Application of the dynamical flexural resonance technique to industrial materials characterisation

The determination of the Young’s modulus and damping coefficient Q⁻¹ by means of non-destructive vibrating techniques has been applied to bulk and coated industrial materials. Extensions of a previous analytic model of composite beam allow to determine accurately the macroscopic modulus of each component of multilayered structural materials as coated superalloys or nitride-hardened steels. Furthermore, the study of glasses and polymers has been investigated. An attempt of normalisation of the modulus versus temperature curves allows to establish master curves depending on the specific structure, from metallic glasses to polymeric glasses. Finally a comparison of dynamical modulus and Q⁻¹ values measured between resonant (>1 kHz) and subresonant techniques (10⁻³ to 10 Hz) in relation to the loading frequencies applied in real conditions has been under folder. For metallic materials such as forged or rolled titanium alloys, the brittle-to-fragile transition occurs abruptly or smoothly with a shift of 300 K following the range of excitation frequencies.     

Implicit integration and consistent tangent modulus of a time‐dependent non‐unified constitutive model

This paper describes the implicit integration and consistent tangent modulus of an inelastic constitutive model with transient and steady strain rates, both of which are time‐ and temperature‐dependent; the transient rate is influenced by the evolution of back stress decomposed into parts, while the steady rate depends only on applied stress and temperature. Such a non‐unified model is useful for high‐temperature structural analysis and is practical owing to the ease in determining material constants. The implicit integration is shown to result in two scalar‐valued coupled equations, and the consistent tangent modulus is derived in a quite versatile form by introducing a set of fourth‐rank constitutive parameters into the discretized evolution rule of back stress. The constitutive model is, then, implemented in a finite element program and applied to a lead‐free solder joint analysis. It is demonstrated that the implicit integration is very accurate if the multilinear kinematic hardening model of Ohno and Wang is employed, and that the consistent tangent modulus certainly affords quadratic convergence to the Newton–Raphson iteration in solving nodal force equilibrium equations. Copyright © 2003 John Wiley & Sons, Ltd.     

THE STICKY ISSUES OF DRYING

Unconrolled agglomeration of particles and adhesion of the particulate mass to wall surfaces are common severe problems in many drying operations. This paper reviews the mechanisms of interparticle and particle-surface attraction as well as the theory and the existing tests for characterising powders in terms of internal strength, wall friction and adhesion. The usefulness of the information obtained from these tests in dryer design and operation is critically reviewed. The importance of powder stickiness in various types of dryers is discussed and established methods of combating the problem are presented Recommendations an made for further research in the area of powder cohesion and adhesion.     

Viscoelastic Windows of Pressure-Sensitive Adhesives

A viscoelastic window (VW) concept has been proposed to identify different types of pressure-sensitive adhesives (PSA's). Such viscoelastic windows are constructed from the values of dynamic storage modulus: G' and dynamic loss modulus G' at frequencies of 10^-2 and 10² rad/sec. These frequencies are chosen because the range covers most of the time scales corresponding to the uses of PSA's at different application rates in performance tests. A four quadrant concept has also been recommended to categorize different types of PSA's based on the location of their VW's on the log-log cross plot of G' and G'. It was found that for most PSA's, the range of G' and G' at room temperature within these selected frequencies falls between 10³ and 10⁶ Pascals. The proposed four-quadrants (top-left hand quadrant of high G' and low G', top-right hand quadrant of high G' and high G', lower left hand quadrant of low G' and low G', and lower right-hand quadrant of low G' and high G') correspond respectively to (1) non-PSA or release coatings (2) high shear PSA's, (3) removable PSA's and medical PSA's and (4) quick and cold stick PSA's. It was also observed that the VW's of general purpose permanent PSA's occupy the central region which straddles part of the four quadrants.     

