Bending plate measurement

In most cases the variation in surface stress has been determined indirectly by measuring the potential dependence of the strain (i.e., electrode deformation) and then obtaining the variation in stress from the appropriate form of Hookes law (-> bending beam or cantilever beam method, bending plate methods e.g., the measurement of the deformation of the electrode with the help of a —r Kosters laser interferometer). 

FIG. 7 Schematic of the bending plate technique. In this case a cantilever with different faces is used. The bending is often detected by measuring the angle of a light beam that is reflected off the cantilever. 

With the bending plate technique no absolute values of the surface stress can be measured. Only changes in the difference between the surface stresses of the two faces are detectable. In the adsorption experiments done in UHV this was achieved by directing the beam of adsorbing molecules to one side only. In liquid the two sides of the cantilever need to be of different composition. 

Electrocapillary curves of various metals under different conditions have been determined with the bending plate technique 1158,159], The deflection of the plate is usually measured by an optical lever. Pangarov and Kolarov used an interferometric method to detect the bending of the plate I60]. Recently the method was improved by using microfabricated cantilevers 1161-163). Bard et al. glued flat metal 1164,165] or semiconductor 1166] electrodes onto piezoelectric disks. When applying a potential to the electrode the resultant bending caused a potential on the piezo, which was detected. 

In a somewhat related experiment, surface stress changes due to an applied electric potential were determined by measuring the bending of a circular plate. This bending was measured interferometrically 1169-172] or with a STM 1173.174],... 

Bending plate method AT Only changes in surface stress differences can be measured... 

Fig. 1 Operational principle (a) and cross-section (b) of hydrogel-based chemical sensor 1 measuring solution 2 hydrogel 3 Si bending plate 4 piezoresistors...

Of other tests which are sometimes applied to high explosives, mention should be made of the tests for brisance. Brisance is an ill-defined word, best described by saying that an explosive of high brisance, when fired unconfined on a steel plate, will bend or shatter that plate more effectively than an explosive of low brisance. The Hess and Kast tests for brisance depend on this property, using the deformation of a metal cylinder by the explosive as a measure of the property. In most countries these tests are now little used. 

The horizontal exposure method is not very adequate for the OSU RHR calorimeter, because the heat reflected from the aluminum foil onto the sample is much lower than the heat generated by the glow bars. Since the OSU calorimeter is based on the adiabaticity of the measurements, any heat losses will represent inaccurate results. The reflection on the aluminum foil is also uneven. Moreover, the use of higher radiant energy causes problems with the mechanical functioning of the instrument (bending and buckling of the back plate). 

Plate Denting Tests, although not actually involving shattering by expls, are used as measures of brisance. In these tests the effect of a cylinder of expl when detonated in contact with a steel plate, is detd under such condirioQs that the more powerful expls depress and dent but never puncture or shatter the plate, while leas powerful expls merely dent or bend it... 

In ISO 3384, the specified accuracy of force measurement is 1% and the compression must be maintained to within 0.01 mm. If a small extra stress or strain is added when force is measured, this must be less than IN or 0.05 mm. The compression plates must be flat to within 0.01mm with surface finish not worse than 0.4 pm Ra and, for ring test pieces, have a central hole to allow the circulation of liquid. The stiffness of the plates must be such that they bend by less than 0.01 mm under load. 

Figure 7.12 shows the result of a fracture measurement using two-point bend geometry. The agreement between observed and predicted behavior is excellent -cracks began to develop in the coating layer at a plate separation between 6 and 7 mm and propagated across the width of the specimen. The point of maximum... 

Experimental techniques such as those used to measure specific values of viscosity (e.g. softening point) are still in common use, but are not as powerful as those in which a range of viscosities can be measured. Hence, only the Margules (1 to 106 Pa-s), parallel plate (103 to 108), and beam bending viscometers (107 to 1014 Pa-s) will be discussed here. These devices are manufactured and marketed by Theta Industries. 

The force Fwas measured by the bending of a spring to which one of the plates was attached. The distance d was estimated with the aid of Newton interference colours. The results obtained confirmed the exponent 3 in expression (1) for the dependence of the force upon the distance but the force-constant A was about 40 times lar r than that predicted. 

All data given above can only indicate an order of magnitude. The Ud value cannot be taken from the physical dimensions only a 90° bend of the tube would prolong the length not by the measured length but by a multiple of I depending on the actual manufacturing of the bend. The same applies for a valve plate. Even if... 

For correlation of the experimental results, a simple plate theory was used. As a theoretical model, an elastic plate model of one of the sub-panels with dimensions 990x620x96 mm was considered. This plate was assumed to be supported along its edges elastically and subjected to a uniformly distributed wind action of 1.5 kN/m2. The aim of this modelling was an indirect determination of the elastic modulus of the recycled rubber material for this purpose the measured deflections were correlated with the bending deflection predicted by the theory of thin elastic plates. 

Flexural strength of core plates and sandwich plates were determined by three point bend test as shown in Fig. 2. The span was 150 mm. Deflection of the center of the span was measured with a laser displacement censor. Vertical movements of the plate on the supporting points were also measured with displacement transducers which were used to delete the rigid body displacement from the measured deflection. The applied load was measured with a load cell. Shear strength of core plates were determined by double shearing test as shown in Fig. 3. 

---