A Method of Estimating the Strength of Adhesive Bonded Joints of Metals

The strength of adhesive bonded joints is investigated both analytically and experimentally. The deformed states of lap joints under tensile shear loading are analysed by the finite element method on the assumption of elastic deformation. A method of using the adhesive strength law is proposed to estimate the joint strength. The adhesive strength law is experimentally determined by subjecting butt joints of two thin-walled tubes to combined axial load and torsion. The strength of lap joints is determined by adopting the adhesive strength law to the adhering interface as well as the strength law of adherend and adhesive resin. The calculated strain distribution and strength of the joints are compared with the experimental results. The effects of the joint configurations on the deformation and strength are discussed. It is shown that the proposed method is useful to predict the joint strength.     

A Method of Estimating the Strength of Adhesive Bonded Joints of Metals

The strength of adhesive bonded joints is investigated both analytically and experimentally. The deformed states of lap joints under tensile shear loading are analysed by the finite element method on the assumption of elastic deformation. A method of using the adhesive strength law is proposed to estimate the joint strength. The adhesive strength law is experimentally determined by subjecting butt joints of two thin-walled tubes to combined axial load and torsion. The strength of lap joints is determined by adopting the adhesive strength law to the adhering interface as well as the strength law of adherend and adhesive resin. The calculated strain distribution and strength of the joints are compared with the experimental results. The effects of the joint configurations on the deformation and strength are discussed. It is shown that the proposed method is useful to predict the joint strength.     

Batch Grinding in Laboratory Ball Mills: Selection Function

The selection functions and the breakage distribution functions are based on the experimentally‐determined particle size distribution on the basis of comminution of one size fraction particles. Therefore, to obtain a clear picture of the product properties during comminution of the “real” polydisperse sample, a number of experiments are needed. This work introduces the tested methodology for the selection function determination based on the starting and maximal values of the selection function. The principle was tested on the planetary ball mill and the horizontal laboratory ball mill, and according to the results obtained, it can be concluded that the proposed methodology can be useful for the evaluation of the selection function during batch comminution in different mills.     

SURFACE MASS TRANSFER COEFFICIENTS FOR WOOD

ABSTRACT

Experimentally determined mass transfer coefficients for wood surfaces are often much lower than theoretically and experimentally determined coefficients for other surfaces. An investigation of this is made by comparing mass transfer coefficients for water and saturated non-wood surfaces, with coefficients measured for wood surfaces. It is found that measurements on wood surfaces are usually evaluated by assuming that Fick's law describes diffusion in wood. As this is not always true, it is proposed that the mass transfer coefficients measured on wood surfaces are low because the internal mass transfer in wood is not well understood. New measurements are presented which support this conclusiou.     

Probing Heterogeneous Structure of Aggregates

Naturally occurring aggregates are considered of fractal or fractal-of-fractals interior structure. Recent studies utilizing dye staining and confocal laser scanning microscopy (CLSM) techniques have revealed the extremely complex, interconnected pore networks for floc interior. Detailed structural analysis on the real floc architecture is determined for building up a comprehensive floc model. This work interprets structural characteristics of flocs using multifractal analysis. A direct method by Chhabra and Jensen properly evaluated the singularity strength and singularity spectrum on architectures of two artificial fractal systems. However, direct evaluation of multifractal characteristics of wastewater flocs has limitations, alternatively acquiring analytical results to be misleading. Particularly, the singularity spectrum presents excessively large values in the limit as q → +∞ and exhibits very large error bars in the limit as q → ?∞. This is attributable to the uneven distribution of mass in flocs and insufficient spatial resolutions provided by CLSM techniques. The flaws in applying multifractal analysis on naturally occurring objects are discussed.     

Crushing characteristics

A method of measuring the basic characteristics of comminution was developed. These characteristics are expressed by the major comminution functions: crushing probability function, energy function and breakage function. The crushing probability function is the strength distribution of particles of a given size. The energy function is the strength of the particles as a function of their sizes. And finally, the breakage function is the size distribution of the crushed material. The functions are defined mathematically. Several natural minerals were tested by drop tests in order to determine their individual comminution functions. From the tests, several crushing properties of the particulate materials can be derived. The comminution functions given in this paper would be the basic elements in developing mathematical models for various crushing and grinding processes.     

SURFACE MASS TRANSFER COEFFICIENTS FOR WOOD

Experimentally determined mass transfer coefficients for wood surfaces are often much lower than theoretically and experimentally determined coefficients for other surfaces. An investigation of this is made by comparing mass transfer coefficients for water and saturated non-wood surfaces, with coefficients measured for wood surfaces. It is found that measurements on wood surfaces are usually evaluated by assuming that Fick's law describes diffusion in wood. As this is not always true, it is proposed that the mass transfer coefficients measured on wood surfaces are low because the internal mass transfer in wood is not well understood. New measurements are presented which support this conclusiou.     

