New Inclusion Assessment Method in Aluminum Alloys——Electrochemical Method for Inclusion Assessment

The existence of inclusion influences the properties of aluminum alloy castings,from which the castings will face scrapping under severe condition.Great efforts on the inclusions in aluminum alloy were made and many inclusion assessment methods were put forward.However,most of the current methods are characterized by time consuming and expensive equipment cost,which limits the application in aluminum industry.Since the aluminum properties are sensitive to the inclusion,this paper tries to establish a new kind of inclusion assessment method.The inclusions were introduced to aluminum melts by adding aluminum scraps.The samples with different inclusion contents were prepared.The microstructure contained inclusions was observed.The inclusion was automatically identified with an image analyzer by setting different grey threshold value,and the inclusion content was obtained.The image analysis shows that inclusions wreck the continuity of the alloy matrix seriously,and the inclusion area percentage increases with the increasing of aluminum scraps.The high and low polarization measurements were conducted in 3.5 wt% NaCl aqueous solution at the temperature of 25 ℃.The electrochemical parameters of the testing materials,such as corrosion potential E k,corrosion current density I k and the linear polarization resistance R p,were obtained.The polarization measurement results show that the linear polarization resistances decrease,the corrosion potentials move towards more negative direction,and the corrosion current densities increase with the increasing of inclusion content.The theoretical analysis of the inclusion content and the corrosion current density was performed.The existence of inclusions makes the microstructure form corrosion microcells between the alloy matrix and inclusions.The impressed current can accelerate the current velocity or corrosion current density.The regression model of the inclusion contents vs.the corrosion current density was obtained.This model can be used to quantitatively analyze the inclusion content in aluminum alloys on the basis of inclusion sensitivity to the inclusion content.It is confirmed that the electrochemical method for inclusion assessment （EcMIA） is simple and reliable,which can provide a new solution for inclusion assessment in aluminum alloy.

Study of Defect and Large Thermal Strain Nature in Organic Crystal of Rubidium Hydrogen Phthalate

Imperfections in the(001) plate of rubidium hydrogen phthalate(RAP, RbC8H5O4) crystals have been studied by means of X-ray topography. The main defects are the grown-in dislocations, inclusions, growth layers and the thermal strain lobes caused by heat. The large thermal strain nature was determined by an Inclusion Probed Method (IPM), which is due to the gradient of the interplanar spacing formed by atomic displacement to <110> directions.

Timoshenko inclusions in elastic bodies crossing an external boundary at zero angle

The paper concerns an analysis of equilibrium problems for 2D elastic bodies with a thin Timoshenko inclusion crossing an external boundary at zero angle. The inclusion is assumed to be delaminated, thus forming a crack between the inclusion and the body. We consider elastic inclusions as well as rigid inclusions. To prevent a mutual penetration between the crack faces, inequality type boundary conditions are imposed at the crack faces. Theorems of existence and uniqueness are established. Passages to limits are investigated as a rigidity parameter of the elastic inclusion going to infinity.

Semi-analytical Modeling of the Influence of Macro Bending Effects on Micro Contact-Inhomogeneity Problems

This study examines the effects of macroscopic bending and microscopic contact loading in inhomogeneous materials using a semi-analytical model based on Eshelby’s equivalent inclusion method.The model accounts for bending effects through the beam theory,with bending stress included in the Eshelby’s equivalent inclusion equations.The macroscopic displacement resulting from bending effects is incorporated into the microscopic contact solver,and the final displacement is determined using the conjugate gradient method in an iterative solution.Computational efficiency can be improved by incorporating the discrete convolution and fast Fourier transform.The core scheme is validated using the finite element method,yielding accurate and efficient results for bending-contact problems in inhomogeneous materials.Simulations reveal the interplay between bending,contact loading,and inhomogeneity,as stress around the inhomogeneity alters and the stress concentration area expands under increasing bending moments.Conversely,low-magnitude negative bending moments reduce both contact pressure and stress around the inhomogeneity.The position where inhomogeneities are least affected shifts from the neutral surface depending on the coupling effect.The model provides a valuable bridge for connecting the macroscopic bending effect and microscale contact-inhomogeneity problems by visualizing stress fields and assessing pressure distributions.

Numerical study of contacts between a flat-ended punch and a half-space embedded with inhomogeneities

This paper presented a numerical approach to solving the problem of a flat-ended punch in contact with a half-space matrix embedded with multiple three dimensional arbitrary-shaped inhomogeneities.Based on the semi-analytical method(SAM)and the equivalent inclusion method,numerical procedures were developed and the effects of inclusion shape and distribution were analyzed.Fast Fourier transform technique was implemented to accelerate the calculation of surface deformation and subsurface stress.Interactions of inter-inclusions and inclusion-matrix were taken into account.Numerical results showed the presence of inhomogeneities(i.e.,microstructures in solids)indeed had a great effect on local contact pressure and a strong disturbance to the subsurface stress field in the vicinity of inclusions.The effects were dependent on the shape and distribution of inclusions and inter-inclusion interactions.The physical significance of this study is to provide an insight into the relation between the material microstructure and its response to the external load,and the solution approach and procedures may find useful applications,for example,the analysis of fatigue and crack propagation for composite materials,prediction of stress field in solids containing material defects,and study of the mechanism of chemical-mechanical polish(CMP)for inhomogeneous materials,etc.

Grandparent-provided childcare and labor force participation of mothers with preschool children in Urban China

This paper investigates the effects of grandparent-provided childcare and the access to daycare services on the labor force participation of mothers with children under 7 years old in urban China.Using two-stage residual inclusion method,the analysis finds that grandparent-provided childcare and the access to daycare services both have strong positive effects on maternal labor force participation(MLFP).Specifically,having grandparent-provided childcare increases MLFP by 38-43%,whereas having access to daycare services increases MLFP by 24-29%.The analysis also finds that having a healthy grandmother is a significant determinant in whether grandparent-provided childcare is utilized and that the demand for grandparent-provided childcare is higher in localities in which daycare services for children under 3 years old are more expensive.These results indicate that grandparents,particularly grandmothers,play an important role in sustaining MLFP,particularly as the supply of publicly funded daycare programs is declining.