Measurement constant load

Ultrasonic Microhardness. A new microhardness test using ultrasonic vibrations has been developed and offers some advantages over conventional microhardness tests that rely on physical measurement of the remaining indentation size (6). The ultrasonic method uses the DPH diamond indenter under a constant load of 7.8 N (800 gf) or less. The hardness number is derived from a comparison of the natural frequency of the diamond indenter when free or loaded. Knowledge of the modulus of elasticity of the material under test and a smooth surface finish is required. The technique is fast and direct-reading, making it useful for production testing of similarly shaped parts. 

Plastic deformation is commonly measured by measuring the strain as a function of time at a constant load and temperature. The data is usually plotted as strain versus time. Deformation strain can be measured under many possible loading configurations. Because of problems associated with the preparation and gripping of tensile specimens, plastic deformation data are often collected using bend and compression tests. 

Creep tests require careful temperature control. Typically, a specimen is loaded in tension or compression, usually at constant load, inside a furnace which is maintained at a constant temperature, T. The extension is measured as a function of time. Figure 17.4 shows a typical set of results from such a test. Metals, polymers and ceramics all show creep curves of this general shape. 

Many designs incorporate the phenomenon of stress-relaxation. For example, in many products, when plastics are assembled they are placed into a permanently deflected condition, as for instance press fits, bolted assemblies, and some plastic springs. In time, with the strain kept constant the stress level will decrease, from the same internal molecular movement that produces creep. This gradual decay in stress at a constant strain (stress-relaxation) becomes important in applications such as preloaded bolts and springs where there is concern for retaining the load. The amount of relaxation can be measured by applying a fixed strain to a sample and then measuring the load with time. 

There are two further related sets of tests that can be used to give information on the mechanical properties of viscoelastic polymers, namely creep and stress relaxation. In a creep test, a constant load is applied to the specimen and the elongation is measured as a function of time. In a stress relaxation test, the specimen is strained quickly to a fixed amount and the stress needed to maintain this strain is also measured as a function of time. 

Abrasion under limited slip used to be, and to some extent still is, measured either with the standard Akron abrader or the Lamboum abrader. In case of the Akron abrader the sample runs under a slip angle at a constant load against the abrasive surface of an alumina grind stone. Speed and load are fixed the side force is not measured. 

Diard J-P. 1998. Impedance measurements of polymer electrol)4e membrane fuel cells running on constant load. J Power Sources 74 244-245. 

A type of test for determining abrasion resistance. Fixed knives, under constant load, scrape across a rotating rubber test piece. The resulting loss in weight is a measure of the abrasion resistance. 

According to the simple Eq. 115 and the full Eq. 140, the lifetime of a fibre measured at a constant load decreases with increasing orientation parameter. The dependence of the slope of the curve, log( b) vs ob, on the initial orientation distribution has been calculated for PpPTA fibres using Eq. 140. Figure 70 shows that at constant load for increasing orientation angle the lifetime curves become steeper, while at the same time the lifetime decreases. This effect has been observed for nylon 66 yarns as shown in Fig. 71, where the lifetime data... 

Oxygen Consumption This can be measured at rest and during exercise on a constant-load bicycle ergometer or a treadmill at a level producing a specified percentage of predicted maximal oxygen consumption. Expired air is collected and measured with a spirometer to determine total expired volume, and samples are analyzed for oxygen and carbon dioxide. 

The elongation of film strips of fixed dimensions subjected to a constant load of 0.17 kg./sq.mm. is measured as a function of temperature. Heating rate is standardized at 10°C. per minute. The temperature range where an appreciable rise in elongation of the films is observed is taken as the softening point (S.P.)... 

Martens followed the first course, but it is far much common to give the results by determining the scratch width at a constant load. This is because of the greater simplicity of measurement and the possibility of using standard instruments. Also a change in scratch width in tests under constant load reflects a change in hardness of the sample under test. 

Tensile tests involve either stretching a sample and monitoring the load or loading it while monitoring the extension. The simplest test uses a tensile testing machine (e.g. an Instron) where the sample is stretched at a constant rate while the load is measured using a (usually hard) load cell. Variations on this test allow the specimen to be extended at a constant strain rate or to be loaded at a constant load, or stress rate. These latter tests are usually carried out on servo hydraulic machines. 

Creep Properties. The creep properties, determined at 100 °C under a constant load of 50 kg/cm2, of some CPVC types A, B, and D and of blends (designated E) obtained by mixing 5, 10, and 15% by weight PVC with CPVC type D, are shown in Figure 11 (see Table V). Similar results were obtained for the measurements carried out at 80 °C under a constant load of 100 kg/cm2 (Figure 12). 

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