Stress measurement

Tensor Field Tomography for Residual Stress Measurement in Class Articles. 

Results of own stress measurements in the pipe joints zone applied in high power, have been shown in Fig 5 and 6. 

Stress Measurement of a Vessel Using the Spate Technique. 

Very shortly, the first one is based on the stress measurement performed using a rosetta strain gauge located in an area of sufficiently uniform stress distribution. In this case, the calibration factor Cr can be easily obtained by the following equation ... 

An experimental activity on the stress measurement of a pressure vessel using the SPATE technique was carried out. It was demontrated that this approach allows to define the distribution of stress level on the vessel surface with a quite good accuracy. The most significant advantage in using this technique rather than others is to provide a true fine map of stresses in a short time even if a preliminary meticolous calibration of the equipment has to be performed. 

Both ultrasonic and radiographic techniques have shown appHcations which ate useful in determining residual stresses (27,28,33,34). Ultrasonic techniques use the acoustoelastic effect where the ultrasonic wave velocity changes with stress. The x-ray diffraction (xrd) method uses Bragg s law of diffraction of crystallographic planes to experimentally determine the strain in a material. The result is used to calculate the stress. As of this writing, whereas xrd equipment has been developed to where the technique may be conveniently appHed in the field, convenient ultrasonic stress measurement equipment has not. This latter technique has shown an abiHty to differentiate between stress reHeved and nonstress reHeved welds in laboratory experiments. 

Description of normal stress measurements on a practical but complex material, paint, is available (150). More recent pubHcations (151—154) give the results of investigations of normal stress differences for a variety of materials. These papers and their references form a useful introduction to the measurement of normal stress differences. 

Rheometric Scientific markets several devices designed for characterizing viscoelastic fluids. These instmments measure the response of a Hquid to sinusoidal oscillatory motion to determine dynamic viscosity as well as storage and loss moduH. The Rheometric Scientific line includes a fluids spectrometer (RFS-II), a dynamic spectrometer (RDS-7700 series II), and a mechanical spectrometer (RMS-800). The fluids spectrometer is designed for fairly low viscosity materials. The dynamic spectrometer can be used to test soHds, melts, and Hquids at frequencies from 10 to 500 rad/s and as a function of strain ampHtude and temperature. It is a stripped down version of the extremely versatile mechanical spectrometer, which is both a dynamic viscometer and a dynamic mechanical testing device. The RMS-800 can carry out measurements under rotational shear, oscillatory shear, torsional motion, and tension compression, as well as normal stress measurements. Step strain, creep, and creep recovery modes are also available. It is used on a wide range of materials, including adhesives, pastes, mbber, and plastics. 

Additional complications can occur if the mode of deformation of the material in the process differs from that of the measurement method. Most fluid rheology measurements are made under shear. If the material is extended, broken into droplets, or drawn into filaments, the extensional viscosity may be a more appropriate quantity for correlation with performance. This is the case in the parting nip of a roUer in which filamenting paint can cause roUer spatter if the extensional viscosity exceeds certain limits (109). In a number of cases shear stress is the key factor rather than shear rate, and controlled stress measurements are necessary. 

K. Parker, Internal Stress Measurements of Electroless Nickel Coatings by the Rigid Strip Method, ASTM STP 947, American Society for Testing and Materials, Philadelphia, Pa., 1987. 

Chhabildas, L.C. and R.A. Graham (1989), Techniques and Theory of Stress Measurements for Shock Applications, AMD-83 (edited by R. Stout, F. Norwood, and M. Fourney), ASME, p. 1. 

G.T. Gray III and P.S. Follansbee, Influence of Peak Pressure and Pulse Duration on the Substructure Development and Threshold Stress Measurements in Shock-loaded Copper, in Impact Loading and Dynamic Behavior of Materials (edited by C.Y. Chiem, H.-D. Kunze, and L.W. Meyer), Deutsche Gesellschaft fuer Metall-kunde, Germany, 1988, 541 pp. 

Atomic structure refinements or determinations and residual stress measurements, all in bulk materials... 

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

A strength value associated with a Hugoniot elastic limit can be compared to quasi-static strengths or dynamic strengths observed values at various loading strain rates by the relation of the longitudinal stress component under the shock compression uniaxial strain tensor to the one-dimensional stress tensor. As shown in Sec. 2.3, the longitudinal components of a stress measured in the uniaxial strain condition of shock compression can be expressed in terms of a combination of an isotropic (hydrostatic) component of pressure and its deviatoric or shear stress component. 

