Fiber elongation test

Once an object is formed, the internal stresses which result from cooling are usually reduced by annealing. The annealing point (cited in various sources as either 10 or 10 " Pa s), which is also determined using a fiber elongation test, is defined as the temperature where the stress is substantially relieved in a few minutes. The strain point (1013.5 ig defined as the temperature where stress is substantially relieved in several hours. The strain point is determined by extrapolation of data from annealing point studies. Other tests are also used for these two reference points, with slightly different results. 

The elastic properties discussed so far relate to stresses applied at relatively low rates. When forces are applied at rapid rates, then dynamic moduli are obtained. The energy relationships and the orders of magnitude of the data are much different [570]. Because of the experimental difficulties, only little work at rapid rates has been carried out with cotton fiber compared to that done with testing at low rates of application of stress. In contrast, cotton also responds to zero rate of loading, i.e., the application of a constant stress. Under this condition the fiber exhibits creep that is measured by determining fiber elongation at various intervals of time after the load has been applied. Creep is time-dependent and may be reversible upon removal of the load. However, even a low load applied to a fiber for a long period of time will cause the fiber to break. 

At least 50 fibers are tested, and the mean breaking force is reported along with the mean elongation at break and their 95% confidence intervals. 

The softening point is more properly termed the Littleton softening point, after the specific test used to define this reference point. The viscosity of 10 Pa s does not represent the deformation temperature for all objects. This particular reference point is defined in terms of a well-specified test involving a fiber -0.7 mm in diameter, with a length of 24 cm. The softening point is defined as the temperature at which this fiber elongates at a rate of 1 mm min when the top 10 cm of the fiber is heated at a rate of 5 K min. In fact, if the density of the fiber is significantly different from that of a typical soda-lime-silica composition, the viscosity will not be exactly 10 Pa s at this temperature. 

For any material requiring impact testing, where the maximum calculated fiber elongation after... 

ISO 178 flexural tests are conducted on beam-shaped test specimens. The preferred dimensions for these test specimens are (1) 80 mm x (rr) 80 mm x (fl) 4 mm, and the specimens are supported at each end and a bending load is applied by a die at the midway point between the supports. Measured forces and deflection are used to calculate characteristic values of flexural strain and outer fiber elongation, for example up to a defined maximum outer fiber elongation or up to fracture of the specimen [8, 66]. 

DIN EN ISO 75-1,-2 (successor to DIN 53461) sets out a method of determining heat deflection temperature (HDT), which is in widespread use, so it is outlined below. The standard test specimens are rectangular in section and should preferably be laid flat and subjected to three-point flexion at constant load. A force F that can vary depending on the thickness of the specimen is applied hy weights and/or springs to achieve an outer fiber elongation of 1.80 (method A), 0.45 (methods), or 8.00 N/mm (method C). The specimens loaded in this way are then heated at a constant rate of 120 K/h (or 50 K/h). When deflection of the specimen reaches an outer fiber elongation of 0.2%, the temperature at which this occurs is the heat deflection temperature (also known as heat distortion temperature). 

The single-fiber fragmentation test is often used to determine the interfacial shear strength of fibers embedded in matrix materials. For this test to be valid the matrix materials should have an elongation to break which is at least three times the elongation to break the fiber. This test is especially applicable to fiber-reinforced composites such as carbon/expoy. In the test a single fiber is embedded in the... 

Standard Test Methods for Tire Yarns, Cords, and Woven Fabrics. ASTM standard D885M-94 includes test methods for characterizing tire cord twist, break strength, elongation at break, modulus, tenacity, work-to-break, toughness, stiffness, growth, and dip pickup for industrial filament yams made from organic base fibers, cords twisted from such yams, and fabrics woven from these cords that are produced specifically for use in the manufacture of pneumatic tires. These test methods apply to nylon, polyester, rayon, and aramid yams, tire cords, and woven fabrics. 

Standard Test Method for Breaking Strength and Elongation of Cotton Fibers (Flat Bundle Method)," ASTM E144S-90, Annual Book ofASTM Standards, Vol 07.01, ASTM, Philadelphia, Pa., 1991, pp. 405—409. 

Tests by Gatenholm et al. [8,10] on PHB-HV copolymers containing cellulose fibers (for example, the tradenamed Biopol) show that the mechanical properties of these systems are determined by the fiber and the fiber matrix interface on the one hand, and on the other hand by the composition of the matrix, that is, of HV proportion in the matrix. At an increased proportion of HV, the stiffness of the composite is reduced up to 30%, whereas elongation at break increases until about 60%. 

Figure 12.10 displays the stress-strain behavior of PET fibers that were prepared from the same spun yam, but drawn to different ratios. The curves represent the elongation and stress in terms of initial fiber area (decitex2). The open circles represent true stress values, where stress values at break are corrected for the decreased area of the fiber after extension on the testing device. 

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