Constant rate of extension

The light intensity of the 3000 A lamps was determined as previously described ( ). Yarn samples were knit on a Lawson Fiber Analysis Knitter (FAK), and yarn tensile testing was performed on an Instron Model 1101 (TM-M) constant rate of extension testing machine. 

L. B. Freund Crack Propagation in an Elastic Solid Subjected to General Loading—I. Constant Rate of Extension, Journal of Mechanics and Physics of Solids, 20, 129-140 (1972). 

ASTM D 4964 Standard Test Method for Tension and Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tensile Testing Machine)... 

Another suitable method for evaluating elastomeric finishes is ASTM D 4964-96 Standard Test Method for Tension and Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tensile Testing Machine) . Fabric samples are formed into loops and are placed through several extension-recovery cycles under controlled conditions. Table 12.2 shows an overview of test methods for elastomeric finishes. 

Figure 13. Distribution of breaking stretch ratio at constant rate of extension ...

It has been shown that the life time in the creep process of rubbery polymers scatters largeley but obeys the specified statistical distribution which are introduced theoretically based on some assumptions. Two assumptions are made here that "one crack leads the body to failure" and "the v th crack leads the body to failure". The former assumption leads the exponential distribution of tg, and the latter the unimodal distribution when v>2. It has been explained from experiments that the distribution of tg for pure rubbers of vulcanized SBR and NR are the exponential, type and for filled systems the unimodal type. Theory introduced here can be applied not only to the creep failiire but also to the failure process varing stress level such as uniaxial extension with constant strain rate. It has been demonstrated that the distribution of Xg, the stretch ratio at breedc in the constant rate of extension, is well estimated by the theory substituting the parameters n and c which are obtained from creep failure experiment to eq(l9). 

Whereas dynamic mechanical measurements are generally preferred for viscoelastic measurements at small strains, studies at large deformations are more conveniently carried out at constant rates of extension... 

The Bueche-Halpin theory accounts well for the principal features of the tensile strength of unfilled rubbers. Because of the direct connection between ab and a viscoelastic function, time-temperature superposition of the strength follows naturally. Halpin (216) also found experimentally that ab was apparently the same function of the reduced time to break, tb/aT, whether the rupture experiment was carried out at constant stress, constant extension or constant rate of extension. 

Individual fibers are extended to rupture at constant rates of extension that may vary between 5 and 20 mm min. For reasons explained above, results of tests conducted at different rates of extension will not of course be directly comparable, but these options are available to enable fibers of different elastic modulus to be tested. 

ASTM D5735. 1995, Tearing strength of non woven fabrics by the tongue (single rip) procedure (constant-rate-of-extension tensile testing machine),... 

ASTM D4964-96, 2012. Standard test method for tension and elongation of elastic fabrics (constant-rate-of-extension type tensile testing machine). ASTM International. 

The range of polymers was designed to reveal the roles of choice of macrodiol and of chain extender in determining the performance as an elastomer. The SS were the polyether PTHF and polyester PEA or PBA, of molar mass 2 000 g/mol. The chain extenders used in the synthesis were EG, BG or DEG. Mechanical tests included load-unload cycles at constant rate of extension, with measurement of hysteresis and strain recovery, and stress relaxation tests. 

The tests included load-unload cycles to a nominal strain of 3, at constant rate of extension, with measurement of hysteresis and strain recovery. They were performed... 

Turkey feathers with their inner quills removed and consisting of pennaceous and plumulaceous fibers attached to the outer quill were supplied by MaXim LLC (Pasadena, CA). Two different processes were used to convert these into fabric, depending on whether they were going to be converted into yam then knit fabric or converted directly into nonwoven fabric. Before processing commenced, the fibers were characterized in terms of length, tenacity, strain, and modulus. One hundred plumulaceous fibers and one hundred pennaceous fibers were tested with an Instron Model 1125 constant-rate-of-extension tester interfaced with an IBM Personal System/2 Model 55 SX computer equipped with Labvantage Series IV software. "... 

If a constant rate of extension is imposed on an unoriented fiber, a load-extension curve like the one shown in Fig. 1 (solid line) is traced out. 

Mlklowitz [5] shows how the curve from A to A is altered when springs of different stiffness are put in series with the specimen. He brings the fiber to the point A under a constant rate of extension, and then he holds the fiber at a constant value of the extension. As the spring stiffness goes up, A approaches A a stiffer machine gives a sharper load drop. If the machine is not too soft (i.e. if A < B) the magnitude of the drop in load is more or less unaffected by the stiffness of the machine. 

Stress—Strain Behavior. The determination of stress-strain behavior in tension is one of the most important test methods for mechanical properties of engineering plastics and is of high importance to the design engineer. The tensile test is usually performed by monitoring the force that develops as the sample is elongated at a constant rate of extension. An often encountered stress-strain curve of a plastics material at equilibrium with any environment can be represented as depicted in Figure 2. 

FIGURE 9.1 The Maxwell model in creep (a), stress relaxation (b), and constant rate of extension (c). 

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