Statistical three-dimensional investigation of the damage evolution in heterogeneous materials

A simulation procedure is implemented for evaluating the damage development though structures or test specimens constituted of heterogeneous materials. Stress and strain fields are obtained using a three-dimensional finite element analysis. Materials are assumed to have a brittle local behaviour and statistical distributions of fracture stresses are considered and distributed randomly through the structure or the test specimen. The influence of the scattering width of the stress distributions is analysed in the case of tensile tests and three-point bending tests. Experimental investigation of the fracture development is carried out in the case of polymer concrete using holography and the results obtained are compared with the results derived from the simulation procedure.     

Impact of volume fiber on distribution of thermal stress residual near fiber/epoxy interface using axisymmetric model

Thermal residual stresses are important in composite materials. The aim of this work is the computation of thermal residual stresses by finite element method and the effect of volume fraction on their distribution. In this work, two cases are considered by using an epoxy matrix with respectively glass and carbon fibers with a different volume fiber using an axisymmetric model. From the results of the numerical calculation, it is shown that the stresses are important and thus should be taken into account. The interface is affected by thermal stresses. The normal stresses and shear stress value have an influence on the behavior of the material. Hence, on the performance of composites during service, is an information of significance for the designers.     

Optimization of peened-surface laser shock conditions by method of finite element and technique of design of experiments

This paper presents a numerical simulation of the laser shock peening (LSP) process using the finite element method. The majority of controlling parameters of the LSP process have been taken into account. The LSP loading has been characterized by the use of a repetitive time Gaussian increment pressure applied uniformly at a circular impacted zone. The utilized model of the treated material behaviour law is the Johnson-Cook’s visco-elastic-plastic coupled with damage. The proposed model leads to determine the LSP surface modifications: (i) the in-depth residual stresses, (ii) the induced plastic strains and (iii) the superficial damage. These modifications can be significantly induced in few cases, particularly when the operating conditions are not well optimized. An application is carried out on the laser peened titanium aero-engine super alloy Ti-6Al-4V. A satisfactory correlation between the computed and experimental results is observed. Also, it is noted that the computed superficial damage values increase with the growth of the maximal peak pressure of the laser spot, which are physically consistent. Otherwise, in order to optimize the laser peening operating conditions, a design of experiments is established. It allows having surface-response relationships between the operating parameters and the three announced induced effects.     

Effect of adsorbed metal ions and buffer nature on IgG separation from human plasma by column chromatography using an ion exchange resin,Amberlite IRC‐718

Fractionation of human plasma on ion exchanger resin was performed on Amberlite IRC‐718 saturated with metal ions. Depletion of human immunoglobulin G was carried out by column chromatography using Tris‐HCl, pH 7 at different concentrations. Results showed that, when Cu⁺² and Ni⁺² were adsorbed on the resin, one or two fractions of purified IgG were obtained, respectively. Whereas Fe⁺² and Zn⁺², both retain IgG and serum albumin or serum albumin alone. Furthermore, the Ni⁺²‐resin retention of serum proteins is too strong that the use of 700 mMTris‐HCl cannot liberate any other proteins than nonadsorbed serum albumin. In conclusion, this investigation demonstrates that immobilized metal ion affinity chromatography with Cu²⁺, Ni²⁺, and Fe²⁺ immobilized on Amberlite IRC‐718 has the potential to be developed as part of a process to purify IgG out of untreated human plasma as acceptable adsorption and elution levels of IgG could be achieved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A fundamental approach and its experimental validation to simulate density as a function of moisture content during drying processes

Although several empirical models are available in the literature to predict density in solid matrices, only a very limited number of theoretical models have been reported. So far, no model considered the possible variation in the initial air volume existing at the beginning of the drying process. In this contribution, a theoretical model to predict bulk density of dried materials was built by considering two mechanisms that might occur during drying processes. These mechanisms are represented by collapse and shrinkage functions. The predictions obtained by this theoretical model were extensively validated with experimental data published by several independent groups for different food products dried with different technologies. In all these cases, the model gave excellent agreement with the experimental data regardless the topology of the curve bulk density versus moisture content. The model was also compared with other published models. The result of this comparison revealed that the errors resulting from the predictions obtained by the present model are among the smallest. Shrinkage and collapse functions were used to analyze the mechanisms by which bulk density varies during air-drying and freeze-drying. The model showed that both shrinkage and collapse phenomena are dramatically involved during air-drying. However, in the case of freeze-drying, no collapse is observed and only partial shrinkage is taking place. Hence, the present model can be used as a tool to predict the bulk density with excellent accuracy, to understand the dynamic mechanisms involved during drying. Moreover, this model can be incorporated to other models involving the variation of density as a function of moisture.     

