Effect of Initial Stress on a Fiber-Reinforced Anisotropic Thermoelastic Thick Plate

The two-dimensional problem of generalized thermoelasticity for a fiber-reinforced anisotropic thick plate under initial stress is studied in the context of the Lord and Shulman theory. The upper surface of the plate is thermally insulated with prescribed surface loading while the lower surface of the plate rests on a rigid foundation and temperature. The problem is solved numerically using a finite element method. Numerical results for the temperature distribution, and the displacement and stress components are given and illustrated graphically. It is found from the graphs that the initial stress significantly influences the variations of field quantities. The results obtained in this paper may offer a theoretical basis and meaningful suggestions for the design of various fiber-reinforced anisotropic thermoelastic elements under loading to meet special engineering requirements.     

Determination of crack tip parameters for ASCB specimen under mixed mode loading using finite element method

In this paper, a new asymmetric semicircular bend specimen (ASCB) is presented. Having more geometric parameters in asymmetric bend elements gives the opportunity of covering a wider range of K_?, K_?? and T-stress in comparison with classical SCB specimens. Finite element method is used to obtain these parameters from pure mode I to pure mode II. Extensive numerical calculations are made to get a wide range data for crack tip parameters of this specimen. It is observed that for ASCB specimens with specified geometries under pure mode II loading, one of the bottom supports can move horizontally without significant variation in Y_I. The complete sets of numerical results are obtained and can be used for verification and interpretation of future experimental results.     

Utilisation of immobilised activated sludge for the biosorption of chromium (VI)

The objective of this investigation was to study the biosorption of Cr (VI) on immobilised activated sludge (IAS) and calcium alginate (CA) using batch system. The optimal pH for Cr (VI) biosorption by IAS and CA was 2.0 and 4.0, respectively. Equilibrium was attained at approximately 120 min for both biosorbents. For both biosorbents, the equilibrium biosorption capacity (mg/g) increased as the initial metal ion concentration increased and the concentration of biosorbent decreased. The rate of biosorption onto IAS and pure CA (as mg/g) increased from 5.02 to 87.66 and 4.97 to 79.09 as the concentration of Cr (VI) ions increased from 10 to 1000 mg/L, respectively. In the case of biosorbent concentration, as the concentration of IAS and pure CA increased from 1 to 20 g/L, the equilibrium uptake (q_e) decreased from 21.33 to 1.57 and 19.41 to 1.38 mg/g, respectively. The biosorption data showed that the Langmuir model was more suitable than the Freundlich model. Also, the results indicated that the pseudo‐second order model was the most suitable for Cr (VI) biosorption onto IAS and CA. © 2011 Canadian Society for Chemical Engineering     

Reliability-based vector nonstationary random critical earthquake excitations for parametrically excited systems

The study considers the earthquake response of stack-like structures subjected to simultaneous action of random horizontal and vertical earthquake acceleration components. The governing equation of motion in this case is approximated by a set of coupled randomly time varying ordinary differential equations. The components of earthquake accelerations are modelled as nonstationary Gaussian random processes that are obtained by multiplying deterministic modulating functions with partially specified stationary random processes. Specifically, it is assumed that the matrix of power spectral density (psd) functions of the stationary components is not known, while, the variance, average rate of zero crossings, entropy rate and frequency range of interest are taken to be known. The unknown input psd matrix is determined such that the reliability index associated with a specified structure performance function is minimized. The solution procedure employed, combines the theory of Hasofer–Lind reliability indices, response surface modelling and constrained nonlinear optimization tools. The critical input psd matrix so obtained leads to the definition of excitation models that produce the least favorable response, which, at the same time, possess a few of the well known properties of earthquake loads. A numerical example that illustrates the concepts developed with reference to a chimney structure is provided.     

Mathematical modeling of axial crushing of cylindrical tubes

Different aspects of mathematical modeling for the axial crushing of cylindrical tubes with straight fold have been discussed. The variation of circumferential strain during the formation of a fold has been taken into account. The present paper tries to answer questions such as (a) how great is the inside and outside folding, and (b) how the crushing load varies. In the present paper, the influence of the consideration of the conservation of mass on the mathematical formulation has been studied. The results of average and varying circumferential strain have also been compared.     

