各向异性双晶和三晶体弹塑性应力场分析

用三维弹塑性晶体滑移有限元程序对不同晶体取向的双昌和三晶体在昌界和三晶交点处的应力集中科技司和滑激活规律进行了计算分析。双晶体在计算时考虑取向的影响,计算结果表明,晶界处应力有较大的出现复杂的变化规律,这种规律与晶体取向相关;三晶交点和晶界使得三晶体应力重新分布,三晶交点可能是应力集中之地,但也可能不造成应力集中,这主要与三个晶体取向相关。本文计算表明,只有仔细地研究细观过程,才能准确理解金属材料     

Thermal Analysis,Microcalorimetry and Combined Techniques for the Study of Pharmaceuticals

Modern thermal analysis, microcalorimetry and new emerging combined techniques which deliver calorimetric, microscopic and spectroscopic data offer a powerful analytical battery for the study of pharmaceuticals. These techniques are very useful in all steps of development of new drug products as well as methods for quality control in production. The characterization of raw materials enables to understand the relationships between polymorphs, solvates and hydrates and to choose the proper development of new drug products with very small amount of material in a very short time. Information on stability, purity is valuable for new entities as well as for marketed drug substances from different suppliers. Excipients which vary from single organic or inorganic entity to complexes matrixes or polymers need to be characterized and properly controlled. The thermodynamic phase-diagrams are the basis of the studies of drug-excipients interactions. They are very useful for the development of new delivery systems. A great number of new formulations need proper knowledge of the behaviour of the glass transition temperature of the components. Semi-liquid systems, interactions in aqueous media are also successfully studied by these techniques. This revised version was published online in August 2006 with corrections to the Cover Date.     

A thin-sheet, combined tension and bending specimen

Validating stress intensity factor solutions for combined tension and bending is an arduous task because the necessary experimental data are not readily available. Toward this end, a tension and bending test specimen was designed to produce controllable levels of both tension stress and bending stress at the crack location. The specimen was made from 2024-T3 clad aluminum, which is commonly used in aircraft structures. The need for testing multiple specimens of various geometries and stress levels prompted the development of an analytical tool for specimen design. An extention of the Schijve line model, based on simple beam theory, was developed to calculate the stress distributions of tension and bending through the length of the specimen. A comparison of measured static strain levels with those predicted by the model showed the model to be accurate to within 5 percent, confirming its efficacy for specimen design. As expected, for the same remote stress (100 MPa), cracks in the tension and bending specimens grew faster than those in middle-cracked tension specimens.     

Static and dynamic response of a multiplexed-array piezoresistive contact sensor

Multiplexed piezoresistive sensor arrays hold great potential for measuring contact stress distributions for orthopedic research applications. However, their acceptance has been handicapped by output drift and the fact that their dynamic response has not been well characterized. In this report, the static and dynamic responses of one device of this class (the K-Scan piezoresistive contact stress sensor) are formally characterized using a specially made pressure vessel that provides spatially homogeneous contact stress. Drift was predominant early in static loading, reaching relationtive errors of approximately 30 percent over a 10-min period. During loading, first-order dynamic analysis showed that the time constant (and time lag) was nearly zero and there was little attenuation of the output up to 20 Hz. A deconvolution algorithm proved capable of compensating for the great majority of static drift.     

Measurements of wall shear stress of a turbulent boundary layer using a micro-shear-stress imaging chip

Measurements of wall shear-stress streaks of a turbulent boundary layer in the channel flow were carried out using a MEMS-based micro-shear-stress imaging chip, which contains about 100 sensors. The chip is designed and fabricated by surface micromachining technology. One arrray of 25 micro-shear-stress sensors in the chip that covers a length of 7.5 mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The statistics of high shear-stress streaks were established. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, were obtained. We found out that a high correlation exists between the peak shear-stress level and front-end shear-stress slope of a high shear-stress streak. This important property is currently being applied to the deisgn of a real-time flow control logic.     

Stress effect decay estimates for anisotropic material in a semi-infinite strip

IntroductionInthetheoryofplanedeformationsoflinearelastotatics,Saint-Venant'sprincipleplaysanimportantroleinbothoftheoryandpracticalapplicahonsandisoftenusedtojushfyapproximationthatneglectedgeeffects.ForhomogenousisotropicmaterialthevalidityofSaintVenant'sprincipleiswellestablished.However,forhomogenousanisotropicmaterial,experimentalresultshaveshownthatedgeeffectsmaypersistmuchfartherintotheinteriorofthebodythanforisotropicmaterialandasaresultcannotbeneglected.Asweknow,theelasticityproblem…     

NEW POINTS OF VIEW ON THE NONLOCAL FIELD THEORY AND THEIR APPLICATIONS TO THE FRACTURE MECHANICS(Ⅱ)--RE-DISCUSS NONLINEAR CONSTITUTIVE EQUATIONS OF NON-LOCAL THERMOELASTIC BODIES

In this paper, nonlinear constitutive equations are deduced strictly according to the constitutive axioms of rational continuum mechanics. The existing judgments are modified and improved. The results show that the constitutive responses of nonlocal thermoelastic body are related to the curvature and higher order gradient of its material space, and there exists an antisymmetric stress whose average value in the domain occupied by thermoelastic body is equal to zero. The expressions of the antisymmetric stress and the nonlocal residuals are given. The conclusion that the directions of thermal conduction and temperature gradient are consistent is reached. In addition, the objectivity about the nonlocal residuals and the energy conservation law of nonlocal field is discussed briefly, and a formula for calculating the nonlocal residuals of energy changing with rigid motion of the spatial frame of reference is derived. Foundation item: the Natural Science Foundation of Province Jiangshu (BK97063)     

Monitoring chemical and physical changes on sub-nanogram quantities of platinum dioxide

We have measured in real-time the chemical reaction-induced weight loss and variation in physical and mechanical properties of sub-nanogram quantities of deposits utilizing the resonance response of microcantilevers. The hydrogen reduction of sub-nanogram quantities of alpha platinum oxide deposited on micromachined silicon cantilevers and resultant weight loss, as well as the kinetics of this process, were investigated. Comparison with theory suggests that this technique could be a powerful tool to measure physical and chemical changes occurring on sub-nanogram deposits.     

用图像运算技术对光弹性条纹进行倍增

在光弹应力分析中,利用分数级条纹可以提高分析精度,于是,产生分数级条纹的方法研究就变得非常重要。利用图像处理技术,首先采集一幅图像,然后通过对这幅图像的算术运算就可以产生分数级条纹。给出了详细的理论分析,并进行实验。利用本文方法,在两条整数级条纹之间,可以相继产生７条分数级条纹。     

Flow and fracture of rocks under general triaxial compression

Recent laboratory studies of the flow and fracture of rocks under general triaxial compression are reviewed. New developments in laboratory techniques have made it possible to measure three principal stresses and strains under general triaxial stress states, in which all three principal stresses are different.Strength and ductility of isotropic rocks are markedly affected not only by the least compression ₃, but also by the intermediate compression ₂, although these two effects are rather additional in strength, but opposite in ductility. The experimental results show that dilatancy is highly anisotropic under the general triaxial stress states.Deformational properties of anisotropic rocks have been also measured under the general triaxial compression. In this case, the effect of the intermediate compression markedly depends on the orientations of the weak planes.