Load-extension curve

Load-extension curves for non-elastic (plastic) behaviour... 

Fig. 8.4. Load-extension curve tor a bor of ductile metal (e.g. annealed copper) pulled in tension.

Yield strength as determined in tensile tests [53] at ambient temperature was plotted in Fig. 6.1 against M 1, the inverse molecular mass between crosslinks. All the samples of polymer A (the most crosslinked polymer) failed before the polymer started to yield. Therefore, load-extension-curves were extrapolated up to a hypothetical yield strain in this case. The extrapolated tensile is marked by brackets (Table 6.1). 

Loaded adsorbents, 1 590 Loaded fiber membranes, 16 2, 3 Load-extension curves, for fibers, 11 181,... 

Schematic load-extension curves for a linear polymer at different temperatures. Well below Tg the polymer Is brittle. Near Tg it is plastic and may show cold-drawing. Above Tg, it is viscous. 

Sookne and Harris (1937) found that the disulfide bonds of wool are modified by treatment with nitrous acid. They considered the similarity of the load-extension curves for untreated and deaminated fibers in 0.1 iV HCl to be fortuitous. 

Fig. 19. Typical load-extension curve of a Corriedale fiber in water at about 20°C after boiling for less than 20 min at a constant strain of 10% (Feughelman, 1960).

The plasticizing action of several hydrogen bonding, low molecular weight compounds such as methanol, ethanol, benzyl alcohol, ethylene ycol, phenol, aniline, and acetic acid has been well established. In one series of experiments, the load-extension curve has been determined for polyacrylonitrile fibers immersed into the respective liquids In another, hydroxy or amino compounds have been added to... 

Fig. 5.20 Load-extension curve of Cotswold wool for humidities vanring from 0 to 100 per cent at 25 C...

In the final example, it is possible to modify the chemical nature of the hp to explore specihc interactions,for example, single polymer load extension curves have been explored by, hrst, using the hp to detach some molecules, reattach them elsewhere and, hnally, monitor the force as they are extended. j deed, another use of AFM is as a means of moving atoms and molecules to build structures. Recent developments include a novel highspeed imaging system. 

Fig. 7.12.3 is an illustrative diagram of a load-extension curve for tensile steel. 

FIGURE 5.1 Typical tensile load-extension curve for a coating with optimal composition on concrete substrate (ASTM D412). (Reprinted from O. Figovsky, V. Karchevky, and D. Beilin, Protective Crack-Resistant Waterborne Coatings Based on Vulcanized Chlorine-Sulpho-Polyethylene, Scientific Israel Technological Advantages 3, nos. 1-2 (2001). With permission.)... 

Over the six-week period of permeation testing, sample containers from each type and temperature set were randomly selected and used for tensile testing. The tensile specimens were prepared and tested following the procedures of ASTM Test Method D1708-79 with the following modifications (i) the bottles were drained, and five specimens were cut parallel to the long axis of the cylinder (machine direction), (ii) the specimens were tested immediately after blotting to remove any surface solvent, (iii) a test speed of 5.08 cm/min. (2 in./min.) was used, and (iv) the tensile modulus of elasticity was calculated from the initial slope of the load-extension curve. 

Fig. 13. Load-extension curves for ethylene-Hexene. 1 copolymers A 4 butyl/103C B 1 butyl/10 0 C homopolymer...

The strength and elongation measurements are taken from autographic load-extension curves. Reduction of area is obtained from direct measurements of the test specimen. Because of the very small diameter of the wire and the importance of accurate measurements, a precise method of measuring the original and final diameters is employed. A microscope with cross hairs and a movable, calibrated stage is used to obtain diameter measurements accurate to 0.0001 in. 

Various possible load-extension curves for polymers are shown schematically in fig. 6.2. The whole range of behaviour shown in fig. 6.2 can be displayed by a single polymer, depending on the temperature and the strain-rate, i.e. how fast the deformation is performed, and whether tensile or compressive stress is used. These curves are discussed further in sections 8.1, 8.2 and 10.2.2. 

Fig. 6.2 Possible forms of the load-extension curve for a polymer (a) low extensibility followed by brittle fraction (b) localised yielding followed by fracture, (c) necking and cold drawing, (d) homogeneous deformation with indistinct yield and (e) rubber-like behaviour.

As discussed in section 6.2.2, the values of Young s modulus for isotropic glassy and semicrystalline polymers are typically two orders of magnitude lower than those of metals. These materials can be either brittle, leading to fracture at strains of a few per cent, or ductile, leading to large but non-recoverable deformation (see chapter 8). In contrast, for rubbers. Young s moduli are typically of order 1 MPa for small strains (fig. 6.6 shows that the load-extension curve is non-linear) and elastic, i.e. recoverable, extensions up to about 1000% are often possible. This shows that the fundamental mechanism for the elastic behaviour of rubbers must be quite different from that for metals and other types of solids. 

Load-Extension Curve Conformation of the Protein Chains in Wool... 

Load-Extension Curves Under Different Conditions.368... 

Effect of Chemical Treatments of Wool on the Load Extension Curve...368... 

LOAD-EXTENSION CURVE CONFORMATION OF THE PROTEIN CHAINS IN WOOL AT DIFFERENT EXTENSIONS... 

When a wool fiber is extended in water, the load-extension curve (Figure 5.12) shows the following features For a small extension, up to about 1%, the gradient of the curve increases as the crimp of the fiber is straightened. The gradient is then constant up to about 3% extension. Thus the extension of the fiber is approximately proportional to the load. Hooke s law is approximated this is the so-called Hookean region of the load-extension curve. 

FIGURE 5.12 Load-extension curve of a Merino wool fiber extended in water. (From J.B. Speakman,... 

At about 3% extension, the yield point, there is a sudden decrease in the gradient of the load-extension curve, and the gradient remains small and constant until about 30% extension. After 30% extension, the fiber becomes increasingly resistant to extension and the gradient of the load-extension curve increases continuously until the fiber breaks, at about 40% extension [274-276],... 

If the fiber is extended by only 30 /o of its length, or less, and if the load is then removed and the fiber immersed without tension in water for 24 h, the fiber returns to its original length. If the load-extension curve for the fiber is determined for the second time, it follows the path of the first load-extension curve [277]. These recovery properties are unique to wool [272] no other natural or synthetic fiber exhibits them. 

When a wool fiber is extended in water to a definite extention—say, halfway along the Hookean region of the load-extension curve—and held at this extension, the stress in the fiber gradually decays and therefore the force necessary to hold the fiber at this extension gradually decreases. The slow decrease of stress with time is responsible for the fact that the Hookean region of the load-extension curve is not exactly straight [280], but concave with respect to the extension axis, since the extension of the fiber takes a finite time. 

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