新淬火状态2B06铝合金板塑性成形各向异性行为研究

通过与轧制轴成0°、45°和90°方向的单向拉伸试验,研究了2B06铝合金板O态和W态(新淬火态)下材料的强度各向异性(3个方向屈服强度的变化)和塑性流动各向异性(3个方向厚向异性指数的变化)行为。发现,虽然屈服强度和应变硬化受热处理状态影响显著,但强度各向异性和塑性流动各向异性受热处理状态影响较小,均在试验数据分散范围之内。获取的试验数据被用来校准Hill48屈服准则。通过绘制的屈服轨迹发现,对于W态可以采用与O态相同的屈服面形状来描述其材料塑性各向异性行为,这样将显著减少W态下本构模型校准需要的试验数。     

5A06-H34厚板生产工艺研究

研究了加工率、稳定化退火温度及保温时间对5A06铝合金板材组织与性能的影响,确定了5A06铝合金H34状态的生产工艺。结果表明,其性能指标达到GJB390标准。     

5A06铝合金材料高温热物理参数的工程估算方法

5A06(LF6)铝合金是一种基本的焊接结构材料,但该合金的热物理参数,尤其是在较高温度范围内的材料属性在一般工程条件下很难确定,对工程计算的准确性有很大影响.基于工程试验结果确定了5A06铝合金结构的最佳退火温度,根据该结构在不同温度退火消应力处理后的变形回弹量,建立有限元模型,应用ANSYS中的灵敏度与概率设计(PDS)系统对该材料的热物理性能进行估算.结果表明,估算所得的热物理参数值基本符合工程实际,所采用的概率分析方法为估算材料的高温热物理参数提供了一种唯象的有效工程手段.     

5A06铝合金油箱氩弧焊热影响区裂纹分析及预防措施

5A06铝合金焊接燃油箱在试车过程中出现漏油,通过对漏油部位焊缝的理化检验,证实该裂纹是由焊接热影响区裂纹引起的,并从成分偏析、温度和应力三个方面分析了5A06铝合金焊接热影响区裂纹的成因,说明该裂纹是由油箱隔板焊接缺陷引起,与母材无关,并提出了焊接工艺的改进方法.     

5A06铝合金变形工艺参数与显微组织关系实验研究

本文主要研究5A06铝合金热变形工艺对组织的影响。在350℃等温压缩时，随变形程度的增大其晶粒变得细小；但当变形程度达到70％左右时，会出现流线状组织，开始发生动态回复，此时力学性能较高；而后，随变形程度的增大，晶粒反而变大；变形程度达到80％时，出现条带状组织，其力学性能呈现各向异性。在变形程度相同（45％左右）的条件下，变形温度越高，晶粒越粗大。     

Order results for Krylov-W-methods

We consider ROW-methods for stiff initial value problems, where the stage equations are solved by Krylov techniques. By using a certain ‘multiple Arnoldi process’ over all stages the order of the fully-implicit one-step scheme can be preserved with low Krylov dimensions. Explicit estimates for minimal order preserving dimensions are derived. They depend on the parameters of the method only, not on the dimension of the ODE. Stability restrictions usually require larger dimensions, of course, but this can be done adaptively. These results justify to adopt the step size control of the underlying ROW-method. The widely used ROW-methods of order 4 are discussed in detail and numerical illustrations are given. For the special class of semilinear systems with stiffness in a constant linear part we establish the order 2 of B-consistency for these Krylov-W-methods. This work was supported by the Deutsche Forschungsgemeinschaft.     

Non-Reflecting Boundary Conditions for Maxwell’s Equations

A new discrete non-reflecting boundary condition for the time-dependent Maxwell equations describing the propagation of an electromagnetic wave in an infinite homogenous lossless rectangular waveguide with perfectly conducting walls is presented. It is derived from a virtual spatial finite difference discretization of the problem on the unbounded domain. Fourier transforms are used to decouple transversal modes. A judicious combination of edge based nodal values permits us to recover a simple structure in the Laplace domain. Using this, it is possible to approximate the convolution in time by a similar fast convolution algorithm as for the standard wave equation.     

Exact learning of DNF formulas using DNF hypotheses

We show the following: (a) For any ε>0, log^(3+ε)n-term DNF cannot be polynomial-query learned with membership and strongly proper equivalence queries. (b) For sufficiently large t, t-term DNF formulas cannot be polynomial-query learned with membership and equivalence queries that use t^1+ε-term DNF formulas as hypotheses, for some ε<1 (c) Read-thrice DNF formulas are not polynomial-query learnable with membership and proper equivalence queries. (d) logn-term DNF formulas can be polynomial-query learned with membership and proper equivalence queries. (This complements a result of Bshouty, Goldman, Hancock, and Matar that -term DNF can be so learned in polynomial time.)Versions of (a)-(c) were known previously, but the previous versions applied to polynomial-time learning and used complexity theoretic assumptions. In contrast, (a)-(c) apply to polynomial-query learning, imply the results for polynomial-time learning, and do not use any complexity-theoretic assumptions.     

基于无线传输的心电心音监护系统设计

针对现有心电心音监测仪覆盖性不足、时效性差等问题,提出了一种基于无线传输的心电(ECG)心音(PCG)监护系统设计.本系统设计有64个监护节点,各节点由传感模块、调理采集模块、存储模块、主控管理模块、通信模块、电源管理模块组成,各节点可对12导联心电信号、HKY-06B心音信号进行同步采集传输,将信息汇总给监护中心并及...     

ZG30Cr06E的焊接性分析研究

对煤矿机械液压支架中新研制的抗拉强度高达800MPa柱窝材料ZG30Cr06E的焊接性进行了研究.采用热影响区最高硬度试验、斜Y型坡口裂纹试验测试了该钢对冷裂纹的敏感性,并研究了不同焊接工艺条件下焊接接头组织转变和性能变化规律.结果表明,在室温下焊接时,其热影响区最高硬度值达387HV,有一定的淬硬倾向,冷裂纹的敏感性大,焊接过程中应采取措施防止冷裂纹的产生;焊接工艺参数对焊接接头组织和性能均有一定的影响,为确保焊接质量,焊接时要采用合适的预热温度,并控制焊接线能量和焊道间温度.