Papers by Author: Li Li

Abstract: In the present study, the microstructure, martensitic transformation and damping characteristics of Fe-17Mn-xNb (x = 0, 0.5, 1, 2, 4 wt. %) alloys were investigated. Nb addition leads to the variation in both the volume fraction and the size of ε martensite, in addition, the formation of Fe₂(Nb, Mn) precipitates. The martensitic transformation exhibits a tiny dependence on the content of Nb. The addition of Nb helps to enhance the damping capacity of Fe-17Mn. The maximum value of tan δ = 0.054 is achieved in Fe-17Mn-1Nb alloy, which is increased by 42% over Fe-17Mn. The damping mechanism caused by adding Nb is discussed in terms of the volume fraction and the size of ε martensite. Besides, the role of Fe₂(Nb, Mn) is also taken into account.

Abstract: Calcium alginate microspheres embedded with silver nanoparticles were prepared by dripping mixed solution of sodium alginate and silver nanoparticles, which were synthesized by reduction of silver nitrate (AgNO3) with sodium alginate as stabilizing agent and sodium borohydride as chemical reducing agent, into a crosslinking bath of calcium chloride solution. The concentration of sodium alginate and sodium borohydride used in synthesis step were found to have effect on the formation and growth of the silver nanoparticles as revealed by UV-visible spectroscopy. The TEM image indicated that uniform silver nanoparticles with particle size range from 20 to 60 nm are fabricated. The XRD spectrums showed that the silver nanoparticles embedded in calcium alginate microspheres exhibit crystalline state. The EDS showed that the higher the ration of AgNO3, the more silver nanoparticles embedded in calcium alginate microspheres. Moreover, X-ray images showed the calcium alginate microspheres embedded with silver nanoparticles exhibited better radiopaque properties than the pure calcium alginate microspheres and the microspheres with higher concentration of AgNO3 solution show sharper X-ray image. All the above facts indicated that these calcium alginate microspheres embedded with silver nanoparticles could therefore be used in embolization.

Abstract: At present, the finite element method (FEM) is used to predict the residual stress distribution of the welding structure. A long computational time is required for the multi-pass welding structure with complex shapes. Therefore, it is necessary to develop time-effective finite element model and computational approaches. In this study, the suitable finite element model is developed to perform the thermal and mechanical analyses for obtaining residual stress data of the tube-plate welding structure with T-shaped sections. The results of the finite element analyses show that the residual stress distribution and radial, hoop and axial direction stress distribution of the welding structure.

Abstract: Equal channel angular pressing (ECAP) is widely studied for its potential to produce ultra-fine grained (UFG) structure in TiNi shape memory alloys (SMA). In the present work, the effect of multipass ECAP parameters on the deformation behavior and strain distribution was investigated, at various deformation temperatures through different planes in the ECAPed billet. Three-dimensional (3D) geometric model with corner angle 120^◦ was designed by finite element method (FEM) software for ECAPing Ti-50.8%Ni by route B_c in DEFORM-3D software. Two methods were used to quantify deformation homogeneity through various planes in the processed billet, including strain standard deviation (SSD) and inhomogenity index (C_i). The simulation results demonstrate that by increasing ECAP passes, the cumulative average strain can increase and obtain UFG structure, but heterogeneity still exist across planes. In addition, temperature has a remarkable effect on homogeneity distribution .As well as C_i exhibits good results for multipass ECAP at various deformation temperature compared to SSD value.

Abstract: Sodium alginate (SA)/polyvinyl alcohol (PVA) matrix-based wound dressing system containing ciprofloxacin hydrochloride, a topical anti-infective drug, were obtained by a casting/solvent evaporation method. The FTIR spectrum indicated that a strong interaction between SA and PVA and a good compatibility between ciprofloxacin hydrochloride and SA/PVA. The surface contact angles showed that the SA/PVA membrane has good compatibility. The water absorption and water retention rate increased when the concentration of PVA increased. The swelling ratio of SA/PVA mixtures indicated that the membrane go to balance in about 30min. Moreover, the release rate of ciprofloxacin hydrochloride was found to be increased with the increment of PVA content for all the composite samples. Thus, SA/PVA wound dressing systems containing ciprofloxacin hydrochloride could be a novel approach in wound care.