A new method of real-time physical simulation of prime movers used in energy conversion chains

This paper focuses on exploring a new method of real-time replication of the dynamic behaviour of prime movers that drive rotating generators involved in energy conversion chains. Their behaviour depends on the mover’s mechanical characteristics and dynamical properties, such as inertia or friction coefficient, which are seldom known precisely. Being also dependent on the variations of the primary energy resource, not always controllable in its natural environment, this behaviour must be simulated by using a smaller and cheaper mover, whose model is sufficiently known such that to render it fully controllable. This paper explores the possibility that the desired real-time replication be achieved by means of a new method of tracking the mover’s rotational speed. To this end, various controllers, both linear and nonlinear can be employed. The design steps are provided for a PI controller, as well as for two nonlinear controllers, while focusing on the practical aspects of controller implementation. Their performance results are assessed comparatively on an experimental rig for two types of prime movers: one whose mechanical torque-speed characteristic is linear and a cross-flow water turbine, having a nonlinear torque-speed characteristic.     

Autonomous smart robot for path predicting and finding in maze based on fuzzy and neuro‐Fuzzy approaches

The navigation of autonomous mobile robots has in recent times gained interest from many researchers in different areas such as the industrial, agricultural, and military sectors. This paper aims at carefully investigating two advanced types of approaches for guiding a non‐holonomic mobile robot to navigate in an environment area cluttered with static obstacles. Firstly, a Fuzzy logic controller (FLC) was designed, using trapezoidal shape Membership functions (MF's). Secondly, an Adaptive neuro fuzzy inference system (ANFIS) controller was used to optimize the results obtained from trapezoidal fuzzy controller. To validate the feasibility and effectiveness of the proposed models, V‐REP and MATLAB software are used. A comparative evaluation is, then, done on the basis of speed. The simulations results showed that the mobile robot could navigate successfully into maze environment with both proposed approaches but ANFIS controller provided better results in comparison to fuzzy controller.     

Thermal characteristics of bagasse

Bagasse is a solid waste that remains after crushing sugarcane. Since bagasse is used as a fuel in sugar mills, characterization of its thermal degradation is rather important in order to use it efficiently. Thermal analysis of bagasse was carried out using differential thermal analysis (DTA) and thermogravimetry (TG) under oxidizing and inert atmospheres. Kinetic studies were based on weight loss obtained from TG analysis. Thermal degradation of bagasse takes place in two stages: volatilization and carbonization. The reaction rate, activation energy, entropy change, enthalpy change, and Gibbs free energy for the two thermal stages were calculated. The results indicated that activation energy for the volatilization stage is higher than that of decarbonization stage, and that both the rate constant and activation energy for combustion are higher than those of pyrolysis. © 1996 John Wiley & Sons, Inc.     

Properties of concrete reinforced with different kinds of industrial waste fibre materials

Nowadays, the use of different types of sub-products in cement-based materials has become a common practice in concrete industry. This paper discusses the feasibility of adding metallic and polypropylene by-product fibres as reinforcement of normal concrete. The effects of the incorporation of various types of waste metallic fibres (WMF) and polypropylene fibres (WPF) on the mechanical properties of fibre-reinforced concrete were experimentally investigated. A normal concrete with a compressive strength of 30 MPa was used as a control mixture. The influence of type, volume and length of WF on the compressive and flexural strengths, and toughness of fibres reinforced concrete (FRC) is evaluated. The results obtained have shown that the WPF decreases the compressive strength of WFRC, especially when using long fibres with high volume fraction. A slight decrease of the compressive strength was also observed with the composites containing more than 2% of the WMF. However, adding the WPF and the hybrid fibres increases the flexural strength of the WFRC. It has been observed that the composites reinforced with the WPF is more advantageous in terms of post-cracking behaviour and load-carrying capacity as compared to the composites reinforced with the WMF even in some cases, the WPF performs better than the multimodal composites. The results have shown that generally, ductility, toughness, and especially the post-cracking behaviour of the WFRC are significantly improved when using the multimodal composites compared to composites reinforced with the mono-fibres system. Results regarding orientation and distribution of fibres into the cement matrix, and porosity and their effect on the WFRC performance were also discussed.     

Amino acid supplementation of a protein-rich mixture of crushed groundnut,chickpea and sesame

Supplementation of a 3 : 2 : 1 crushed groundnut-chickpea-sesame mixture (in a 10% protein diet) with methionine to raise the level of sulphur-containing amino acids from 187 to 228 mg/g N resulted in improved growth and lactation in the rat, but further supplementation with both methionine and tryptophan to the levels proposed by the FAO committee (1957) did not increase this effect.