横波速度各向异性初步探讨：—多波勘探资料的应用

在纵波、SH 型横波资料处理和解释过程中,我们发现四川 HBC 地区地下介质普遍存在方向各向异性。当横波通过方向各向异性介质时,分裂成两个波:一个波的偏振方向与裂缝平行,叫快横波;另一个波的偏振方向与裂缝走向垂直,叫慢横波。采用相应的观测和处理方法,便可获得快横波和慢横波剖面。根据同一界面的快、慢横波的旅行时可以求得各向异性系数。同样,还可以利用 SH 波与转换波的速度比求取各向异性系数。各向异性系数的大小,反映了裂缝的发育程度。如果野外作了 X、Y 分量观测,室内又作了坐标旋转处理,那么,就可以进一步确定裂缝带的方向。如果未作上述工作,也可以根据构造线走向,大致确定裂缝带的发育方向。     

宽带智能天线系统中的频率补偿技术

在无线通信中,智能天线系统在抑制窄带多径干扰方面具有得天独厚的优势,但是用于宽带无线通信系统中时,就需要采用频率补偿方法.重点介绍基于频谱分解、聚焦和插值算法的补偿技术,并对这3种频率补偿技术的性能进行比较,结果表明在应用补偿技术的系统中,系统性能有显著的改善,其中插值算法具有最优的性能.     

Determination of Boundary Shear Stress and Reynolds Shear Stress in Smooth Rectangular Channel Flows

A method for computing three-dimensional Reynolds shear stresses and boundary shear stress distribution in smooth rectangular channels is developed by applying an order of magnitude analysis to integrate the Reynolds equations. A simplified relationship between the lateral and vertical terms is hypothesized for which the Reynolds equations become solvable. This relationship has the form of a power law with an exponent of n = 1, 2, or infinity. The semiempirical equations for the boundary shear distribution and the distribution of Reynolds shear stresses are compared with measured data in open channels. The power-law exponent of 2 gave the best overall results while n=infinity gave good results near the boundary.     

Investigation of Boundary Shear Stress and Pollutant Detachment from Impervious Surface during Simulated Urban Storm Runoff

Pollutant detachment rates have been determined for four chloride salts during simulated urban storm runoff. Under rainfall and/or overland flow conditions, chloride mass flux was measured and related to boundary shear stress of the test surface. Washoff coefficients, presumed to depend only on pollutant characteristics, were computed based on the slopes of dimensionless mass flux versus dimensionless time plots. Washoff coefficients were found to vary among and between the chloride compounds studied. In general, higher overland flow rates produced lower boundary shear and lower washoff coefficients. The combination of simulated rainfall and overland flow resulted in an increased boundary shear and an increased washoff coefficient. An empirical washoff coefficient based on a load characteristic curve derived from an exponential washoff relationship was also computed from the runoff data and compared with the previous washoff coefficient. A linear correlation between these two washoff coefficients was observed. The magnitude of the latter coefficient under simulated rainfall was consistent with reported values obtained from field data.     

Suppression of void coalescence in thermal aging of tin-silver-copper-X solder joints

Addressing the potential for drop impact failure of Pb-free interconnects, the shear ductility after extensive aging of Sn-Ag-Cu (SAC) solders has been improved radically by Co or Fe modifications. Several other SAC+X candidates (X=Mn, Ni, Ge, Ti, Si, Cr, and Zn) now have been tested. Solder joint microstructures and shear strength results show that new SAC+X alloys also suppress void formation and coalescence at the Cu (substrate)/Cu₃Sn interface (and embrittlement) after aging at 150°C for up to 1,000 h. Microprobe measurements of 1,000 h aged samples suggest that Cu substitution by X is usually accentuated in the intermetallic layers, consistent with X=Co and Fe results.     

工字梁的抗剪极限承载力

对工字梁腹板抗剪极限承载力的研究进行总结,对各种公式与文献中的试验结果进行对比,将拉力场理论和转向应力场理论的假定与ANSYS分析揭示的腹板应力发展变化规律进行对比,指出了假定和数值分析结果的不一致。提出了翼缘对腹板转动约束的合理参数,得到精度良好的考虑翼缘约束的腹板剪切屈曲系数。利用得到的屈曲系数,考虑翼缘抗弯承载力的贡献,提出新的工字梁抗剪极限承载力的计算公式。与现有试验数据和ANSYS非线性有限元分析结果的对比,证实建议方法离散性较小,适用范围广,尤其是对于通用高厚比较大的梁,较以往方法有了较大改进。