Effectiveness of sliding isolators with variable curvature in near‐fault ground motions

Recent studies have revealed that a sliding isolator with variable curvature (SIVC) can mitigate the resonance phenomenon likely to occur in seismic response of a conventional friction pendulum system (FPS) isolator due to its constant isolation frequency. The present study simulates four SIVC isolators and an FPS to find the optimum range of initial isolation period and coefficient of friction and employ them in comparing the effectiveness of SIVC in different peak ground acceleration (PGA) scales of near‐fault earthquakes. Velocity‐dependent coefficient of friction and modified viscoplasticity model have been used to simulate nonlinear friction force of the isolators. Results indicate identical performance of all SIVC isolators in PGA scales up to 0.4 g. When subjected to PGA scales from 0.4 g to 1.0 g, polynomial friction pendulum isolator (PFPI) and variable curvature friction pendulum system (VCFPS) reduce base displacement greatly, while conical friction pendulum isolator (CFPI) and variable frequency pendulum isolator (VFPI) show amplified responses. However, in mitigating structural acceleration, performance of CFPI and VFPI, unlike PFPI and VCFPS, which perform poorly, is excellent. Thus, in a strong near‐fault earthquake, PFPI and VCFPS or CFPI and VFPI can be chosen based on whether reduction of base displacement or super‐structural acceleration is the main concern of designer, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of reverse yielding on residual stresses induced by autofrettage

The paper investigates the influence of reverse yielding on residual stresses induced by autofrettage. On the basis of reverse loading tests, a material model is developed and implemented into analytical procedures capable of treating the elasto-plastic deformation behaviour of thick-walled tubes during both loading and unloading phases. The results show that residual hoop stresses are drastically reduced near the tube bore as compared with residual stresses obtained from conventional isotropic hardening analysis. Pure kinematic hardening analysis is also shown to overestimate residual hoop stress induced by autofrettage.     

Application of perfectly matched layer to soil-foundation interaction analysis

Despite of the limitation in modeling infinite space, the finite element method (FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer (PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without reflection. In this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral elements. The analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.     

Hair mercury levels in pregnant women in Mahshahr, Iran: Fish consumption as a determinant of exposure

MeHg is a well-documented neurotoxicant even at low levels of exposure. Developing brain, in particular, is vulnerable to that. Through bioaccumulating to differing degrees in various fish species, it can have serious adverse effects on the development and functioning of the human central nervous system, especially during prenatal exposure. Therefore, the purpose of this study was to investigate mercury concentration in hair samples of pregnant women living in Mahshahr located in Khuzestan province, Iran. It assessed the association between fish consumption and specific characteristics that can influence exposure. From April to June 2008, 149 pregnant women were invited to participate in this study. An interview administered questionnaire was used to collect information about age, body weight, height, fish (fresh, canned and shrimp) consumption, pregnancy stage, residence duration, education level, family income and number of dental amalgam fillings. The obtained results showed that the geometric mean and range for hair total Hg concentration was 3.52 μg/g (0.44-53.56 μg/g). About 5.4% of mothers had hair total Hg levels in excess of 10 μg/g. Maternal hair mercury level was less than threshold level of WHO (5 μg/g). As expected, there was a clear increase in hair Hg with reported fresh marine fish consumption (p = 0.04). The highest mean for hair mercury level in a group who consumed fish several times per week, was 4.93 μg/g. Moreover, a significant effect of age and residential time on Hg concentration in the hair of the women was found. Pregnant women in Mahshahr consumed large amounts of fish; consequently, most of their offspring were prenatally exposed to moderately high levels of mercury. The results found suggest that pregnant women should decrease their fish consumption.     

Intermittent swelling and shrinkage of a highly expansive soil treated with polyacrylamide

This laboratory study examines the potential use of an anionic polyacrylamide(PAM)-based material as an environmentally sustainable additive for the stabilization of an expansive soil from South Australia.The experimental program consisted of consistency limits,sediment volume,compaction and oedometer cyclic swell-shrink tests,performed using distilled water and four different PAM-to-water solutions of P_D=0.1 g/L,0.2 g/L,0.4 g/L and 0.6 g/L as the mixing liquids.Overall,the relative swelling and shrinkage strains were found to decrease with increasing number of applied swell-shrink cycles,with an‘elastic equilibrium’condition achieved on the conclusion of four cycles.The propensity for swelling/shrinkage potential reduction(for any given cycle)was found to be in favor of increasing the PAM dosage up to P_D=0.2 g/L,beyond which the excess PAM molecules self-associate as aggregates,thereby functioning as a lubricant instead of a flocculant;this critical dosage was termed‘maximum flocculation dosage’(MFD).The MFD assertion was discussed and validated using the consistency limits and sediment volume properties,both exhibiting only marginal variations beyond the identified MFD of P_D=0.2 g/L.The accumulated axial strain progressively transitioned from‘expansive’for the unamended soil to an ideal‘neutral’state at the MFD,while higher dosages demonstrated undesirable‘contractive’states.