Fibrils stress-strain curves, figure

Figure 6.6. Stress-strain curve for skin. Stress-strain curves for wet back skin from rat at strain rates of 10 and 50% per minute. The low modulus region involves the alignment of collagen fibers along the stress direction that are directly stretched in the linear region. Disintegration of fibrils and failure occurs at the end of the linear region. (Adapted from Silver, 1987.)...

Figure 7.6. Effective mechanical fibril length versus fibril segment length. Plot of effective fibril length in pm determined from viscous stress-strain curves for rat tail tendon and self-assembled collagen fibers versus fibril segment length. The correlation coefficient (R2) for the line shown is 0.944 (see Silver et al., 2003).

Figure 10.2. Mean elastic and viscous stress-strain curves for cartilage. Plot of elastic (A) and viscous (B) stress-strain curves for cartilage as a function of visual grade. The visual grade used was 1, shiny and smooth 2, slightly fibrillated 3, mildly fibrillated 4, fibrillated 5, very fibrillated and 6, fissured. The equation for the linear approximation for the stress-strain curve for each group is given, as well as the correlation coefficient. Note the decreased slope with increased severity of osteoarthritis. This data is consistent with down-regulation of mechanochemical transduction and tissue catabolism.

As could be expected, the mechanical properties of a crazed polymer differ from those of the bulk polymer. A craze containing even 50% microcavities can still withstand loads because fibrils, which are oriented in the direction of the load, can bear stress. Some experiments with crazed polymers such as polycarbonate were carried out to get the stress-strain curves of the craze matter. To achieve this aim, the polymer samples were previously exposed to ethanol. The results are shown in Figure 14.24 where the cyclic stress-strain behavior of bulk polycarbonate is also illustrated (32). It can be seen that the modulus of the crazed polymer is similar to that of the bulk polymer, but yielding of the craze occurs at a relatively low stress and is followed by strain hardening. From the loading and unloading curves, larger hysteresis loops are obtained for the crazed polymer than for the bulk polymer. 

Figure 7a and b show typical three-dimensional surface topographic images of the PHB fibers drawn at a draw ratio of 4.0 and 7. The surfaces of the fibers differ considerably. Depending on the draw ratio, spherulitic or fibril-like surface structures were formed. The textile physical properties of the fibers can be explained by these different structures. The fibers, spun at a draw ratio of 4.0, are brittle without a sufficient elongation at break visible in the stress-strain curve (Fig. 5). The fibers spun at a draw ratio of 7 show a completely different stress-strain behavior with a sufficient elongation at break and a sufficient tenacity, as can be seen from the stress-strain curve (Fig. 5).

Figure 1 Schematic two-dimensional drawing of major features of a craze A, microvoiding B, formation of fibrils C, extension of fibrils D, fracture of fibrils. The stress-strain curves indicate the load-bearing capability of the material at different stages of crcize formation and the effect of plasticization.

The stress-strain curves of individual kenaf and sisal fiber samples are presented in Figure 14.6. Each curve displays a different initial curve, especially at small strain (below 1%), which is attributed to the orientation of the fibrils along the axis of the fiber under tension [82]. WG-treated kenaf fiber displayed a slight decrease of approximately 1.6% in the failure strain, when compared to the untreated fibers. For the sisal fibers, the enhanced strain could have occurred because axial spUtting was promoted and transverse cracking was delayed as a result of the WG treatment [75, 78]. This enhances the tearing type failure of the elementary fibers, which is... 

The mechanical response of fibrils in the direction of the applied stress has been determined for polycarbonate [83] and polystyrene [120]. Figure 9.12 shows a stress-strain curve of craze material obtained by Kambour and Kopp [83] for PC. It may be noted that the craze material can sustain tensile stresses only slightly less than the yield stress Up of the bulk material. The strains, however, are enormously greater in the craze - between 40 and 140% as compared to the bulk yield strain of about 2%. 

Figure 10.7 Effect of the modulus of elasticity of fibrillated polypropylene on the stress-strain curve of a composite prepared with 10% fibre by volume (after Hughes and Hannant [28]).

Figure 10.9 Tensile stress-strain curve and bending load-deflection curve of a composite containing 5.7% by volume of fibrillated polypropylene mat (after Hannant and Zonsveld [10]).

Figure 13.3 Stress-strain curves in tension of cement composites prepared with asbestos fibres (12% mass), fibrillated polypropylene network (Netcem) and polyethylene (both 18% by volume) (a) low strain range (b) high strain range (after BIjen and Geurtz [IS]).

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