薄膜/基体界面的层裂行为研究

近年来，薄膜/基体结构在微/纳米工程中得到广泛的应用，研究薄膜/基体界面的力学性能得到广泛的关注。为了检验薄膜和基体间的黏结强度，早在20世纪50年代，人们就设计了一种简单的实验方法－－撕裂试验，该试验由于其简单易于操作至今仍在许多领域都有广泛的应用。早期对于撕裂试验的研究多局限于弹性撕裂，即将薄膜和基体都作为弹性材料来处理。后来，对于韧性薄膜，为了预测由于塑性耗散引起能量释放率(撕裂力)的增大，Kim及其合作者提出并采用了梁的弯曲模型对撕裂中的塑性耗散进行预测。Wei和Hutchinson在分析弹塑性薄膜的撕裂问题时，采用了一种不同于Kim的弯曲模型的方法，除已脱胶部分之外，薄膜的脱胶过程由平面应变弹塑性有限元方法模拟，在分析过程中采用黏聚力模型来刻画韧性薄膜沿基体界面被撕裂或脱胶过程，所得结果无论是在定性还是定量上均与Kim的梁弯曲模型结果有很大区别。\newline 鉴于几种关于韧性薄膜撕裂模型对结果预测的不一致，几位学者联名倡议提出开展关于薄膜撕裂实验刻画模型有效性检验的国际合作。在倡议中指出无论采用何种方法，都须采用黏聚力模型来刻画界面断裂过程。而此后有很多工作都采用黏聚力模型来刻画界面。\newline 如果考虑残余应力的影响，涂层或黏结于基体上的薄膜或多层材料中的单独片层等均不可避免地承受着残余应力的作用。薄膜中的残余应力的主要来源于沉积过程，外延，以及热膨胀失配等因素。承受应力状态的薄膜/基体体系往往在边缘处产生很强的应力集中，极易导致其在该处界面起始层裂发生。如何评价残余应力对薄膜/基体体系界面的影响也显得至关重要。\newline 本文将对撕裂试验以及热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为展开研究。薄膜/基体体系界面采用混合性黏聚力模型来刻画。研究了对应不同薄膜材料参数和不同界面参数情况下的撕裂行为，给出了撕裂力和界面分离功以及界面分离强度等参数之间的关系，并对界面层裂模式进行了分析。同时对多角度撕裂的界面破坏形式进行了系统的研究，给出了稳态撕裂力及相角与撕裂角度之间的关系。\newline 对由于热失配引起残余应力作用下的薄膜/基体体系的界面层裂行为的研究。假设薄膜和基体材料分别为弹塑性材料和弹性材料。研究了对应不同薄膜材料参数和不同界面参数情况的界面层裂发生机制，给出了层裂发生时临界温度荷载与薄膜/基体几何参数、材料参数以及模型参数之间的关系。

Multi-strip MRPCs for FOPI

During the last years FOPI has developed a new ToF system as an upgrade of the existing detector based on Multi-strip Multi-gap Resistive Plate Chambers (MMRPCs). The intention is to increase the charged Kaon identification up to a laboratory momentum of 1 GeV/c and to enhance the azimuthal detector granularity. The new ToF barrel has an active area of 5 m(2) with 2400 individual strips (900 x 1.6 mm(2)) [A. Schuttauf, et al., Nucl. Phys. B 158 (2006) 52] which are read out on both sides by a custom designed electronics [M. Ciobanu, et al., IEEE Trans. Nucl. Sci. NS-54 (4) (2007) 1201; K. Koch, et al., IEEE Trans. Nucl. Sci. NS-52(3) (2005) 745]. To reach the envisaged goal a time resolution of 100 ps is needed, at a flight path of 1-1.3 m. Due to the rare production of the K- at SIS energies the efficiency of the MMRPCs has to be above 95%. We report on measurements with the detectors and electronics from the mass production line. For this purpose we used a proton beam at 2.0 and 1.25 GeV, at rates between 0.1 and 5 kHz/cm(2) to determine the timing, efficiency and rate capability of the MMRPCs

Vortices in (Abelian) Chern-Simons gauge theory

The vortex solutions of various classical planar field theories with (Abelian) Chern-Simons term are reviewed. Relativistic vortices, put forward by Paul and Khare, arise when the Abelian Higgs model is augmented with the Chern-Simons term. Adding a suitable sixth-order potential and turning off the Maxwell term provides us with pure Chern-Simons theory, with both topological and non-topological self-dual vortices, as found by Hong-Kim-Pac, and by Jackiw-Lee-Weinberg. The non-relativistic limit of the latter leads to non-topological Jackiw-Pi vortices with a pure fourth-order potential. Explicit solutions are found by solving the Liouville equation. The scalar matter field can be replaced by spinors, leading to fermionic vortices. Alternatively, topological vortices in external field are constructed in the phenomenological model proposed by Zhang-Hansson-Kivelson. Non-relativistic Maxwell-Chern-Simons vortices are also studied. The Schrodinger symmetry of Jackiw-Pi vortices, as well as the construction of some time-dependent vortices, can be explained by the conformal properties of non-relativistic space-time, derived in a Kaluza-Klein-type framework. (c) 2009 Elsevier B.V. All rights reserved.

Void swelling in a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions at elevated temperatures

In this work the void swelling behavior of a 9Cr ferritic/martensitic steel irradiated with energetic Ne-ions is studied. Specimens of Grade 92 steel (a 9%Cr ferritic/martensitic steel) were subjected to an irradiation of Ne-20-ions (with 122 MeV) to successively increasing damage levels of 1, 5 and 10 dpa at a damage peak at 440 and 570 degrees C, respectively. And another specimen was irradiated at a temperature ramp condition (high flux condition) with the temperature increasing from 440 up to 630 degrees C during the irradiation. Cross-sectional microstructures were investigated with a transmission electron microscopy (TEM). A high concentration of cavities was observed in the peak damage region in the Grade 92 steel irradiated to 5 dpa, and higher doses. The concentration and mean size of the cavities showed a strong dependence on the dose and irradiation temperature. Enhanced growth of the cavities at the grain boundaries, especially at the grain boundary junctions, was observed. The void swelling behavior in similar 9Cr steels irradiated at different conditions are discussed by using a classic void formation theory. (c) 2008 Elsevier B.V. All rights reserved.

Systematics of central heavy ion collisions in the 1A GeV regime

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): Ca-40 + Ca-40 (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), Ni-58 + Ni-58 (0.15, 0.25, 0.4), Ru-96+Ru-96 (0.4, 1.0. 1.5), (96)zr+(96)zr 1.0, 1.5), Xe-129+CsI (0.15, 0.25, 0.4), Au-197 + Au-197 (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations. (C) 2010 Elsevier B.V. All rights reserved.