Materials Science Forum Vols. 505-507

Abstract: This study demonstrated that DNA associated with magnetic nanoparticles can be attracted to specific areas of cell surfaces under magnetic fields, which highly increased the DNA concentration at specific areas and further enhanced the gene transfection in an electroporation (EP) method. The superparamagnetic nanoparticle’s distribution could be operated by magnetic field, where the gravity effect could be neglected. Compared with the electroporation with and without electrostatic attracting force, the magneto-electroporation with magnetic attracting force showed higher delivery rate (63.05 %) in the electroporation processes. Simulating an asymmetric magnetic field helps to create experiment environment with different intensities of magnetic flux density. The resultant difference can be identified by the profile of fluorescence. This report focused on enhancement and targeting of gene transfection using 6 nm γ-Fe2O3 nanoparticles and electroporation microchips.

Abstract: This paper described and characterized the quantum dots (QDs) with/without the polymeric PLGA applied in MC3T3E-1 delivery. Neat QDs were treated with various solvents, temperatures, exposure time and concentration to evaluate their stability and efficacy. We found that the intensity degree of fluorescence spectra (QDs) in different solvents follows the order: ether > THF > acetone > chloroform > methanol. Importantly, the QDs become inactive after 8-hr dissolution in the solvents of ether, THF or chloroform. According to this result, acetone and methanol are ideal solvents for QDs. The optimum concentration range of QDs in acetone is 5 to 10 mg/mL. We found that no obvious difference of fluorescence intensity was detected in QDs stored respectively at 4 °C, 24 °C and 44 °C (8-hour). When QDs were exposed to UV light (312 nm) for 2 hr, serious decay of fluorescence intensity was observed. In order to extend the application of QDs in medical areas, we encapsulated them in individual biocompatible poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles for in-vitro imaging of endocytosis in MC3T3E-1 cells. We demonstrated that the polymeric PLGA have the ability to permeate the cells for cellular internalization; the endocytotic activity could be enhanced by the polymeric QDs-encapsulated PLGA.

Abstract: The electricity is the most important motive power in the world for the economy and the industry. But today the electricity is always generating by natural gas, oil, and coal, hence environment pollution caused by fossil fuel will be more serious, and crude oil will be used up in 40-50 years (according to the report of Statistical Review of World’s Energy’s Research), it is need to develop a high efficiency and zero-emission in new energy.

Abstract: Titanium is an attractive material for orthopedic implants, although it is expensive and difficult to manufacture. Hot forging is usually used, but the tool life is always not good since the forging tools sustain higher temperature and the working pressure induces wear. In this research proposes a procedure to obtain forging parameter design optimization considering tool wear using a combination of FEM simulation and Taguchi method. A modified Archard’s wear model is used to predict the tool wear. This procedure is used to evaluate titanium artificial acetabulum cup forging. Based on the minimum tool wear, but maintaining the microstructure required to satisfy the properties needed by orthopedic implants, the titanium acetabulum cup development is successful and the tool life is better than our expectations.

Abstract: This paper combines Feasible Sequential Quadratic Programming (FSQP) and elasto-plastic finite element method to perform the inverse estimation of the material constitutive constants and friction coefficient in the nosing process. The aim is to improve the accuracy of constitutive constants and working parameters in the classical analysis based on the material flow homogeneity or trial and error. In the prediction of the friction coefficient at the interface between metal and tool surface, the simulated load, calculated from the optimal material constants, shows good coincidence with the experimental load when the optimal friction coefficient is reached. The investigation of these inverse models identify that the combination of FSQP and elasto-plastic finite element method can supply a useful optimal approach in the industrial application.

Abstract: Stretching forming test was utilized to evaluate the influence of die material upon formability and galling of hot-dip galvanized steel sheets. SS41 and SKD11 were used as the substrate of die materials which CrN, TiN and DLC (diamond like carbon) were coated on SS41 and SKD11 substrate. It was found that die with coated materials performs better than that without coated materials in terms of formability and friction. Moreover, DLC coated die material shows the best performance on formability, friction and galling comparing to other coated materials.

Abstract: In this paper, a rigid-plastic hybrid element method is formulated, which is a mixed approach of the rigid-plastic domain-BEM and the rigid-plastic FEM based on the theory of slightly compressible plasticity. Since compatibilities of velocity and velocity's derivative between adjoining boundary elements and finite elements can be met, the velocity and the derivative of velocity can be calculated with the same precision for this hybrid element method. While, the compatibility of the velocity's derivative cannot be met for the rigid-plastic FEMs.

Abstract: This study aims to clarify the process conditions of the hat-type drawing of a sheet metal of steel. It provides a model that predicts not only the correct punch load for drawing, but also the precise final shape of products after unloading, based on the tensile properties of the material and the geometry of the tools used. An elasto-plastic incremental finite-element computer code, based on an updated Lagrangian formulation, was developed to simulate the hat-type drawing of sheet metal. In particular, selective reduced integration was adopted to formulate the stiffness matrix. The extended r-minimum technique was used to deal with the elasto-plastic state and contact problems at the tool-metal interface. A series of simulations were performed to validate the formulation in the theory, leading to the development of the computer codes. The whole deformation history and the distribution of stress and strain during the forming process were obtained by carefully considering the moving boundary condition in the finite-element method. Results in this study clearly demonstrated that the computer code for simulating the hat-type drawing process was efficient.

Abstract: Currently, the numerical simulations of metal forming are developed rapidly and widely. In this investigation, a dynamic-explicit FEM code, LS-DYNA, is adopted. Attention on applications of the velocity and mass scaling techniques for the quasi-static upsetting process are modeled. With the differences being variations in the die and punch velocities, the material density, and the mesh type, their effects on the predicted load-reduction height are assessed. Through comparison with experiments, the numerical results have a same tendency as in test works. The influences of the velocity and mass factors are presented, the usage of these scaling factors at proper time also discussed.