Internal structure analysis of Polypropylene/quartz composites related to their toughness

The mechanical performance of composite materials has been related to a wide range of factors. The complexity of analysis lays on the fact that any single variation normally affects many characteristics or properties of the composite material. For this reason, different theoretical and experimental characterizations should be considered. In this work the internal structure, interactions and fracture surfaces of PP‐based composites reinforced with quartz particles are investigated. Particle size distributions, rheological measurements and multifractal spectra suggest favorable filler dispersion into the PP matrix. A yield strength model and rheological data evidence low internal interactions. In addition, these composites characteristics could promote the effective activation of energy consumption mechanisms improving the material toughness. The fracture surfaces analysis allows correlating fractography, multifractal spectra and material toughness. However, the experimental procedure of multifractal theory should be improved to define the most sensitive parameter for fractographic studies. POLYM. COMPOS., 37:1488–1496, 2016. © 2014 Society of Plastics Engineers     

Strength distribution of particles under compression

From time immemorial people dealt with size reduction processes (mill, mineral liberation, etc.). As time has passed industrial units for comminution processes have become larger and more sophisticated, but still they perform with low efficiencies [1], [2] and [3]. The strength of a particle is one of its most crucial characteristics due to the mechanical stresses experienced by each particle within an industrial unit. This is because the final size of particles is mostly dependant on the strength distribution of the raw material [4]. In this present study, the ability of a number of statistical formulations to accurately describe the strength distribution of particles was examined. Additionally, selected equations were analyzed and a general expression including the effect of the material and particle size was developed. A number of approaches to define particle strength were considered, and strength in terms of crushing force was chosen. Particle strength in terms of force and in terms of energy was also compared and found to be size independent. Finally, particle strength in terms of stress was examined and compared to the particle strength in terms of force.The ability to describe the compression strength distribution will significantly improve the accuracy of the comminution processes simulation, design and optimization.     

A micromechanical derivation of the macroscopic strength statistics for pristine or corroded/abraded float glass

The macroscopic strength of float glass is governed by the presence of micro-cracks, whose size, orientation and distribution affects the corresponding statistics. A micro-mechanically motivated model is here proposed, which spells out the connection between crack population and strength statistics, leading to generalized distributions of the Weibull type. Aging in the form of corrosion or abrasion can produce a variation of the defectiveness scenario originally present on the pristine glass surface, and we discuss how such a modification can statistically affect the macroscopic strength. A practical application is made to justify the change in strength experimentally observed passing from the “air” to the “tin” side of float glass. Assuming that the contact with the tin bath and the rollers produce a damage equivalent to the abrasion of the glass surface, we theoretically derive a bimodal Weibull statistics that agrees with the experimental evidence.     

Energy and population balances in comminution process modelling based on the informational entropy

The results of theoretical and experimental studies of a comminution process are presented. There are two random functions: the selection function and the breakage function in the stochastic model based on a population balance. This model enables prediction of particle size distributions of comminution products after determination of both random functions. Maximum entropy method is used in the entropy model for determining the breakage function. Two cases are analysed, based on continuous and discrete particle size distribution functions of the fed material. Apart from mass balance, the energy balance of comminution process is also used. Searched form of breakage function is determined with the application of methodology of calculus of variations. The results of experimental identification of both models are presented. The parameters that occur in the discrete form of the selection and breakage functions were the identification objects. The results of experimental investigations of quartz sand single comminution in a laboratory jet mill provided an identification base. The experimentally identified results of the entropy model confirmed the adequacy of the theoretical analysis and demonstrated the possibility of adequate prediction of particle size distributions resulting from single comminution.     

不同粘土与含量对硅酸盐钻井液性能的影响

在总结粘土结构及其对各种硅酸盐钻井液体系性能影响的机理和原因的基础上,通过大量的室内实验,分析归纳出粘土类型与含量对硅酸盐钻井液性能的影响规律,实验表明钠膨润土含量为3％～4％时,硅酸盐钻井液的性能容易控制,能够满足工程要求,抗高温能力强,稳定性好.     

Separation of Mercury from Aqueous Mercuric Chloride Solutions by Onion Skins

Abstract

The separation of mercury from aqueous HgCl₂ solutions by onion skins (outermost coat) was studied both experimentally and theoretically. The distribution equilibria were measured by the batchwise method. The experimental results revealed that onion skin is a useful material for separating mercury from aqueous systems. The distribution data obtained at 25°C were analyzed by using the theory based on the law of mass action. The separation of dissolved mercury by onion skins was found to be a process accompanied by an ion-exchange reaction of the cationic complex HgCl⁺ and an adsorption of the neutral complex HgCl₂. The equilibrium constants of the ion-exchange and adsorption processes at 25°C and the mercury-binding capacity of onion skins were determined. Further, it was found that the distribution equilibrium of mercury is comparatively insensitive to temperature.     

