Standard tension

WRV (Water Retention Value). The water retained when fibers are subjected to external force Is known as the Water Retention Value. Water retained by surface tension forces In addition to adsorbed water may be Involved In this determination. The methods used In determining this value are centrifuging (water retained under standard centrifuging) (11,12), hydrostatic tension (water retained under standard tension) (13), and suction (water retained under suction or vacuum) (14). All these methods can be employed at any temperature and the experimental techniques are quite simple. 

Index Standard tension (KN) Sampling voltage (V) Measurement tension (KN) Error (KN)... 

ASTM G 49, Recommended Practice for Preparation and Use of Direct Tension Stress-Corrosion Test Specimens— This presents the design, preparation, and use of ASTM standard tension test specimens for investigating susceptibiUty to SCC. Specimens are generally tested in a selected environment imder axial load conditions until fracture occurs. This standard describes the apparatus for providing the load to the stressed specimens along with exposure considerations and inspection methods. 

Slow strain-rate tests, in which standard tension test specimens are subjected to a constant extension rate of 10-4 to 10-6 m/s while being exposed to a corrosive environment, provide a relatively quick method for SGG screening of metals. Such methods are described in the following standards ... 

NACE Standard Test Method for Testing of Metals for Resistance to Sulfide Stress Cracking in HjS Environments (TM0177) describes foiu- test methods in which specimens stressed in tension are exposed to acidified brine saturated with H2S. In Method A of this test, standard tension test specimens are used and the tensile stress is applied by either... 

The tests are performed using a standard tension and compression apparatus, which can be operated at a controlled rate of crosshead movement. The load-extension curve should be recorded and the specimen tested until it breaks. If extensometers are used, it is necessary to minimize the stress on the sample at the contact points of specimen and indicator. 

The samples are conditioned to room temperature.They are then centered on the supports of the standard tension and compression test apparatus with the long axis of the specimen perpendicular to the loading nose and support. The samples are loaded at the defined speed... 

Some belt manufacturers, and some specialty belts, may still use the older, couventioual matching system. Each belt is measured under industry standard tension in V sheaves and marked with a punch or match number designating the small increment of length within the... 

Surfa.ce Energy. The surface energies of Parylenes N, C, and D were measured by observing the contact angles for several standard probe hquids. AH three have surface energies of approximately 45 mj/m (= dyn/cm), ie, all test Hquids having less than 45 mj/m surface tension completely wet the as-deposited parylene surfaces (43). 

The atoms and molecules at the interface between a Hquid (or soHd) and a vacuum are attracted more strongly toward the interior than toward the vacuum. The material parameter used to characterize this imbalance is the interfacial energy density y, usually called surface tension. It is highest for metals (<1 J/m ) (1 J/m = N/m), moderate for metal oxides (<0.1 J/m ), and lowest for hydrocarbons and fluorocarbons (0.02 J /m minimum) (4). The International Standards Organization describes weU-estabHshed methods for determining surface tension, eg, ISO 304 for Hquids containing surfactants and ISO 6889 for two-Hquid systems containing surfactants. 

The physical characteristics of /i /f-amyl alcohol diverge from the standard trends for the other alcohols it has a lower boiling point, higher melting point, higher vapor pressure, and low surface tension. Most notably, organic molecules are highly soluble in /i /f-amyl alcohol. 

The standard conventional finishing process has been modified to suit the purposes for different fabrics and garments. Eor example, tubular knits are frequently handled using specialized equipment to control tension and to get adequate padding. Some tubular knits are subjected to wet-on-wet padding, dried and cured in large dmm dryers, and steam-treated to achieve a relaxed and nondistorted knit. 

There are many laboratory methods for testing the relative merits of one defoamer against another. It is a simple matter to measure foam height as a function of time to compare the performance of various foam surfactants and defoamers. Unfortunately, this simplicity has led to a wide variety of methods and conditions used with no standard procedure that would make the measurement of foaminess as characteristic of a solution as its surface tension or viscosity. It has been suggested that the time an average bubble remains entrapped ia the foam is such a quantity (49), but very few workers ia the defoamer iadustry have adopted this proposal. Ia practice, a wide variety of methods are used that geaerally fall iato oae of five maia categories ... 

CT = Standard deviation (statistics), or interfacial tension T = Torque on shaft, consistent units, FL or MLVt ... 

Effective length The effective length is measured on a length-inspection machine. The machine consists of two parallel shafts on movable centers with a scale to accurately measure the center distance between shafts. Inspection pulleys of equal diameter and grooved in accordance with industry standards are mounted on these shafts. A belt is mounted on these pulleys and tensioned to a specified force. The belt is rotated through at least three complete revolutions to ensure that the tension is equalized around the belt and that the belt is properly seated in the grooves. 

The National Electrical Manufacturers Association (NEMA) has developed a standard that specifies minimum pulley diameters that should be used on electric motors. Since motor bearings are specified using a relatively small maximum overhung load, minimum pulley diameters can have a dramatic effect on motor bearings. The increase in tension that is created by smaller pulleys can transmit a potentially destructive side-load on the bearings. 

In addition, when installing multiple belts, it is imperative that the slack side of each belt be on the same side, either top or bottom. Tables 58.2 and 58.3 show the minimum movement below and above the standard center distance required between the pulleys. This movement allows the center distance to be shortened for new belt installation. It also allows the center distance to be increased to take up the slack and to maintain proper tension as the belt stretches (Figure 58.6). 

Standard- length designation Minimum allowance below standard center distance for installation of belts Minimum allowances above standard center distance for maintaining tension (all cross-sections)... 

Other effects. In addition to the compound formation and ionisation effects which have been considered, it is also necessary to take account of so-called matrix effects. These are predominantly physical factors which will influence the amount of sample reaching the flame, and are related in particular to factors such as the viscosity, the density, the surface tension and the volatility of the solvent used to prepare the test solution. If we wish to compare a series of solutions, e.g. a series of standards to be compared with a test solution, it is clearly essential that the same solvent be used for each, and the solutions should not differ too widely in their bulk composition. This procedure is commonly termed matrix matching. 

For those not familiar with this type information recognize that the viscoelastic behavior of plastics shows that their deformations are dependent on such factors as the time under load and temperature conditions. Therefore, when structural (load bearing) plastic products are to be designed, it must be remembered that the standard equations that have been historically available for designing steel springs, beams, plates, cylinders, etc. have all been derived under the assumptions that (1) the strains are small, (2) the modulus is constant, (3) the strains are independent of the loading rate or history and are immediately reversible, (4) the material is isotropic, and (5) the material behaves in the same way in tension and compression. 

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