多孔材料吸能行为对相对密度和冲击速度的依赖性

多孔材料是一种优异的吸能缓冲材料,但由于其变形模式的非单一性以及动态应力应变曲线的难获取性,其吸能行为对相对密度和冲击速度的依赖性关系还并不完全明朗.论文基于不需要提前作本构假定的波传播法,开展了多孔材料的吸能行为研究.采用多孔材料的细观有限元模型进行Taylor冲击虚拟实验,获取全场质点速度时程曲线,结合Lagrange分析法得到多孔材料的局部应力应变信息,进而探讨了动态吸能性能对材料相对密度和冲击速度的依赖性.研究结果表明多孔材料的吸能行为可依据变形模式分为三个阶段.在冲击模式下,多孔材料单位体积吸能与相对密度成线性增加关系,此时惯性起主导作用;在过渡模式下,惯性的主导作用减弱,单位体积吸能量的增加速率随相对密度的增加而减弱;在准静态模式下,多孔材料只能发生微小的变形,其吸能很少.论文进一步获得了区别于多孔材料准静态应力-应变曲线的动态应力-应变状态曲线,并考察了其与相对密度之间的关系.结果表明:随着相对密度的增加,多孔材料的动态压实应变将变小,而动态塑性平台应力将提高.

复合材料结构-功能一体化技术与吸能结构的研究

复合材料的结构一体化技术包括结构整体化和结构 功能一体化两个方面。复合材料吸能结构属于典型的结构 功能一体化结构。以复合材料管形件为基础,发现提高管形件轴向性能如增加编织结构的轴向纤维纱数,或调整预浸料复合材料铺层尽可能地平行于轴向,或提高复合材料层间韧性(即高CAI值)等,都有利于提高吸能效果。在整体化制造方面,研制和验证了织物复合材料正弦波梁的液态成型制造技术。

Elastic Behaviors of Adsorbed Protein-like Chains

Elastic behaviors of protein-like chains are investigated by Pruned-Enriched-Rosenbluth method and modified orientation-dependent monomer-monomer interactions model. The protein-like chain is pulled away from the attractive surface slowly with elastic force acting on it. Strong adsorption interaction and no adsorption interaction are both considered. We calculate the characteristic ratio and shape factor of protein-like chains in the process of elongation. The conformation change of the protein-like chain is well depicted. The shape of chain changes from “rod” to “sphere” at the beginning of elongation. Then, the shape changes from “sphere” to “rod”. In the end, the shape becomes a “sphere” as the chain leaves away from the surface. In the meantime, we discuss average Helmoholtz free energy per bond, average energy per bond, average adsorbed energy per bond, average α-helical energy per bond, average β-sheet energy per bond and average contact energy per bond. On the other hand, elastic force is also studied. It is found that elastic force has a long plateau during the tensile elongation when there exists adsorption interaction. This result is consistent with SMFS experiment of general polymers. Energy contribution to elastic force and contact energy contribution to elastic force are both discussed. These investigations can provide some insights into the elastic behaviors of adsorbed protein chains.

Freeze-thaw Effects on Sorption/Desorption of Dissolved Organic Carbon in Wetland Soils

The effects of freeze-thaw cycles on sorption/desorption of dissolved organic carbon （DOC） in two wetland soils and one reclaimed wetland soil were investigated. DOC concentrations added were 0-600 mg/L. Laboratory incubations of sorption/desorption of DOC had been carried out at -15℃ for 10 h, and then at ＋5℃ for 13 h. Soil samples were refrozen and thawed subsequently for 5 cycles. Initial Mass model was used to describe sorption behavior of DOC. The results indicate that freeze-thaw cycles can significantly increase the sorption capacity of DOC and reduce the desorption capacity of DOC in the three soils. The freeze-thaw effects on desorpfion of DOC in soils increase with the increasing freeze-thaw cycles. The conversion of natural wetlands to soybean farmland can decrease the sorption capacity and increase the desorption capacity of DOC in soils. Global warming and reclamation may increase DOC release, and subsequently increase the loss of carbon and the emission of greenhouse gas.

Hydrogen storage behaviours of nanocrystalline and amorphous Mg_(20)Ni_(10-x)Co_x(x=0-4) alloys prepared by melt spinning

The Mg2Ni-type alloys with nominal compositions of Mg20Ni10-xCox(x=0,1,2,3,4,%,mass fraction) were prepared by melt-spinning technology.The structures of the alloys were studied by XRD,SEM and HRTEM.The hydrogen absorption/desorption kinetics and the electrochemical performances of the alloys were measured.The results show that no amorphous phase forms in the as-spun Co-free alloy,but the as-spun alloys containing Co show a certain amount of amorphous phase.The hydrogen absorption capacities of the as-cast alloys first increase and then decrease with the incremental change of Co content.The hydrogen desorption capacities of as-cast and spun alloys rise with increasing Co content.The melt spinning significantly improves the hydrogenation and dehydrogenation capacities and kinetics of the alloys.The substitution of Co for Ni clearly enhances the discharge capacities of the alloys and the cycle stability of the as-spun alloys.

