Cyclic tension, effect

Effects of cyclic tension. Cyclic compounds including six bonds present maximum stability. This rapidly decreases when the number of bonds increases... 

Anderson et al. [20] studied the effects of combined cyclic tension or compression loading and torsional loading on [ 30/90]s aramid/epoxy tubes. They reported that in the case of predominandy axial loading the combinafion with a small torsion... 

In order to demonstrate the predictability of the above model, the macroscopic behavior of the SMPF is estimated and the prediction is compared with the test result. In the following, three such predictions and/or comparisons are made. The first one investigates the effect of the heating rate on fully constrained stress recovery. The second one evaluates the effect of the amount of the amorphous phase and the crystalline phase on the stress-strain behavior under cyclic tension. The last one examines the growth of the crystalline phase due to stress induced crystallization. In all cases, the SMPF has a diameter of 0.04 mm. The material parameters for the stress recovery and strain hardening modeling as well as for the amorphous and crystalline subphase modules and for crystalline phase shp systems are summarized in Tables 5.2 to 5.4, respectively. 

Several criticisms of these parameters have recently been pointed out. First, they have no specific association with a material plane (i.e., they are scalar parameters), despite the fact that cracks are known to nucleate on specific material planes. With traditional parameters it is difficult to account for the effects of crack closure under compressive loading. Traditional parameters have not been successful at unifying experimental results for simple tension and equibiaxial tension fatigue tests. Finally, a nonproportional loading history can always be constmcted for a given scalar equivalence parameter that holds constant the value of the scalar parameter, but which results in cyclic loading of material planes. For such histories, scalar parameters incorrectly predict infinite fatigue life. 

Acid flooding can be successful in formations that are dissolvable in the particular acid mixture, thus opening the pores. Hydrochloric acid is common, in a concentration of 6% to 30%, sometimes also with hydrofluoric acid and surfactants added (e.g., isononylphenol) [130,723]. The acidic environment has still another effect on surfactants. It converts the sulfonates into sulfonic acid, which has a lower interfacial tension with oil. Therefore a higher oil forcing-out efficiency than from neutral aqueous solution of sulfonates is obtained. Cyclic injection can be applied [4,494], and sulfuric acid has been described for acid treatment [25,26,1535]. Injecting additional aqueous lignosulfonate increases the efficiency of a sulfuric acid treatment [1798]. 

Among the microbial surfactant producers, Bacillus subtilis strains generate a lipopeptide called surfactin, one of the most effective biosurfactants known. This biomolecule is usually a cyclic compound consisting of seven amino acids bonded to a lipid moiety. Surfactin is effective in lowering the surface tension of water to <30 dyn/cm (17), which is comparable with the values obtained by conventional synthetic surfactants. Additionally, surfactin preparations have other interesting characteristics, including antibiotic and antiviral properties (18). In fact, surfactin is one of the few biosurfactants that has found commercial use (19). 

Additional factors which must be taken into account are environmental effects (thermal as well as chemical), effects of defects, statistical variability of the material, long-term behavior, and cyclic versus static loading effects. Assessment of these effects requires the end user to conduct a large series of tests using multiple specimens. A typical series will examine a unidirectional material in tension in the 0, 90, and cross-ply directions 0, 90, and cross-ply in compression and 1-2, 1-3, and 2-3 shear at different temperatures ranging from —54°C to the expected service temperature creep rupture at temperatures up to the expected service temperature and fatigue at room and elevated temperature. This series of tests, shown in Table 12.1, may require over 400 specimens. 

Diamond, J., and Holmes, TG (1975). Effects of potassium chloride and smooth muscle relaxants on tension and cyclic nucleotide levels in rat myometrium. Can J Physiol Pharmacol 53(6) 1099-1107. 

Diamond, J., and Blisard, KS (1976). "Effects of stimulant and relaxant drugs on tension and cyclic nucleotide levels in canine femoral artery. Mol Pharmacol 12(4) 668-692. 

An octopamine-sensitive adenylate cyclase is not the only means by which octopamine may exert its effects. Whilst DUMETi and octopamine modulate the amplitude and rate of relaxation of twitch tension in the extensor tibiae muscle of locusts via cyclic AMP, their effects upon the myogenic rhythm are mediated via a different route (86) Thus, elevated cyclic AMP does not induce a decrease in the frequency of myogenic rhythm as does octopamine, and the effects of octopamine are not potentiated by IBMX. In fact the mode of action of octopamine in reducing the frequency of myogenic contractions remains unknown. 

The tension leads to a decrease of the C-C bond energy to the value E = Eq-yc, where y is the structure coefficient determining the distribution of tensile stresses in the bonds (see reference 14). Not only the tensile stress, but also the energy of the M-0 bond and the conformation of the cyclic complex, is important because a local stress of C-C bonds diminishes the potential barrier of their rupture. A mutual effect of the tensile stress and thermal motion have been analyzed in reference 15. 

To conclude the analysis of the influence of biaxiality ratios, it is worth mentioning the work by Perevozchikov et al. [19]. They investigated the fatigue behavior of unidirectional glass/epoxy mbular samples under the combined effect of shear stresses and transverse tension or compression stresses and reported the negative effect of cyclic shear stress components in the case of both tensile and compressive transversal stress. It was also shown that the increase of Xu ratio induced a reduction in the fatigue strength. 

Fujii T, Lin F, Morita Y. Fatigue behavior of plain woven glass-fabric laminates under tension/torsion combined loading (Effect of shear stress and cyclic condition on fatigue failure). Nippon Kikai Gakkai Ronbunshu, A Hen/Trans Jpn Soc Mech Eng Part A 1994 60 650—7 [in Japanese]. 

Inoue A, Fuji T, Kawakami H. Effect of loading path on mechanical response of a glass fabric composite at low cyclic fatigue under tension/torsion biaxial loading. J Reinf Plast Compos 2000 19(2) lll-23. 

The lateral deflections of the upper portion of the pile will lead to reduced axial skin friction and thus affect axial pile behavior. For an anchorage pile in tension, the lateral effects may prove significant. The cyclic axial loads on a pile in sustained tension are initially carried mainly by the upper portion of the pile. With time the cyclic effects will gradually extend deeper and will progress even further down because of lateral cycling, imtil a stable condition is reached. 

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