CRACK PROPAGATION IN POLYCRYSTALLINE ELASTIC-VISCOPLASTIC MATERIALS USING COHESIVE ZONE MODELS

Cohesive zone model was used to simulate two-dimensional plane strain crack propagation at the grain level model including grain boundary zones. Simulated results show that the original crack-tip may not be separated firstly in an elastic-viscoplastic polycrystals. The grain interior's material properties (e.g. strain rate sensitivity) characterize the competitions between plastic and cohesive energy dissipation mechanisms. The higher the strain rate sensitivity is, the larger amount of the external work is transformed into plastic dissipation energy than into cohesive energy, which delays the cohesive zone rupturing. With the strain rate sensitivity decreased, the material property tends to approach the elastic-plastic responses. In this case, the plastic dissipation energy decreases and the cohesive dissipation energy increases which accelerates the cohesive zones debonding. Increasing the cohesive strength or the critical separation displacement will reduce the stress triaxiality at grain interiors and grain boundaries. Enhancing the cohesive zones ductility can improve the matrix materials resistance to void damage.     

多晶X射线衍射测量结果的一些影响因素

讨论了多晶X射线衍射测量中实验结果的一些影响因素.分别对粉末样品自身颗粒的大小、粉末装填到样品架中所处的表面平整度以及少量样品采用横式填充还是竖式填充等问题进行了分析和探讨.结果表明,在X射线衍射分析测量中,要想得到理想的衍射数据,试样颗粒应小于50μm,而且装填后样品与样品架表面保持平齐,对少量或微量试样应采取横式填充法.     

室温铁磁Sr3YCo4O10.5+δ多晶的制备及其性能研究

采用传统简便的固相烧结法制备了四方相的室温铁磁Sr3YCo4O10.5+δ多晶.热分析、X射线衍射和扫描电镜结果表明Sr3 YCo4 O10.5+δ多晶最终烧结温度应在963℃以上,较佳的烧结温度为1180℃.Sr3YCo4O10.5+δ多晶在80～300K为半导体电输运行为,较佳烧结温度多晶的室温电阻率～78.8 mΩ·cm;多晶热电势在317～1018 K随温度增加而减小,317 K时为70.74 μV/K.磁化强度-温度曲线、磁滞回线结果表明,多晶在受外加磁场、温度及晶体场的影响下,内部Co3+自旋态及磁畴壁、磁矩方向发生改变,导致多晶磁化强度变化及多晶磁性的改变.外磁场(0.1 T)下的ZFC曲线在320 K出现磁化强度最大为0.46 emu/g的Hopkinson峰,居里温度(Tc) =323 K,而FC曲线在奈尔温度(TN)=264 K时磁化强度达到最大为1.1 emu/g,TC=320 K.ZFC、FC方式下多晶均表现为室温铁磁性.     

AgGaS2多晶合成工艺改进研究

按同成分熔化点配料,采用改进了合成温控条件的双温区气相输运法成功合成出AgGaS2多晶原料,通过精确控温,有效避免了反应过程中由S蒸汽压过大引发的合成石英安瓿炸裂,提高了AgGaS2多晶合成的质量和成功率.经过XRD、DSC测试分析,结果表明:经改进方法合成的AgGaS2多晶材料是高纯单相、均匀致密的,为高质量AgGaS2单晶的生长提供了优质原料.     

Evolution of the characteristics of Parametric X-ray Radiation from textured polycrystals under different observation angles

The Parametric X-Ray radiation (PXR) spectra and yield dependencies on the orientation angle are measured during the interaction of 7 MeV electrons with a tungsten textured polycrystalline foil for different observation angles. The effects of PXR spectral density increase and PXR yield orientation dependence broadening in the backward direction is shown experimentally for the first time. The experimental results are compared with PXR kinematical theories for both mosaic crystals and polycrystals.     

On the micromechanical modelling of the effective diffusion coefficient of a polycrystalline material

This study focuses on calculation of the effective diffusion coefficient of a polycrystalline material accounting for the grain size and shapes. Polycrystal is modelled as a composite consisting of a matrix with high diffusivity (grain boundaries and triple junctions) and inhomogeneities with low diffusivity (bulk grains including crystal defects like dislocations). The segregation at the grain boundaries is accounted for. Typical micromechanical models are re-written for diffusivity assuming that the grains have the shape of ellipsoids of revolution (spheroids). The results are compared with (1) numerical results for hydrogen diffusion in an imaginary polycrystalline material and (2) experimental results for diffusion of hydrogen in nickel polycrystal available in the literature. The approach can be used for extraction of information on diffusivity along the grain boundaries.     

助熔剂NaCl－CdCl2对CdS∶Cu, In结晶状态作用规律研究

发现在确定的热处理温度和时间下，随炉料中助熔剂ＮａＣｌ－ＣｄＣｌ２总含量的增加，ＣｄＳ：Ｃｕ，Ｉｎ多晶的粒度分布变窄，数均粒径具有最大值，晶粒外型趋于规整且表面平滑。进而证明，多晶的结晶状态对其光电性能具有显著的影响。     

基于Voigt模型和Reuss模型的三方晶粒各向异性集合的弹性本构关系

多晶体材料的宏观力学性质与晶粒的化学成分和多晶体的微结构（晶粒的尺寸、取向分布、边界结构）有关，研究多晶体微结构与材料宏观力学性质的关系具有重要的理论意义和工程应用背景。利用三方晶粒的D3对称性给出了三方晶粒的弹性本构关系，通过引入ODF描述多晶体材料的取向分布，基于Voigt模型和Reuss模型分别找出带有织构系数影响的三方晶粒任意集合的多晶体材料弹性本构关系上、下限。     

N i50.5Mn24Ga25.5取向晶体相变应变性能的研究

采用区熔法制备了Ni505_50.5Mn24₂₄Ga255_25.5取向晶体，在底部、中部和顶部各切取一块样品进行相变应变测试.在中部样品中获得了高达14%的相变应变，应变随加热冷却循环次数的增加而逐步降低，第9次和第10次相变时应变为08%.在底部和顶部样品中，降温过程的应变随温度的变化呈现先收缩后膨胀或先膨胀后收缩的现象，我们认为这是由于样品中高度择优取向的马氏体变体竞争的结果所致. 关键词： NiMnGa 取向晶体 相变应变     

Diffusion processes in silver-conducting solid electrolyte in terms of the Grafov-Ukshe model of adsorption relaxation of double layer

The results of impedance studies of an interface formed by solid electrolyte RbAg₄I₅ with iodine vapors and certain iodine complexes are compared with the results on the diffusion of minority charge carriers and color centers. The impedance results are analyzed based on the Grafov-Ukshe model for the adsorption relaxation of the double layer (ARDL) [1]. The obtained kinetic parameters agree within the experimental error with the diffusion coefficients found by independent methods. It is shown that the experimental data of impedance measurements agree with the results of calculations in terms of the Grafov-Ukshe ARDL model.