超声诊断仪声强测量不确定度的评定

文章依据JJG639—1998国家规程的检定要求对医用超声诊断仪进行测量不确定度的评定，文中详细介绍了输出声强不确定度的来源、评定方法和自由度的计算。     

脆性材料在双向应力下的断裂和失效研究

采用热力学方法对脆性薄片试样成功地进行了双向和单向平面拉伸试验,通过观察和记录试片中心的直通裂纹的扩展和断裂过程,测试出玻璃和陶瓷薄片的断裂韧性在双向和单向拉伸载荷时的差别．结果表明双向拉伸使裂纹阻力增强,平行于裂纹的应力对裂纹扩展有影响．该研究表明,对线弹性材料在双向载荷作用下,传统的应力强度因子准则不适用．裂纹张开的应变依赖性被证实在双向应力的断裂评价中．     

带旋转自由度的广义协调三角形膜元

应用广义协调元理论,通过增加内参位移的方法,构造了两个具有旋转自由度的三角形膜元。本文单元能通过任意三角形分片检验,符合连续介质力学关于旋转自由度的定义,并且没有引入刚性转角假设。数值算例表明其具有较高的计算精度。     

第二代基于性能地震工程中的地震易损性模型及正逆概率风险分析

基于多种地震动强度指标,采用因子分析提取地震动强度指标的特征因子,将提取的主因子进行线性组合,构造地震动多元强度主因子。以不同恢复力模型的单自由度以及多自由度体系为研究对象,基于2766条地震动记录,选取9个基本强度指标并采用因子分析提取其特征,同时对构造的地震动多元强度主因子与不同结构损伤指标进行相关性分析。研究结果表明：不同场地类别下各地震动强度指标所属的主因子趋于稳定;通过因子分析提取的两个主因子具备较好的可解释性;场地类别、强度折减系数和恢复力模型对构造的地震动多元强度主因子与结构损伤指标的相关性影响较小;构造的地震动多元强度主因子考虑了更多地震动信息,保持了其与不同结构损伤指标稳定且良好的相关性。     

精密压力表示值误差测量结果的不确定度评定

文章介绍了精密压力表示值误差测量结果的不确定度评定的一般方法、步骤、内容和表示方法。     

动态爆生裂纹相互影响的试验研究

采用以有机玻璃(PMMA)为材料的模型试验方法,分析了试件的破坏形态和裂纹尖端的应力特征,研究了对向切槽炮孔的不同竖向间距对爆生裂纹扩展的影响。结果表明:爆生裂纹扩展过程中,裂纹速度震荡减小,裂纹尖端应力变化经历两个阶段,Ⅰ阶段(0~110μs)裂纹尖端动态应力强度因子迅速减小,试件破坏以拉伸破坏为主;Ⅱ阶段(110μs~止裂)裂纹尖端动态应力强度因子先增大后减小,试件破坏兼有拉伸破坏和剪切破坏。炮孔的竖向间距的不同对爆生裂纹Ⅰ阶段扩展影响不大,对Ⅱ阶段扩展影响显著。对向裂纹起到自由面作用并引导己方裂纹向其发生偏转,从对向裂纹面处反射的应力波加强了己方裂纹尖端的应力集中。     

双扭法及其在脆性材料力学性能评定中的应用

本文介绍了一种新的脆性材料力学性能评定方法一双扭法,提出修正的双扭试样应力强度因子表达式.由于双扭试样裂纹尖端应力强度子与试样裂纹长度无关,因而对材料有广泛的适应性.其研究范围较广,可测定裂纹亚临界扩展、断裂韧性、高温或应力腐蚀条件下的力学行为等.本文比较了双扭法在电工陶瓷、结构陶瓷、硅酸盐玻璃、有机玻璃以及滚珠轴承钢等脆性材料中实际应用的结果,讨论了适用于双扭法应力分析的试样裂纹长度及其标定等问题.     

体绘制及三维交互技术在地质数据可视化中的应用

对地质勘探所提供的大规模三维规则风格数据进行可视化处理。     

模切机机架的有限元分析

当卧式平压平模切机工作时,模切压力会引起两侧墙板和上平台的变形。为了研究模切压力与两侧墙板或上平台之间的关系,通过理论计算确定了墙板和上平台的厚度,在此基础上对墙板以及上平台进行了有限元分析,得出了墙板和上平台在强度和刚度方面都符合要求,并得出了模切压力与机架应力、应变的函数关系。     

弹塑性 SDOF 系统的地震输入能量谱

以4种场地土条件下40条强震记录为输入,分析了弹塑性单自由度(Single Degree of Freedom,SDOF)系统的地震输入能量谱,并对地震动强度和SDOF系统参数对地震输入能量谱的影响进行了研究。结果表明:能量谱峰值主要由地震动强度决定,阻尼比和延性系数有很大影响。在长周期范围,延性系数一定时,随着阻尼比的增大,能量谱值也有所增大;随延性系数增大,能量谱值随阻尼比增加而增大的趋势有所减缓。采用归一化方法,根据能量谱的特征建议了简化三段式地震输入能量谱,并根据能量谱分析结果的统计,建议了弹塑性SDOF系统能量谱峰值和能量谱曲线参数的确定方法。     