Abstract: Self-healing materials offer tremendous potential for providing long-lived structural materials. In this study, isophorone diisocyanate (IPDI) microcapsules as self-healing materials were synthesized via in situ polymerization. Thermogravimetric analysis characterized the thermal ability of IPDI, microcapsules and microcapsule shells. The morphology of microcapsules and microcapsule shells were characterized by FE-SEM. Scanning micro-reference electrode technique demonstrated that epoxy resin coatings with IPDI microcapsules on the surface of reinforcing steel Q235 could cure the scratched crevice by immersion in 0.01 M NaCl solution after the coating was scratched. The self-healing epoxy resin coating could protect Q235 from corrosion.

Abstract: In this paper, calcium–alginate beads have been manufactured by physically cross-linked technology, by dripping an aqueous alginate solution into a solution of calcium salt as a crosslinker. The effect of various elements controlling beads shape such as solution concentration, flow rate and the distance between the orifice tip and surface of the cross-linking solution were studied. The various elements affected the gelling rate and diameter and weight were studied. The findings indicated that shape of alginate beads in the hydrated state was strongly dependent on the flow rate and concentration of sodium alginate solutions.

Abstract: The Paclitaxel-eluting stents (PTX) with biodegradable copolymer coating were studied in investigations. The polymer blend composition of PLGA (polylactic acid-co-glycolic acid) and PEG (poly ethylene glycol) have been applied as drug carrier and fabricated on the surface of 316L stainless steel stents by ultrasonic atomization spraying method. Were explored three doses: low-dose (~80μg per stent, 10 wt%), moderate-dose (~150μg per stent , 20 wt%), and high-dose (~220μg per stent , 30 wt%). The weight ratio of Paclitaxel to PLGA/PEG blends was 10:90, 20:80, and 30:70. Pre- and post-expansion surface morphologies of the Paclitaxel-eluting copolymer coating stents were examined by scanning electron microscopy (SEM). The quantitative analysis of Paclitaxel release in vitro and hemocompatibility by hemolysis ratio and dynamic clotting time measurement also were investigated.

Abstract: PMMA/PS copolymers were synthesized by radical polymerization techniques. And the 1H NMR results illustrate that the molar contents of PMMA are respectively 19%, 53%, 69% and 84%. The coatings of those PMMA/PS copolymers were prepared by spin-coating. The surface structures and protein resistance of copolymer coatings were investigated respectively by AFM and BSA absorption experiment. It is showed that the copolymer coating surfaces have micro-phase separation structure. Furthermore, with the increase in the PMMA content, the surface pattern changes from interpenetration network pattern to island structure that the PMMA-rich phase surrounded by the PS-rich phase. In addition, all coatings prepared in this study, especially the coating with PMMA content of 69%, have good resistance to BSA protein.

Abstract: Residual stresses and residual plastic strains of the welded structures are the products of nonlinear behaviors during welding. The residual stresses will cause errors during the assembly of the structure and injure the beauty of appearance of the structure. Based on an elastic-plastic-model, finite element numerical simulation of a representative tube sheet penetration assembly with loop welding line joined by multi-pass welding is carried out and the influence of welding conditions on residual stresses of the tube sheet welds is studied in this paper. Nonlinear three dimensional transient temperature fields and real-time dynamic stresses field are analyzed by FEM. The heat source is modeled as a moving heat flux following a double ellipsoid distribution and the temperature-dependent properties of materials are considered. The method of birth and death of element in finite element analysis is applied to simulate the gradual growth of weld pass metal. It is shown that welding sequence, size of groove welding and weld toes dressing will obviously change the magnitude of the residual stresses of tube sheet welds.