Much of the difficulty in demonstrating the mechanism of breakaway in a particular case arises from the thinness of the reaction zone and its location at the metal-oxide interface. Workers must consider (a) whether the oxide is cracked or merely recrystallised (b) whether the oxide now results from direct molecular reaction, or whether a barrier layer remains (c) whether the inception of a side reaction (e.g. 2CO - COj + C)" caused failure or (d) whether a new transport process, chemical transport or volatilisation, has become possible. In developing these mechanisms both arguments and experimental technique require considerable sophistication. As a few examples one may cite the use of density and specific surface-area measurements as routine of porosimetry by a variety of methods of optical microscopy, electron microscopy and X-ray diffraction at reaction temperature of tracer, electric field and stress measurements. Excellent metallographic sectioning is taken for granted in this field of research. 

Fig. 10. Concentration dependence of a modulus in the region of low-frequency plateau (i.e. yield stress , measured by a dynamic modulus). Dispersion medium poly (butadiene) with M = 1.35 x 105 (7), silicone oil (2) polybutadiene with M = 1 x I04 (3). The points are taken from Ref. [6], The straight line through these points is drawn by the author of the present paper. In the original work the points are connected by a curve in another manner...

Interpretation of data obtained under the conditions of uniaxial extension of filled polymers presents a severe methodical problem. Calculation of viscosity of viscoelastic media during extension in general is related to certain problems caused by the necessity to separate the total deformation into elastic and plastic components [1]. The difficulties increase upon a transition to filled polymers which have a yield stress. The problem on the role and value of a yield stress, measured at uniaxial extension, was discussed above. Here we briefly regard the data concerning longitudinal viscosity. 

Photoelastic measurement is a very useful method for identifying stress in transparent plastics. Quantitative stress measurement is possible with a polarimeter equipped with a calibrated compensator. It makes stresses visible (Fig. 5-2). The optical property of the index of refraction will change with the level of stress (or strain). When the photoelastic... 

R surfaee stress measurement (ribbon extension method)... 

A. W. Chow, S. W. Sinton, J. H. Iwa-miya, T. S. Stephens 1994, (Shear-induced particle migration in Couette and parallel-plate viscometers NMR imaging and stress measurements. Phys. Fluids 6, 2561. 

Konrad was the first to address the issue of pulsed piston transport using the properties of the solids as they slide through the pipe in a plug-like motion. The friction generated in such systems often can be likened to bin and hopper flow and design, requiring shear stress measurements such as carried out by the Jenike shear stress unit. The final expression using the Konrad approach can be written for horizontal flow as... 

In terms of understanding the mercury/electrolyte interface, it is clear from the above discussion that the measurement of the surface free energy (in terms of the surface tension), is central. If the clectrocapillarity technique could be applied to solid electrodes, then it is capable of supplying information extremely difficult to obtain by any other technique. Sato has indeed developed a technique to measure the surface tension of a metal electrode which he terms piezoelectric surface stress measurement and is based upon the previous work of Gokhshtein (1970). 

McNally DS et al (1996) In vivo stress measurement can predict pain on discography. Spine 21(22) 2580-2587... 

Except at very low strains, up to about 15%, the ratio of stress to strain in vulcanised rubber is not a constant. Modulus is the tensile stress (measured in MPa, lb/in2 or kg/cm2) required to stretch the rubber to a given strain (or elongation) the elongation must always be stated, otherwise the expression is meaningless. A more precise expression is stress per square unit (in2 or cm2) at the given strain . 

The above findings are supported in the other studies of the inhibitory effects of flavonoids on iron-stimulated lipid peroxidation. Quercetin was found to be an inhibitor of iron-stimulated hepatic microsomal lipid peroxidation (/50 = 200 pmol I ) [134]. Flavonoids eriodictyol, luteolin, quercetin, and taxifolin inhibited ascorbate and ferrous ion-stimulated MDA formation and oxidative stress (measured by fluorescence of 2,7,-dichlorodihydro-fluorescein) in cultured retinal cells [135]. It should be mentioned that in recent work Heijnen et al. [136] revised the structure activity relationship for the protective effects of flavonoids against lipid peroxidation. 

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