Deformation measurements

The classic way that we perform force versus deformation measurements is to deform a sample at a constant rate, while we record the force induced within it. We normally carry out such tests in one of three configurations tensile, compressive, or flexural, which are illustrated in Fig. 8.1. We can also test samples in torsion or in a combination of two or more loading configurations. For the sake of simplicity, most tests are uni-axial in nature, but we can employ bi-axial or multi-axial modes when needed,... 

Fig. 6a. Schematic illustration of deformation measurement of PVA-PAA gel film in electric fields, b Deflection curves of PVA-PAA gel film under sinusoidally varied electric fields...

Deformational measurements were carried out in a uniaxial compression of cylindrical samples and the equilibrium shear modulus G was determined from [11]... 

Model networks can be considered as a new class of tridimensional polymeric material, with elastic chains of known and rather constant length, and branch points of almost constant functionality, with few defects, and of very satisfactory homogeneity. By combination of structural determinations and of swelling and deformation measurements it was shown that the existing theories of rubber elasticity are applicable, even though some ambiguity still exists as to what concerns the value and the meaning of the memory term. 

In the present paper we extend our analysis of the experimental results obtained from this small deformation regime and we show that the result found by Reissner for the deformation of shallow spherical caps represents an excellent analytical approximation for the interpretation of the measurements. This result is varified by finite element modelling (FEM) and by experimental variation of the force probe geometry and radius as well as wall thickness of the studied capsules. This result is also applicable for other capsule deformation measurements, since it is independent of the specific Young s modulus. Furthermore, we report on speed dependent measurements that indicate the glassy nature of PAH/PSS multilayers. 

In this paper, we report some rheological results on the effect of addition of sodium bentonite, a commonly-used antisettling system, to a pesticide suspension concentrate. Steady state shear stress-shear rate measurements were carried out to obtain the yield value and viscosity as a function of shear rate. These e]q>eriments were supplemented by low deformation measurements to investigate the viscoelastic... 

The rheological results obtained using both high and low deformation measurements are all consistent, showing a rapid increase in the rheological parameters, Tg, G, and G... 

Another important large deformation measurement is the three point bending test (Figure 17.19). Here a mold of the solid fat is plaeed on two beams and a third beam applies an external force between the other two beams. The Young s modulus ( ) and yield force may be determined depending on the cross-section as (rectangular Equation (17.18) or circular Equation (17.19)) ... 

Fig. 3.6. Deformability measured as filterability. (A) Cells passing through the pores of the filter are collected in siliconized tubes at 2 sec intervals. Cells in each tube are counted, and a curve generated of cell N vs. time. The steejjer the curve, the more deformable the cells. (B) The time for a defined cell concentration to pass through the filter at constant pressure is recorded, and a curve is generated as a function of variable cell concentrations. HIGH and LOW in the graph legend refer to more and less deformable cells.

For both mathematical and physical reasons, there are many instances in which the spatial variations in the field variables are sufficiently gentle to allow for an approximate treatment of the geometry of deformation in terms of linear strain measures as opposed to the description including geometric nonlinearities introduced above. In these cases, it suffices to build a kinematic description around a linearized version of the deformation measures discussed above. Note that in component form, the Lagrangian strain may be written as... 

One method that attempts to characterize the viscoelastic behavior is the force-deformation measurement. In this approach, a force point is applied... 

Measurements are taken on the three principal joint directions and in 6-cm diameter boreholes. Each measurement point corresponds to two boreholes, both perpendicular to the joints and 20 cm apart (see Fig. 3). A pressure gauge for measuring hydrostatic pressure is placed in the first borehole and a vibrating wire extensometer is installed in the second in order to monitor deformation normal to the joint. This extensometer is positioned within a concrete cylinder. The deformation measurement is thus that of the cylinder with a 6-cm diameter and 50-cm length. The recorded deformations are then transformed into normal displacements by referring to the basic measurement length, i.e. the 15-cm extensometer length. 

The eight simultaneous pressure measurements (using pressure gauge M) and deformation measurements (using extensometer E) are conducted near the floodgate, where pressure variations are highest. The instrumented volume corresponds to a parallelepiped of 1,500 m . 

The normal stresses obtained at measurement points El and E2 with displacement boundary conditions are ten times weaker than those obtained with stress boundary conditions. Equivalent results have been obtained for variable ranges of normal and shear fracture stiffnesses. Without on-site stress measurements, choosing between these various boundary conditions is difficult. The simultaneous pressure-deformation measurements at the Coaraze site have however enabled carrying out an analysis on the measurement points as well as determining a threshold for normal stress in the joints (see Table 2). The selected boundary conditions are those that more accurately reproduce the initial stresses at Coaraze (i.e. displacement boundary conditions). 

Fig. 32.13 Joint deformation measurement points for the TR08 on the Lathen test track.

---