Fracture analysis for ceramic ball in backflow valve

Ceramic balls have been used as components of devices, such as those found in high‐pressure pumps for automobiles and industrial machines. In the backflow valve, for example, a ceramic ball is in contact with a conical surface. Fractures of ceramic balls are extremely rare. It is important to investigate the cause of these rare fractures to guarantee higher reliability in the backflow valve. In this paper, the fracture mechanism and strength are discussed for an equivalent normal stress σ_eq beneath the contact region and the maximum principal stress σ_p near the contact boundary using stress intensity from fracture mechanics. The fracture surface of the ceramic ball was formed perpendicular to load direction. We assumed that fracture origins (defect/crack) existed on lines through three high stresses that analysed by finite element method. Actual fracture of a ceramic ball was found to be caused by the equivalent normal stress beneath contact region and not to be caused by the Hertz principal stress. Stress intensity factor (SIF) was clarified to depend on pressure, taper angle, CrN‐coating thickness and the friction factor of the inside of the valve hole. A pre‐existing defect size involved in failure was estimated by the SIF using three‐dimensional elliptic defects and equivalent normal stress. Therefore, the actual fracture of a ceramic ball, which rarely occurs, could be evaluated by considering three‐dimensional elliptic defects and the Weibull distribution of defects.     

Weight functions and stress intensity factors for quarter-elliptical corner cracks in fastener holes

Approximate weight functions for a quarter‐elliptical crack in a fastener hole were derived from a general weight function form and two reference stress intensity factors. Closed‐form expressions were obtained for the coefficients of the weight functions. The derived weight functions were validated against numerical data by comparison of stress intensity factors calculated for several nonlinear stress fields. Good agreements were achieved. These derived weight functions are valid for the geometric range of 0.5 ≤a/c≤ 1.5 and 0 ≤a/t≤ 0.8 and R/t= 0.5; and are given in forms suitable for computer numerical integration. The weight functions appear to be particularly suitable for fatigue crack growth prediction of corner cracks in fastener holes and fracture analysis of such cracks in complex stress fields.     

The discrete method of separation of variables for composite material problems

In this paper, we propose the discrete method of separation of variables for the numerical solutions of the composite material problems on a polygon. After a suitable transformation of coordinates, the original boundary value problem is reduced to a discontinuous coefficients problem on a semi-infinite strip. Then we get the semi-discrete approximation of the discontinuous coefficients problem which is equivalent to a boundary value problem of a system of ordinary differential equations (O.D.E's) with constant coefficients. After solving the boundary value problem of the system by a direct method, then the semi-discrete approximation of the original problem is obtained. Especially we can see that the semi-discrete approximation in form of separable variables naturally possesses the singularity of the original problem. Finally, the numerical examples show that our method is feasible and very effective for solving composite material problems numerically.     

Overload failure curve and fatigue behavior of spot-welded specimens

The mechanical behavior of a spot-welded specimen is generally approached in angles of overload and fatigue failures. The primary issue in an overload failure is to establish an overload failure criterion. Fatigue failure of spot-welded specimens can be dealt with a fracture parameter, since a spot-weld forms a singular geometry of external crack type. In this work, we express the limit loads in terms of base metal yield strength and specimen geometries. We then present a master overload failure curve for a single spot-welded specimen in a mixed-mode load domain. The coordinates of the domain are normalized by the limit loads of single spot-welded specimens. Recasting the load vs. fatigue life relations experimentally obtained, we attempt to predict the fatigue life of various spot-weld specimens with a single parameter denoting the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and load type in an inclusive manner. The suggested fatigue life formula for a single spot-weld can be used in the assessment of spot-welded panel structures as the fatigue strength of multi-spots is eventually determined by that of each single spot-weld.     

Comparison of semi-elliptical cracks in cylinders with a thickness transition and in a straight cylinders - Elastic-plastic behaviour

This paper presents a study of a circumferential external semi-elliptical crack in a cylinder with a thickness transition. Crack harmfulness is compared to the harmfulness of a similar crack in a straight cylinder, on the basis of J-integral calculations. Loads considered are pure tensile stress and bending moment. A numerical analysis is performed considering elastic plastic behaviour of material. A crack mesh was designed for 3D models. The results show that the cylinder with a thickness transition is more vulnerable to the defect. A simple method for J calculation at the deepest point of the crack in the transition zone is also proposed.     

地震动多元强度参数主成分与结构损伤的相关性分析

采用主成分分析方法,考虑多个地震动强度参数,综合分析多元地震动强度参数主成分与结构损伤之间的相关性。以单自由度体系为研究对象,使用三种恢复力模型,选择80条真实地震动记录作为输入,分析得到体系在地震作用下的最大位移和滞回能量。采用挑选的10个地震动强度参数,基于主成分分析方法,构造地震动强度的主成分线性组合,并对地震动强度参数主成分与结构损伤之间的相关性进行分析。结果表明：由于考虑了多个地震动强度参数,相比于单个地震动强度参数与结构损伤之间的相关性,地震动多元强度参数主成分与结构损伤之间的相关性更为稳定。