Tensile behavior

Proportion of Hard Segments. As expected, the modulus of styrenic block copolymers increases with the proportion of the hard polystyrene segments. The tensile behavior of otherwise similar block copolymers with a wide range of polystyrene contents shows a family of stress—strain curves (4,7,8). As the styrene content is increased, the products change from very weak, soft, mbbedike materials to strong elastomers, then to leathery materials, and finally to hard glassy thermoplastics. The latter have been commercialized as clear, high impact polystyrenes under the trade name K-Resin (39) (Phillips Petroleum Co.). Other types of thermoplastic elastomers show similar behavior that is, as the ratio of the hard to soft phase is increased, the product in turn becomes harder. 

Whitman, L., and Wright, J.P., Tensile Behavior of Geological Material in Ground Shock Calculations, Weidlinger Associates Technical Report for Contract No. DNA001-75-C-0076, New York, 42 pp., June 1975. 

To complete the mechanical response description in this book, the phenomena of viscoelasticity, spall (dynamic tensile behavior), melting, and compression of porous solids are briefly considered. 

Fibrous fillers are now gaining more importance over particulate fillers due to the high performance in mechanical properties. The influence of fiber diameter on the tensile behavior of short glass fiber on polyimide was reported [95], At higher concentrations thick fibers seem to be more advantageous probably because of the... 

Why do the tensile behaviors of rubbery amorphous, glassy amorphous and semicrystalline polymers differ as they do ... 

Equilibrium Tensile Behavior of Model Silicone Networks of High Junction Functionality... 

Until recently ( 1 5 ) investigations utilizing model networks had been limited to functionalities of four or less. Networks with higher functionality are predicted by the various theories of rubber elasticity to display unique equilibrium tensile behavior. As such, these multifunctional networks provide insight into the controversy surrounding these theories. The present study addresses the synthesis and equilibrium tensile behavior of endlinked model multifunctional poly(diraethylsilox-ane) (PDMS) networks. 

The two network precursors and solvent (if present) were combined with 20 ppm catalyst and reacted under argon at 75°C to produce the desired networks. The sol fractions, ws, and equilibrium swelling ratio In benzene, V2m, of these networks were determined according to established procedures ( 1, 4. Equilibrium tensile stress-strain Isotherms were obtained at 25 C on dumbbell shaped specimens according to procedures described elsewhere (1, 4). The data were well correlated by linear regression to the empirical Mooney-Rivlin (6 ) relationship. The tensile behavior of the networks formed In solution was measured both on networks with the solvent present and on networks from which the oligomeric PEMS had been extracted. 

This suggests that network chain length distribution had negligible effect on the equilibrium tensile behavior for the range of investigated in this study = 1.1-2.5). 

Networks Formed in the Presence of Diluent, s>0.9. A series of six networks were prepared both in bulk and in the presence of oligomeric PDMS (Mn = 1170, no vinyl groups) using as junctions a 0 = 43.9 linear PMHS and as chains a,o>-divinyl PDMS ranging in Mn from 9,320 to 28,600 g mol . The volume fraction of solvent present during network formation, v s, was 0.30 for all six networks and was calculated assuming simple additivity of volumes. The tensile behavior of the networks formed in bulk was measured in bulk, vt = Vf/V = 1. The tensile behavior of the networks formed in solution was measured both on networks with solvent present (vt =1) and on networks from which the oligomeric PDMS had been extracted (vt 1.47). 

Stars with 32% PSt, (PSt/15-h-PIB/34)g-C8, showed -26 MPa tensile stress. There was no appreciable difference in the tensile properties of unextracted and MEK extracted star blocks [see (PSt/15-h-PIB/34)g-C8 and (PSt/16-h-PIB/34)g-C8]. The modulus and Shore A hardness were slightly higher for the unextracted star, (PSt/16-h-PIB/34)g-C8, which maybe due to the presence of PSt contamination which acts as a rigid filler. A dramatic difference in the tensile behavior was observed when PSt content was increased. Stars with low PIB block molecular weight and high PSt content (46%), e.g., (PSt/21-h-PIB/25)g-C8, showed plasticlike behavior, i.e., it showed a high modulus, a yield point, and a short draw. Ex-... 

Rheological Properties. Rheological studies show that ammonia affects the compressive mechanical behavior of wood to a much higher extent than the tensile behavior (55,16). Since the compression strength is highly dependent on lignin content,... 

If a Neo-Hookean constitutive equation is used to describe the tensile behavior of the cross-linked interlayer... 

Models of mechanical behavior of tissues have been difficult to develop primarily because of the time dependence of the viscoelasticity. Analysis of viscoelastic behavior of even simple polymers at strains greater than a few percent is not accurate. In addition, most tissues undergo strains larger than a few percent, which makes the analysis require an understanding of the elongation behavior. In this chapter we focus on using modeling techniques to analyze the physical basis for determination of the tensile behavior of ECMs found in connective tissue. 

Figure 19. Tensile behavior of carbon fibers, based on polyacrylonitrile (PAN) or mesophase pitch (MPP), and compared with polyaramide and glass fibers (48).

Globally, carbon nanotubes have a positive effect on the mechanical properties of all the composites with PVA matrices described in the previous sections. However, the enhancement of mechanical properties differs substantially from a material to another, depending on the type of nanotubes, or on the process used to manufacture the composite. The Young s modulus and the strength are deduced from usual tensile experiments. As depicted in Figure 11.4, PVA/nanotube composites generally follow the same tensile behavior, with a short elastic regime on the first percent strain, followed by a more or less extended plastic behavior. 

K. M. Prewo, Silicon Carbide Fiber-Reinforced Glass-Ceramic Composite Tensile Behavior at Elevated Temperature, J. Mat. Sci., 24,1373 (1989). 

The SA polymer exhibited a two-phase structure in which the filler particles of radius ca. 0.26 /x are dispersed in the plastic matrix. The impact and tensile behavior of this polyblend was compared with that of an MBAS polyblend (graft diene rubber approximately the same size) which was examined previously by the laser light scattering technique. 

Figure 8. Effect of TEOS content (Xj on the tensile behavior of a series of TEOS(X)-PTMO(2000)-100-0.04-RT materials. RT is room temperature. See text for sample nomenclature.

Figure 10. Effect of aging on the tensile behavior of a titanium isopropox-ide-TEOS-PTMO(2900) (30 20 50 wt %) system after casting and drying at...

Figure 25 shows that the tensile behavior of PMMA and PS, stretched some 10-30 °C below Tg, is very similar to that of PC. Like PC both PMMA and PS exhibit extensive stress-whitening at high extension ratios, k", where the peak or inflection of the stress-strain curve is observed. In Table 3, the value of k" measured for PMMA is compared to the maximum extension ratio, k , of chains between entanglement points. The fact that k" = k provides further evidence that the cavitation in PMMA must be attributed to the same deformation mechanism as discussed in Section 4.2 for PC. The value of k" = kikj" = 6.8 measured for pre-oriented PS is higher than the theoretical value of k = 4.1 included in Table 3. This result is not... 

The mechanical properties of a craze were first investigated by Kambour who measured the stress-strain curves of crazes in polycarbonate (Lexan, M = 35000) which had first been grown across the whole cross-section of the specimen in a liquid environment and subsequently dried. Figure 25 gives examples of the stress-strain curves of the craze determined after the 1st and 5th tensile loading cycle and in comparison the tensile behavior of the normal polymer. The craze becomes more and more elastic in character with increasing load cycles and its behavior has been characterized as similar to that of an opencell polymer foam. When completely elastic behavior is observed the apparent craze modulus is 25 % that of the normal poly-... 

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