Measurement of contact angles and evaluation of surface coatings

Stable surface treatments for 301 stainless steel, copper, and aluminum alloy contact with liquid

Computational analysis of projectile impact resistance on aluminium (a356) curvilinear surface reinforced with carbon nanotubes (cnts) for applications in systems of protection

Computational tests for ballistic impact energy absorption were developed on A356/CNTs composite material with the goal of estimating the improvement of the material’s mechanical properties by the contribution of the CNTs [1]. For the implementation of computational tests on the material exposed to projectile impact, A356/CNTs was configured by means of generalized Hooke’s model for anisotropic materials [1] and Johnson-Cook’s model was used to determine material failure and propagation of energy [2]. A curvilinear surface (semi-spheres on a plaque) with an area of 23x23 cm and thickness of 12 mm was elaborated to represent the composite material. The impact on surface was done with a 9 mm projectile and the surface was developed with 4.5 mm radium semi-spheres. It was used a 0.3% of nanotube insertions on the composite total volume. The results indicated the plaque stopped the impact without drilling. Incidence of damage to wearer, as well as possibility of composite material improvement and the diffusion/dispersion analysis on the curvilinear surface was also done

Stochastic solution of geotechnical problems in truly discrete media

This research deals with the solution of geotechnical problems on intermediate length scales, i.e. when the length scale of interest is larger than the size of the grains of the soil (or rockfill) but the medium cannot be considered as a continuous body. This is because on such scales, despite the large number of involved grains, the volumetric average stress fluctuates around the mean value and the fluctuation is due to the truly discrete nature of the soil. Then, the smooth stress field that would be predicted by continuum mechanics approaches is replaced by a stochastic system of interparticle forces forming force chains. The forces can be transformed into equivalent stresses by means of homogenization techniques, but the obtained fields are again non-smooth and stochastic. A classical statistical mechanics framework is followed to anticipate the probability distribution functions of equivalent (extensive) stresses according to the macroscopic constraints of the problem. In particular, we get stochastic models for two seminal problems in geotechnics: the at rest lateral earth pressure acting on a retaining wall and the vertical stress at a given point in the soil that is caused by a vertical surface load. The theory is validated through massive numerical simulation with the Discrete Element Method. Mesoscale geotechnical analysis can find its main applications in the case of rockfill or other very coarse granular materials. However, it could be useful as well for laboratory, numerical and theoretical researches that are approached on small length scales. This theoretical framework contributes to fill the gap between micro and macro geotechnics and the resulting stochastic models may be useful for reliability analyses

Statistical mechanics as guidance for particle-based computational methods

Particle-based methods apply some laws of Classical Mechanics to all the particles of a granular system. On the other hand, classical Statistical Mechanics deals with systems consisting of a lot of particles, focusing on the statistical distribution of some intensive properties. Consequently, the macroscopic behaviour and the average properties of the system in equilibrium are based on some microscopic considerations. To do that, statistical tools and mechanical laws are used together. For an implemented particle-based method to be realistic enough, then the obtained simulations should satisfy some basic underlying physical requirements, and Statistical Mechanics is a useful tool to establish such requirements. This paper presents some results based on Statistical Mechanics that are useful for a realistic modelling of granular systems using Particle-based methods. Examples of the discussed issues include that the same protocol makes a disordered granular medium attain always the same packing ratio; that some local arrangements are less probable than others; that there is a well-established limit to the achievable density of granular assemblies of hard spheres; and that the equilibrium of disordered granular systems does not coincide to the state of minimum potential energy (which would be get in a completely ordered arrangement). The consideration of such issues in practical applications could be helpful to save time in computational methods, to avoid mistakes or, at least, to verify that the implementations are realistic

Seleccion en generaciones tempranas de frijoles volubles en asociacion con maiz

Studies were conducted at CIAT to test a new methodology (1) to improve F3, yields through the use of a hierarchical exptl design (a 9 x 9 lattice with 3 replications, with lines grouped according to the design, without taking into accont the family of origin) and (2) to select beans in association with maize in search for a greater complementation between the 2 crops. Analysis of yield data was lst done on the basis of mean family yields (main plots) and afterwards on those of individual lines. A good correlation exists between the yields of bean famines in the F3 and their corresponding yields in the following generation. The advantage of this method over more traditional ones is that it is possible to eliminate entire families of limited potential already in the F3. The best lines are always found in the best families. The efficiency of the methodology is greater when families with more than one line are always used since the exptl error decreased as the no. of lines/family increased. This methodology is also good for evaluating the productivity of beans in association with maize. There are bean genotypes that combine better with maize; these desirable genotypes can already be detected in the F3 generation. (CIAT

Flux creep in Bi2Sr2CaCu2O8(sub +x) single crystals

The results of a magnetic study on a Bi2Sr2CaCu2O(8+x) single crystal are reported. Low field susceptibility (dc and ac), magnetization cycles and time dependent measurements were performed. With increasing the temperature the irreversible regime of the magnetization cycles is rapidly restricted to low fields, showing that the critical current J(sub c) becomes strongly field dependent well below T(sub c). At 2.4 K the critical current in zero field, determined from the remanent magnetization by using the Bean formula for the critical state, is J(sub c) = 2 10(exp 5) A/sq cm. The temperature dependence of J(sub c) is satisfactorily described by the phenomenological law J(sub c) = J(sub c) (0) (1 - T/T(sub c) (sup n), with n = 8. The time decay of the zero field cooled magnetization and of the remanent magnetization was studied at different temperatures for different magnetic fields. The time decay was found to be logarithmic in both cases, at least at low temperatures. At T = 4.2 K for a field of 10 kOe applied parallel to the c axis, the average pinning energy, determined by using the flux creep model, is U(sub o) = 0.010 eV