高增益、低h_(FE)温度系数硅横向MIS隧道结晶体管

设计并研制出直流电流增益为842、交流电流增益为1080的高增益挂横向MIS隧道晶体管。测量了器件的电学特性和hFE的温度特性，发现孩器件在较大的温度范围内hFE具有很小的负温度系数．并对测量结果进行了分析讨论。     

Lamb波频散特性和波结构特性的有限元仿真

采用ANSYS有限元仿真软件模拟超声Lamb波在4 mm厚的钢板结构中的传播过程,计算S0模态和A0模态超声Lamb波的群速度和沿钢板厚度方向上的位移波结构,绘制频散曲线和波结构特性曲线,理论分析与仿真结果基本吻合;为超声Lamb波群速度测定和缺陷检测提供理论依据.     

Analysis and optimal design of plates and shells under dynamic loads – I: finite element and sensitivity analysis

In this paper we consider the development, integration, and application of reliable and efficient computational tools for the geometry modeling, mesh generation, structural analysis, and sensitivity analysis of variable-thickness plates and free-form shells under dynamic loads. A flexible shape-definition tool for surface modeling using Coons patches is considered to represent the shape and the thickness distribution of the structure, followed by an automatic mesh generator for structured meshes on the shell surface. Nine-node quadrilateral Mindlin–Reissner shell elements degenerated from 3D elements and with an assumed strain field, the so-called Huang–Hinton elements, are used for the FE discretization of the structure. The Newmark direct integration algorithm is used for the time discretization of the dynamic equilibrium equations for both the structural analysis and the semi-analytical (SA) sensitivity analysis. Alternatively, the sensitivities are computed by using the global finite difference (FD) method. Several examples are considered. In a companion paper, the tools presented here are combined with mathematical programming algorithms to form a robust and reliable structural optimization process to achieve better dynamic performance on the shell designs.     

A criterion for omission of variable amplitude loading histories

The standard random loading sequence EC9 and the cycle-by-cycle sequences TWIST and MiniTWIST have been edited by a procedure based on notch or local (hot spot) stress, and the results of tests on specimens of FE 690 and AIMg4.5Mn using original and edited spectra are compared. Omission of small cycles below a filter level of about 50% of the materials' constant amplitude endurance limit was found to be ‘allowable’; this figure was confirmed by a variety of literature data. Using this level, the crack initiation lives (compared with the fatigue life under the unedited sequence) were longer by 10–30% for EC9 and by 20–55% for TWIST and MiniTWIST. In addition, for the latter two spectra, the crack propagation lives were longer by up to 90% with a detrimental influence of higher loading levels. Total life of the notched aluminium specimens increased by 30–70% using a filter level of 50% of the material's endurance limit.     

Essential and Non-essential Work of Fracture of PI/SiO<Subscript>2</Subscript> Hybrid Thin Films

Essential work of fracture (EWF) analysis is used to study the effect of the silica doping level on fracture toughness of polyimide/silica (PI/SiO₂) hybrid films. By using double-edge-notched-tension (DENT) specimens with different ligament lengths, it seems that the introduction of silica additive can improve the specific essential work of fracture (w _e ) of PI thin films, but the specific non-essential work of fracture (βw _p ) will decease significantly as the silica doping level increasing from 1 to 5 wt.%, and even lower than that of neat PI. The failure process of the fracture is investigated with online scanning electron microscope (SEM) observation and the parameters of non-essential work of fracture, β and w _p , are calculated based on finite element (FE) method.     

Multiaxial creep–fatigue life prediction for cruciform specimen

This paper describes the high temperature multiaxial creep–fatigue life prediction for type 304 stainless steel. Finite element analyses were performed for determining the stress–strain state in the gage part of a cruciform specimen subjected to creep–fatigue loading under four strain waves at three principal strain ratios. Creep–fatigue lives of cruciform specimens were discussed in relation to the principal stress amplitude calculated by finite element analysis. Creep–fatigue damage was evaluated by linear damage rule and the suitability of three low cycle fatigue and three creep damage parameters was discussed.     

A new hybrid velocity integration method applied to elastic wave propagation

We present a novel space–time Galerkin method for solutions of second‐order time‐dependent problems. By introducing the displacement–velocity relationship implicitly, the governing set of equations is reformulated into a first‐order single field problem with the unknowns in the velocity field. The resulting equation is in turn solved by a time‐discontinuous Galerkin approach (Int. J. Numer. Anal. Meth. Geomech. 2006; 30 :1113–1134), in which the continuity between time intervals is weakly enforced by a special upwind flux treatment. After solving the equation for the unknown velocities, the displacement field quantities are computed a posteriori in a post‐processing step. Various numerical examples demonstrate the efficiency and reliability of the proposed method. Convergence studies with respect to the h‐ and p‐refinement and different discretization techniques are given. Copyright © 2007 John Wiley & Sons, Ltd.     

Numerical study on the deformation behaviors of the flexible die forming by using viscoplastic pressure-carrying medium

The flexible die forming (FDF) of sheet metal with the aid of viscoplastic pressure-carrying medium (VPCM) is one of the advanced forming technologies for forming complex sheet metal components with large plastic deformation. The technology has been used in industries by employing different VPCMs, the epistemological understanding of the deformation and process behaviors of this process, however, has not yet been fully addressed. In this paper, numerical study is conducted to look into the deformation behaviors of this process by explicit 3D-FE simulation under the ABAQUS platform, in which the counter pressure variations of VPCM is applied via user subroutine VDLOAD and the ductile fracture criterion is implemented by using VUMAT. Three case study parts, viz., barrel, conic and parabolic parts with large Limit Drawing Ratio (LDR) are studied. The comparison between the conventional deep drawing (CDD) and VPCM-based FDF is conducted in terms of wall-thickness reduction, hydrostatic pressure, principal stress distribution and damage factor. The uniqueness and the deformation behaviors of the VPCM-based FDF are then highlighted. The simulation results show that the higher VPCM pressure could result in the higher hydrostatic pressure throughout the process and further resist wall thinning and prevent fracture of the sheet metal. The formability is thus increased significantly.     

河谷坡度对高面板堆石坝应力变形特征的影响

以玛尔挡水电站面板坝工程为例,建立了不同河谷坡度方案下的面板坝三维有限元模型,研究不同河谷坡度下高面板堆石坝坝体的静动位移和应力分布情况,分析了河谷坡度对坝体应力变形特征的影响,探讨了地震工况下河谷坡度对坝体结构稳定性的影响。结果表明:河谷坡度为50°时堆石体内部将会出现较明显的应力拱效应现象,河谷边坡陡缓临界值近似为50°;坝体沉降与坡度变化之间呈负相关关系;地震作用未对拱效应存在下的坝体产生显著的不利影响。