Protein adsorption onto diethylaminoethyl dextran modified anion exchanger:Effect of ionic strength and column behavior

Our previous studies on bovine serum albumin （BSA） adsorption to diethylaminoethyl dextran （DEAE dextran, DexD, grafting-ligand） and DEAE （D, surface-ligand） modified Sepharose FF resins found that all the grafted resins （FF-DexD and FF-D-DexD） exhibited extremely fast uptake rate （effective diffusivity, De, De/Do 〉 1.4）, which was six times greater than the ungrafted resins （De/Do 〈 0.3）. In this work, the influence of ionic strength （IS） on 6 typical DEAE dextran-grafted resins was investigated. Bath adsorption equilibria and kinetics, breakthrough, and linear gradient elution experiments were conducted. Commercial DEAE Sepharose FF was used for comparison. It is found that protein adsorption capacities on DEAE dextran-FF resins and the commercial resin decreased with increasing IS, but DEAE dextran-FF resins exhibited much higher capacity sensitivity to salt concentration. Besides, steeper decrease of adsorption capacities could be obtained at higher graftingligand or surface-ligand density. It is worth noting that the facilitating role of surface-ligand to the ＂chain delivery＂ effect was weakened after adding salt, leading to the less improvement in uptake rate by increasing surface-ligand density at higher IS. Although the uptake rates of the DEAE dextran-FF resins increased first and then decreased with increasing fS, they kept the extremely high level of De values （De/Do 〉 1.1 ） at the their working/binding IS range. Moreover, the DEAE dextran-FF resin displayed much higher adsorption capacities and De values than commercial ungrafted resin in their working condition. Furthermore, the column results of DEAE dextran-FF resins presented higher dynamic binding capacities than and similar elution ISs with DEAE Sepharose FF to achieve similar （or even higher） recoveries suggest the excellent chromatographic column performance of the DEAE dextran-FF resins. Finally, both high recovery and purity of BSA and γ-globulin could be easily achieved using the typical DEAE dextran-FF column, FF-D60-DexD160, to separate their binary mixtures, by step gradient elution. The research has provided new insights into the practical application of the series of DEAE-dextran grafted resins in protein chromatography and proved their superiority.

Efficient energy absorption of functionally-graded metallic foam-filled tubes under impact loading

The deformation behavior and crashworthiness of functionally-graded foam-filled tubes(FGFTs)under drop-weight impact loading were investigated.Closed cell aluminum,A356 alloy and zinc foams fabricated by the liquid state processing were used as axial grading fillers for the manufacture of single-layer and multilayer structures with different configurations.The results indicate that the deformation of multilayer foam filled tubes initiates from the low-strength components,and then propagates in the high-strength components through the gradual increment of stress.The use of more A356 alloy and aluminum foam layers provides greater specific energy absorption(SEA)for the graded structures,whereas the high-strength zinc foam has no positive effect on the crash performance.The progressive collapse of graded structures consisting of the aluminum and A356 alloy foams occurs in a symmetric mode under quasi-static and drop-weight impact conditions.However,the zinc foam causes a combination of symmetric and extension modes as well as greater localized deformation under dynamic loading and greater local rupture in quasi-static loading condition.The Al−A356 foam-filled tubes with a combination of the highest SEA(10 J/g)and the lowest initial peak stress(σmax of 10.2 MPa)are considered as the best lightweight crashworthy structures.

Microstructure and properties of co-continuous(β-TCP+MgO)/Zn-Mg composite fabricated by suction exsorption for biomedical applications

The biomedical co-continuous(β-TCP+MgO)/Zn-Mg composite was fabricated by infiltrating Zn-Mg alloy into porousβ-TCP+MgO using suction exsorption technique.The microstructure,mechanical properties and corrosion behaviors of the composite were evaluated by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),mechanical testing,electrochemical and immersion test.It was found that the molten Zn-Mg alloy had infiltrated not only into the pores but also into the struts of the porousβ-TCP+MgO scaffold to form a compact composite.The Zn-Mg alloy contacted to theβ-TCP+MgO scaffold closely,and no reaction layer can be found between the alloy and the scaffold.The compressive strength of the composite was as high as244MPa,which was about1000times higher than that of the original porousβ-TCP+MgO scaffold and2/3of the strength of the Zn-Mg bulk alloy.The electrochemical and immersion tests in simulated body fluid(SBF)solution indicated that the corrosion resistance of the composite was better than that of the Zn-Mg bulk alloy.The corrosion products on the composite surface were mainly Zn(OH)2.Appropriate mechanical and corrosion properties indicated that the(β-TCP+MgO)/Zn?Mg composite fabricated by suction exsorption would be a very promising candidate for bone substitute.

An on-chip intestine-liver model for multiple drugs absorption and metabolism behavior simulation

A double-layer microfluidic chip integrated with a hollow fiber(HF)was developed to reconstitute the intestine-liver functionality for studying the absorption and metabolism of combination drugs.Caco-2 cells were inoculated in the HF cavity at the top of the serpentine channel to simulate the intestinal tissue for drug absorption and transport studied,and Hep G2 cells,seeded in the bottom chamber,were used to mimic the liver for metabolism-related studies.Genistein and dacarbazine were selected for combination drug therapy and its effects on cell viability,hepatotoxicity,and cell cycle arrest under drug-conditioned culture were investigated.The results suggested that the combined concentration below-100μg/m L had no significant inhibitory effect on Hep G2 cell viability,and therefore Hep G2 cells maintained their drug metabolism ability.When the drug concentration was increased above 250μg/m L,Hep G2 cells underwent apoptosis.Detection of metabolites by mass spectrometry proved the effective metabolism in the microchip model.This dynamic,co-culture microchip successfully provided a podium for long-term observation of absorption,transport,and metabolism of combination drugs,and could be an effective in vitro simulation model for further clinical research.