Clamping samples

One major consequence of the Ml project was the development of a modified filament stretching instrument by Sridhar. In this device, the test sample is held horizontally between two Teflon discs and pulled equally at both ends at a programmable exponential rate such that a constant strain rate is achieved and the stress growth at a constant stretch rate is obtained (40). It appears though that the test sample has to adhere to the plates as the technique does not use aids to clamp samples. Consequently, it is not clear if the technique can be applied to products that are non-sticky or exhibit slip, which could be limiting factors for testing food products. 

Electric resistivity. The electric resistance measurement is the same as discussed below under volume resistivity, to which this measurement is temporary adapted. For flexible materials, special electrode systems are developed to clamp sample and electric wires. The measuring equipment is based on a Wheatstone bridge circuit. The conductivity of metal powder-containing epoxy was measured in special dies equipped with built-in brass electrodes inserted to the die. The material was cured in the die to assure good contact with electrodes. Special sample holders and clamping devices are used for precise determination of rubber compounds containing carbon black. ... 

Fixed Clamp Sample Sample Fixed Clamp... 

In the in-house-built extensiometer, see Fig. 28.27, samples were clamped. Samples were connected via a probe (Tektronix, TPPO101-Voltage Probe 100 MHz with lOx magnification) to the PC oscilloscope (Picoscope 2204 Pico Technology). From a starting position when the sample was horizontal above the table, repeated extension relaxations were performed. Avoiding any transients, after 10 min measurement... 

As the contact pressure (load divided by total surface area) increases, the removal rate also increases. But the roughness (peak-to-valley height) and depth of damage increase by a similar proportion. For example, in the case of six clamped samples, each with a diameter of 25 mm, under a total load of 200 N, the contact pressure measures 0.07 N/mm. In the technical literature, however it is customary to specify only the rotational speed of the disk in rpm and the load in N instead of the removal rate and contact pressure. When testing recommendations for the preparation of polished sections, the rotational speed and load must be converted accordingly. 

All loads specified in N apply to a set of six clamped samples of diameter 25 nun. 

Clamp sample Stretch Mask UVO treatment Remove mask Release stretch ... 

S.2. Composites Sample end Corrections, Composite Specimen Geometry Effects Sample geometry modes with clamped samples (shear and three-point bending are not clamped) will exhibit errors due to clamping of the sample. Generally speaking, tension suffers the least error, compression... 

The calculation of the strain and stress from the bubble shape data depends on the deformation theory chosen. The plate theory is valid when the deformation is small compared with the film thickness. In this case, the film deforms mainly by bending. This will occur when the pressure applied is small or the film thickness is large compared with the hole diameter or the material is in the glassy state. For a clamped sample, the deflection as a function of radial position is given as [9] ... 

There are also strap-on type Brinell testers in which the anvil is supplanted by a chain or other clamping device and the indenter is spring-loaded. These have the advantage of being able to test direcdy very large objects without the need for cutting samples. 

Definitions of the commonly measured tensile properties are as follows Unear density (tex) is the weight in grams of 1000 m of yam. Tenacity is the tensile stress at break and is expressed in force-per-unit linear density of unstrained specimen, N /tex. Knot tenacity is the tensile stress required to mpture a single strand of yam with an overhand knot tied in the segment of sample between the testing clamps. It is expressed as force-per-unit linear density and is an approximate measure of the britdeness of the yam. Toop tenacity is the tensile stress required to mpture yam when one strand of yam is looped through... 

Welding (qv) of titanium requires a protected atmosphere of iaert gas. Furthermore, parts and filler wire are cleaned with acetone (trichloroethylene is not recommended). The pieces to be welded are clamped, not tacked, unless tacks are shielded with iaert gas. A test sample should be welded. Coated electrodes are excluded and higher purity metal (lower oxygen content) is preferred as filler. Titanium caimot be fusion-welded to other metals because of formation of brittle intermetallic phases ia the weld 2oae. 