Weibull strength size effect of diamond wire sawn photovoltaic silicon wafers

A good comprehension of the mechanical properties of photovoltaic silicon wafers is crucial to maintain low breakage rates during solar cell manufacturing. As brittle material, silicon wafers are theoretically subject to a strength size effect. This study aims at determining whether this effect should be considered when comparing the strength of photovoltaic wafers. We derive a theoretical strength scaling law and perform an extensive experimental study on 240 diamond-wire sawn silicon wafers, which have the particularity of exhibiting an anisotropy in Weibull parameters. We compare test results from three different bending configurations and show that a size effect is only observable when loading the wafers perpendicular to the saw marks. Strength values obtained when loading the wafers in the direction of the wire yield identical results regardless of the size of the tested area. These findings can open up prospects for the standardization of testing methods for photovoltaic wafers.     

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.     

External and internal mass transfer effect on photocatalytic degradation

A rational approach is proposed in determining the effect of internal and external mass transfer, and catalyst layer thickness during photocatalytic degradation. The reaction occurs at the liquid–catalyst interface and therefore, when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters, namely, external mass transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass transfer coefficient, and effective diffusivity were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thickness under two different illuminating configurations was analyzed theoretically and later experimentally verified. It was observed that an optimal catalyst layer thickness exists for SC (substrate-to-catalyst) illumination.     

Reaction Kinetics in Restricted Spaces

Reactions in restricted spaces rarely get stirred vigorously by convection and are thus controlled by diffusion. Furthermore, the compactness of the Brownian motion leads to both anomalous diffusion and anomalous reaction kinetics. Elementary binary reactions of the type A + A → Products, A + B → Products, and A + C → C + Products are discussed theoretically for both batch and steady-state conditions. The anomalous reaction orders and time exponents (for the rate coefficients) are discussed for various situations. Global and local rate laws are related to particle distribution functions. Only Poissonian distributions guarantee the classical rate laws. Reactant self-organization leads to interesting new phenomena. These are demonstrated by theory, simulations, and experiments. The correlation length of reactant production affects the self-ordering length scale. These effects are demonstrated experimentally, including the stability of reactant segregation observed in chemical reactions in one-dimensional spaces, e.g., capillaries and microcapillaries. The gap between the reactant A (cation) and B (anion) actually increases in time and extends over millimeters. Excellent agreement is found among theory, simulation, and experiment for the various scaling exponents.     

Modelling of comminution processes in Spex Mixer/Mill

It is well known that mathematical models which simulate comminution processes represent a useful tool in several fields of academic and industrial research, with particular emphasis on nano-material and pharmaceutical production. In the present work a mathematical model which is able to quantitatively describe comminution processes in a ball milling system (i.e., Spex-Mixer/Mill) has been developed. The proposed approach takes into account three different contributions: dynamics of the vial, dynamics of spheres motion and simulation of the comminution process. The vial dynamics has been modelled by taking advantage of an appropriate roto-translation matrix. Model results have been successfully compared with literature experimental data. The spheres motion within the Spex Mixer/Mill has been simulated using a 3D dynamic model based on classical mechanics as well as the so-called discrete element method, which is widely adopted to quantitatively describe multi-body collision behaviour. In particular, existing models of impact with dissipation as well as the classical Hertz impact theory have been taken into account. This part of the global model allows one to obtain, for different operating conditions, the impact specific energy and impact velocity as a function of time. The latter ones represent input parameters for the simulation of comminution processes that is performed through suitable population balances, where different breakage functions as well as appropriate breakage probabilities have been considered. Model results are reported in terms of granulometric distribution of powders within the mixer-mill as a function of time, minimal grain size obtainable and time needed to complete the comminution process for various operating conditions (i.e., mill frequency and charge ratio).     

Emergence of falsified kinetics as a consequence of multi-particle interactions in dense-phase comminution processes

Particle breakage during dense-phase comminution processes is significantly affected by mechanical multi-particle interactions, which are neglected in traditional discrete linear population model (DL-PBM). A discrete non-linear PBM (DNL-PBM) has been recently proposed to account for multi-particle interactions; however, the inverse problem, i.e., the estimation of the model parameters, has not been addressed. In this paper, a method for the estimation of DNL-PBM parameters is presented with a purpose of determining the consequences of neglecting multi-particle interactions in the traditional DL-PBM. The model parameters were obtained from a constrained, non-linear, least-squares minimization of the residuals between comminution data and discrete PBM prediction. Comminution data exhibiting multi-particle interactions were obtained from a DNL-PBM simulation followed by addition of 0%, 10%, and 20% random error. A comprehensive statistical analysis of the goodness of fit and certainty of the parameters was performed to discriminate the models. Using the estimated parameters, predictive capability of both models was further assessed by comparing their prediction with additional computer-generated data obtained with a different feed particle size distribution. The parameter estimation method was shown to be highly accurate and robust. DNL-PBM can predict the influence of different feed conditions better than DL-PBM when multi-particle interactions are significant. This study has demonstrated that neglecting multi-particle interactions in dense-phase comminution processes via the use of DL-PBM can lead to falsified kinetics with erroneous breakage functions.