increase in mutation frequency. We recently showed that the important broad-spectrum antiviral drug ribavirin (currently used to treat hepatitis C virus infections, among others) is an RNA virus mutagen, and we proposed that ribavirin's antiviral effect is by forcing RNA viruses into error catastrophe. However, a direct demonstration of error catastrophe has not been made for ribavirin or any RNA virus mutagen. Here we describe a direct demonstration of error catastrophe by using ribavirin as the mutagen and poliovirus as a model RNA virus. We demonstrate that ribavirin's antiviral activity is exerted directly through lethal mutagenesis of the viral genetic material. A 99.3% loss in viral genome infectivity is observed after a single round of virus infection in ribavirin concentrations sufficient to cause a 9.7-fold increase in mutagenesis. Compiling data on both the mutation levels and the specific infectivities of poliovirus genomes produced in the presence of ribavirin, we have constructed a graph of error catastrophe showing that normal poliovirus indeed exists at the edge of viability. These data suggest that RNA virus mutagens may represent a promising new class of antiviral drugs.

Assessment of the properties to characterize the interface between clay brick substrate and strengthening mortar

The behaviour of masonry elements under in-plane and out-of-plane loads can be improved through the application of strengthening systems based on reinforcing overlays. After strengthening, the transition region between the original substrate and the strengthening layer is especially stressed, and premature failure of the strengthened masonry is reached if insufficient interfacial capacity is assured. Therefore, the assessment of the mechanical behaviour of the interface is critical to the development of the masonry strengthening system based on the application of strengthening overlays. In this research a method for the characterization of the interface behaviour between two different materials, a polypropylene fibre reinforced mortar (PFRM) and a ceramic brick used for masonry construction is presented. Direct shear tests were carried out in couplet specimens. Due to the orthotropic nature of the bricks surface, the shear load was applied along three different directions in order to perform an overall estimation of the interface behaviour. The peak and residual shear stresses, as well as the failure modes, were obtained at different levels of the normal stress. Based on these experimental results constitutive laws were assessed for the simulation of the interface mechanical behaviour based on the Mohr and Mohr-Coulomb failure criteria.

Modelagem numérica de estruturas de contenção atirantadas em areia

A numerical study on the behavior of tied-back retaining walls in sand, using the finite element method (FEM) is presented. The analyses were performed using the software Plaxis 2D, and were focused on the development of horizontal displacements, horizontal stresses, shear forces and bending moments in the structure during the construction process. Emphasis was placed on the evaluation of wall embedment, tie-back horizontal spacing, wall thickness, and free anchor length on wall behavior. A representative soil profile of a specific region at the City of Natal, Brazil, was used in the numerical analyses. New facilities built on this region often include retaining structures of the same type studied herein. Soil behavior was modeled using the Mohr-Coulomb constitutive model, whereas the structural elements were modeled using the linear elastic model. Shear strength parameters of the soil layers were obtained from direct shear test results conducted with samples collected at the studied site. Deformation parameters were obtained from empirical correlations from SPT test results carried out on the studied site. The results of the numerical analyses revealed that the effect of wall embedment on the investigated parameters is virtually negligible. Conversely, the tie-back horizontal spacing plays an important role on the investigated parameters. The results also demonstrated that the wall thickness significantly affects the wall horizontal displacements, and the shear forces and bending moments within the retaining structure. However, wall thickness was not found to influence horizontal stresses in the structure

Determinación del coeficiente de rozamiento grano-pared en silos de pared corrugada mediante el método de los elementos discretos

El comportamiento de los materiales granulares almacenados en silos se ve afectado por varios parámetros, tanto aquellos característicos del material como de la geometría del silo. La determinación del coeficiente de rozamiento pared-partícula es uno de los parámetros de mayor importancia, siendo habituales en su determinación el uso de ensayos de corte directo. En el presente trabajo se estudia dicho coeficiente para el supuesto de una pared corrugada, el cual, teóricamente, debe representar a un valor efectivo que depende tanto del coeficiente de rozamiento grano-pared (para el caso de una pared lisa) y el ángulo de rozamiento interno del material. La determinación del rozamiento efectivo se ha realizado a través de la simulación por elementos discretos de un ensayo de corte sobre una pared corrugada. Los valores obtenidos han sido comparados con las prescripciones expuestas en la normativa vigente. La potencialidad del método de los elementos discretos permite el estudio de diversas configuraciones geométricas de la pared corrugada de los silos sin necesidad de realizar ensayos de laboratorio. Esto permitirá, en trabajos sucesivos, investigar la influencia de muy diversos factores en el valor del rozamiento efectivo grano-pared en este tipo de paredes. The mechanical behaviour of granular materials stored in silos is affected by numerous parameters, some of them being related to the characteristic of the stored materials and others to the geometry of the silo. The determination of the particle-wall friction coefficient (or wall friction) is of great importance and direct shear tests are usually conducted in order to obtain its value. In this work this variable is analysed for the case of a corrugated wall. This value is expected to be an effective value between the particle-wall friction coefficient (obtained for a flat wall) and the internal friction coefficient of the material under study. The effective wall friction determination has been carried out by using a discrete element model to simulate a direct shear test on a corrugated wall. The values obtained have been compared with prescriptions given in the current standards. The potential of the discrete element method allows different geometries of the silo corrugated wall to be considered without the necessity of developing laboratory tests. In future works it will allow the influence of numerous parameters on the effective wall friction in corrugated walls to be studied.