Stress transducer

Lee, L.M., D.G. Fogelson, and W.D. Williams (1984), Dynamic Stress Transducers Qualification, in Shock Waves In Condensed Matter—1983 (edited by J.R. Asay, R.A. Graham, and G.K. Straub), Elsevier Science, New York, pp. 229-232. 

The fracture resistance of a homopolymer is controlled by (i) the number of tie-molecules, which act as stress transducers between the crystallites and (ii) by the disentanglement resistance of the individual chains [112-115]. The higher the molecular weight, the more likely both factors are high fi-nucleated polypropylene does not infringe this rule [33,72,74,116]. 

Bertolotti, A., Y. Zhang, L. M. Hendershot, H. P. Harding, and D. Ron. 2000. Dynamic interaction of BiP and ER stress transducers in the unfolded-protein response. Nature Cell Biol. 2 326-332. 

Alignment of the Relative Positions of the Transducers. The stress transducer (transducer 1), the strain transducer (transducer 2), and the center of the drive shaft (Figure 1) must be positioned colinearly. This is done first by the use of the micropositioner to which the strain transducer is attached. Then for an accurate alignment, the hysteresis loops of Figure 3 are generated with the drive shaft rotated in the forward and... 

Current thinking dictates that the left ventricle attempts to normalize its peak wall stress values during systole and diastole by altering its dimensions [50]. There are several reasons to doubt the validity of this concept. First, anatomical locations of systoHc and diastoHc stress transducers have not been identified. Second, the value of waU stress cannot be determined from basic physical knowledge. Instead, wall stress is assumed to be regulated by an unknown mechanism. Last, this theory cannot explain ventricular size alterations due to metaboHc disturbance, as opposed to a mechanical disturbance. Alternatively, integrative modeling is appHed to the problem of cardiac hypertrophy. 

The viscoelastic behavior of biomaterials is typically measured using DMA. In rheological terms, viscoelastic is the concomitance of viscous (fluid-like) and elastic (solid-like) elements. The proportion of viscous and elastic properties is depending on the used material as well as on the measuring conditions such as the temperature. In DMA measurements, a sinusoidal shear load is applied to the sample while measuring the shear stress (cr ) with a stress transducer. The strain induced... 

Fig. 1. Film stretching machine (1) FTIR detector, (2) pneumatically rotatable pt rizer unit, (3) clamp, (4) polymer film sample, stress transducer, (6) displaconent transducer, (7) driving motor, (8) heating accessory, (9) cartridge heater, (10) temperature control, (11) KBr window, (12) specimen preparation and transfer device...

Figure 2-44. (a) Principle of rheo-optical FTIR spectroscopy of polymer films, (b) Variable-temperature stretching machine for rheo-optical FTIR and FT-Raman spectroscopy. (A) stretching machine (B) sample transfer mechanism (1) stress transducer (2) strain transducer (3) film sample (4) sample clamps [17, 18]. 

The first main feature of the System 4 RMS is its ability to characterize a wider range of the above systems than any other current rheometer. Several drives and stress transducers are required the wide range of modes, rates and materials to be handled would mean that no single drive/transducer combination would be sufficiently flexible and accurate. Instead, the System 4 RMS uses a turret with four different drive or transducer units one unit is used for steady shear tests, one for oscillatory shear, one for tension-compression and bending and one unit is used for low-viscosity-high-shear-rate tests on fluids. The second main feature of the new machine is its completely automatic microprocessor control coupled with data acquisition and reduction. Without doubt, this new rheometer will result in rheo-metrical tests being carried out more reliably, accurately and quickly than previously. 

Figure 9 shows an example of a nonresonance forced vibration apparatus. A sinusoidal deformation is applied to the specimen, and the amplitude of the deformation is measured using a strain transducer, and the magnitude of the response force is measured using a stress transducer. If the deformation and force are recorded on a recorder, the output data are as shown in Fig. lOA. 

The cone and plate viscometer can be used for oscillatory shear measurements as well. In this case, the sample is deformed by an oscillatory driver which may be mechanical or electromagnetic. The amplitude of the sinusoidal deformation is measured by a strain transducer. The force deforming the sample is measured by the small deformation of a relatively rigid spring or tension bar to which is attached a stress transducer. On account of the energy dissipated by the viscoelastic polymer system, a phase difference develops between the stress and the strain. The complex viscosity behavior is determined from the amplitudes of stress and strain and the phase angle between them. The results are usually interpreted in terms of the material functions, p, G, G" and others [33-40]. 

Figure 8.2.6 also illustrates a sliding plate shear rheometer design. If a wall shear stress transducer is not used, then the total force on the fixed plate is usually measured with a strain gage load cell. The linear actuators used have time constants in the... 

Wall shear stress transducer mounted in a sliding plate rheometer. Shear between the sample and the wall causes die cantilever to deflect slighdy, which motion is detected by the capacitance probe. Adapted from Interlaken (1992). 

Principle of rtieo-optical F-IR spectroscopy (a) and miniaturized stretching machine (b). A, stretching machine B, sample preparation/ transfer mechanism 1, stress transducer 2, strain transducer 3, polymer film sample 4, clamps. 

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