Water Transport. Two methods of measuring water-vapor transmission rates (WVTR) ate commonly used. The newer method uses a Permatran-W (Modem Controls, Inc.). In this method a film sample is clamped over a saturated salt solution, which generates the desired humidity. Dry air sweeps past the other side of the film and past an infrared detector, which measures the water concentration in the gas. For a caUbrated flow rate of air, the rate of water addition can be calculated from the observed concentration in the sweep gas. From the steady-state rate, the WVTR can be calculated. In principle, the diffusion coefficient could be deterrnined by the method outlined in the previous section. However, only the steady-state region of the response is serviceable. Many different salt solutions can be used to make measurements at selected humidity differences however, in practice,... 

Greater attention is usually paid to the results of a vertical test, in which the sample is clamped at the top end and a bunsen flame of height 19 mm is applied to the lower end at a point 9.5 mm above the top of the bunsen burner (i.e. halfway along the flame). The material is classified as V-2, V-1 or V-0 in increasing order of flammability rating by reference to the conditions given in Table 5.14. 

On the basis of the principle of grafted TLC, reversed-phase (RP) and normal-phase (NP) stationary phases can also be coupled. The sample to be separated must be applied to the first (2.5 cm X 20 cm) reversed-phase plate (Figure 8.16(a)). After development with the appropriate (5ti 5yi) mobile phase (Figure 8.16(b)), the first plate must be dried. The second (20 cm X 20 cm) (silica gel) plate (Figure 8.16(c)) must be clamped to the first (reversed-phase) plate in such a way that by use of a strong solvent system (Sj/, SyJ the separated compounds can be transferred to the second plate (Figure 8.16(d)). Figure 8.16(e) illustrates the applied, re-concentrated... 

Figure 8.16 Views from above (a-c, e, and f) of coupled RP-NP cliromatographic plates (without lines, RP stationaiy phase light shading, NP stationaiy phase), and schematic diagram of a cross-section (d) tlrrough the clamped plates using a strong mobile phase (S-j-/, 5vj) for the transfer of the sample to be further separated.

Based on the results of the calculations, it should be mentioned that the first pyroelectric coefficient seems to be significantly higher than the measured value even at room temperature. This high value of the coefficient can be achieved by clamping (compressing) the sample. 

The H-type cell devised by Lingane and Laitinen and shown in Fig. 16.9 will be found satisfactory for many purposes a particular feature is the built-in reference electrode. Usually a saturated calomel electrode is employed, but if the presence of chloride ion is harmful a mercury(I) sulphate electrode (Hg/Hg2 S04 in potassium sulphate solution potential ca + 0.40 volts vs S.C.E.) may be used. It is usually designed to contain 10-50 mL of the sample solution in the left-hand compartment, but it can be constructed to accommodate a smaller volume down to 1 -2 mL. To avoid polarisation of the reference electrode the latter should be made of tubing at least 20 mm in diameter, but the dimensions of the solution compartment can be varied over wide limits. The compartments are separated by a cross-member filled with a 4 per cent agar-saturated potassium chloride gel, which is held in position by a medium-porosity sintered Pyrex glass disc (diameter at least 10 mm) placed as near the solution compartment as possible in order to facilitate de-aeration of the test solution. By clamping the cell so that the cross-member is vertical, the molten... 

The popular Izod impact tester can use different size specimens depending on the type of plastic and their method of fabrication. The specimen is usually 1/8 in. x l/2 in. x 2 in. other sizes are also used. Specimens can be notched or unnotched. A notch is cut in a specified manner on the narrow face of the specimen. The sample is clamped in the base of a pendulum testing machine so that it is cantilevered upward with the notch facing the direction of impact. The pendulum is released, and the force expended in breaking the sample is calculated from the height the pendulum reaches on the follow-through. The speed of the pendulum at impact is controlled. 

---